Flue gas waste heat utilization system based on vacuum heat pipe technology and optimized operation method of flue gas waste heat utilization system

Abstract

The invention discloses a flue gas waste heat utilization system based on a vacuum heat pipe technology and an optimized operation method thereof, and the system combines supercritical water gasification, synthesis gas combustion power generation and vacuum heat pipe waste heat recovery to form an efficient integrated energy conversion system. The system core comprises a supercritical water gasification reactor, a combustor, a supercritical turbine and a waste heat recovery network composed of high-temperature, medium-temperature and low-temperature vacuum heat pipes, and is coupled with an organic Rankine cycle to achieve deep utilization of low-grade heat energy. The vacuum heat pipe is of a sectional type structural design, thorough isolation of the smoke side and the water side is achieved, rapid heat transfer is completed under the small temperature difference based on self-circulation formed by phase change heat transfer of an internal medium and capillary force driving, and gradient utilization of smoke waste heat is achieved. Through optimal matching of the vacuum heat pipe network and the supercritical water gasification power generation system, the technical problems that a traditional waste heat recovery device is low in heat exchange efficiency and prone to ash deposition corrosion are solved, and the comprehensive energy efficiency of the system is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy recovery and energy conservation, and particularly relates to a flue gas waste heat utilization system based on vacuum heat pipe technology and an optimized operation method thereof. Background Art

[0002] In energy utilization, flue gas emission, as an important form of energy waste, has imposed great pressure on the environment and resources. Especially during the operation of combustion boilers, thermal power plants, and other industrial furnaces, a large amount of flue gas waste heat is directly discharged into the atmosphere, which not only causes energy waste but also increases environmental pollution. Therefore, how to effectively recover and utilize the waste heat in these flue gases has become an important research direction in the current energy utilization field.

[0003] Traditional flue gas waste heat recovery technologies mainly rely on heat exchangers and heat transfer equipment to transfer the waste heat to a cooling medium for recovery. However, while the existing technologies can recover flue gas waste heat efficiently, they still face many technical bottlenecks. For example, problems such as low heat exchange efficiency, serious equipment fouling, poor adaptability, and limited energy recovery capacity often lead to unsatisfactory waste heat recovery effects and cannot meet the requirements of high energy efficiency and low pollution emissions in industrial production. Summary of the Invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a flue gas waste heat utilization system based on vacuum heat pipe technology and an optimized operation method thereof. By reasonably arranging the vacuum heat pipe network, the cascade utilization of flue gas waste heat is efficiently realized, the thermal energy utilization efficiency is improved, energy waste is reduced, and the goal of energy conservation and emission reduction is achieved.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A flue gas waste heat utilization system based on vacuum heat pipe technology, comprising a supercritical water gasification reactor 1, a high-temperature vacuum heat pipe 2, a burner 3, a supercritical turbine 4, a medium-temperature vacuum heat pipe 5, a low-temperature vacuum heat pipe 6, an organic working fluid heat exchanger 7, an organic working fluid turbine 8, an organic working fluid condenser 9, an organic working fluid pump 10, a cooler 11, a gas-liquid separator 12, and a feed water pump 13; coal is connected to the inlet of the supercritical water gasification reactor 1 via a coal conveying pipeline, ash is discharged from the supercritical water gasification reactor 1 via an ash discharging pipeline, the outlet of the supercritical water gasification reactor 1 is connected to the inlet of the evaporation section of the high-temperature vacuum heat pipe 2, the outlet of the evaporation section of the high-temperature vacuum heat pipe 2 is connected to the inlet of the burner 3, oxygen is connected to the inlet of the burner 3, and the outlet of the burner 3 is connected to the inlet of the supercritical turbine 4; the intermediate extraction of the supercritical turbine 4 is connected to the inlet of the evaporation section of the medium-temperature vacuum heat pipe 5, the outlet of the evaporation section of the medium-temperature vacuum heat pipe 5 and the exhaust gas of the supercritical turbine 4 are respectively connected to the inlet of the evaporation section of the low-temperature vacuum heat pipe 6, the outlet of the evaporation section of the low-temperature vacuum heat pipe 6 is connected to the hot end inlet of the organic working fluid heat exchanger 7, the hot end outlet of the organic working fluid heat exchanger 7 is connected to the inlet of the cooler 11, and the outlet of the cooler 11 is connected to the inlet of the gas-liquid separator 12; the carbon dioxide at the gas phase outlet of the gas-liquid separator 12 is discharged from the system, a part of the feed water at the liquid phase outlet of the gas-liquid separator 12 is discharged from the system, a part of the feed water is recycled to the system and connected to the inlet of the feed water pump 13, the outlet of the feed water pump 13 is connected to the inlet of the condensation section of the low-temperature vacuum heat pipe 6, the outlet of the condensation section of the low-temperature vacuum heat pipe 6 is connected to the inlet of the condensation section of the medium-temperature vacuum heat pipe 5, the outlet of the condensation section of the medium-temperature vacuum heat pipe 5 is connected to the inlet of the condensation section of the high-temperature vacuum heat pipe 2, and the outlet of the condensation section of the high-temperature vacuum heat pipe 2 is connected to the inlet of the supercritical water gasification reactor 1; the cold end outlet of the organic working fluid heat exchanger 7 is connected to the inlet of the organic working fluid turbine 8, the outlet of the organic working fluid turbine 8 is connected to the inlet of the organic working fluid condenser 9, the outlet of the organic working fluid condenser 9 is connected to the inlet of the organic working fluid pump 10, and the outlet of the organic working fluid pump 10 is connected to the cold end inlet of the organic working fluid heat exchanger 7.

[0007] The operating temperature of the supercritical water gasification reactor 1 is 600°C - 800°C, and the operating pressure is 23 MPa - 30 MPa.

[0008] The oxygen coefficient at the inlet of the burner 3 is 1.05 - 1.20. A complete oxidation reaction of syngas occurs in the burner 3, and the outlet of the burner 3 is a mixed working fluid mainly composed of supercritical water and supercritical carbon dioxide.

[0009] The inlet temperature of the supercritical turbine 4 is 600°C - 700°C, and the exhaust pressure at the outlet is 0.1 - 0.2 MPa.

[0010] The interiors of the high-temperature vacuum heat pipe 2, the medium-temperature vacuum heat pipe 5, and the low-temperature vacuum heat pipe 6 are in a vacuum state, and the vacuum degree is 10 -3 -10 -1Pa.

[0011] The high-temperature vacuum heat pipe 2, medium-temperature vacuum heat pipe 5, and low-temperature vacuum heat pipe 6 adopt a segmented structure, which is divided into two independent chambers, a condensation section and an evaporation section, and the upper and lower chambers are separated by a partition. The length of the evaporation section accounts for 30%-60% of the total length of the heat pipe.

[0012] The evaporation section of the high-temperature vacuum heat pipe 2 is inserted into the gasification synthesis gas channel and is connected to the supercritical water gasification reactor 1 and the burner 3 respectively. The condensation section is connected to the gasification feed water pipeline; the evaporation sections of the medium-temperature vacuum heat pipe 5 and the low-temperature vacuum heat pipe 6 are inserted into the flue gas channel at the outlet of the supercritical turbine 4, and the condensation sections are connected to the gasification feed water pipeline.

[0013] The cooling temperature at the outlet of the cooler 11 is 20°C - 32°C.

[0014] An optimized operation method for a flue gas waste heat utilization system based on vacuum heat pipe technology is as follows: Coal enters the supercritical water gasification reactor 1 through the coal conveying pipeline. The gasification feed water enters the supercritical water gasification reactor 1 from the outlet of the condensation section of the high-temperature vacuum heat pipe 2. In the supercritical water gasification reactor 1, coal undergoes a supercritical water gasification reaction with the gasification feed water to generate synthesis gas. The nitrogen and sulfur elements in the coal are deposited as inorganic salts and are discharged from the supercritical water gasification reactor 1 along with the ash. The synthesis gas enters the burner 3 through the evaporation section of the high-temperature vacuum heat pipe 2 and undergoes a complete oxidation reaction with the oxygen entering the burner 3 to generate a mixed working fluid mainly composed of supercritical water and supercritical carbon dioxide. The mixed working fluid at the outlet of the burner 3 enters the supercritical turbine 4 to expand and do work. The intermediate extraction of the supercritical turbine 4 enters the evaporation section of the medium-temperature vacuum heat pipe 5, and then is mixed with the exhaust gas of the supercritical turbine 4 and enters the evaporation section of the low-temperature vacuum heat pipe 6. The flue gas at the outlet of the evaporation section of the low-temperature vacuum heat pipe 6 sequentially recovers low-temperature waste heat at the hot end of the organic working fluid heat exchanger 7, and then enters the gas-liquid separator 12 after being cooled by the cooler 11 for gas-liquid separation. The gas-phase outlet of the gas-liquid separator 12 is carbon dioxide, which can be used for subsequent carbon capture. The liquid-phase outlet is water. Part of the liquid-phase water is pressurized by the feed water pump 13 and circulated back to the system, and the remaining liquid-phase water is discharged from the system through the water conveying pipeline. The gasification feed water at the outlet of the feed water pump 13 sequentially passes through the condensation sections of the low-temperature vacuum heat pipe 6, medium-temperature vacuum heat pipe 5, and high-temperature vacuum heat pipe 2, and then enters the supercritical water gasification reactor 1. The flue gas at the outlet of the evaporation section of the low-temperature vacuum heat pipe 6 still has a large amount of low-temperature latent heat. In order to further recover flue gas waste heat for power generation, an organic Rankine cycle is integrated into the system. Among them, the organic working fluid absorbs heat at the cold end of the organic working fluid heat exchanger 7 and then enters the organic working fluid turbine 8 to expand and do work. The exhaust gas of the organic working fluid turbine 8 is sequentially cooled by the organic working fluid condenser 9 and pressurized by the organic working fluid pump 10 and then enters the cold-end inlet of the organic working fluid heat exchanger 7, thus forming a complete organic Rankine cycle.

[0015] The vaporized feed water at the outlet of the feed water pump 13 is heated successively through the condensation sections of the low-temperature vacuum heat pipe 6, the medium-temperature vacuum heat pipe 5, and the high-temperature vacuum heat pipe 2. Based on the phase change heat transfer of the medium inside the vacuum heat pipe and the self-circulation formed by the capillary force drive, the vaporized feed water absorbs the waste heat of the flue gas, the waste heat of the extracted gas, and the waste heat of the syngas respectively to achieve the purpose of preheating. By reasonably arranging the vacuum heat pipe network according to the temperature range of the heat source in the evaporation section, the cascade utilization of the waste heat of the flue gas is realized, and the heat transfer efficiency of the system is improved.

[0016] The vacuum heat pipe utilizes the principle of phase change heat transfer of the working medium and forms a self-circulation working mode through the evaporation end and the condensation end to achieve efficient heat energy transfer. The vacuum heat pipe heat exchanger has good heat conduction ability, low temperature gradient, and high heat transfer efficiency, showing great advantages in waste heat recovery. Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) By adopting the segmented structure of the vacuum heat pipe, the present invention divides the vacuum heat pipe into two independent chambers, namely the condensation section and the evaporation section, to achieve the complete isolation of the flue gas side and the water side, solve the risk of medium mixing caused by the corrosion and perforation of the pipe wall of the traditional heat exchange equipment, improve the overall service life of the equipment, and greatly reduce the maintenance cost.

[0018] (2) The present invention constructs a multi-stage waste heat recovery network based on temperature matching. Through the coordinated arrangement of high-temperature, medium-temperature, and low-temperature vacuum heat pipes, the accurate capture and efficient cascade utilization of the energy in multiple temperature zones of the flue gas are realized, the preheating temperature of the vaporized feed water is increased, the energy loss in the heat transfer process is reduced, and the energy conversion efficiency of the system is improved.

[0019] (3) The present invention combines supercritical water gasification, syngas combustion power generation, and vacuum heat pipe waste heat recovery to form an efficient integrated energy conversion system, solves the technical problems of low heat transfer efficiency and easy ash accumulation and corrosion of the traditional waste heat recovery device, realizes the efficient and clean conversion of coal, and further realizes the deep utilization of the low-grade flue gas heat energy by coupling with the organic Rankine cycle. At the same time, carbon dioxide capture is carried out, with significant energy conservation and environmental protection benefits. Brief Description of the Drawings

[0020] Figure 1 It is a schematic diagram of a flue gas waste heat utilization system based on vacuum heat pipe technology in the present invention.

[0021] Figure 1 In the figure: 1 is a supercritical water gasification reactor, 2 is a high-temperature vacuum heat pipe, 3 is a burner, 4 is a supercritical turbine, 5 is a medium-temperature vacuum heat pipe, 6 is a low-temperature vacuum heat pipe, 7 is an organic working medium heat exchanger, 8 is an organic working medium turbine, 9 is an organic working medium condenser, 10 is an organic working medium pump, 11 is a cooler, 12 is a gas-liquid separator, and 13 is a feed water pump. Detailed Embodiment

[0022] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0023] As Figure 1 shown, a flue gas waste heat utilization system based on the vacuum heat pipe technology of the present invention includes a supercritical water gasification reactor 1, a high-temperature vacuum heat pipe 2, a burner 3, a supercritical turbine 4, a medium-temperature vacuum heat pipe 5, a low-temperature vacuum heat pipe 6, an organic working fluid heat exchanger 7, an organic working fluid turbine 8, an organic working fluid condenser 9, an organic working fluid pump 10, a cooler 11, a gas-liquid separator 12, and a feed water pump 13; coal is connected to the inlet of the supercritical water gasification reactor 1 via a coal conveying pipeline, ash is discharged from the supercritical water gasification reactor 1 via an ash discharge pipeline, the outlet of the supercritical water gasification reactor 1 is connected to the inlet of the evaporation section of the high-temperature vacuum heat pipe 2, the outlet of the evaporation section of the high-temperature vacuum heat pipe 2 is connected to the inlet of the burner 3, oxygen is connected to the inlet of the burner 3, and the outlet of the burner 3 is connected to the inlet of the supercritical turbine 4; the intermediate extraction of the supercritical turbine 4 is connected to the inlet of the evaporation section of the medium-temperature vacuum heat pipe 5, the outlet of the evaporation section of the medium-temperature vacuum heat pipe 5 and the exhaust gas of the supercritical turbine 4 are both connected to the inlet of the evaporation section of the low-temperature vacuum heat pipe 6, the outlet of the evaporation section of the low-temperature vacuum heat pipe 6 is connected to the hot end inlet of the organic working fluid heat exchanger 7, the hot end outlet of the organic working fluid heat exchanger 7 is connected to the inlet of the cooler 11, and the outlet of the cooler 11 is connected to the inlet of the gas-liquid separator 12; the carbon dioxide at the gas phase outlet of the gas-liquid separator 12 is discharged from the system, a part of the feed water at the liquid phase outlet of the gas-liquid separator 12 is discharged from the system, a part of the feed water is circulated to the system and connected to the inlet of the feed water pump 13, the outlet of the feed water pump 13 is connected to the inlet of the condensation section of the low-temperature vacuum heat pipe 6, the outlet of the condensation section of the low-temperature vacuum heat pipe 6 is connected to the inlet of the condensation section of the medium-temperature vacuum heat pipe 5, the outlet of the condensation section of the medium-temperature vacuum heat pipe 5 is connected to the inlet of the condensation section of the high-temperature vacuum heat pipe 2, and the outlet of the condensation section of the high-temperature vacuum heat pipe 2 is connected to the inlet of the supercritical water gasification reactor 1; the cold end outlet of the organic working fluid heat exchanger 7 is connected to the inlet of the organic working fluid turbine 8, the outlet of the organic working fluid turbine 8 is connected to the inlet of the organic working fluid condenser 9, the outlet of the organic working fluid condenser 9 is connected to the inlet of the organic working fluid pump 10, and the outlet of the organic working fluid pump 10 is connected to the cold end inlet of the organic working fluid heat exchanger 7.

[0024] The operating temperature of the supercritical water gasification reactor 1 is 600°C - 800°C, and the operating pressure is 23 MPa - 30 MPa to ensure that the supercritical water gasification reaction of coal can occur under these conditions.

[0025] The oxygen coefficient at the inlet of the burner 3 is 1.05 - 1.20 to ensure the complete oxidation reaction of the syngas in the burner 3 and convert the chemical energy of the high-quality syngas into high-temperature heat energy. The outlet of the burner 3 is a mixed working fluid mainly composed of supercritical water and supercritical carbon dioxide, which is beneficial to the subsequent separation and capture of carbon dioxide.

[0026] The inlet temperature of the supercritical turbine 4 is 600°C - 700°C, and the exhaust pressure at the outlet is 0.1 - 0.2 MPa, so as to meet the inlet parameter requirements of the supercritical turbine, improve the work capacity of the supercritical turbine, and facilitate the waste heat utilization of the turbine exhaust and the separation of carbon dioxide.

[0027] The interiors of the high-temperature vacuum heat pipe 2, the medium-temperature vacuum heat pipe 5, and the low-temperature vacuum heat pipe 6 are in a vacuum state, and the degree of vacuum is 10 -3 -10 -1 Pa. By adopting the vacuum heat pipe type heat exchanger, the heat transfer efficiency is greatly improved.

[0028] The high-temperature vacuum heat pipe 2, the medium-temperature vacuum heat pipe 5, and the low-temperature vacuum heat pipe 6 adopt a segmented structure, which is divided into two independent chambers, namely the condensation section and the evaporation section, and the upper and lower chambers are separated by a partition to achieve a complete separation between the flue gas side and the gasified feed water side. The vacuum heat pipe heat exchange unit optimizes the heat transfer efficiency by adjusting the heat transfer area ratio of the evaporation end and the condensation end, and the length of the evaporation section accounts for 30% - 60% of the total length of the heat pipe.

[0029] The evaporation section of the high-temperature vacuum heat pipe 2 is inserted into the gasified syngas channel and is respectively connected to the supercritical water gasification reactor 1 and the burner 3, and the condensation section is connected to the gasified feed water pipeline; the evaporation sections of the medium-temperature vacuum heat pipe 5 and the low-temperature vacuum heat pipe 6 are inserted into the flue gas channel at the outlet of the supercritical turbine 4, and the condensation sections are connected to the gasified feed water pipeline. By reasonably arranging the high-temperature, medium-temperature, and low-temperature vacuum heat pipe networks, the waste heat of the system flue gas is effectively recovered, and the preheating temperature of the gasified feed water is increased.

[0030] The cooling temperature at the outlet of the cooler 11 is 20°C - 32°C, so as to ensure that the working medium at the outlet of the cooler 11 can be subjected to gas-liquid separation and high-concentration carbon dioxide capture can be achieved.

[0031] Such as Figure 1As shown in the figure, an optimized operation method for a flue gas waste heat utilization system based on vacuum heat pipe technology of the present invention is as follows: Coal enters the supercritical water gasification reactor 1 through a coal conveying pipeline. The gasification feed water enters the supercritical water gasification reactor 1 from the outlet of the condensation section of the high-temperature vacuum heat pipe 2. In the supercritical water gasification reactor 1, the coal undergoes a supercritical water gasification reaction with the gasification feed water to generate syngas. The nitrogen and sulfur elements in the coal are deposited as inorganic salts and discharged from the supercritical water gasification reactor 1 along with the ash. The syngas enters the combustor 3 through the evaporation section of the high-temperature vacuum heat pipe 2 and undergoes a complete oxidation reaction with the oxygen entering the combustor 3 to generate a mixed working fluid mainly composed of supercritical water and supercritical carbon dioxide. The mixed working fluid at the outlet of the combustor 3 enters the supercritical turbine 4 to expand and do work. The intermediate extraction of the supercritical turbine 4 enters the evaporation section of the medium-temperature vacuum heat pipe 5, and then is mixed with the exhaust gas of the supercritical turbine 4 and enters the evaporation section of the low-temperature vacuum heat pipe 6. The flue gas at the outlet of the evaporation section of the low-temperature vacuum heat pipe 6 sequentially recovers low-temperature waste heat at the hot end of the organic working fluid heat exchanger 7, and then enters the gas-liquid separator 12 after being cooled by the cooler 11 for gas-liquid separation. The gas-phase outlet of the gas-liquid separator 12 is carbon dioxide, which can be used for subsequent carbon capture. The liquid-phase outlet is water. Part of the liquid-phase water is pressurized by the feed water pump 13 and circulated back to the system, and the remaining liquid-phase water is discharged from the system through a water conveying pipeline. The gasification feed water at the outlet of the feed water pump 13 sequentially passes through the condensation sections of the low-temperature vacuum heat pipe 6, the medium-temperature vacuum heat pipe 5, and the high-temperature vacuum heat pipe 2, and then enters the supercritical water gasification reactor 1. The flue gas at the outlet of the evaporation section of the low-temperature vacuum heat pipe 6 still has a large amount of low-temperature latent heat. In order to further recover the flue gas waste heat for power generation, an organic Rankine cycle is integrated into the system. Among them, the organic working fluid absorbs heat at the cold end of the organic working fluid heat exchanger 7 and then enters the organic working fluid turbine 8 to expand and do work. The exhaust gas of the organic working fluid turbine 8 is sequentially cooled by the organic working fluid condenser 9 and pressurized by the organic working fluid pump 10 and then enters the cold-end inlet of the organic working fluid heat exchanger 7, thus forming a complete organic Rankine cycle.

[0032] The gasification feed water at the outlet of the feed water pump 13 is sequentially heated through the condensation sections of the low-temperature vacuum heat pipe 6, the medium-temperature vacuum heat pipe 5, and the high-temperature vacuum heat pipe 2. Based on the phase change heat transfer of the medium inside the vacuum heat pipe and the self-circulation formed by the capillary force drive, the gasification feed water absorbs the flue gas waste heat, the extraction waste heat, and the syngas waste heat respectively to achieve the purpose of preheating. The present invention reasonably arranges the vacuum heat pipe network according to the temperature range of the heat source in the evaporation section, realizes the cascade utilization of the flue gas waste heat, and improves the heat exchange efficiency of the system.

Claims

1. A flue gas waste heat utilization system based on vacuum heat pipe technology, characterized in that: The system comprises a supercritical water gasification reactor (1), a high-temperature vacuum heat pipe (2), a burner (3), a supercritical turbine (4), a medium-temperature vacuum heat pipe (5), a low-temperature vacuum heat pipe (6), an organic working fluid heat exchanger (7), an organic working fluid turbine (8), an organic working fluid condenser (9), an organic working fluid pump (10), a cooler (11), a gas-liquid separator (12) and a water feed pump (13); coal is connected to the inlet of the supercritical water gasification reactor (1) via a coal transportation pipeline, ash is discharged from the supercritical water gasification reactor (1) via an ash discharge pipeline, and the outlet of the supercritical water gasification reactor (1) is connected to the inlet of the supercritical water gasification reactor (1). The evaporation section inlet of the high-temperature vacuum heat pipe (2) and the evaporation section outlet of the high-temperature vacuum heat pipe (2) are connected to the inlet of the burner (3), oxygen is connected to the inlet of the burner (3), and the outlet of the burner (3) is connected to the inlet of the supercritical turbine (4); the intermediate exhaust of the supercritical turbine (4) is connected to the evaporation section inlet of the medium-temperature vacuum heat pipe (5), the evaporation section outlet of the medium-temperature vacuum heat pipe (5) and the exhaust of the supercritical turbine (4) are both connected to the evaporation section inlet of the low-temperature vacuum heat pipe (6), the evaporation section outlet of the low-temperature vacuum heat pipe (6) is connected to the hot end inlet of the organic working fluid heat exchanger (7), and the organic working fluid heat exchanger (7) is connected to the hot end inlet of the organic working fluid heat exchanger (7). The hot end outlet is connected to the inlet of the cooler (11), and the outlet of the cooler (11) is connected to the inlet of the gas-liquid separator (12); the carbon dioxide discharge system of the gas phase outlet of the gas-liquid separator (12), the partial water supply discharge system of the liquid phase outlet of the gas-liquid separator (12), and the partial water supply is circulated in the system and connected to the inlet of the water supply pump (13), and the outlet of the water supply pump (13) is connected to the condensation section inlet of the low-temperature vacuum heat pipe (6), and the condensation section outlet of the low-temperature vacuum heat pipe (6) is connected to the condensation section inlet of the medium-temperature vacuum heat pipe (5), and the condensation section outlet of the medium-temperature vacuum heat pipe (5) is connected to the The condensation section inlet and the condensation section outlet of the high-temperature vacuum heat pipe (2) are connected to the inlet of the supercritical water gasification reactor (1); by rationally arranging the vacuum heat pipe network according to the temperature range of the evaporation section heat source, the step-by-step utilization of flue gas waste heat is achieved, thereby improving the heat exchange efficiency of the system; the cold end outlet of the organic working fluid heat exchanger (7) is connected to the inlet of the organic working fluid turbine (8), the outlet of the organic working fluid turbine (8) is connected to the inlet of the organic working fluid condenser (9), the outlet of the organic working fluid condenser (9) is connected to the inlet of the organic working fluid pump (10), and the outlet of the organic working fluid pump (10) is connected to the cold end inlet of the organic working fluid heat exchanger (7).

2. The flue gas waste heat utilization system based on vacuum heat pipe technology according to claim 1 is characterized in that: The operating temperature of the supercritical water gasification reactor (1) is 600°C-800°C, and the operating pressure is 23MPa-30MPa.

3. The flue gas waste heat utilization system based on vacuum heat pipe technology according to claim 1 is characterized in that: The oxygen coefficient at the inlet of the burner (3) is 1.05-1.20, a complete oxidation reaction of the synthesis gas occurs in the burner (3), and the outlet of the burner (3) is a mixed working fluid mainly composed of supercritical water and supercritical carbon dioxide.

4. The flue gas waste heat utilization system based on vacuum heat pipe technology according to claim 1 is characterized in that: The inlet temperature of the supercritical turbine (4) is 600°C-700°C, and the exhaust pressure at the outlet is 0.1-0.2MPa.

5. The flue gas waste heat utilization system based on vacuum heat pipe technology according to claim 1 is characterized in that: The interiors of the high-temperature vacuum heat pipe (2), the medium-temperature vacuum heat pipe (5) and the low-temperature vacuum heat pipe (6) are in a vacuum state, with a vacuum degree of 10 -3 -10 -1 Pa.

6. The flue gas waste heat utilization system based on vacuum heat pipe technology according to claim 1 is characterized in that: The high-temperature vacuum heat pipe (2), the medium-temperature vacuum heat pipe (5) and the low-temperature vacuum heat pipe (6) adopt a segmented structure, which is divided into two independent upper and lower chambers of a condensation section and an evaporation section, and the upper and lower chambers are separated by a partition, wherein the length of the evaporation section accounts for 30%-60% of the total length of the heat pipe.

7. The flue gas waste heat utilization system based on vacuum heat pipe technology according to claim 1 is characterized in that: The evaporation section of the high-temperature vacuum heat pipe (2) is inserted into the gasification synthesis gas channel and is respectively connected to the supercritical water gasification reactor (1) and the burner (3), and the condensation section is connected to the gasification water supply pipeline; the evaporation sections of the medium-temperature vacuum heat pipe (5) and the low-temperature vacuum heat pipe (6) are inserted into the flue gas channel at the outlet of the supercritical turbine (4), and the condensation sections are connected to the gasification water supply pipeline.

8. The flue gas waste heat utilization system based on vacuum heat pipe technology according to claim 1 is characterized in that: The cooling temperature at the outlet of the cooler (11) is 20°C-32°C.

9. The method for optimizing the operation of a flue gas waste heat utilization system based on vacuum heat pipe technology according to any one of claims 1 to 8, characterized in that: Coal enters a supercritical water gasification reactor (1) through a coal transportation pipeline, and gasification feed water enters the supercritical water gasification reactor (1) from the outlet of the condensation section of a high-temperature vacuum heat pipe (2). In the supercritical water gasification reactor (1), the coal and the gasification feed water undergo a supercritical water gasification reaction to generate synthesis gas, and the nitrogen and sulfur elements in the coal are deposited as inorganic salts and discharged from the supercritical water gasification reactor (1) along with the ash; the synthesis gas enters a burner (3) through the evaporation section of the high-temperature vacuum heat pipe (2), and reacts with oxygen entering the burner (3). A complete oxidation reaction occurs to generate a mixed working fluid mainly composed of supercritical water and supercritical carbon dioxide; the mixed working fluid at the outlet of the burner (3) enters the supercritical turbine (4) to expand and perform work, the intermediate exhaust gas of the supercritical turbine (4) enters the evaporation section of the medium-temperature vacuum heat pipe (5), and then mixes with the exhaust gas of the supercritical turbine (4) and enters the evaporation section of the low-temperature vacuum heat pipe (6); the flue gas at the outlet of the evaporation section of the low-temperature vacuum heat pipe (6) passes through the hot end of the organic working fluid heat exchanger (7) to recover the low-temperature waste heat, and then passes through the cooler ( 11) After cooling, it enters the gas-liquid separator (12) for gas-liquid separation; the gas phase outlet of the gas-liquid separator (12) is carbon dioxide for subsequent carbon capture, and the liquid phase outlet is water. Part of the liquid phase water is pressurized by the water supply pump (13) and circulated into the system, and the remaining liquid phase water is discharged from the system through the water pipeline; the gasified water supply at the outlet of the water supply pump (13) passes through the condensation section of the low-temperature vacuum heat pipe (6), the medium-temperature vacuum heat pipe (5) and the high-temperature vacuum heat pipe (2) in sequence, and then enters the supercritical water gasification reactor (1); the low-temperature vacuum heat pipe (6) is used for the gasification of the supercritical water. The flue gas at the outlet of the evaporation section of the air heat pipe (6) still has a large amount of low-temperature latent heat. In order to further recover the waste heat of the flue gas for power generation, an organic Rankine cycle is integrated in the system, wherein the organic working fluid absorbs heat at the cold end of the organic working fluid heat exchanger (7) and then enters the organic working fluid turbine (8) to expand and perform work. The exhaust gas of the organic working fluid turbine (8) is cooled by the organic working fluid condenser (9) and pressurized by the organic working fluid pump (10) in turn before entering the cold end inlet of the organic working fluid heat exchanger (7), thereby forming a complete organic Rankine cycle.

10. The method for optimizing the operation of the flue gas waste heat utilization system based on the vacuum heat pipe technology according to claim 9, characterized in that: The gasified feed water at the outlet of the feed water pump (13) is heated by passing through the condensation section of the low-temperature vacuum heat pipe (6), the medium-temperature vacuum heat pipe (5) and the high-temperature vacuum heat pipe (2) in sequence. Based on the phase change heat transfer of the medium inside the vacuum heat pipe and the self-circulation formed by capillary force driving, the gasified feed water absorbs the waste heat of the flue gas, the waste heat of the exhaust gas and the waste heat of the synthesis gas respectively, thereby achieving the purpose of preheating.

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