Municipal sludge reduction and resource utilization method

Abstract

The invention relates to the technical field of sludge reduction and resource utilization, in particular to a municipal sludge reduction and resource utilization method. According to the method disclosed by the invention, a sludge reduction technical means of performing high-temperature drying and crushing on the sludge, then performing combined granulation with biomass and performing gasification is adopted, in the high-temperature drying process of the sludge, through a powder adding system and an auxiliary adding system, the stability and the safety in the sludge drying process are ensured, the drying efficiency is improved, and the energy consumption is reduced. The system can be comprehensively utilized through the circulating air system, so that energy is saved and consumption is reduced; in addition, through combined granulation with biomass, biomass solid waste treatment is realized, and the heat value of sludge gasification is synergistically improved; in addition, the powder and auxiliaries added in the sludge drying process can also play an important role in improving the porosity, increasing the heat value, fixing sulfur, fixing heavy metal and the like in the sludge gasification stage, and the obtained sludge gasification slag has wide application prospects in the fields of garden planting, building materials, sewage treatment and the like.

Description

Technical Field

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

[0002] Activated sludge is the general term for microbial communities and the organic and inorganic substances they adhere to. A large amount of excess sludge is generated during the process of treating sewage by biological methods. Since the excess sludge contains a large amount of organic substances, it is a reusable resource. If not treated in time and stacked randomly, it will cause pollutants such as nitrogen and phosphorus, heavy metals, and harmful chemicals to seep out, polluting the land, rivers, lakes, and groundwater, and also causing harm to the environment.

[0003] The treatment and disposal of activated sludge are particularly important. Since the water content in activated sludge is relatively high, reaching more than 98%, necessary reduction during the treatment and disposal process is crucial. Existing methods such as sludge dewatering, drying, and gasification / incineration are used for sludge reduction, achieving sludge reduction and resource utilization; with the development of sludge treatment technologies, existing low-temperature drying has become the mainstream. On the one hand, low-temperature drying has higher safety, and on the other hand, it can effectively retain the nutrients in the sludge, but correspondingly, it will bring about a reduction in drying efficiency. In the current situation of increasing sludge production, it is difficult to carry out efficient treatment; on the other hand, the utilization rate of existing sludge gasification products is relatively low, generally used as garden planting soil and building materials, resulting in lower added value and restricting the further utilization of sludge gasification slag.

[0004] Therefore, the present invention proposes a method for sludge reduction and resource utilization, which comprehensively treats and utilizes sludge from aspects such as improving the efficiency of sludge reduction, increasing the calorific value of gasification, and resource utilization of gasification slag, so as to achieve the purpose of high-efficiency, safe, and 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 municipal sludge reduction and resource utilization to solve the problems of low treatment efficiency of existing low-temperature drying methods and large limitations in resource utilization after sludge reduction.

[0006] To achieve the above purpose, the present invention adopts the following technical scheme: A method for municipal sludge reduction and resource utilization, including the steps of drying and gasification. The drying includes a circulating air system, a powder spraying system, and an additive adding system;

[0007] In the circulating air system, the circulating air is heated and then used for high-temperature drying of the sludge. The used circulating air forms a cycle after dust removal, condensation, and re-heating, and the circulating air exchanges heat with the sludge in a countercurrent manner;

[0008] In the described powder spraying system, powder is sprayed before the inlet of the sludge dryer. The powder is quicklime powder. After the powder is sprayed, the sludge enters the sludge cutting machine for cutting and then enters the sludge dryer for high-temperature drying.

[0009] The described auxiliary agent adding system is arranged attached to the circulating air system; a Venturi tube is provided on the conveying pipeline of the circulating air after heating up, and the Venturi tube cooperates with the auxiliary agent adding system; the auxiliary agents include modified carbon black with a positive charge on the surface and modified zeolite powder. After the modified carbon black and the modified zeolite powder are evenly dispersed in water, they are inhaled into the conveying pipeline of the circulating air through the Venturi tube and evenly dispersed.

[0010] The described sludge gasification utilizes the powder and auxiliary agents added in the sludge drying step, and generates combustible gas, gasification slag and fly ash; the combustible gas generated by the sludge gasification is returned to the sludge drying step for utilization, and the gasification slag and fly ash generated by the sludge gasification are comprehensively utilized.

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

[0012] Further, in the described circulating air system, part of the condensed circulating air is deodorized and then discharged, and fresh air is supplemented before reheating; the combustible gas returned from the gasification step heats the air medium, the heated air medium exchanges heat with the circulating air, part of the heat-exchanged air medium is used as the supplementary fresh air for the circulating air, and part of it is mixed and preheated with the fresh air required for the combustion of the combustible gas.

[0013] Further, the described powder spraying system includes a silo, the powder in the silo is continuously conveyed to a powder bin, a fan is arranged at the outlet of the powder bin, and the powder is evenly sprayed above the sludge with the air conveyed by the fan as the carrier through a nozzle.

[0014] Further, in the described auxiliary agent adding system, the modified carbon black is made by pre-oxidizing carbon black with concentrated sulfuric acid and then grafting with an amino silane coupling agent; the modified zeolite powder is made by grafting zeolite powder with an amino silane coupling agent.

[0015] Further, it also includes the steps of crushing and granulating. The crushing step includes the crushing of the dried sludge and the crushing of biomass, the crushed sludge and biomass are mixed, and then granulated.

[0016] Further, the dust generated by dust removal in the described circulating air system goes to the granulating step for granulation.

[0017] Further, 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 inlet air temperature of the circulating air is 150-200 °C, the outlet air temperature of the circulating air is 100-120 °C, and the drying time is 60-90 min; the ratio of the circulating air volume to the sludge mass is 2-5 m 3 / kg; the dry matter content in the auxiliary agent 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, and the mass ratio of the dried sludge to the biomass in the granulation step is 10:1-2, and the particle size after granulation is controlled to be 2-4 mm.

[0018] Further, the porosity of the sludge gasification slag is 50-70%, and the sludge gasification slag is used for the preparation of ceramsite, and the prepared ceramsite is used for the adsorption of refractory COD in the water body of the advanced wastewater treatment section.

[0019] Further, the raw materials for the preparation of the ceramsite include 50-100 parts by weight of sludge gasification slag, 10-30 parts of fly ash, 3-8 parts of binder, and 3-8 parts of water; after mixing the raw materials, granulating, aging, drying, steam curing, and cooling, the ceramsite of the present invention can be obtained. The secondary removal rate of refractory COD by the ceramsite of the present invention is >70%.

[0020] The beneficial effects of the present invention:

[0021] 1. By adding modified carbon black to the circulating air, on the one hand, the sludge can be dried at a relatively high temperature, and on the other hand, the static electricity generated at high temperature can be eliminated by the conductivity of the modified carbon black, ensuring the safety of drying at high temperature;

[0022] 2. By adding modified zeolite powder to the circulating air, the odor generated during the sludge drying process can be adsorbed, which helps to ensure a good working environment and reduce the treatment load of the odor removal equipment in the rear-end outlet air, helping to save costs;

[0023] 3. The modified carbon black and modified zeolite powder are added by means of atomization and dispersion of the circulating air. Water vapor and water droplets can adsorb the dust generated during the high-temperature drying process of the sludge, thereby reducing the dust generation amount of the system, helping to ensure operation safety and reducing the load of the rear-end dust removal equipment. At the same time, the dust can be reused, helping to save and comprehensively utilize resources;

[0024] 4. By adding quicklime powder, the quicklime powder acts on the high-moisture-content sludge, which helps to improve the sludge dehydration efficiency, and calcium hydroxide powder is generated and heat is released during the process, further promoting the improvement of the sludge dehydration efficiency. At the same time, the calcium hydroxide formed in the air flow is also beneficial to the adsorption of odor, helping to maintain a good working environment;

[0025] 5. The modified carbon black added in the dry chemical section of the present invention can increase the porosity of the gasification slag and improve 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 in the desulfurization of flue gas and has a positive effect on reducing the flue gas treatment cost and environmental protection. At the same time, the modification of carbon black and zeolite powder also plays a positive role in improving 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, and can be comprehensively utilized. For example, it can be compounded with garden soil, used as building materials, and prepared into granular ceramsite for the adsorption of COD in the in-plant deep treatment section, etc., realizing the reduction and resource utilization of sludge, and contributing to resource conservation and environmental protection. Brief Description of the Drawings

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

[0028] Figure 2 is a schematic process flow diagram of the sludge drying system of the present invention. Detailed Embodiments

[0029] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention.

[0030] Such as Figure 1-2As shown in the figure, the sludge (with a moisture content of 60-80%) from the pressure filtration section of the sewage treatment plant is sent to the sludge dryer after being cut into strips by a slitting machine. The sludge dryer can be a belt-type sludge dryer. The sludge dryer is equipped with a circulating air system, and the circulating air system includes a heating device. The heating device includes a gas burner. The combustible gas purified in the gasification section is burned by the gas burner to heat the air. The heated air exchanges heat with the circulating air through a heat exchange device to raise the temperature of the circulating air, so that the temperature of the circulating air after heat exchange reaches 150-200°C. The circulating air after temperature rise goes to the sludge dryer to dry the sludge. The circulating air after drying the sludge is dust-removed by a dust-removal device. The dust-removal device can be a combination of a multi-stage cyclone separator and a pulse bag filter. The dust collected by the dust-removal device can go to the granulation section. The circulating air after being dust-removed by the dust-removal device is condensed by a condensation device. The condensation device can be a shell-and-tube condenser. Among them, the cold medium such as cooling water can flow through the tube side, and the circulating air flows through the shell side, so that the water vapor in the circulating air condenses on the pipeline and is discharged, realizing the drying of the circulating air. Part of the dried circulating air is deodorized and then discharged. Deodorization can be carried out by adsorption with activated carbon. The remaining part is supplemented with fresh air and maintains the required air volume of the system to go to the heat exchange device for circulation. The heat exchange device can adopt a finned heat exchanger, etc.; during the process, the fresh air can heat the air heat medium after being heated by the burner. Another part of the air heat medium returns to the burner to preheat the fresh air supplemented to the burner, improving the energy utilization efficiency; the circulating air discharged after deodorization can also go to the waste heat boiler for further utilization and then be discharged.

[0031] A powder spraying system is arranged 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. The quicklime powder in the silo is transported to a powder bin through a conveyor, such as a screw conveyor, etc. A blower is arranged at the lower outlet of the powder bin. The blower extracts air and sprays the powder evenly above the sludge through a nozzle; during the sludge drying process, the initial moisture content of the sludge is relatively high. By spraying quicklime powder, during the drying process, the quicklime powder reacts with some water and / or water vapor in the sludge, which helps to improve the sludge dehydration efficiency. It should be noted that since the powder spraying is arranged at the front end of the inlet of the sludge dryer, after the powder is sprayed, the sludge passes through the slitting machine and then enters the sludge dryer. The slitting machine also plays a role in mixing during the process. On the one hand, it helps to improve the dehydration efficiency. On the other hand, since there is an upward countercurrent circulating air in the sludge dryer, the preliminary mixing can also effectively reduce the dust volume of the system. Calcium hydroxide in the dust is also beneficial to the adsorption of odors. A small amount of dust in the subsequent drying process is collected and can go to the granulation section for comprehensive utilization.

[0032] During the sludge dewatering process, additives are added to the sludge dryer through an additive dosing system. The additive dosing system adds the additives from the bottom to the top of the sludge dryer. Among them, the additives in the additive dosing system are transported to the sludge dryer together by being carried by 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 dispersion device. During the process, a high-speed disperser can be used as the dispersion device. 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 at the same time, the additives are also uniformly dispersed. The circulating air with uniformly dispersed additives heats the sludge in the sludge dryer. On the one hand, the modified carbon black adheres to the surface of the sludge. Since the moisture content of the sludge at the bottom of the sludge dryer is relatively low and the temperature is relatively high, the conductive effect of the modified carbon black can eliminate the static electricity generated during the sludge drying process, ensuring the safety of high-temperature drying. On the other hand, the modified zeolite powder can partially adsorb the odors and volatile organic compounds during the sludge drying process, helping to reduce the pressure on the subsequent deodorization equipment, avoiding the large loss of nutrients, and contributing to cleaner production. In addition, the partial water vapor supplemented in the additive suspension can also play a role in reducing the amount of dust generated during the high-temperature drying process, helping to reduce the working load of the subsequent dust removal equipment.

[0034] The sludge dried by the sludge dryer has a moisture content controlled at 10-20%. The dried sludge goes to the crushing stage and is crushed by a crusher. At the same time, biomass such as straw is crushed by the crusher. The crushed straw and the crushed sludge are mixed by a mixer. The mixed material is granulated by a granulating device such as a twin-screw extruder. The granulated material goes to a sludge gasifier for gasification. When gasifying 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 raw limestone added at the front end plays a role in fixing sulfur at high temperature, helping to reduce the sulfur emission in the flue gas during the sludge drying process and reducing the flue gas treatment cost. The added modified carbon black burns to generate carbon dioxide at high temperature. On the one hand, the 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 combustible gas. In addition, the added modified zeolite powder can also play a role in solidifying heavy metals, 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. The sludge gasification slag can be used for compounding with garden planting soil. In the present invention, the sludge gasification slag has a high porosity, which helps to maintain soil moisture, and at the same time, heavy metals are solidified in the gasification slag, preventing heavy metal pollution of the soil. In addition, the sludge gasification slag and fly ash can be mixed, and by adding a binder such as sodium silicate and granulating, granular ceramsite can be made. The granular ceramsite can remove the refractory COD in the water body of the deep treatment section of the plant area, effectively ensuring the effluent quality, realizing the replacement of activated carbon and the resource utilization of waste, reducing costs and being more environmentally friendly.

[0037] Example 1

[0038] This example is for 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 (kg / L) of carbon black to concentrated sulfuric acid is 1 - 5:10. Under a stirring intensity of 60 - 120 rpm, reflux at 60 - 80 °C for 2 - 4 h, filter with a sintered glass funnel, wash with water, and dry to obtain pretreated carbon black.

[0041] Take the pretreated carbon black and absolute ethanol. The mass - volume ratio (kg / L) of carbon black to absolute ethanol is 1 - 5:10. Under a stirring intensity of 60 - 120 rpm, add 3 - aminopropyltriethoxysilane (APTES), where APTES is 1 - 5% of the mass of carbon black. Add acetic acid to adjust the pH of the mixed solution to 4 - 5, and stir - react at 60 °C for 6 - 12 h. After the reaction ends, filter and separate, wash with water, and dry to obtain the modified carbon black of the present invention.

[0042] Preparation of modified zeolite powder:

[0043] Take microporous zeolite, crush it, and the particle size of the crushed zeolite powder is 50 - 100 μm. Take the zeolite powder and absolute ethanol. The mass - volume ratio (kg / L) of zeolite powder to absolute ethanol is 1 - 5:10. Under a stirring intensity of 60 - 120 rpm, add 3 - aminopropyltriethoxysilane (APTES), where APTES is 1 - 5% of the mass of zeolite powder. Add acetic acid to adjust the pH of the mixed solution to 4 - 5, and stir - react at 80 °C for 6 - 12 h. After the reaction ends, filter and separate, wash with water, and dry 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 the mass ratio of modified carbon black to modified zeolite powder being 1 - 5:1, and set aside. Add the above-mentioned modified carbon black and modified zeolite powder to water, with the mass ratio of the two to the volume of water (kg / L) being 1 - 5:10, and perform pre-dispersion using ultrasonic waves (200W, 20kHz), with a dispersion time of 20 - 30 min.

[0046] After the pre-dispersion is completed, add water to the pre-dispersed dispersion liquid and further disperse it using a high-speed disperser. During the process, add acetic acid to adjust the pH of the system to 6 - 7; after adding water, make the mass fraction of the modified carbon black and modified zeolite powder be 1 - 3%, with a stirring speed of 1000 - 2000 rpm and a dispersion time of 10 - 30 min.

[0047] The prepared modified carbon black / modified zeolite powder suspension is prepared and used immediately in production, and is stirred while in use, with a stirring intensity of 300 - 400 rpm.

[0048] During the preparation of the modified carbon black / modified zeolite powder suspension, a non-ionic dispersant polyvinylpyrrolidone (PVP K30) can also be added. The addition amount of the dispersant is 0.5 - 1% of the total mass of the dispersion liquid. Add the dispersant first during the preparation process, stir evenly, and then add the pre-dispersed dispersion liquid; this suspension also follows the principle of being prepared and used immediately, and is stirred while in use, with a stirring intensity of 300 - 400 rpm.

[0049] For the modified carbon black / modified zeolite powder suspension prepared in this example, due to the introduction of -NH 3 + groups, in the process of this invention, it is more conducive to combining with the sludge, enhancing the conductivity between the sludge, thereby eliminating a large amount of static electricity during the sludge drying process and playing an anti-static role.

[0050] Example 2

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

[0052] The sludge discharged from the pressure filtration section (with a moisture content of 60 - 80%) is transported to the sludge dryer for drying. In this example, a belt-type sludge dryer is selected for the sludge dryer, and a sludge cutting machine is integrally arranged at the inlet of the belt-type sludge dryer. This equipment is an existing mature equipment.

[0053] Before the activated sludge enters the sludge cutting machine, spray powder onto the sludge through a powder spraying system. The powder is quicklime powder (200 - 500 mesh), and the addition amount is 1 - 5% of the mass of the sludge. The sludge after spraying is cut in the sludge cutting machine, and the cutting process can promote the mixing of the sludge and quicklime powder.

[0054] The shredded sludge enters the sludge dryer and is dried therein. The inlet temperature of the circulating air is 150 - 200 °C, and the outlet temperature of the circulating air is 100 - 120 °C. The ratio of the circulating air volume to the sludge is 2 - 5 m 3 / kg. The drying time is 60 - 90 min, and the additive is added at a dry weight of 3 - 5% of the dry weight of the sludge. The water content of the dried sludge obtained is 10 - 20%.

[0055] The dried sludge is pulverized using a pulverizer, and the particle size of the pulverized sludge is 1 - 2 mm. At the same time, the biomass straw is pulverized using a pulverizer, and the particle size after pulverization is 1 - 2 mm. The sludge and the straw are mixed in a mixer according to a ratio of 10:1 - 2, and after mixing, granulation is carried out using 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 elaborated here. However, it should be noted that no additional limestone needs to be added during the sludge gasification process in the present invention.

[0057] The combustible gas generated by sludge gasification is purified and returned to the sludge drying stage for comprehensive utilization. During the process, a part of fresh air needs to be supplemented for the combustion of the combustible gas. The hot air medium after combustion exchanges heat with the circulating air, and after the heat-exchanged air medium is mixed with a part of the combustible gas and fresh air, combustion is carried out again to achieve circulation.

[0058] The dust generated by the dust removal equipment during the drying process directly goes to the granulation section and is used as sludge. During the drying process, some odors will inevitably be generated. In order to avoid continuous circulation in the system, it needs to be discharged quantitatively and supplemented quantitatively. 5 - 10% of the total circulating gas volume is discharged after the circulating gas is condensed, and then it is supplemented with the air medium after heat exchange by the combustion of the combustible gas.

[0059] On the premise of ensuring the same sludge - biomass ratio, by adopting the powder additive system and the additive system of the present invention, the calorific value of the combustible gas can be increased by about 10 - 15%. The increase in calorific value comes from the addition of carbon black and the combined action of the modification of carbon black and zeolite powder, involving an increase in the content of carbon monoxide and hydrogen. The porosity of the sludge gasification slag can be increased by about 10 - 20%. The increase in the porosity of the gasification slag comes from the combined action of the addition of zeolite powder, the combustion of carbon black, and the decomposition of calcium hydroxide. Moreover, during the sludge drying process, the workshop environment is significantly improved. Leaching experiments (HJ / T 299 - 2007) are carried out on heavy metals, and they all meet the relevant environmental standards (GB 5085.3 - 2007).

[0060] Example 3

[0061] In this example, the sludge gasification slag is utilized.

[0062] Take a certain batch of sludge gasification slag from Example 2 of the present invention. After testing, the porosity is 68.2%. This sludge gasification slag is used for the preparation of ceramsite.

[0063] Collect the fly ash generated during the purification (dust removal equipment) of sludge gasification slag and combustible gas. Crush the sludge gasification slag 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 sodium silicate as a binder. After mixing evenly, add 5 parts of water and stir into a paste, and then form spherical ceramsite embryos. The particle size of the ceramsite embryos is 10 mm ± 1 mm.

[0065] Age the prepared ceramsite embryos at room temperature for 6 h, put them into a drying oven for drying, and then transfer them to a standard constant temperature and humidity curing box with a relative humidity of 90%. Steam-cure at 80 °C for 12 h, and then obtain the ceramsite of the present invention after natural cooling.

[0066] After testing, the porosity of the ceramsite of the present invention reaches 56.3%, the 1-h water absorption rate is 32.4%, and the compressive strength is 22.6 Mpa.

[0067] Use the ceramsite of the present invention for the removal of refractory COD in the water body in the advanced treatment section of the sewage treatment process.

[0068] Take the influent water from the advanced treatment section of the sewage treatment plant. After measuring, the COD in the influent water is 22.3 mg / L. Take 1 L of the influent water and add 5 g of the ceramsite of the present invention. Stir at room temperature for 30 min. After measurement, the content of COD in the water body drops to 11.7 mg / L, and the removal rate is 47.5%; Filter the adsorbed water body, remove the ceramsite and then add 5 g of new ceramsite. Stir at room temperature for 30 min. After measurement, the content of COD in the water body drops to 5.8 mg / L, and the removal rate is 74.0%; The effluent content of COD in the obtained water body drops to 5.8 mg / L. Compared with the 10 - 15 mg / L in the activated coke adsorption tank in the plant, the effluent effect is improved by nearly 3 times, which is more convenient for use in sewage treatment.

[0069] The present invention is not limited to the above best implementation mode. Anyone can obtain various other forms of products under the inspiration of the present invention. However, no matter what changes are made in its shape or structure, as long as it has a technical solution identical or similar to the present application, it falls within the protection scope of the present invention.

Claims

1. A method for reducing municipal sludge and recycling it, characterized in that: 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, and the used circulating air is dedusted, condensed and heated again to form a cycle, and the circulating air and the sludge are countercurrently exchanged for heat; In the powder spraying system, powder is sprayed before the inlet of the sludge dryer, and the powder is quicklime powder. After the sludge is sprayed with powder, it 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 arranged on the conveying pipeline of the circulating air after heating, and the venturi tube cooperates with the additive adding system; the additives include modified carbon black and modified zeolite powder with positive charges on the surface, and the modified carbon black and modified zeolite powder are evenly dispersed in water and then sucked into the conveying pipeline of the circulating air through the venturi tube and evenly dispersed; 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.

2. A 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. A method for reducing and recycling municipal sludge according to claim 2, characterized in that: In the circulating air system, part of the circulating air after condensation 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, and 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 comprises a silo, the powder in the silo is continuously transported to the powder silo, a fan is arranged 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 also includes crushing and granulation steps. The crushing step includes crushing the dried sludge and the biomass. The crushed sludge and the biomass are mixed and then granulated.

7. A 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. A 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 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 1-2mm, the mass ratio of the dried sludge to the biomass in the granulation step is 10:1-2, and the particle size after granulation is controlled to be 2-4mm.

9. The method for reducing and recycling municipal sludge according to claim 1, characterized in that: The porosity of the sludge gasification slag is 50-70%. The sludge gasification slag is used for preparing ceramsite, and the prepared ceramsite is used for adsorbing the refractory COD in the water body of the deep treatment section of sewage treatment.

10. A method for reducing and recycling municipal sludge according to claim 9, characterized in that: The raw materials for preparing the ceramsite include the following weight parts: 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 of the present invention. The secondary removal rate of the ceramsite of the present invention for difficult-to-degrade COD is greater than 70%.

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