JPH1163458A - Method for processing sludge by incineration - Google Patents

Abstract

PROBLEM TO BE SOLVED: To incinerate sludge while reducing the concentration of sulfur oxide in exhaust gas by adding slaked lime or quick lime to sludge being fed into an incinerator and mixing them in advance. SOLUTION: In the method of the incinerating process of the sludge from the industrial wastewater sludge, a dewaterer 2 dehydrates sludge 1 reducing the water content of the sludge and forms dewatering cakes (dewatered sludge) 1a. The dewatered sludge 1a is fed to a dryer 3 for drying by heating. The slaked lime or quick lime 1b together with the dewatered sludge 1a is fed to the dryer 3 and dried by heating agitating them. It is desirable to determine the quantity of feeding the slaked lime 1b into the dryer 3 in relation with the contents of sulfur component in the dried sludge 1c for optimum reduction of the generation of the sulfur oxide at the combustion. Putting it concretely, it will be desirable to add 0.5 to 4 mole of the slaked lime to a mole of sulfur contents in the sludge and to mix them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for incinerating sewage sludge such as industrial wastewater sludge and human waste, and more specifically, to incinerating sludge containing sulfur components in a circulating fluidized bed furnace or the like. The present invention relates to a sludge incineration method in which an incinerator is subjected to an incineration treatment and an exhaust gas discharged from the incinerator is subjected to a desulfurization treatment.

[0002]

2. Description of the Related Art Generally, sewage sludge such as industrial wastewater sludge and human waste is dewatered and dried, and then put into an incinerator to be incinerated.

[0003] Since industrial wastewater sludge and sewage sludge contain sulfur components, a large amount of sulfur oxides are generated by the combustion of the sulfur components during incineration, and the exhaust gas discharged from the incinerator has a high concentration. Of sulfur oxides. The emission of such an exhaust gas containing sulfur oxides into the atmosphere as it is should be avoided for reasons such as air pollution and acid rain. Legally,
Sulfur oxides are designated as air pollutants.

Therefore, conventionally, desulfurization treatment has been performed on exhaust gas discharged from an incinerator.
That is, an appropriate desulfurization device, for example, a gas-cooled desulfurization tower is arranged in an exhaust gas path from an incinerator to a chimney, and a desulfurizing agent such as caustic soda or magnesium hydroxide (alkaline chemical agent) is added to exhaust gas passing through the desulfurization tower together with cooling water. ) Is usually sprayed and contacted to remove sulfur oxides in the exhaust gas. For example, when the exhaust gas is desulfurized using caustic soda, the sulfur oxide is converted into “SO ₂ + 2NaOH → Na ₂ SO ₃ + H ₂ ” by caustic soda.
It is neutralized and removed by the reaction "O".

[0005]

However, the exhaust gas treatment using such a desulfurization apparatus has a high treatment cost and is a problem in incinerating sludge. In other words, since the concentration of sulfur oxides in the exhaust gas is high, a large amount of alkali chemicals is required, so that the cost of chemicals increases and the maintenance and management costs are increased due to the increase in the size of desulfurization equipment (chemical spraying equipment, etc.). Get higher.

[0006] The present invention has been made to solve such a problem, and it is possible to incinerate sludge while reducing the sulfur oxide concentration of exhaust gas discharged from an incinerator as much as possible. It is an object of the present invention to provide a sludge incineration method that has been devised.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a method for incinerating sludge, wherein sludge containing a sulfur component is incinerated by an incinerator and exhaust gas discharged from the incinerator is subjected to desulfurization. To achieve the above objectives,
In particular, the present invention proposes adding slaked lime or quick lime to sludge fed into an incinerator in advance and mixing the slaked lime or quicklime. In such an incineration method, a circulating fluidized bed furnace is used as an incinerator, and the dewatered sludge is dried with slaked lime or quick lime added thereto, and then put into a circulating fluidized bed furnace. It is preferable to do so. Also,
Slaked lime or quick lime is added to and mixed with sludge at a ratio of 0.5 to 4 moles (more preferably 0.8 to 1.2 moles) per mole of sulfur component in sludge. Is preferred.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be specifically described below with reference to FIG.

FIG. 1 shows an example of a system for carrying out the sludge incineration method according to the present invention. Industrial wastewater sludge and sewage sludge 1 are incinerated as follows.

First, the sludge 1 is subjected to a dehydration treatment by a dehydrator 2 to obtain a dewatered cake (hereinafter, referred to as "dewatered sludge") 1a having a reduced water content to a certain extent.

The dewatered sludge 1a is supplied to a drying device 3
And dried by heating. At this time, slaked lime (Ca (OH) ₂ ) or quicklime (CaO) (hereinafter referred to as “slaked lime or the like” 1b) 1b is put into the drying device 3 together with the dehydrated sludge 1a, and the dehydrated sludge 1a is slaked lime or quicklime. Is heated and dried while being stirred. The dewatered sludge 1a is generally in the form of a viscous rice cake, but is heated and dried while being sheared and fragmented by the action of a stirring blade or the like in the drying device 3, and added during that time. It is mixed and stirred with slaked lime or the like 1b to form a granular dried product (hereinafter referred to as “dry sludge”) 1c containing slaked lime or the like 1b.

The amount of slaked lime or the like 1b charged to the drying device 3 is related to the sulfur component content in the dried sludge 1c in order to reduce the amount of sulfur oxides generated during combustion as much as possible. It is preferable to set in. Specifically, slaked lime or the like 1b is added in an amount of 0.5 to 4 mol (more preferably, 1 mol) to 1 mol of the sulfur component in the sludge.
(0.8 to 1.2 mol) is preferably set so as to be added and mixed.

The dried sludge 1c to which the slaked lime or the like 1b has been added and mixed in this way is introduced into the incinerator 5 from the drying device 3 by an appropriate supply means 4, and incinerated. In this embodiment, as shown in FIG. 1, a circulating fluidized bed furnace 5 comprising a furnace body 6 and a cyclone 7 for circulating a granular medium 8 such as sand is used as the incinerator. In the furnace main body 6, the medium 8 is maintained in a circulating fluidized state by ejecting primary combustion air 9 from a lower portion thereof, and the dried sludge 1 c supplied to the furnace main body 6 by the supply means 4 is supplied to the medium 8. The mixture 8 is burned while being mixed and stirred, and is incinerated. In the upper region (freeboard) of the furnace main body 6, the air for secondary combustion is supplied, and the medium 8 is blown up, and the unburned component in the exhaust gas 1d is combined with the stirring action therewith. Complete combustion (secondary combustion) is performed. The blown-up medium 8 is introduced into the cyclone 7 from the upper outlet of the furnace main body 6 together with the exhaust gas 1d, separated from the exhaust gas 1d by the cyclone action, and returned to the furnace main body 6 from the lower part of the cyclone 7. On the other hand, cyclone 7
The exhaust gas 1d separated from the medium 8 is discharged from the chimney 15 to the atmosphere through appropriate exhaust gas treatment devices 10 to 14 including a desulfurization device. That is, the exhaust gas 1d discharged from the circulating fluidized-bed furnace 5 is first heat-recovered by the waste heat boiler 10, the combustion air preheater 11, and the white smoke prevention air preheater 12. The steam obtained by the waste heat boiler 10 is used as a heat source of the drying device 3 and the like. Further, the exhaust gas 1d is:
After being subjected to dust removal by a dust collector 13 such as a bag filter, the gas is subjected to desulfurization in a gas-cooled desulfurization tower 14 serving as a desulfurizer, and is discharged from a chimney 15. Gas cooled desulfurization tower 14
As described at the beginning, the alkaline chemicals 14a such as caustic soda are sprayed and contacted with the exhaust gas 1d to remove sulfur oxides in the exhaust gas 1d.

As described above, the dried sludge 1c introduced into the circulating fluidized-bed furnace 5 is burned in the furnace main body 6 and incinerated as described above. The substance reacts with slaked lime or the like 1b added to the dried sludge 1c to form calcium sulfate. That is, SO
By the reaction of ₂ + Ca (OH) ₂ → CaSO ₄ + H ₂ O, the sulfur oxide becomes calcium sulfate which is a solid substance (gypsum) and is discharged from the furnace body 6 as ash. In addition,
Even when quicklime is added to the dewatered sludge 1a, the above reaction is finally performed.

[0015] At this time, the above-mentioned compounding amount in the dry sludge 1c (the compounding amount such that slaked lime or the like 1b is 0.5 to 4 mol (more preferably 0.8 to 1.2 mol) per 1 mol of the sulfur component). By adding slaked lime or the like 1b) in the step (1), the reaction of sulfur oxides generated in the combustion process can be effectively performed. Moreover, by using the circulating fluidized bed furnace 5 as an incinerator, the dried sludge 1c is burned while being sufficiently mixed and stirred, so that the reaction between the sulfur oxide and the slaked lime etc. 1b is promoted and performed effectively. .

[0016] From these facts, the removal rate of sulfur oxides is extremely high, and the sulfur oxides are reduced to about 80 to 90% as compared with incineration of dry sludge without adding slaked lime or the like 1b. Can be. Therefore, the exhaust gas 1d discharged from the circulating fluidized bed furnace 5 contains only the unreacted sulfur oxide, and the sulfur oxide concentration in the exhaust gas 1d is extremely reduced. This has been confirmed by comparative experiments performed using the above-described circulating fluidized bed furnace. That is, in this experiment, slaked lime was added as described above (added at a ratio of 0.8 to 1.2 mol with respect to 1 mol of the sulfur component in the sludge). Was continuously charged into a circulating fluidized bed furnace at 300 kg / h, and the concentration of sulfur oxides (SO _x ) in the exhaust gas discharged from the circulating fluidized bed furnace was measured. the incinerated at all without the addition of dried sludge (65% of polymer-based sludge water) was measured SO _x concentration in the exhaust gas.
This experiment was performed four times while changing the amount of combustion air. The results are as shown in Table 1. In any of the first to fourth experiments, when the dried sludge to which slaked lime was added was incinerated, compared with the case where the dried sludge to which slaked lime was not added was incinerated, SO _x concentration in the is reduced to 80-90%.

[0017]

[Table 1]

As described above, most of the sulfur oxides generated in the combustion process in the circulating fluidized bed furnace 5 are removed by the reaction with slaked lime or the like 1b mixed in the dry sludge 1c to be burned. Exhaust gas 1 discharged from the bed furnace 5
d contains only a small amount of unreacted sulfur oxide. Therefore, the amount of the alkali chemicals 14a required for desulfurizing the exhaust gas 1d in the gas cooling desulfurization tower 14 can be greatly reduced, and the alkali chemicals 14a
Since the slaked lime or the like 1b is inexpensive as compared with the conventional method, the chemical cost required for removing sulfur oxides can be significantly reduced as compared with the conventional method described at the beginning.

That is, the reaction formula “SO_Two+ 2N
aOH → Na_TwoSO_Three+ H_TwoO, SO_Two+ Ca (O
H)_Two→ CaSO_Four+ H_TwoO ", it is clear that 1
Mole SO_Two2 moles of NaOH required to remove
, Ca (OH)_TwoIs 1 mole. Meanwhile, at the moment
For the market price per mole in
a (OH)_TwoAbout 2.5 to 5 times. Therefore, 1
Mole SO_TwoThe cost of NaOH required to remove
1 mole of SO_Two(OH) necessary for removing methane _TwoOf 5
Up to 6 times. As a result, it is not necessary to remove sulfur oxides.
The cost of all chemicals is the sulfur oxides generated during the combustion process.
The majority (80-90%) of Ca (OH)_TwoAnd remove
Sulfur oxidation of residual (10-20%) contained in gas 1d
When removing substances with NaOH, sulfur generated in the combustion process
The total amount of oxides was desulfurized with NaOH as an exhaust gas-containing component.
About 1/3 to 1/4 of the cost of medicine
To be reduced.

Further, as described above, the gas-cooled desulfurization tower 1
4, the amount of use of the alkali agent 14a required for desulfurizing the exhaust gas 1d is greatly reduced, so that the spraying equipment for the alkali agent 14a can be downsized,
The initial cost and running cost can be reduced together with the reduction of the chemical cost, and the incineration of sludge can be performed extremely economically.

[0021]

As will be easily understood from the above description, according to the present invention, slaked lime or quick lime is added and mixed in advance to sludge introduced into an incinerator such as a circulating fluidized bed furnace.
Since sulfur oxides are removed as much as possible during the incinerator incineration, the concentration of sulfur oxides contained in the exhaust gas is greatly reduced, and the amount of chemicals required for the desulfurization of the exhaust gas is reduced. In addition, the size of the desulfurization device can be reduced. As a result, the reduction of the total chemical cost required for removing sulfur oxides is reduced, and the incineration of sludge can be performed extremely economically.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an example of a system for implementing a sludge incineration method according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sludge, 1a ... Dehydrated sludge, 1b ... Slaked lime etc. (slaked lime or quicklime), 1c ... Dry sludge, 1d ... Exhaust gas, 2 ... Dehydration device, 3 ... Drying device, 5 ... Circulating fluidized bed furnace (incinerator), 1
4 ... gas-cooled desulfurization tower (desulfurizer), 14a ... alkali agent (exhaust gas desulfurizer).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01D 53/81 F23G 5/00 ZABD C02F 11/12 ZAB 5/30 ZABM F23G 5/00 ZAB B01D 53/34 124Z 5/30 ZAB

Claims (3)

[Claims] 1. A method for incinerating sludge, wherein sludge containing a sulfur component is incinerated by an incinerator and exhaust gas discharged from the incinerator is subjected to desulfurization treatment.
A sludge incineration method characterized by adding slaked lime or quick lime to sludge fed into an incinerator in advance and mixing the slaked lime or quicklime. 2. A circulating fluidized bed furnace is used as an incinerator, and the dewatered sludge is dried with slaked lime or quick lime added thereto, and then put into a circulating fluidized bed furnace. The sludge incineration method according to claim 1, characterized in that: 3. The slaked lime or quick lime is added to and mixed with the sludge at a ratio of 0.5 to 4 mol per mol of the sulfur component in the sludge.
Or the sludge incineration treatment method according to claim 2.