A method for reducing municipal sludge and utilizing it as a resource

Abstract

The present invention relates to the technical field of sludge reduction and resource utilization, and specifically to a method for municipal sludge reduction and resource utilization. The method of the present invention adopts a sludge reduction technical means of high-temperature drying of sludge, pulverizing it and then co-granulating it with biomass, and gasifying it. During the high-temperature drying of the sludge, a powder addition system and an auxiliary agent addition system are used to ensure the stability and safety of the sludge drying process, improve the drying efficiency, and enable comprehensive utilization of the system through a circulating air system, thereby saving energy and reducing consumption. In addition, by co-granulating it with biomass, biomass solid waste is treated and the calorific value of sludge gasification is synergistically increased. The powder and auxiliary agents added during the sludge drying process can also play an important role in the sludge gasification stage, such as increasing porosity, increasing calorific value, fixing sulfur, and fixing heavy metals. The resulting sludge gasification slag has broad application prospects in the fields of gardening, construction materials, and sewage treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of sludge reduction and resource utilization, and in particular to a method for municipal sludge reduction and resource utilization. Background Art

[0002] Activated sludge is a general term for microbial communities and the organic and inorganic substances they are attached to. A large amount of residual sludge is produced in the process of biological sewage treatment. Since the residual sludge contains a large amount of organic matter, it is a recyclable resource. However, if it is not treated in time and randomly piled up, pollutants such as nitrogen, phosphorus, heavy metals and harmful chemicals will seep out, polluting the land, rivers, lakes and groundwater, and causing harm to the environment.

[0003] The treatment and disposal of activated sludge is particularly important. Since the water content in activated sludge is relatively high, reaching more than 98%, it is crucial to reduce the amount of activated sludge during the treatment and disposal process. The existing methods of sludge reduction include sludge dehydration, drying, and gasification / incineration, which achieve sludge reduction and resource utilization. With the development of sludge treatment technology, the existing low-temperature drying has become the mainstream. On the one hand, low-temperature drying is safer, and on the other hand, it can effectively maintain the nutrients in the sludge, but it will correspondingly reduce the drying efficiency. Under the current situation of increasing sludge production, it is difficult to carry out efficient treatment. On the other hand, the existing utilization rate of sludge gasification products is low, and they are generally used as garden planting soil and building materials, which brings low added value and limits the further utilization of sludge gasification residue.

[0004] Therefore, the present invention proposes a method for sludge reduction and resource utilization, which comprehensively treats and utilizes sludge from the aspects of improving the efficiency of sludge reduction, increasing the gasification calorific value, and resource utilization of gasification slag, so as to achieve the purpose of efficient, safe, high calorific value reduction of sludge and better added value utilization of sludge gasification slag. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for reducing and recycling municipal sludge, so as to solve the problems of low treatment efficiency of existing low-temperature drying methods and large limitations in recycling sludge after reduction.

[0006] To achieve the above-mentioned object, the present invention adopts the following technical solution: a method for reducing and resource-utilizing municipal sludge, comprising the steps of drying and gasification, wherein the drying comprises a circulating air system, a powder spraying system, and an additive adding system;

[0007] In the circulating air system, the circulating air is heated to dry the sludge at high temperature. The used circulating air is dust-removed, condensed, and heated again to form a cycle, and the circulating air and the sludge are subjected to countercurrent heat exchange.

[0008] In the powder spraying system, powder is sprayed before the inlet of the sludge dryer. The powder is quicklime powder. The sludge after the powder spraying is cut into strips by the sludge cutter and then enters the sludge dryer for high-temperature drying.

[0009] The additive addition system is arranged in conjunction with the circulating air system; a venturi tube is provided on the conveying pipe of the heated circulating air, and the venturi tube cooperates with the additive addition system; the additives include modified carbon black and modified zeolite powder with positive surface charges, which are evenly dispersed in water and then sucked into the conveying pipe of the circulating air through the venturi tube and evenly dispersed;

[0010] The sludge gasification utilizes the powder and additives added in the sludge drying step to obtain combustible gas, gasification slag and fly ash; the combustible gas produced by the sludge gasification is returned to the sludge drying step for utilization, and the gasification slag and fly ash produced by the sludge gasification are comprehensively utilized.

[0011] Furthermore, in the circulating air system, the combustible gas returned from the sludge gasification step is used as a heat source for heating the circulating air.

[0012] Furthermore, in the circulating air system, part of the condensed circulating air is deodorized and discharged, and is supplemented with fresh air before being heated again; the combustible gas returned from the gasification step heats the air medium, and the heated air medium exchanges heat with the circulating air. Part of the air medium after heat exchange is used as supplementary fresh air for the circulating air, and part of it is mixed and preheated with the fresh air required for combustion of the combustible gas.

[0013] Furthermore, the powder spraying system includes a silo, the powder in the silo is continuously transported to the powder silo, a fan is set at the outlet of the powder silo, and the powder is evenly sprayed above the sludge through the nozzle using the air transported by the fan as a carrier.

[0014] Furthermore, in the auxiliary agent addition system, the modified carbon black is prepared by pre-oxidizing carbon black with concentrated sulfuric acid and then grafting with an aminosilane coupling agent; the modified zeolite powder is prepared by grafting zeolite powder with an aminosilane coupling agent.

[0015] Furthermore, the method further includes the steps of crushing and granulating. The crushing step includes crushing the dried sludge and crushing the biomass, mixing the crushed sludge and biomass, and then granulating.

[0016] Furthermore, the dust generated by dust removal in the circulating air system is sent to the granulation step for granulation.

[0017] Furthermore, the moisture content of the sludge feed in the drying step is 60-80%, the moisture content of the sludge discharge is 10-20%; the circulating air inlet temperature is 150-200°C, the circulating air outlet temperature is 100-120°C, the drying time is 60-90 minutes; the ratio of the circulating air volume to the sludge mass is 2-5m 3 / kg; the dry matter content in the additive is 1-3% of the dry weight of the sludge; the particle size of the dried sludge and biomass after crushing is controlled to be 1-2 mm, the mass ratio of dried sludge to biomass in the granulation step is 10:1-2, and the particle size after granulation is controlled to be 2-4 mm.

[0018] Furthermore, the porosity of the sludge gasification slag is 50-70%, the sludge gasification slag is used to prepare ceramsite, and the prepared ceramsite is used to adsorb refractory COD in water bodies in the advanced treatment section of sewage treatment.

[0019] Furthermore, the raw materials for preparing the ceramsite include the following parts by weight: 50 to 100 parts of sludge gasification slag, 10 to 30 parts of fly ash, 3 to 8 parts of adhesive, and 3 to 8 parts of water; the raw materials are mixed and granulated, and then aged, dried, steamed, and cooled to obtain the ceramsite of the present invention. The secondary removal rate of the ceramsite of the present invention for difficult-to-degrade COD is greater than 70%.

[0020] Beneficial effects of the present invention:

[0021] 1. The present invention adds modified carbon black to the circulating air, which can, on the one hand, dry the sludge at a higher temperature. On the other hand, the conductivity of the modified carbon black can eliminate static electricity generated at high temperatures, ensuring the safety of drying at high temperatures.

[0022] 2. The present invention adds modified zeolite powder to the circulating air, so that the odor generated during the sludge drying process can be adsorbed, which helps to ensure a good working environment and reduces the processing load of the deodorization equipment in the rear air outlet, which helps to save costs;

[0023] 3. The present invention adds modified carbon black and modified zeolite powder by circulating air atomization dispersion. Water vapor and water droplets can adsorb dust generated during the high-temperature drying process of sludge, thereby reducing the amount of dust generated in the system, contributing to operational safety and reducing the load on back-end dust removal equipment. At the same time, dust can be reused, contributing to resource conservation and comprehensive utilization.

[0024] 4. The present invention adds quicklime powder, which reacts with sludge with high moisture content, thereby promoting the improvement of sludge dewatering efficiency. In the process, calcium hydroxide powder is generated and releases heat, further promoting the improvement of sludge dewatering efficiency. At the same time, the calcium hydroxide formed in the air flow is also conducive to the adsorption of odor, helping to maintain a good working environment.

[0025] 5. The modified carbon black added in the drying process of the present invention can increase the porosity of the gasified slag and the calorific value of the combustible gas during the gasification stage. At the same time, the modified zeolite powder can solidify heavy metals during the gasification stage. In addition, the added quicklime powder can also play a role in sulfur fixation during the gasification process, which helps desulfurize the flue gas and has a positive effect on reducing flue gas treatment costs and protecting the environment. At the same time, the modification of carbon black and zeolite powder also plays a positive role in increasing the calorific value of the combustible gas in the subsequent sludge gasification.

[0026] 6. The sludge gasification slag of the present invention has a high porosity and realizes the solidification of heavy metals. It can be comprehensively utilized, such as compounding with garden soil, used as a building material, and prepared into granular ceramsite for COD adsorption in the deep treatment section of the plant, etc., realizing the reduction and resource utilization of sludge, which is conducive to resource conservation and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the process flow of the present invention;

[0028] Figure 2 It is a schematic flow chart of the sludge drying system of the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0030] like Figure 1-2As shown, the sludge (water content 60-80%) coming out of the filter press section of the sewage treatment plant is cut into strips by a strip cutter and then transported to a sludge dryer. The sludge dryer can be a mesh belt type sludge dryer. The sludge dryer is provided with a circulating air system. The circulating air system includes a heating device. The heating device includes a gas burner. The combustible gas purified by the gasification section is burned by the gas burner and the air is heated. The heated air is heated by the heat exchange device to heat the circulating air, so that the temperature of the circulating air after heat exchange reaches 150-200°C. The heated circulating air is sent to the sludge dryer to dry the sludge. The circulating air after drying the sludge is dusted by a dust removal device. The dust removal device can be a combination of a multi-stage cyclone separator + a pulse bag dust collector. The dust obtained by the dust removal device is collected and It can go to the granulation section, and the circulating air after dust removal by the dust removal equipment is condensed through the condensing equipment. The condensing equipment can be a shell and tube condenser, in which the cold medium such as cooling water can go through the tube side, and the circulating air goes through the shell side, so that the water vapor in the circulating air is condensed on the pipeline and discharged, thereby achieving the drying of the circulating air. The circulating air after drying is partially deodorized and discharged. Deodorization can be done by adsorption with activated carbon, and the remaining part is supplemented with fresh air and maintains the air volume required by the system to go to the heat exchange equipment for circulation. The heat exchange equipment can use a finned heat exchanger, etc.; in the process, the fresh air can use a burner to heat the air heat medium after heat exchange, and the other part of the air heat medium returns to the burner to preheat the fresh air added to the burner, thereby improving the energy utilization efficiency; the circulating air discharged after deodorization can also go to the waste heat boiler for further utilization before discharge.

[0031] A powder spraying system is provided at the front end of the inlet of the sludge dryer, and quicklime powder is sprayed into the sludge through the powder spraying system; the powder spraying system includes a silo, and the quicklime powder in the silo is transported to the powder silo through a conveyor, such as a screw conveyor, and a fan is provided at the lower outlet of the powder silo, which draws air through the fan and sprays the powder evenly on the top of the sludge through the nozzle; in the process of sludge drying, the initial moisture content of the sludge is relatively high, and by spraying quicklime powder, the quicklime powder reacts with part of the water and / or water vapor in the sludge during the drying process, which helps To improve the efficiency of sludge dewatering, it should be noted that since the powder spraying is set at the front end of the sludge dryer's inlet, after the powder spraying, the sludge passes through the strip cutter and enters the sludge dryer. The strip cutter also plays a mixing role in the process. On the one hand, it helps to improve the dewatering efficiency. On the other hand, since the sludge dryer is equipped with an upward countercurrent circulating air, the initial mixing can also effectively reduce the amount of dust in the system. The calcium hydroxide in the dust is also conducive to the adsorption of odor. A small amount of dust in the subsequent drying process is collected and can be sent to the granulation section for comprehensive utilization.

[0032] During the sludge dewatering process, additives are added to the sludge dryer through the additive adding system. The additive adding system adds additives from the bottom to the top of the sludge dryer. Among them, the additives in the additive adding system are transported to the sludge dryer together with the circulating air.

[0033] The additives of the present invention include modified carbon black and modified zeolite powder. The modified carbon black and modified zeolite powder are uniformly dispersed in water through a dispersing device. The dispersing device in the process can adopt a high-speed disperser. The dispersed additive suspension is sucked into the circulating air duct through the throat of the venturi tube on the circulating air duct. The moisture is vaporized due to the high-temperature circulating air, and the additive is also uniformly dispersed. The circulating air with the additive uniformly dispersed heats the sludge in the sludge dryer. On the one hand, the modified carbon black adheres to the surface of the sludge. Due to the moisture content of the sludge below the sludge dryer, the modified carbon black adheres to the surface of the sludge. The temperature is high while the temperature is low. The conductive effect of the modified carbon black can eliminate the static electricity generated during the sludge drying process to ensure the safety of high-temperature drying. On the other hand, the modified zeolite powder can partially adsorb the odor and volatile organic compounds in the sludge drying process, which helps to reduce the pressure of the back-end deodorization equipment, avoid the large-scale loss of nutrients and contribute to clean production. In addition, the water vapor added to the auxiliary agent suspension can also reduce the amount of dust generated during the high-temperature drying process, which helps to reduce the workload of the back-end dust removal equipment.

[0034] The moisture content of the sludge after drying by the sludge dryer is controlled at 10-20%. The dried sludge goes to the crushing stage and is crushed by the crusher. At the same time, the crusher crushes biomass, such as straw, and mixes the crushed straw with the crushed sludge through a mixer. The mixed material is granulated by granulating equipment, such as twin-screw extruder, and the granulated material goes to the sludge gasifier for gasification. During gasification in the sludge gasifier, the combustible gas generated is returned to the front-end sludge dryer for recycling, and the gasification slag and fly ash generated during the gasification process are comprehensively utilized.

[0035] During the gasification process, the quicklimestone added at the front end plays a role in fixing sulfur at high temperature, which helps to reduce the emission of sulfur in the flue gas during the sludge drying process and reduce the flue gas treatment cost. The added modified carbon black burns at high temperature to generate carbon dioxide. On the one hand, carbon dioxide helps to increase the porosity of the sludge gasification slag, and on the other hand, it can also increase the calorific value of the fuel gas. In addition, the added modified zeolite powder can also play a role in solidifying heavy metals, thereby making the sludge gasification slag obtained by the method of the present invention more convenient for resource utilization.

[0036] The sludge gasification slag and fly ash are comprehensively utilized, wherein the sludge gasification slag can be used to be compounded with garden planting soil. In the present invention, the sludge gasification slag has a high porosity, which is helpful to maintain soil moisture, and at the same time, heavy metals are solidified in the gasification slag, and there will be no heavy metal pollution in the soil; in addition, the sludge gasification slag can be mixed with fly ash, and granulated by adding an adhesive, such as sodium silicate, to produce granular ceramsite, which can be used to remove the difficult-to-degrade COD in the water body of the deep treatment section of the plant area, effectively ensure the effluent water quality, realize the replacement of activated carbon and the resource utilization of waste, reduce costs and be more environmentally friendly.

[0037] Example 1

[0038] This example is the preparation of modified carbon black and modified zeolite powder.

[0039] Preparation of modified carbon black:

[0040] Take carbon black (particle size 20-100 nm) and concentrated sulfuric acid, the mass volume ratio of carbon black to concentrated sulfuric acid (kg / L) is 1-5:10, under the stirring intensity of 60-120 rpm, reflux at 60-80 ° C for 2-4 hours, filter with a sand core funnel, wash with water, and dry to obtain pretreated carbon black.

[0041] Take pretreated carbon black and anhydrous ethanol, the mass volume ratio of carbon black to anhydrous ethanol (kg / L) is 1-5:10, and 3-aminopropyltriethoxysilane (APTES) is added at a stirring intensity of 60-120 rpm, and APTES is 1-5% of the mass of carbon black. Acetic acid is added to adjust the pH of the mixed solution to 4-5, and the mixture is stirred at 60°C for 6-12 hours. After the reaction is completed, the modified carbon black of the present invention is obtained by filtration, separation, water washing, and drying.

[0042] Preparation of modified zeolite powder:

[0043] Microporous zeolite is taken and crushed. The particle size of the crushed zeolite powder is 50-100 μm. Zeolite powder and anhydrous ethanol are taken. The mass volume ratio (kg / L) of zeolite powder to anhydrous ethanol is 1-5:10. 3-aminopropyltriethoxysilane (APTES) is added at a stirring intensity of 60-120 rpm. The APTES is 1-5% of the mass of the zeolite powder. Acetic acid is added to adjust the pH of the mixed solution to 4-5. The mixture is stirred at 80° C. for 6-12 hours. After the reaction is completed, the mixture is filtered, separated, washed with water, and dried to obtain the modified zeolite powder of the present invention.

[0044] Preparation of modified carbon black / modified zeolite powder suspension:

[0045] Take the modified carbon black and modified zeolite powder prepared above, with a mass ratio of modified carbon black to modified zeolite powder of 1 to 5:1, and set aside; add the modified carbon black and modified zeolite powder to water, with a mass ratio of the two to the volume of water (kg / L) of 1 to 5:10, and use ultrasound for pre-dispersion (200W, 20kHz) for 20 to 30 minutes.

[0046] After pre-dispersion is completed, water is added to the pre-dispersed dispersion and further dispersed using a high-speed disperser. Acetic acid is added during the process to adjust the pH of the system to 6-7. After adding water, the mass fraction of modified carbon black and modified zeolite powder is 1-3%, the stirring speed is 1000-2000 rpm, and the dispersion time is 10-30 minutes.

[0047] The modified carbon black / modified zeolite powder suspension prepared above is ready for use during production and is stirred at a stirring intensity of 300-400 rpm while being used.

[0048] During the preparation of the modified carbon black / modified zeolite powder suspension, a non-ionic dispersant polyvinylpyrrolidone (PVP K30) can be added. The amount of the dispersant added is 0.5-1% of the total mass of the dispersion. During the preparation process, the dispersant is first added, stirred evenly, and then the pre-dispersed dispersion is added. The suspension also adopts the principle of ready-to-use and is stirred during use at a stirring intensity of 300-400 rpm.

[0049] The modified carbon black / modified zeolite powder suspension prepared in this embodiment has -NH3 + The groups are more conducive to combining with the sludge in the process of the present invention, thereby enhancing the conductivity between the sludge, thereby eliminating a large amount of static electricity in the sludge drying process and playing an anti-static role.

[0050] Example 2

[0051] This embodiment relates to the process flow of sludge reduction of the present invention.

[0052] The sludge (water content 60-80%) discharged from the filter press section is transported to the sludge dryer for drying. In this embodiment, the sludge dryer is a belt sludge dryer, and a sludge strip cutter is integrated at the inlet of the belt sludge dryer. This equipment is an existing mature equipment.

[0053] Before the activated sludge enters the sludge strip cutter, powder is sprayed into the sludge through the powder spraying system. The powder is quicklime powder (200-500 mesh), and the addition amount is 1-5% of the sludge mass. After spraying, the sludge is cut into strips in the sludge strip cutter. The strip cutting process can promote the mixing of sludge and quicklime powder.

[0054] The chopped sludge enters the sludge dryer and is dried in the sludge dryer. The circulating air inlet temperature is 150-200℃, the circulating air outlet temperature is 100-120℃, and the ratio of circulating air volume to sludge is 2-5m 3 / kg, drying time is 60-90min, the dry weight of the additive is 3-5% of the dry weight of the sludge; the moisture content of the dried sludge is 10-20%.

[0055] The dried sludge is crushed by a crusher, and the particle size of the sludge after crushing is 1-2 mm; at the same time, the biomass straw is crushed by the crusher, and the particle size after crushing is 1-2 mm. The sludge and straw are mixed in a mixer at a ratio of 10:1-2, and after mixing, they are granulated by a granulator, and the particle size after granulation is controlled to be 2-4 mm.

[0056] The granulated sludge biomass is transported to a sludge gasifier for gasification. The sludge gasifier is an existing device and the process is relatively mature, so it will not be described in detail. However, it should be noted that the present invention does not require additional limestone to be added during the sludge gasification process.

[0057] The combustible gas produced by sludge gasification is purified and returned to the sludge drying stage for comprehensive utilization. During the process, the combustion of combustible gas requires the addition of a portion of fresh air. The hot air medium after combustion exchanges heat with the circulating air. The air medium after heat exchange is mixed with a portion of combustible gas and fresh air and then burned again to realize the cycle.

[0058] The dust generated by the dust removal equipment during the drying process is directly sent to the granulation section and used as sludge. Some odor will inevitably be generated during the drying process. In order to avoid continuous circulation in the system, it needs to be discharged and replenished in a quantitative manner. After the circulating gas is condensed, 5-10% of the total circulating gas is discharged, and then it is replenished with air medium after combusting combustible gas and undergoing heat exchange.

[0059] Under the premise of ensuring the same sludge-to-biomass ratio, by adopting the powder addition system and the additive addition system of the present invention, the calorific value of the combustible gas can be increased by about 10 to 15%. The increase in calorific value comes from the combined effect of the addition of carbon black and the modification of carbon black and zeolite powder, involving an increase in the carbon monoxide and hydrogen content; the porosity of the sludge gasification slag can be increased by about 10 to 20%. The increase in the porosity of the gasification slag comes from the combined effect of the addition of zeolite powder, the combustion of carbon black, the decomposition of calcium hydroxide, etc.; and during the sludge drying process, the workshop environment is significantly improved, and a heavy metal leaching experiment (HJ / T299-2007) is carried out, which complies with the relevant environmental standards (GB5085.3-2007).

[0060] Example 3

[0061] In this embodiment, sludge gasification residue is utilized.

[0062] A batch of sludge gasification slag according to Example 2 of the present invention was taken and tested to have a porosity of 68.2%. The sludge gasification slag was used to prepare ceramsite.

[0063] Collect the sludge gasification residue and fly ash generated during the combustible gas purification (dust removal equipment), crush the sludge gasification residue, and then pass it through a 100-mesh sieve.

[0064] Take 80 parts of sludge gasification slag, 20 parts of fly ash, and 5 parts of bonding sodium silicate, mix them evenly, add 5 parts of water and stir into a paste, and then make spherical ceramsite embryos with a particle size of 10mm±1mm.

[0065] The prepared ceramsite embryo was aged at room temperature for 6 hours, placed in a drying oven for drying, and then moved into a standard constant temperature and humidity curing box with a relative humidity of 90%, steamed at 80° C. for 12 hours, and naturally cooled to obtain the ceramsite of the present invention.

[0066] According to tests, the porosity of the ceramsite of the present invention is 56.3%, the water absorption rate in 1 hour is 32.4%, and the compressive strength is 22.6 MPa.

[0067] The ceramsite of the present invention is used for removing the refractory COD in the water body of the deep treatment section in the sewage treatment process.

[0068] The influent of the deep treatment section of the sewage treatment plant was taken, and the COD content in the influent was measured to be 22.3 mg / L. 1 L of the influent was taken, and 5 g of the ceramsite of the present invention was added, and stirred at room temperature for 30 minutes. The COD content in the water was measured to be reduced to 11.7 mg / L, and the removal rate was 47.5%. The adsorbed water was filtered to remove the ceramsite and then 5 g of new ceramsite was added. The water was stirred at room temperature for 30 minutes. The COD content in the water was measured to be reduced to 5.8 mg / L, and the removal rate was 74.0%. The COD effluent content in the obtained water was reduced to 5.8 mg / L, which is nearly 3 times higher than the 10-15 mg / L of the activated coke adsorption tank in the plant, and is more convenient for use in sewage treatment.

[0069] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, any technical solution that is the same or similar to that of the present application falls within the scope of protection of the present invention.

Claims

1. A method for reducing and recycling municipal sludge, characterized by: The method comprises the steps of drying and gasification, wherein the drying comprises a circulating air system, a powder spraying system and an additive adding system; In the circulating air system, the circulating air is heated to dry the sludge at high temperature. The used circulating air is dust-removed, condensed, and heated again to form a cycle, and the circulating air and the sludge are subjected to countercurrent heat exchange. In the powder spraying system, powder is sprayed before the inlet of the sludge dryer. The powder is quicklime powder. The sludge after the powder spraying is cut into strips by the sludge cutter and then enters the sludge dryer for high-temperature drying. The additive adding system is arranged in dependence on the circulating air system; A venturi tube is installed on the conveying pipe of the heated circulating air, and the venturi tube cooperates with the additive adding system; the additives include modified carbon black with a positive charge on the surface and modified zeolite powder with a positive charge on the surface. The modified carbon black and modified zeolite powder are evenly dispersed in water and then sucked into the conveying pipe of the circulating air through the venturi tube and evenly dispersed; Sludge gasification utilizes the powder and additives added in the sludge drying step to obtain combustible gas, gasification slag and fly ash; the combustible gas produced by sludge gasification is returned to the sludge drying step for utilization, and the gasification slag and fly ash produced by sludge gasification are comprehensively utilized.

2. The method for reducing and recycling municipal sludge according to claim 1, characterized in that: In the circulating air system, the combustible gas returned from the sludge gasification step is used as a heat source for heating the circulating air.

3. The method for reducing and recycling municipal sludge according to claim 2, characterized in that: In the circulating air system, part of the condensed circulating air is deodorized and then discharged, and is supplemented with fresh air before being heated again; the combustible gas returned from the gasification step heats the air medium, and the heated air medium exchanges heat with the circulating air. Part of the air medium after heat exchange is used as supplementary fresh air for the circulating air, and part of it is mixed and preheated with the fresh air required for combustion of the combustible gas.

4. The method for reducing and recycling municipal sludge according to claim 1, characterized in that: The powder spraying system includes a silo, the powder in the silo is continuously transported to the powder silo, a fan is set at the outlet of the powder silo, and the powder is evenly sprayed above the sludge through a nozzle using the air transported by the fan as a carrier.

5. The method for reducing and recycling municipal sludge according to claim 1, characterized in that: In the auxiliary agent adding system, the modified carbon black is prepared by pre-oxidizing carbon black with concentrated sulfuric acid and then grafting with an aminosilane coupling agent; the modified zeolite powder is prepared by grafting zeolite powder with an aminosilane coupling agent.

6. The method for reducing and recycling municipal sludge according to claim 1, characterized in that: The method further includes crushing and granulating steps. The crushing step includes crushing the dried sludge and the biomass, mixing the crushed sludge and the biomass, and then granulating.

7. The method for reducing and recycling municipal sludge according to claim 6, characterized in that: The dust generated by dust removal in the circulating air system is sent to the granulation step for granulation.

8. The method for reducing and recycling municipal sludge according to claim 6, characterized in that: The moisture content of the sludge feed in the drying step is 60-80%, and the moisture content of the sludge discharge is 10-20%; the circulating air inlet temperature is 150-200°C, the circulating air outlet temperature is 100-120°C, and the drying time is 60-90 minutes; the ratio of circulating air volume to sludge mass is 2-5m 3 / kg; the dry matter content in the additive is 1-3% of the dry weight of the sludge; the particle size of the dried sludge and biomass after crushing is controlled to be 1-2 mm, the mass ratio of dried sludge to biomass in the granulation step is 10:1-2, and the particle size after granulation is controlled to be 2-4 mm.

9. The method for reducing and recycling municipal sludge according to claim 1, characterized in that: The porosity of sludge gasification residue is 50~70%. The sludge gasification residue is used to prepare ceramsite, and the prepared ceramsite is used to adsorb difficult-to-degrade COD in the water body of the deep treatment section of sewage treatment.

10. The method for reducing and recycling municipal sludge according to claim 9, characterized in that: The raw materials for preparing the ceramsite include the following parts by weight: 50-100 parts of sludge gasification slag, 10-30 parts of fly ash, 3-8 parts of adhesive, and 3-8 parts of water; the raw materials are mixed and granulated, and then aged, dried, steamed, and cooled to obtain the ceramsite. The secondary removal rate of the ceramsite for refractory COD is greater than 70%.

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