GB2381572A

GB2381572A - Incineration of waste plastics with sludge

Info

Publication number: GB2381572A
Application number: GB0304004A
Authority: GB
Inventors: Akira Nakamura; Takashi Noto; Hajime Akiyama; Seiji Kinoshita; Yoshinari Fujisawa; Seiichi Noguchi
Original assignee: NKK Corp; Nippon Kokan Ltd
Current assignee: JFE Engineering Corp
Priority date: 1998-11-24
Filing date: 1999-11-19
Publication date: 2003-05-07
Anticipated expiration: 2019-11-19
Also published as: GB0304005D0; GB2381572B; GB0304004D0; GB2381573B; GB2381573A

Abstract

An incinerator 21 combusts high calorific value waste plastics with sludge to reduce the generation of dioxins. The temperature 22 and the oxygen concentration 23, are both measured at the outlet and controlled within predetermined ranges. The incinerator 21 may have a fluidised bed 4 comprising sand whose temperature is also controlled within a predetermined range.

Description

Specification WASTE DISPOSAL INCINERATION METHOD FIELD OF THE INVENTION The present invention relates to a method and an apparatus for incinerating a waste.

BACKGROUND OF THE INVENTION Most of a municipal refuse and an industrial waste (when simply stated as a waste, both or any one of them will be designated hereafter) are incinerated and disposed of by landfill. Many of the waste incinerating facilities are provided with fire grate incinerators, and some of them are provided with fluidized bed incinerators.

A waste incineration in an incinerating facility provided with the fire grate incinerator is carried out as follows. At first, the waste is charged into the incinerator, its temperature is raised while being dried by the combustion air blown from-below the fire grate and by the radiant heat inside of the incinerator, and it catches fire. Subsequently, the waste is burned and reduced ~.,.. 1 : 0 an ash, and discharged as an incineration ash outside of the incinerator.

On the other hand, since an exhausting gas contains a combustible gas such as H CO, and CH4 generated in a drying- step, in a temperature-raising step and in an initial combustion-step, an air is blown in a secondary combustion

chamber for burning a combustible gas. The exhausting gas from uhe'secondary combustion chamber is subjected to heat recovery by a boiler or to cooling in a gas cooling device such as a gas cooler, and sent to an exhausting gas treating step. After the harmful gas removal treatment and the dust removal one, it is released from a stack.

As shown-in FIG. 2, the waste incineration in the incineration facility provided with a fluidized bed incinerator is carried out as follows. The waste is charged into the fluidized bed incinerator 1 by a non-industrial waste charger 2, and then, its temperature is raised while being dried in a fluidized layer 9 on the fluidized bed 4, and the waste is burnt. However, since the exhausting gas generated in the fluidized bed contains a combustible gas such as Hz, CO, and CH,, an air is blown into a freeboard section of the incinerator for burning the combustible gas. After that, the exhausting gas is subjected to cooling in a gas cooling facility, and sent to a exhausting gas treating facility 5, where it is subjected to a harmful gas removal treatment and a dust removal treatment, and released into the atmosphere from a stack 6. The fluidized bed incinerator shown in Patent Laid Open No. 9-303743 is one example in this way.

In a fluidized bed incinerator as above, RDF is sometimes burnt. RDF (Refuse Derived Fuel) means a waste converted into a fuel; that is, a fuel made by adding calcium compound to an industrial waste, a municipal refuse and has a lower calorific value of 3000 to 6000 kcal/kg with a water contenir of 1 to 20 wt%. There happens one problem when burning RDF; that is to say,

much chlorine is contained in the RDF, and the reaction thereof with aromatic compounds is likely to generate a sort of dioxins such as dioxin or furan.

Recently it has been found that an exhausting gas generated in a waste incinerating facilities contains some sorts of dioxins such as chlorodibenzodioxan and chlorodibenzofuran, or other organic chlorine compounds, and it causes a serious problem against protecting an environmental conditions. Therefore, regulations over dioxins emissions are being tightened.

Under these circumstances, various technological developments are being carried out for reducing dioxins in an exhausting gas. However, many of them intend to catch dioxins together with a fly ash, and a treatments of making a fly ash nontoxic needs to be independently carried out. By that reason, they result in no fundamental solution. In-addition, a technology for, decomposing dioxins accompanies a large-scale treating apparatus, and when applying to the present waste incinerating facilities, a substantial facility renovation is required, and. --it is difficult to implement that renovation. For

example, the technology disclosed in Patent Laid Open No. 5-161822 , requires to install a ceramic filter for treating an exhausting gas.

DISCLOSURE OF THE INVENTION The present invention has been realized to solve these < * : problems, and accordingly oneof the objects of the present invention is to provide a waste incineration method for an

incinerator by introducing a relatively simple combustion method which does not cause problems as mentioned above. It maintains a constant combustion in an incinerator thereby suppressing emissions or a harmful gas and an unburnt gas.

The present invention is to further solve the abovementioned problems, and one of the objects of the present invention is to provide a waste incineration method and a facility thereof by equipping a very simple apparatus and just by adding cheap substances, thereby enabling to reduce the amount of generated dioxins itself.

In order to accomplish the above-mentioned objects, firstly, the present invention is to provide a waste incineration method, which means; preparing a sludge which has the water content of 65 to 90 wt%, the sulfur content of 0.1 to 2.0 wt% in a drying condition, and a nitrogen content of 1 to 10 wt% ; preparing one selected from the group consisting of RDF, which has a lower calorific value of 3, 000 to 6,000 kcal/kg and the water content of 1 to 20 wt%, and a non-industrial waste including a municipal refuse which has the lower calorific value of 1,500 to 4,000 kcal/kg and the water content of 30 to 70 wt% ; and performing a mixed fuel combustion of the sludge and one selected from the group consisting of the RDF and the non-industrial waste including the municipal refuse in a waste incinerator.

Secondly, the present invention is to provide a waste incineration method, as follows: preparing a sludge and a waste plastic of a lower calorific value of 4,500 kcal/kg or more ; performing a mixed fuel combustion of the sludge and the waste plastic in a waste incinerator; and controlling an outlet temperature of the waste . incinerator at 900-1., 200 C and an oxygen concentration at 3- 12 wt%.

Thirdly, the present invention is to provide a waste incineration method, as follows: performing a mixed fuel combustion of the waste and a sludge in a waste incinerator; measuring a SOx concentration in an exhausting gas in the waste incinerator; and, controlling at least one selected from the group consisting of the sludge supply amount and the waste supply amount in accordance with a measured value of the SOx concentration.

Fourthly, the present invention is to provide a waste incineration method, as follows: performing a mixed fuel combustion of a waste and a sulfur contained material; and measuring a SOx concentration in an exhausting gas in a waste incinerator; and controlling at least one selected from the group

consisting of a supply amount of the sulfur contained material and the supply amount of the waste in accordance with a measured value of the SOx concentration.

Fifthly, the present invention is to provide a waste incineration method, as follows: performing a mixed fuel combustion of a sulfur contained material and RDF in a waste incinerator; measuring the SOx concentration in an exhausting gas in the waste incinerator; controlling at least one selected from the group consisting of the supply amount of the sulfur contained material and RDF in accordance with the measured value of the SOx concentration.

Sixthly, the present invention is to provide a waste incineration method, as follows: supplying a sulfur contained powder to a waste incinerator by way'of at least one selected from the group consisting of a sludge-supply line and a waste-supply line; and, performing a mixed fuel combustion of the sludge and waste in waste incinerator; and measuring a SOx concentration in an exhausting gas in the waste incinerator ; and controlling a supply amount of the sulfur contained powder in accordance with a measured value of the SOx concentration.

Seventhly, the present invention is to provide a waste incineration method, as follows: supplying dispersedly at least one selected from the group consisting of a sludge and a sulfur contained'material and supplying it to a dust hopper of the waste incinerator; and performing a mixed fuel combustion of the waste and at least one selected from the group consisting of the sludge and the sulfur contained material.

Eighthly, the present invention is to provide a waste incineration method, as follows : supplying dispersedly at least one selected from the group consisting of a sludge and a sulfur contained material onto a fire grate in a drying stage of a waste incinerator ; and, performing a mixed fuel combustion of the waste and, at least one selected from the group consisting of the sludge and the sulfur contained material.

Ninthly, the present invention is to provide a waste incineration method, as follows: adding a nitrogen compound to a waste; charging a waste into the incinerator ; and incinerating the waste in the incinerator. lOthly, the present invention is to provide a waste incineration method, as follows :

feeding a waste inzo a drying zone 0 : a fire grate incinerator; adding a nitrogen compound to the fed waste; and, incinerating the waste to which the nitrogen compound is added. llthly, the present invention is to provide a waste incineration method, as follows: charging a waste into a fluidized bed incinerator; incinerating a waste in a incinerator; and, blowing a nitrogen compound into a zone prior to secondary combustion in a freeboard section positioned above the fluidized bed.

12thly, the present invention is to provide a waste incineration method, as follows: adding a nitrogen compound to the waste; charging the waste into an incinerator; incinerating the waste, and, blowing the nitrogen compound to an exhausting gas flow path through which the exhausting gas having 650 C or lower temperature flows.

13thly, the present invention is to provide a waste incineration method, as follows: preparing a waste incineration device having an incinerator, a temperature reducing device and an electrostatic

precipitator; performing a mixed fuel combustion of the waste and a sludge; and controlling the temperature reducing device so that an exhausting gas temperature is 230 C or lower at an inlet of the electrostatic precipitator.

14thly, the present invention is to provide a waste incineration apparatus, as follows: an incinerator located in a waste incineration device; a waste feeding device and a sludge feeding device for performing a mixed fuel combustion of the waste and the sludge in the waste incinerator; a SOx concentration meter for measuring the SOx concentration inside of the incinerator or at the outlet of the incinerator; and a control device for controlling a supply amounts of at least one selected from the group consisting of the sludge and the waste in accordance with the SOx concentration.

15thly, the present invention is to provide a waste incineration apparatus, as follows : an incinerator located in a waste incineration device; a sulfur-contained material feeding device and a waste feeding device for performing a mixed fuel combustion of the sulfur-contained material and the waste in the incinerator.

a SOx concentration meter for measuring the SOx concentration in or at the outlet of the incinerator; and, a control apparatus for controlling the supply amount of at least one of the sulfur-containing substance and waste in accordance with the SOx concentration.

16thly, the present invention is to provide a waste incineration apparatus, an incinerator located in a waste incineration device; a sulfur-contained material feeding device and a RDF feeding device for performing a mixed fuel combustion of a sulfur-contained material and a RDF in the incinerator ; a SOx concentration meter for measuring a SOx concentration in or at an outlet of the incinerator or in a stack ; and a control device for controlling a supply amounts of at least one selected from the group consisting of a sulfurcontained material and the RDF.

17thly, the present invention is to provide a waste incineration apparatus, as follows: an incinerator located in a waste incineration device; a sludge feeding device and a waste feeding device to the incinerator ; and a sulfur-contained powder feeding device provided in a feed line of the sludge and the waste ino the incinerator.

18thly, the present invention is to provide a waste incineration apparatus, as follows : an incinerator for performing a mixed fuel combustion of a waste and at least one selected from the group consisting of a sludge and a sulfur-contained material. substance; a waste hopper attached to the incinerator; and a lance for dispersing at least one of the sludge and sulfur-containing substance and feeding to the waster hopper.

19thly, the present invention is to provide a waste incineration apparatus, as follows : an incinerator for performing a mixed fuel combustion t of the waste and at least one selected from the group consisting of a sludge and a sulfur-contained material: a fire grate in the drying stage located in the incinerator; and a lance for. dispersing at least one of the sludge and sulfur-containing substance and feeding it on the rire grate) of the dry step.

20thly, the present invention is to provide a waste incineration apparatus, as follows : an device for adding the nitrogen compound to the waste to be charged into an incinerator; and an device for blowing the nitrogen compound into a flow path of an exhausting gas.

21stly, the present invention is to provide a waste incineration apparatus, as follows: an incinerator having a fire grate; and, a nitrogen compound adding device for supplying a nitrogen compound to a drying zone above a fire grate provided in an incinerator.

22ndly, the present invention is to provide a waste incineration apparatus, as follows: an incinerator having a fluidized bed; and,

a nitrogen compound adding device for supplying the ,,.. nitrogen compound to a zone prior to secondary combustion in a freeboard section located above the fluidized bed.

23rdly, the present invention is to provide a waste incineration apparatus, as follows: an incinerator located in a waste incineration device; a nitrogen compound adding device for adding the nitrogen compound to the waste to be charged into the incinerator; a heat recovery boiler located behind the incinerator along a gas flow direction ; and a device for blowing the nitrogen compound into a flow path of an exhausting gas at the outlet of the boiler.

24thly, the present invention is to provide a waste incineration apparatus, as follos :

an incinerator located in a waste incineration device ; a nitrogen compound adding device for adding a nitrogen compound to the waste to be charged into the incinerator ; a gas cooler located behind the incinerator along the gas flow direction; and a device of blowing the nitrogen compound into a flow path of an exhausting gas at the outlet of the gas cooler.

25thly, the present invention is to provide a waste incineration device, as follows: a waste incineration device, structured by connecting in series, via a flue, an incinerator, temperature reducing device, an exhausting gas treating device, an electrostatic precipitator, an induced draft fan, and a stack; a waste supply hopper provided to the incinerator; a sludge supply hopper provided to the incinerator; an exhausting gas temperature control device at the inlet of the electrostatic precipitator, connecting with the temperature reducing device and the electrostatic precipitator ; and, a temperature sensor for sensing a temperature of the exhausting gas at an inlet of the electrostatic precipitator, which is located inside of a temperature control device for the inlet exhausting gas of the electrostatic precipitator.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a cross sectional view showing a schematic structure of a fluidized bed incinerator, used in embodiments of the present invention; FIG. 2 is a view showing a schematic structure of a prior art fluidized bed incinerator; FIG. 3 is a cross sectional view showing a schematic structure of a fire grate incinerator used in embodiments of the present invention; FIG. 4 is a cross sectional view showing a schematic structure of the fluidized bed incinerator used in embodiments of the present invention; FIG. 5 is a flow chart showing one form of embodiment of the present invention; FIG. 6 is a graph illustrating one form of embodiment of the present invention and shows he relationship between the SOx concentration and the dioxins and poisonous substance (HS + S03) concentration at the outlet of the incinerator; FIG. 7 is a schematic view showing one example of the fluidized bed incinerator of the present invention; FIG. 8 is a flow chart showing one form of embodiment of the present invention; FIG. 9 is a flow chart showing one form of embodimen-t crf-the- present invention ; FIG. 10 is a schematic view showing one example of a waste incineration apparatus-of the present invention; FIG. 11 is a schematic chart showing another example

of the incinerating apparatus of T : he present invention ; FIG. 12 is a schematic chart showing a structure of one example of the incinerating apparatus of the present invention; FIG. 13 is a schematic chart showing a structure of another example of the incinerating apparatus of the present invention; FIG. 14 is a schematic view showing a structure of a further example of a waste incinerating apparatus of the present invention ; FIG. 15 is an explanatory view showing the first example of one form of embodiment of the present invention; FIG. 16 is an explanatory view showing the second example of one form of embodiment of the present invention; FIG. 17 is an explanatory view showing the, third example of one form of embodiment of the present invention; FIG. 18 is an explanatory view showing the fourth example of one form of embodiment of the present invention; FIG. 19 is an explanatory view showing the first example of another form of embodiment of the present invention; FIG. 20 is an explanatory view showing the second example of another form of embodiment of the present invention; FIG. 21 is an explanatory view showing the third example of another form of embodiment of the present invention; FIG. 22 is an explanatory view showing the fourth example of another form of embodiment of the present invention; FIG. 23 is an explanatory view showing the first example of another form of embodiment of the present invention ; FIG. 24 is an explanatory view showing the second example

of another form of embodiment of the present invention ; FIG. 25 is an explanatory view showing the third example of another form of embodiment of the present invention; FIG. 26 is an explanatory view showing the fourth example of another form of embodiment of the present invention ; FIG. 27 is an explanatory view showing the first example of another form of embodiment of the present invention; FIG. 28 is an explanatory view showing the second example of another form of embodiment of the present invention ; FIG. 29 is an explanatory view showing the third example of another form of embodiment of the present invention; FIG. 30 is an explanatory view showing the fourth example of another form of embodiment of the-present invention; FIG. 31 is a view showing one example of an exhausting gas treating step in a waste incineration facility-of the preset invention, where a boiler is installed; FIG. 32 is a view showing one example of an exhausting gas treating step in a waste incineration facility of the present invention,'where a gas cooler is installed; FIG. 33 is a system configuration chart of a waste incineration facility in one form of embodiment of the present invention ; FIG. 34 is a graph of the present invention, showing the relationship between the operating temperature of an electrostatic precipitator and the rate of increase of dioxin ;

and FIG. 35 is a system configuration chart of a prior art wasre

incineration facility.

BEST MODE OF EMBODIMENT IN THE INVENTION Detailed explanation will be made one by one for best mode of embodiment of the invention.

BEST MODE 1 This best mode 1 has accomplished the object of the invention by a waste incineration method in a waste incinerator which is characterized by a mixed fuel combustion at a mixed fuel combustion ratio of 10-70% of sludge, which has the water content of 65-90 wt%, dry sulfur content of 0.1-2. 0 wt%, and nitrogen

content of 1-10 wt%, and RDF, which has the lower calorific value of 3, 000-6, 000 kcal/kg and water content of 1-20 wt%.

Herein, a mixed fuel combustion ratio is defined by sludge supply weight/ (sludge supply weight + RDF supply weight).

This method of embodiment is characterized by addition of sludge to RDF for combustion, and the sulfur content in sludge stays in the incinerator as H2S, CS, COS, SO :, or SO) during the combustion process. These substances have a poisoning effect to copper and similar substances which act as catalysts for the generation of dioxins, and can effectively restrain dioxins in the waste gas line from the high temperature combustion field in the incinerator to behind the outlet of the incinerator. The nitrogen consent in sludge generates ammonia in the combustion process, particularly in the reducing atmosphere of the primary combustion field, and by reacting with chloride compounds,

ammonia suppresses the dioxin generating reaction by C1 in the course of generating dioxins. Further, by controlling the concentration of water in sludge and restraining the combustion reaction rate of combustible matters, soot generation can be lowered. If the soot generation amount is able to be restrained, the concentration of aromatic organic compounds derived from soot is reduced, resulting in lowering the concentration of dioxins, which are products of incomplete combustion.

The current mode of embodiment can be applied to any type of waste incinerators. However, in order to raise the mixing property of RDF and sludge and increase the combustibility of sludge, it is preferable to carry out combustion by fluidizing the burning materials; in particular a fluidized bed incinerator is preferable.

RDF is as mentioned above a fuel formed by adding a calcium compound to industrial waste, municipal refuse, and other types of waste. Municipal waste is a mixture of household garbage, leftover food, plastic containers, waste papers, and wood chips.

Calcium carbonate or calcium hydroxide is used as a calcium compound.

RDF thus produced has the lower calorific value of around 3000 to 6000 kcal/kg and the water content of around 1 to 20 wt%.

Sludge is discharged from a wastewater treatment facility.

Any type of sludge is applicable, including sewage sludge, night

soil sludge, sludge generated when performing an activated sludge s c) L 11--t) treatment of organic wastewater, sludge generated when performing a solid-liquid separation of wastewater containing

organic materials, sludge generated in closed water areas as in river dredging, and other sludge generated in the course of treating wastewater. Sludge preferable for the method of this invention is one which has the nitrogen content of around 1 to 10 wt%, sulfur content of around 0.1 to 2.0 wt%, both in dry contents, and the water content of around 65 to 90 wt%. If the sulfur and nitrogen contents in sludge are lower than 0.1% and 1% respectively, the absolute concentrations ofHS, CS, COS, SO2, SO3 or similar components become too low, and effects thereof become weak. Conversely, if the S and N contents in sludge are higher than 2.0% and 10% respectively, the concentrations of SO and NO., from a stack become too high, and there arises a possibility that regulated values may not be accomplished.

Further, if the concentration of water in sludge is lower than 65%, it is difficult to effectively control the combustion reaction rate of combustible materials. Conversely, if the concentration of water in sludge is higher than 90%, it is difficult to maintain the temperature in the incinerator.

The mixed combustion ratio of sludge and RDF is 10 to 70%.

This is because the S content of 10 plus ppm and the N content of several 10 ppm at the lowest respectively are necessary for expecting the above mentioned effects, and the mixed combustion ratio needs to be more than 10% at the lowest. Conversely, if the mixed fuel combustion ratio exceeds 70%, the water content becomes too high, and even if operated by squeezing down the air ratio, it is difficult to maintain the temperature at the outlet of the incinerator at 800 C.

It is sufficient to perform mixed fuel combustion of sludge and RDF in the incinerator. They may be mixed before charging, or charged into the incinerator separately.

The adequate combustion temperature (in the fluidized bed type, the temperature at the freeboard section) is usually around 850 to 1000OC.

FIG. l shows a structure of the incinerator used in an example of embodiment.

This incinerator 1 is a fluidized bed type. In the interior, a sand layer to form the fluidized layer 9 is prevented from moving down by a dispersing plate. Under the dispersing plate, there is a wind box into which combustion air is blown. This incinerator 1 is separately provided with a RDF charger 2 and a sludge charger 3. For the combustion treatment, sludge and RDF are charged from the respective chargers into the incinerator, dried in the sand layer fluidized by the air sent from the wind box under the dispersing plate, their temperatures are raised and they catch fire. Sludge and RDF are burned in the fluidized layer above the fluidized bed 4 and in the freeboard section further above, and complete the combustion by the time L. hey reach the outlet of the incinerator. After combustion, the waste gas is discharged outside through the outlet of the incinerator, goes through the waste gas treating facility, and released from a stack.

By using the above mentioned incinerator, mixed fuel combustion of RDF and sludge was performed, where RDF was made from municipal refuse and has the value of 4000 kcal/kg and the

water concentration of 8%, and sludge has the water concentration of 80%, N content of 7%, and S content of 0.6%. Combustion was carried out by maintaining the temperature in the incinerator at 850t and changing the temperature in the fluidized layer between 500 and 8500C and that at the freeboard section between

850 and 1000 C. In the case of burning merely RDF, the average value of the dioxins concentrations was 2. 1 ng/Nm3-teq, but when RDF of 1 t/h and sludge of 0.5 t/h were burned at the mixed combustion ratio of 33.3%, the average value was able to be suppressed down to 0.2 ng/Nm-teq.

Further, RDF, which was made from municipal refuse and has the value of 6000 kcal/kg and the water concentration of 5%, and sludge, which has the water concentration of 90%, N content of 7%, and S content of 0.6%, were burnt. At first, only RDF was burnt and the temperature in the incinerator was controlled merely by water spraying inside the incinerator. RDF of 0.6 t/h and sludge of 1.4 t/h were burnt at the mixed fuel combustion ratio of 70%. At this time, the temperature at the outlet of the incinerator was controlled to be the same as when burning merely RDF. Comparing with the combustion of just RDF, the dioxins concentration at mixed fuel combustion with sludge was brought down by about half in average.

As seen from the above, the present mode is characterized by mixed fuel combustion at the ratio between 10 to 70% of sludge, which has the S content of 0.1 to 2.0%, water concentration of 65 to 90%, and N content of 1 to 10%, and RDF. By carrying out mixed fuel combustion of sludge, which has the high water content

and reduced lower calorific value, and RDF, which has the high lower calorific value, stable combustion is made possible so that the generation of poisonous gas or unburnt gas can be suppressed.

Further, by carrying out mixed combustion of sludge having the above concentration, the S, N and water contents in sludge can effectively restrain the generation of dioxins.

When incinerating sludge, sludge of the high water content has the reduced lower calorific value, so that it is difficult to keep the burning conditions in the incinerator constant, and the temperature in the combustion chamber or the distribution of concentrations in the combustion gas inevitably becomes non-uniform both over time and space. This not only makes the control difficult but also causes a problem that poisonous gas is likely to be generated.

However, sludge, which is so difficult to burn, can be burnt smoothly by this mode.

BEST MODE 2 This mode of embodiment has accomplished the object of the invention by a waste incineration method in a waste incinerator characterized by mixed fuel combustion at a mixed combustion ratio of 10-40% of sludge, which has the water content of 65-90 wt%, dry sulfur content of 0.1-2. 0 wt% and nitrogen content 1-10 wt%, and non-industrial waste such as municipal refuse, which has the lower calorific value of 1500-4000 kcal/kg and water content 30-70 Wl%.

Herein, a mixed combustion ratio is defined by sludge supply

weight/ (sludge supply weight + supply weight of non-industrial wasze such as municipal refuse).

This method of embodiment is characterized by addition of sludge to non-industrial waste such as municipal refuse for combustion, and the sulfur content in sludge stays in the incinerator as HS, CS, COS, SO or SO) during the combustion process. These substances have a poisoning effect to copper and similar substances which act as catalysts for the generation of dioxins, and can effectively restrain dioxins in the waste gas line from the high temperature combustion field in the incinerator to behind the outlet of the incinerator. The nitrogen content in sludge generates ammonia in the combustion process, particularly in the reducing atmosphere of the primary combustion field, and by reacting with chloride compounds, ammonia suppresses the dioxin generating reaction of Cl in the course of generating dioxins. Further, by controlling the concentration of water in sludge and restraining the combustion reaction rate of combustible matters, soot generation can be lowered. If the soot generation amount is able to be restrained, the concentration of aromatic organic compound derived from soot is reduced, resulting in lowering the concentration of dioxins, which are products of incomplete combustion.

The current mode of embodiment can be applied to any type of waste incinerators, and the fire grate type incinerator or the fluidized bed incinerator can be used.

Municipal waste is a mixture of household garbage, leftover food, plastic containers, waste papers, and wood chips, and the

lower calorific value is around 1000 ro 3000 kcal/kg and the water content is around 30 to 70 w%.

The mixed fuel combustion ratio of sludge and municipal waste is 10 to 40%. This is because the S content of 10 plus ppm and the N content of several 10 ppm at the lowest respectively are necessary for expecting the above mentioned effects and the mixed combustion ratio needs to be more than 10% at the lowest.

Conversely, if the mixed fuel combustion ratio exceeds 40%, the water content becomes too high, and even if operated by squeezing down the air ratio, it is difficult to keep the temperature at the outlet of the incinerator at 800oC.

It is sufficient to perform a mixed fuel combustion of sludge and municipal waste in the incinerator. They may be mixed before charging, or charged into the incinerator separately.

The adequate combustion temperature (in the fluidized bed type, the temperature is at the freeboard section) is usually around 850 to 1000 C.

FIG. 3 shows a structure of the incinerator used in an example of embodiment.

This incinerator is the fire grate type, and the fire grate of the furnace bed of the main combustion chamber, that is, a drying stage 11,. combustion stage 12, and post combustion stage 13, has a structure inclined downward in three steps. The main combustion chamber is equipped with a waste chute 10 at the uppermost part of the fire grate, and at the end of the lowest part of the fire grate is a main ash chute 15. Above the main combustion chamber, a secondary combustion chamber 14 is

furnished for carrying out the secondary combustion of an exhausting gas. Sludge and waste are charged into the incinerator from the waste chute 10, sent to a drying stoker, where they are dried by the air from below and radiant heat in the incinerator, their temperatures are raised, and they catch fire. Sludge and waste which caught fire and started to burn are fed to a combustion stoker, and are burnt by the combustion air sent from below, and the unburnt portion completes the combustion in the post combustion step. Ash left after combustion is taken out through the main ash chute 15. The combustion is performed in the main combustion chamber, and exhausting gas (gas staying in the furnace) is mixed in the secondary combustion chamber 14, where the secondary combustion takes place and the unburnt portion completes the combustion, and is sent to the exhausting gas treating facility.

By using the above mentioned incinerator, mixed fuel combustion of municipal refuse and sludge was performed, where municipal refuse has the value of 2300 kcal/kg, and sludge has the water concentration of 80%, N content of 7%, and S content of 0. 6%, and the combustion was carried out by keeping the temperature in the incinerator at 850'C and changing the temperature in the fluidized layer between 650 and 8500C and that at the freeboard section between 900 and 1000 C. In the case of burning merely municipal refuse, the average value of the dioxins concentrations was 1.6 ng/Nm3-teq, but when urban refuse of 2 t/h and sludge of 1 t/h were burned at the mixed fuel combustion ratio of 33. 3%, the average value was able to be

suppressed down to 0.25 ng/Nm-teq.

Further, municipal refuse, which has the value of 2800 kcal/kg, and sludge, which has the water concentration of 90 wtl,-,, N content of 7 wt%, and S content of 0.6 wt%, were burnt in the fluidized bed incinerator. Comparing the combustion of merely municipal refuse with the mixed fuel combustion of municipal refuse and sludge, the dioxins concentration was reduced by about 60% in average when mixed combustion was carried out. Both experiments were carried out at the equal temperature at the outlet of the incinerator.

As seen from the above, the present embodiment is characterized by mixed fuel combustion at the ratio between 10 to 40% of sludge, which has the S content of 0.1 to 2.0%, water concentration of 65 to 90%, and N content of 1 to 10%, and non-industrial waste such as urban refuse. By carrying out mixed fuel combustion of sludge, which has the high water content and reduced lower calorific value, and the urban waste, which has the relatively high lower calorific value, stable combustion is made possible so that the generation of poisonous gas or unburnt gas can be suppressed. Further, with the above concentration, the S, N and water contents in sludge can effectively restrain the generation of dioxins.

Sludge of the high water content has the reduced lower calorific value is low, so that it is difficult to decrease the temperature in the incinerator and maintain the burning conditions constant. Deriving therefrom, the temperature in the combustion chamber or the distribution of concentrations in

combustion gas becomes non-uniform over time and space. This makes the control difficult, and also causes a problem that unburnt gas and poisonous gas are likely to be generated. In addition, in a fire grate type incinerator widely used as the waste incinerator, sludge drops down from the fire grate, and complete combustion is not carried out, and the blowing air path under the fire grate is often choked, so that in general it is not used for sludge incineration.

However, sludge, which is so difficult to burn, can be burnt smoothly by this best mode.

BEST MODE 3 When incinerating waste plastics in a fluidized bed incinerator, there is a problem that chlorine contained in waste plastics reacts with aromatic compound and is likely to generate dioxins such as dioxin and furan. Since waste plastic has a high lower calorific value, the temperature in the incinerator becomes high, and the combustion reaction rapidly progresses, which generates soot or unburnt portion. Thus, the concentration of aromatic organic compounds, which contribute to dioxins generation, becomes high and as a result, dioxins concentration becomes high.

As resolution of this problem, various combustion control and air blowing methods have been proposed as prior technologies.

However, depending upon properties of waste plastic charged, the temperature and flow rate of waste gas are largely varied, and it is difficult to effectively control poisonous gas such as

dioxins.

This mode is to solve the above problem, and its object is to provide a waste plastic incineration method which introduces a comparatively simple combustion method without causing the above problem, keeps the combustion condition in the incinerator stable, and thus restrain the emission of poisonous gas and unburnt gas.

The present mode of embodiment is to achieve the above object by a waste plastic combustion method characterized by mixed fuel combustion of waste plastic, of which combustible matters have the lower calorific value of 4500 kcal/kg or more, with sludge at the temperature at the outlet of the incinerator of 900 to 12000C and the oxygen concentration at the outlet of 3 to 12%.

By carrying out mixed fuel combustion of sludge of high water content and reduced lower calorific value and waste plastic of high lower calorific value, it is possible to control the temperature of the fluidized bed to a low level and keep that of the freeboard section at a high level. As the burning conditions in the incinerator is made stable, poisonous gas or unburnt gas can be prevented from releasing.

Dioxins generation can be more suppressed by mixed combustion of waste plastic and sludge than combustion of waste plastics only.

The S content in sludge stays in the incinerator as H, S, CS.,., COS, 802 or S03 during the combustion process. These substances have a poisoning effect to copper and similar substances which

act as catalysts for the generation of dioxins, and can effectively restrain dioxins in the waste gas line from the high temperature combustion field in the incinerator to behind the outlet of the incinerator. Nitrogen content in sludge generates ammonia in the combustion step, particularly in the reducing atmosphere of the primary combustion field, and by reacting with chloride compounds, ammonia suppresses the dioxin generating reaction of Cl in the course of generating dioxins. Further, by controlling the concentration of water in sludge and restraining the combustion reacting rate of combustible matters, soot generation can be lowered. If the soot generation amount is able to be restrained, the concentration of aromatic organic compound derived from soot is reduced, resulting in lowering the concentration of dioxins, which are products of incomplete combustion.

Further, by lowering the temperature of the sand layer to 380-450 C, the reaction speed of waste plastics in the fluidized layer is lowered. Thereby, gasification of sold waste plastic is slowed down, and the balance in mixing agitation is kept between combustible gas, which is generated from waste plastics, and air.

As a result, generation of soot, which is unburnt matter, can be suppressed and also, generation of dioxins, which is an incomplete combustion substance in broad sense, can be suppressed.

Gasified plastics and combustible content in sludge are burnt in the freeboard section maintained at a high temperature, and poisonous gas generation is further restrained. The temperature at the exit becomes to be 900 to 1200 C. As air is supplied into

the incinerator so as to kee ? the outlet oxygen concentration at 3 to 12%, combustion is completed before the gas reaches the exit of the incinerator.

The current mode of embodiment can be applied to any type of waste incinerators including the fire grate type. However,' in order to raise the mixing property of waste plastic and sludge and increase the combustibility of sludge, it is preferable to carry out combustion by fluidizing the burning materials; in particular a fluidized bed incinerator is preferable.

Preferable waste plastic is those of which the combustible matter has the low calorific value of more than 4500 kcal/kg, preferably around 4500 to 12000 kcal/kg, more preferably around 4500 to 8000 kcal/kg. The chlorine content shall be 20 wt% or less, preferably 0.1 to 10 wt%.

The mixed combustion ratio of waste plastics and sludge is 10 to 70%. This is because the S content of 10 plus ppm and the N content of several 10 ppm at the lowest respectively are necessary for expecting the above mentioned effects, and the mixed combustion ratio needs to be more than 10% at the lowest. Conversely, if the mixed combustion ratio exceeds 70%, the water content becomes too high, and even if operated by squeezing down the air ratio, it is difficult to keep the temperature at the outlet of the incinerator at 9000C.

It is sufficient to perform mixed combustion of sludge and waste plastics in the incinerator. They may be mixed before charging, or charged into the incinerator separately.

Desirable burning conditions are that the temperature at

the outlet of : he incinerator is around 900 to 1200 C, the oxygen concentration at the outlet is around 3 to 10%, and when a fluidized bed type incinerator is used, the temperature of the sand layer is around 380 to 450oC. When solely burning municipal refuse or waste plastic, it is usually difficult to keep the temperature of the sand layer at 4500C or less, but by performing mixed fuel combustion with sludge, the temperature of the sand layer can be kept at 380 to 4500C due to the contribution of the solid carbon content in the sludge. Waste plastic and sludge are slowly gasified in the fluidized layer and burn. Desirable conditions are that the fluidizing magnification is 2 to 8, the air ratio in the fluidized layer is 0. 1 to 1.0, and the temperature of fluidizing air sent into the fluidized layer is 20 to 500 C.

Subsequently, combustion is completed in the freeboard section kept at a high temperature, and the temperature becomes 900 to 1200 C at the outlet. After combustion, the exhausting gas is discharged outside through the exit of the incinerator, where the oxygen content is maintained at 3 to 12%, goes through the exhausting gas treating facility, and released from a stack.

FIG. 4 shows a structure of the incinerator used in an example of the embodiment.

The incinerator is a fluidized bed type. In the interior, a sand layer to form the fluidized bed is prevented from moving down by a dispersing plate. Under the dispersing plate, there is a wind box into which combustion air is blown.'This incinerator is separately provided with a waste plastics charger 20 and a sludge charger 3. For the combustion treatment, sludge

and waste plastics are charged from the respective chargers into the incinerator, dried in the sand layer fluidized by the air sent from the wind box under the dispersing plate, their temperature are raised, and they catch fire. Sludge and waste plastic are burned in the fluidized layer 4 and at the freeboard section above, and complete the combustion by the time they reach the exit of the incinerator. After the combustion, the waste gas is discharged outside through the exit of the incinerator, goes through the waste gas treating facility, and released from a smoke stack.

A thermometer 21 of the sand layer, a thermometer 22 of the exit of the incinerator, and a sensor 23 of the oxygen concentration of the exit are respectively equipped. It is sufficient to control those values so as ra fall into predetermined ranges. In case of automatic control, it is sufficient to incorporate them into operation parameters. In place of the sensor of oxygen concentration at the exit, it is also sufficient to provide a concentration sensor in the vicinity of the smoke stack and estimate the oxygen concentration at the exit from its value.

By using the above mentioned incinerator, mixed combustion was performed by supplying waste plastic, which is mainly composed of polyethylene and have the lower calorific value of 8500 kcal/kg, and sewage sludge, which has the chlorine content of 1 wot%, water content 0= 88wt%, N content of 6.0 wt%, and S content of 1.0 wt%, each in the amount of 500 kg/h. The temperature of the sand layer was maintained at 380 o 450 C,

temperature of the fluidizing air at 20 to 280 , temperature a-c the exit at goo to 12000C, and the. oxygen concentration ar the exit at 3 to 12%. As a result, the concentration of dioxins was reduced about by half in average in comparison with combustion of waste plastics only. In particular, when combustion was

carried out at the sand layer temperature of 440 C, fluidized air temperature of 2000C, freeboard temperature of 950 C, exit temperature of 920 C, and oxygen concentration at the exit of 8 2%, the concentration of dioxins at the exit was able to be M3~-eq. suppressed to 0. 06 ng/Nm-teq.

As explained above, the present invention is a combustion method characterized by mixed combustion 0= waste plastics, of which combustible matter has the lower calorific value of 4500 kcal/kg or more, with sludge, maintaining the temperature at the exit of the incinerator and the oxygen concentration at the exit of the incinerator within specific ranges.

Stable combustion is effected by performing the mixed combustion of sludge of the high water content and reduced lower calorific value and plastic of high lower calorific value, so that emission of poisonous gas or unburnt part is restrained.

In addition, by bringing down the temperature of the sand layer to 380-450oC, the reacting rate of. primary combustion is lowered, thereby the balance between mixing agitation with air and the reaction therewith is fully maintained, so that the generating amount of soot and dioxins can be restrained. Gasified waste plastics and combustible matter in sludge are burned at the freeboard section maintained at a high temperature and poisonous

gas is further restrained, and the temperature becomes 900 to 12000C at the exit. Oxygen concentration at the exit is kept at 3 to 12%, and by this time, combustion is completed. In case of automatic control, it is sufficient to incorporate the values of each thermometer and oxygen concentration meter in the parameters.

BEST MODE 4 In this mode, the inventors diligently made investigations on efficient suppression of dioxins in waste treatment by mixed combustion of waste and sludge in an incinerator, and have obtained following findings from the present mode.

Namely, for controlling the charging ratio of sludge and waste and the charging amount of sludge so as to realize stable burning conditions in the waste treatment, the concentration of SOx in the incinerator or at the outlet of the same shall be used as a parameter for judging burning conditions in the incinerator, and be kept within a predetermined range, thereby enabling to effectively suppress generation of dioxins.

The dioxins suppressing effect is further improved by setting the S content, N content, and water content in sludge within predetermined ranges.

The present mode has been built based on such findings, and is characterized by the following structure.

This mode provides a waste treating method characterized by mixed fuel combustion of waste and sludge in an incinerator, where the SOx concentration in the incinerator or at the outlet

of the same is measured, and the supply amounts of sludge and/or waste are controlled in accordance with the measured values.

In the current mode, it is preferable that the incinerator is a fluidized bed type, and the supply amounts of sludge and/or waste are controlled so that the SO, concentration is 100 to 2000 ppm.

Further preferably, the above sludge shall have, by dry weight percent, the S content of 0.1 to 2. 0%, N content of 1 to 10%, and water content of 65 to 90 wt%.

Further, this embodiment provide a waste treating apparatus characterized by mixed combustion of waste and sludge in an incinerator, which equips a SO" concentration meter for measuring the SOX concentration in the incinerator or at the outlet of the same, and a control apparatus for controlling the supply amounts of sludge and/or waste in accordance with the measured values.

In this mode, it is preferable that the incinerator is a fluidized bed type, and the supply amounts of sludge and/or waste are controlled so that the SOx concentration is 100 to 2000 ppm.

Further preferably, the apparatus of this embodiment shall treat the sludge which has, by dried weight percentage, the S

content of 0. 1 to 2. 0%, N content ofl to 10%, and water content of 65 to 90 wt%.

In waste treatment by mixed fuel combustion of waste and sludge using the incinerator of this mode, by monitoring the SO,. concentration in the incinerator or at the outlet of the same, dioxins emissions can be effectively reduced.

The SO, concentration in the incinerator or at the outlet

of the same can be used as an index of burning reactions in the incinerator. Further, since SOx is mostly derived from the S content in sludge, the SOx concentration can also be used as an index for the charge amount of sludge. In other words, it can be used as an index to judge at what ratio sludge is to be charged relative to waste, and in what extent combustion is progressing in the incinerator. Therefore, by adjusting the SOx concentration in the incinerator or at the outlet of the same within a predetermined range, it is possible to determine the charge ratio of sludge and waste for realizing a stable burning condition and effectively restrain dioxins.

For accomplishing this object, it is sufficient to install a SOx concentration meter in the incinerator or at the outlet of the same, and for automatic control, it is sufficient to incorporate values thereof into operating parameters. It can be realized at a relatively low cost without special renovation.

If it is difficult to install a SOx concentration meter in the incinerator or at the exit of the same, the effect of this mode can be obtained by installing a SOx concentration meter in the stack so as to adjust the SOx concentration in the stack in a predetermined range.

Detailed explanation will be made referring to FIG. 5.

FIG. 5 shows one example of a waste treating apparatus in the present mode. This treating apparatus is provided with a fluidized bed incinerator 101, a waste charger 102, and a sludge charger 103. The incinerator 101 is connected to an exhausting gas treating apparatus 110 which is connected to a stack 112.

At the outlet 105 of the incinerator 101, a SOx concentration meter 106 is provided, from which a concentration sensing signal is input to a control apparatus, or a gauge, 107.

Sludge and waste charged into the fluidized bed incinerator 101 from the respective chargers 102 and 103 contact a sand layer fluidized by a fluidizing gas (e. g. , air) sent from below a dispersing plate 104, are dried, and catch fire. The sludge and waste which caught fire burn within the incinerator 101. While doing so, for suppressing generation of soot which causes the increase the dioxins concentration, the residence time shall desirously be more than three seconds, and the temperature of the exhausting gas shall preferably be less than 700 C at the outlet.

In FIG. 5, charge amounts of sludge and/or waste is determined so that measured values of the SO, concentration meter 106 provided at the outlet 105 of the incinerator fall within predetermined ranges. Namely, a concentration sensing signal is input from the concentration meter 106 to the control apparatus or gauge 107, and based on this signal the charge amounts of sludge and/or waste are determined so that the measured values of the SOx concentration meter 106 provided at the outlet 105 of the incinerator are within'the predetermined ranges. If the SO, concentration is low, the charge amount of sludge is increased and/or the charge amount of waste is increased, on the other hand, if rhe S (\ concentration is high, the charge amount of sludge is decreased and/or "the charge amount of waste is decreased.

In the present mode, the appropriate SOx concentration at

the outlet is 100 to 2000 ppm. If the SOx concentration at the cutler is less than 100 ppm, the effect of suppressing dioxins is not sufficient, and if it exceeds 2000 ppm, the concentration of HS or S03 in waste gas goes up, and much consideration on operating environments becomes necessary.

In this mode, the same effect as mentioned above can also be brought about when a concentration meter 106 is provided in the incinerator 101, and the charge amounts of sludge and/or waste are controlled so that the SOx concentration in the incinerator 101 falls into the predetermined range, preferably 100 to 2000 ppm. If it is difficult to provide the SOx concentration meter in the incinerator or at its exit, the SOx concentration meter may be provided in the stack. In such a case, white smoke prevention air may join in the waste gas line at the upstream of the stack as shown in FIG. 5, and influence the SOx concentration in the stack. In this case, the concentration may be converted for consideration using, for example, the oxygen-12% conversion.

The type of incinerator for the present mode is not especially limited, but the fluidized bed type is particularly preferable, which carries out the combustion by fluidizing the materials to burnt in the incinerators, and provides excellent combustibility of sulfur containing substances. This type includes the fluidized bed incinerator and the fluidized bed thermal decomposition incinerator.

In addition, in the treatment of waste relating to the present mode, dioxins can be more effectively decreased by adjusting the S, N, and water content in sludge to be supplied

to the incinerator.

Sludge is discharged from a wastewater treatment facility.

Any type of sludge is applicable, including sewage sludge, night soil sludge, sludge generated when performing an activated sludge treatment of organic wastewater, sludge generated when performing a solid-liquid separation of wastewater containing organic materials, sludge generated in closed water areas as in river dredging, and other sludge generated in the course of treating wastewater.

With respect to waste treatment in the fluidized bed incinerator, examples of the present mode will be explained, but the present mode is not limited to these.

In the fluidized bed incinerator, the sludge, which has, by dried weight, the S content of 0. 7%, N content of 6% and water content of 75 wt%, and urban refuse, which has the lower calorific value of 2300 kcal/kg, were burnt by adjusting temperature in

the incinerator to 650-700 C. FIG. 6 is a graph showing the relation of the SO,. concentration with the dioxins concentration at the outlet of the incinerator and the concentration of poisonous substance (HS+SO). From this result, when the sludge supply amount is controlled so that the SOx concentration at the outlet is 100 to 2000 ppm, dioxins can be effectively removed and the concentration of poisonous or corrosive substances can be suppressed.

FIG. 7 shows one example of performing mixed combustion of waste and sludge without controlling the sludge supply amount based on the SOx concentration. FIG. 7 shows a waste charger 102,

sludge charger 103, fluidized bed incinerator 104, outlet 105, exhausting treating apparatus 110, and stack 112.

As explained in FIG. S, the present mode measures the SOx concentration in the incinerator or the outlet of the same as indexes for judging burning conditions in the incinerator. Based on the measured values, the charge ratio of sludge and waste is determined for realizing stable burning conditions, and it is possible to efficiently restrain generation of dioxins and emission of poisonous gas together with realizing the stable combustion. It can be realized at a relatively low cost without requiring any large scale renovation.

BEST MODE 5 In this mode, the inventors diligently made investigations on efficient suppression of dioxins in waste treatment by an incinerator, and have obtained the following findings.

Namely, dioxins can be reduced by performing mixed fuel combustion of waste and sulfur containing substance. Further, the SOx concentration in the incinerator or at the outlet of the same can be used as an index for judging burning conditions in the incinerator, and by keeping it in a predetermined range, it is possible to effectively suppress generation of dioxins.

This mode provides a waste treating method characterized by mixed fuel combustion of sulfur contained material and waste in an incinerator, where the SOx concentration in the incinerator

or at the outlet of the same is measured, and the supply amounts of the sulfur contained material and/or waste are controlled i : 1 accordance wit-h the measured values.

In the current mode, it is preferable that the incinerator is a fluidized bed type, and the supply amounts of sulfur contained material and/or waste are controlled so that the SOx concentration is 100 to 2000 ppm.

Further, this mode provide a waste treating apparatus characterized by combustion of waste in an incinerator, which equips a sulfur contained material charger, a waste charger, a SOx concentration meter for measuring the SOx concentration in the incinerator or at the outlet of the same, and a control apparatus for controlling the supply amounts of sulfur contained material and/or waste in accordance with the measured values.

In this mode, it is preferable that the incinerator is a fluidized bed type, and the supply amounts of sulfur contained material and/or waste are controlled so that the SOx concentration is 100 to 2000 ppm.

In the waste treating technology of this mode, by performing mixed fuel combustion of sulfur contained material and waste in the incinerator, and observing the SOx concentration in the incinerator or at the'outlet of the same, dioxins can be effectively reduced.

The S content in sludge stays in the incinerator as HS, Ces2, COS, S02 or SO) during the combustion step. These substances have a poisoning effect to copper and similar substances which act as catalysts for the generation of dioxins, and can effectively

restrain dioxins in the exhausting gas line from the high temperature combustion field within the incinerator to behind the outlet of the incinerator.

The SOx concentration in the incinerator or at the outlet of the same can be used as an index of burning reactions in the incinerator. Further, since SOY. is mostly derived from the S content in the sulfur contained material, the SOx concentration can also be an index for the charge amount of the sulfur contained substance. In other words, it can be used as an index to judge at what ratio sulfur contained material is to be charged relative to waste, and in what extent combustion is progressing in the incinerator. Therefore, by adjusting the SOx concentration in the incinerator or at the outlet of the same within a predetermined range, it is possible to determine the charge amount of sulfur contained material for realizing a stable burning condition and more effectively restrain dioxins.

For accomplishing this object, it is sufficient to install

a SO a SOx concentration meter in the incinerator or the outlet of the same, and for automatic control, it is sufficient to incorporate values thereof into operating parameters. It can be realized at a relatively low cost without special renovation.

If it is difficult to install the SOx concentration meter in the incinerator or at the outlet of the same, the effect of this mode can be obtained by installing the SOx concentration in the stack so as to adjust the SO concentration in the stack in a predetermined range.

Detailed explanation will be made referring to Fig. 8.

FIG. 8 shows one example of a waste treating apparatus in the present mode. This treating apparatus is provided with a fluidized bed incinerator 101, a sulfur contained material charger 103 and a waste charger 102, and the incinerator 101 is connected to an exhausting gas treating apparatus 110, which is connected to a stack 112. At the outlet 105 of the incinerator 101, a SOx concentration meter 106 is provided from which a concentration sensing signal is input to a control apparatus, or a gauge, 107.

Sulfur contained material and waste charged in the incinerator 101 from the respective chargers 102 and 103 contact a sand layer fluidized by a fluidizing gas (e. g. , air) sent from below a dispersing plate 104, are dried, and catch fire. The sulfur contained material and waste which caught fire burn in the incinerator 101. While doing so, for suppressing generation of soot which causes the increase of the dioxins concentration, the residence time shall desirously be more than three seconds, and the temperature of the waste gas shall preferably be less than 7000C at the outlet. Subsequently, the exhausting gas is discharged from the outlet 105, goes through the exhausting gas treating apparatus 110, and is released outside from the stack 112.

In FIG. 8, the charged amounts of sulfur contained material and/or waste are determined so that measured values of the SO, concentration meter 106 provided at the exit 105 of the incinerator 101 fall within the predetermined ranges. Namely, a concentration sensing signal is input from the concentration

meter 106 to the control apparatus or gauge 107, and based on this signal, the charged amounts of sulfur contained material and/or waste are determined so that the measured values of the S (\ concentration meter 106 provided at the outlet 105 of the incinerator are within the predetermined ranges. If the SOx concentration is low, the charged amounts of sulfur contained material is increased and/or the charged amounts of waste is decreased, on the other hand, if the SOx concentration is high, the charged amount of sulfur contained material is decreased and/or the charge amounts of waste is increased.

In the present mode, the appropriate SOx concentration at the outlet is 100 to 2000 ppm. If the SOx concentration at the outlet is less than 100 ppm, the effect of suppressing dioxins is not sufficient, and if it exceeds 2000 ppm, the concentration of H2S or S03 in waste gas goes up, and much consideration on safety and health becomes necessary.

In this mode, by providing the SOx concentration meter 106 in the incinerator 101, it is possible to control the charged amounts of sulfur contained material and/or waste so that the SOx concentration in the incinerator 101 falls within the predetermined range, preferably 100 to 2000 ppm. If it is difficult to provide the SOx concentration meter in the incinerator or at its outlet, the SOx concentration meter may be provided in the stack. In such a case, white smoke prevention air may join in the exhausting gas line as shown in FIG. 8, and influence the SO concentration in the stock. In this case, the concentration may be converted for consideration using, for

example, the oxygen-12% conversion.

The type of incinerator for the present mode is not especially limited, but the fluidized bed type is particularly preferable, which carries out the combustion by fluidizing the materials to be burnt in the incinerators, and provides excellent combustibility of sulfur contained material. This type includes the fluidized bed incinerator and the fluidized bed thermal decomposition incinerator.

As explained above, based on the SOx concentration values measured in the incinerator or at the outlet of the same, it is possible to determine the charged ratio of sulfur contained material and waste and to efficiently restrain generation of dioxins. It can be realized at a relatively low cost without requiring any large scale renovation.

BEST MODE 6 The present mode provides a RDF treatment method and a apparatus thereof by introducing a relatively simple apparatus, which keeps the burning condition in the incinerator constant, thereby suppresses the emission of poisonous gas or unburnt gas and efficiently reduces dioxins.

In this mode, the inventors diligently made investigations on efficient suppression of dioxins in the RDF treatment by an incinerator, and have obtained the following findings.

Namely, dioxins can be reduced by performing mixed combustion of RDF and sulfur contained material. Further, the SOx concentration in the incinerator, at the outlet of the same

or at a stack can be used as an index for judging burning conditions in the incinerator, and by keeping it in a predetermined range, it is possible to effectively suppress generation of dioxins.

This mode provides a RDF treating method characterized by mixed fuel combustion of sulfur contained material and RDF, where the SO, concentration in the incinerator, at the outlet of the same, or at the stack, is measured, and the supply amounts of the sulfur contained material and/or RDF are controlled in accordance with the measured values.

In the current mode, it is preferable that the incinerator is a fluidized bed type, and the supply amounts of sulfur contained material and/or RDF are controlled so that the SO, concentration at the stack is 50 to 400 ppm.

Further, this embodiment provides a RDF treating apparatus characterized by mixed fuel combustion of sulfur contained substance and RDF in the incinerator, which equips a sulfur contained material charger, a RDF charger, a SOL concentration meter for measuring the SOx concentration in the incinerator, at the outlet of the same, or at the stack, and a control apparatus for controlling the supply amounts of sulfur contained material and/or RDF in accordance with the measured values.

In this mode, it is preferable that the incinerator is a fluidized bed type and a control apparatus is provided for controlling the supply amounts of sulfur contained material

and/or RDF so that the SOx concentration at the stack is 50 to 400 ppm.

In the RDF rearing technology of this mode, by performing the mixed fuel combustion of RDF and sulfur contained material in the incinerator, and observing the concentration of SOx in the incinerator, at the outlet of the same, or at the stack, dioxins can be effectively reduced.

The sulfur content stays in the incinerator as H2S, CS2, COS, S02 or S03 during the combustion process. These substances have a poisoning effect to copper and similar substance which act as catalysts for the generation of dioxins, and can effectively restrain dioxins in the exhasuting line from the high temperature combustion field in the incinerator to behind the outlet of the incinerator. Some of these substances restrain the reaction for generating dioxins of Cl in the course of generating dioxins. As a result, the generation of dioxins in the combustion step and its downstream is restrained.

The SOx concentration in the incinerator, at the outlet of the same, or in the stack can be used as an index of burning reactions in the incinerator. Further, since SOx is mostly derived from the S content in the sulfur contained material, the SO concentration can also be an index for charge amounts of the sulfur contained material. In other words, it can be used as an index to judge at what ratio sulfur contained material is to be charged relative to waste, and in what extent combustion is progressing in the incinerator. That is, this is to be an index for efficient reaction to contribute to the reduction of dioxins.

For accomplishing this realization, it is sufficient to install a SO, concentration meter in the incinerator, the outlet of the same or in the stack, and for automatic control, it is enough to incorporate values thereof into operating parameters.

Detailed explanation will be made referring to Fig. 9.

FIG. 9 shows one example of a RDF treating apparatus in the present mode. This treating apparatus is provided with a fluidized bed incinerator 101, a RDF charger 130 and a sulfur contained material charger 132, and the incinerator 101 is connected to a exhausting gas. treating apparatus 110 which is connected to a stack 112. The stack 112 is provided with a SOx concentration meter 127 from which a concentration sensing signal is input to a control apparatus or a gauge 128.

RDF and sulfur contained material charged in the incinerator 101 from the respective chargers 130 and 132 contact a sand layer fluidized by fluidizing gas (e. g. , air) sent from below a dispersing plate 104 and catch fire. RDF and sulfur contained material which caught fire burn in the incinerator 101. The exhausting gas is discharged from the exit 106, goes though the exhausting gas facility 110, and is released outside from the stack 112.

In Fig. 9, charged amounts of RDF and/or sulfur contained material are determined so that measured values of the SOx concentration meter 127 provided in the stack fall within predetermined ranges. Namely, a concentration sensing signal is input from the SO, concentration meter 127 to the control apparatus or gauge 107 connected to the concentration meter 127

provided in the stack 112, and based on this signal, the charged amounts of RDF and/or sulfur contained material are determined so that the measured values of the SOx concentration meter 106 provided in the stack are within the predetermined ranges. If the SOx concentration is low, the charged amounts of sludge is increased and/or the charge amounts of RDF are decreased. On the other hand, if the SOx concentration is high, the charged amounts of sludge are decreased and/or the charged amounts of RDF are increased.

White smoke prevention air may join in the exhausting gas line at the upstream of the stack as shown in FIG. 9, and influence the SOx concentration in the stock. In this case, the concentration may be converted for consideration using, for example, the oxygen-12% conversion. For automatic control, values of SOx concentration may be added to operation parameters.

In the present mode, the appropriate concentration at the outlet is 50 to 400 ppm. If the SOx concentration at the outlet is less than 50 ppm, the reaction by the S content cannot be carried out efficiently, and if it exceeds 400 ppm, a corrosion possibility deriving from sulfur oxide in a down stream becomes large.

In this mode, the SOx concentration meter 106 may be provided in the incinerator or at the, outlet thereof, and the charged amounts of RDF and/or sulfur contained material may be controlled so that the SO, concentration in the incinerator or at the outlet thereof falls into the predetermined range, preferably 60 to 600 ppm. Also in this case, the same effect as mentioned above can

be obtained.

The type of incinerator in the present mode is not especially limited, but the fluidized bed incinerator, which carries out the combustion by fluidizing the materials to be burnt, is particularly preferable for providing excellent combustibility of sulfur contained material.

As explained above, by this mode for the treatment of refuse solid fuel in the incinerator, it became possible to determine the charged ratio of sulfur contained material and RDF for realizing stable burning conditions and to efficiently restrain generation of dioxins. It can be realized at a relatively low cost without requiring any large scale renovation.

BEST MODE 7 The present mode is to provide a waste treating method and an apparatus thereof, which keep burning conditions in an incinerator constant by performing mixed fuel combustion of sludge and waste, thereby to efficiently reduce dioxins.

The inventors diligently made investigations on effective suppression of dioxins in the waste treatment by an incinerator, and have obtained the following findings.

In the waste treating technology of carrying out the mixed fuel combustion of sludge and waste, by supplying sulfur contained material into feeding lines of sludge or waste to the incinerator, it is possible to supply, under stable conditions, the S content which has the effect of reducing the concentration of dioxins.

Further, for controlling the charged amounts of sulfur contained powder to realize stable burning conditions, by using the SOx concentration in the incinerator, at the outlet of the same or in the stack as an index for judging the burning condition, and keeping it within a predetermined range, the effect of suppressing dioxins is more improved.

The present mode is based on such findings, and characterized by the following structure.

This mode is to provide the waste treating method characterized by supplying sulfur contained material into the feed line of sludge or waste to an incinerator when performing waste treatment by mixed fuel combustion of sludge and waste in an incinerator.

In this mode, the SOx concentration is measured in the incinerator, at the outlet of the same or in the stack, and based on the measured value, the supply amount of the sulfur contained powder is controlled. The supply amount is preferably controlled so that the SOx concentration in the stack is 50 to 400 ppm, and the incinerator is preferably a fluidized bed type.

Further, the mode is to provide the waste treating apparatus characterized by provision of an apparatus for supplying sulfur contained material into the feeding line of sludge or waste to the incinerator when performing waste treatment by mixed fuel combustion of sludge and waste in an incinerator.

In addition, this mode is to provide the waste treating apparatus characterized by provision of a SOx concentration meter for measuring the SOx concentration in the incinerator, ai : T : he

outlet of the same or in the stack, and a control apparatus for controlling, based on the measured value, the supply amount of the sulfur contained powder. The supply amount is preferably controlled so that the SO, concentration in the stack is 50 to 400 ppm, and the incinerator is preferably a fluidized bed type.

Herein, the above mentioned"apparatus for supplying sulfur contained powder" means a sulfur powder storage bin and a sulfur powder supply line connected with a sludge supply line, or a sulfur powder storage bin and a waste supply line.

In the waste treating technology relating to this mode, by supplying the sulfur contained powder into the sludge or waste supply line to the incinerator, it is possible to supply the S content, efficiently and in a stable condition, when it is in shortage for effectively reducing dioxins.

By connecting the sulfur supply line for supplying sulfur containing powder to the sludge supply line or the waste supply line to the incinerator and supplying the sulfur contained powder mixed with the sludge or waste, the mixture composed of the sulfur powder and the sludge or waste can be supplied, in uniform properties, into the incinerator. In this way, it is also possible to avoid non-uniformity in the incinerator caused by directly supplying the sulfur containing powder into the incinerator, or danger of waste explosion. In the operation, since the supply of the S content can be started or ended together with starting or ending of the sludge or waste supply, operational simplicity and safety can be established. Further, enough S, N and water contents are supplied into the incinerator, and so

dioxins can be effectively reduced due to the above mentioned reasons.

The SOx concentration in waste gas in the incinerator, at the outlet of the same or in the stack is determined by burning conditions such as the temperature in the incinerator and the amount of S powder supplied through the sludge supply line or waste supply line, and it can be used as an index for the generation of dioxins. In other words, by observing the value of SOx concentration and adjusting the combustion so that the SOx concentration in the incinerator, at the outlet of the same or in the stack is within a predetermined range, it is possible to determine the amount of the sulfur powder required for realizing a stable burning condition and to efficiently restrain the generation of poisonous gas such as dioxins.

For realizing this, it is sufficient to install a SOx concentration meter in the incinerator, at the outlet of the same or in the stack. It can be realized at a low cost without requiring any special renovation.

Detailed explanation will be made referring to FIG. 10.

However, this mode is not limited thereto.

FIG. 10 shows one example of the waste treating apparatus of this invention. This treating apparatus is equipped with a waste storage bin 201, sludge storage bin 202, S powder storage bin 203 and an incinerator 204. The waste storage bin 201 and the incinerator 204 are connected by a waste supply line 205 for supplying waste in the waste storage bin 201 to the incinerator 204. The sludge storage bin 202 and the incinerator 204 are

connected by a sludge supply line 206 for supplying sludge in the sludge storage bin 202 to the incinerator 204. The sulfur powder storage bin 203 and the sludge supply line 206 are connected by a sulfur powder supply line 207 for supplying sulfur powder in the sulfur powder storage bin 203 to the incinerator 204.

In the present example, the sludge in the sludge storage bin 202 is sent under pressure by a pump (not shown) to the incinerator 204 via the sludge storage line 206. The sulfur powder sent under pressure from the sulfur powder storage bin 203 is supplied into the sludge supply line 206, mixed with the sludge, made into a uniform property while being transferred downstream, and supplied to the incinerator 204.

By such an arrangement, it is possible to avoid nonuniformity in the incinerator caused by directly supplying the sulfur containing powder into the incinerator, or danger of waste explosion, and efficiently reduce dioxins while maintaining a balance among the S, N and water contents in the incinerator. In the operation, since the supply of the S content can be started or ended together with starting or ending of the sludge or waste supply, operational simplicity and safety can be established.

In this embodiment, the S content to be supplied into the sludge supply line is not limited to powder, and any forms, e. g., slurry, may be suitably used.

FIG. 10 shows an example of connecting the sulfur power line to the sludge supply line. However, it also is possible to connect the sulfur powder supply line to the waste supply line, and also in this case the waste and the sulfur powder are mixed

and sent to the incinerator in a uniform property, and the same effect as mentioned above can be brought about. The same effect is obtained by a more simple method than the one exemplified here such as sulfur powder supply to a water supply line for controlling the temperature of the incinerator or a wastewater supply line.

FIG. 11 shows another example of the waste treating apparatus of this invention. This treating apparatus is equipped with a waste storage bin 211, sludge storage bin 212, sulfur powder storage bin 213 and a fluidized bed incinerator 214 to which a waste gas treating apparatus 222 is connected, and a smoke stack 224 is connected to the waste gas treating apparatus 222. The waste storage bin 211 and the incinerator 214 are connected by a waste supply line 215 for supplying waste in the waste storage bin 211 to the incinerator 214. The sludge storage bin 212 and the incinerator 214 are connected by a sludge supply line 216 for supplying sludge in the sludge storage bin 212 to the incinerator 214. The sulfur powder storage bin 213 and the sludge supply line 216 are connected by a sulfur powder supply line 217 for supplying sulfur powder in the sulfur powder storage bin 213 to the incinerator 214. The smoke stack 224 is provided with a SOx concentration meter 220 from which a concentration sensing signal is input to a control apparatus or a gauge 221.

In this example, the sulfur contained powder supplied to the sludge supply line 216 is completely mixed with sludge in the line 216 and is sent to the incinerator 214 in a uniform property. This sludge and the waste sent via the waste supply line 215 from the waste storage bin 211 are dried in the sand

layer fluidized by the air from the wind box 225 under the dispersing plate 218, their temperature being raised, and catch fire. The waste which caught fire burns in the freeboard section, and the combustion is perfectly completed. The exhausting gas is released outside from the stack 224 via the exhausting gas treating apparatus 222. Based on the concentration sensing signal from the SOx concentration meter installed in the stack 224, the supply amount of the sulfur powder is determined by the control apparatus or the gauge 221 so that the SOx concentration in the stack is within the predetermined range. More concretely, if the SOx concentration is too low, the sulfur powder supply amount is increased, and conversely if it is too high, the amount is decreased.

In this embodiment, the appropriate SOx concentration in the stack is 50 to 400 ppm. If it is less than 50 ppm, the effect of suppressing dioxins is not sufficient, while if it exceeds 400 ppm, the SOx concentration cannot achieve a regulated value.

White smoke prevention air may join in the exhausting gas line at the upstream of the stack as shown in Fig. 11, and influence the SO, concentration in the stack, In this case, the concentration may be converted for consideration using, for example, the oxygen-12 conversion. For automatic control, values of SOx concentration may be incorporated into operation parameters.

-1 concentration meter is Further, in this example, the SO, concentration meter is installed at the smoke stack, but the SOx concentration meter may be installed in the incinerator 214 or at the outlet 219, and

the supply amount of the sulfur contained powder is controlled so that the SOx concentration in the incinerator or at the outlet of the same is within the predetermined range, preferably 60-600 ppm in either case. This drawing shows the fluidized bed incinerator, not limiting thereto, and it is applicable to a fire grate type incinerator.

As explained above, by this mode, in the waste treatment performing mixed fuel combustion of the waste and sludge, the sulfur powder can be efficiently supplied in a stable condition, which supplements the S concentration to obtain the effect of reducing dioxins.

The burning condition can be judged in accordance with the SOx concentration in the incinerator, at the outlet of the same or the stack, so that the supply amount of the sulfur powder can be decided for realizing the stable burning condition so as to efficiently reduce dioxins.

BEST MODE 8 The present mode is to provide a wasre treating method performing mixed fuel combustion of waste and sludge and/or sulfur contained material in the waste incinerator, characterized by dispersed supply of the sludge and/or sulfur containing substance into a waste hopper.

This mode is to further provide a waste treating apparatus performing the mixed fuel combustion of waste and sludge and/or sulfur contained material in the waste incinerator, characterized by provision of a dispersed supply means for

performing the dispersed supply of the sludge and/or sulfur contained material into a waste hopper.

Below, detailed explanation will be made on this mode.

In this mode, sludge and/or sulfur contained material are dispersed and supplied into the waste chute by a dispersed supply apparatus which has the function of performing dispersed supply.

No limitation is especially made to a dispersed supply apparatus, and any type is applicable as far as it has a function of uniformly dispersing sludge and/or sulfur contained material into the waste chute. For example, screw conveyor or sliding conveyor, or their combination will be enumerated.

It is desirable that waste has been supplied in the waste hopper prior to dispersed supply of sludge and/or sulfur containing substance.

When sludge is dispersed and supplied, it penetrates into the waste in the waste hopper due to its own weight, and the combustible matter and water content are dispersed evenly and mixed uniformly with the waste. In the case of sulfur contained material, it is evenly dispersed over the waste and mixed uniformly therewith. Since mixed sludge and/or sulfur contained material are supplied in company with the supply of the waste into the incinerator, sections which have extremely low calorific value or extremely high water content are not formed, and stable combustion takes place over a wide range, and soot generation is avoided.

As the apparatus of dispersed supply of sludge and/or sulfur containing substance, it is preferably to employ a lance which

mixes them with gas and perform dispersed supply into the waste hopper. By using a lance which uses air or CO2 as a transferring gas, sludge and/or sulfur contained material can be dispersed more uniformly and effectively in the waste hopper together with the transferring gas.

The dispersed supply of sludge and/or sulfur containing substance into the waste hopper from the dispersed supply apparatus is preferably carried out by meeting the timing of waste charging into the waste hopper by the waste crane. Ordinarily, the waste stored in a waste pit is supplied by the waste crane to the waste hopper at appropriately determined intervals. If sludge and/or sulfur containing substances are continued to be supplied when the amount of waste in the waste hopper is small, only these are fed into the incinerator. If sludge and/or sulfur containing substances are continued to be supplied when the waste crane is supplying waste into the waste hopper, sulfur containing substance and waste are considered to be scattered around the waste hopper. If the dispersed supply apparatus is, therefore, operated meeting the charge timing of waste into the hopper, appropriate amounts of sludge and/or sulfur containing substances can be efficiently supplied.

For example, the dispersed supply apparatus is operated in the following manners.

(1) After waste is supplied into the hopper by the crane, the sludge and/or sulfur containing substances of fixed amount are dispersed and supplied.

(2) The amount of waste in the hopper is sensed by a sensor, and

sludge and/or sulfur contained material of the most appropriate amount relative to the amount of the waste staying in the waste hopper at that time is dispersed and supplied so that sludge and/or sulfur containing substances are uniformly mixed.

(3) When the crane is charging the waste into the hopper, sludge and/or sulfur contained material are stopped to be supplied.

(4) The weight of waste charged into the hopper by the crane is sensed by a weight sensor, and sludge and/or sulfur contained material of the appropriate amount relative to the waste weight are dispersed and supplied after waste charging.

These manners may be carried out in combination. Manners are not limited to the above four, and other manners may be employed for dispersed supply of waste, meeting the charge timing at the hopper.

The dispersed supply of sludge and/or sulfur contained material by the above mentioned manners should be preferably stopped at latest one hour prior to stopping the operation of the incinerator. Usually, the incinerator enters the operation adjustment several hours prior to stopping the operation, and begins to reduce charge amounts of waste. If sludge and/or sulfur containing substances are continued to be supplied in this period, troubles will occur as follows. If the supply of sludge is continued, it. is foreseen that the whole calorific value goes down so that a burning condition becomes unstable. If sulfur contained material is continued to be supplied, the combustion rate thereof goes up in the incinerator, so that SOy concentration increases in the exhausting gas.

By stopping the supply of sludge and/or sulfur contained material by using the dispersed supply apparatus at latest one hour prior to stopping the operation of the incinerator, the above mentioned troubles can be avoided, and the burning condition can be prevented from becoming unstable during the period to stopping the operation.

The invention will be explained more in detail referring to the drawing.

FIG. 12 is a schematic view showing one example of the waste treating apparatus of this invention, illustrating the waste hopper section of the waste incinerator. Waste is charged into the waste hopper 302 from the waste crane 301, and on the other hand, sludge and/or sulfur contained material are transferred from an introducing inlet 305 of sludge and/or sulfur contained material onto the conveyor 304 and are dispersed over waste in the hopper.

Sludge subsequently penetrates into the waste in the hopper 302 due to its own weight, and the combustible matter and water content are mixed evenly. Sulfur contained material is also dispersed evenly over the waste in the hopper and mixed uniformly.

In certain circumstances, mixed sulfur contained material is subsequently supplied along with the supply of the waste into the incinerator. Thus, sludge and/or sulfur contained material are supplied together with waste into the incinera1 : or (not shown) from the waste chute 303.

FIG. 13 is a schematic view showing another example of the waste treating apparatus of this invention, illustrating a waste

hopper section of the waste incinerator. In the same manner as in FIG. 12, waste is charged into the waste hopper 302 by the waste crane 301. On the other hand, sludge and/or sulfur contained material are introduced from the introducing inlet 305 of sludge and/or sulfur contained material and are transferred from the lance 306 together with the transferring gas sent from a transferring gas outlet 307, dispersed and supplied into the waste hopper 302. Thus, sludge and/or sulfur contained material are dispersed widely over the waste in the hopper 302. As the transferring gas, other than the air, CO2 or nitrogen, recirculating waste gas may be employed. A flow rate thereof is not especially limited as far as it is in a range enabling to disperse sludge and/or sulfur containing substance.

Sludge subsequently penetrates into the waste in the hopper 302 due to its own weight, and the combustible matter and water content are mixed evenly. Sulfur containing substance is also dispersed evenly over the waste in the hopper and mixed uniformly.

Thus, sludge and/or sulfur containing substance are supplied together with waste into the incinerator (not shown) from the waste chute 303.

As sludge for mixed fuel combustion with waste in the present mode, any type of sludge is applicable, including sewage sludge, night soil sludge, sludge generated when performing an activated sludge treatment of organic wastewater, sludge generated when performing a solid-liquid separation of wastewater containing organic materials, sludge generated in closed water areas as in river dredging, and other sludge generated in the course of

treating wastewater. No special limitation is made-Eo the water content in sludge, and those with the water content in a usual range such as 10 to 90% can be used.

As sulfur contained material, sulfur powder, industrial wastewater (because it contains sulfur), waste rubber such as waste tires can be used. When using waste rubber such as waste tires, the operation should be carried out taking the calorific value into consideration.

In addition, the above mentioned sludge may be used in combination with sulfur containing substance.

* This mode does not limit the type of incinerator, and any type of incinerator such as a fluidized bet incinerator, fire grate incinerator or kiln incinerator may be applied for performing the mixed fuel combustion of waste and sludge and/or sulfur contained material. The temperature in the combustion chamber may be in an ordinary range.

Below, this invention will be explained more in detail, showing actual examples.

(Example 1) The fire grate incinerator was employed as the waste incinerator, and municipal refuse and sludge were mixed and incinerated, according to the method of this invention.

Firstly, sludge and air were mixed, and using a lance which has the function of dispersing the sludge, supplied into the waste hopper in which waste had previously been charged. The transferring gas for sludge was CO ; ;. Municipal refuse was with

the value of 2300 kcallkg and the sludge ratio was 80%. The mixed fuel combustion of municipal refuse and sludge was carried out by changing the temperature of the drying stage from 700 to 850 C and the temperature in the combustion chamber from 850 to 1000 C.

As a result, comparing with a case of charging municipal refuse and sludge into the incinerator from separate chutes, the CO concentration was reduced to less than half, and the concentration of dioxins was also reduced by 30%. During the combustion, the incinerator could be operated under stable conditions, and no abnormality was seen in the waste gas concentration or conditions of ashes.

(Example 2) The fire grate incinerator was employed as the waste incinerator, and municipal refuse and sludge were mixed and incinerated, according to the method of this invention.

Firstly, sulfur powder was used as sulfur contained material and using a lance which has the function of dispersing the sulfur contained material, supplied into the waste hopper in which waste had previously been charged. The transferring gas for sulfur contained material was C02. Municipal refuse was with the value of 2300 kcal/kg'and the sulfur contained material ratio was 80%. The mixed fuel combustion of municipal refuse and sulfur powder was carried out by changing the temperature of the drying stage from 700 to 850 C and the temperature in the combustion chamber from 850 to 1000 C.

As a result, comparing with a case of charging municipal

refuse and sulfur powder into the incinerator from separate chutes, the CO concentration was reduced to less than half, and the concentration of dioxins was also reduced by 20%. During the combustion, the incinerator could be operated under stable conditions, and no abnormality was seen in the waste gas concentration or conditions of ashes.

As mentioned above, the present mode provides a waste treating method and an apparatus which keep burning conditions constant, and efficiently perform the mixed combustion of sludge and/or sulfur contained material and waste such as municipal refuse so as to reduce the concentration of dioxins in an exhausting gas.

By using the present mode, it is possible to uniformly supply sludge and/or sulfur contained material and waste into the waste hopper and therefore it is possible to supply these in the incinerator. Accordingly, a stable combustion progresses without generating any range of extremely low calorific value in the incinerator, and consequently, generation of dioxins in the exhausting gas can be effectively reduced.

By this mode, the mixed fuel combustion of sludge and/or sulfur contained material can be applied not only to a conventional fluidized bed incinerator but also to a fire grate incinerator, bringing about great industrial value.

BEST MODE 9 The present mode is to offer a waste treating method performing the mixed fuel combustion of waste and sludge and/or

sulfur contained material in a waste incinerator using a fire grate, characterized by dispersed supply of the sludge and/or sulfur contained material onto the fire grate of a drying stage.

The present mode is to further provide a waste treating apparatus performing the mixed fuel combustion of waste and sludge and/or sulfur contained material in the waste incinerator using the fire grate, characterized by providing a dispersed supply means of dispersing the sludge and/or sulfur contained material and supply them onto the fire grate of the drying stage Below, detailed explanation will be made on this mode.

In this mode, sludge and/or sulfur contained material are dispersed and supplied onto the fire grate of the drying stage of the fire grate incinerator by a dispersed supply apparatus which has the function of performing the dispersed supply of these.

As a dispersed supply apparatus, no limitation is especially made as far as it has a function of uniformly dispersing sludge and/or sulfur contained material onto the fire grate of the drying stage, and arbitrary types can be used.

When sludge is dispersed and supplied, as it mixes into the waste being dried on the fire grate due to its own weight, it is dried and soon catches fire. Also in a case of sulfur contained material, it is evenly dispersed over the waste being dried on the fire grate, dried together with waste, and starts combustion.

A stable combustion takes place without partially forming ranges where the temperature is low. As sludge evenly mixes with waste, sludge before burning does not fall onto an ash chute under the fire grate through openings of the fire grate such as holes formed

by being pushed by blowing air.

As an apparatus for dispersed supply of sludge and/or sulfur contained material, it is preferably to employ a lance which performs dispersed supply onto the fire grate of the drying step by mixing them with gas. This type of lance, using air or CO2 as a transferring gas, can disperse sludge and/or sulfur contained material uniformly and effectively on the fire grade of the drying stage. In the present invention, sludge and/or sulfur contained material are dispersed and supplied on the fire grate, and in case the surface temperature of the lance becomes high, a cooling mechanism is desired to be installed outside of the lance.

The dispersed supply of sludge and/or sulfur contained material onto the fire grate of the drying step should be preferably stopped at latest one hour before the operation of

the incinerator is stopped. Usually, the incinerator enters the operation adjustment several hours before stopping the operation, and begins to reduce charge amounts. If sludge and/or sulfur contained material, are continued to be supplied in this period, troubles may occur as follows. If the supply of sludge goes on, it is foreseen that the whole calorific value goes down so that a burning condition becomes unstable. When sulfur contained material is continued to be supplied, the combustion fuel ratio thereof goes up in the incinerator, so that the SO, concentration increases in an exhausting gas.

When the dispersed supply of sludge and/or sulfur contained material are stopped at latest one hour before the operation of

the incinerator is stopped, the above mentioned troubles can be avoided, and the burning condition can be prevented from becoming unstable before the operation is stopped.

The invention will be explained more in detail referring to the drawing.

FIG. 14 is a schematic view showing one example of fire grate waste incinerators of this invention. Waste charged into the waste hopper 401 is sent to the fire grate of the drying stage 401 through the waste chute 402.

On the other hand, sludge and/or sulfur contained material are introduced from an introducing inlet 408 of sludge and/or sulfur contained material, sent through the lance 407 together with the transferring gas supplied from a transferring gas inlet 409 and are dispersed over the fire grate 403. Thus, sludge and/or sulfur contained material are dispersed efficiently and widely over the waste on the fire grate. As the transferring gas, other than air, CO : : or nitrogen, a re-circulating waste gas may be employed.

It is preferable that a flow rate thereof is enough to disperse sludge and/or sulfur contained material without influencing the combustion in the incinerator.

In the illustrated incinerator, the lance 407 for dispersed supply of sludge and/or s containing substance on the fire grate of (he drying stage 403 is provided along a moving direction of waste, but it is not limited thereto. It is also possible to provide the lance in a direction perpendicular thereto for dispersed supply of sludge and/or sulfur containing substance on the fire grate 403.

Sludge penetrates subsequently into the waste on the fire grate 403 due to its own weight, and the combustible matter and water content mix evenly. Sulfur contained material is also dispersed evenly over the waste on the fire grate and mixed uniformly. Thus, sludge and/or sulfur contained materiaal are dried together with waste by the air 406 blown from below and by the radiant heat in the incinerator, their temperature is raised and catch fire.

When the combustion starts, sludge and/or sulfur contained material are transferred together with waste to the fire grate of the combustion step 404 and burnt by the combustion air 306 sent from below the fire grate 403. Unburnt parts are sent to the fire grate 405 of a post combustion step and completely burnt, and ashes remaining after the combustion are taken out outside from a main ash chute 410.

The combustion takes place in a main combustion chamber 411, and exhausting gas (gas in the incinerator) is subjected to secondary combustion in a secondary combustion chamber 412, so that the unburnt parts are perfectly burnt. The exhausting gas is discharged outside of the incinerator and sent to downstream steps such as a waste gas treating facility (not shown).

As sludge for mixed combustion with waste in the present mode, any type of sludge is applicable, including sewage sludge, night soil sludge, sludge generated when performing an activated sludge treatment of organic wastewater, sludge generated when performing a solid-liquid separation of wastewater containing organic materials, sludge generated in closed water areas as in river dredging, and other sludge generated in the course of

treating wastewater. A special limitation is not made to the water content in sludge, and those containing the usual water content such as 10 to 90% can be used.

As sulfur contained material, arbitrary sulfur contained material may be employed such as in powder, liquid, solid or other states, and preferable are those easy to be transferred and without the dangers such as explosion.

In addition, the above mentioned sludge and sulfur contained material may be used in combination.

This mode does not especially limit the temperature in the drying stage and temperature in the combustion chamber. The mixed fuel combustion of sludge and/or sulfur contained material and waste can be efficiently carried out at temperature in the drying stage and at temperature in the combustion chamber within ordinary ranges.

More detailed explanation will be made to the present mode, showing actual examples.

(Example 1) The fire grate incinerator as shown in FIG. 14 was used, and municipal refuse and sludge were treated by mixed fuel combustion, according to the present mode.

Firstly, sludge and nitrogen were mixed, and supplied onto the fire grate by means of a lance which has the function of dispersing the sludge. A transferring gas of sludge was CO2, Municipal refuse was with the value of 2000 kcal/kg and the sludge ration was 80%. The mixed fuel combustion of municipal refuse

and sludge was carried out by changing the temperature of the drying stage from 700 to 850 C and that in the combustion chamber from 850 to 1000 C.

As a result, comparing with the case of not performing the mixed fuel combustion of municipal refuse and sludge, the average CO concentration was reduced to less than one half, and the concentration of dioxins was also reduced by 70% on average. During the combustion, the incinerator was able to be operated under stable conditions, and any abnormalities were not seen in waste gas concentration or conditions of ashes.

(Example 2) The fire grate incinerator as shown in FIG. 14 was used, and municipal refuse and sludge were treated by mixed fuel combustion, according to the method of this invention.

Firstly, sulfur powder was employed as sulfur contained material, and was supplied onto the fire grate by means of a lance which has the function of dispersing the sulfur contained material.

A transferring gas of sludge was CO.. Municipal refuse had general composition. The mixed fuel combustion of municipal refuse and sulfur powder was carried out at usual test conditions.

As a result, comparing with a case of not performing the mixed fuel combustion of municipal refuse and sulfur contained material, the average CO concentration was reduced to less than one half, and the concentration of dioxins was also reduced by 50% on average. During the combustion, the incinerator was able to be operated under stable conditions, and any abnormalities

were not seen in waste gas concentration or conditions of ashes.

As explained above, by the present invention, the waste treating method and apparatus are provided, which keep the combustion condition in the fire grate incinerator constant, and efficiently carry out the mixed fuel combustion of waste such as municipal refuse with sludge and/or sulfur contained material, so that the concentration of dioxins in the exhausting gas can be effectively reduced.

By using this mode, along with sludge and/or sulfur contained material, waste can be evenly supplied onto the fire grate of the drying stage without creating ranges where the calorific value is extremely low, resulting in efficient reduction of dioxins generation.

By this mode, it became possible to apply the mixed fuel combustion with sludge and/or sulfur contained material to the fire grate incinerator, bringing about great industrial value.

BEST MODE 10 In this mode, the inventors made various experiments of incineration treatment of waste, and found that by performing mixed fuel combustion of waste with sludge such as sewage sludge, the dioxins content in combustion waste gas is lowered.

".

Therefore, the inventors carried out various investigations as to how the effect of reducing dioxins was brought about by mixed fuel combustion with sludge.

One of the causes generating dioxins in combustion of waste is known to be that waste is burnt in an oxygen-poor atmosphere.

The burning conditions under such a state correspond to the conditions at the early stage of combustion where waste charged in the incinerator is heated and its temperature is raised. From this, it is considered that substances produced by thermal decomposition of sludge in the early stage of combustion restrains the generation of dioxins.

Therefore, as general sludge contains the N content of 2 to 10 weight % (dried), substances suppressing the generation of dioxins are considered to be those produced by thermal decomposition of N containing substances in sludge, and experiments were carried out. In the experiments, N compounds were added to waste and combustion was performed, and reduction of dioxins in the combustion waste gas was acknowledged. From this fact, it is supposed that the substance suppressing the generation of dioxins is ammonia (NH3) and compounds having a NH, radical generated at thermal decomposition of N containing substances in sludge.

A mechanism that thermally decomposed products of N containing substances suppresses the generation of dioxins is not clear, but it is considered that such products have a poisoning effect to copper and other substances which act as catalysts for generating dioxins. This poisoning effect is assumed to be one cause of bringing about the effect of suppressing the generation of dioxins.

As above, since N compounds produced by thermal decomposition of sludge restrains the generation of dioxins when burning waste, it has been found that if waste is combusted after

N compounds are added to it, the generation of dioxins is suppressed.

Further, in the present mode, studies were made on problems that dioxins are also generated in an'exhausting gas flow path behind the outlet of the incinerator, and a method of restraining such generation of dioxins was found. It is assumed that in the waste gas flow path, certain components in fly ash act as catalysts, and reaction between unburnt aromatic compounds and chlorine progresses, and dioxins are generated. Therefore, experiments were carried out for blowing N compounds into the exhausting gas flow path following the outlet of the incinerator, and reduction of dioxins in the exhausting gas was acknowledged. This is considered that N compounds blown into the exhausting gas flow path suppress the generation of dioxins similarly to charging of N compounds into the incinerator.

Thus, when N compounds are charged into the incinerator and further into the waste gas flow path, the amount of dioxins to be generated in these two locations are reduced respectively, and dioxins in the exhausting gas are more lowered. The present mode has been realized on the ground of the these experiments and investigations.

Of the present mode, the lst is the waste combustion method characterized by adding N compounds to waste to be charged into the incinerator, and blowing N compounds in the flow path of combustion waste gas behind the outlet of the incinerator.

In his mode, the generation of dioxins is suppressed at he, wo locations as mentioned above by charging N compounds into

waste to be charged to the incinerator and into waste gas in T : he exhausting gas path. Accordingly, dioxins in an exhausting gas are substantially reduced.

In this mode, the outlet of the incinerator means the outlet of the secondary combustion chamber.

Sludge herein means sludge such as sewage sludge, night soil sludge, sludge generated when performing an activated sludge treatment of organic wastewater, sludge generated when performing a solid-liquid separation of wastewater containing organic materials, sludge generated in closed water areas as in river dredging.

N compounds means organic and inorganic compounds containing nitrogen. Examples of preferable N compounds are low-cost compounds such as ammonia or urea. N compounds may be used in a form of gas, liquid, solid, or water solution, and depending on locations to be added at, an appropriate form may be selected.

Of the present embodiments, the 2nd is the waste combustion method characterized by charging sludge together with waste into the incinerator, and blowing N compounds into the combustion waste gas path behind the exit of the incinerator.

In this invention, combustion of sludge is carried out together with waste. By combustion of sludge, an effect of suppressing the generation of dioxins can be provided. By blowing N compounds into the path of combustion waste gas, dioxins generation in the incinerator and the combustion waste gas path can be suppressed. In general, waste and sludge are incinerated independently by different incineration facilities, but by

concurrent incineration of waste and sludge, additional merits can be enjoyed such as saving in capital cost and operation cost.

Of the present mode, the 3rd is the waste combustion method characterized by adding N compounds to waste and/or sludge when charging waste and sludge into the incinerator.

In this mode, N compounds are added to either waste or sludge, or to both before charging them into the incinerator. Sludge to be burnt such as sewage sludge are clay-like matter, and contains much water (65 to 90 wt%) even if it is dewatered. If those dewatered sludge are charged in a large amount, combustion conditions in the incinerator becomes deteriorated. Therefore, there occurs a case where enough sludge for supplying the N content of a required amount cannot be charged. In such a case, the invention adds separately N compounds for supplementing the shortage in the N content, thereby enabling to substantially decrease dioxins generation in the incinerator while maintaining the normal combustion.

When mixed combustion of waste and sludge is carried out in the waste incineration facility, the merit of saving costs as mentioned above is brought about.

Of the present mode, the 4th is the waste incineration facility characterized by provision of a means for adding N compounds to waste to be charged into the incinerator and provision of a means for blowing N compounds into the exhausting gas path.

By this mode, N compounds can be added to waste, and the generating amount of dioxins in the incinerator can be decreased.

Further, as N compounds can be blown into the exhausting gas path, the generating amount of dioxins in the waste gas path can be decreased.

Of the present embodiments, the 5th is the waste incinerating characterized by provision of a means for charging sludge into the incinerator, and addition, to this means for charging sludge, of a means for blowing N compounds in the sludge, and further provision of a means for blowing N compounds into the combustion waste gas path.

By this mode, as sludge can be charged into the incinerator, generation of dioxins in the incinerator is restrained. Further, as N compounds can be added to sludge, if the effect of restraining dioxins generation is insufficient only by the N content in the sludge to be charged, the N content to be charged in the incinerator can be supplemented. The merit of saving costs is brought about by mixed combustion of waste and sludge.

In each of the above mode, the position for blowing the N compounds into the combustion waste gas flow path may be anywhere in the range from the exit of the incinerator to the stack.

However, preferably it should be done before collecting fly ash which contains a catalyst component, that is, at the position upstream of the dust collector.

FIG. 15 is an explanatory view showing the 1st example for carrying out the embodiment. A shown, the incineration facility is provided wiry t fire grate incinerator, and in the drawing, 510 is the fire grate incinerator, 511 is a wase hopper for

charging waste such as urban refuse into the incinerator, 515 L is a waste gas treating process which carries out gas cooling, acid gas removal, and dust collection.

As an auxiliary facility of the incinerator 510, a means 550 for adding N compounds to waste to be charged into the incinerator 510 is provided. The N compound adding means 550 is composed of storage bin 551 of urea solution, which is one kind of N compounds, a urea supply pump 552, and a urea spraying nozzle 553. As an auxiliary facility of the waste gas treating process 515, a means 570 for blowing N compounds into the combustion waste gas path is provided. The N compound blowing means 570 is composed of an ammonia gas holder 571, a flow rate controller 572, and a spray nozzle (not shown).

A combustion chamber 512 of the incinerator is stepwise and provided with a fire gate 513a of the drying step, a fire grate 513b of the combustion step, and a fire grate 513c of the post combustion step. Thus, the interior of the combustion chamber 512 is sectioned into an area for mainly drying charged waste (drying zone), an area for burning the dried waste (combustion zone) and an zone for reducing those sent in a combustion state into ash.

In the waste incinerating facility composed as above, waste is charged into the waste hopper 511 and over this waste, the urea solution is sprayed from the urea spray nozzle 553. The waste to which urea is added is sent from the hopper 511 to the combustion chamber 512. In the combustion chamber 512, the charged waste is sent on the respective fire grates and changed

into ash while going through the drying, combustion and the post combustion steps, and discharged. Since the operation is performed where the supply amount of the combustion air is restrained at the upstream side, combustion proceeds in an oxygen poor state in the drying step fire grate 513a (drying zone) and part of the combustion step fire grate 513b (combustion zone).

At such incomplete combustion, in the prior art, aromatic compound and chlorine easily react and generate dioxins, but in the present embodiment, urea added to waste is thermally decomposed to generate compounds having the ammonia (NH3) or NH, radical, so that the dioxins generating reaction is suppressed.

As combustion waste gas generated in the combustion chamber 512 contains combustible gas generated in the drying step fire grate 513a and part of the combustion step fire grate 513b, by blowing the air into the secondary combustion chamber 514, secondary combustion treatment takes place for combusting the combustible gas.

The combustion waste gas exhausted from the secondary combustion chamber 514 is sent to the waste treating process 515, subjected to the cooling treatment, the poisonous gas removing treatment and the dust removing treatment, and is released from the smoke stack 516. Ammonia gas supplied from gas holder 571 is blown into these apparatuses of performing the waste gas treatment or into flues connecting each apparatus, and dioxins generation in the combustion waste gas flow path is reduced.

\ As above, by supplying N compounds into the incinerator and the waste gas flow path, it is possible to reduce dioxins

generation in the incinerator and the waste gas flow path.

FIG. 16 is an explanatory view showing the 2nd example for carrying out the embodiment. With respect to the same structural parts as Fig. 15, the same numerals are given and explanation is omitted.

In this embodiment, a new sludge supply means is provided as an auxiliary facility for charging sludge together with waste into the waste hopper 511. Numeral 540 designates a sludge charger. Further, a N compound blowing means 570 for blowing N compounds into the combustion waste gas flow path is provided as an auxiliary facility of a waste gas treating process.

In the waste incinerating facility composed as above, waste and sludge charged in the waste hopper 511 are sent to the combustion chamber 512. In the incinerator 512, waste and sludge are reduced into ash while going through the drying, combustion, and post combustion steps, and exhausted. As mentioned above, in the drying process and in the early period of the combustion process, N containing components in sludge charged with waste is thermally decomposed to generate compounds having the ammonia (NH3) or NH2 radical so that the dioxins generating reaction is suppressed. Accordingly, the amount of dioxins contained in the combustion waste gas generated in the combustion chamber 512 is decreased.

The exhausting gas generated in the combustion chamber 512 is sent to the waste gas treating step 515 through the secondary combustion chamber 514 in a similar manner to the facility of FIG. 15, into which ammonia gas supplied from a gas holder 571 is blown, so that dioxins generation in the combustion waste gas

flow path is decreased.

As above, by charging sludge into the incinerator together with waste, and blowing N compounds into the waste gas flow path, the generation of dioxins is restrained at two locations of the incinerator and the waste gas flow path.

FIG. 17 is an explanatory view showing the 3rd example for carrying out the embodiment. With respect to the same structural parts as FIG. 15 and 16, the same numerals are given and explanation is omitted. In this mode, in addition to the structure of FIG. 16, a N compound adding means 560 for adding N compounds to the sludge charger 540 is equipped, which is composed of a hopper 561 for storing urea powder and a urea charger 562. As an auxiliary facility of the waste gas treating process, a N compound blowing means 570 for blowing N compound into the combustion waste gas flow path is provided.

In the waste incinerating facility composed as above, waste is charged into the waste hopper 511, and sludge is supplied from the sludge charger 540. When supplying sludge, urea powder is supplied from the urea charger 552 to the sludge charger 540.

The sludge mixed with urea is charged into the waste hopper 511.

Subsequently, the sludge and waste to which urea is added are sent into the combustion chamber 512.

In the incinerator 512, waste and sludge are reduced into ash while going through the drying, combustion, post combustion processes, and exhausted. As mentioned above, in the drying process and in the early period of the combustion process, the N containing component in sludge charged with waste and urea

separately added are thermally decomposed to generate compounds having the amonia (NH3) or NH2 radical, so that the dioxins generating reaction is suppressed. Accordingly, the amount of dioxins contained in-he combustion waste gas generated in the combustion chamber 512 is decreased.

The combustion waste gas generated in the combustion chamber 512 is sent to the waste gas treating process 515 through the secondary combustion chamber 514 in a similar manner to the facility of Fig. 15, into which ammonia gas is blown from a gas holder 571, so that dioxins generation in the combustion waste gas flow path is decreased.

As above, by adding urea when sludge is charged into the incinerator to increase he N content to be charged into the incinerator 510, dioxins generation in the incinerator can be further reduced.

FIG. 18 is an explanatory view showing the 4th example for carrying out the embodiment. The incinerating facility shown in the figure is provided with the fluidized bed incinerator, numeral 520 is the fluidized bed incinerator, and 540 is a sludge charger. 526 designates a exhausting gas treating process for carrying out the gas cooling, acid gas removal and dust collection.

The fluidized bed incinerator 520 is sectioned into a fluidized layer section 523 where a fluidized layer is formed by the air blown from a wind box 521 a1 operation, and the freeboard section 524, which is furnished with a nozzle 525 for blowing a secondary combustion air.

As an auxiliary facility of the waste gas treating process 526, a means 570 for blowing N compounds into the combustion waste gas flow path is provided, which is composed of an ammonia gas holder 571, a flow rate controller 572 and a spray nozzle (not shown).

In the waste incinerating facility composed as above, waste is charged into the incinerator from the waste charger 530, and sludge is charged from the sludge charger 540. The charged waste and sludge are dried in the fluidized bed, heated, and burnt.

Since the air blowing amount is suppressed in the fluidized bed, it is in a state where dioxins is easily generated when applying the prior art. But in this practice, the N containing substance in sludge charged with waste is thermally decomposed to generate compounds having the ammonia (NH3) orNH radical, and the dioxins generating reaction is suppressed.

The exhausting gas generated in the fluidized layer section 523 contains combustible gas such as H, CO or CH < , and so the air is blown from the nozzle 525 at the freeboard section 524 so as to perform the secondary combustion of the combustible gas.

The exhausted gas from the incinerator 520 is sent to the waste gas treating process 526, subjected to the cooling treatment, poisonous gas removal and dust removal, and released from the stack 527. Ammonia gas supplied from the gas holder 571 is blown into these apparatuses of performing the waste gas treatment or into flues connecting each apparatus, and dioxins generation in the combustion waste gas flow path is reduced.

As above, dioxins in exhausting gas are substantially

decreased by charging sludge together with waste into the incinerator and blowing N compounds into the zone prior to secondary combustion in the freeboard section.

FIG. 15 to 18 show the waste incinerating facilities equipped with the fire gate incinerator or the fluidized bed incinerator, but incinerators to which the present embodiment is applicable are not limited to the above two, but also applicable, for example, to a kiln type.

FIG. 15 to 18 show the fire grate incinerators which are provided with the stepwise fire grate, but application of the mode is not limited to these stepwise structures, and it also is applicable to those which have the section functioning as a drying zone in the incinerator.

In the facility of FIG. 15, urea is added to materials to be charged into the incinerator in a solution state, and in the facility of FIG. 17, it is added to sludge in a powder state, but the invention does not limit states of the N compound to be added.

When adding N compounds to waste, for dispersing a small amount of N compounds to a large amount of bulky waste as uniformly as possible, solution is desirable. When adding N compounds to sludge, for lessening water content, powder is desirable.

In the facilities of FIG. 15 to 18, the N compound to be blown into the waste gas flow path is ammonia gas, but it is not limited to a gaseous state, and solution of ammonium or urea is also applicable.

(Example 1)

Explanation will be made to results of burning was-ce, using the fire grate testing apparatus. Waste tested was urban refuse, and sludge tested was sewage sludge (water content = 77% and N = 6% in dry weight). Ammonia gas was used as the N compound to be charged into the waste gas flow path. Urban refuse of 2000 kg/H and sewage sludge of 200 kg/H were charged. After combustion waste gas was cooled, ammonia gas was blown into the waste gas duct at the rate of 0.35 Nm3/H. Temperature within the waste gas duct was around 300 C.

The concentration of dioxins in the released combustion waste gas was measured during waste incineration by the above condition, and average values of dioxins concentration in 2,3, 7,8-TCDD toxicity equivalent were as low as around 25% in comparison with the values in a case where only urban refuse was burnt and only ordinary waste gas treatment was carried out. Thus, when burning waste, it is confirmed that the amount of dioxins contained in the combustion waste gas is substantially decreased by charging sludge together with waste and blowing ammonia gas into the waste gas flow path.

By the present mode, sludge or N compounds are charged together with waste into the incinerator, and the N containing component is thermally decomposed to generate the N compound serving to suppress generation of dioxins. Further, the N compound is blown into the combustion waste gas flow path behind the exit of : he incinerator so as to restrain generation of dioxins

ierati on o' in the combustion waste gas flow path, so that generation of dioxins is greatly reduced at the two sections of the interior

of the incinerator and the combustion waste gas flow path. In addition, by the waste incinerating facility installed with N compound supply apparatuses at two sections of the incinerator and the combustion waste gas treating process, N compound can be supplied to the two sections of the incinerator and the exhausting gas treating process, and the above effect can be brought about.

BEST MODE 11 In this mode, through various tests of burning treatments of waste, it was found that, by carrying out mixed fuel combustion of waste and sludge such as sewage sludge, the amount of dioxins contained in exhausting gas is lowered. The inventors made studies as to how the effect of reducing dioxins is brought about by mixed fuel combustion.

It is known that one of main causes of dioxins generation by combustion of waste is to burn waste in an oxygen-poor atmosphere, and the burning condition under this state corresponds to the condition in the stage where waste charged in the incinerator is heated and its temperature is raised. From this fact, it is considered that materials generated by thermal decomposition of sludge in the early stage of combustion serves to suppress the generation of dioxins.

Therefore, since general sludge contains the N content of 2 to 10 weight% (in dry weight), it is assumed that materials suppressing the generation of dioxins are those generated by thermal decomposition of the N containing substance in sludge,

and tes. s were carried out. In the tests, when a N compound was added to waste to be burnt, it was acknowledged that dioxins in the combustion waste gas were decreased. From this, it is assumed that a substance suppressing the generation of dioxins is a compound having an ammonia (NH) or NH2 radical generated when the N containing substance is thermally decomposed.

A mechanism that N compounds generated by thermal decomposition suppresses the generation of dioxins is not clear, but such substances are considered to have a poisoning effect to copper and other substances which act as catalysts for generating dioxins. This poisoning effect is assumed to be one cause bringing about the effect of suppressing the generation of dioxins.

As above, when burning waste, by charging N compounds together with waste, the generation of dioxins is also restrained.

The present invention has been realized based on the findings from the above mentioned tests and investigations. Accordingly, the above mentioned problems are solved by the invention as follows.

Of this mode, the 1st is the waste incineration method characterized by adding N compounds to waste and charging it into the incinerator.

In this mode, if N compounds are charged together with waste, the formation of dioxins is controlled, and it is possible to decrease dioxins in combustion waste gas by installing a very simple apparatus.

The 2nd of this mode is the waste incineration method of

charging sludge together with waste into the incinerator, characterized by adding N compounds before charging the waste and/or sludge.

Incineration of waste and sludge is in general performed by separate incinerating facilities respectively, but by burning the waste and sludge together, there occurs a merit of saving equipment cost and operation cost and an effect of controlling the formation of dioxins by combustion of sludge. But sludge to be incinerated such as sewage sludge is clay-like matter containing much water (65 to 90 weight%) even if it is dewatered.

If those dewatered sludge is charged in a large amount, the combustion conditions in the incinerator becomes deteriorated.

Therefore, there occurs a case where enough sludge for supplying the N content of a required amount cannot be charged. The invention deals with such cases by adding N compounds to waste and/or sludge before charging into the incinerator and supplementing the shortage of the N content.

The 3rd of this mode is the waste incineration method of charging sludge together with waste into the incinerator, characterized by adding N compounds to waste and sludge charged in the waste hopper of the incinerator.

In this mode, as N compounds are added to both of waste and sludge, N compounds are uniformly dispersed over the charged materials, so that the formation of dioxins is evenly suppressed.

The 4th of this mode is the waste incinerating of burning sludge together with waste, characterized in-hat a N compound addition means is provided for adding N compounds to waste to

be charged into the incinerator.

In this mode, as N compounds are added to waste, it is possible to uniformly add a small amount of N compounds 1 : 0 a large amount of bulky waste, so that the formation of dioxins is evenly suppressed.

The 5th of this mode is the waste incinerating of burning sludge together with waste, characterized in that a N compound addition means is provided to a sludge charger, so that sludge and N compounds are mixed and charged into the incinerator.

This mode is useful in particular when a N compound in powder is added. If a N compound is added in a powder state and the water content of materials to be charged in the incinerator is lessened, the combustion efficiency can be heightened.

In the above respective mode, sludge means sewage sludge, night soil sludge, sludge generated when performing an activated sludge treatment of organic wastewater, sludge generated when performing a solid-liquid separation of wastewater containing organic materials, sludge generated in closed water areas as in river dredging, and other sludge.

The N compounds mean organic or inorganic compounds containing nitrogen. Preferable examples of N compounds are low-cost compounds such as ammonia or urea. The N compound may be gaseous, liquid, solid or solution, and suitable forms are selected by position at which it is added.

FIG. 19 is an explanatory view showing the 1st example for carrying OU this mode. The incinerating facility shown is provided with the fire grate incinerator. 610 designates the

fire grate incinerator, 611 is a waste hopper for charging waste such as urban refuse into the incinerator, and 615 is a waste gas treating process which carries out the gas cooling, acid gas removing treatment and dust collection by means of a boiler and gas cooler. As an auxiliary facility of the incinerator 610, a means 650 for adding N compounds to waste is provided. 651 designates a storage bin of urea solution, which is one kind of N compounds. 652 is a urea supply pump, 653 is a urea spray nozzle, and 670 is waste such as urban refuse.

In the interior of the combustion chamber 612 of the incinerator, a drying step fire grate 613a, combustion step fire grate 613b and post combustion step fire grate 613c are provided stepwise, each having the transfer function. Thus, the combustion chamber is sectioned into an area for drying the charged waste 670 (drying zone), an area for burning the dried waste (combustion zone) and an area for reducing materials sent in a combusting state into ash (post combustion zone).

In the waste incinerating facility composed as above, waste is charged into the waste hopper 611, and the urea solution is sprayed over the waste from the urea spray nozzle 653. The waste to which urea is added is sent into the combustion chamber 612 from the waste hopper 611.

In the combustion chamber 612, the charged waste is transferred through the respective fire grates and is reduced to ash by going through the drying, combustion and post combustion steps, and exhausted. As the operation is carried out with the supply amount of combustion air lessened at the upstream fire

grate, the combustion is carried our under an oxygen-poor state in the drying stage fire grate 613a (drying zone) and part of the combustion stage fire grate 613b (combustion zone). If such incomplete combustion takes place, reaction between aromatic compound and chlorine easily forms dioxins, but in this mode, urea added to waste is thermally decomposed to generate compounds having an ammonia (NH3) or NH2 radical, so that the progress of dioxins generating reaction is restrained.

The exhausting gas generated in the combustion chamber 612 contains combustible gas generated in the drying stage fire grate 613a and part of the combustion stage fire grate 613b, and the combustible gas is burnt by blowing the air into the secondary combustion chamber 614. The exhausting gas exhausted from the secondary combustion chamber 614 is sent to the exhausting treating process 615, subjected to the cooling treatment, poisonous gas removing treatment and dust removing treatment, and is released from the stack 616.

As above, when waste to which urea is added is burnt, the forming amount of dioxins in the incinerator is decreased, so that the amount of dioxins contained in the combustion waste gas is substantially lowered.

FIG. 20 is an explanatory view showing the 2nd example for carrying out the present mode. With respect to the same parts as those in Fig. 19, the same numerals are given and explanation

is omitted. In addition to the structure of FIG. 19, a sludge L supply means is provided for supplying sludge together with waste T 0 into the waste hopper 611. 640 is a sludge charger which is

equipped with a N compound addition means 660 for mixing the'N compound with sludge. 661 is a storage bin of urea powder, and 662 is a urea powder charger.

In the waste incinerating facility composed as above, waste and sludge charged into the waste hopper 611 are sent to the combustion chamber 612 where waste and sludge pass through the drying, combustion, post combustion processes, reduced to ash and are exhausted. In the drying process and in the early period of the combustion process, the N compound in sludge and urea added to sludge are thermally decomposed to generate compounds having the ammonia (NH3) or NH2 radical, so that the forming reaction of dioxins is restrained, and the amount of dioxins contained in exhausting gas is substantially decreased.

Exhausting gas generated in the combustion chamber 612 is, as in the facility of FIG. 15, subjected to the secondary combustion treatment, gas cooling treatment, poisonous gas removing treatment, and dust removing treatment, and then is released from the stack 616.

FIG. 21 is an explanatory view showing the 3rd example for carrying out the present embodiment. With respect to the same structure as in FIG. 19, the same numerals are given, and explanation is omitted.

In this mode, a means 650 for adding the N compound to waste and sludge charged into the waste hopper 611 is provided. 651 is a storage bin of urea solution, 652 is a urea supply pump and 653 is a urea spray nozzle.

In the waste incinerating facility composed as above, the

urea solution is sprayed over waste and sludge from the spray nozzle 652. The waste and sludge over which urea is sprayed are sent into a combustion chamber 612 from the waste hopper 611.

In a incinerator 612, waste and sludge are reduced into ash while going through the drying, combustion and post combustion processes, and are exhausted. Similarly to the facility of FIG.

20, the N compound in sludge and urea separately added are thermally decomposed to generate compounds having the ammonia (NH3) or NH2 radical and suppress the forming reaction of dioxins, so that ehe amount of dioxins contained in combustion waste gas is substantially decreased.

Exhausting gas generated in the combustion chamber 612 is treated in a similar manner to the case in the facility of FIG.

19, and is released from the stack 616.

FIG. 22 is an explanatory view showing the 4th of this mode for carrying out the present mode. 630 is a waste charger, 640 is a sludge charger, and 620 is a fluidized bed incinerator. 626 is a waste gas treating process for gas cooling, acid gas removing and dust removing.

The interior of the fluidized bed incinerator. 620 is sectioned into a fluidized layer section 623 forming a fluidized layer by air supplied from a wind box 621 and a freeboard section 624 which is provided with an air blowing nozzle 625.622 is a dispersing plate for rectifying the air to be blown into the fluidized layer from the wind box 621. The sludge charger 640 is provided with an addition means of the N compound for mixing

the N compound into sludge. 661 is a storage bin of urea powder Li

and 662 is a urea powder charger.

In the waste incinerating facility composed as above, waste is charged into the incinerator 620 from the waste charger 630, and sludge is charged from the sludge charger 640. Then, urea powder is supplied into the sludge charger 640 from the urea charger 662, and the sludge mixed with urea is charged. The charged waste and sludge are dried in the fluidized layer, their temperature raised, and are burnt.

As the amount of air blown into the fluidized layer is suppressed, it is in a combustion state likely to form dioxins.

In this invention, the N compound in sludge and urea added into sludge are thermally decomposed to generate compounds having the ammonia (NH) or NH, radical and suppress the dioxins forming reaction. Unburnt materials in waste are taken out from the bottom of the incinerator.

As combustible gas such as H, CO or CH4 is included in combustion waste gas generated in the fluidized layer section, air is blown from the nozzle 625 at the freeboard section 624 so as to perform the secondary combustion of the combustible gas.

Combustion waste gas exhausted from the secondary combustion chamber 614 is sent to the waste gas treating process 626, subjected to the cooling treatment, poisonous gas removal and dust removal, and released from the stack 627.

By charging waste together with sludge to which urea, one kind of N compounds, is added, and combusting them, the amount of dioxins contained in exhausting gas is substantially lowered.

FIG. 19 to 22 show waste incinerating facilities furnished

with the fire grate incinerator or the fluidized bed incinerator, but applicability of the present embodiment is not limit to these two types.

FIG. 19 to 21 show the fire grate incinerators provided with the stepwise fire grates, but applicability of the present mode is not limit to the stepwise type and it is applicable to a type with fire grates arranged horizontally.

In the facilities of FIG. 19 to 22, two cases are described; in one case, urea is added as a N compound in a powder state and in another, in a solution state. However, no limitation is made to its state when added. When adding a N compound to bulky waste, it is preferable to add it in a solution state and make it adhere to waste for adding as uniformly as possible. When adding a N compound to sludge, it is preferable to add it in a powder state and make it mix with sludge in the sludge charger for preventing the water content of charged material from becoming too high.

(Example 1) Below, explanation will be made on results of burning waste, using a testing apparatus of the similar composition to the fire grate incinerator shown in FIG. 20. Municipal refuse was used as testing material of waste and sewage (water content = 77% and N = 6% (in dry)-) was used as testing material of sludge. Municipal refuse of 2000 kg/H, sewage of 200 kg/H and urea of 1 kg/H were charged.

The concentration of dioxins in the released exhausting gas was measured during combustion by the above condition, and average values of dioxins concentration in 2,3, 7, 8-TCDD

toxicity equivalent were as low as around 20% in comparison with values in a case where only municipal refuse was burnt and only ordinary waste gas treatment was carried out.

Thus, when burning waste, it is confirmed that the amount of dioxins contained in the combustion waste gas is substantially decreased by charging sludge or further by adding a N compound.

By this mode, the N compound or the sludge and N compound are added when waste is charged into the incinerator, and the sludge and N compound are thermally decomposed to suppress dioxins generation, so that the generating amount of dioxins in the incinerator is decreased and the amount of dioxins contained in the exhausting gas is substantially reduced. Further, by means of the waste incinerating facility equipped with the N compound adding apparatus, it becomes possible to add the N compound to waste to be charged into the incinerator so as to bring about the above mentioned effect.

BEST MODE 12 The present mode is to provide the waste incineration method and the facility thereof, which make it possible to reduce the generated amount of dioxins only by installing a very simple apparatus and adding low-cost substances.

In the course of carrying out various tests of burning waste with this embodiment, it was found that, by carrying out the mixed fuel combustion of waste and sludge such as sewage sludge, the amount of dioxins contained in exhausting gas was lowered.

Therefore, the inventors carried out various studies as to how

the effect of reducing dioxins is brought about by the mixed fuel combustion with sludge.

It is known that one of main causes generating dioxins by burning waste is combustion of waste in an oxygen-poor atmosphere.

The combustion condition under such state corresponds to a condition in the early period of the combustion step where waste charged in the incinerator is heated and its temperature is raised.

From this fact, it is considered that substances by generated by thermal decomposition of sludge acts to suppress dioxins generation.

Since general sludge contains a N content as high as 2 to 10 wt% (in dry), it is assumed that substances suppressing the generation of dioxins are those that are generated by thermal decomposition of the N containing substances in sludge, and tests were carried out. In the tests, when waste is burnt with a N compound added to it, it was acknowledged that dioxins in the exhausting gas were decreased. From this, it is assumed that substances suppressing the generation of dioxins are compounds having ammonia (NH3) or NH radicals generated by thermal decomposition of N containing substances.

A mechanism that thermally decomposed products of N contained substance suppresses the generation of dioxins is not clear, but it is considered that such products have a poisoning action to copper and other substances which act as catalysts for generating dioxins. This poisoning effect is assumed to be one cause of bringing about the effect of suppressing the generation of dioxins.

The 1 st of the present mode is the waste incineration method by the incinerating facility equipped with the fire grate incinerator, characterized by adding N compounds to waste charged in the incinerator and sent to the drying zone, and burning it.

As mentioned above, at the early combustion step, the combustion is carried out under the condition likely to generate dioxins. Therefore, by adding N compounds to waste heated and dried, or to waste in the drying zone and started to be thermally decomposed, it is possible to decrease the amount of dioxins to be generated by thermal decomposition in this drying zone and by combustion in the following combustion zone.

The 2nd of the present mode is the waste incineration method by the incinerating facility equipped with the fire grate incinerator, characterized by charging sludge together with waste, adding N compounds to waste sent in the drying zone of the incinerator, and. burning it.

The combustion of waste and sludge is in general performed by separate incinerating facilities respectively, but by burning the waste and sludge together, there occur a merit of saving equipment cost and operation cost and further, an effect of controlling the formation of dioxins by the combustion of sludge.

But sludge such as sewage sludge is clay-like matter, and contains much water po 90 wt%) even if it is dewatered. If these dewatered sludge is charged in a large amount, combustion conditions in the incinerator becomes deteriorated. Therefore, there occurs a case where enough sludge for supplying the N content of a required amount cannot be charged. This invention deals with such cases by adding N compounds to waste and sludge in the drying zone of the incinerator, and supplementing the shortage of the N content.

The 3rd of the present mode is the waste incineration method by the incinerating facility equipped with the fluidized bed incinerator, characterized by charging waste into the incinerator for combustion and blowing N compounds into a zone prio. r to secondary combustion in the freeboard section. In this embodiment, the zone prior ro secondary combustion in the freeboard section means a zone between the upper end of the fluidized layer and the position where secondary combustion air is blown in.

Waste charged in the fluidized bed incinerator is burnt in the fluidized layer. However, in particular, the early period of combustion, where charged waste is dried and starts to burn, is in a state which is likely to generate dioxins. Accordingly, the zone to which the combustion gas generated in the fluidized layer rises and preceding the section where air is blown in for secondary combustion in the freeboard is also in a state which is likely to generate dioxins. By adding a N compound into this zone, the dioxins generating amount can be decreased.

The 4th of the present mode is the waste incineration method as set forth in the 3rd of the present mode, characterized by charging sludge together with waste into the incinerator.

In this mode, sludge is charged into the incinerator, and N compounds are blown into the zone prior to secondary combustion in the freeboard, so that the dioxins generating amount can be decreased.

The 5th of the present mode is the waste incinerating facility equipped with the fire grate incinerator, characterized by provision of a N compound adding means for supplying N compounds into the drying zone of the incinerator.

In this mode, the N compound is supplied into the drying zone where dioxins are started to be generated, thereby to decrease the generating amount of dioxins in the drying zone and the combustion zone.

The 6th of the present mode is the waste incinerating facility equipped with the fire grate incinerator, characterized by provision of a means for supplying sludge into the incinerator, and a N compound adding means for supplying a N compound into the drying zone of the incinerator.

In this mode, sludge is charged together with waste, and waste and sludge are treated concurrently, resulting in saving in the equipment cost and operation cost in addition to suppression of dioxins generation. Further, the N compound is supplied into the drying zone of the incinerator, supplementing the shortage of nitrogen in sludge.

The 7th of the present mode is the waste incinerating

facility equipped with the fluidized bed incinerator, characterized by provision of a N compound adding means for blowing a N compound into the zone prior to secondary combustion in the freeboard of the incinerator.

By this mode, the N compound is supplied to the zone prior to secondary combustion in the freeboard, decreasing the amount of dioxins generated downstream of the freeboard section.

The 8th of the present mode is the waste incinerating facility equipped with the fluidized bed incinerator, characterized by provision of a means for supplying sludge into the incinerator and a N compound adding means for blowing the N compound into the zone prior to secondary combustion in the freeboard section of the incinerator.

In this mode, sludge is charged into the incinerator, and the N compound is blown into the zone prior to secondary combustion in the freeboard section, decreasing the amount of dioxins to be generated downstream of the fluidized layer and the freeboard section.

In each mode above, sludge means sewage sludge, night soil sludge, sludge generated when performing an activated sludge treatment of organic wastewater, sludge generated when performing a solid-liquid separation of wastewater containing organic materials, sludge generated in closed water areas as in river dredging, and other sludge.

The N compounds means organic or inorganic compounds containing nitrogen. Examples of preferable N compounds are low-cost compounds such as ammonia or urea. The N compound may

be gaseous, liquid, solid or solution, and suitable forms are selected by position at which it is added.

FIG. 23 is an explanatory view showing the. 1st example for carrying out this mode. The incinerating facility shown is provided with the fire grate incinerator. 710 designates the fire grate incinerator, 711 is a waste hopper for charging waste such as municipal refuse into the incinerator, and 715 is a waste gas treating process which carries out the gas cooling, acid gas removing treatment and dust collection by means of a boiler and gas cooler.

In the interior 712 of the incinerator, a drying stage fire grate 713, combustion stage fire grate 713b and post combustion stage fire grate 713c are provided stepwise. Thus, the combustion chamber is sectioned into an area for drying the charged waste (drying zone), an area for burning the dried waste (combustion zone) and an area for reducing these sent in a combustion state into ash (post combustion zone).

As an auxiliary facility of the incinerator 710, a means 750 for adding N compound to waste in the combustion chamber 712 is provided, which is composed of a storage bin 751 of urea solution as one kind of N compounds, a urea supply pump 752 and a urea spray nozzle 753. The urea spray nozzle 753 passes through a wall of the incinerator 710 above the drying step fire grate 713a. The urea spray nozzle 753 may be plural if required, and scatter the urea solution allover in the width direction of the drying stage fire grate 713a.

In the waste incinerating composed as above, waste is

charged into the waste hopper 711 and sent onto the drying step fire grate 713a in the combustion chamber, and the urea solution is sprayed over the waste from the urea spray nozzle 753.

In the combustion chamber 712, the charged waste is transferred on the respective fire grates as above and is reduced to ash while going through the drying, combustion and post combustion processes, and exhausted. As the operation is carried out with the supply amount of combustion air lessened at the upstream fire grates, the combustion is carried out under an oxygen-poor state in the drying stage fire grate 713a (drying zone) and part of the combustion stage fire grate 713b (combustion zone). If such incomplete combustion takes place, reaction between aromatic compound and chlorine easily generates dioxins, but in this embodiment, urea added to waste in the drying step fire grate 713a (drying zone) is thermally decomposed to generate compounds having ammonia (NH3) or NH2 radicals, so that the progress of dioxins generating reaction of is restrained.

The combustion waste gas generated in the combustion chamber 712 contains combustible gas generated in the drying step fire grate 713a and part of the combustion step fire grate 713b, and the combustible gas is burnt by blowing the air into the secondary combustion chamber 714. The combustion waste gas exhausted from the secondary combustion chamber 714 is sent to the waste gas treating process 715, subjected to the cooling treatment, poisonous gas removing treatment and dust removing treatment, and is released from the stack 716.

As above, by burning the waste with urea added to it, the

amount of dioxins to be generated in the incinerator is decreased, so that the amount of dioxins contained in the combustion waste gas is substantially lowered.

FIG. 24 is an explanatory view showing the 2nd example for carrying out the present mode. With respect to the same parts as those in FIG. 23, the same numerals are given and explanation is omitted. In addition to the structure of FIG. 23, a sludge supply means is provided for supplying sludge together with waste into the waste hopper 711.740 is a sludge charger.

In the waste incinerating facility composed as above, waste and sludge charged in the waste hopper 711 are sent onto the drying step fire grate 713a in the combustion chamber 712 on which the urea solution is sprayed from the urea spray nozzle 753. In the incinerator 712, waste and sludge pass through the drying, combustion, post combustion processes, reduced to ash and are exhausted. In the drying process and the early period of the combustion process, the N compound in sludge and urea added to sludge are thermally decomposed to generate compounds having ammonia (NH) or NH radicals, so that the dioxins forming reaction is restrained, and the amount of dioxins contained in combustion waste gas is substantially decreased.

Exhausting gas generated in the combustion chamber 712 is, as in the facility of FIG. 23, subjected to the secondary combustion treatment, gas cooling treatment, poisonous gas removing treatment, and dust removing treatment, and then is released from the smoke stack 716.

FIG. 25 is an explanatory view showing the 3rd example for

carrying out he present-embodiment. The incinerating facility is provided with the fluidized bed incinerator, and 720 is the fluidized bed incinerator, and 730 is a waste charger. 726 is a waste gas treating process of gas cooling, acid gas removing and dust removing.

The interior of the fluidized bed incinerator 720 is sectioned into a fluidized layer section 723 forming a fluidized layer by the air supplied from a wind box 721 and a freeboard section 724 which is provided with an air blowing nozzle 725 for secondary combustion.

As an auxiliary facility of the fluidized bed incinerator 720, is provided for blowing the N compound to the freeboard section 724 of the incinerator. The N compound adding means 750 is composed of a storage bin 751 of urea solution as one kind of N compounds, a urea supply pump 752 and a urea spray nozzle 753. The urea spray nozzle 753 is furnished at a level lower than a position of the air blowing nozzle 725 so that the urea solution is blown into combustion waste gas which is in an incomplete combustion state.

In the operation of the waste incinerating facility composed as above, waste is charged into the incinerator 720 from the waste charger 730, and the charged waste is heated up while being dried in the fluidized layer 723. As the blowing amount of the air to the fluidized layer 723 is restrained, the freeboard section 724, where combustion waste gas goes up, is in a combustion state which is likely to form dioxins in the prior art. BUT : in this mode, Lhe urea blown in is thermally decomposed to generate

n 4 compounds having ammonia (No3) or NH radicals, so that the progress of dioxins generating reaction is restrained.

As combustible gas such as H, CO or CH4 is included in exhausting gas generated in the fluidized layer section 723, air is blown in from the nozzle 725 so as to perform secondary combustion of the combustible gas. Exhausting gas exhausted from the incinerator 720 is sent to the exhausting gas treating process 726, subjected to the cooling treatment, poisonous gas removal and dust removal, and released from the stack 727.

As above, the amount of dioxins contained in combustion waste gas is reduced by blowing the N compound into the zone prior to secondary combustion in the freeboard section.

FIG. 26 is an explanatory view showing the 4th example for carrying out the present mode. The incinerating facility shown is equipped with the fluidized bed incinerator. With respect to the same parts as those in FIG. 25, the same numerals are given and explanation is omitted. In addition to the structure of FIG.

25, a sludge supply means is provided for supplying sludge together with waste into the incinerator 720.740 is a sludge charger.

In the waste incinerating facility composed as above, waste is charged into the incinerator 720 from the waste charger 730, and sludge is charged from the sludge charger 740. The charged waste and sludge is heated up while being dried. As the air blowing amount is lessened in the fluidized layer 723, dioxins are easily generated in the prior art. But in this mode of practice, sludge is charged, and the generation of dioxins is

suppressed in the fluidized layer 723 by 1 :. he N compound generated by thermal decomposition of sludge.

Further, at the freeboard section 724, urea solution is sprayed into combustion waste gas arising from the fluidized layer 723. By the N compound formed by thermal decomposition of the urea blown in, the formation of dioxins is restrained downstream of the freeboard section 724.

As mentioned above, by charging sludge into the incinerator, and blowing the N compound into the zone prior to secondary combustion in the freeboard section, the generation of dioxins is suppressed at the two parts of the fluidized layer and the freeboard section. Accordingly, the amount of dioxins contained in exhausting gas can be lowered.

FIG. 23 and 24 show the fire grate incinerator of stepwise structure, but applicability of this mode is not limited to such structure, and it is applicable to those with the function of the drying zone incorporated in them.

In the waste incinerating facility shown in FIG. 25, the N compound is blown into the zone prior to secondary combustion in the freeboard section, thereby decreasing dioxins generation downstream of the freeboard section. When there is added a structure for charging sludge together with waste, the generation of dioxins is further decreased. That is, N compounds are formed by thermal decomposition of the N content in sludge, so that the generation of dioxins in the fluidized layer 723 is restrained, and the amount of dioxins contained in the exhausting gas can be substantially reduced.

In the facilities of FIG. 23 to 25, urea as a N compound is described to be added in a solution state, but the state in which it is added is not limited to solution. When adding it to waste on the drying zone of a fire grate incinerator, urea powder is applicable, and when blowing it into the freeboard section of the fluidized bed incinerator, ammonia gas is applicable.

(Example 1) Explanation will be made on results of burning waste using the fire grate type testing apparatus. Testing material of waste was a municipal refuse and testing material of sludge was a sewage sludge (water content = 77 wt. % and N = 6 wt. % (in dry)). A nitrogen compound to be blown into the incinerator was urea in solution. Municipal refuse of 2000 kg/H and sewage of 200 kg/H were charged. Urea solution was sprayed over waste on the drying stage of the incinerator. For blowing urea in, the flow rate was set at 1 kg/H.

The concentration of dioxins in the exhausting gas was measured during combustion by Lhe above condition, and average values of dioxins concentration in 2,3, 7,8-TCDD toxicity equivalent were as low as around 20% in comparison with values in a case where only municipal refuse was burnt and only ordinary waste gas treatment was carried out.

Thus, when incinerating waste, by charging sludge containing nitrogen or adding a N compound, it is confirmed that the amount of dioxins contained in the combustion waste gas is substantially decreased.

By the present example, the N compound is added to waste or waste and sludge sent into the dry zone of the incinerator so as to generate substances suppressing the generated dioxins by thermally decomposing the sludge and added N compound, so that the amount of dioxins to be generated in the incinerator can be substantially decreased. Further, by the waste incinerating facility equipped with the nitrogen supply apparatus, it is possible to supply the N compound to be added to waste, bringing about the above mentioned effect.

BEST MODE 13 In this mode, in the course of carrying out various tests of incinerating waste, by carrying out the mixed fuel combustion of waste and sludge such as sewage sludge, it was found that the amount of dioxins contained in combustion waste gas was lowered.

The inventors made various studies as to how the effect of reducing dioxins is brought about by the mixed fuel combustion of sludge.

It is known that one of main causes generating dioxins by incinerating waste is combustion of waste in an oxygen-poor atmosphere. The combustion condition under such state corresponds to a condition in the early period of the combustion step where waste in the incinerator is heated and its temperature is raised. From this fact, it is considered that substances generated by thermal decomposition of sludge acts for suppressing the formation of dioxins.

Since general sludge contains the N content of 2 to 10 wt%

(in dry), it is assumed that substances suppressing the generation of dioxins are those generated by thermal decomposition of N containing substances in sludge, and tests were carried out. In the tests, when waste is burnt with N compounds added to it, dioxins in the combustion waste gas were decreased. From this, it is assumed that substances suppressing the generation of dioxins are compounds having ammonia (NH3) or NH. radicals generated when N containing substances are thermally decomposed.

A mechanism that N compounds generated by thermal decomposition of N containing substances suppress the generation of dioxins is not clear, but such substances are considered to have a poisoning effect to copper and other substances which act as catalysts for generating dioxins. This poisoning effect is assumed to be one cause bringing about suppression of the generation of dioxins.

As above, since N compounds generated by thermal decomposition of sludge works to suppress the generation of dioxins when incinerating wase, it has been found that the generation of dioxins can be suppressed by adding N compounds to waste.

Further, in this mode, were also made on generating dioxins in combustion waste gas exhausted from the incinerator, and a method of restraining their generation was found. In the flow path of exhausting gas, certain kinds of fly ash work as catalysts, so that the reaction between unburnt aromatic compounds and chlorine progresses and dioxins are

generated.

Also in this case, tests were carried out by blowing N compounds in combustion waste gas exhausted from the incinerator, and it was confirmed that dioxins in exhausting gas decreased. It is considered that N compounds blown into the waste gas flow path decreases the generation of dioxins in a similar manner to the case where N compounds are charged into the incinerator.

It is said that the temperature range likely to generate

dioxins is from 200 to 800 C. When N compounds are blown into the exhausting gas of more than 700 oc, the N compounds blown in are consumed in a reducing reaction of NO, and suppression of dioxins generation is not efficiently performed.

Accordingly, when blowing N compounds into combustion waste gas, the temperature of combustion waste gas should be 7000 C or lower, preferably around 650 C or lower. Therefore, in this invention, positions at which the N compounds are blown in is limited to those of the waste gas flow path cooled to below 650 C The exhausting gas exhausted from the secondary combustion chamber of the incinerator is generally 850 to 950 C, and after it is cooled to below 650 C, N compounds are blown in. For example, in a facility equipped with a boiler, when N compounds are blown in at an appropriate position of the boiler which is cooled to below 650 C or at the exhausting gas flow path of a boiler outlet, the generation of dioxins can be efficiently suppressed. In a facility equipped with a gas cooler, the generation of dioxins can be efficiently suppressed by blowing N compounds into the gas cooler or its outlet.

The present mode has been realized based on the findings from the results of the above tests and investigations.

The 1st of this mode is the waste incinerating method characterized by adding N compounds to waste to be charged into the incinerator, and blowing N compounds into the exhausting gas flow path at a position where the temperature is 6500C or lower.

In this mode, the generation of dioxins is suppressed at the two positions, that is, in the incinerator and in the exhausting gas flow path, by charging N compounds in waste to be charged into the incinerator, and in the exhausting gas path.

Thus, dioxins in exhausting gas are substantially decreased. Blowing of N compounds into the exhausting gas path is carried out by selecting a position of below 650 C where N compounds effectively works, so that the formation of dioxins is decreased.

The 2nd of this mode is the waste incinerating method characterized by charging sludge together with waste into the incinerator, and blowing N compounds into the 3 exhausting gas flow path at a position where the temperature is 6500C or lower.

In this mode, sludge is burnt together with waste. The generation of dioxins is effectively restrained by N compounds generated by combustion of sludge. Further, by blowing N compounds into the exhausting gas path, the formation of dioxins in the incinerator and in the exhausting gas path is restrained.

In general, waste and sludge are burnt by separate facilities respectively, but by burning waste and sludge at the same time, further merits of saving in equipment cost and operation cost can be enjoyed.

The 3rd of this mode is the waste incinerating method as set forth in the 2nd mode, characterized by adding N compounds to waste and/or sludge when charging waste and sludge into the incinerator.

In this mode, N compounds are added to waste or sludge or to both before charging into the incinerator. Sludge such as sewage sludge to be burnt are clay-like matter containing much water (65 to 90 wt%) even if it is dewatered, and if such dewatered sludge is charged in a large amount, the combustion state in the incinerator becomes deteriorated. There may be a case where enough sludge for supplying the N content of a required amount cannot be charged.

In such a case, the N compound is separately added to supplement the shortage of the nitrogen content, thereby substantially reducing dioxins generated in the incinerator while maintaining the combustion state normal. By performing the mixed combustion of waste and sludge, the merit of saving in costs is effected.

The 4th of this mode is the waste incinerating facility equipped with a boiler recovering heat of waste gas after secondary combustion, characterized by provision of a means for adding N compounds to waste to be charged into the incinerator and a means for blowing N compounds into the combustion waste gas flow path of the boiler outlet.

According to this mode, as N compounds can be added to waste, the forming amount of dioxins in the incinerator can be decreased.

There is provided the means of blowing N compounds into exhausting

gas in the combustion waste gas path, so that N compounds can be blown in at a position of 6500C or lower where dioxins are efficiently reduced.

The 5th of this mode is the waste incinerating facility equipped with a gas cooler for cooling waste gas after secondary combustion, characterized by provision of a means for adding N compounds to waste to be charged into the incinerator and a means for blowing N compounds into the exhausting gas flow path of the gas cooler outlet.

According to this mode, N compounds can be added to waste, and in addition, N compounds can be blown into the gas cooler outlet of 650 C or lower where dioxins are efficiently reduced.

The 6th of this mode is the waste incinerating facility as set forth in the 4th or 5th mode, characterized by provision of a means for charging sludge into the incinerator in place of a means of adding N compounds to waste to be charged into the incinerator.

According to this mode, as sludge is charged into the incinerator in place of N compounds, the formation of dioxins in the incinerator is restrained by combustion of sludge, and the effects of the 4th and 5th mode are brought about.

The 7th of this mode is the waste incineration facility as set forth in the 6th mode, characterized by addition, to the sludge charging means, of a means for adding N compounds.

According to this mode, when charging sludge, N compounds can be added, and in case the dioxins restraining effect is insufficient with only the nitrogen content in sludge to be

charged, it is possible to supplement the nitrogen content to be charged into the incinerator.

In each mode, the exhausting gas flow path means devices such as a heat recovery device, gas cooling device and waste gas treating device, and flues connecting them, through which exhausting gas after secondary combustion treatment flows.

Sludge means sewage sludge, night soil sludge, sludge generated when performing an activated sludge treatment of organic wastewater, sludge generated when performing a solid-liquid separation of wastewater containing organic materials, sludge generated in closed water areas as in river dredging, and other sludge. The N compound means organic or inorganic compounds containing nitrogen. Preferable examples of N compounds are low-cost compounds such as ammonia or urea. N compounds may be gaseous, liquid, solid or solution, and suitable forms are selected by position at which it is added.

FIG. 27 is an explanatory view showing the 1st one for carrying out this mode. The incinerating facility shown is provided with a fire grate incinerator. The incinerating facility shown is also equipped with a boiler. 810 designates the fire grate incinerator, 811 is a waste hopper for charging waste 880 such as municipal refuse into the incinerator, and 815 is the boiler and 816 is the dust collecter such as a bag filter.

* As an auxiliary facility of the incinerator 810, there is provided a means 850 for adding N compounds to waste 1 :. 0 be charged in the incinerator 810, which is composed of a storage bin 851 of urea solution as one kind of N compounds, a urea supply pump

852 and a urea spray nozzle 853.

As the auxiliary facility of the waste gas treating process, there is provided a means 870 for blowing N compounds into the exhausting gas flow path. This means 870 for blowing N compounds in comprises an ammonia gas holder 871, a flow rate regulator 872 and a not shown spray nozzle. The ammonia gas spray nozzle is inserted in the exhausting gas path at the outlet of the boiler 815.

At the combustion chamber 812 of the incinerator, a drying stage fire grate 813a, combustion stage fire grate 613b and post combustion stage fire grate 613c are provided stepwise. Thus, the combustion chamber 812 is sectioned into an area for drying the charged waste 880 (drying zone), an area for burning the dried waste (combustion zone) and an area for reducing materials sent in a combusting state into ash (post combustion zone).

In the waste incinerating composed as above, waste is charged into the waste hopper 811, and the urea solution is sprayed over the waste from the urea spray nozzle 853. The waste to which urea is added is sent into the combustion chamber 812 from the waste hopper 811.

In the combustion chamber 812, the charged waste is transferred onto the respective fire grates and is reduced to ash while going through the drying, combustion and post combustion stages, and exhausted. Since the'operation is carried out with the supply amount of the combustion air is lessened at the upstream fire grate, the combustion is carried out under an oxygen-poor state at the drying stage fire grate 813a (drying

zone) and part of the combustion stage fire grate 813b (combustion zone).

If such incomplete combustion takes place, reaction between aromatic compound and chlorine easily forms dioxins in the prior art, but in this mode, urea added to waste is thermally decomposed to generate compounds having ammonia (NH) or NH2 radicals, so that the progress of dioxins generating reaction is restrained.

The exhausting gas generated in the combustion chamber 812 contains combustible gas generated at the drying stage fire grate 813a and part of the combustion stage fire grate 813b, and the combustible gas is burnt by blowing the air in the secondary combustion chamber 814.

The exhausting gas exhausted from the secondary combustion chamber 814 is thermally recovered at the boiler 815, cooled to around 200 to 300 C, sent to the dust collector for removing dust, and is released into the atmosphere. At that time, ammonia gas is blown into the exhausting gas flow path at the outlet of the boiler 814 from the N compound blowing-in means 870. By blowing ammonia gas in, dioxins to be generated in the exhausting flow path is decreased.

As above, the amount of dioxins generation can be decreased at the two positions, that is, in the incinerator and in the exhausting gas path, by charging N compounds into the incinerator and the combustion waste gas path.

FIG. 28 is an explanatory view showing the 2nd example for carrying out the present mode. With respect to the same parts as those in Fig. 27, the same numerals are given and explanation

is omitted. As the auxiliary facility of the incinerator, a sludge supply means is provided for supplying sludge together with waste into the waste hopper 811.840 is a sludge charger.

As the auxiliary facility of the waste gas treating process, a N compound blowing-in means 870 is installed for the exhausting gas flow path.

In the above waste incinerating facility, waste and sludge charged in the waste hopper 811 are sent to the combustion chamber 812 where waste and sludge pass through the drying, combustion, post combustion processes, reduced to ash and are exhausted. In the drying step and in the early period of the combustion step, the N compound in sludge and urea added to sludge are thermally decomposed to generate compounds having ammonia (NH3) or NH2 radicals, so that the dioxins forming reaction is restrained, and the amount of dioxins contained in exhausting gas generated in the combustion chamber 812 is decreased.

Exhausting gas generated in the combustion chamber 812 is, as in the facility of Fig. 27, is exhausted from the secondary combustion chamber 814, and is released into the atmosphere via the boiler 815 and the dust collector 816. At that time, ammonia gas is blown into the combustion waste gas flow path at the outlet of the boiler 814 from the N compound blowing-in means 870. By blowing ammonia gas in, dioxins to be generated in the exhausting gas flow path is decreased.

As above, the amount of dioxins generation can be decreased at the two positions, that is, in the incinerator and in the exhausting gas path, by charging N compounds into the incinerator

and the exhausting gas path.

FIG. 29 is an explanatory view showing the 3rd one for carrying out the present mode. With respect to the same parts as those in FIG. 27-or 28, the same numerals are given and explanation is omitted.

This mode is equipped with a N compound adding means 860 for adding N compounds to the sludge charger 840 in addition to the structure of FIG. 28. The N compound adding means 860 comprises a hopper 861 for storing urea powder and the urea charger 862. As the auxiliary facility of the exhausting gas treating process, a N compound blowing-in means 870 is provided for blowing N compound into the exhausting gas path.

In the waste incinerating facility composed as above, waste is charged into the waste hopper 811, and sludge is supplied from the sludge charger 840. When supplying sludge, urea powder is supplied to the sludge charger 840 from the urea charger 862, and sludge mixed with urea is charged into the waste hopper 811, and subsequently, sludge and waste to which urea is added are sent into the combustion chamber 812.

In the incinerator 812, waste and sludge pass through the drying, combustion, post combustion processes, reduced to ash and are exhausted. As mentioned before, in the drying step and in the early period of the combustion step, the N compound in sludge and urea added to sludge are thermally decomposed to generate compounds having ammonia (NH3) or NH radicals, so that the forming reaction of dioxins is restrained, and the amount of dioxins contained in combustion waste gas is substantially

decreased.

The exhausting gas generated in the combustion chamber 812 is exhausted from the secondary combustion chamber 814 in a similar manner to the facility of FIG. 27, and is released into the atmosphere through the boiler 815 and the dust collector 816.

At that time, ammonia is blown into the exhausting gas flow path of the exit of the boiler 815 from the N compound blowing-in means 870, thereby decreasing the formation of dioxins in the exhausting gas flow path.

As mentioned above, when sludge is charged in the incinerator, urea is added to increase the nitrogen content to be charged in the incinerator 810, whereby dioxins to be generated in the incinerator are further decreased.

FIG. 30 is an explanatory view showing the 4th one for carrying out the present mode. In the drawing, 820 is the fluidized bed incinerator, 830 is a waste charger, 840 is a sludge charger, and 825 is a gas cooler for directly cooling combustion waste gas by spraying water, and 826 is a electrostatic precipitator.

The interior of the fluidized bed incinerator 820 is sectioned into a fluidized layer section 823 forming a fluidized layer by the air supplied from a wind box 621 and a freeboard section 824 which is provided with an air blowing nozzle for secondary combustion.

As the auxiliary facility of the waste gas treating step, there is provided a means 870 for blowing the N compound into the exhausting gas path. This blowing-in means 870 comprises

the ammonia gas holder 871, the flow rate regulator 872 and a not shown spray nozzle which is inserted into the exhausting gas path at the outlet of the gas cooler 825.

In the waste incinerating facility composed as above, waste is charged into the incinerator 820 from the waste charger 830, and sludge is charged from the sludge charger 840. The charged waste and sludge is heated up while being dried in the fluidized layer, and burn. As the air blowing amount is lessened in the fluidized layer, dioxins are easily generated in the prior art.

But in the present mode of practice, the N content in the sludge charged with waste is thermally decomposed to generate compounds having ammonia (NH) or NH2 radicals, so that the dioxins generating reaction is suppressed.

Combustible gas such as H2, CO or CH4 is included in combustion waste gas generated in the fluidized layer section 823, and so the air is blown in at the freeboard section 824 so as to perform the secondary combustion of the combustible gas.

Combustion waste gas exhausted from the incinerator 820 is cooled to around 200 to 400oC, is sent to the dust collector 826 for removing dust, and is released into the atmosphere. At that time, ammonia is blown into the combustion waste gas flow path at the exit of the gas cooler 825 from the N compound blowing-in means 870, thereby decreasing the formation of dioxins in the combustion waste gas flow path.

FIG. 27 to 30 show waste incinerating facilities furnished with the fire grate incinerator or the fluidized bed incinerator, but applicability of the present mode is not limited to these

two types, and it is applicable to, for example, a kiln type.

FIG. 27 to 30 show the fire grate incinerators provided with stepwise fire grates, but applicability of the present mode is not limited to a stepwise type, and it also is applicable to those which have the section functioning as a drying zone in the incinerator In FIG. 27 to 30, the spray nozzle of the N compound blowing-in means 870 installed to the waste gas treating process is inserted into the outlet of the boiler 815 for blowing the N compound to the outlet of the boiler 815, but this is one example for a case where a boiler is equipped, and the position for blowing the N compound in is not limited to a boiler outlet. In a facility equipped with a gas cooler, the position for blowing the N compound in is not limited to a gas cooler outlet. Thus, the N compound blowing-in position is not limited to the outlet of the boiler or the gas cooler, and the N compound may be blown in at an appropriate position of a boiler cooled to below 630 C or in the gas cooler.

In the facility of FIG. 27, urea is added to material before charging into the incinerator in a solution state, and in FIG.

29, it is in a powder state, but the invention does not limit states of the N compound to be added. When adding N compounds to waste, for dispersing a small amount of N compounds to a large amount of bulky waste as uniformly as possible, solution is desirable. When adding N compounds to sludge, for lessening water content, powder is desirable.

In the facilities of FIG. 27 to 30, the N compound to be blown

into the combustion waste gas flow path is ammonia gas, but the N compound to be blown into the exhausting gas flow path is not limited to a gaseous state, and solution of ammonia or urea is also applicable.

(Example 1) Explanation will be made to results of burning waste, using the fire grate testing apparatus. Testing material of waste was municipal refuse and testing material of sludge is sewage sludge (water content = 77 weight. % and N = 6 weight. % (in dry)).

The N compound to be blown into the incinerator was ammonia in solution. Municipal refuse of 2000 kg/H and sewage of 200 kg/H and were charged. Urea was added to sludge at a rate of 1 kg/H. The generated exhausting gas was cooled by the gas cooler, and ammonia gas was blown at a flow rate of 0.35 Nm3/H into the exhausting gas duct. The temperature in the exhausting gas duct was around 300 C.

The concentration of dioxins in the released exhausting gas was measured during combustion by the above condition, and average values of dioxins concentration in 2,3, 7,8-TCDD toxicity equivalent were as low as around 10% in comparison with the values in a case where only municipal refuse was burnt and only ordinary waste gas treatment was carried out. Thus, when burning waste, it was confirmed that the amount of dioxins contained in the combustion waste gas is substantially decreased by charging sludge to which urea is added together with waste, and ammonia gas is blown into the combustion waste gas path.

By the present mode, sludge and N compounds are charged together with waste into the incinerator, and the N containing component is thermally decomposed to generate the N compound working to suppress generation of dioxins. Further, the N compound is blown into the exhausting gas path, so that the forming amount of dioxins is substantially decreased at the two positions of in the incinerator and in the exhausting gas path. Further, as the N component is blown into the exhausting gas path where the temperature of the exhausting gas is below 650 C, denitrification reaction is difficult to occur so that the formation of dioxins is effectively restrained.

There is provided an apparatus for charging sludge or N compounds in the incinerator, and by using the waste incinerating facility equipped with the N compound blowing-in apparatus at the outlet of the boiler or the gas cooler, it becomes possible to charge sludge or N compounds into the incinerator for suppressing the generation of dioxins and to blow N compounds into the combustion waste gas path at a position where the generation of dioxins is effectively restrained, thereby obtaining the above mentioned effect.

BEST MODE 14 The present mode relates to a waste incineration method and an apparatus thereof which burn waste in an incinerator, releases generated waste gas into the atmosphere after treatment, while efficiently decreasing dioxins generation.

FIG. 35 shows the structure of the waste incinerating

system, in which 901 is an incinerator having a waste supply hopper 901a, 902 is a temperature reducing device comprising, e. g. , a temperature reducing tower, boiler, or heat exchanger, 903 is a waste gas treating facility for removing acid gas such as HCl or SO, from the waste gas cooled down in the temperature reducing device 902.904 is an electric precipitator, 905 is an induction fan, and 906 is a stack. Those are connected in series by flues.

In this system, waste charged into the incinerator by the crane from a waste pit is dried and burnt in the incinerator 901, and unburnt parts are completely burnt. After combustion, exhausting gas is discharged outside, goes through the temperature reducing device 902, waste gas treating facility 903 and electrostatic precipitator 904, and exhausted from the stack 906.

The electric precipitator 904 has, as is well known, the characteristics that it is not influenced by properties of gas or dust and can catch fine particles. But, in this waste incinerating system, the waste gas from the outlet of the incinerator 901 first goes through the temperature reducing device 902 and the waste gas treating facility 903, and is introduced at about 3000C into the electrostatic precipitator 904 for dust collection. The temperature of about 300 C is the one where dioxins are easily generated, and if exhausting gas is passed at about 3000C through the electrostatic precipitator, a problem arises that the high concentration of dioxins is exhausted from the stack 906.

A technological problem to be addressed by the present mode

is to keep the combustion conditions in the incinerator constant by introducing a relatively simple apparatus, so that the concentration of dioxins in the incinerator is lowered, and also the formation of dioxins in the electrostatic precipitator is suppressed.

The waste incineration method in the present mode is to use a waste incineration system composed of an incinerator, temperature reducing device, waste gas treating facility, electrostatic precipitator, induced fan, and stack connected in series, where the incinerator is provided with a waste supply hopper and a sludge supply hopper, waste is burnt mixed with sludge, and a temperature controller is provided at the inlet of the dust collector for controlling the electric dust collector to operate at a temperature below 2300C.

The present waste incinerating method is characterized by control of the temperature reducing device so that the temperature of the exhausting gas at the inlet of the electrostatic precipitator is below 230 C.

Further, the electrostatic precipitator is provided at its inlet with a temperature sensor for sensing the temperature of exhausting gas so as to control the temperature reducing device for keep the temperature at the inlet of the electrostatic precipitator below 2300C.

Explanation will be provided on the waste incinerating method and apparatus for carrying out the present mode, referring to FIG. 33. FIG. 33 is the system configuration of the waste incinerating apparatus of the present mode. For the same

sections as in the prior example (FIG. 35), the same numerals are given.

In the waste incinerating apparatus of the present mode, the incinerator 901 is provided with not only the waste supply hopper 901a but also the sludge supply hopper 901b, as well as the temperature sensor 907 installed for sensing the waste gas temperature at the inlet of the electrostatic precipitator 904, and further the electrostatic precipitator inlet temperature controller 908 is furnished for operating the electrostatic precipitator 904 at the temperature below 230 C by controlling the temperature reducing device 902 so as to make the rate of temperature reduction of the high temperature exhausting gas larger when the temperature sensed by the temperature sensor 907 exceeds 230 C or when the temperature sensed by the temperature sensor 907 does not exceed 230 C yet, but is rising too quickly.

In this system, the temperature reducer 902 comprises the temperature reducing tower which lowers the temperature of the high temperature waste gas by passing it through the water spray atmosphere, and when a command is issued from the electrostatic precipitator inlet temperature controller 908 for increasing the water spray amount, the temperature reducing device increase the water spray amount.

Further explanation will be provided on the method of burning waste by this system. First, waste is transferred by the crane from the waste pit and is charged into the incinerator 901 from the supply hopper 901a, while organic sludge generated at sewage treating, for example, is charged by the sludge supply

hopper 901b. Sludge and waste charged in the incinerator 901 are dried in the incinerator, catch fire, and is subjected to mixed combustion, and waste gas is sent downstream from the outlet of the incinerator. Thereby, the concentration of dioxins is lowered in comparison with a case of burning only waste.

The reason of dioxins suppression has been mentioned for other mode, and is omitted.

By the present mode, it has been found that, when carrying out the mixed combustion of waste and sludge, by using the electrostatic precipitator 904 and lowering its operating temperature, the concentration of dioxins is decreased. It is assumed that, by carrying out the operation at a temperature lower than the range of around 300 Oc where dioxins are easily generated, dioxins generation is restrained. FIG. 34 shows the findings obtained from the inventors'experimental studies. This is a graph showing the relation of the rate of increase of dioxins between the inlet and outlet of the electrostatic precipitator.

The axis of ordinate is the rate of increase of dioxins and the axis of abscissa is the temperature at the inlet of the electrostatic precipitator.

From this result, it is seen that when the temperature of the electrostatic precipitator is below 230 C, preferably below 210 C, the concentration of dioxins does not increase in the electrostatic precipitator 904, and the concentration of dioxins is efficiently lowered.

Accordingly, observing the waste gas temperature by the temperature sensor 907 installed at the inlet of the

electrostatic precipitator and by the temperature controller 908, when the temperature sensed by the temperature sensor exceeds 2300C or when the temperature sensed by the temperature sensor does not exceed 230 C yet, but is rising too quickly, a command for increasing the water spray amount is issued from the electrostatic precipitator inlet temperature controller 908 to the temperature reducer 902 so as to increase the water spray amount in the temperature reducing device, increase the rate of temperature reduction of high temperature exhausting gas. In this way, by controlling the operating temperature of the electrostatic precipitator 904 to below 230 C, dioxins can be decreased. By the synergistic effect of this effect and the effect of decreasing dioxins due to supply of sludge, the concentration of dioxins can be more effectively decreased.

When the whole system is automatically controlled, it is sufficient to incorporate a sensed value of the temperature sensor 907 as one of the operating parameters.

The air made clean by the electrostatic precipitator 904 removing fine particles is released into the atmosphere from the stack 906.

In order to confirm the effect of this mode, municipal refuse and waste were burnt by a fire grate incinerator, the temperature of the exhausting gas was lowered to 2100C by a temperature reducing tower, and dust was removed by an electrostatic precipitator. The resultant concentration of dioxins was compared with that obtained when only municipal refuse was burnt and the electrostatic precipitator was operated at 270 C. It

was confirmed that in the former case of the present mode, the concentration of dioxins is lowered by about 90% in comparison with the latter case.

As mentioned above, by the present mode, in the waste incinerating system composed of an incinerator, temperature reducing device, waste gas treating facility, electrostatic precipitator, induced fan, and stack connected in series, the generation of dioxins can be efficiently decreased, due to mixed combustion with sludge and operation of the electrostatic precipitator at a temperature below 230 C.

INDUSTRIAL APPLICABILITY As above, the waste incineration method and apparatus thereof relating to this invention provides the effect of suppressing the generated dioxins by performing the mixed fuel combustion of waste, sludge, plastic, RDF, sulfur contained material, and others in a fire grate incinerator or a fluidized bed incinerator, and controlling the combustion in accordance with the SO, concentration, and further by generating N compounds, thereby bringing about very large industrial effects.

Claims

Claims : 1. A method for incinerating a waste, the method comprising the steps of: preparing a sludge and a waste plastic having a lower calorific value of 18, 828kJ/kg (4,500 kcal/kg) or more; performing a mixed fuel combustion of the sludge and the waste plastic in a waste incinerator; and controlling an outlet temperature of the waste incinerator at 900-1, 200 C and an oxygen concentration at 3-12 wt%.
2. A method according to Claim 1, wherein the waste incinerator has a fluidized layer on a fluidized bed, and a sand layer forming the fluidized layer is at a temperature of 380 to 450 C.