A municipal sludge pyrolysis carbonization treatment system and treatment process

Abstract

The invention discloses a municipal sludge pyrolysis carbonization treatment system and a treatment process. The system comprises a sludge treatment device, a flue gas treatment device, a pyrolysis gas purification device, a heating device, a blower, a heat exchanger and an air mixing tank. After the wet sludge is squeezed by a vertical filter press and dried in an internal heating rotary drying kiln, it is sent to a vertical pyrolysis machine for pyrolysis and carbonization. In addition to the sludge-based biochar product output system, the product pyrolysis gas enters a spray tower for separation and purification, and the purified combustible gas is all sent to a burner as a recycled heat source. The purified and separated heavy components are mixed with the sludge for secondary pyrolysis. The excess flue gas generated by the entire system is treated and discharged in compliance with the standards. The system changes the properties of the sludge through chemical reactions, meets the final treatment requirements of the sludge, has the advantages of simple production process, stable output state, no secondary pollution, etc., realizes the requirements of sludge treatment for reduction, stabilization, harmlessness and resource utilization, and meets the "four transformations" principle of sludge disposal.

Description

Technical Field

[0001] The invention relates to the technical field of solid waste treatment, and in particular to a municipal sludge pyrolysis carbonization treatment system and a treatment process. Background Art

[0002] Municipal sludge, as a byproduct of sewage treatment, can be said to be the last mile of sewage treatment. However, due to factors such as price mechanism, technology, and upstream and downstream management, sludge treatment and disposal has become one of the more prominent problem areas in the current environmental industry. The phenomenon of "focusing on water and neglecting sludge" is prevalent, and sludge lacks standardized and effective treatment. In 2015, the "Ten Water Regulations" were issued, which clearly promoted sludge treatment and disposal, and stipulated that sludge generated by sewage treatment facilities should be treated and disposed of in a reduced, stabilized, harmless and resource-based manner, and that sludge that does not meet the treatment and disposal standards should be prohibited from entering cultivated land.

[0003] Sludge generally comes from the residues at the bottom of the primary sedimentation tank, the secondary sedimentation tank and the deep treatment structure in the wastewater treatment system. The main structure of sludge is a complex floc, which is mainly composed of a large number of microorganisms, organic matter, and inorganic matter floccules. This results in the sludge not only having a high water content, but also containing a large amount of organic matter. The water in the sludge includes interstitial water, adsorbed water, capillary water and internal water. Although most of the interstitial water and capillary water can be removed after the sludge is dehydrated, the adsorbed water and internal water of the cells in the sludge are difficult to remove, so the water content of the dehydrated sludge is still high (generally 78-82%). Most of the organic matter in the sludge comes from organic matter adsorbed by the flocs without microbial treatment, and the intracellular organic matter of the microorganisms. Among them, the carbohydrate content is high, while the content of substances such as protein and fat is relatively low; in addition, the sludge also contains a large number of nutrients that can be used by plants, such as nitrogen, phosphorus, potassium, etc., which will be limiting factors for sludge treatment, challenging traditional sludge treatment methods and can no longer meet environmental requirements. At the same time, the investment and operating costs of sludge treatment and disposal are high. If it is not handled properly, it will cause "secondary pollution", which has become a difficult problem in the field of environmental protection and has attracted much attention.

[0004] In recent years, emerging sludge treatment technologies have developed rapidly, among which thermochemical treatment technology has demonstrated its unique advantages in heat generation, power generation, production of renewable fuels and environmentally friendly materials, and is also of great significance in reducing greenhouse gas emissions and mitigating environmental issues such as climate change. Thermochemical treatment is a process that uses high temperature to convert organic components in solid matter into different forms of high-grade energy and products, mainly including pyrolysis technology, hydrothermal technology, and gasification technology. Among them, pyrolysis technology is mainly divided into slow pyrolysis, conventional pyrolysis, and rapid pyrolysis according to different heating temperatures. It refers to the thermochemical reaction of heating the pyrolysis raw material to 500-1000°C in the absence of oxygen or oxidants (theoretically in an inert atmosphere). The pyrolysis process is extremely complex, including physical processes such as heat transfer and material diffusion, as well as many parallel chemical reactions, such as intramolecular (inter) dehydration, macromolecular cracking, molecular isomerization, dehydrogenation, aromatization, coking, condensation, and functional group rearrangement. The pyrolysis reaction eventually generates sludge-based biochar, tar, water vapor and combustible gas (pyrolysis gas). The yield and composition of each product are affected by many factors, such as pyrolysis temperature, heating rate and residence time. Due to different pyrolysis technologies, the pyrolysis products are different, but the common point is that the raw materials are densified to obtain more stable and cleaner energy carriers, and the storage space and transportation costs are reduced. Sludge pyrolysis has become a hot topic of research in recent years because it can promote its resource utilization. Since the traditional treatment methods of municipal sludge still have many defects: such as easy to cause secondary pollution, great impact on the environment, high operating costs, etc., therefore, for the key technologies of sludge pyrolysis treatment, it is urgent to develop a municipal sludge pyrolysis carbonization treatment system and treatment process to solve the above technical problems.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The purpose of the present invention is to provide a municipal sludge pyrolysis carbonization treatment system and treatment process, which changes the properties of the sludge through chemical reactions under the conditions of closed micro-positive pressure and anaerobic combustion, thereby realizing the resource utilization of municipal sludge and the circular development of "waste treatment with waste", greatly reducing and controlling the operating costs, reducing external energy, and avoiding secondary pollution to the environment by traditional sludge treatment methods. The generated flue gas and pyrolysis gas are treated by a flue gas treatment device and a pyrolysis gas purification device and then reused in the system, which complies with the "four principles" of sludge disposal reduction, stabilization, harmlessness, and resource utilization, has broad application prospects, and is conducive to promotion and application.

[0007] In order to achieve the above-mentioned object, the present invention provides a municipal sludge pyrolysis carbonization treatment system, including a sludge treatment device, a flue gas treatment device, a pyrolysis gas purification device, a heating device, a blower I, a heat exchanger and an air mixing tank;

[0008] The sludge treatment device includes a plunger pump and a conveying device, a storage bin I, a vertical filter press, a pulverizer, a screw feeder, a primary internal heating rotary drying kiln, a secondary internal heating rotary drying kiln, a storage bin II, a screw conveyor, a feed sealing machine I, a primary vertical pyrolysis machine, a discharge sealing machine I, a feed sealing machine II, a secondary vertical pyrolysis machine and a discharge sealing machine II, and the discharge port and the feed port are sequentially connected in the above order to form a sludge circulation pipeline;

[0009] The flue gas treatment device includes a primary cyclone dust collector, a secondary cyclone dust collector and a washing tower. A flue gas recycling pipeline is formed between the primary internal heating rotary drying kiln, the secondary internal heating rotary drying kiln, the primary cyclone dust collector, the secondary cyclone dust collector, the blower I and the air mixing tank. The flue gas outlet of the blower I is also connected to the washing tower through a heat exchanger, and the washing tower discharges excess exhaust gas.

[0010] The pyrolysis gas purification device comprises a pressure relief water tank and a spray tower. The first-stage vertical pyrolysis machine, the second-stage vertical pyrolysis machine, the spray tower, the pyrolysis gas outlet of the burner and the pyrolysis gas inlet are sequentially connected to form a pyrolysis gas recycling pipeline. The pyrolysis gas outlet of the second-stage vertical pyrolysis machine is also connected to the pressure relief water tank.

[0011] The heating device includes a burner, a hot air furnace and a blower II. The burner, the hot air furnace, the first-stage vertical pyrolysis machine, the second-stage vertical pyrolysis machine, and the hot air outlet and the hot air inlet of the air mixing tank are connected in sequence to form a hot air recycling pipeline. The hot air outlet of the heat exchanger is connected to the hot air furnace through the blower II.

[0012] Preferably, it also includes a biomass bin, the content of which is straw, husk, wood chips or coal powder, and the discharge port of the biomass bin is connected to the screw conveyor.

[0013] Preferably, a drum is provided inside the first-stage internal heating rotary drying kiln and the second-stage internal heating rotary drying kiln, the rotation speed of the drum can be adjusted by variable frequency in the range of 2-10r / min, a crushing device is provided inside the drum, and an insulation layer is provided outside the drum, the crushing device includes a crushing shaft and a plurality of spiral blades arranged on the crushing shaft along the length direction of the drum, and the rotation speed of the crushing shaft can be adjusted by variable frequency.

[0014] Preferably, the first-stage vertical pyrolysis machine and the second-stage vertical pyrolysis machine are both externally heated, and a heating device is provided outside the reactor, and hot air is provided by a burner to heat the reactor to maintain the temperature inside the reactor. The external burner uses natural gas as fuel, and the natural gas is decompressed by a decompression device and then burned by the burner with air distribution.

[0015] Preferably, both the first-stage internal heating rotary drying kiln and the second-stage internal heating rotary drying kiln are in a slightly negative pressure environment.

[0016] Preferably, the first-stage vertical pyrolysis machine and the second-stage vertical pyrolysis machine are both anaerobic and slightly positive pressure environments.

[0017] A municipal sludge pyrolysis carbonization treatment process includes the following steps:

[0018] S1: Reduction process, using a plunger pump and a conveying device to send the wet sludge to a vertical filter press for extrusion and dehydration, and the dehydrated sludge is stored in storage bin I;

[0019] S2: Drying process. The sludge in the storage bin I is crushed by a pulverizer and then enters the primary internal heating rotary drying kiln and the secondary internal heating rotary drying kiln in sequence through a screw feeder for drying treatment. The drying temperature is 130-250°C. The dried sludge enters the storage bin II for storage. Both the primary internal heating rotary drying kiln and the secondary internal heating rotary drying kiln are in a slightly negative pressure environment. The heating gas used is provided by the hot air furnace after being used by the primary vertical pyrolysis machine and the secondary vertical pyrolysis machine and mixed with the recycled flue gas through a mixing tank for cooling.

[0020] S3: Pyrolysis and carbonization process, the sludge in the storage bin II enters the first-level vertical pyrolysis machine through the screw conveyor and the feed sealing machine I for the first-level pyrolysis and carbonization, and the sludge after the first-level pyrolysis and carbonization enters the second-level vertical pyrolysis machine through the discharge sealing machine I and the feed sealing machine II for the second-level pyrolysis and carbonization. The pyrolysis and carbonization temperature is 500-800℃. The first-level vertical pyrolysis machine and the second-level vertical pyrolysis machine are both anaerobic and slightly positive pressure environments, and are both externally heated. The heating device outside the reactor is used for heating, and the burner provides hot air to heat the reactor to maintain the temperature inside the reactor. The external burner uses natural gas as fuel. After the natural gas is reduced in pressure by the pressure reducing device, it is burned by the burner with air distribution;

[0021] S4: tail gas treatment process, including flue gas treatment process and pyrolysis gas purification process;

[0022] Flue gas treatment process: The flue gas generated by the primary internal heating rotary drying kiln and the secondary internal heating rotary drying kiln enters the primary cyclone dust collector and the secondary cyclone dust collector for dust removal and drying. The non-condensable gas is returned by the blower I as the air supply and sent to the air mixing tank. The cooled gas is reused by the primary internal heating rotary drying kiln and the secondary internal heating rotary drying kiln. The excess gas is sent to the heat exchanger for cooling and removal of water vapor, and then is treated in a conventional washing tower before being discharged in compliance with the emission standards. The water vapor is condensed and collected and discharged to the front end of the sewage treatment plant for treatment, which does not pollute the environment.

[0023] Pyrolysis gas purification process: The gaseous products produced in the pyrolysis and carbonization process pass through a spray tower to remove most of the tar and dust, and then the gas is transported to the burner of the heating device for secondary ablation and then fully reused. The heavy components separated from the gaseous products will be collected and recycled, and mixed with the sludge for secondary pyrolysis.

[0024] Preferably, in the pyrolysis carbonization process, cheap biomass is added and mixed from the biomass bin to the screw conveyor. The biomass may be straw, rice husk, wood chips or coal powder, and the added amount is 0-10% of the weight of the sludge.

[0025] Preferably, a stable solid product sludge-based biochar mixture is finally generated in the secondary vertical pyrolysis machine, in which heavy metals in the sludge are sintered and discharged from the reactor through the discharge sealer II. After cooling, it is collected and discharged outside the system and can be exported as a biochar product.

[0026] Preferably, the moisture content of the mud discharged from the vertical filter press is ≤60%, the moisture content of the mud discharged from the primary internal heating rotary drying kiln is ≤30%, and the moisture content of the mud discharged from the secondary internal heating rotary drying kiln is ≤20%.

[0027] The municipal sludge pyrolysis carbonization treatment system and treatment process provided by the present invention have the following beneficial effects.

[0028] This system uses a vertical filter press to squeeze and dehydrate the sludge with a moisture content of about 80% to form a mud cake with a moisture content of ≤60%, and then sends it to the first-level internal heating rotary drying kiln and the second-level internal heating rotary drying kiln for drying to form a material with a moisture content of ≤20%. Finally, it is pyrolyzed by the first-level vertical pyrolysis machine and the second-level vertical pyrolysis machine. After pyrolysis, 1 ton of 80% sludge can finally obtain 170-180 kg of stable carbon slag with a moisture content of about 3%. It not only meets the requirements of "four modernizations", but also turns sludge into treasure. At the same time, it also has the characteristics of solidifying heavy metals, high energy utilization and low energy loss. It is highly efficient and low cost. It is a well-deserved energy-saving and environmentally friendly system. This system has the following characteristics:

[0029] (1) The secondary cracking is carried out by connecting two vertical pyrolysis machines, which reduces the amount of tar, increases the pyrolysis gas output, and improves the calorific value of the pyrolysis gas.

[0030] (2) By adding cheap biomass such as straw, rice husk, and sawdust to wet sludge, the moisture content of the sludge is reduced, the calorific value of the feed material is increased, the output of pyrolysis gas is increased, the consumption of external fuel is reduced, and the operating cost is greatly reduced.

[0031] (3) Through the comprehensive utilization of thermal energy, a circular economy can be achieved, further reducing operating costs.

[0032] (4) The drying process and pyrolysis carbonization process use separate water vapor and pyrolysis gas channels, which has the following advantages:

[0033] 1) The water vapor content in the pyrolysis gas is low and the calorific value is high, so it can be directly recycled;

[0034] 2) Water vapor does not enter the high-temperature pyrolysis carbonization process, but is separated in advance in the drying process. The separation temperature is low, which reduces the energy consumption of the pyrolysis carbonization process;

[0035] 3) Water vapor is discharged at low temperature during the drying process, does not contain tar, and avoids environmental pollution;

[0036] 4) The superheated steam discharged from the drying process can be used to supply heat to the outside.

[0037] (5) The sludge is dried, pyrolyzed and carbonized in a closed device, and the non-condensable gas and pyrolysis gas produced are sent into the combustion system under slight positive pressure for combustion, which is environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A schematic structural diagram of a municipal sludge pyrolysis and carbonization treatment system provided by the present invention.

[0039] In the figure:

[0040] 1. Plunger pump and conveying device 2. Vertical filter press 3. Storage bin I 4. Crusher 5. Screw feeder 6. First-stage internal heating rotary drying kiln 7. Second-stage internal heating rotary drying kiln 8. Storage bin II 9. Biomass bin 10. Screw conveyor 11. Feed sealing machine I 12. Discharge sealing machine I 13. First-stage vertical pyrolysis machine 14. Second-stage vertical pyrolysis machine 15. Air mixing tank 16. Heat exchanger 17. Heating device 18. Flue gas treatment device 19. Pyrolysis gas purification device 20. Blower I 21. Second-stage cyclone dust collector 22. First-stage cyclone dust collector 23. Scrubber 24. Burner 25. Hot air furnace 26. Blower II 27. Spray tower 28. Pressure relief water tank 29. Feed sealing machine II 30. Discharge sealing machine II. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with specific embodiments and drawings to help understand the content of the present invention.

[0042] like Figure 1 The figure is a schematic diagram of the structure of a municipal sludge pyrolysis carbonization treatment system provided by the present invention. The municipal sludge pyrolysis carbonization treatment system includes a sludge treatment device, a flue gas treatment device 18, a pyrolysis gas purification device 19, a heating device 17, a blower Ⅰ20, a heat exchanger 16 and an air mixing tank 15;

[0043] The sludge treatment device comprises a plunger pump and a conveying device 1, a storage bin Ⅰ3, a vertical filter press 2, a pulverizer 4, a screw feeder 5, a primary internal heating rotary drying kiln 6, a secondary internal heating rotary drying kiln 7, a storage bin Ⅱ8, a screw conveyor 10, a feed sealing machine Ⅰ11, a primary vertical pyrolysis machine 13, a discharge sealing machine Ⅰ12, a feed sealing machine Ⅱ29, a secondary vertical pyrolysis machine 14 and a discharge sealing machine Ⅱ30, and the discharge port and the feed port are sequentially connected in the above order to form a sludge circulation pipeline;

[0044] The flue gas treatment device 18 includes a primary cyclone dust collector 22, a secondary cyclone dust collector 21 and a washing tower 23. A flue gas recycling pipeline is formed between the primary internal heating rotary drying kiln 6, the secondary internal heating rotary drying kiln 7, the primary cyclone dust collector 22, the secondary cyclone dust collector 21, the blower I 20 and the air mixing tank 15. The flue gas outlet of the blower I 20 is also connected to the washing tower 23 through the heat exchanger 16, and the washing tower 23 discharges the excess exhaust gas.

[0045] The pyrolysis gas purification device 19 includes a pressure relief water tank 28 and a spray tower 27. The first-stage vertical pyrolysis machine 13, the second-stage vertical pyrolysis machine 14, the spray tower 27, and the pyrolysis gas outlet of the burner 24 are connected to the pyrolysis gas inlet in sequence to form a pyrolysis gas recycling pipeline. The pyrolysis gas outlet of the second-stage vertical pyrolysis machine 14 is also connected to the pressure relief water tank 28.

[0046] The heating device 17 includes a burner 24, a hot air furnace 25 and a blower II 26. The hot air outlet and the hot air inlet of the burner 24, the hot air furnace 25, the first-stage vertical pyrolysis machine 13, the second-stage vertical pyrolysis machine 14, and the air mixing tank 15 are connected in sequence to form a hot air recycling pipeline. The hot air outlet of the heat exchanger 16 is connected to the hot air furnace 25 through the blower II 26.

[0047] Preferably, it also includes a biomass bin 9, the content of which is straw, husk, sawdust or coal powder, and the discharge port of the biomass bin 9 is connected to the screw conveyor 10. The first-level internal heating rotary drying kiln 6 and the second-level internal heating rotary drying kiln 7 are provided with a drum inside, and the rotation speed of the drum can be adjusted by variable frequency in the range of 2-10r / min. A crushing device is provided inside the drum, and an insulation layer is provided outside the drum. The crushing device includes a crushing shaft and a plurality of spiral blades arranged on the crushing shaft along the length direction of the drum, and the rotation speed of the crushing shaft can be adjusted by variable frequency. The first-level internal heating rotary drying kiln 6 and the second-level internal heating rotary drying kiln 7 are both in a slightly negative pressure environment to prevent dust and odor from leaking out. The first-stage vertical pyrolysis machine 13 and the second-stage vertical pyrolysis machine 14 are both in an oxygen-free, slightly positive pressure environment, and are both externally heated. A heating device 17 is provided outside the reactor, and hot air is provided through a burner 24 to heat the reactor to maintain the temperature inside the reactor. The external burner 24 uses natural gas as fuel. After the natural gas is reduced in pressure by a pressure reducing device, it is burned with air supplied by the burner 24.

[0048] The present invention also provides a municipal sludge pyrolysis carbonization treatment process, comprising the following steps:

[0049] S1: reduction process, using a plunger pump and a conveying device 1 to send the wet sludge to a vertical filter press 2 for extrusion and dehydration, and the dehydrated sludge enters a storage bin Ⅰ 3 for storage;

[0050] S2: Drying process, the sludge in the storage bin Ⅰ3 is crushed by the pulverizer 4, and then enters the first-level internal heating rotary drying kiln 6 and the second-level internal heating rotary drying kiln 7 for drying treatment through the screw feeder 5, and the drying temperature is 130-250°C. The dried sludge enters the storage bin Ⅱ8 for storage. Both the first-level internal heating rotary drying kiln 6 and the second-level internal heating rotary drying kiln 7 are in a slightly negative pressure environment. The heating gas used is provided by the hot air furnace 25 after being used by the first-level vertical pyrolysis machine 13 and the second-level vertical pyrolysis machine 14 and mixed with the recycled flue gas through the mixing tank 15 for cooling;

[0051] S3: Pyrolysis carbonization process, the sludge in the storage bin II 8 enters the first-level vertical pyrolysis machine 13 through the screw conveyor 10 and the feed sealing machine I 11 for first-level pyrolysis carbonization, and the sludge after the first-level pyrolysis carbonization enters the second-level vertical pyrolysis machine 14 through the discharge sealing machine I 12 and the feed sealing machine II 29 for second-level pyrolysis carbonization, the pyrolysis carbonization temperature is 500-800°C, the first-level vertical pyrolysis machine 13 and the second-level vertical pyrolysis machine 14 are both anaerobic and slightly positive pressure environments, and are both externally heated, and are heated by the heating device 17 outside the reactor, and the reactor is heated by hot air provided by the burner 24 to maintain the temperature inside the reactor, and the external burner 24 uses natural gas as fuel, and the natural gas is reduced in pressure by the pressure reducing device and then burned by the burner 24 with air distribution;

[0052] S4: tail gas treatment process, including flue gas treatment process and pyrolysis gas purification process;

[0053] Flue gas treatment process: The flue gas generated by the primary internal heating rotary drying kiln 6 and the secondary internal heating rotary drying kiln 7 enters the primary cyclone dust collector 22 and the secondary cyclone dust collector 21 for dust removal and drying, and the non-condensable gas is returned through the blower I 20 as the air supply and sent to the air mixing tank 15. The cooled gas is reused by the primary internal heating rotary drying kiln 6 and the secondary internal heating rotary drying kiln 7, and the excess gas is sent to the heat exchanger 16 for cooling and removal of water vapor, and then is treated in the washing tower 23 in a conventional manner before being discharged to meet the standards. The water vapor is condensed and collected and discharged to the front end of the sewage treatment plant for treatment, which does not pollute the environment;

[0054] Pyrolysis gas purification process: After the gaseous products produced in the pyrolysis carbonization process pass through the spray tower 27 to remove most of the tar and dust, the gas is transported to the burner 24 of the heating device 17 for secondary ablation and then fully reused. The heavy components separated from the gaseous products will be collected and recycled, and mixed with the sludge for secondary pyrolysis.

[0055] Preferably, in the pyrolysis carbonization process, cheap biomass is added and mixed into the screw conveyor 10 from the biomass bin 9. The biomass may be straw, husk, sawdust or coal powder, and the amount added is 0-10% of the weight of the sludge. A stable solid product sludge-based biochar mixture is finally generated in the secondary vertical pyrolysis machine 14, and the heavy metals in the sludge are sintered therein, and discharged from the reactor through the discharge sealer II 30, and collected and discharged from the system after cooling, and can be exported as a biochar product. The moisture content of the mud discharged from the vertical filter press 2 is ≤60%, the moisture content of the mud discharged from the primary internal heating rotary drying kiln 6 is ≤30%, and the moisture content of the mud discharged from the secondary internal heating rotary drying kiln 7 is ≤20%.

[0056] Example:

[0057] The implementation location is a municipal sewage treatment plant in the north. The core process (starting from the drying process) is designed to have a sludge intake of 25 tons / day of sludge (sludge with a moisture content of 60%), and the annual treatment of municipal sludge with a moisture content of 60% is about 8,000 tons. In this embodiment, the moisture content of the sludge discharged from the vertical filter press 2 is ≤60%, the moisture content of the sludge fed to the vertical pyrolysis machine is ≤20%, the drying temperature is 130-250°C, the pyrolysis carbonization temperature is 500-800°C, the internal heating rotary drying kiln is slightly negative pressure, and the vertical pyrolysis machine is oxygen-free and slightly positive pressure.

[0058] The process is:

[0059] The sludge with a moisture content of about 80% is pumped to the sludge reduction workshop by a plunger pump. The sludge reduction treatment uses a new vertical filter press 2 to squeeze and dehydrate the sludge to form a mud cake with a moisture content of ≤60%, and then it is sent to the drying process. The sludge drying process consists of two internally heated rotary drying kilns with a crushing device used in series, as well as a matching flue gas treatment device 18 and a flue gas recycling pipeline. The sludge with a moisture content of ≤60% is dried to a moisture content of ≤20% by a two-stage deep drying device, and then enters the pyrolysis carbonization process. The sludge pyrolysis carbonization process consists of two vertical pyrolysis machines used in series, as well as a matching heating device 17, an inlet (outlet) material sealing machine, a pyrolysis gas purification device 19, and a pyrolysis gas recycling pipeline. The traditional bedroom pyrolysis machine has a low filling rate (filling rate is less than 25%), resulting in a large single-machine equipment volume and high cost; while the vertical pyrolysis machine has a filling rate greater than 65%, and the production cost is reduced by half compared to the bedroom pyrolysis machine. At the same time, it also solves the problem that the silo is unevenly heated in the circumferential direction and easily deformed into an elliptical shape due to the accumulation of materials under the silo in the bedroom pyrolysis machine, which causes the copying plate to scratch the cylinder wall or the gap between the copying plate and the cylinder wall is too large.

[0060] In the reduction process, the concentrated sludge is fully mixed with a certain concentration of iron salt flocculant, and the amount of iron salt added is about 5% of the weight of the sludge. The tiny solid particles in the sludge are aggregated into larger floccules, and some free water is separated at the same time. The flocculated sludge is transported to the filter belt for concentrated gravity dehydration. Under the action of gravity, the free water is separated to form stagnant sludge, and then sent to the pre-pressing area (first grid) of the dehydration turntable. The sludge is first clamped in the middle of the folded filter cloth for pre-pressing, and then passes through the low-pressure area (second grid) and high-pressure area (third grid) of the dehydration turntable. Under the vertical pressure from small to large, the sludge is gradually squeezed to achieve the maximum separation of mud and water, and finally discharged in the fourth grid as a filter cake. During the discharge process, due to gravity drop, the mud cake is broken into small clumps of about 15-40mm, and then sent to the storage bin Ⅰ3.

[0061] In the drying process, the two stages of the internal heating rotary drying kiln are connected in series and placed up and down. The screw feeder 5 pushes the sludge into the first-stage internal heating rotary drying kiln 6 according to the set feeding rate. After the first-stage drying, the sludge enters the second-stage internal heating rotary drying kiln 7 for secondary drying. The specific drying process is: the sludge is constantly turned in the first-stage internal heating rotary drying kiln 6 and the second-stage internal heating rotary drying kiln 7, heated by the hot flue gas through the furnace wall, and removed from the hot flue gas by contact; finally, the dried mixed product with a moisture content of ≤20% is transported to the storage bin II 8 for storage through the lower discharge port of the second-stage internal heating rotary drying kiln 7. The entire drying process is carried out in a closed environment, the drying temperature is 130-250℃, and the drying time is 45-60min.

[0062] In the pyrolysis carbonization process, the sludge in the storage bin II8 enters the primary vertical pyrolysis machine 13 through the screw conveyor 10 and the feed sealer I11 for primary pyrolysis carbonization. The screw conveyor 10 has the functions of conveying, sealing, homogenizing and stirring, and can evenly convey the dry mixed products with low viscosity powder, granular and small particles with a moisture content of ≤20% from the storage bin II8 to the screw conveyor 10. The biomass bin 9 is used to store biomass. During the conveying process, cheap straw, husk, sawdust or coal powder and other biomass are added to the screw conveyor 10 at the same time, and the added amount is 0-10% of the weight of the crushed sludge. The setting of the storage bin II8 can not only be used to store the dried sludge, but also play a role of buffering and material sealing before the sludge enters the primary vertical pyrolysis machine 13. The setting of the inlet (outlet) material sealer is used to input or output sludge, and secondly, it plays a sealing role to prevent air from entering the reactor and affecting the pyrolysis reaction. When in use, the semi-dry sludge is fed into the hopper of the feed sealing machine or the discharge sealing machine, which rotates continuously under the action of external force. A spiral grabber is added to the top of the drum. The feed speed can be controlled by the spiral speed, and the sludge is continuously grabbed into (out of) the rotating drum, thereby realizing forced feeding (discharging) and improving the feeding (discharging) capacity.

[0063] The pyrolysis carbonization process includes two vertical pyrolysis machines connected in series, and a pyrolysis carbonization reactor heat conduction cavity is arranged between the insulation layer and the central axis, and a burner 24 is connected to the pyrolysis carbonization reactor heat conduction cavity. The semi-dry sludge is stirred in the reactor of the first-stage vertical pyrolysis machine 13 through the central axis under high-temperature oxygen-isolated conditions, and is evenly heated and heated to produce pyrolysis carbonization, pyrolysis gas, tar, and carbon slag, all of which enter the second-stage vertical pyrolysis machine 14, and the sludge undergoes secondary cracking. During the pyrolysis process, the organic components in the sludge generate high-temperature gas (pyrolysis gas, a small amount of water vapor) under high-temperature oxygen-isolated conditions. After being treated by the pyrolysis gas purification device 19, it is sent to the heating device 17 through the pyrolysis gas recycling pipeline, and mixed with auxiliary fuel (liquefied petroleum gas, natural gas or biomass, etc.) for combustion. The high-temperature gas generated by the combustion is used to heat the vertical pyrolysis machine and provide a heat source for the vertical pyrolysis machine. The burner 24 in the heating device 17 is a combined burner used together with the hot air furnace 25. It can use natural gas or pyrolysis gas alone, or use natural gas and pyrolysis gas at the same time: use natural gas when the device is heated; use natural gas and pyrolysis gas at the same time after pyrolysis gas is generated after adding materials; or when the pyrolysis gas is sufficient, turn off the natural gas and use the pyrolysis gas alone. The hot air furnace 25 in the heating device 17 is used to ablate the harmful gas generated in the device, and at the same time directly supply the generated heat to the vertical pyrolysis machine, eliminating pollution and saving energy.

[0064] The phased operation of this embodiment shows that the thermal efficiency of this process system is ≥70%, the sludge reduction is ≥80% (based on a water content of 80%), and 100% resource recovery is achieved.

[0065] The secondary pollutants generated in this process embodiment are wastewater and waste gas: (1) Waste gas is the excess flue gas discharged in the drying process, which meets the emission standards after dust removal, cooling, washing and other process treatments. It meets the relevant index requirements in the "Standard for Pollution Control of Incineration of Domestic Waste" (GB18485-2014). (2) Wastewater is mainly the condensed water of water vapor in the drying process and the spray wastewater generated in the waste gas treatment process. The pH, COD, suspended solids, animal and vegetable oils, ammonia nitrogen and various heavy metal detection concentrations in the condensed water and spray water meet the third-level standard requirements in the "Comprehensive Sewage Discharge Standard" (GB8978-1996), and its water quality meets the relevant index requirements in the "Water Quality Standard for Sewage Discharge into Urban Sewers" (GB / T31962-2015), and is discharged into the front-end treatment of the sewage treatment plant.

[0066] The technical problem solved by this process is: in view of the bottleneck problem of sludge dehydration being sludge treatment, a set of municipal sludge pyrolysis treatment processes is provided, which can realize the relative separation of the three phases of liquid phase, gas phase and solid phase in sludge treatment, and the harmless treatment process of the precipitation of three phases, so as to overcome the defect that the traditional treatment method of municipal sludge is easy to cause secondary pollution. On the one hand, pyrolysis carbonization can improve the dehydration performance of sludge, and on the other hand, the sludge pyrolysis method can produce gas and solid (biochar material with high aromatic structure and mesoporous structure) with utilization value, the operating system is closed, no polluting gas is discharged, almost all heavy metals are fixed in the solid residue, the impact on the environment is small, and the operating cost is low. It is worth noting that since this process uses sludge with a water content of 80% before sludge reduction, the sewage plant will not cause waste of original equipment (such as belt thickening filter press) when it is rebuilt.

[0067] Compared with the traditional sludge treatment method, this process embodiment truly achieves the "reduction, stabilization, harmlessness and resource utilization" of sludge, solves the problems of environmental safety, and has the following advantages and positive effects:

[0068] (1) Reduction: Every 10 tons of sludge (water content 80%) can be reduced to 1.7-1.8 tons of sludge-based biochar after carbonization;

[0069] (2) Stabilization: The pyrolysis final product, sludge-based biochar, contains almost no degradable organic matter, and is completely stabilized;

[0070] (3) Harmlessness: Since the sludge is pyrolyzed and carbonized in a completely closed device without oxygen, the heavy metals are solidified at high temperature, which avoids secondary pollution to the environment to the greatest extent. The sludge solid product (sludge-based biochar) treated by this process has significantly lower heavy metal leaching than the original sludge. The toxicity leaching test results show that nickel is not detected, the lead detection value is 14.1mg / kg, the cadmium detection value is 0.41mg / kg, the chromium detection value is 10.3mg / kg, the copper detection value is 106mg / kg, the arsenic detection value is 12.4mg / kg, and the zinc detection value is 678mg / kg. Its pollutant indicators all meet the requirements of "Municipal Sewage Treatment Plant Sludge Disposal for Landscaping" (GB / T23486-2009);

[0071] (4) Resource utilization: Sludge itself is a combination of organic matter. After harmless treatment, the biomass energy and biochar products produced can be sold to landscaping, gardening and other units as raw materials for landscaping base fertilizer and soil improvement materials for landscaping and nursery cultivation, thus realizing the resource utilization of municipal sludge;

[0072] (5) Economical: The pyrolysis carbonization method is used to treat sludge in a fully enclosed state, with low heat loss and low energy consumption;

[0073] (6) Controllability: The pyrolysis process is used to treat sludge in sewage treatment plants. The government and sewage treatment plants have control over the entire sludge treatment process.

[0074] The invention concept is described in detail using specific examples herein, and the description of the above embodiments is only used to help understand the core idea of ​​the invention. It should be pointed out that any obvious modification, equivalent substitution or other improvement made by a person of ordinary skill in the art without departing from the invention concept should be included in the protection scope of the present invention.

Claims

1. A municipal sludge pyrolysis carbonization treatment system, characterized in that: It includes a sludge treatment device, a biomass bin, a flue gas treatment device, a pyrolysis gas purification device, a heating device, a blower I, a heat exchanger and an air mixing tank; The sludge treatment device includes a plunger pump and a conveying device, a storage bin I, a vertical filter press, a pulverizer, a screw feeder, a primary internal heating rotary drying kiln, a secondary internal heating rotary drying kiln, a storage bin II, a screw conveyor, a feed sealing machine I, a primary vertical pyrolysis machine, a discharge sealing machine I, a feed sealing machine II, a secondary vertical pyrolysis machine and a discharge sealing machine II, and the discharge port and the feed port are sequentially connected in the above order to form a sludge circulation pipeline; The contents in the biomass bin are straw, husk, sawdust or coal powder, and the discharge port of the biomass bin is connected to a screw conveyor; The flue gas treatment device includes a primary cyclone dust collector, a secondary cyclone dust collector and a washing tower. A flue gas recycling pipeline is formed between the primary internal heating rotary drying kiln, the secondary internal heating rotary drying kiln, the primary cyclone dust collector, the secondary cyclone dust collector, the blower I and the air mixing tank. The flue gas outlet of the blower I is also connected to the washing tower through a heat exchanger, and the washing tower discharges excess exhaust gas. The pyrolysis gas purification device comprises a pressure relief water tank and a spray tower. The first-stage vertical pyrolysis machine, the second-stage vertical pyrolysis machine, the spray tower, the pyrolysis gas outlet of the burner and the pyrolysis gas inlet are sequentially connected to form a pyrolysis gas recycling pipeline. The pyrolysis gas outlet of the second-stage vertical pyrolysis machine is also connected to the pressure relief water tank. The heating device includes a burner, a hot air furnace and a blower II. The burner, the hot air furnace, the first-stage vertical pyrolysis machine, the second-stage vertical pyrolysis machine, and the hot air outlet and the hot air inlet of the air mixing tank are connected in sequence to form a hot air recycling pipeline. The hot air outlet of the heat exchanger is connected to the hot air furnace through the blower II.

2. A municipal sludge pyrolysis carbonization treatment system according to claim 1, characterized in that: The first-stage internal heating rotary drying kiln and the second-stage internal heating rotary drying kiln are provided with a drum inside, the rotation speed of the drum can be adjusted by variable frequency in the range of 2-10 r / min, a crushing device is provided inside the drum, and a heat preservation layer is provided outside the drum, the crushing device includes a crushing shaft and a plurality of spiral blades arranged on the crushing shaft along the length direction of the drum, and the rotation speed of the crushing shaft can be adjusted by variable frequency.

3. A municipal sludge pyrolysis carbonization treatment system according to claim 2, characterized in that: The first-stage vertical pyrolysis machine and the second-stage vertical pyrolysis machine are both externally heated, and a heating device is provided outside the reactor to heat the reactor by hot air to maintain the temperature inside the reactor. The external burner uses natural gas as fuel. After the natural gas is reduced in pressure by a pressure reducing device, it is burned by the burner with air distribution.

4. A municipal sludge pyrolysis carbonization treatment system according to claim 3, characterized in that: The first-stage internal heating rotary drying kiln and the second-stage internal heating rotary drying kiln are both in a slightly negative pressure environment.

5. A municipal sludge pyrolysis carbonization treatment system according to claim 4, characterized in that: The first-stage vertical pyrolysis machine and the second-stage vertical pyrolysis machine are both in an anaerobic and slightly positive pressure environment.

6. A municipal sludge pyrolysis carbonization treatment process, characterized in that: Including the following processes: S1: Reduction process, using a plunger pump and a conveying device to send the wet sludge to a vertical filter press for extrusion and dehydration, and the dehydrated sludge is stored in storage bin I; S2: Drying process. The sludge in the storage bin I is crushed by a pulverizer and then enters the primary internal heating rotary drying kiln and the secondary internal heating rotary drying kiln in sequence through a screw feeder for drying treatment. The drying temperature is 130-250°C. The dried sludge enters the storage bin II for storage. Both the primary internal heating rotary drying kiln and the secondary internal heating rotary drying kiln are in a slightly negative pressure environment. The heating gas used is provided by the hot air furnace after being used by the primary vertical pyrolysis machine and the secondary vertical pyrolysis machine and mixed with the recycled flue gas through a mixing tank for cooling. S3: Pyrolysis carbonization process, the sludge in the storage bin II enters the first-level vertical pyrolysis machine through the screw conveyor and the feed sealing machine I for the first-level pyrolysis carbonization, and the sludge after the first-level pyrolysis carbonization enters the second-level vertical pyrolysis machine through the discharge sealing machine I and the feed sealing machine II for the second-level pyrolysis carbonization. The pyrolysis carbonization temperature is 500-800℃. The first-level vertical pyrolysis machine and the second-level vertical pyrolysis machine are both anaerobic and slightly positive pressure environments, and are both externally heated. The heating device outside the reactor is used to heat the reactor by hot air to maintain the temperature inside the reactor. The external burner uses natural gas as fuel. After the natural gas is reduced in pressure by the pressure reducing device, it is burned by the burner with air distribution; S4: tail gas treatment process, including flue gas treatment process and pyrolysis gas purification process; Flue gas treatment process: The flue gas generated by the primary internal heating rotary drying kiln and the secondary internal heating rotary drying kiln enters the primary cyclone dust collector and the secondary cyclone dust collector for dust removal and drying. The non-condensable gas is returned by the blower I as the air supply and sent to the air mixing tank. The cooled gas is reused by the primary internal heating rotary drying kiln and the secondary internal heating rotary drying kiln. The excess gas is sent to the heat exchanger for cooling and removal of water vapor, and then is treated in a conventional washing tower before being discharged in compliance with the emission standards. The water vapor is condensed and collected and discharged to the front end of the sewage treatment plant for treatment, which does not pollute the environment. Pyrolysis gas purification process: The gaseous products produced in the pyrolysis and carbonization process pass through a spray tower to remove most of the tar and dust, and then the gas is transported to the burner of the heating device for secondary ablation and then fully reused. The heavy components separated from the gaseous products will be collected and recycled, and mixed with the sludge for secondary pyrolysis.

7. A municipal sludge pyrolysis carbonization treatment process according to claim 6, characterized in that: In the pyrolysis carbonization process, cheap biomass is added and mixed from the biomass bin to the screw conveyor. The biomass is straw, rice husk, wood chips or coal powder, and the added amount is 0-10% of the sludge weight.

8. A municipal sludge pyrolysis carbonization treatment process according to claim 7, characterized in that: The two-stage vertical pyrolysis machine eventually generates a stable solid product sludge-based biochar mixture, in which the heavy metals in the sludge are sintered and discharged from the reactor through the discharge sealer II. After cooling, it is collected and discharged outside the system and can be exported as a biochar product.

9. A municipal sludge pyrolysis carbonization treatment process according to claim 8, characterized in that: The moisture content of the mud discharged from the vertical filter press is ≤60%, the moisture content of the mud discharged from the first-stage internal heating rotary drying kiln is ≤30%, and the moisture content of the mud discharged from the second-stage internal heating rotary drying kiln is ≤20%.

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