JPH08168800A - Method of efficiently incinerating organic sludge - Google Patents

Abstract

PURPOSE: To provide a method for efficiently incinerating an org. sludge assuming a solid state. CONSTITUTION: In the incinerating method of the org. sludge assuming a solid state, the org. sludge is kept at >=150 deg.C and under a pressure higher than saturated vapor pressure of a temp. concerned to be fluidized, and this fluidized matter under high temp. and high pressure is subjected to flash depressurization and the resultant flash depressurized residue is incinerated.

Description

Detailed Description of the Invention [Industrial applications]

[0001]

TECHNICAL FIELD The present invention relates to an efficient method for incinerating organic sludge in a solid state.

[0002]

2. Description of the Related Art Sewage sludge, which is a typical organic sludge, is about 50 million m ³ (water content of 98
%), Which is increasing year by year. 2. Description of the Related Art In recent years, in a large city, in order to efficiently treat and dispose of sludge, sludge generated from a plurality of sewage treatment plants is collected and treated in a dedicated sludge treatment plant. In this case, the sludge is pipe-pumped from the sewage treatment plant in the form of concentrated sludge having a high moisture content, or is subjected to dehydration treatment at the sewage treatment plant, and is transported by a dump truck in the form of dewatered sludge. The former has a drawback that sludge has a high water content and therefore has a large capacity and requires a large-capacity pump, that is, a high transportation cost. Further, in this case, it is indispensable to install a biological treatment facility such as a dewatered filtrate or a digestion / desorption solution in the sludge treatment plant. On the other hand, in the latter case, there are many voids in the dewatered sludge, that is, because the apparent density is low, efficient transport is not possible, and since the container for containing the sludge is difficult to have a closed structure, the odor and sludge fall from the viewpoint. Environmentally unfavorable. In addition, when transporting dehydrated sludge in the treatment plant, a belt conveyor is mainly used, but the belt conveyor is greatly restricted in space when installed, and it is difficult to have a closed structure like truck transportation, which is an environmental problem. Cause recently,
Although pipe pressure feeding is also used for transporting dehydrated sludge in the treatment plant, the pressure loss in the pipe is extremely large, and the transport is limited to short-distance transport. Furthermore, dewatered sludge is temporarily stored in a tank or a hopper before treatment and disposal. However, as described above, the apparent density is low, so efficient storage is not possible, and the tank volume etc. is large, that is, equipment costs are high. Has led to an increase. As described above, the method of transporting and storing organic sludge in a solid state such as dewatered sludge has many problems, and the treatment of such organic sludge also has the following problems. There is.

[0003] That is, regarding the treatment of organic sludge,
Although various methods have been conventionally known, the incineration method is widely used because it can be made harmless and its volume can be reduced relatively easily. The conventional incineration method is generally a method of incinerating cake-like dehydrated sludge obtained by dehydrating organic sludge,
In this case, the dewatered sludge has high adhesion and poor fluidity, and the cake properties of the dewatered sludge are non-uniform, and the dewatered sludge is a solid mass,
There are various problems as described below. (1) When supplying dewatered sludge to an incinerator via a raw material hopper, it is very difficult to perform quantitative supply because the fluidity of the dewatered sludge is poor. (2) It is very difficult to control the temperature in the furnace because the properties of the dehydrated sludge are non-uniform and it is difficult to supply a fixed amount. (3) Since dewatered sludge is a solid mass, it is difficult to perform efficient combustion, and there are also cases where complete combustion is not possible.

[0004] In order to solve the above-mentioned problem observed in the incineration of dehydrated sludge, a method has been proposed in which dehydrated sludge is once dried and then incinerated without being directly incinerated. However, also in this case, due to the large adhesion of the dewatered sludge, (1) when the dewatered sludge is supplied to the dryer through the raw material supply hopper, the fluidity of the dewatered sludge is poor. (2) When drying the dewatered sludge in the dryer, the dewatered sludge adheres to the wall of the container and is dried due to the high adhesion of the dewatered sludge. The solids are poor in quality, and the drying efficiency of the dryer is significantly deteriorated. As described above, the conventional incineration method of dewatered sludge has many practical problems.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems found in the conventional incineration of organic sludge having a solid state.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, when incinerating an organic sludge in a solid state, the organic sludge is fluidized while being held at a temperature of 150 ° C. or higher and a pressure of saturated steam pressure of the temperature or higher, There is provided a method for incinerating organic sludge, which comprises flash decompressing a fluidized product under high temperature and high pressure and incinerating the obtained flash decompression residue.

In the present invention, the solid organic sludge used as a raw material to be treated includes sewage sludge discharged from a normal sewage treatment plant and surplus sludge discharged from various organic wastewater biological treatment apparatuses. Examples include various organic sludge dehydrates and solid organic sludge discharged from various manufacturing processes. As a method of dehydrating the organic sludge, a mechanical dehydration method such as vacuum dehydration, belt press dehydration, and centrifugal dehydration is adopted, and is not particularly limited. When performing this dehydration, it is preferable to add a sludge conditioning agent, particularly preferably a polymer flocculant, to the organic sludge. In the present invention, the amount of water in the solid sludge as the raw material to be treated is 50 to 50%.
It is 90% by weight, preferably 70-80% by weight. Hereinafter, the present invention will be described in detail for each process.

(Method for Incineration of Organic Sludge in Solid State) To carry out the method of the present invention, first, the organic sludge in solid state is kept at high temperature and high pressure to form a fluidized product.
In this case, it is also possible to set the organic sludge under alkaline conditions in order to promote the fluidization reaction of the organic sludge. In this case, an alkaline substance is usually used to form the alkaline condition, and as the alkaline substance,
For example, alkali metal compounds such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium formate and potassium formate, and alkaline earth compounds such as calcium oxide, calcium hydroxide and magnesium hydroxide. Examples thereof include metal compounds.

The fluidizing treatment in the present invention is carried out under high temperature and high pressure, in which case the reaction temperature is generally 150 ° C.
The above is preferably about 200 to 225 ° C., and the reaction pressure may be equal to or higher than the saturated vapor pressure at the reaction temperature, for example, at 200 ° C., 16 kg / cm ² abs or more. At this time, the holding time at the reaction temperature (reaction time)
Is generally 60 minutes or less, though it depends on the target sludge. To improve fluidity, use higher temperature,
Alternatively, the holding time may be longer, but the solids tend to settle accordingly. Therefore, in order to prevent sedimentation of solids during transportation and storage after fluidization, it is necessary to set appropriate temperatures and holding times. The fluidizing device of the present invention may be any heat exchanger of the indirect heating type, but since it handles sludge presenting a solid state, a scraping type heat exchanger having a scraper inside and a screw type heat exchanger having a helical blade are used. The use of exchangers is desirable.

In the present invention, the pressure may be a self-generated pressure due to water vapor from the organic sludge. However, if necessary, the pressure may be increased by using nitrogen gas, carbon dioxide gas, argon gas or the like. You can also.

In the present invention, the product obtained by maintaining the organic sludge under the above-mentioned high temperature and high pressure has remarkably good fluidity, and can be sufficiently pumped during transportation. Therefore, it goes without saying that a vacuum car or a tank truck can be used instead of a truck for the transportation. Further, the product obtained in the present invention has an apparent density higher than sludge before fluidization because there are almost no voids. Therefore, the water can be efficiently stored, and the required tank capacity and the like can be reduced. The water content in the fluidized product is 50-90% by weight, preferably 70-80% by weight.
% By weight.

[0012] The fluidized organic sludge is, as described above,
Since it is very rich in fluidity, it can be easily transported from the fluidizer or fluidized material storage container to the incinerator by pumping, etc., and the supply of organic sludge to the incinerator is performed by using a spray gun or the like. Since it can be supplied in the form of fine particles, the combustion can be performed efficiently and the supply to the incinerator can be performed quantitatively. Further, the fluidized organic sludge exhibits uniform properties and can be supplied in a fixed amount as described above, so that the furnace temperature can be easily controlled in combination with the control of the air amount.

Next, FIG. 1 shows a flow sheet of a preferred embodiment of the present invention. In FIG. 1, 3
Reference numeral 1 denotes a dehydrating device, 32 denotes a fluidizing device, 33 denotes a flash tank, 34 denotes a pressure pump, 35 denotes a condensing device, 36 denotes an incinerator, and 37 denotes a waste heat boiler. The concentrated organic sludge having a water content of about 98% passes through a line 38 and a dewatering device 31.
Will be introduced to. The separated filtrate is returned to a water treatment facility through a line 39, and the dewatered sludge is introduced into a fluidization device 32 by a line 40. The fluidizer is a heat exchange reactor, in which a heating medium is introduced via line 48 and heats the organic sludge in the reactor to the fluidization temperature. As the heat source used here, it is desirable to use steam recovered by the waste heat boiler 37 in the subsequent stage. As the conditions at this time, the fluidization temperature is 150 ° C. or higher, preferably 20 ° C.
The reaction pressure may be 0 to 220 ° C. and the reaction pressure may be higher than the saturated steam pressure at the reaction temperature. The reaction time is usually within 60 minutes. The fluidizing device adopted here is preferably a scraping surface heat exchanger or a screw type heat exchanger,
There is no particular restriction. The fluidized material is introduced into the flash tank 33 through the line 41, and the pressure is rapidly reduced to atmospheric pressure or reduced pressure. At this time, a part (about 10 to 20%) of the moisture of the fluidized material evaporates. This water vapor is introduced into the condenser 35 through the line 43 to be a liquid. This liquid is returned to the water treatment facility via line 45.
On the other hand, the fluidized material (evaporation residue) 42 remaining without evaporating in the flash tank 33 enters the pressure pump 34 and is pressure-fed through the line 44 to the incinerator 36. In the incinerator 36, the combustion air introduced from the line 46 and the fluidized material are mixed to form a combustion state. This time,
If necessary, auxiliary fuel such as heavy oil is added. However, since the fluidized product is in a liquid state, it can be sprayed to a fine particle size and has a high solid content concentration, so it may self-combust. The combustion conditions are 600-1000 ° C, preferably 750-800 ° C. The incinerator that can be used here is preferably a simple spray incinerator, but other types such as a fluidized bed furnace will not cause any problems in combustion. The hot exhaust gas after combustion is introduced into the waste heat boiler 37 through the line 47, and heat is recovered in the form of steam. The steam generated here passes through the line 48 and is used as a heating source of the fluidizer 32. Exhaust gas after heat recovery in the heating boiler 37 passes through an exhaust gas treatment device (not shown) through a line 49, is led to a chimney, and is released to the atmosphere.

As described above, according to the present invention, organic sludge having a solid state, such as dehydrated sludge, can be handled as a liquid material, and there is a great merit in transportation and combustion. Pumping can be used for transfer instead of belt conveyor, and spray incineration can be used for combustion. These provide the following advantages. (1) Pumping can be performed even if the dewatering yard and the incineration yard are far apart, and planning can be done freely without restrictions on space arrangement. (2) Stable supply of sludge to the incinerator, quantitative transfer and distribution are good. (3) Easy odor control and maintenance. (4) Installation space is small. (5) The incinerator can be downsized. (6) Low air ratio combustion is possible, NOx can be reduced, and exhaust fan can be downsized. (7) Sludge flow rate can be measured and incineration volume can be easily controlled. (8) Fluidized sludge has uniform properties, and it is easy to control the temperature inside the furnace. (9) There is no drive unit and fluid medium in the furnace, and it is easy to increase the size. As is clear from the above, it can be said that the fluidized incineration method of organic sludge exhibiting a solid state of the present invention is a technically and economically very advantageous method.

[0015]

EXAMPLES Next, the present invention will be described in more detail by way of examples. The percentages shown below are based on weight.

Example 1 Sewage sludge was selected as an organic sludge, and dewatered cakes of three types of mixed raw sludge discharged from a treatment plant of a standard activated sludge method were used in the following tests. These sludges are dehydrated by a belt press after adding a polymer flocculant. The typical properties are shown in Table 1.

[0017]

[Table 1]

Approximately 80 g of the above dehydrated sludge is used, and the content volume is 300 ml
The autoclave of No. 2 was filled and hermetically sealed, purged sufficiently with N ₂ gas, and pressurized to 30 kg / cm ² G. Next, stirring was started using an electromagnetic induction type stirrer, and simultaneously heating was started in an electric furnace. After the temperature in the autoclave reaches a predetermined reaction temperature (150 to 250 ° C.), the temperature is maintained for a predetermined time, and then the internal pressure of the autoclave is used to allow the contents of the autoclave to flow out to a flash tank. A fluidized product (flash reduced pressure residue) having a temperature of about 100 ° C. and a pressure of atmospheric pressure was obtained. The pressure in the autoclave during the reaction was maintained at a pressure equal to or higher than the saturated steam pressure at the reaction temperature by a pressure-holding valve. The fluidized product was allowed to stand for a whole day and night, and after confirming the state of solid matter precipitation, a coaxial double cylindrical viscometer with a thermostat,
The apparent viscosity at 20 ° C was measured.

Table 2 shows the apparent viscosity of the fluidized product (shear rate 10 s ^-1 ). As you can see from this table, Sludge A is 1
75 ℃ or higher, Sludge B is 150 ℃ or higher, Sludge C is 200 ℃
Fluidization was possible at the above reaction temperature. Also, by increasing the reaction temperature or increasing the holding time, the apparent viscosity was reduced and the fluidity was improved. By the way, concentrated sludge collected separately from the sewage treatment plant (water content 96.8%,
The apparent viscosity was 80 cP under the same viscosity measurement conditions (organic matter ratio 78.4%). Therefore, it was determined that by setting appropriate reaction conditions, the viscosity of the dewatered sludge could be reduced to the same level as that of the concentrated sludge, and pipe transport by a pump was sufficiently possible. On the other hand, if the fluidized sludge is left to stand overnight, 25
Precipitation of solids was observed in the sludge fluidized at 0 ° C. Moreover, the fluidized sludge was in a liquid state and could be sucked with a dropper. Therefore, it can be determined that it can be loaded and transported in a vacuum car or the like.

[0020]

[Table 2] Note)-* indicates that the sludge did not fluidize and the viscosity could not be measured.

Example 2 (Incineration of Fluidized Product) As the organic sludge, the sludge C used in Example 1 was used.
The mixture was fluidized at 200 ° C. for 60 minutes. The specific procedure is the same as in the first embodiment, and a description thereof will be omitted. After depressurization, fluidized sludge (flash depressurization residue) was collected and subjected to a spray incineration test. As a result, it was confirmed that the fluidized sludge can be incinerated efficiently.

[Brief description of drawings]

FIG. 1 shows a flow sheet for one example of a method of dehydrating, fluidizing, and then incinerating organic sludge.

[Explanation of symbols]

 31 Dehydrator 32 Fluidizer 33 Flash tank 36 Incinerator 37 Waste heat boiler

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location C02F 1/06 ZAB F23G 5/02 ZAB E 7/00 ZAB 104 A (72) Inventor Shinya Yokoyama Ibaraki 16-3 Onogawa, Tsukuba City, Japan Institute of Industrial Science and Technology (72) Inventor Tomoko Ogi 16-3 Onogawa, Tsukuba City, Ibaraki Institute of Industrial Science and Technology (72) Inventor Hiroshi Dote Tsukuba, Ibaraki Prefecture 16-3 Onogawa City, Institute of Industrial Science, National Institute for Resources and Environmental Technology (72) Inventor Tomoaki Minowa, Tsukuba City, Ibaraki Prefecture 16-3, Onogawa Institute, Institute of Advanced Industrial Science and Technology (72) Tokuji Annaka Tsukuba, Ibaraki Prefecture Asahi No. 1 Asahi in the Civil Engineering Research Institute, Ministry of Construction (72) Inventor Kazuaki Sato No. 1 Asahi Civil Engineering Research Institute (72) Inventor Takashi Masuda 2-3-1 Kasumigaseki, Chiyoda-ku, Tokyo Construction Bureau, Ministry of Urban Affairs Sewerage Department (72) Inventor Tadashi Nakamura 5-5-16 Hongo, Bunkyo-ku, Tokyo Organo Stock In-company (72) Inventor Akira Suzuki 5-5-16 Hongo, Bunkyo-ku, Tokyo Organo Co., Ltd. (72) Inventor Shinji Ito 5-5-16 Hongo, Bunkyo-ku, Tokyo Organo Co., Ltd.

Claims (2)

[Claims] 1. When incinerating an organic sludge in a solid state, the organic sludge is fluidized while being kept at a temperature of 150 ° C. or higher and a pressure of saturated steam pressure of the temperature or higher, and under high temperature and high pressure. A method for incinerating organic sludge, which comprises decompressing the fluidized product of No. 2 by flash decompression and incinerating the obtained flash decompression residue. 2. The method according to claim 1, wherein the incineration waste heat of the flash vacuum residue is used as at least a part of the heat required for fluidizing the organic sludge.