Domestic sludge self-sustaining incineration process and device

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 domestic sludge self-sustaining incineration process and equipment

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application with application number 202311395320.7 filed with the Patent Office of China on October 25, 2023, entitled “A process and equipment for self-sustaining incineration of domestic sewage sludge”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] 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

[0004] 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 solid suspended matter after the treatment of domestic sewage. The common organic matter is sugar, fat and protein. The sludge treatment problem is very serious.

[0005] Sludge incineration is one of the most direct and effective methods for reducing sludge volume. Traditionally, sludge incineration typically involves transporting mechanically dewatered sludge to a dedicated waste incineration site or power plant, where it is then co-combusted with large amounts of auxiliary fuel. This consumes significant amounts of auxiliary fuel, making it both uneconomical and environmentally unsuitable. Alternatively, some processes, to reduce auxiliary fuel consumption during co-combustion, pre-dry the sludge prior to incineration, requiring high energy consumption. Drying reduces the sludge's moisture content, minimizing the amount of auxiliary fuel required for subsequent co-combustion. However, sludge pre-drying still presents numerous challenges. Sludge pre-drying can be categorized as either full drying or partial drying. Fully dried sludge has a higher calorific value and is easier to incinerate, but it also generates dust and poses the risk of spontaneous combustion and explosion. Partially dried sludge, on the other hand, still contains significant moisture upon entry into the furnace, impacting the furnace temperature, leading to 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 be co-processed with waste incineration power plants, cement kilns, coal-fired power plants, etc., or 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 pre-drying sludge before incineration. However, in these methods, the incineration of the 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 during 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 generated by combustion can easily cause secondary pollution of the environment, making the incineration process of dried pretreated sludge difficult to achieve industrial promotion and application.

[0006] Therefore, it is necessary to provide a new sewage sludge incineration process to reduce the cost of the process and improve its energy conservation and environmental protection. At the same time, it does not require the consumption of auxiliary fuel for co-combustion, but allows the low-calorific value domestic sludge to achieve safe and stable self-sustaining combustion after drying pretreatment. This will significantly enhance the industrial applicability of the sewage sludge incineration process.

[0007] Summary of the Invention

[0008] 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, and ultimately achieve industrial reduction treatment of domestic sludge.

[0009] Another object of the present application is to provide equipment for the above-mentioned treatment process, so that the above-mentioned process can be implemented efficiently and further enhance the industrial application value of the process.

[0010] The above-mentioned purpose of this application is achieved through the following technical solutions:

[0011] First, the present application provides a self-sustaining incineration process for domestic sludge, which includes at least a first drying, a second drying, a crushing and an incineration process performed in sequence; specifically, the following steps:

[0012] 1) Drying the domestic sludge with a moisture content of 60% to 75% with hot dry air for the first time to obtain sludge with a moisture content of 40% to 55% and moist air;

[0013] 2) drying the sludge with a moisture content of 40% to 55% obtained in 1) for a second time using hot flue gas from the incineration to obtain sludge with a moisture content of no more than 20% and moisture-carrying flue gas;

[0014] 3) crushing the sludge obtained in 2) with a moisture content of no more than 20% 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 produce high-temperature flue gas and high-temperature slag;

[0015] 4) The high-temperature flue gas obtained in 3) is subjected to solid-gas separation, 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.

[0016] 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 moist flue gas will increase, and the waste heat loss will increase. Above this range, the mud temperature will be too high or difficult to control after the second drying, and pyrolysis gas will be precipitated.

[0017] In the preferred treatment process of the present application, in order to avoid as much as possible the generation of volatile combustible gases such as CO and / or H2 in the wet flue gas obtained in 2), the sludge temperature during the second drying discharge described in 2) is controlled to be no higher than 120°C.

[0018] In the preferred treatment process of this application, to improve the combustibility of the dried sludge, the pulverization step (3) involves pulverizing the sludge, which has a moisture content of no more than 20%, to a particle size of no more than 5 mm. This significantly increases the specific surface area of ​​the dried sludge to be burned, further improving its combustibility.

[0019] In the preferred treatment process of the present application, in order to fully recycle and utilize 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.

[0020] In the treatment process described in this application, after the self-sustaining incineration of the sludge occurs in the incinerator described in 3), the high-temperature flue gas produced contains ash and unburned components; while recycling the gases in the high-temperature flue gas, this application also fully recycles the solids therein. To this end, in the preferred embodiment of this application, a cyclone dust collector is used for the solid-gas separation. This allows 95% of the solids in the high-temperature flue gas to be returned as feed to the dried sludge before incineration for heating, bringing the dried sludge temperature close to the ignition point. At the same time, the volatile combustible gas produced can also enter the incinerator along with the dried sludge for combustion.

[0021] In a more preferred treatment process of the present application, in order to further ensure that the temperature of the sludge 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 pulverized sludge.

[0022] 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:

[0023] ① The sludge generated by the sewage treatment plant is subjected to the first drying, second drying, crushing and incineration treatment in sequence; specifically including:

[0024] 1) Drying the domestic sludge with a moisture content of 60%-75% with hot dry air for the first time to obtain sludge with a moisture content of 40%-55% and moist air;

[0025] 2) drying the sludge with a moisture content of 40% to 55% obtained in 1) for a second time using hot flue gas from the incineration to obtain sludge with a moisture content of no more than 20% and moisture-carrying flue gas;

[0026] 3) crushing the sludge obtained in 2) with a moisture content of no more than 20% 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 produce high-temperature flue gas and high-temperature slag;

[0027] 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 then returning the dry hot air to the first drying step in 1);

[0028] 5) performing solid-gas separation on the high-temperature flue gas obtained in 3) and returning the obtained solid as hot ash to 3) for mixing with the pulverized sludge. Part of the obtained gas is returned to 2) as hot flue gas for the second drying, and the remaining part is used as a heat source to heat the mixture of the hot ash and the pulverized sludge.

[0029] 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.

[0030] 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 water washing is passed into the sewage inlet of the sewage treatment plant where it is located.

[0031] The sludge harmless treatment process set up in situ at the sewage treatment plant described in this application can treat the sludge produced in the sewage treatment plant, saving the cost of sludge transportation, and can fully utilize the existing equipment and resources of the sewage treatment plant, such as water washing equipment, reclaimed water, aeration tank, etc., by using local materials. After the sludge is fully self-sustainingly incinerated, the incineration flue gas can be harmlessly treated, and the sewage treatment efficiency can also be improved. The flue gas generated by burning sludge is introduced into the aeration tank of the sewage treatment process. Aeration can generate and maintain effective gas-liquid contact, and maintain a certain dissolved oxygen concentration in the water while the biological oxidation process continuously consumes oxygen, generate sufficient mixing 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 the emission of pollutants, removes particulate matter, sulfur dioxide, hydrogen chloride, nitrogen oxides and other harmful substances dissolved in sewage in the flue gas, and 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, preventing environmental pollution, and avoiding a large amount of thermal pollution.

[0032] In addition, the present application also provides a set of domestic 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;

[0033] The feeding unit is used to transport domestic sewage sludge with a moisture content of 60%-75% to the drying pretreatment unit through a pipeline;

[0034] The drying pretreatment unit is used to dry domestic sewage sludge with a moisture content of 60%-75% in stages to a moisture content of no more than 20%. The drying pretreatment unit specifically includes a first drying section and a second drying section connected in sequence by a pipeline. The first drying section is also connected to a gas heat exchange unit via a pipeline for recovering waste heat from the gas discharged from the first drying section and the second drying section through heat exchange.

[0035] 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 via 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 via pipelines respectively;

[0036] 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.

[0037] The preferred equipment of the present application is further provided with a water washing unit and a biochemical aeration tank; 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.

[0038] 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.

[0039] In the preferred equipment of the present application, the feed inlet and the air inlet of the first drying section are positioned so as to form countercurrent heat exchange in the first drying section to improve heat exchange efficiency.

[0040] 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 after the second-stage heat exchange into the first drying section.

[0041] In the preferred equipment of this 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.

[0042] 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.

[0043] 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.

[0044] 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 into 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%. At the same time, the water evaporates to turn the dry hot air into moist air. After the moist 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 fed into the second drying section through a pipeline. The incinerator of the self-sustaining incineration unit produces After being discharged from the top of the incinerator, the high-temperature flue gas 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 the pipeline. The sludge is further dried by the hot flue gas in the second drying section to a moisture content of no more than 20%. At the same time, water is evaporated to form wet flue gas. The sludge temperature at the outlet of the second drying section is controlled below 120°C to prevent volatile combustible gases such as CO and / or H2 from entering the wet flue gas during drying. After being discharged from the second drying section, the wet flue gas enters the gas heat exchange unit through the pipeline and enters the dry air after heat exchange with the wet air and heating. In one step, the wet flue gas is heated and cooled, and then the wet flue gas is passed through a pipeline to a flue gas post-treatment device, such as a water washing unit and an aeration unit, together with the cooled wet air. In the gas heat exchange unit, the dry air that has successively exchanged heat with the wet air and the wet flue gas is heated step by step to form dry hot air. After the dry hot air leaves the gas heat exchange unit, it is passed through a pipeline into the first drying section for drying. 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 is first crushed to a particle size of less than 5mm in the crushing device, and then separated from the hot ash by the solid-gas separation device. The sludge is mixed and heated to near the ignition point by the hot ash, and then enters the incinerator together with the hot ash through the 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 the pipeline for heat exchange 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 the pipeline to separate and obtain hot air and cooled slag; the hot air enters the incinerator through the pipeline to assist combustion, and the cooled slag is discharged out of the system through the slag discharge pipe.

[0045] The beneficial effects of this application are mainly reflected in the following aspects:

[0046] 1. Achieve self-sustaining combustion after drying of domestic sludge

[0047] The self-sustaining incineration process and equipment of domestic sludge provided in this application gradually dry and heat the domestic sludge at room temperature 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 specific surface area of ​​the sludge 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.

[0048] 2. Can fully recover waste heat and realize cascade utilization of energy

[0049] During the step-by-step drying and heating process of the sludge, the process and equipment of this application fully utilize the system's internal heat through stepped heat exchange, particularly recovering the latent heat of water vapor in the moist flue gas and moist air. Throughout the process, the incinerator is the highest point in the system temperature. The heat carried by the high-temperature flue gas from the incinerator is gradually reversed back to the second and first drying stages through drying and heat exchange. The step-by-step temperature reduction of the flue gas fully meets the requirements of the stepped temperature increase in the two drying stages.

[0050] 3. Make full use of 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.

[0051] This application uses the solid hot ash contained in the high-temperature flue gas as a separate return material to perform 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 heat provides a vital 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.

[0052] 4. Can be combined with sewage treatment technology to improve industrial application value

[0053] When the process system described in this application is installed in situ at a sewage treatment plant, its industrial application value can be further enhanced. The process and equipment of this application can treat the sludge generated in the sewage treatment plant in situ, or the sewage treatment plant can be built nearby, which can save a lot of transportation costs for sludge transportation and treatment. It can also make good use of the existing equipment and resources of the sewage treatment plant, treat the flue gas through the scrubber, use the sewage plant's recycled water, drain the water into the sewage plant's sewage inlet, and discharge the flue gas into the aeration tank, thereby achieving a two-way promotion of sewage treatment and sludge treatment, and ultimately achieving effective reduction, harmlessness, and resource-based treatment of domestic sludge. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 is a flow chart of the overall process of a specific embodiment 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.

[0055] FIG2 is a schematic diagram of the overall composition of the equipment used in the specific embodiment of the present application.

[0056] FIG3 is a schematic diagram of the overall composition of the equipment used in the preferred embodiment of the present application.

[0057] Explanation of the accompanying symbols: 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-humidified air outlet, 4-second drying section, 41-second sludge inlet, 42-second sludge outlet, 43-flue gas inlet, 44-humidified 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 silo, 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

[0058] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0059] 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.

[0060] The overall structure of the device is shown in Figure 2. First, there is a sludge silo 1, below which is an extruder 2 for forming sludge into sludge strips. The outlet of the extruder 2 is connected to the first drying section 3. The first drying section 3 is equipped with a first sludge inlet 31, a sludge conveyor belt 32, a first sludge outlet 33, a hot dry air inlet 34, and a moist air outlet 35. The moist air outlet 35 is connected to the first-stage heat pipe exchanger 16 via a pipe, and the outlet of the first-stage heat pipe exchanger 16 is connected to the water scrubber 18 via a pipe. The hot dry air inlet 34 is connected to the second-stage heat pipe exchanger 17, the first-stage heat pipe exchanger 16, and the drying blower 15 in sequence via pipes. The dry air pipe connected to the drying blower 15 is connected to the moist air pipe leading from the moist air outlet 35 through the first-stage heat pipe exchanger 16, performing the first-stage heat exchange, reducing the moist air temperature to below the dew point and recovering the sensible heat of the moist 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 by a pipe. 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 pipe leading out of the wet flue gas outlet 44 is connected to the dry air pipe leading 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 the water vapor. The second sludge outlet 42 of the second drying stage 4 is connected to the spiral crushing conveyor 5 via a pipeline. The dried sludge is crushed into a powder with a particle size no larger than 5 mm in the spiral crushing conveyor 5. The outlet of the spiral crushing conveyor 5 is connected to the return valve 7 via a pipeline. In the return valve 7, the crushed sludge powder mixes with the hot ash returned from the flue gas cyclone 6, where it is heated to a temperature close to the ignition point of the sludge powder. The sludge powder then enters the incinerator 8 for self-sustaining combustion. The volatile combustible gases produced also enter the incinerator 8 and burn there. The incinerator 8 is equipped 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 6. The hot flue gas outlet 62 of the flue gas cyclone 6 is connected to the flue gas inlet 43 of the second drying stage 4. The hot ash outlet 63 of the flue gas cyclone 6 is connected to the return valve 7. An air distribution plate 9 is provided at the lower part of the incinerator 8, and a slag discharge pipe 10 is provided on the air distribution plate 9. The slag discharge pipe 10 is connected to an intensified air flow heat exchanger 12 through a pipeline with a valve 11, and the intensified air flow heat exchanger 12 is further connected to a combustion-supporting blower 14 through a pipeline.The air is blown into the enhanced airflow 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.

[0061] 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 accommodate 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 solution, 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 amount of hot flue gas introduced into the return bin 71.

[0062] 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.

[0063] The flue gas cyclone dust collector 6 and the air cyclone dust collector 13 in this application can be cyclone dust collectors of the same type and specifications. Cyclone dust collectors have a dust removal efficiency of over 95%, a long service life, are easy to install and maintain, are compact, have a simple structure, and are inexpensive to manufacture. They are suitable for purifying dense dust with a particle size greater than 5 μm. They utilize special high-temperature resistant materials to withstand even higher temperatures. When equipped with a wear-resistant lining, the dust collector can be used to purify flue gas containing highly abrasive dust.

[0064] The water for the scrubbing tower 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 inlet pool, making full use of the conditions of the sewage treatment plant and reducing costs. The purification principle of smoke treatment with water is mainly to separate the pollutants by immersion and dissolution. The specific process is to first disperse the pollutants in the air flow through mechanical equipment, and the water mist in the air flow 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. Finally, the residue is collected and removed by equipment. The discharge port of the scrubbing tower is set at the top of the tower body. After the flue gas is tested, the clean gas can be discharged directly into the atmosphere. The pollutants in the flue gas are removed by the scrubbing tower. The method is simple and the recycling of water in the sewage treatment plant is realized at the same time.

[0065] In some embodiments, a scrubber tower comprises a tower body, a packing layer, a spray system, an inlet pipe, an outlet pipe, and an exhaust port. Flue gas enters the tower body from the inlet pipe and, as it passes through the packing layer, comes into contact with a liquid, absorbing pollutants. The packing layer increases the contact area, ensuring sufficient contact between the flue gas and the liquid, thereby improving purification efficiency. The spray system evenly sprays the liquid onto the packing layer, ensuring sufficient contact between the liquid and the flue gas, thereby absorbing pollutants.

[0066] In some embodiments, the induced draft fan 19 can be replaced with an air aerator system, which consists of a blower, an air delivery duct, and an aerator. During implementation, flue gas is introduced through the blower of the air aerator system, diffused along the air delivery duct, and enters the aeration tank through the aerator, allowing the flue gas to fully contact the sewage. The aerator forcibly transfers oxygen from the air or flue gas to the aeration tank, where it is diffused by the aerator equipment, ensuring that the activated sludge system maintains sufficient dissolved oxygen and keeps the activated sludge 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 is a diaphragm-type microporous aerator. A blower transports the flue gas through an air delivery pipe to the aerator installed at the bottom of the aeration tank, causing the flue gas to form bubbles with a diameter of 1.5-3.0 mm. The diaphragm-type microporous aerator has a base made of polypropylene and a microporous aeration diaphragm made of synthetic rubber. The diaphragm has holes arranged in concentric circles. The synthetic rubber can be thermoplastic polyurethane rubber or silicone. During implementation, when using a diaphragm-type microporous aerator, the diaphragm-type microporous aerator has a base made of polypropylene and a microporous aeration diaphragm made of synthetic rubber, such as a rubber aeration diaphragm or a silicone aeration diaphragm. The diaphragm has holes arranged in concentric circles. During aeration, air enters between the aerator diaphragm and the base through the vent holes in the base, causing the aerator diaphragm to bulge slightly and the holes to open, thereby achieving the purpose of aeration and diffusion. When the air supply stops and the pressure disappears, the elasticity of the aerator diaphragm closes the perforations. Under the action of water pressure, the aerator diaphragm is pressed against the aerator base, preventing clogging of the perforations. The bubbles produced by this aerator have a diameter of 1.5-3.0mm, allowing even small amounts of dust to pass through the perforations without clogging, eliminating the need for air purification equipment.

[0067] In the sludge drying and incineration process using the above-described apparatus, sludge with a moisture content of 60% to 75% is fed into the sludge silo and first enters the first drying stage 3. Dry hot air is used within this stage to dry the sludge to a moisture content of 40% to 55%, creating moisture-laden air. The sludge, with a moisture content of 40% to 55%, is then dried to a moisture content of 20% in the second drying stage 4 using the residual heat from the high-temperature flue gas of the incinerator 8. Countercurrent heat exchange is employed within the second drying stage 4. To minimize the evaporation of volatile combustible gases such as CO and H₂, the sludge temperature at the second sludge outlet 42 of the second drying stage 4 is controlled to be less than 120°C. To ensure that the gas evaporated from the second drying stage 4 does not contain volatile combustible gases such as CO and H₂, and that only water is evaporated, a flue gas detection device can be installed within the second drying stage 4 to monitor the generation of volatile combustible gases such as CO and H₂, and the drying temperature can be adjusted based on 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 ash discharged from the flue gas cyclone dust collector 6 in the return valve 7. The dried sludge, which has been heated to a temperature close to the ignition point, is sent from the return valve 7 to the incinerator 8 for self-sustaining combustion at 850°C-950°C. The high-temperature flue gas generated 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 flue gas cyclone dust collector 6 flows back to the second drying section 4, and forms moist flue gas after drying. The dry air undergoes first-stage heat exchange and second-stage heat exchange with the moist air formed by the first drying section 3 and the moist flue gas formed by the second drying section 4, respectively. The resulting dry hot air returns to the first drying section 3 for drying. The moist air cooled by the first stage of heat exchange is mixed with the moist flue gas cooled by the second stage of heat exchange before entering scrubber 18, where dust and pollutants are removed through spray water scrubbing. The air is then discharged through induced draft fan 19 into the sewage treatment plant's aeration tank for biological deodorization and treatment. Scrubber 18 uses recycled water from the sewage treatment plant, and its effluent is fed to the plant's inlet, fully utilizing the plant's existing resources.

[0068] The implementation method of the present application adopts the method of in-situ distribution setting at the sewage treatment plant, and treats domestic sludge by burning, and passes the flue gas generated by the combustion into the scrubbing tower of the sewage treatment plant, thereby removing pollutants in the flue gas, 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 for mixed burning, 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 occupation 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 ash. The ash can be used as a building material, 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 sludge. In an incinerator that uses only dried sludge as raw material, it can stably ignite without the addition of 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, and uses the waste heat of the flue gas to heat and dry the sludge to be burned, avoiding heat waste and improving heat utilization. The dust 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 a 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 maximum reduction, harmlessness and resource utilization. The carbon content of the sludge combustion ash under the process of the present application is less than 1%.

[0069] Example 1:

[0070] 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 to obtain sludge with a moisture content of 55% and moist air. The sludge with a moisture content of 55% is dried for a second time with 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 an incinerator together for self-sustaining incineration 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 turn and the temperature is gradually increased, and then returned to the first drying unit as dry hot air. The high-temperature flue gas is subjected to solid-gas separation, and the obtained solid is returned to the incinerator as hot ash to be 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 successive heat exchanges, the moist air and the moist flue gas are mixed, 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 0.8%.

[0071] Example 2:

[0072] The No. 2 domestic sludge generated by the sewage treatment plant has an initial moisture content of 68%. It is dried for the first time to obtain sludge with a moisture content of 48% and moist air. The sludge with a moisture content of 48% is dried for a second time with hot flue gas from incineration to obtain sludge with a moisture content of 15% 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 an incinerator together for self-sustaining incineration 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 flue gas in turn and the temperature is gradually increased, and then returned to the first drying unit as dry hot air. The high-temperature flue gas is subjected to solid-gas separation, and the obtained solid is returned to the incinerator as hot ash to be 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 moisture-laden air and the moisture-laden flue gas are mixed after the successive heat exchanges, 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%.

[0073] Example 3:

[0074] 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 obtained sludge with a moisture content of 40% is dried for a second time with hot flue gas from incineration to obtain sludge with a moisture content of 10% and moist flue gas; 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 an 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 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 subjected to solid-gas separation, and the obtained solid is returned to the incinerator as hot ash to be 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 moisture-laden air and the moisture-laden flue gas are mixed after the successive heat exchanges, 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 0.5%. Industrial Applicability

[0075] The self-sustaining incineration process of domestic sludge provided by the present invention has a simple process flow and high system safety performance: it can realize self-sustaining combustion of domestic 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 pollutant emissions; the waste heat is fully recovered through secondary drying, and the step-by-step utilization of energy is realized, avoiding 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, avoiding the impact on the furnace temperature and realizing safe and stable combustion of domestic sludge; by combining with the sewage treatment process, the transportation process can be eliminated, the floor space occupied can be reduced, the cost can be reduced, the secondary pollution to the environment can be avoided, and low-cost treatment of sludge with a high water content can be achieved.

[0076] The equipment provided by the present invention for the self-sustaining incineration process of domestic sewage sludge has a compact structure and occupies a small area. It fully utilizes the waste heat of the flue gas in the system and uses the waste heat of the flue gas to heat and dry the sludge to be burned, thereby improving the heat utilization rate, avoiding environmental pollution, and being conducive to the efficient implementation of the above process and enhancing the industrial application value of the above process.

Claims

1. A self-sustaining incineration process for domestic sewage sludge, characterized in that: At least including the first drying, the second drying, the crushing and the incineration in sequence; specifically including 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.

2. The process according to claim 1, 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 gradually increased, and then returned as dry hot air to the first drying described in 1).

3. The process according to claim 1, characterized in that: 3) The pulverization is to pulverize the sludge with a moisture content not higher than 20% to a particle size not greater than 5 mm.

4. The process according to claim 1, characterized in that: Control 2) that the sludge temperature is not higher than 120°C during the second drying and discharging.

5. The process according to claim 1, characterized in that: The high-temperature slag obtained in 3) is mixed vigorously 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 in 3) for combustion assistance.

6. The process according to claim 1, characterized in that: A portion of the gas obtained in 4) is used to provide heat for the crushed sludge.

7. The process according to claim 1, characterized in that: The solid-gas separation is carried out by using a cyclone dust collector.

8. 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 include: (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.

9. The process according to claim 8, characterized in that: ② The water washing is completed using the reclaimed water of the sewage treatment plant, and the effluent after the water washing is passed into the sewage inlet of the sewage treatment plant.

10. The equipment used in the self-sustaining incineration process of domestic sewage sludge according to claim 1, characterized in that: It includes a feeding unit, a drying pretreatment unit, a crushing and heating unit, and a self-sustaining incineration unit which are sequentially connected 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.

11. The device according to claim 10, 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.

12. The device according to claim 10, characterized in that: The feeding unit is provided with an extrusion device for conveying materials to the drying pretreatment unit by extrusion.

13. The device according to claim 10, characterized in that: The feed inlet and the air inlet of the first drying section are preferably positioned to form a countercurrent heat exchange in the first drying section to improve the heat exchange efficiency.

14. The device according to claim 10, 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, and sends the dry hot air heated after the second-stage heat exchange into the first drying section.

15. The device according to claim 10, 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.

16. The device according to claim 10, characterized in that: The solid-gas separation device of the crushing and heating unit and the self-sustaining incineration unit is a cyclone dust collector.

17. The device according to claim 10, characterized in that: In the pulverizing and heating unit, a communicating flue gas duct is further provided between the pulverizing device and the solid-gas separation device, for introducing a portion of hot flue gas from the solid-gas separation device into the discharging section of the pulverizing device.

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