WO2025087244A1 - Domestic sludge self-sustaining incineration process and device - Google Patents

Abstract

The present application provides a domestic sludge self-sustaining incineration process, comprising primary drying, secondary drying, crushing, and incineration, comprising: performing primary drying on domestic sludge by using dry hot air to obtain sludge having a moisture content of 40% to 55%; then performing secondary drying by using hot flue gas produced during incineration to obtain sludge having a moisture content not higher than 20%; further crushing the sludge and mixing the crushed sludge with hot flue ash produced during incineration, and feeding the mixture into an incinerator to undergo self-sustaining incineration at 850°C to 950°C; and performing solid-gas separation on high-temperature flue gas produced after combustion, wherein the obtained hot flue gas is returned back for secondary drying and the obtained hot flue ash is mixed with the crushed sludge. The present application further provides a device for the treatment process. According to the treatment process of the present application, self-sustaining combustion can be safely and stably completed after drying pretreatment is performed on domestic sludge having a high moisture content; no auxiliary fuel needs to be added during incineration, and heat energy of the system can be fully utilized; reduction treatment of domestic sludge can be achieved.

Description

A self-sustaining incineration process and equipment for domestic sewage sludge

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of the Chinese patent application with application number 202311395320.7 and title “A Self-sustaining Incineration Process and Equipment for Domestic Sludge” filed with the Chinese Patent Office on October 25, 2023, the entire contents of which are incorporated by reference into this application.

Technical Field

The present application relates to a sludge treatment process, and further to a sludge combustion treatment process, and equipment used in the process.

Background Art

In recent years, the process of rural urbanization has accelerated. After the sewage pipeline network was unified, the amount of sludge was large and the composition was complex. Some of the sludge came from the solid suspended matter after the treatment of domestic sewage. The common organic matter is sugars, fats and proteins. The sludge treatment problem is very serious.

Sludge incineration is one of the most direct and effective ways to reduce sludge. In traditional treatment processes, sludge incineration treatment mostly involves transporting mechanically dehydrated sludge to a special waste incineration site or power plant, and adding a large amount of auxiliary fuel for blending. The consumption of auxiliary fuel is huge, which is neither economical nor environmentally friendly. In addition, in order to reduce the consumption of auxiliary fuel during blending, some treatment processes will perform high-energy drying pretreatment on the sludge before incineration, reduce the water content of the sludge by drying, and reduce the amount of auxiliary fuel required for subsequent blending. However, there are still many problems that need to be solved in the drying pretreatment of sludge. The drying pretreatment of sludge can be divided into full drying and semi-drying. After the sludge is fully dried, the calorific value is higher and it is easy to incinerate, but it is also easy to generate dust and there is a risk of spontaneous combustion and explosion. When the semi-dried sludge enters the furnace, it still contains a lot of water, which impacts the furnace temperature, resulting in furnace temperature fluctuations and unstable furnace conditions. This results in that most of the sludge in the prior art can only be used as a blended combustion material after semi-drying, and is co-disposed with waste incineration power plants, cement kilns, and coal-fired power plants, or it still needs to be blended with auxiliary fuel during incineration. For example, Chinese patent documents CN108892349A, CN105948459A, CN110104935A, and CN107420915A all disclose treatment processes for drying sludge before incineration. However, in these methods, the incineration of sludge after drying still requires the addition of a large amount of auxiliary fuel. In short, most of the existing semi-dried sludge can only be blended with combustion, and not only is the blending amount in the treatment limited, but the blending of semi-dried sludge will bring about a series of disadvantages such as lowering the temperature in the furnace and the softening point of the ash, increasing the amount of fly ash generated, increasing the dust removal and flue gas purification load, and reducing the boiler efficiency. The investigation found that the main combustion substance of the semi-dried pretreated sludge is still the high calorific value combustion material, which obviously cannot meet the large-scale treatment of low calorific value sludge. In addition, the flue gas produced by combustion can easily cause secondary pollution of the environment, making it difficult to achieve industrial promotion and application of the incineration process of dried pretreated sludge.

Therefore, it is necessary to provide a new sludge incineration process to reduce the cost of the sludge incineration process, improve the energy conservation and environmental protection of the process, and at the same time, it does not need to consume auxiliary fuel for blending, but allows low calorific value domestic sludge to achieve safe and stable self-sustaining combustion after drying pretreatment. This significantly improves the industrial applicability of the domestic sludge incineration process.

Summary of the invention

In view of the above technical background, the primary purpose of this application is to provide a domestic sludge incineration treatment process, which can safely and stably complete self-sustaining combustion after drying and pre-treating high-water content domestic sludge. Not only does the incineration process not require the addition of auxiliary fuel, but it can also make full use of the system's thermal energy, ultimately achieving industrial reduction treatment of domestic sludge.

Another object of the present application is to provide an apparatus for the above-mentioned treatment process so that the above-mentioned process can be carried out efficiently. Further enhance the industrial application value of the process.

The above-mentioned purpose of the present application is achieved through the following technical solutions:

First, the present application provides a self-sustaining incineration process for domestic sewage sludge, which includes at least first drying, second drying, crushing and incineration performed in sequence; specifically, the following steps are included:

1) Drying the domestic sewage sludge with a moisture content of 60%-75% with dry hot air for the first time to obtain sewage sludge with a moisture content of 40%-55% and moist air;

2) drying the sludge with a moisture content of 40% to 55% obtained in 1) for a second time with the hot flue gas from the incineration to obtain sludge with a moisture content of no more than 20% and moisture-carrying flue gas;

3) crushing the sludge with a moisture content of no more than 20% obtained in 2) and mixing it with the hot ash from the incineration, heating the crushed sludge to a temperature close to the ignition point, and then entering the crushed sludge into an incinerator for self-sustaining incineration at 850-950° C. to obtain high-temperature flue gas and high-temperature slag;

4) The high-temperature flue gas obtained in 3) is subjected to solid-gas separation, and the obtained gas is returned to 2) as hot flue gas for the second drying, and the obtained solid is returned to 3) as hot ash to be mixed with the crushed sludge.

In the preferred treatment process of the present application, in order to fully recycle the heat energy from the incinerator, the dry air is heat-exchanged with the moist air obtained in 1) and the moist flue gas obtained in 2) in sequence and the temperature is gradually increased, and then returned as dry hot air to the first drying described in 1). In the first drying, the sludge moisture content is reduced from more than 60% to 40%-55%, which is the optimal drying effect that can be achieved by returning the dry hot air to the first drying described in 1). If the drying range is lower than this range, the exhaust temperature of the moist air and the moist flue gas will increase, and the waste heat loss will increase. If it is higher than this range, the mud temperature will be too high or difficult to control after the second drying, and pyrolysis gas will be precipitated.

In the preferred treatment process of the present application, in order to avoid the generation of volatile combustible gases such as CO and/or _H2 in the wet flue gas obtained in 2) as much as possible, the sludge temperature during the second drying discharge described in 2) is controlled to be no higher than 120°C.

In the preferred treatment process of the present application, in order to improve the combustibility of the dried sludge, the pulverization described in 3) is to pulverize the sludge with a moisture content of no more than 20% to a particle size of no more than 5 mm. This can significantly increase the specific surface area of the dried sludge to be burned, thereby further improving the combustibility of the sludge.

In the preferred treatment process of the present application, in order to fully recycle the heat energy from the incinerator, the high-temperature slag obtained in 3) is vigorously mixed with air for heat exchange to obtain slag-containing hot air, and then the slag-containing hot air is subjected to solid-gas separation to obtain hot air and cooled slag; the hot air is returned to the incinerator described in 3) to assist combustion.

In the treatment process described in the present application, after the sludge self-sustaining incineration occurs in the incinerator described in 3), the high-temperature flue gas produced contains ash and unburned components; while recycling the gas in the high-temperature flue gas, the present application also fully recycles the solids therein. For this reason, in the preferred solution of the present application, a cyclone dust collector is used for the solid-gas separation, so that 95% of the solids in the high-temperature flue gas can be returned as return material to the dried sludge before incineration for heating, so that the temperature of the dried sludge is close to the ignition point, and the volatile combustible gas produced can also enter the incinerator with the dried sludge for combustion.

In a more preferred treatment process of the present application, in order to further ensure that the sludge temperature is close to the ignition point before entering the incinerator, a portion of the gas obtained in 4) is used to provide heat for the crushed sludge.

Based on the self-sustaining incineration process of domestic sewage sludge described in this application, this application further provides a sludge harmless treatment process set up in situ in a sewage treatment plant, which can use the existing process of the sewage treatment plant to treat the sludge generated by sewage treatment on site. The specific process flow is shown in Figure 1, including:

① The sludge generated by the sewage treatment plant is subjected to first drying, second drying, crushing and incineration in sequence; specifically including:

1) Dry the domestic sludge with a moisture content of 60%-75% with hot dry air for the first time to obtain a moisture content of 40%-55% of sludge and moist air;

2) drying the sludge with a moisture content of 40% to 55% obtained in 1) for a second time with the hot flue gas from the incineration to obtain sludge with a moisture content of no more than 20% and moisture-carrying flue gas;

3) crushing the sludge with a moisture content of no more than 20% obtained in 2) and mixing it with the hot ash from the incineration, heating the crushed sludge to a temperature close to the ignition point, and then entering the crushed sludge into an incinerator for self-sustaining incineration at 850-950° C. to obtain high-temperature flue gas and high-temperature slag;

4) exchanging heat with the moist air obtained in 1) and the moist flue gas obtained in 2) in sequence and raising the temperature step by step, and then returning the dry air to the first drying step in 1) as dry hot air;

5) performing solid-gas separation on the high-temperature flue gas obtained in 3), returning the obtained solid as hot flue gas to 3) for mixing with the crushed sludge, returning part of the obtained gas as hot flue gas to 2) for the second drying, and the other part as a heat source for heating the mixture of the hot flue gas and the crushed sludge;

② After mixing the moist air and the moist flue gas after the step-by-step heat exchange in 4), the air is first washed with water to remove pollutants, and then introduced into the aeration tank of the sewage treatment plant for biological deodorization and treatment.

In the preferred solution of the present application, the water washing described in ② is completed using the reclaimed water of the sewage treatment plant where it is located, and the effluent after the water washing is passed into the sewage inlet of the sewage treatment plant where it is located.

The sludge harmless treatment process set up in situ in the sewage treatment plant described in the present application can treat the sludge produced in the sewage treatment plant on site, saving the sludge transportation cost, and can make full use of the existing equipment and resources of the sewage treatment plant, such as water washing equipment, reclaimed water, aeration tank, etc., and can achieve harmless treatment of the incineration flue gas after the sludge is fully self-sustainingly incinerated, and can also improve the sewage treatment efficiency. The flue gas generated by the burning sludge is introduced into the aeration tank of the sewage treatment process. Aeration can produce and maintain effective gas-liquid contact, and maintain a certain dissolved oxygen concentration in the water while the biological oxidation continuously consumes oxygen, produce sufficient mixing action and water circulation in the aeration zone, and maintain a sufficient speed of the liquid to keep the biological solids in the water in a suspended state. The introduction of flue gas into the aeration tank not only plays a positive role in sewage treatment, but also effectively treats the flue gas produced by sludge combustion, reduces pollutant emissions, removes particulate matter, sulfur dioxide, hydrogen chloride, nitrogen oxides and other harmful substances dissolved in sewage in the flue gas, achieves the effects of desulfurization, denitrification and dust removal. The flue gas carries a large amount of heat, which reduces the flue gas temperature, thereby achieving the purpose of controlling flue gas pollutants and preventing environmental pollution, and also avoiding a large amount of thermal pollution.

In addition, the present application also provides a set of domestic sewage sludge self-sustaining incineration equipment, including a feeding unit, a drying pretreatment unit, a crushing and heating unit, and a self-sustaining incineration unit connected in sequence through pipelines;

The feeding unit is used to transport the domestic sewage sludge with a moisture content of 60%-75% to the drying pretreatment unit through a pipeline;

The drying pretreatment unit is used to dry the domestic sewage sludge with a moisture content of 60%-75% in stages until the moisture content is not higher than 20%; the drying pretreatment unit specifically includes a first drying section and a second drying section connected in sequence through a pipeline; the first drying section is also connected to a gas heat exchange unit through a pipeline, which is used to recover and utilize the waste heat of the gas discharged from the first drying section and the second drying section through heat exchange;

The pulverizing and heating unit is used to pulverize the sludge after drying pretreatment and further preheat it to a temperature close to the ignition point; the pulverizing and heating unit includes a pulverizing device and a solid-gas separation device; the feed port of the pulverizing device is connected to the second drying section through a pipeline; the solid-gas separation device is connected to the self-sustaining incineration unit, the second drying section and the discharge port of the pulverizing device through pipelines respectively;

The self-sustaining incineration unit is used to incinerate the crushed and heated sludge at 850-950°C; it includes an incinerator, a solid-gas heat exchange device and a solid-gas separation device that are interconnected; the incinerator is connected to the discharge port of the crushing device through a pipeline; the solid-gas heat exchange device is further connected to a blower; and the solid-gas separation device is further provided with a slag discharge pipe.

In the preferred equipment of the present application, a water washing unit and a biochemical aeration tank are further provided; the water washing unit is used to wash the gas discharged from the gas heat exchange unit, the air inlet of the water washing unit is connected to the gas heat exchange unit through a pipeline, and the air outlet is connected to the biochemical aeration tank through a pipeline.

In the preferred equipment of the present application, the feeding unit is provided with an extrusion device for conveying materials to the drying pretreatment unit by extrusion.

In the preferred device of the present application, the feed inlet and the air inlet of the first drying section are positioned so as to form a countercurrent heat exchange in the first drying section to improve the heat exchange efficiency.

In the preferred equipment of the present application, the gas heat exchange unit includes a blower, a first-stage heat exchange device and a second-stage heat exchange device connected in series in sequence, the blower is used to generate dry air, the first-stage heat exchange device is used to exchange heat between the dry air and the gas discharged from the first drying section, and the second-stage heat exchange device is used to exchange heat between the gas heated by the first-stage heat exchange and the gas discharged from the second drying section; the second-stage heat exchange device is further connected to the first drying section through a pipeline, and sends the dry hot air heated by the second-stage heat exchange into the first drying section.

In the preferred equipment of the present application, the second drying section is a variable cross-section furnace, and the cross-section of the furnace gradually decreases with the direction of the airflow and gradually increases with the direction of the sludge, thereby forming countercurrent heat exchange in the second drying section, which can improve the heat exchange efficiency.

In the preferred equipment of the present application, the solid-gas separation device of the pulverizing and heating unit and the self-sustaining incineration unit is a cyclone dust collector.

In the preferred equipment of the present application, in the pulverizing and heating unit, a connected flue gas duct is further provided between the pulverizing device and the solid-gas separation device for introducing a portion of the hot flue gas from the solid-gas separation device into the discharge section of the pulverizing device.

When the equipment described in the present application is used for continuous sludge incineration treatment, the feeding unit feeds the sludge into the first drying section, and the gas heat exchange unit connected to the first drying section inputs dry hot air to the first drying section. The sludge is dried by the dry hot air in the first drying section to a moisture content of 40%-55%, and at the same time, the water evaporates to turn the dry hot air into humid air. After the humid air is discharged from the first drying section, it enters the gas heat exchange unit through a pipeline to exchange heat with the dry air for cooling. The semi-dried sludge with a moisture content of 40%-55% is sent to the second drying section through a pipeline; the high-temperature flue gas generated by the incinerator of the self-sustaining incineration unit is discharged from the top of the incinerator and is first divided into hot flue gas and hot ash by the solid-gas separation device of the crushing and heating unit. The hot flue gas is sent to the second drying section through a pipeline. The sludge is further dried by the hot flue gas in the second drying section to a moisture content of not more than 20%, and at the same time, the water evaporates to form humid flue gas. The sludge temperature at the outlet of the second drying section is controlled below 120°C to avoid the generation of CO and/or H during drying. _2. The volatile combustible gas enters the wet flue gas; the wet flue gas is discharged from the second drying section and enters the gas heat exchange unit through a pipeline, and the dry air heated by heat exchange with the wet air further exchanges heat with the wet flue gas. After the wet flue gas is cooled, it enters the flue gas post-treatment device, such as the water washing unit and the aeration unit, through a pipeline together with the cooled wet air; in the gas heat exchange unit, the dry air that has exchanged heat with the wet air and the wet flue gas in sequence is heated step by step to form dry hot air, and the dry hot air is passed into the first drying section through a pipeline for drying after leaving the gas heat exchange unit; the sludge with a moisture content of no more than 20% obtained in the second drying section is sent to the crushing and heating unit through a pipeline, and first in the crushing device The sludge is crushed to a particle size of less than 5mm, and then mixed with the hot ash separated by the solid-gas separation device, heated to a point close to the ignition point by the hot ash, and then enters the incinerator together with the hot ash through a pipeline. The crushed sludge is self-sustainingly incinerated at 850℃-950℃ in the incinerator to generate high-temperature slag and high-temperature flue gas; the high-temperature flue gas is recycled in the above manner, and the high-temperature slag enters the solid-gas heat exchange device through a pipeline to exchange heat with the air provided by the blower to obtain slag-containing hot air. After the slag-containing hot air is discharged from the solid-gas heat exchange device, it enters the solid-gas separation device through a pipeline to separate hot air and cooled slag; the hot air enters the incinerator through a pipeline to assist combustion, and the cooled slag is discharged out of the system through a slag discharge pipe.

The beneficial effects of this application are mainly reflected in the following aspects:

1. It can realize self-sustaining combustion after drying of domestic sludge

The self-sustaining incineration process and equipment of domestic sludge provided in the present application gradually dry and heat the room-temperature domestic sludge with a moisture content of 60%-75%, so that the sludge finally reaches a moisture content of no more than 20%, a temperature close to its own ignition point and a calorific value close to 2900kcal/kg before entering the incinerator. At the same time, the sludge specific surface area is increased by crushing, so that after the sludge enters the incinerator, it can self-sustain combustion at 850℃-950℃ without adding any auxiliary fuel.

2. Can fully recycle waste heat and realize cascade utilization of energy

During the step-by-step drying and heating process of the sludge, the process and equipment of the present application fully utilize the heat in the system through step-by-step heat exchange, especially recovering the latent heat of water vapor in the humid flue gas and humid air. In the whole process, the incinerator is the highest point of the system temperature. The heat carried by the high-temperature flue gas from the incinerator is reversed step by step to the second drying stage and the first drying stage through drying and heat exchange. The step-by-step reduction in the temperature of the flue gas itself fully meets the requirements of the step-by-step heating of the two drying stages.

3. Make full use of the hot ash return material to heat the dried sludge to a temperature close to the ignition point before entering the incinerator to ensure that the self-sustaining combustion of the dried sludge can occur stably.

This application uses the solid hot ash contained in the high-temperature flue gas as a separate return material, and performs the final heating on the dried sludge before entering the incinerator. The hot ash is mixed with the crushed sludge particles in solid form, so that the temperature of the sludge particles quickly approaches the ignition point. At the same time, all the volatile gases can be recycled into the furnace for combustion, avoiding the loss of calorific value and the impact on the furnace temperature. The combustion of the incinerator is stable. The recycling of the return material heat provides a crucial boost and guarantee for the self-sustaining incineration of the sludge after entering the incinerator. This boost and guarantee comes entirely from the full utilization of the heat inside the system, without the need for additional consumption of energy and materials outside the system.

4. Can be combined with sewage treatment technology to improve industrial application value

When the process system described in this application is set in situ in a sewage treatment plant, its industrial application value can be further improved. The process and equipment of this application can treat the sludge generated in the sewage treatment plant in situ, or build the sewage treatment plant nearby, which can save a lot of transportation costs for sludge transportation and treatment, and can make good use of the existing equipment and resources of the sewage treatment plant, treat the flue gas through the scrubber, use the recycled water of the sewage plant, drain the water into the sewage inlet of the sewage plant, and discharge the flue gas into the aeration tank, so as to achieve the two-way promotion of sewage treatment and sludge treatment, and finally achieve the effective reduction, harmlessness and resource treatment of domestic sludge.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an overall process flow chart of a specific implementation method of the present application, wherein the triangular arrows represent the direction of solid materials, and the broken line arrows represent the direction of gas materials.

FIG. 2 is a schematic diagram of the overall composition of the equipment used in the specific implementation manner of the present application.

FIG3 is a schematic diagram of the overall composition of the equipment used in the preferred specific implementation of the present application.

Description of reference numerals:
1-sludge silo, 2-extruder, 3-first drying section, 31-first sludge inlet, 32-sludge conveyor belt, 33-first sludge outlet, 34-dry hot air inlet, 35-humid air outlet, 4-second drying section, 41-second sludge inlet, 42-second sludge outlet, 43-flue gas inlet, 44-humid flue gas outlet, 45-sludge conveying device, 5-screw crushing conveyor, 6-flue gas cyclone dust collector, 61-high temperature flue gas inlet, 62-hot flue gas outlet, 63-hot ash outlet, 64-hot flue gas Diverter pipe, 65-induced draft fan, 66-regulating valve, 7-return valve, 71-return bin, 8-incinerator, 81-high-temperature flue gas outlet, 82-hot air inlet, 83-dried sludge inlet, 9-air distribution plate, 10-slag discharge pipe, 11-valve, 12-enhanced air flow heat exchanger, 13-air cyclone dust collector, 131-slag discharge port, 132 hot air outlet, 14-combustion-supporting blower, 15-drying blower, 16-first-stage heat pipe heat exchanger, 17-second-stage heat pipe heat exchanger, 18-washing tower, 19-induced draft fan.

DETAILED DESCRIPTION

In order to make the purpose, technical solution and advantages of the present application more clearly understood, the invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

The present application provides a device and method for drying and incinerating sludge in a sewage treatment plant to achieve the purpose of sludge reduction.

The overall composition of the device is shown in FIG2. First, a sludge silo 1 is provided, and an extruder 2 for making sludge into sludge strips is provided under the sludge silo 1. The outlet of the extruder 2 is connected to the first drying section 3. The first drying section 3 is provided with a first sludge inlet 31, a sludge conveyor belt 32, a first sludge outlet 33, a dry hot air inlet 34 and a wet air outlet 35. The wet air outlet 35 is connected to the first-stage heat pipe heat exchanger 16 through a pipeline, and the outlet of the first-stage heat pipe heat exchanger 16 is connected to the water washing tower 18 through a pipeline. The dry hot air inlet 34 is connected to the second-stage heat pipe heat exchanger 17, the first-stage heat pipe heat exchanger 16 and the drying blower 15 in sequence through a pipeline. The dry air pipeline connected to the drying blower 15 is connected to the wet air pipeline led out of the wet air outlet 35 through the first-stage heat pipe heat exchanger 16, and the first-stage heat pipe heat exchanger 16 is connected to perform the first-stage heat exchange, reduce the temperature of the wet air to below the dew point, and recover the sensible heat of the wet air and the latent heat of vaporization of the water vapor. The second drying section 4 is provided with a second sludge inlet 41, a second sludge outlet 42, a flue gas inlet 43, a wet flue gas outlet 44 and a sludge conveying device 45. The first sludge outlet 33 of the first drying section 3 is connected to the second sludge inlet 41 of the second drying section 4 through a pipeline. The second drying section is a variable cross-section furnace, and the second sludge inlet 42 and the flue gas inlet 43 are respectively arranged at both ends of the furnace to form a countercurrent heat exchange, thereby improving the heat exchange efficiency. The wet flue gas outlet 44 is connected to the second-stage heat pipe heat exchanger 17. The wet flue gas pipeline led out of the wet flue gas outlet 44 is connected to the dry air pipeline led out of the first-stage heat pipe heat exchanger 16 through the second-stage heat pipe heat exchanger 17 to perform a second-stage heat exchange, thereby reducing the temperature of the wet flue gas to below the dew point, and recovering the sensible heat of the wet flue gas and the latent heat of vaporization of water vapor. The second sludge outlet 42 of the second drying section 4 is connected to the spiral crushing conveyor 5 through a pipeline, and the dried sludge is crushed into powder with a particle size not greater than 5 mm in the spiral crushing conveyor 5. The outlet of the spiral crushing conveyor 5 is connected to the return valve 7 through a pipeline. In the return valve 7, the crushed sludge powder is mixed with the hot ash returned from the flue gas cyclone dust collector 6, heated by the hot ash, and the temperature is raised to a temperature close to the ignition point of the sludge powder, and then enters the incinerator 8 together for self-sustaining combustion, and the volatile combustible gas generated at the same time also enters the incinerator 8 for combustion. The incinerator 8 is provided with a high-temperature flue gas outlet 81 at the top, a hot air inlet 82 at the bottom, and a dried sludge inlet 83 in the middle. The high-temperature flue gas outlet 81 is connected to the high-temperature flue gas inlet 61 at the top of the flue gas cyclone dust collector 6, the hot flue gas outlet 62 of the flue gas cyclone dust collector 6 is connected to the flue gas inlet 43 of the second drying section 4, and the hot ash outlet 63 of the flue gas cyclone dust collector 6 is connected to the return valve 7. The lower part of the incinerator 8 is provided with an air distribution plate 9, on which a slag discharge pipe 10 is provided. The slag discharge pipe 10 is connected to the enhanced air flow heat exchanger 12 through a pipeline with a valve 11, and the enhanced air flow heat exchanger 12 is further connected to the combustion-supporting blower 14 through a pipeline. The air is blown into the enhanced air flow heat exchanger 12 through the combustion-supporting blower 14, where it exchanges heat with the high-temperature slag from the slag discharge pipe 10, and then enters the air cyclone dust collector 13 to achieve solid-gas separation. The air cyclone dust collector 13 is provided with a slag discharge port 131 and a hot air outlet 132. The cooled slag is discharged out of the system through the slag discharge port 131, and the hot air enters the incinerator 8 through the pipeline to support combustion.

In some preferred embodiments, as shown in FIG3 , in order to further ensure that the mud temperature before entering the incinerator is close to the ignition point, a return bin 71 can be provided below the return valve 7 to hold the hot ash from the flue gas cyclone dust collector 6 and the crushed sludge powder from the spiral crushing conveyor 5. At the same time, a hot flue gas diversion pipe 64 is provided on the pipeline outside the hot flue gas outlet 62 of the flue gas cyclone dust collector 6 to connect the return bin 71. In this way, a portion of the hot flue gas from the flue gas cyclone dust collector 6 can be introduced into the return bin 71 after coming out of the hot flue gas outlet 62 to further heat the sludge powder. In a more preferred scheme, an induced draft fan 65 and a regulating valve 66 can also be provided on the hot flue gas diversion pipe 64 to regulate the hot flue gas introduced into the return bin 71. Generosity.

The specific type of the incinerator 8 in the present application is not particularly limited, and it can be any one of a grate incinerator, a fluidized bed incinerator, a multi-chamber incinerator, and a rotary kiln incinerator.

The flue gas cyclone dust collector 6 and the air cyclone dust collector 13 in the present application can be cyclone dust collectors of the same type and specification. The dust removal efficiency of the cyclone dust collector can reach more than 95%, and it has a long service life, is easy to install and maintain, has a small size, a simple structure, and a low equipment cost. It is suitable for purifying dust with a large density and a particle size greater than 5μm. It uses special high-temperature resistant materials to achieve resistance to higher temperatures. After the dust collector is equipped with a wear-resistant lining, it can be used to purify flue gas containing highly abrasive dust.

The water of the scrubber in this application comes from the recycled water of the sewage treatment process. After the scrubbing process is completed, the muddy water enters the sewage treatment plant's water inlet pool, making full use of the conditions of the sewage treatment plant and reducing costs. The purification principle of using water to treat smoke is mainly to separate pollutants by immersion and dissolution. The specific process is to first disperse the pollutants in the airflow through mechanical equipment, and the water mist in the airflow can adsorb them. Then, the self-purification effect of water is used to loosen the pollutants through chemical and physical effects, and combine with water to form a residue, and finally the residue is collected and removed by equipment. The discharge port of the scrubber is set at the top of the tower body. After the flue gas is tested, the clean gas can be directly discharged into the atmosphere. The pollutants in the flue gas are removed by the scrubber, the method is simple, and the recycling of water in the sewage treatment plant is realized at the same time.

In some embodiments, the scrubber is composed of a tower body, a packing layer, a spray system, an inlet pipe, an outlet pipe, an exhaust port, etc. The flue gas enters the tower body from the inlet pipe, and when passing through the packing layer, the flue gas contacts the liquid, and the pollutants are absorbed. The packing layer increases the contact area, so that the flue gas and the liquid are fully in contact, thereby improving the purification efficiency. The spray system sprays the liquid evenly on the packing layer, so that the liquid and the flue gas are fully in contact, thereby achieving the absorption of pollutants.

In some embodiments, the induced draft fan 19 can be replaced by an air aerator system, which is composed of a blower, an air delivery pipe and an aerator. During the implementation process, the flue gas is introduced by the blower of the air aerator system, and the flue gas diffuses along the air delivery pipe and enters the aeration tank through the aerator, so that the flue gas is fully in contact with the sewage. The aerator forces the oxygen in the air or flue gas to be transferred to the aeration tank and diffused by the aerator equipment, so that the activated sludge system maintains sufficient dissolved oxygen, and the activated sludge is always in a suspended state, fully contacting and mixing with the organic matter and dissolved oxygen in the sewage, completing the organic process of microbial degradation. In some embodiments, the aerator uses a diaphragm-type microporous aerator, and the blower conveys the flue gas to the aerator installed at the bottom of the aeration tank through the air delivery pipe, so that the flue gas forms bubbles with a bubble diameter of 1.5-3.0 mm. The diaphragm-type microporous aerator is made of a polypropylene base, and a synthetic rubber microporous aeration diaphragm is made of a synthetic rubber. The diaphragm has holes arranged in concentric circles. The synthetic rubber can be thermoplastic polyurethane rubber or silicone. In the implementation process, when a diaphragm-type microporous aerator is used, the diaphragm-type microporous aerator is made of a polypropylene base, and a synthetic rubber microporous aeration diaphragm is made of a rubber aeration diaphragm, such as a rubber aeration diaphragm and a silicone aeration diaphragm, and the diaphragm has holes arranged in concentric circles. During aeration, air enters between the aerator diaphragm and the base through the vents on the base, causing the aerator diaphragm to bulge slightly and the holes to open, thereby achieving the purpose of aeration and diffusion. After the air supply stops and the pressure disappears, the holes are closed under the elastic action of the aerator diaphragm, and the aerator diaphragm is pressed on the aerator base under the action of water pressure, so the holes will not be blocked. The bubble diameter generated by the aerator is 1.5-3.0mm, and a small amount of dust can also pass through the holes without clogging, and no air purification equipment is required.

In the process of sludge drying and incineration using the above device, the feed of the sludge silo is sludge with a water content of 60% to 75%, which first enters the first drying section 3. In the first drying section 3, the sludge is dried to a water content of 40%-55% using dry hot air, and humid air is formed. The sludge with a water content of 40%-55% is dried to a water content of 20% in the second drying section 4 using the waste heat of the high-temperature flue gas of the incinerator 8. Countercurrent heat exchange is adopted in the second drying section 4. In order to avoid the evaporation of volatile combustible gases such as CO and _H2 as much as possible, the sludge temperature at the second sludge outlet 42 of the second drying section 4 is controlled to be <120°C. In order to better control the gas components evaporated in the second drying section 4 to not contain volatile combustible gases such as CO and _H2 , and to ensure that only water evaporates, a flue gas detection device can also be set in the second drying section 4 to monitor whether volatile combustible gases such as CO and _H2 are generated. The drying temperature is regulated in combination with the monitoring results. The dried sludge with a moisture content of 20% output from the second drying section 4 is crushed into powder by a spiral crushing conveyor and mixed with the hot smoke ash discharged from the flue gas cyclone dust collector 6 in the return valve 7. The dried sludge heated to a temperature close to the ignition point is sent to the incinerator 8 from the return valve 7, and self-sustainingly burns at 850°C-950°C. The high-temperature flue gas produced stays in this temperature range for more than 2 seconds, generating high-temperature flue gas and high-temperature slag. The hot flue gas separated by the high-temperature flue gas cyclone dust collector 6 flows back to the second drying section 4, and forms moist flue gas after drying. The dry air and the moist air formed by the first drying section 3 and the moist flue gas formed by the second drying section 4 are sequentially subjected to the first-stage heat exchange and the second-stage heat exchange, and the obtained dry hot air is returned to the first drying section 3 for drying. The wet air cooled by the first stage heat exchange is mixed with the wet flue gas cooled by the second stage heat exchange and then enters the scrubber 18, where smoke and pollutants are removed by spraying water, and then discharged into the aeration tank of the sewage treatment plant through the induced draft fan 19 for biological deodorization and treatment. The scrubber 18 uses the recycled water from the sewage treatment plant, and the effluent of the scrubber 18 is sent to the water inlet of the sewage treatment plant, making full use of the existing resources of the sewage treatment plant.

The implementation method of the present application adopts the method of in-situ distribution and setting in the sewage treatment plant. By burning and treating domestic sludge, the flue gas generated by the combustion is passed into the scrubbing tower of the sewage treatment plant, and the pollutants in the flue gas are removed, achieving the effect of scrubbing, and reducing the emission of pollutants such as particulate matter, sulfur dioxide, nitrogen oxides, hydrogen chloride, and dioxins. By adopting the above-mentioned implementation method of the present application, domestic sludge can be directly burned in the sewage treatment plant without the need for other auxiliary materials such as coal and domestic garbage to be mixed and burned. The operating cost is low, the environment of the sewage treatment plant is fully utilized, the transportation process is eliminated, the cost is reduced, the secondary pollution to the environment is avoided, the land area is reduced, and the environmental pollution is reduced. During the implementation of the present application, the incinerator burns the dried sludge and converts it into water, carbon dioxide, a small amount of nitrogen oxides, a small amount of sulfur oxides and ashes. The ashes can be used as building materials, realizing the resource utilization and harmlessness of the combustion of low calorific value sludge. The present application sets the combustion temperature of the incinerator to 850-950°C, which can achieve harmless treatment of domestic sewage sludge. In an incinerator that uses only dried sludge as raw material, it can stably ignite without burning any auxiliary fuel, burn out efficiently and achieve NOx emission standards. The equipment of the present application has a compact structure and a small footprint. It makes full use of the waste heat of the flue gas in the system. The waste heat of the flue gas is used to heat and dry the sludge to be burned, avoiding heat waste and improving heat utilization. The ash after incineration can be used as building materials or paving, which solves the technical problem that the existing process cannot perform low-cost treatment of sludge with high moisture content. The process flow of the implementation method of the present application is simple, the system has high safety performance, and it achieves reduction, harmlessness and resource utilization to the greatest extent. The carbon content of the sludge combustion ash under the process of the present application is less than 1%.

Embodiment 1:

The No. 1 domestic sludge generated by the sewage treatment plant has an initial moisture content of 75%. It is dried for the first time in sequence to obtain sludge with a moisture content of 55% and moist air; the sludge with a moisture content of 55% is dried for the second time with the hot flue gas from incineration to obtain sludge with a moisture content of 20% and moist flue gas; the obtained sludge is crushed and mixed with hot ash, the crushed sludge is heated to a temperature close to the ignition point, and then introduced into the incinerator together, and self-sustainingly incinerated at 850°C to obtain high-temperature flue gas and high-temperature slag; the dry air is heat-exchanged with the moist air and the moist flue gas in sequence and the temperature is gradually increased, and then returned to the first drying unit as dry hot air; the high-temperature flue gas is separated into solid and gas, and the obtained solid is returned to the incinerator as hot ash to be mixed with the crushed sludge, a part of the obtained gas is used for the second drying, and the other part is used as a heat source to provide heat for the hot ash and sludge mixture. After the moisture-carrying air and the moisture-carrying flue gas are mixed after the step-by-step heat exchange, they are first washed with water to remove pollutants, and then introduced into the aeration tank of the sewage treatment plant for biological deodorization and treatment. The carbon content of the sludge combustion ash is 0.8%.

Embodiment 2:

The No. 2 domestic sludge produced by the sewage treatment plant has an initial moisture content of 68%. It is dried for the first time in sequence to obtain sludge with a moisture content of 48% and moist air; the obtained sludge with a moisture content of 48% is dried for the second time with the hot flue gas from incineration to obtain sludge with a moisture content of 15% and moist air; the obtained sludge is crushed and mixed with hot ash, and the crushed sludge is heated to a temperature close to the ignition point, and then introduced into the incinerator together, and self-sustainingly incinerated at 900°C to obtain high-temperature flue gas and high-temperature slag; the dry air is heat-exchanged with the moist air and the moist air in sequence, and the temperature is gradually increased step by step, and then returned to the first drying unit as dry hot air. Element; solid-gas separation of high-temperature flue gas, the obtained solid as hot ash returned to the incinerator and mixed with the crushed sludge, part of the obtained gas is used for the second drying, and the other part is used as a heat source to provide heat for the hot ash and sludge mixture. After the moist air and moist flue gas after the step-by-step heat exchange are mixed, they are first washed with water to remove pollutants, and then passed into the aeration tank of the sewage treatment plant for biological deodorization and treatment. The carbon content of the sludge combustion ash is 0.6%.

Embodiment 3:

The No. 3 domestic sludge generated by the sewage treatment plant has an initial moisture content of 60%. It is dried for the first time in sequence to obtain sludge with a moisture content of 40% and moist air; the sludge with a moisture content of 40% is dried for the second time with the hot flue gas from incineration to obtain sludge with a moisture content of 10% and moist air; the obtained sludge is crushed and mixed with hot ash, the crushed sludge is heated to a temperature close to the ignition point, and then introduced into the incinerator together, and self-sustainingly incinerated at 950°C to obtain high-temperature flue gas and high-temperature slag; the dry air is heat-exchanged with the moist air and the moist air and the moist air in sequence, and the temperature is gradually increased, and then returned to the first drying unit as dry hot air; the high-temperature flue gas is separated into solid and gas, and the obtained solid is returned to the incinerator as hot ash to be mixed with the crushed sludge, a part of the obtained gas is used for the second drying, and the other part is used as a heat source to provide heat for the hot ash and sludge mixture. After the moisture-carrying air and the moisture-carrying flue gas are mixed after the step-by-step heat exchange, they are first washed with water to remove pollutants, and then introduced into the aeration tank of the sewage treatment plant for biological deodorization and treatment. The carbon content of the sludge combustion ash is 0.5%.

Industrial Applicability

The self-sustaining incineration process of domestic sewage sludge provided by the present invention has a simple process flow and high system safety performance: it can realize self-sustaining combustion of domestic sewage sludge after drying, and no auxiliary fuel needs to be added during the incineration process, thereby reducing the cost of the sludge incineration treatment process and reducing the emission of pollutants; the waste heat is fully recovered through secondary drying to realize the step-by-step utilization of energy and avoid a large amount of thermal pollution; the hot ash is returned to the dried sludge to a temperature close to the ignition point before entering the incinerator, thereby avoiding the impact on the furnace temperature and realizing safe and stable combustion of domestic sewage sludge; by combining with the sewage treatment process, the transportation process can be avoided, the floor space occupied can be reduced, the cost can be reduced, the secondary pollution to the environment can be avoided, and the low-cost treatment of sludge with a high water content can be realized.

The equipment for the self-sustaining incineration process of domestic sewage sludge provided by the present invention has a compact structure and occupies a small area. It makes full use of the waste heat of the flue gas in the system and heats and dries the sludge to be burned by using the waste heat of the flue gas, thereby improving the heat utilization rate and avoiding environmental pollution. It is conducive to the efficient implementation of the above process and enhances the industrial application value of the above process.

Claims (17)

A self-sustaining incineration process for domestic sewage sludge, characterized by at least comprising first drying, second drying, crushing and incineration performed in sequence; specifically comprising the following steps: 1) Drying the domestic sewage sludge with a moisture content of 60%-75% with dry hot air for the first time to obtain sewage sludge with a moisture content of 40%-55% and moist air; 2) drying the sludge with a moisture content of 40% to 55% obtained in 1) for a second time with the hot flue gas from the incineration to obtain sludge with a moisture content of no more than 20% and moisture-carrying flue gas; 3) crushing the sludge with a moisture content of no more than 20% obtained in 2) and mixing it with the hot ash from the incineration, heating the crushed sludge to a temperature close to the ignition point, and then entering the crushed sludge into an incinerator for self-sustaining incineration at 850-950° C. to obtain high-temperature flue gas and high-temperature slag; 4) The high-temperature flue gas obtained in 3) is subjected to solid-gas separation, and the obtained gas is returned to 2) as hot flue gas for the second drying, and the obtained solid is returned to 3) as hot ash to be mixed with the crushed sludge. The process as claimed in claim 1 is characterized in that the dry air is heat-exchanged with the moist air obtained in 1) and the moist flue gas obtained in 2) in sequence and the temperature is raised step by step, and then the dry air is returned to the first drying in 1) as dry hot air. The process as claimed in claim 1 is characterized in that: 3) the pulverizing is to pulverize the sludge with a moisture content not higher than 20% to a particle size not greater than 5 mm. The process as described in claim 1 is characterized in that: the sludge temperature is controlled to be no higher than 120°C during the second drying discharge described in 2). The process as described in claim 1 is characterized in that: the high-temperature slag obtained in 3) is vigorously mixed with air for heat exchange to obtain slag-containing hot air, and then the slag-containing hot air is subjected to solid-gas separation to obtain hot air and cooled slag; and the hot air is returned to the incinerator described in 3) to assist combustion. The process as claimed in claim 1 is characterized in that a portion of the gas obtained in 4) is used to provide heat for the crushed sludge. The process as described in claim 1 is characterized in that the solid-gas separation is carried out using a cyclone dust collector. A sludge harmless treatment process set up in situ in a sewage treatment plant, comprising: ① The sludge generated by the sewage treatment plant is subjected to first drying, second drying, crushing and incineration in sequence; specifically including: (1) Drying the domestic sewage sludge with a moisture content of 60% to 75% with dry hot air for the first time to obtain sewage sludge with a moisture content of 40% to 55% and moisture-carrying air; (2) drying the sludge with a moisture content of 40% to 55% obtained in (1) for a second time with the hot flue gas from the incineration to obtain sludge with a moisture content of no more than 20% and moisture-carrying flue gas; (3) crushing the sludge with a moisture content of no more than 20% obtained in (2) and mixing it with the hot ash from the incineration, heating the crushed sludge to a temperature close to the ignition point, and then feeding the crushed sludge into an incinerator for self-sustaining incineration at 850-950° C. to obtain high-temperature flue gas and high-temperature slag; (4) exchanging heat with the moist air obtained in (1) and the moist flue gas obtained in (2) in sequence, raising the temperature step by step, and returning the dry air as hot dry air to the first drying step in (1); (5) The high-temperature flue gas obtained in (3) is subjected to solid-gas separation, and the obtained solid is returned to (3) as hot flue gas to be mixed with the crushed sludge, and part of the obtained gas is returned to (2) as hot flue gas for the second drying, and the other part is used as The heat source is a mixture of the hot ash and the crushed sludge. ② After mixing the moist air and the moist flue gas after the step-by-step heat exchange described in (4), the air is first washed with water to remove pollutants, and then introduced into the aeration tank of the sewage treatment plant for biological deodorization and treatment. The treatment process as described in claim 8 is characterized in that: ② the water washing is completed using the reclaimed water of the sewage treatment plant where it is located, and the effluent after the water washing is passed into the sewage inlet of the sewage treatment plant where it is located. The equipment used for the self-sustaining incineration process of domestic sewage sludge according to claim 1 is characterized in that it comprises a feeding unit, a drying pretreatment unit, a crushing and heating unit and a self-sustaining incineration unit connected in sequence by pipelines; The feeding unit is used to transport the domestic sewage sludge with a moisture content of 60%-75% to the drying pretreatment unit through a pipeline; The drying pretreatment unit is used to dry the domestic sewage sludge with a moisture content of 60%-75% in stages until the moisture content is not higher than 20%; the drying pretreatment unit specifically includes a first drying section and a second drying section connected in sequence through a pipeline; the first drying section is also connected to a gas heat exchange unit through a pipeline, which is used to recover and utilize the waste heat of the gas discharged from the first drying section and the second drying section through heat exchange; The pulverizing and heating unit is used to pulverize the sludge after drying pretreatment and further preheat it to a temperature close to the ignition point; the pulverizing and heating unit includes a pulverizing device and a solid-gas separation device; the feed port of the pulverizing device is connected to the second drying section through a pipeline; the solid-gas separation device is connected to the self-sustaining incineration unit, the second drying section and the discharge port of the pulverizing device through pipelines respectively; The self-sustaining incineration unit is used to incinerate the crushed and heated sludge at 850-950°C; it includes an incinerator, a solid-gas heat exchange device and a solid-gas separation device that are interconnected; the incinerator is connected to the discharge port of the crushing device through a pipeline; the solid-gas heat exchange device is further connected to a blower; and the solid-gas separation device is further provided with a slag discharge pipe. The equipment as described in claim 10 is characterized in that: a water washing unit and a biochemical aeration tank are further provided; the water washing unit is used to wash the gas discharged from the gas heat exchange unit, the air inlet of the water washing unit is connected to the gas heat exchange unit through a pipeline, and the air outlet is connected to the biochemical aeration tank through a pipeline. The device as described in claim 10 is characterized in that: the feeding unit is provided with an extrusion device for conveying materials to the drying pretreatment unit by extrusion. The device as described in claim 10 is characterized in that the positions of the feed inlet and the air inlet of the first drying section are preferably such as to form countercurrent heat exchange in the first drying section to improve the heat exchange efficiency. The device as claimed in claim 10 is characterized in that: the gas heat exchange unit includes a blower, a first-stage heat exchange device and a second-stage heat exchange device connected in series in sequence, the blower is used to generate dry air, the first-stage heat exchange device is used to exchange heat between the dry air and the gas discharged from the first drying section, and the second-stage heat exchange device is used to exchange heat between the gas heated by the first-stage heat exchange and the gas discharged from the second drying section; the second-stage heat exchange device is further connected to the first drying section through a pipeline to send the heated dry hot air after the second-stage heat exchange into the first drying section. The device as described in claim 10 is characterized in that: the second drying section is a variable cross-section furnace, and the cross-section of the furnace gradually decreases with the direction of the airflow and gradually increases with the direction of the sludge, thereby forming countercurrent heat exchange in the second drying section. The equipment as described in claim 10 is characterized in that the solid-gas separation device of the pulverizing and heating unit and the self-sustaining incineration unit is a cyclone dust collector. The device as described in claim 10 is characterized in that: in the pulverizing and heating unit, a connected flue gas duct is also provided between the pulverizing device and the solid-gas separation device, which is used to introduce a part of the hot flue gas from the solid-gas separation device into the discharge section of the pulverizing device.