JPS6157964B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for incinerating sludge containing organic matter. In recent years, the treatment and disposal of wastewater has progressed, and as a result of this treatment, a huge amount of organic water-containing sludge is finally generated. These sludges contain a large amount of water, and the evaporation of this water and the incineration of organic matter must be met by the calorific value held by the sludge or by supplementary fuel. In recent years, due to repeated price hikes and quantitative constraints on heavy oil, it is no longer acceptable to use large amounts of fuel, even for pollution treatment purposes.

Generally, when incinerating water-containing materials such as sludge,
Countercurrent incineration methods such as rotary kilns and multistage furnaces are economical, but in these countercurrent incinerators, materials with a large amount of volatile components, such as sludge, are carbonized, resulting in unburned losses and at the same time generating bad odors. This vicious cycle of consuming fuel for deodorization is repeated.
On the other hand, in incinerators such as fluidized bed furnaces, the entire amount of gas including combustion gas and evaporated steam is heated to the incineration temperature, which not only increases the amount of exhaust gas and increases the heat loss of the gas, but also constantly builds up the sand layer of the heating medium. Since it is necessary to keep it flowing, it is uneconomical in terms of power.

A method that improves these drawbacks is the floating combustion ash melting method, which pulverizes dry sludge, incinerates it at a small air ratio, maintains the furnace temperature above the melting point of the sludge ash, and melts the ash. However, this method has the disadvantage that molten ash adheres to the boiler walls and tubes, requiring various measures.

When incinerating water-containing sludge, the present invention aims to eliminate the drawbacks associated with the conventional incineration method in which dry incineration is carried out in the same machine.The present invention is designed to control the internal temperature of the incinerator while simultaneously controlling the temperature in the incinerator when drying and incineration are performed separately. The purpose of this invention is to provide a method for economically drying and incinerating water-containing sludge while maintaining high heat utilization efficiency.

The present invention is a method for drying sludge using self-combustion heat and/or auxiliary fuel, pulverizing it into fine powder, injecting it into an incinerator, and burning it in a suspended state in the space inside the furnace. In order to perform combustion with an air ratio close to the theoretical air amount and to prevent the ash in the sludge from melting, the exhaust heat of the high-temperature exhaust gas from the incinerator is effectively used, and the exhaust gas that has become low temperature is A part of the incinerator is circulated to the incinerator to control the temperature inside the incinerator to be lower than the temperature at which the ash melts.

In the present invention, if steam generated from a waste heat boiler attached to the incinerator is used as a heat source for the drying process, and the drain of the steam generated in the drying process is circulated to the waste heat boiler, the The exhaust heat of exhaust gas from the incinerator can be used extremely rationally and efficiently. In addition, if the humid air generated from the water-containing sludge in the drying process is cooled to reduce the moisture content, and the air is transferred to the air preheater attached to the incinerator, the residual heat of the humid air can be effectively utilized, and the humid air It has the advantage that the unpleasant odor gas inside can be incinerated at the same time.

In the present invention, it is particularly desirable to set the amount of air supplied for incineration to the minimum amount necessary to completely burn the pulverized sludge.
Furthermore, it is further preferable that this supply air source is the drying process, and the entire amount is covered by the humid air generated from the drying process. Furthermore, it is important to use the minimum amount of fresh air as a cooling gas to prevent the ash from melting. As a result of the above, it is possible to minimize the amount of heat taken out from the incineration process, and it is possible to perform incineration treatment with high thermal efficiency.

To explain the embodiment of the present invention in detail with reference to the drawings, sludge containing organic matter with a water content of 95% or more obtained from a settling tank or the like is dehydrated by filtration or centrifugation, and the water content is reduced to 60 to 80%.
% sludge cake. Next, the dehydrated cake is guided to the dryer 2 by the conveyor 1 and dried with steam 23 generated by the waste heat boiler 8. However, if the dehydrated cake has a high water content and lacks heat, auxiliary fuel is supplied from the oil pump 17. Assist combustion. The solid matter dried to a moisture content of approximately 5% or less is temporarily stored in a storage tank 3, cut out in a fixed amount by a quantitative feeder 4, and then pulverized by a pulverizer 5.
It is pulverized to a size of 50 to 300 mesh by
The air is injected into the incinerator 7 by the air conveyor 6.
Burns in a suspended state in the inner space.

What is important here is to adjust the amount of air supplied for sludge incineration to a small excess air ratio close to the theoretical air amount (in this case, the amount of combustion exhaust gas discharged outside the system is G _a ) The combustion gas is cooled to a combustion temperature of about 800 to 1000° C. at which the ash does not melt by the circulating exhaust gas 14 (the amount of gas at this time is G _r ).

In this case, if the circulating exhaust gas 14 with the gas amount G _r is not used and the fresh air 22 with the gas amount V _a is used to cool it to the same temperature as the former, the amount of gas that will eventually go out of the system will be G in the former. _a , the latter becomes G _a +V _a , and the former is a more economical incineration method because the amount of heat taken out of the gas is small. Note that the amount of gas flowing into the incinerator 7 is Ga ₊ G _r in the former case, and Ga ₊ V _a in the latter case.

The exhaust heat of the exhaust gas completely combusted in the incinerator 7 is recovered by the waste heat boiler 8 and the air preheater 9, and the ash in the sludge is collected by the cyclone 10 and then attracted by the induction fan 11. _r is circulated to the incinerator 7 as circulating gas, and the remainder of the gas amount G _a is sent to the electrostatic precipitator 12.
After removing dust, it is discharged to the atmosphere (outside the system) from the chimney 13. Incidentally, the ash collected by each device is discharged to the outside through the rotary valve 15.

On the other hand, the steam 23 generated in the waste heat boiler 8 is supplied to the dryer 2, gives latent heat of vaporization to the dehydrated cake, condenses it, passes through the steam trap 18, enters the water supply tank 19, and passes through the water supply pump 20 to waste water. It is circulated to the heat boiler 8. In addition, the moisture evaporated from the dryer 2 is accompanied by the carrier gas air, and the water is transferred to the gas cooler 1.
6, moisture is removed from the air, heated through an air preheater 9, and supplied to the pulverizer 5 as air for combustion of dried sludge (gas amount G _a ). Regarding the gas amounts in the figure, those with parentheses indicate the case where the circulating exhaust gas 14 is not used, and those without the parentheses indicate the case where the circulating gas is used.

Next, an embodiment of the present invention will be shown which is carried out in accordance with the system explanation shown in the drawings.

First, the sludge containing organic matter with a solid content of 5% or less obtained from the sludge thickening tank is passed through a dehydrator to achieve a water content of 70%.
It was made into a sludge cake. This was supplied to the dryer 2 by the conveyor 1 at a rate of 200 kg per batch to obtain 60 kg of dry solids with a moisture content of 1% or less, which was stored in the storage tank 3. Next, it is passed through a quantitative feeder 4 attached to the lower part of the storage tank 3, pulverized into 50 to 300 meshes by a pulverizer 5, and then transported from the top into an incinerator 7 by an air conveyor 6 at a rate of 210 m ³ per hour. It was sprayed downward.

The calorific value of this dry and pulverized material is approximately
It was 3000kcal. Incinerator 7 has a diameter of 560 mm.
A vertical cylindrical furnace with a height of 1,500 mm is used, and the oil pump 17 is heated to minimize heat radiation.
The inside of the incinerator 7 is heated to 800℃ by the auxiliary fuel 21 from
The amount of air required for combustion was 3.5 ^m3 per 1 kg of dry solids, but if this continues, the temperature inside the incinerator 7 will reach 1300-1400°C, and the ash will melt, so the heat After recovery, the exhaust gas at 300℃ is reduced to approximately 610℃.
m ³ was circulated and the temperature inside the incinerator 7 was controlled at 800°C.

The waste heat from the sludge incineration was recovered as saturated steam of 4 to 7 kg/cm ² in a boiler and used as a heat source for the dryer 2. The drain from the dryer 2 was recovered at 80 to 90°C and circulated to the waste heat boiler 8. The heated waste gas from the dryer 2 is heated to 40°C by using 20°C treated sewage water in the gas cooler 16.
After cooling and dehumidifying, the air was preheated to 100°C using an air preheater 9 and used as combustion air. The sludge ash was extracted from the rotary valves 15 of the lower hopper of the incinerator 7 and the lower hopper of the waste heat boiler 8.
The ash in the exhaust gas is collected by a cyclone 10 and an electrostatic precipitator 12, and after removing dust to about 0.1mg/ ^m3 , it is removed from the chimney 1.
3 was released into the atmosphere.

As described above, the present invention uses self-combustion heat or auxiliary fuel to turn dried sludge into powder, and by making the powder suspended in the incinerator space, oxygen in the combustion air is removed. This improves the contact between the two and increases the heat transfer area for radiation, convection, heat conduction, etc., and enables smooth and reliable combustion even with a small amount of excess air, reducing the amount of exhaust gas. By increasing the heat recovery efficiency of the incinerator and reducing the amount of auxiliary fuel, reducing the capacity of the exhaust gas treatment equipment, and at the same time controlling the temperature inside the incinerator by circulating low-temperature exhaust gas to the incinerator, preventing the melting of ash and reducing the amount of ash. It prevents troubles such as adhesion and accumulation on dryers and boiler walls, improves the operability of the incinerator, and allows the use of inexpensive refractories with low fire resistance in the incinerator, reducing construction costs. This sludge incineration treatment method has many advantages, such as lowering the air flow rate, having a small excess air ratio, and being able to achieve the same level of thermal efficiency as high-temperature combustion, which has high thermal efficiency.

[Brief explanation of the drawing]

The drawings are system explanatory diagrams showing embodiments of the present invention. 1...Conveyor, 2...Dryer, 3...Storage tank, 4...Quantitative feeder, 5...Fine crusher, 6...
Air conveyor, 7... Incinerator, 8... Waste heat boiler, 9... Air preheater, 10... Cyclone, 1
1...Induction fan, 12...Electrostatic precipitator, 13...
... Chimney, 14 ... Circulating exhaust gas, 15 ... Rotary valve, 16 ... Gas cooler, 17 ... Oil pump, 18 ... Steam trap, 19 ... Water supply tank, 20 ... Water supply pump, 21 ... Auxiliary fuel , 22...Fresh air, 23...Water vapor, G _a ,
G _r , V _a ...Gas amount.

Claims (1)

[Scope of Claims] 1. The sludge is dried using self-combustion heat and/or auxiliary fuel and then turned into powder, and then this powder is injected into an incinerator to be burned in a floating suspended state, and the incineration A sludge incineration treatment method characterized in that the temperature inside the incinerator is controlled to a temperature at which sludge ash does not melt by circulating the exhaust gas to the incinerator after recovering the exhaust heat of the exhaust gas from the incinerator. . 2. The drying step is performed using steam generated by a waste heat boiler using exhaust gas from the incinerator as a heat source, and the drain generated in the drying step is circulated to the waste heat boiler. The treatment method according to claim 1, which is used. 3. The treatment method according to claim 1 or 2, wherein the combustion step is performed by supplying a minimum amount of air necessary to completely burn the powdered sludge. 4. In the combustion step, the heated waste gas generated from the sludge in the drying step is cooled and dehumidified, and then transferred to an air preheater attached to the incinerator;
The treatment method according to claim 1, 2 or 3, wherein the treatment is performed by using the air as combustion air.