A coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as working fluid and its operation method

Abstract

This invention discloses a coal supercritical water gasification power generation system and its operation method using circulating supercritical carbon dioxide as the working fluid. The system includes a gasifier, an oxidizer, a mixed working fluid turbine, a heat exchanger, a gas-liquid separator, a feedwater precooler, a feedwater pump, an oxygen preheater, a carbon dioxide precooler, a main compressor, an interstage cooler, and a re-compressor. Based on supercritical water gasification technology, this invention efficiently, cleanly, and with low carbon emissions, converts the chemical energy of coal into electricity required by the user. By circulating supercritical carbon dioxide as the working fluid, the heat exchange temperature difference between the hot and cold ends of the heat exchanger and the irreversible heat transfer loss of the system are effectively reduced, thereby improving the system's power generation efficiency. It also enables the recycling of water and the complete capture of excess carbon dioxide. The heat required for the core gasification process is provided through partial oxidation of the fuel for self-heating, and the compression process of the supercritical carbon dioxide employs multi-stage compression. This invention features simple synergy, achieves low-energy carbon capture, and boasts high system power generation efficiency.

Description

Technical Field

[0001] This invention relates to the field of efficient, clean, and low-carbon coal power generation technology, specifically to a coal supercritical water gasification power generation system and its operation method using a circulating supercritical carbon dioxide working fluid. Background Technology

[0002] Supercritical water gasification (SGM) technology converts the chemical energy of coal into hydrogen-rich syngas, providing a potential technological foundation for building efficient and low-carbon coal-fired power generation systems. In the supercritical water gasification atmosphere, elements such as nitrogen and sulfur are converted into inorganic salts and deposited with the ash, avoiding air pollution. Due to their different solubilities in high-pressure water, carbon dioxide is easily separated from the gasified syngas. When the syngas is completely oxidized with oxygen to produce a mixed working fluid containing only water and carbon dioxide, complete carbon dioxide capture can be achieved through a gas-liquid separation process.

[0003] Currently, coal-fired power generation systems based on supercritical water gasification technology mainly combine steam Rankine cycles. However, in the construction of these systems, the heat source mismatch leads to a large temperature difference in the supercritical water heating process, resulting in significant irreversible heat transfer losses.

[0004] Compared to the steam Rankine cycle, the supercritical carbon dioxide Brayton cycle exhibits higher thermal efficiency under the same turbine inlet parameters. By circulating supercritical carbon dioxide as the working fluid within the system, it is expected to improve temperature matching between the hot and cold ends during heat exchange, thereby reducing irreversible losses in the heat exchange process and increasing the system's net power generation efficiency. Therefore, there is an urgent need to combine supercritical carbon dioxide as the working fluid to fully realize the technological advantages of high-efficiency, low-carbon power generation from coal supercritical water gasification. Summary of the Invention

[0005] To overcome the problems existing in the prior art, the present invention aims to provide a coal supercritical water gasification power generation system and its operation method using a circulating supercritical carbon dioxide working fluid. The system, based on supercritical water gasification technology, efficiently, cleanly, and with low carbon emissions converts the chemical energy of coal into the electrical energy required by the user. By circulating supercritical carbon dioxide as the working fluid, the heat exchange temperature difference between the hot and cold ends of the heat exchanger and irreversible heat transfer losses are effectively reduced, thereby improving the system's power generation efficiency. It also enables the recycling of water and the complete capture of excess carbon dioxide. The heat required for the core gasification process is provided through partial oxidation of the fuel, which simplifies the system layout and avoids the introduction of other heat sources. The supercritical carbon dioxide compression process employs multi-stage compression and interstage cooling to further reduce compression power consumption and improve the system's power generation efficiency.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as the working fluid includes a gasifier 1, with coal connected to the inlet of the gasifier 1 via a pipeline; preheated gasification feedwater connected to the inlet of the gasifier 1 from the cold side outlet of a heat exchanger 4; preheated oxygen connected to both the inlet of the gasifier 1 and the inlet of an oxidizer 2 from the cold side outlet of the heat exchanger 4; ash discharged from the ash outlet of the gasifier 1 and connected to the external environment via an ash discharge pipeline; the outlet of the gasifier 1 connected to the inlet of the oxidizer 2; preheated supercritical carbon dioxide connected to the inlet of the oxidizer 2 from the cold side outlet of the heat exchanger 4; the outlet of the oxidizer 2 connected to the inlet of a mixed working fluid turbine 3; the outlet of the mixed working fluid turbine 3 connected to the hot side inlet of the heat exchanger 4; and the hot side outlet of the heat exchanger 4 connected to the inlet of a gas-liquid separator 5.

[0008] The liquid phase outlet of gas-liquid separator 5 is connected to the inlet of feedwater precooler 6; excess water from the liquid phase outlet of gas-liquid separator 5 is discharged through a drain pipe; the outlet of feedwater precooler 6 is connected to the inlet of feedwater pump 7; the outlet of feedwater pump 7 is connected to the cold side inlet of heat exchanger 4; the gas phase outlet of gas-liquid separator 5 is connected to the hot side inlet of oxygen preheater 8; the hot side outlet of oxygen preheater 8 is connected to the inlet of carbon dioxide precooler 9; excess carbon dioxide from the hot side outlet of oxygen preheater 8 is completely captured; the outlet of carbon dioxide precooler 9 is connected to the inlet of main compressor 11; the outlet of main compressor 11 is connected to the inlet of interstage cooler 12; the outlet of interstage cooler 12 is connected to the inlet of recompressor 13; the outlet of recompressor 13 is connected to the cold side inlet of heat exchanger 4; oxygen is connected to the cold side inlet of oxygen preheater 8 through a pipe; the cold side outlet of oxygen preheater 8 is connected to the cold side inlet of heat exchanger 4.

[0009] The gasifier 1 operates at a temperature of 600–700°C and a pressure of 23–33 MPa.

[0010] By adjusting the amount of oxygen entering gasifier 1, coal undergoes a supercritical water gasification reaction with oxygen and gasification feedwater in gasifier 1, resulting in partial oxidation. The oxygen split ratio entering gasifier 1 is 0 to 0.2.

[0011] The gasified syngas and oxygen undergo a complete oxidation reaction in the oxidation furnace 2, and the oxygen split ratio entering the oxidation furnace 2 is 0.8 to 1.

[0012] The supercritical carbon dioxide working medium separated by the gas-liquid separator 5 is recycled to the system. After being preheated by the heat exchanger 4, it enters the oxidation furnace 2 to form a mixed working medium of supercritical carbon dioxide and supercritical water, with supercritical carbon dioxide as the main working medium. The mass fraction of supercritical carbon dioxide in the mixed working medium is 92-98%.

[0013] The inlet temperature of the mixed working fluid turbine 3 is 850–1200°C.

[0014] The exhaust pressure of the mixed working fluid turbine 3 is 7.6 to 8.5 MPa.

[0015] The working fluid outlet temperature of the carbon dioxide precooler 9 is 31–36°C.

[0016] The compression process of the supercritical carbon dioxide working medium at the outlet of the carbon dioxide precooler 9 adopts a multi-stage compression and interstage cooling method, and the working medium outlet temperature of the interstage cooler 12 is 31-36℃.

[0017] The operation method of a coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as the working fluid is as follows: Oxygen is preheated by oxygen preheater 8 and heat exchanger 4 and then enters gasifier 1 and oxidizer 2 respectively; gasification feedwater and oxygen preheated by heat exchanger 4 enter gasifier 1 and undergo a supercritical water gasification reaction with coal to partially oxidize it, so that the released heat just provides the heat required for supercritical water gasification, achieving the self-heating balance of the system; the high-calorific-value syngas generated during the gasification process enters oxidizer 2 and undergoes a complete oxidation reaction with oxygen, and then mixes with supercritical carbon dioxide preheated by heat exchanger 4 to form a mixed working fluid of supercritical carbon dioxide and supercritical water, with supercritical carbon dioxide as the main component; by adjusting the outlet temperature of the supercritical carbon dioxide working fluid on the cold side of heat exchanger 4, the inlet temperature of the mixed working fluid turbine 3 is changed to meet different turbine inlet temperature requirements and improve the flexibility of unit operation.

[0018] The high-temperature, high-pressure mixed working fluid enters the mixed working fluid turbine 3 for expansion and work; the exhaust heat from the mixed working fluid turbine 3 is used to preheat the gasification feedwater, supercritical carbon dioxide, and oxygen through the heat exchanger 4; the exhaust of the mixed working fluid after waste heat recovery enters the gas-liquid separator 5; the liquid phase outlet of the gas-liquid separator 5 enters the heat exchanger 4 for preheating after passing through the feedwater precooler 6 and the feedwater pump 7; the excess water from the liquid phase outlet of the gas-liquid separator 5 is discharged to the system for recycling; the gas phase outlet of the gas-liquid separator 5 passes sequentially through the oxygen preheater 8 and the carbon dioxide precooler 9, and then sequentially through the main compressor 11, the interstage cooler 12, and the recompressor 13 to be compressed to the gasification pressure; the supercritical carbon dioxide from the outlet of the recompressor 13 enters the heat exchanger 4 for preheating; the excess carbon dioxide from the gas phase outlet of the gas-liquid separator 5 is completely captured.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) Based on supercritical water gasification technology, this invention avoids the generation of nitrogen and sulfur pollutants, and enables the recycling of water and complete capture of excess carbon dioxide, thereby achieving efficient, clean and low-carbon power generation from coal.

[0021] (2) The heat required for the core gasification process of the present invention is provided by the self-heating of the fuel through partial oxidation, so as to achieve self-heating balance of the gasification process, simplify the system layout and avoid the introduction of other heat sources.

[0022] (3) By circulating supercritical carbon dioxide working fluid in the system, the present invention can effectively improve the heat exchange temperature difference between the hot and cold ends of the heat exchanger, reduce the irreversible loss in the heat transfer process, and thus improve the power generation efficiency of the system.

[0023] (4) This invention adjusts the outlet temperature of the supercritical carbon dioxide working fluid on the cold side of the heat exchanger, thereby changing the inlet temperature of the mixed working fluid turbine to meet different turbine inlet temperature requirements and improve the flexibility of unit operation. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as the working fluid according to the present invention.

[0025] Figure 2 This is a graph showing the temperature-heat exchange rate changes of the working fluid at the hot and cold ends of the heat exchanger.

[0026] Figure 3 The graph shows the system efficiency as a function of the turbine inlet temperature of the mixed working fluid.

[0027] Figure 1 In the middle section: 1 is the gasifier, 2 is the oxidizer, 3 is the mixed working fluid turbine, 4 is the heat exchanger, 5 is the gas-liquid separator, 6 is the feedwater precooler, 7 is the feedwater pump, 8 is the oxygen preheater, 9 is the carbon dioxide precooler, 11 is the main compressor, 12 is the interstage cooler, and 13 is the re-compressor. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0029] like Figure 1 As shown, the present invention discloses a coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as the working fluid, comprising a gasifier 1, with coal connected to the inlet of the gasifier 1 via a pipeline; preheated gasification feedwater connected to the inlet of the gasifier 1 from the cold side outlet of a heat exchanger 4; preheated oxygen connected to the inlet of the gasifier 1 and the inlet of an oxidizer 2 from the cold side outlet of the heat exchanger 4; ash connected to the external environment from the ash outlet of the gasifier 1 via an ash discharge pipeline; the outlet of the gasifier 1 connected to the inlet of the oxidizer 2; preheated supercritical carbon dioxide connected to the inlet of the oxidizer 2 from the cold side outlet of the heat exchanger 4; the outlet of the oxidizer 2 connected to the inlet of a mixed working fluid turbine 3; the outlet of the mixed working fluid turbine 3 connected to the hot side inlet of the heat exchanger 4; and the hot side outlet of the heat exchanger 4 connected to the inlet of a gas-liquid separator 5.

[0030] The liquid phase outlet of gas-liquid separator 5 is connected to the inlet of feedwater precooler 6; excess water from the liquid phase outlet of gas-liquid separator 5 is discharged through a drain pipe; the outlet of feedwater precooler 6 is connected to the inlet of feedwater pump 7; the outlet of feedwater pump 7 is connected to the cold side inlet of heat exchanger 4; the gas phase outlet of gas-liquid separator 5 is connected to the hot side inlet of oxygen preheater 8; the hot side outlet of oxygen preheater 8 is connected to the inlet of carbon dioxide precooler 9; excess carbon dioxide from the hot side outlet of oxygen preheater 8 is completely captured; the outlet of carbon dioxide precooler 9 is connected to the inlet of main compressor 11; the outlet of main compressor 11 is connected to the inlet of interstage cooler 12; the outlet of interstage cooler 12 is connected to the inlet of recompressor 13; the outlet of recompressor 13 is connected to the cold side inlet of heat exchanger 4; oxygen is connected to the cold side inlet of oxygen preheater 8 through a pipe; the cold side outlet of oxygen preheater 8 is connected to the cold side inlet of heat exchanger 4.

[0031] In a preferred embodiment of the present invention, the gasifier 1 operates at a temperature of 600-700°C and an operating pressure of 23-33 MPa, thereby enabling the supercritical water gasification reaction of coal to occur under these conditions.

[0032] In a preferred embodiment of the present invention, by adjusting the amount of oxygen entering the gasifier 1, the coal, oxygen and gasification feedwater undergo a partially oxidized supercritical water gasification reaction in the gasifier 1. The oxygen split ratio entering the gasifier 1 is 0 to 0.2, so that the heat released by the partial oxidation of the fuel can just provide the heat required for supercritical water gasification, thus achieving the self-heating balance of the system.

[0033] In a preferred embodiment of the present invention, the gasified syngas and oxygen undergo a complete oxidation reaction in the oxidation furnace 2. The oxygen split ratio entering the oxidation furnace 2 is 0.8 to 1, which can produce a high-temperature and high-pressure mixed working fluid, and the main components of the mixed working fluid are only water and carbon dioxide.

[0034] In a preferred embodiment of the present invention, the supercritical carbon dioxide working fluid separated by the gas-liquid separator 5 is circulated into the system. After being preheated by the heat exchanger 4, it enters the oxidation furnace 2 to form a mixed working fluid of supercritical carbon dioxide and supercritical water, with supercritical carbon dioxide as the main working fluid. The mass fraction of supercritical carbon dioxide in the mixed working fluid is 92-98%. This can effectively improve the heat exchange temperature difference between the hot and cold ends of the heat exchanger 4, reduce irreversible losses in the heat transfer process, and thus improve the power generation efficiency of the system.

[0035] In a preferred embodiment of the present invention, the inlet temperature of the mixed working fluid turbine 3 is 850-1200°C, which satisfies the requirement that the mixed working fluid turbine 3 has high inlet parameters.

[0036] In a preferred embodiment of the present invention, the exhaust pressure of the mixed working fluid turbine 3 is 7.6 to 8.5 MPa, which can maintain the mixed working fluid turbine 3 with high output power and ensure that the carbon dioxide working fluid remains in a supercritical state throughout the entire system cycle.

[0037] In a preferred embodiment of the present invention, the working fluid outlet temperature of the carbon dioxide precooler 9 is 31-36°C. This results in a lower average heat release temperature during the cycle, higher cycle efficiency of the system, and ensures that the carbon dioxide working fluid is near the critical point, thereby reducing the compression power consumption of the main compressor 11.

[0038] In a preferred embodiment of the present invention, the compression process of the supercritical carbon dioxide working medium at the outlet of the carbon dioxide precooler 9 adopts a multi-stage compression and interstage cooling method. The working medium outlet temperature of the interstage cooler 12 is 31-36°C, which can further reduce compression power consumption and improve system power generation efficiency.

[0039] like Figure 1 As shown, the operation method of a coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as the working fluid according to the present invention is as follows: oxygen is preheated by oxygen preheater 8 and heat exchanger 4 and then enters gasifier 1 and oxidizer 2 respectively; gasification feedwater and oxygen preheated by heat exchanger 4 enter gasifier 1 and undergo a supercritical water gasification reaction with coal to partially oxidize it, so that the released heat just provides the heat required for supercritical water gasification, achieving the self-heating balance of the system; the high-calorific-value syngas generated during the gasification process enters oxidizer 2 and undergoes a complete oxidation reaction with oxygen, and then mixes with supercritical carbon dioxide preheated by heat exchanger 4 to form a mixed working fluid of supercritical carbon dioxide and supercritical water, with supercritical carbon dioxide as the main component; by adjusting the outlet temperature of the supercritical carbon dioxide working fluid on the cold side of heat exchanger 4, the inlet temperature of the mixed working fluid turbine 3 is changed to meet different turbine inlet temperature requirements and improve the flexibility of unit operation.

[0040] The high-temperature, high-pressure mixed working fluid enters the mixed working fluid turbine 3 for expansion and work; the exhaust heat from the mixed working fluid turbine 3 is used to preheat the gasification feedwater, supercritical carbon dioxide, and oxygen through the heat exchanger 4; the exhaust of the mixed working fluid after waste heat recovery enters the gas-liquid separator 5; the liquid phase outlet of the gas-liquid separator 5 enters the heat exchanger 4 for preheating after passing through the feedwater precooler 6 and the feedwater pump 7; the excess water from the liquid phase outlet of the gas-liquid separator 5 is discharged to the system for recycling; the gas phase outlet of the gas-liquid separator 5 passes sequentially through the oxygen preheater 8 and the carbon dioxide precooler 9, and then sequentially through the main compressor 11, the interstage cooler 12, and the recompressor 13 to be compressed to the gasification pressure; the supercritical carbon dioxide from the outlet of the recompressor 13 enters the heat exchanger 4 for preheating; the excess carbon dioxide from the gas phase outlet of the gas-liquid separator 5 is completely captured.

[0041] like Figure 2 As shown, the hot-end working fluid of heat exchanger 4 is a mixed working fluid turbine exhaust, while the cold-end working fluid is supercritical water, supercritical carbon dioxide, and oxygen. The minimum temperature difference between the hot and cold ends of heat exchanger 4 is 10℃, and the maximum temperature difference is approximately 98℃. Therefore, circulating supercritical carbon dioxide as the working fluid in the system can effectively improve the heat exchange temperature difference between the hot and cold ends of heat exchanger 4 and reduce irreversible losses in the heat transfer process.

[0042] like Figure 3 As shown, when the inlet temperature of the mixed working fluid turbine 3 is increased from 850℃ to 1200℃, the net power generation efficiency of the system can be increased from 47.03% to 54.00%. Efficiency can be increased from 45.88% to 52.68%.

Claims

1. A coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as the working fluid, characterized in that: The system includes a gasifier (1), with coal connected to the inlet of the gasifier (1) via a pipeline; preheated gasification feedwater connected to the inlet of the gasifier (1) from the cold side outlet of the heat exchanger (4); preheated oxygen connected to the inlet of the gasifier (1) and the inlet of the oxidizer (2) from the cold side outlet of the heat exchanger (4); ash connected to the external environment from the ash outlet of the gasifier (1) via an ash discharge pipeline; the outlet of the gasifier (1) connected to the inlet of the oxidizer (2); preheated supercritical carbon dioxide connected to the inlet of the oxidizer (2) from the cold side outlet of the heat exchanger (4); the outlet of the oxidizer (2) connected to the inlet of the mixed working fluid turbine (3); the outlet of the mixed working fluid turbine (3) connected to the hot side inlet of the heat exchanger (4); and the hot side outlet of the heat exchanger (4) connected to the inlet of the gas-liquid separator (5). The liquid phase outlet of the gas-liquid separator (5) is connected to the inlet of the feedwater precooler (6); excess water from the liquid phase outlet of the gas-liquid separator (5) is discharged through a drain pipe; the outlet of the feedwater precooler (6) is connected to the inlet of the feedwater pump (7); the outlet of the feedwater pump (7) is connected to the cold side inlet of the heat exchanger (4); the gas phase outlet of the gas-liquid separator (5) is connected to the hot side inlet of the oxygen preheater (8); the hot side outlet of the oxygen preheater (8) is connected to the inlet of the carbon dioxide precooler (9); the hot side outlet of the oxygen preheater (8) is connected to the inlet of the carbon dioxide precooler (9); the hot side outlet of the oxygen preheater (8) is connected to the inlet of the carbon dioxide precooler (9); the hot side outlet of the oxygen preheater (8) is connected to the inlet of the carbon dioxide precooler (9). Excess carbon dioxide at the side outlet is completely captured; the outlet of the carbon dioxide precooler (9) is connected to the inlet of the main compressor (11); the outlet of the main compressor (11) is connected to the inlet of the interstage cooler (12); the outlet of the interstage cooler (12) is connected to the inlet of the re-compressor (13); the outlet of the re-compressor (13) is connected to the cold side inlet of the heat exchanger (4); oxygen is connected to the cold side inlet of the oxygen preheater (8) through a pipeline; the cold side outlet of the oxygen preheater (8) is connected to the cold side inlet of the heat exchanger (4); The exhaust pressure of the mixed working fluid turbine (3) is 7.6–8.5 MPa; The supercritical carbon dioxide working medium separated by the gas-liquid separator (5) is recycled to the system. After being preheated by the heat exchanger (4), it enters the oxidation furnace (2) to form a mixed working medium of supercritical carbon dioxide and supercritical water, with supercritical carbon dioxide as the main working medium.

2. The coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as the working fluid according to claim 1, characterized in that: The gasifier (1) operates at a temperature of 600-700℃ and a pressure of 23-33MPa.

3. The coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as the working fluid according to claim 1, characterized in that: By adjusting the amount of oxygen entering the gasifier (1), the coal, oxygen, and gasification feedwater undergo a partially oxidized supercritical water gasification reaction in the gasifier (1), and the oxygen split ratio entering the gasifier (1) is 0 to 0.

2.

4. The coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as the working fluid according to claim 1, characterized in that: The gasified syngas and oxygen undergo a complete oxidation reaction in the oxidation furnace (2), and the oxygen split ratio entering the oxidation furnace (2) is 0.8 to 1.

5. The coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as the working fluid according to claim 1, characterized in that: The mass fraction of supercritical carbon dioxide in the mixed working fluid is 92-98%.

6. The coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as the working fluid according to claim 1, characterized in that: The inlet temperature of the mixed working fluid turbine (3) is 850-1200℃.

7. The coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as the working fluid according to claim 1, characterized in that: The working fluid outlet temperature of the carbon dioxide precooler (9) is 31-36℃.

8. The coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as the working fluid according to claim 1, characterized in that: The compression process of the supercritical carbon dioxide working medium at the outlet of the carbon dioxide precooler (9) adopts a multi-stage compression and interstage cooling method, and the working medium outlet temperature of the interstage cooler (12) is 31-36℃.

9. The method of operating a coal supercritical water gasification power generation system using circulating supercritical carbon dioxide as the working fluid according to any one of claims 1 to 8, characterized in that: After being preheated by the oxygen preheater (8) and the heat exchanger (4), the oxygen enters the gasifier (1) and the oxidizer (2) respectively. The gasification feedwater and oxygen, which are preheated by the heat exchanger (4), enter the gasifier (1) and undergo a supercritical water gasification reaction with the coal to partially oxidize it. The heat released is just enough to provide the heat required for supercritical water gasification, so as to achieve the self-heating balance of the system. The high-calorific-value syngas generated during the gasification process enters the oxidizer (2) and undergoes a complete oxidation reaction with the oxygen. Then it is mixed with the supercritical carbon dioxide, which is preheated by the heat exchanger (4), to form a mixed working medium of supercritical carbon dioxide and supercritical water, which is mainly composed of supercritical carbon dioxide. By adjusting the outlet temperature of the supercritical carbon dioxide working medium on the cold side of the heat exchanger (4), the inlet temperature of the mixed working medium turbine (3) is changed to meet the different turbine inlet temperature requirements and improve the flexibility of unit operation. The high-temperature and high-pressure mixed working fluid enters the mixed working fluid turbine (3) to expand and do work; the exhaust heat of the mixed working fluid turbine (3) is used to preheat the gasification feedwater, supercritical carbon dioxide and oxygen through the heat exchanger (4); the exhaust of the mixed working fluid after waste heat recovery enters the gas-liquid separator (5); the liquid phase outlet of the gas-liquid separator (5) enters the heat exchanger (4) for preheating after passing through the feedwater precooler (6) and the feedwater pump (7); the excess water at the liquid phase outlet of the gas-liquid separator (5) is output to the system for recycling; the gas phase outlet of the gas-liquid separator (5) passes through the oxygen preheater (8) and the carbon dioxide precooler (9) in sequence, and then passes through the main compressor (11), the interstage cooler (12) and the recompressor (13) in sequence to be compressed to the gasification pressure; the supercritical carbon dioxide at the outlet of the recompressor (13) enters the heat exchanger (4) for preheating; the excess carbon dioxide at the gas phase outlet of the gas-liquid separator (5) is completely carbon captured.

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