Reliability improvement system for preparing liquid fuel by coupling sludge liquefaction and upgrading

Abstract

The present invention belongs to the technical field of municipal sludge disposal, and discloses a reliability improvement system for preparing liquid fuel by coupling sludge liquefaction and upgrading, comprising a hydrothermal liquefaction reaction and separation unit, a hydrogenation upgrading and re-separation unit, and a flushing unit. The hydrothermal liquefaction reaction and separation unit is used to perform hydrothermal liquefaction reaction on sludge and obtain a bio-crude oil dichloromethane mixed oil phase; the hydrogenation upgrading and re-separation unit is used to separate dichloromethane from the bio-crude oil dichloromethane mixed oil phase and catalytically hydrogenate the bio-crude to prepare liquid fuel; the flushing unit is used to flush the hydrothermal liquefaction reaction unit and the separation unit and the hydrogenation upgrading and re-separation unit. The present invention ensures that the municipal sludge hydrothermal liquefaction coupled hydrogenation upgrading continuous preparation of liquid fuel system has stability and continuous reliability.

Description

Technical Field

[0001] The invention belongs to the technical field of urban sludge disposal, and in particular relates to a reliability improvement system for preparing liquid fuel by coupling sludge liquefaction and quality improvement. Background Art

[0002] Municipal sludge (abbreviated as: sludge) is an important solid by-product of conventional urban sewage treatment. Its water content is usually as high as 80% or more. It contains a large amount of organic matter, pathogens, inorganic salts and other substances. It has both harmful and resource properties. Due to population growth, urbanization and rapid development of sewage networks, the output of urban sludge continues to increase. Traditional disposal methods face difficulties such as large land area, secondary pollution, or high costs. The efficient and economical harmless treatment and disposal of urban sludge still faces many challenges and has become one of the problems that urgently need to be solved in the field of energy and environment. Therefore, the development of advanced and efficient sludge disposal technology, while carrying out harmless disposal, to achieve its resource utilization purpose has become an important development direction of sludge disposal technology.

[0003] Hydrothermal liquefaction is an advanced thermochemical treatment technology for municipal sludge, which has significant technical and economic advantages and good development prospects. It does not require a high-energy drying process. After hydrothermal liquefaction, organic matter is converted into bio-crude oil, and high-quality biofuel can be obtained after further quality improvement and modification. At the same time, it can achieve harmlessness and resource utilization of by-products without generating secondary pollutants, thus achieving efficient and economical treatment and disposal of sludge, which is of great significance for solving the problem of harmless treatment and resource utilization of sludge. However, the bio-crude oil produced by hydrothermal liquefaction of municipal sludge has high heteroatom content, high viscosity, low acid value, etc., and cannot be used directly. It must be further improved and modified to achieve engineering application.

[0004] At present, the research on the preparation of liquid fuel by hydrothermal liquefaction of municipal sludge still faces the following major problems: 1) Municipal sludge is a material with high ash content, and the inorganic salt content even exceeds 50% of the dry mass of the sludge, so it becomes the main solid by-product after hydrothermal liquefaction of sludge. The water-insoluble inert inorganic salts are prone to deposition during the transportation process after the reactor, and there is a high risk of clogging or even wearing the system pipelines, equipment, pressure reducing valves, etc., especially these inorganic salts and the high-viscosity bio-crude oil generated by the reaction are mixed and transported at low temperature. The risk of clogging is even greater, which seriously threatens the continuous reliability of the system operation; 2) The bio-crude oil generated by hydrothermal liquefaction of sludge has high viscosity, high content of heavy components, poor fluidity at room temperature, and is easy to clog the pipeline or remain in the container during the subsequent separation and transportation process, threatening the continuous and reliable operation of the system.

[0005] In view of the above problems, there have been no research reports on the realization of continuous hydrothermal liquefaction coupled with hydrogenation upgrading of municipal sludge in the same system. The existing systems and methods cannot continuously and reliably realize the hydrothermal liquefaction coupled with hydrogenation upgrading of municipal sludge to prepare liquid fuel. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a sludge liquefaction coupled quality upgrading system for preparing liquid fuel with improved reliability, which solves the problems in the prior art that the bio-crude oil generated by sludge hydrothermal liquefaction has high viscosity, high content of heavy components, poor fluidity at room temperature, and easy clogging of pipelines.

[0007] In order to achieve the above object, the present invention adopts the following technical scheme to achieve it: a reliability improvement system for preparing liquid fuel by coupling sludge liquefaction and upgrading, including a hydrothermal liquefaction reaction unit and a separation unit, a hydrogenation upgrading and re-separation unit and a flushing unit;

[0008] The hydrothermal liquefaction reaction and separation unit is used to perform hydrothermal liquefaction reaction on sludge and obtain a bio-crude oil dichloromethane mixed oil phase; it includes a tube-in-tube heat exchanger and a tubular liquefier connected by pipelines, the outlets of the tubular liquefier are connected to the first high-temperature and high-pressure solid phase filter and the second high-temperature and high-pressure solid phase filter, the first outlet of the first high-temperature and high-pressure solid phase filter is connected to the inlet of the first high-pressure partition cooler through a pipeline, the first outlet of the second high-temperature and high-pressure solid phase filter is connected to the inlet of the second high-pressure partition cooler through a pipeline, the second outlet of the first high-temperature and high-pressure solid phase filter and the second outlet of the second high-temperature and high-pressure solid phase filter are connected to the jacket of the tube-in-tube heat exchanger and the pressure reducing valve through pipelines in sequence, the nitrogen bottle is connected to the dichloromethane storage tank, and the pipeline provided with the pressure reducing valve is connected in parallel to the pipeline of the first outlet of the dichloromethane storage tank and is connected in sequence to the medium-pressure gas-liquid separator and the medium-pressure centrifugal extractor;

[0009] The hydrogenation and re-separation unit is used to separate the dichloromethane in the dichloromethane mixed oil phase of the bio-crude oil and catalytically hydrogenate the bio-crude oil to prepare liquid fuel; the first outlet of the medium-pressure centrifugal extractor and the outlet of the hydrogen cylinder are connected to the inlet of the first cascade temperature hydrogenation reactor and the inlet of the second cascade temperature hydrogenation reactor, and the first outlet of the first cascade temperature hydrogenation reactor and the first outlet of the second cascade temperature hydrogenation reactor are connected to the hydrogenation product cooler, the back pressure valve and the low-pressure gas-liquid separator in sequence;

[0010] The flushing unit is used to flush the hydrothermal liquefaction reaction unit, the separation unit, and the hydrogenation upgrading and re-separation unit; it includes a high-pressure water pump and a second outlet of the dichloromethane storage tank connected to the first high-temperature and high-pressure solid phase filter, the second high-temperature and high-pressure solid phase filter, the first step temperature hydrogenation reactor and the second step temperature hydrogenation reactor through a pipeline.

[0011] Preferably, the first high-temperature and high-pressure solid phase filter and the second high-temperature and high-pressure solid phase filter are both provided with a heating device.

[0012] Preferably, the pressure of the dichloromethane storage tank is 0.5-1.5Mpa;

[0013] The first outlet of the dichloromethane storage tank is provided with an interlocked dichloromethane flowmeter and a regulating valve, and the mass ratio of the flow of dichloromethane to the bio-crude oil is set to 2:1 to 5:1.

[0014] Preferably, the feeding time of the first step temperature hydrogenation reactor and the second step temperature hydrogenation reactor is 7 to 10 hours;

[0015] The temperatures of the first-stage temperature hydrogenation reactor and the second-stage temperature hydrogenation reactor are increased in steps. The temperature of the first stage is 50-100°C and is maintained for 1-2 hours to discharge dichloromethane. When setting the second stage, hydrogen is filled and the temperature is set to 400-450°C, and the maintenance time is 1-4 hours to hydrogenate and upgrade the bio-crude oil.

[0016] The pressure at the outlet of the hydrogen cylinder is 2-6 MPa.

[0017] Preferably, the flushing unit is provided with three stages. In the first stage, the high-pressure water pump is used to pump water to backwash the first high-temperature and high-pressure solid phase filter and the second high-temperature and high-pressure solid phase filter screen to collect the solid phase, and the flushing time is 1 to 2 hours. In the second stage, the dichloromethane at the second outlet of the dichloromethane storage tank is opened to flush the first high-temperature and high-pressure solid phase filter and the second high-temperature and high-pressure solid phase filter screen to collect the residual bio-crude oil, and the flushing time is 20 to 30 minutes. In the third stage, the high-pressure water pump is used to replenish water to the first high-temperature and high-pressure solid phase filter and the second high-temperature and high-pressure solid phase filter, and the heating device is turned on so that the temperature and pressure of the first high-temperature and high-pressure solid phase filter and the second high-temperature and high-pressure solid phase filter are consistent with the temperature and pressure of the tubular liquefier.

[0018] Compared with the prior art, the present invention has the following beneficial effects: the present invention discloses a system for improving the reliability of preparing liquid fuel by coupling liquefaction of sludge to improve the quality of the sludge, which realizes effective and continuous removal of solid products and water-insoluble inert inorganic salts after hydrothermal liquefaction of municipal sludge by setting high-temperature and high-pressure solid-phase filters in parallel, thereby preventing blockage and wear of the pressure reducing valve and even wear of system pipelines, pressure reducing valves and other equipment; realizes continuous hydrogenation and quality improvement of bio-crude oil by setting step-temperature hydrogenation reactors in parallel; the hydrogenation and quality improvement re-separation unit realizes the separation and recovery of dichloromethane and the hydrogenation and quality improvement of bio-crude oil; and the effective cleaning of the separation unit and the hydrogenation and quality improvement re-separation unit is ensured by setting a flushing unit, thereby further improving the reliability of the operation of the system for continuously preparing liquid fuel by coupling hydrothermal liquefaction of sludge to improve the quality of the ... The reliability improvement system for preparing liquid fuel by coupling sludge liquefaction and upgrading is achieved by pretreating the sludge slurry and performing a hydrothermal liquefaction reaction. The bio-crude oil after hydrothermal liquefaction is transported to a temperature hydrogenation reactor with the assistance of dichloromethane, which makes the fluidity of the bio-crude oil better. This system can realize the continuous preparation of liquid fuel by hydrogenation upgrading of bio-crude oil from hydrothermal liquefaction of municipal sludge.

[0019] Furthermore, the high-temperature and high-pressure solid phase filter is provided with a heating device, so that when the flushing function is realized, the water in the high-temperature and high-pressure solid phase filter can be heated, so that the temperature and pressure of the water are consistent with the temperature and pressure of the tubular liquefier, thereby preventing the system pressure and temperature from fluctuating violently when the two parallel high-temperature and high-pressure solid phase filters are switched, thereby improving the stability and reliability of the continuous operation of the system.

[0020] Furthermore, the low viscosity and high fluidity of bio-crude oil under high temperature conditions are used to separate the inert inorganic salts from the bio-crude oil after the reaction; adding dichloromethane to the bio-crude oil can reduce the viscosity of the bio-crude oil, forming a bio-crude oil dichloromethane mixed oil phase with good fluidity, ensuring continuous, stable and reliable transportation, avoiding high-viscosity bio-crude oil from clogging the system pipelines or equipment, and improving the transportation characteristics of the fluid after the reaction, thereby ensuring the continuous reliability of the reaction fluid after the hydrothermal liquefaction of municipal sludge in the system pipelines and equipment transportation. Accurately controlling the flow mass ratio of dichloromethane to bio-crude oil allows dichloromethane to extract more bio-crude oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the present invention;

[0022] Among them: 1. Tube-in-tube heat exchanger, 2. Tubular liquefier with heating, 3. First high-temperature and high-pressure solid phase filter, 4. Pressure reducing valve, 5. Nitrogen cylinder, 6. Dichloromethane storage tank, 7. Dichloromethane flowmeter, 8. Medium-pressure gas-liquid separator, 9. Medium-pressure centrifugal extractor, 10. First cascade temperature hydrogenation reactor, 11. Hydrogenation upgrading product cooler, 12. Back pressure valve, 13. Low-pressure gas-liquid separator, 14. Second cascade temperature hydrogenation reactor, 15. Hydrogen cylinder, 16. High-pressure water pump, 17. Water tank, 18. Second high-temperature and high-pressure solid phase filter, 19. Second high-pressure partition cooler, 20. First high-pressure partition cooler, 21. Stop valve. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0024] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0025] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0026] See also Figure 1 , a reliability improvement system for sludge liquefaction coupled with upgrading to prepare liquid fuel, including a hydrothermal liquefaction reaction and separation unit, a hydrogenation upgrading and re-separation unit, and a flushing unit;

[0027] The hydrothermal liquefaction reaction and separation unit is used to perform hydrothermal liquefaction reaction on sludge and obtain a bio-crude oil dichloromethane mixed oil phase; it includes a tube-and-tube heat exchanger 1 and a tube-and-tube liquefier 2 connected by pipelines; the outlets of the tube-and-tube liquefier 2 are both connected to the first high-temperature and high-pressure solid phase filter 3 and the second high-temperature and high-pressure solid phase filter 18, the first outlet of the first high-temperature and high-pressure solid phase filter 3 is connected to the inlet of the first high-pressure partition cooler 20 through a pipeline, the first outlet of the second high-temperature and high-pressure solid phase filter 18 is connected to the inlet of the second high-pressure partition cooler 19 through a pipeline, the second outlet of the first high-temperature and high-pressure solid phase filter 3 and the second outlet of the second high-temperature and high-pressure solid phase filter 18 are connected to the jacket of the tube-and-tube heat exchanger 1 and the pressure reducing valve 4 in sequence through pipelines, the nitrogen bottle 5 is connected to the dichloromethane storage tank 6, the pipeline provided with the pressure reducing valve 4 and the pipeline of the outlet of the dichloromethane storage tank 6 are connected in parallel to the medium-pressure gas-liquid separator 8 and the medium-pressure centrifugal extractor 9 in sequence;

[0028] The hydrogenation and re-separation unit is used to separate the dichloromethane in the dichloromethane mixed oil phase of the bio-crude oil and catalytically hydrogenate the bio-crude oil to prepare liquid fuel; the first outlet of the medium-pressure centrifugal extractor 9 and the outlet of the hydrogen bottle 15 are connected to the inlet of the first step temperature hydrogenation reactor 10 and the inlet of the second step temperature hydrogenation reactor 14, and the first outlet of the first step temperature hydrogenation reactor 10 and the first outlet of the second step temperature hydrogenation reactor 14 are connected to the hydrogenation product cooler 11 and the low-pressure gas-liquid separator 13 in sequence;

[0029] The flushing unit is used to flush the separation unit and the hydrogenation upgrading and re-separation unit; it includes a high-pressure water pump 16 and a second outlet of the dichloromethane storage tank 6, which are connected to the first high-temperature and high-pressure solid phase filter 3, the second high-temperature and high-pressure solid phase filter 18, the first step temperature hydrogenation reactor 10 and the second step temperature hydrogenation reactor 14 through pipelines, and the high-pressure water pump 16 is connected to the water tank 17.

[0030] A stop valve 21 is provided on the pipeline of the first high-pressure partition cooler 20 and the second high-pressure partition cooler 19. The stop valve 21 is opened to discharge the solid residue of the first high-pressure partition cooler 20 and the second high-pressure partition cooler 19.

[0031] The pore sizes of the first high-temperature and high-pressure solid phase filter 3 and the second high-temperature and high-pressure solid phase filter 18 are 30-50 μm.

[0032] The pretreated sludge slurry is preheated to about 300°C through a tube-in-tube heat exchanger 1, and transported to a tubular liquefier 2 to obtain a hydrothermal liquefied reaction fluid (about 350°C, 17MPa, 20min); the hydrothermal liquefied reaction fluid is passed through a first high-temperature and high-pressure solid phase filter 3 and a second high-temperature and high-pressure solid phase filter 18 to obtain a solid phase product and bio-crude oil, with a filtration temperature of 350°C and a filtration pressure of 17MPa. The bio-crude oil is transported to the jacket of the tube-and-tube heat exchanger 1 to preheat the pretreated sludge slurry, and at the same time, the water phase, the oil phase and the gas phase are cooled to 80°C, and the pressure is reduced to 0.5-1.5MPa through the pressure reducing valve 4; the dichloromethane storage tank 6 is pressurized by the nitrogen bottle 5, and the outlet of the dichloromethane pressurized storage tank 6 is provided with a dichloromethane flowmeter 7 and a regulating valve V1, and the regulating valve is interlocked with the flowmeter. The ratio of the dichloromethane flow rate to the bio-crude oil flow rate is 2:1-5:1 through the regulation of the regulating valve V1, and the bio-crude oil passing through the pressure reducing valve 4 and the dichloromethane flowmeter 7 and the regulating valve V1 are adjusted. The dichloromethane regulated by the valve V1 is transported to the inlet of the medium-pressure gas-liquid separator 8, and a small amount of gas products after the hydrothermal liquefaction of the sludge are separated at the first outlet of the medium-pressure gas-liquid separator 8. The oil phase is output from the second outlet of the medium-pressure gas-liquid separator 8 and transported to the inlet of the medium-pressure centrifugal extractor 9. The water phase is separated at the first outlet of the medium-pressure centrifugal extractor 9, and the bio-crude dichloromethane mixed oil phase is output from the second outlet of the medium-pressure centrifugal extractor 9. The liquid levels of the medium-pressure gas-liquid separator 8 and the medium-pressure centrifugal extractor 9 are respectively controlled by regulating valves V2 and V3; the bio-crude dichloromethane mixed oil phase is transported to the first The step temperature hydrogenation reactor 10 and the second step temperature hydrogenation reactor 14, the heating temperature of the first step temperature hydrogenation reactor 10 and the second step temperature hydrogenation reactor 14 is 50-100°C, the dichloromethane outlet valve is opened, the dichloromethane outlet valve is closed after the dichloromethane is discharged, and the hydrogen inlet valve is opened, the pressure of the hydrogen cylinder 15 outlet is 2-6MPa, the heating temperature of the first step temperature hydrogenation reactor 10 and the second step temperature hydrogenation reactor 14 is 400-450°C, the heating time is 1-4h, and the product is obtained; the product is transported to the hydrogenation quality upgrading product The product is cooled by the material cooler 11 and the temperature drops to about 45°C. The cooled product is transported to the low-pressure gas-liquid separator 13 through the back pressure valve 12. The first outlet of the low-pressure gas-liquid separator 13 outputs gas, and the second outlet of the low-pressure gas-liquid separator 13 outputs liquid fuel. When the pressure difference between the inside and outside of the first high-temperature and high-pressure solid phase filter 3 and the second high-temperature and high-pressure solid phase filter 18 exceeds 2MPa, they are switched with each other. After the high-temperature and high-pressure solid phase filter is shut down, the filter is cleaned by the multi-stage backwashing program set up to ensure the stability and reliability of the high-temperature and high-pressure solid phase filter equipment during operation.Specific flushing procedure: In the first stage, a high-pressure water pump 16 connected to a water tank 17 is used to pump water to backwash the high-temperature and high-pressure solid phase filter screen and collect the solid phase in the filter, and the flushing time is 1 to 2 hours; in the second stage, dichloromethane is further used to flush the high-temperature and high-pressure solid phase filter screen and the residual biocrude oil in the filter is collected, and the flushing time is 20 to 30 minutes; in the third stage, after the cleaning is completed, the high-pressure water pump 16 is used to replenish water into the high-temperature and high-pressure solid phase filter, so that the heating device in the high-temperature and high-pressure solid phase filter heats the water, so that the temperature and pressure of the water in the high-temperature and high-pressure solid phase filter are consistent with the temperature and pressure of the tubular liquefier 2, so as to prevent the system pressure and temperature from fluctuating violently when the first high-temperature and high-pressure solid phase filter 3 and the second high-temperature and high-pressure solid phase filter 18 are switched, thereby improving the stability and reliability of the continuous operation of the system. In addition, a dichloromethane flushing device is provided on the first and second step temperature hydrogenation reactors 10 / 14. The dichloromethane used for flushing also comes from the dichloromethane pressurized storage tank 6, which can fully extract and clean the residual bio-oil products after upgrading during the shutdown of the first / second step temperature hydrogenation reactors 10 / 14, so as to prepare for the next round of hydrogenation and upgrading reaction, and avoid the accumulation of upgraded bio-oil in the step temperature hydrogenation reactor, resulting in uneven heating of the equipment and affecting the reliability and stability of continuous operation.

[0033] By interlocking the dichloromethane flowmeter 7 with the opening of the regulating valve V1, the flow rate of dichloromethane is controlled to ensure the mass ratio of dichloromethane to bio-crude oil flow. By using less extractant, the viscosity of the bio-crude oil is fully reduced to form a bio-crude oil dichloromethane mixed oil phase with good fluidity, thereby ensuring continuous, stable and reliable transportation and avoiding high-viscosity bio-crude oil from clogging system pipelines or equipment.

[0034] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. The reliability improvement system of sludge liquefaction coupled with upgrading to prepare liquid fuel is characterized by: It includes a hydrothermal liquefaction reaction unit and a separation unit, a hydrogenation upgrading and re-separation unit and a flushing unit; The hydrothermal liquefaction reaction and separation unit is used for performing a hydrothermal liquefaction reaction on sludge and obtaining a bio-crude oil dichloromethane mixed oil phase; it comprises a tube-in-tube heat exchanger (1) and a tubular liquefier (2) connected by pipelines, the outlets of the tubular liquefier (2) are both connected to a first high-temperature and high-pressure solid phase filter (3) and a second high-temperature and high-pressure solid phase filter (18), the first outlet of the first high-temperature and high-pressure solid phase filter (3) is connected to an inlet of a first high-pressure partition wall cooler (20) through a pipeline, and the outlet of the second high-temperature and high-pressure solid phase filter (18) is connected to an inlet of a first high-pressure partition wall cooler (20) through a pipeline. The first outlet is connected to the inlet of the second high-pressure partition cooler (19) through a pipeline, the second outlet of the first high-temperature and high-pressure solid phase filter (3) and the second outlet of the second high-temperature and high-pressure solid phase filter (18) are connected to the jacket of the tube-in-tube heat exchanger (1) and the pressure reducing valve (4) in sequence through pipelines, the nitrogen bottle (5) is connected to the dichloromethane storage tank (6), the pipeline provided with the pressure reducing valve (4) is connected in parallel to the pipeline of the first outlet of the dichloromethane storage tank (6), and is connected to the medium-pressure gas-liquid separator (8) and the medium-pressure centrifugal extractor (9) in sequence; The first outlet of the dichloromethane storage tank (6) is provided with an interlocked dichloromethane flow meter (7) and a regulating valve, and the mass ratio of the flow of dichloromethane to the bio-crude oil is set to 2:1-5:1; The hydrogenation and re-separation unit is used to separate dichloromethane from the dichloromethane mixed oil phase of the bio-crude oil and to catalytically hydrogenate the bio-crude oil to prepare liquid fuel; the first outlet of the medium-pressure centrifugal extractor (9) and the outlet of the hydrogen bottle (15) are both connected to the inlet of the first step temperature hydrogenation reactor (10) and the inlet of the second step temperature hydrogenation reactor (14); the first outlet of the first step temperature hydrogenation reactor (10) and the first outlet of the second step temperature hydrogenation reactor (14) are connected in sequence to the hydrogenation product cooler (11), the back pressure valve (12) and the low-pressure gas-liquid separator (13); The feeding time of the first step temperature hydrogenation reactor (10) and the second step temperature hydrogenation reactor (14) is 7 to 10 hours; The temperatures of the first-stage temperature hydrogenation reactor (10) and the second-stage temperature hydrogenation reactor (14) are increased in a stepwise manner, wherein the temperature of the first stage is 50-100°C and is maintained for 1-2 hours for discharging dichloromethane, and when the second stage is set, hydrogen is filled and the temperature is set to 400-450°C and maintained for 1-4 hours for hydrogenation and upgrading of the bio-crude oil; The flushing unit is used to flush the hydrothermal liquefaction reaction unit, the separation unit, and the hydrogenation upgrading and re-separation unit; it comprises a high-pressure water pump (16) and a second outlet of the dichloromethane storage tank (6) connected to a first high-temperature and high-pressure solid phase filter (3), a second high-temperature and high-pressure solid phase filter (18), a first step-temperature hydrogenation reactor (10), and a second step-temperature hydrogenation reactor (14) through a pipeline.

2. The reliability improvement system for preparing liquid fuel by coupling sludge liquefaction and upgrading according to claim 1 is characterized in that: The first high-temperature and high-pressure solid phase filter (3) and the second high-temperature and high-pressure solid phase filter (18) are both provided with a heating device.

3. The reliability improvement system for preparing liquid fuel by coupling sludge liquefaction and upgrading according to claim 1 is characterized in that: The pressure of the dichloromethane storage tank (6) is 0.5-1.5 Mpa.

4. The reliability improvement system for preparing liquid fuel by coupling sludge liquefaction and upgrading according to claim 1 is characterized in that: The pressure at the outlet of the hydrogen cylinder (15) is 2-6 MPa.

5. The reliability improvement system for preparing liquid fuel by coupling sludge liquefaction and upgrading according to claim 1 is characterized in that: The flushing unit is provided with three stages. In the first stage, the high-pressure water pump (16) is used to pump water to backwash the filter screens of the first high-temperature and high-pressure solid phase filter (3) and the second high-temperature and high-pressure solid phase filter (18) to collect the solid phase, and the flushing time is 1 to 2 hours. In the second stage, the dichloromethane at the second outlet of the dichloromethane storage tank (6) is opened to flush the filter screens of the first high-temperature and high-pressure solid phase filter (3) and the second high-temperature and high-pressure solid phase filter (18) to collect the residual bio-crude oil, and the flushing time is 20 to 30 minutes. In the third stage, the high-pressure water pump (16) is used to replenish water to the first high-temperature and high-pressure solid phase filter (3) and the second high-temperature and high-pressure solid phase filter (18), and the heating device is turned on so that the temperature and pressure of the first high-temperature and high-pressure solid phase filter (3) and the second high-temperature and high-pressure solid phase filter (18) are consistent with the temperature and pressure of the tubular liquefier (2).

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