A combined system and method for the treatment of municipal sludge by alkaline thermal hydrolysis and multi-stage flash evaporation

Abstract

The application discloses a municipal sludge multi-stage flash evaporation treatment system and method combined with alkaline thermal hydrolysis, which comprises a sludge receiving and storing device, a sludge adjusting and preheating device, a sludge multi-stage hydrolysis flash evaporation unit, a condensing device and a product collecting unit which are sequentially connected, the condensing device is also connected with the sludge adjusting and preheating device and the outside world respectively, and the sludge multi-stage hydrolysis flash evaporation unit comprises a first-stage flash evaporation tank, a hydrolysis reaction kettle and a second-stage flash evaporation tank which are sequentially connected; the first-stage flash evaporation tank is connected with the sludge adjusting and preheating device. By using the system, the water content of the municipal sludge dewatering cake reaches 15%, which is reduced by 40% compared with the prior art; the COD, ammonia nitrogen and total nitrogen values in the hydrolysis liquid are increased by about 60% compared with the prior art. The water vapor discharged in the flash evaporation pressure relief process is condensed, absorbs soluble gas and is mixed with the hydrolysis liquid to serve as liquid fertilizer; the insoluble gas such as methane can be purified to serve as fuel. Finally, the municipal sludge treatment is realized in a way of reduction and resource utilization.

Description

Technical Field

[0001] This invention relates to a multi-stage flash evaporation treatment system and method for municipal sludge using alkaline hot water hydrolysis, belonging to the field of sludge treatment and disposal technology. Background Technology

[0002] Because sludge contains toxic and harmful microorganisms and heavy metals, direct discharge without treatment can easily cause environmental pollution. Furthermore, sludge also contains a large amount of usable organic matter and substances such as nitrogen, phosphorus, and potassium. Sludge treatment has become an important part of modern wastewater treatment plants.

[0003] To address the aforementioned problems, various sludge treatment methods have been developed, including composting, landfilling, anaerobic digestion, thermal hydrolysis, and incineration. Thermal hydrolysis of sludge is currently a commonly used technology in sludge treatment. During thermal hydrolysis, sludge flocs decompose, cells break down, and organic matter is released, achieving sludge harmlessness and volume reduction, while also reducing the content of volatile organic compounds and stabilizing the sludge. For example, patent CN108191192A discloses a method and system for alkaline thermal hydrolysis of sludge, which solves the technical problem that conventional sludge treatment processes fail to effectively maximize resource utilization. Patent CN117088592A discloses a thermal hydrolysis device for sludge, which uses microwave heating and ultrasonic-assisted cell disruption technology to improve thermal hydrolysis efficiency and reduce energy consumption.

[0004] However, the current industrial-scale promotion of sludge hot hydrolysis technology in many cities faces problems such as low hydrolysis efficiency, incomplete hydrolysis, and poor solid-liquid separation. This leads to problems such as low fertilizer efficiency of end-product liquid fertilizer and high moisture content of sludge cake, ultimately resulting in poor quality of end products that cannot meet the needs of sludge resource utilization. Summary of the Invention

[0005] Objectives of the Invention: The first objective of this invention is to provide a multi-stage flash evaporation treatment system for municipal sludge using combined alkaline hot water hydrolysis. The second objective is to provide a method for treating municipal sludge using this system. This treatment method and system operate stably and efficiently, significantly improving the hydrolysis efficiency and degree of hydrolysis of municipal sludge, enhancing solid-liquid separation efficiency and the fertilizer efficacy of the final product, thereby achieving both sludge reduction and resource recovery.

[0006] Technical Solution: The present invention discloses a multi-stage flash evaporation treatment system for municipal sludge using alkaline hot water hydrolysis, comprising a sludge receiving and storage device, a sludge mixing and preheating device, a multi-stage hydrolysis flash evaporation unit, a condensation device, and a product collection unit connected in sequence. The multi-stage hydrolysis flash evaporation unit comprises a primary flash tank, a hydrolysis reactor, and a secondary flash tank connected in sequence. The primary flash tank is connected to the sludge mixing and preheating device, and both the primary and secondary flash tanks are connected to the condensation device. The condensation device is also connected to both the sludge mixing and preheating device and the outside environment. The primary flash tank, the secondary flash tank, and the product collection unit are all connected to the outside environment.

[0007] Furthermore, a filter device is installed at the bottom of the discharge port of the primary flash tank, which allows the material after primary flash evaporation to achieve solid-liquid separation. The hydrolysate is discharged outside the boundary, and the remaining sludge is fed into the hydrolysis reactor.

[0008] Furthermore, both the top of the primary flash tank and the top of the secondary flash tank are equipped with pressure relief and exhaust valves, and the steam outlets of the primary flash tank and the secondary flash tank are connected to the steam inlet of the condenser through the pressure relief and exhaust valves.

[0009] Furthermore, the inner diameter of the pipes connecting the primary flash tank, the secondary flash tank, and the condenser is 20-100cm.

[0010] Furthermore, the sludge preparation and preheating device is connected to the sludge multi-stage hydrolysis flash evaporation unit via a screw pump, and the condenser tubes inside the condensation device are spiral-shaped.

[0011] Furthermore, the product collection unit includes a liquid collection tank and a gas collection tank, which are connected by a check valve.

[0012] Furthermore, the inlet of the liquid collection tank is connected to the outlet of the condensing device, the outlet of the condensing device is submerged below the liquid level in the liquid collection tank, the outlet of the liquid collection tank is connected to the outside, and the outlet of the liquid collection tank is connected to the inlet of the gas collection tank through a check valve.

[0013] The method for treating municipal sludge using the multi-stage flash evaporation treatment system for municipal sludge combined with alkaline hot water hydrolysis as described in this invention includes the following steps:

[0014] (1) Sludge preparation and preheating: municipal sludge and calcium oxide powder in the sludge receiving and storage device are put into the sludge preparation and preheating device, and water is added to prepare the sludge into slurry.

[0015] (2) Multi-stage hydrolysis flash evaporation of sludge: The sludge is fed into the first-stage flash tank for flash evaporation. The first-stage flash tank is vented and depressurized in a short time. After the first-stage flash evaporation, the material is filtered and the filtrate is discharged. The remaining sludge is fed into the hydrolysis reactor for alkaline hot water hydrolysis reaction. The sludge after the reaction is transported to the second-stage flash tank for flash evaporation. After the flash evaporation is completed, the material is discharged and solid-liquid separation is performed.

[0016] (3) Collection of sludge hydrolysis products: The gas discharged during the flash evaporation process is condensed by a condensing device through a connecting pipe and then discharged to the product collection unit.

[0017] Furthermore, in step (1), the municipal sludge is residual activated sludge with a moisture content of 80-85%.

[0018] Furthermore, in step (1), the water content of the mud is 90-95%.

[0019] Furthermore, in step (1), the amount of calcium oxide powder added is 18-22% of the dry weight of the sludge.

[0020] Furthermore, in step (1), the preheating temperature in the sludge preparation and preheating device is 160-200℃ and the pressure is 2.5-3.5MPa.

[0021] Furthermore, in step (2), both the primary flash tank and the secondary flash tank release pressure to atmospheric pressure within 1-60 seconds during exhaust and depressurization.

[0022] Furthermore, in step (2), the temperature of the alkaline hot water hydrolysis reaction is 160-200℃, and the time of the alkaline hot water hydrolysis reaction is 2-4h.

[0023] Furthermore, in step (3), the condensate and soluble gas collected by the product collection unit are mixed with the filtrate discharged from the first-stage flash tank and the hydrolysate after solid-liquid separation of the remaining material discharged from the second-stage flash tank in step (2) and then recycled as liquid fertilizer.

[0024] Furthermore, in step (3), the insoluble gas collected by the product collection unit includes methane, which can be purified and used as fuel.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0026] (1) This invention first preheats the sludge to kill microorganisms and insect eggs in the sludge; after heating and pressurizing, the sludge is then fed into a multi-stage hydrolysis flash evaporation unit. This unit uses a pre-flash evaporation method, which causes a rapid change in pressure within the flash tank in a very short time, thereby destroying the cell walls of the sludge microorganisms and releasing the cell contents, proteins, and water from the flocs into the hydrolysate; then, the material in the tank is separated from the water through filtration, the hydrolysate is discharged, and the remaining sludge is fed into a hydrolysis reactor for alkaline hot water hydrolysis, which decomposes the organic matter in the sludge and hydrolyzes the hydrophilic organic colloidal substances; after hydrolysis, the material in the tank is fed into a secondary flash evaporation tank for flash evaporation, which completely destroys the cell walls of the sludge microorganisms and releases all the water from the cells. The process of this invention greatly improves the hydrolysis efficiency and degree of hydrolysis of municipal sludge, enhances the dewatering performance of the sludge, and thus improves the solid-liquid separation efficiency and the fertilizer effect of the end product.

[0027] (2) Through experimental simulation verification, the process of the present invention can release the contents of sludge microbial cells to a great extent into the hydrolysate. The water content of the municipal sludge dewatering cake after treatment by the process of the present invention reaches 15%, which is 40% lower than the process disclosed in the previous patent; the COD, ammonia nitrogen and total nitrogen values ​​in the hydrolysate are about 60% higher than those of the process disclosed in the previous patent.

[0028] (3) The water vapor discharged during the flash evaporation and depressurization process is condensed and absorbs soluble gases before flowing into a liquid collection tank, where it is then mixed with the hydrolysate to form liquid fertilizer; insoluble gases such as methane are passed into a gas collection tank, purified, and used as fuel. Through the above technical means, the reduction and resource utilization of municipal sludge treatment are ultimately achieved. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the multi-stage flash evaporation treatment system for municipal sludge using alkaline hot water hydrolysis as described in this invention;

[0030] In the diagram: 1-Sludge receiving and storage device, 2-Sludge blending and preheating device, 3-Screw pump, 4-Sludge multi-stage hydrolysis flash evaporation unit, 401-First-stage flash tank, 402-Hydrolysis reactor, 403-Second-stage flash tank, 404-Pressure relief and exhaust valve, 405-Filter device, 5-Condensation device, 6-Product collection unit, 601-Liquid collection tank, 602-Gas collection tank, 603-Check valve.

[0031] Figure 2 This is a process flow diagram of the present invention. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0033] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0034] The municipal sludge was taken from a municipal wastewater treatment plant in Nanjing, Jiangsu Province. Its water content was 85%, pH value was 7.5, TCOD was 94.12 g / L, C / N ratio was 12.56, and VS / TS ratio was 65%. The above values ​​are the average values ​​during this round of experiments.

[0035] Example 1

[0036] like Figure 1 As shown, the present invention discloses a multi-stage flash evaporation treatment system for municipal sludge using alkaline hot water hydrolysis. The system comprises a sludge receiving and storage device 1, a sludge mixing and preheating device 2, a multi-stage hydrolysis flash evaporation unit 4, a condensation device 5, and a product collection unit 6, connected in sequence. The condensation device 5 is connected to both the sludge mixing and preheating device 2 and the outside environment. Both the multi-stage hydrolysis flash evaporation unit 4 and the product collection unit 6 are connected to the outside environment. The sludge mixing and preheating device 2 is connected to the multi-stage hydrolysis flash evaporation unit 4 via a screw pump 3.

[0037] The multi-stage sludge hydrolysis flash unit 4 includes a primary flash tank 401, a hydrolysis reactor 402, and a secondary flash tank 403 connected in sequence. The inlet of the primary flash tank 401 is connected to the outlet of the sludge mixing and preheating device 2 via a screw pump 3. The outlet of the primary flash tank 401 is connected to the inlet of the hydrolysis reactor 402. The outlet of the hydrolysis reactor 402 is connected to the inlet of the secondary flash tank 403. Both the top of the primary flash tank 401 and the top of the secondary flash tank 403 are equipped with pressure relief and exhaust valves 404. The steam outlets of both the primary flash tank 401 and the secondary flash tank 403 are connected to the steam inlet of the condensing device 5 via pressure relief and exhaust valves 404. The outlets of both the primary flash tank 401 and the secondary flash tank 403 are connected to the outside environment. A filter device 405 is installed at the bottom of the discharge port of the primary flash tank 401, allowing the material after primary flash evaporation to undergo solid-liquid separation through the filter device 405. The hydrolysate is discharged externally, and the remaining sludge is fed into the hydrolysis reactor 402. The inner diameter of the pipe connecting the primary flash tank 401, the secondary flash tank 403, and the condenser 5 is 20-100cm to ensure that the flash evaporation exhaust and pressure relief process can be achieved in a very short time.

[0038] The product collection unit 6 includes a liquid collection tank 601 and a gas collection tank 602, which are connected by a check valve 603. The liquid inlet of the liquid collection tank 601 is connected to the liquid outlet of the condenser 5, and the liquid outlet of the liquid collection tank 601 is connected to the outside. The gas outlet of the liquid collection tank 601 is connected to the gas inlet of the gas collection tank 602 through the check valve 603.

[0039] The discharge port of the sludge receiving and storage device 1 is connected to the inlet of the sludge blending and preheating device 2. The discharge port of the sludge blending and preheating device 2 is connected to the inlet of the first-stage flash tank 401 through the screw pump 3. The condenser tube inside the condenser device 5 is spiral to increase the heat exchange area between the discharged gas and the condensate, so as to ensure that the discharged gas can be fully condensed. The end of the condenser tube should be below the liquid level in the liquid collection tank 601. The inlet of the condenser device 5 is connected to the outside, and the outlet of the condenser device 5 is connected to the sludge blending and preheating device 2. Most of the water discharged from the condenser device 5 is discharged externally, and a small portion can be returned to the sludge blending and preheating device 2 for sludge blending.

[0040] like Figure 2 As shown, the method for treating municipal sludge using the aforementioned multi-stage flash evaporation treatment system combining alkaline hot water hydrolysis includes the following steps:

[0041] (1) Sludge preparation and preheating: municipal sludge and calcium oxide powder in sludge receiving and storage device 1 are put into sludge preparation and preheating device 2, and water is added to prepare the sludge into slurry.

[0042] (2) Multi-stage hydrolysis flash evaporation of sludge: The sludge is fed into the first-stage flash tank 401 for flash evaporation. The pressure relief valve 404 is opened to release the pressure in a short time. The material after the first-stage flash evaporation is filtered by the filter device 405 and the filtrate is discharged. The remaining sludge is fed into the hydrolysis reactor 402 for alkaline hot water hydrolysis reaction. The sludge after the reaction is transported to the second-stage flash tank 403 for flash evaporation. After the flash evaporation is completed, the material is discharged and solid-liquid separation is performed.

[0043] (3) Collection of sludge hydrolysis products: The gas discharged during the flash evaporation process is condensed by the condensing device 5 through the connecting pipe and then discharged into the product collection unit 6. The water vapor is condensed and absorbs the soluble gas and flows into the liquid collection tank 601, while the insoluble gas is discharged into the gas collection tank 602.

[0044] In step (1), the municipal sludge is residual activated sludge with a moisture content of 80-85%, the sludge has a moisture content of 90-95%, the calcium oxide powder is added at 18-22% of the dry weight of the sludge, and the preheating temperature in the sludge mixing and preheating device 2 is 160-200℃, and the pressure is 2.5-3.5MPa; in step (2), during the exhaust and depressurization process of the primary flash tank 401 and the secondary flash tank 403, the pressure inside the tank is reduced to atmospheric pressure within 1-60s. The temperature of the alkaline hot water hydrolysis reaction is 160-200℃, and the time of the alkaline hot water hydrolysis reaction is 2-4h; in step (3), the condensate and soluble gas collected in the liquid collection tank 601 are mixed with the filtrate discharged from the first flash tank 401 in step (2) and the hydrolysate after solid-liquid separation of the remaining material discharged from the second flash tank 403 and then recycled as liquid fertilizer; the insoluble gas collected in the gas collection tank 602 includes methane, which can be purified and used as fuel.

[0045] Example 2

[0046] The municipal sludge treatment system using the combined alkaline hot water hydrolysis multi-stage flash evaporation method described in Example 1 includes the following steps:

[0047] (1) Sludge preparation and preheating: municipal sludge with a moisture content of 85% and calcium oxide powder with an addition ratio of 20% of the dry weight of sludge are put into sludge preparation and preheating device 2, water is added to prepare sludge with a moisture content of 95%, and heated to 180°C without setting a heat preservation time. The pressure inside sludge preparation and preheating device 2 is 2.8MPa at this time, according to the pressure gauge reading.

[0048] (2) Multi-stage hydrolysis flash evaporation of sludge: The preheated sludge is pumped to the first-stage flash tank 401 by the screw pump 3 for flash evaporation. The pressure relief valve 404 is opened to release the pressure. Within 20 seconds, the pressure in the first-stage flash tank 401 drops to atmospheric pressure. After flash evaporation, the material in the first-stage flash tank 401 is filtered by the filter device 405. The filtrate is discharged and the remaining sludge is fed into the hydrolysis reactor 402. The sludge in the hydrolysis reactor 402 is then heated to 180°C and held for 2 hours for alkaline hot water hydrolysis reaction. After the alkaline hot water hydrolysis reaction is completed, the sludge is fed into the second-stage flash tank 403 for flash evaporation. The pressure gauge reading shows that the pressure in the second-stage flash tank 403 is 2.5 MPa. The pressure relief valve 404 is opened to release the pressure. Within 20 seconds, the pressure in the second-stage flash tank 403 drops to atmospheric pressure. After flash evaporation, the remaining material in the second-stage flash tank 403 is cooled and discharged for solid-liquid separation.

[0049] (3) Sludge hydrolysis gas collection: During the flash evaporation process, the gas discharged from the primary flash tank 401 and the secondary flash tank 403 is condensed by the condensing device 5 through the connecting pipe and then discharged into the product collection unit 6. At this time, water vapor condenses and absorbs soluble gases, flowing into the liquid collection tank 601, while insoluble gases such as methane are discharged into the gas collection tank 602, which can be purified and used as fuel. The condensate and soluble gases collected in the liquid collection tank 601 are mixed with the filtrate discharged from the primary flash tank 401 and the hydrolysate after solid-liquid separation of the remaining material discharged from the secondary flash tank 403, and then sent to the outside as liquid fertilizer for recycling.

[0050] After dehydration and centrifugation of the remaining material discharged from the secondary flash tank 403 in step (2), the moisture content of the dehydrated cake and the COD, ammonia nitrogen and total nitrogen of the hydrolysate were determined. The results are as follows: the moisture content of the dehydrated cake is 15%; the COD value of the hydrolysate is 86500 mg / L, the ammonia nitrogen value is 2441 mg / L, and the total nitrogen value is 6788 mg / L.

[0051] Comparative Example 1

[0052] A method and system for acid-base hydrolysis of municipal sewage sludge, disclosed in CN115259597A, includes the following steps:

[0053] Step (1): Start the stirrer of the alkaline reactor, then add the alkaline agent calcium oxide (calcium oxide dosage is 20% of the dry weight of municipal sludge) and municipal sludge with a water content of 85% in sequence. Add water to adjust the material moisture content to 90%, heat to 120°C, and then keep warm for 60 minutes to obtain the hydrolyzed alkaline sludge mixture.

[0054] Step (2): The alkaline sludge mixture is output to the acid reactor, an acid solution (sulfuric acid solution) is added, the pH of the alkaline sludge mixture is adjusted to 5, saturated steam is introduced to heat it to 120°C, and then the temperature is maintained for 60 minutes to obtain the hydrolyzed acid sludge mixture.

[0055] Step (3) outputs the acidic sludge mixture to the flash evaporation system, and the material temperature is reduced to 60°C by the flash evaporation system;

[0056] Step (4) involves outputting the cooled acidic sludge mixture to a solid-liquid separation device, through which the filtrate and sludge cake are separated.

[0057] The moisture content of the mud cake obtained in step (4) and the COD, ammonia nitrogen and total nitrogen of the filtrate were determined. The results are as follows: the moisture content of the mud cake was 55%; the COD value of the filtrate was 54500 mg / L, the ammonia nitrogen value was 1567 mg / L, and the total nitrogen value was 4436 mg / L.

[0058] Comparing the results of Example 2 with those of Comparative Example 1, it was found that the moisture content of the dehydrated cake in Example 2 was 40% lower than that in Comparative Example 1; and the COD value, ammonia nitrogen value, and total nitrogen value of the hydrolysate were 58.72%, 55.78%, and 53.02% higher than those in Comparative Example 1, respectively.

[0059] In summary, the multi-stage flash evaporation treatment system and method for municipal sludge using combined alkaline hot water hydrolysis disclosed in this invention can greatly improve the hydrolysis efficiency and degree of hydrolysis of municipal sludge, exhibiting excellent performance in the treatment of municipal sludge and realizing the reduction and resource utilization of municipal sludge.

[0060] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for treating municipal sewage sludge, characterized in that, A multi-stage flash evaporation treatment system for municipal sludge using combined alkaline hot water hydrolysis is described. The system comprises a sludge receiving and storage device (1), a sludge mixing and preheating device (2), a multi-stage hydrolysis flash evaporation unit (4), a condensation device (5), and a product collection unit (6), connected in sequence. The multi-stage hydrolysis flash evaporation unit (4) includes a primary flash tank (401), a hydrolysis reactor (402), and a secondary flash tank (403), connected in sequence. The primary flash tank (401) is connected to the sludge mixing and preheating device (2), and the primary flash tank (401) and the secondary flash tank (403) are connected in sequence. All flash tanks (403) are connected to the condensing device (5). The condensing device (5) is also connected to the sludge mixing and preheating device (2) and the outside. The first-stage flash tank (401), the second-stage flash tank (403) and the product collection unit (6) are all connected to the outside. The bottom of the discharge port of the first-stage flash tank (401) is equipped with a filter device (405), which allows the material after the first-stage flash to pass through the filter device (405) to achieve solid-liquid separation. The hydrolysate is discharged outside the boundary, and the remaining material is fed into the hydrolysis reactor (402). The product collection unit (6) includes a liquid collection tank (6). 01) and gas collection tank (602), liquid collection tank (601) and gas collection tank (602) are connected by check valve (603); the top of the first-stage flash tank (401) and the top of the second-stage flash tank (403) are equipped with pressure relief and exhaust valve (404), the steam outlet of the first-stage flash tank (401) and the steam outlet of the second-stage flash tank (403) are connected to the steam inlet of the condensing device (5) through pressure relief and exhaust valve (404); the pipeline connecting the first-stage flash tank (401), the second-stage flash tank (403) and the condensing device (5) The inner diameter is 20-100cm; the sludge preparation and preheating device (2) is connected to the sludge multi-stage hydrolysis flash evaporation unit (4) through the screw pump (3); the condenser tube inside the condenser (5) is spiral; the inlet of the liquid collection tank (601) is connected to the outlet of the condenser (5); the outlet of the condenser (5) is below the liquid surface in the liquid collection tank (601); the outlet of the liquid collection tank (601) is connected to the outside; the outlet of the liquid collection tank (601) is connected to the inlet of the gas collection tank (602) through the check valve (603); The processing method includes the following steps: (1) Sludge preparation and preheating: municipal sludge and calcium oxide powder in sludge receiving and storage device (1) are put into sludge preparation and preheating device (2), and water is added to prepare sludge into slurry; municipal sludge has a water content of 80-85% and is residual activated sludge, slurry has a water content of 90-95%, calcium oxide powder is added at 18-22% of the dry weight of sludge, the temperature of alkaline hot water hydrolysis reaction is 160-200℃, and the time of alkaline hot water hydrolysis reaction is 2-4h; (2) Multi-stage hydrolysis flash evaporation of sludge: The sludge is fed into the first-stage flash tank (401) for flash evaporation. The first-stage flash tank (401) is vented and depressurized in a short time. After the first-stage flash evaporation, the material is filtered and the filtrate is discharged. The remaining sludge is fed into the hydrolysis reactor (402) for alkaline hot water hydrolysis reaction. The sludge after the reaction is transported to the second-stage flash tank (403) for flash evaporation. After the flash evaporation is completed, the material is discharged and solid-liquid separation is performed. (3) Collection of sludge hydrolysis products: The gas discharged during the flash evaporation process is condensed by the condensation device (5) through the connecting pipe and then discharged to the product collection unit (6). In step (1), the preheating temperature in the sludge preparation and preheating device (2) is 160-200℃ and the pressure is 2.5-3.5MPa. In step (2), the pressure inside the primary flash tank (401) and the secondary flash tank (403) is reduced to normal pressure within 1-60s when the tank is vented and depressurized.

2. The method according to claim 1, characterized in that, In step (3), the condensate and soluble gas collected by the product collection unit (6) are mixed with the filtrate discharged from the first-stage flash tank (401) and the hydrolysate of the remaining material discharged from the second-stage flash tank (403) after solid-liquid separation in step (2) and then recycled as liquid fertilizer; the insoluble gas in the product collection unit (6) includes methane, which can be purified and used as fuel.

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