System for achieving efficiency improvement and carbon reduction of SOFCs power generation system through LNG cold energy

Abstract

The invention discloses a system for realizing efficiency improvement and carbon reduction of an SOFCs power generation system by using LNG cold energy, which is characterized in that the high-grade cold energy of LNG is subjected to three-stage utilization of deep cooling, intercooling and shallow cooling, and is respectively used for liquefying CO2 in anode tail gas of the SOFCs power generation system; the air at the cathode inlet in the SOFCs is dehumidified and dried, so that the energy consumption required by the temperature rise of the air is reduced; high-grade waste heat in SOFCs tail gas is recycled, LNG is efficiently gasified, meanwhile, anode tail gas dehydration is achieved, condensate water is recycled for a methane reforming process, in addition, liquid carbon dioxide captured by the system can be prepared into part of dry ice and part of low-temperature gaseous CO2 in a dry ice machine through an internal heat extraction method, the part of dry ice and the part of low-temperature gaseous CO2 can be transported outwards for commercial use, and the energy consumption is low. And the latter can be stored to be used for entering the SOFCs system through the fire-fighting bypass under the condition that the SOFCs are accidentally on fire, so that emergency fire extinguishing of the SOFCs system is realized.

Description

Technical Field

[0001] The present invention relates to the technical field, and in particular to a system for improving efficiency and reducing carbon emissions in a SOFCs power generation system by utilizing LNG cold energy. Background Art

[0002] Solid oxide fuel cells (SOFCs), as a device that directly converts chemical energy into electrical energy, are gradually subverting traditional energy utilization methods with their advantages of high energy density, high efficiency, and low pollution. SOFCs systems are high-temperature power generation devices. The system can generate electricity at a temperature of 750 to 1000°C by electrochemical reaction using hydrogen-rich fuel gas such as natural gas wet reforming gas (mainly composed of H2 and CO) and oxygen in the air. In coastal cities, the annual average relative humidity of air is above 80%. The air has a high humidity content, and the water contained in it will absorb part of the system's heat during the heating process in SOFCs, reducing the system's heat generation efficiency; at the same time, high-humidity air will also dilute the oxygen concentration in the cathode, affecting the mass transfer rate, and thus reducing the system's power generation. The products in the SOFCs anode tail gas mainly contain CO2 and H2O, among which the high-temperature water vapor content is the highest, diluting the CO2 concentration in the anode tail gas, making carbon capture more difficult. Since SOFCs are high-temperature fuel cells, sealing failure may occur during operation, causing fire safety issues such as contact between the anode and cathode gases.

[0003] LNG itself has high-grade cold energy. The gasified natural gas (NG) can be used in gas turbine power plants and civil natural gas. It can also be used as anode fuel gas in SOFCs systems after reforming. However, since the LNG gasification process often uses environmental heat sources, a large amount of cold energy it possesses is released into the environment and cannot be fully utilized, resulting in energy waste and possible cold pollution of the environment. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a system that utilizes LNG cold energy to achieve efficiency improvement and carbon reduction in SOFCs power generation systems. The high-grade cold energy of LNG is utilized in three stages: deep cooling, medium cooling, and shallow cooling, which are respectively used to liquefy CO2 in the anode tail gas of the SOFCs power generation system; the cathode inlet air in the SOFCs is dehumidified and dried to reduce the energy consumption required for air heating; the high-grade waste heat in the SOFCs tail gas is recovered to efficiently gasify LNG while achieving dehydration of the anode tail gas, and the condensed water is recovered for use in the methane reforming process. In addition, the liquid carbon dioxide captured by the system can be converted into part dry ice and part low-temperature gaseous CO2 in a dry ice machine through an internal heat rejection method. The former can be transported for commercial use, and the latter can be stored and used to enter the SOFCs system through a fire bypass in the event of an accidental fire in the SOFCs, thereby realizing emergency fire extinguishing of the SOFCs system.

[0005] The object of the present invention is achieved in that:

[0006] A system for improving the efficiency and reducing the carbon emissions of a SOFCs power generation system by using LNG cold energy, comprising a SOFCs power generation system, wherein the SOFCs power generation system comprises an LNG pipeline, an air pipeline, and SOFCs, wherein the SOFCs comprise a SOFCs cathode (15) and a SOFCs anode (19), wherein a branch is provided downstream of the LNG pipeline, wherein a first control valve (8), an NG compressor (9), a natural gas reforming reaction tower (14), and a SOFCs anode (19) are sequentially connected in series on the branch, wherein gasified NG passes through the first control valve (8) into the NG compressor (9), is compressed, and then enters the natural gas reforming reaction tower (14), undergoes a reforming reaction with steam, and is converted into H2 and CO, and the H2 and CO are used as fuel and then enter the SOFCs anode;

[0007] The air pipeline comprises an air compressor (34) and a second separator (32) which are connected in series in sequence. The air outlet of the second separator (32) is connected to the SOFCs cathode (15). The air is compressed by the air compressor (34) and then enters the SOFCs cathode (15). The anode fuel and the cathode air undergo an electrochemical reaction to generate direct current.

[0008] The first channel of the LNG heat exchanger (35), the first channel of the first NG heat exchanger (33), and the first channel of the second NG heat exchanger (7) are sequentially connected in series upstream of the LNG pipeline network;

[0009] A first channel of a heat exchanger 1 (10) and a heat exchanger 4 (13) are sequentially connected in series between the NG compressor (9) and the natural gas reforming reaction tower (14);

[0010] The second channel of the first NG heat exchanger (33) is connected in series with the air outlet of the second separator (32), the first channel of the second heat exchanger (11), the first channel of the third heat exchanger (12) and the cathode (15) of the SOFCs;

[0011] It also includes a circulating water storage tank (30), and a water supply pump (29), a steam generator (28), a first channel of a heat exchanger six (27), a first channel of a heat exchanger five (25), and a second control valve (22) are sequentially connected in series between the circulating water storage tank (30) and the natural gas reforming reaction tower (14);

[0012] The anode outlet of SOFCs is connected in series with a third control valve (20), a CO water vapor shift reaction tower (23), a second channel of a heat exchanger five (25), a second channel of a heat exchanger four (13), a second channel of a heat exchanger three (12), a second channel of a second NG heat exchanger (7), and a first separator (6); the anode tail gas enters the CO water vapor shift reaction tower (23), undergoes a water vapor shift reaction, and converts the remaining carbon monoxide in the anode tail gas into CO2; since the water vapor shift reaction is an exothermic reaction, the temperature of the anode tail gas is further increased, and then enters the heat exchanger five (25), the heat exchanger four (13), and the heat exchanger three (12) in sequence for heat recovery, thereby increasing the temperature of the fuel and air entering the SOFCs;

[0013] The gas outlet of the first separator (6) is connected in series with the CO2 compressor (4) and the second channel of the LNG heat exchanger (35). The CO2 separated by the first separator (6) is compressed by the CO2 compressor (4) and then enters the LNG heat exchanger (35) for heat exchange and absorption of cold energy to produce liquid carbon dioxide, thereby forming a carbon capture system.

[0014] The cathode outlet of SOFCs is connected in series with the second channel of heat exchanger 2 (11), the second channel of heat exchanger 1 (10), the second channel of heat exchanger 6 (27), and the heating unit (26); the cathode tail gas is sequentially passed through heat exchanger 2 (11), heat exchanger 1 (10), and heat exchanger 6 (27) for heat recovery, thereby increasing the temperature of the fuel and air entering the SOFCs, and then enters the heating unit (26) after heat recovery;

[0015] The first separator (6), the circulating water storage tank (30), the second separator (32), the air compressor (34), the first NG heat exchanger (33), and the second NG heat exchanger (7) form a dehumidification system. The wet air is compressed by the air compressor (34) and then enters the first NG heat exchanger (33). After cooling and dehumidification, it enters the second separator (32). The second separator (32) separates liquid water and dehumidified air. The air is heated by the second heat exchanger (11) and the third heat exchanger (12) and then enters the SOFCs reaction. The SOFCs anode tail gas enters the second NG heat exchanger (7) for heat exchange and dehumidification and then enters the first separator (6). The first separator (6) separates liquid water and CO2. The liquid water separated by the first separator (6) and the second separator (32) are both collected in the circulating water storage tank (30) as system circulating water.

[0016] Preferably, the SOFCs anode outlet is respectively connected to the fourth control valve (21) and the third control valve (20), the downstream end of the fourth control valve (21) is connected to the natural gas reforming reaction tower (14), and an NG sensor (18) is arranged at the SOFCs anode outlet. When the NG sensor detects unreacted natural gas, the third control valve (20) is closed, the fourth control valve (21) is opened, and the anode tail gas enters the natural gas reforming reaction tower through the fourth control valve (21) for secondary reforming. When the NG sensor does not detect natural gas, the fourth control valve (21) is closed, and the third control valve (20) is opened.

[0017] Preferably, a liquid level sensor (31) is provided in the circulating water storage tank (30), and when the liquid level in the circulating water storage tank (30) exceeds 2 / 3, the fifth control valve (5) is opened to lower the water level.

[0018] Preferably, the CO water vapor shift reaction tower (23) is connected to the fuel storage unit (24), and the H2 generated by the water vapor shift reaction tower (23) enters the fuel storage unit (24) as a system backup fuel.

[0019] Preferably, the downstream end of the second channel of the LNG heat exchanger (35) is connected to a dry ice machine (36), and the liquid carbon dioxide is converted into dry ice in the dry ice machine (36);

[0020] An N2 sensor (17) is arranged at the SOFCs anode outlet, and the gas outlet of the dry ice machine (36) is connected in series with a CO2 gas storage unit (1), a sixth control valve (2), and an SOFCs cathode (15) to form an emergency fire fighting system;

[0021] Part of the liquid carbon dioxide in the dry ice machine is vaporized into low-temperature gaseous CO2, which is then stored in the CO2 gas storage unit (1) as an emergency fire extinguishing agent. When SOFCs are damaged by high temperature or the seal fails, the anode fuel and cathode air come into contact and catch fire. The N2 sensor (17) detects nitrogen at the anode outlet, closes the first control valve (8), cuts off the fuel source, opens the sixth control valve (2), and directly passes the low-temperature gaseous CO2 in the CO2 gas storage unit (1) into the cathode to achieve cooling and fire extinguishing.

[0022] Preferably, the CO2 gas storage unit (1) is connected to the gas inlet of the CO2 compressor (4) via a check valve (3). When the CO2 in the CO2 gas storage unit (1) exceeds a set value, it is introduced into the anode tail gas before compression through the check valve (3) for pre-cooling and recirculation.

[0023] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0024] 1. The present invention is a process method for utilizing LNG cold energy to achieve efficiency improvement, carbon reduction and emergency fire fighting of SOFC power generation system.

[0025] 2. The present invention utilizes LNG cryogenic refrigeration to liquefy the enriched carbon dioxide in the SOFCs anode tail gas, thereby significantly reducing carbon emissions and reducing the cost of carbon capture and treatment.

[0026] 3. The present invention utilizes LNG intercooling to cool and dehumidify the air at the cathode inlet of the SOFCs system, thereby reducing the moisture content of the air entering the SOFCs, thereby reducing the energy consumption required to heat the inlet air to the SOFCs reaction temperature, improving the overall energy efficiency of the system, and increasing the mass transfer rate of oxygen ions, thereby increasing the power generation capacity.

[0027] 4. The present invention uses LNG shallow cooling to cool the high-temperature tail gas at the SOFCs anode outlet, so that LNG can be efficiently gasified to meet the pipeline transportation standard, and at the same time, a large amount of H2O in the tail gas at the anode outlet is separated by condensation, so that CO2 in the tail gas is extremely enriched, creating good conditions for the subsequent carbon capture process. A large amount of H2O condensed and separated from the tail gas can be used as circulating water for the methane reforming hydrogen production process.

[0028] 5. The present invention utilizes the good fire extinguishing properties of low-temperature CO2 to set up a fire bypass to connect the SOFCs cathode. In an emergency, the low-temperature CO2 captured and stored in the system can be directly introduced into the fire bypass to quickly extinguish the fire, thereby ensuring the fire safety of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the present invention.

[0030] Reference numerals

[0031] In the attached figure, 1. CO2 gas storage unit; 2. sixth control valve; 3. check valve; 4. CO2 compressor; 5. fifth control valve; 6. first separator; 7. second NG heat exchanger; 8. first control valve; 9. NG compressor; 10. heat exchanger 1; 11 heat exchanger 2; 12. heat exchanger 3; 13. heat exchanger 4; 14. natural gas reforming reaction tower; 15. SOFCs cathode; 16. inverter; 17. N2 sensor; 18. NG sensor; 19. SOFCs anode; 20. Third control valve; 21. Fourth control valve; 22. Second control valve; 23. CO water vapor shift reaction tower; 24. Hydrogen storage unit; 25. Heat exchanger five; 26. Heating unit; 27. Heat exchanger six; 28. Steam generator; 29. ​​Feed water pump; 30. Circulating water storage tank; 31. Liquid level sensor: 32. Second separator; 33. First NG heat exchanger; 34. Air compressor; 35. LNG heat exchanger; 36. Dry ice machine. DETAILED DESCRIPTION

[0032] like Figure 1As shown, a system that uses LNG cold energy to improve efficiency and reduce carbon emissions in SOFCs power generation systems is used. The high-grade cold energy of LNG is used for deep cooling, intermediate cooling, and shallow cooling, which are used to liquefy CO2 in the anode tail gas of SOFCs power generation systems; dehumidify and dry the air at the cathode inlet of SOFCs to reduce the energy consumption required for air heating; recover the high-grade waste heat in the SOFCs tail gas, so that LNG can be efficiently gasified while achieving anode tail gas dehydration, and recovering condensed water for methane reforming process. In addition, the liquid carbon dioxide captured by the system can be made into part of dry ice and part of low-temperature gaseous CO2 in the dry ice machine through the internal heat removal method. The former can be transported for commercial use, and the latter can be stored for use in the event of an accidental fire in SOFCs, and enter the SOFCs system through the fire bypass to achieve emergency fire extinguishing of the SOFCs system.

[0033] The system of the present invention mainly consists of four parts: a SOFCs power generation system, a dehumidification system, a carbon capture system and an emergency fire fighting system.

[0034] The SOFCs power generation system includes a first control valve 8, an NG compressor 9, a heat exchanger 1 10, a heat exchanger 2 11, a heat exchanger 3 12, a heat exchanger 4 13, a natural gas reforming reaction tower 14, a SOFCs cathode 15, an inverter 16, an NG sensor 18, a SOFCs anode 19, a third control valve 20, a fourth control valve 21, a second control valve 22, a CO water vapor shift reaction tower 23, a fuel storage unit 24, a heat exchanger 5 25, a heating unit 26, a heat exchanger 6 27, a steam generator 28, a water supply pump 29, a circulating water storage tank 30, and an air compressor 34.

[0035] The SOFCs power generation system is the main equipment for generating heat and electricity. Its working principle is that part of the gasified NG passes through the first control valve 8, enters the NG compressor 9, is compressed to the system working pressure, and then enters the natural gas reforming reaction tower 14. After the reforming reaction with the steam generated by the system circulating water in the circulating water storage tank 30, it is converted into H2 and CO and enters the SOFCs anode. After the air is compressed by the air compressor 34 and participates in dehumidification, it enters the SOFCs cathode. The anode fuel and the cathode air undergo an electrochemical reaction, and the generated DC power is converted into AC power through the inverter 16 for plant power and grid connection. An NG sensor 18 is set at the SOFCs anode outlet to avoid increasing the subsequent carbon capture cost and natural gas waste due to incomplete reaction. When the NG sensor detects unreacted natural gas, the third control valve 20 is closed, the fourth control valve 21 is opened, and the anode tail gas enters the natural gas reforming reaction tower through the fourth control valve 21 for secondary reforming. When the NG sensor does not detect natural gas, the fourth control valve 21 is closed, the third control valve 20 is opened, and the anode tail gas enters the CO water vapor shift reaction tower 23, where a water vapor shift reaction occurs to convert the remaining carbon monoxide in the tail gas into CO2, which is convenient for the subsequent carbon capture process. The H2 produced by the water vapor shift enters the fuel storage unit 24 as a system backup fuel. Since the water vapor shift reaction is an exothermic reaction, the temperature of the anode tail gas is further increased, and then it enters the heat exchanger five 25, the heat exchanger four 13, and the heat exchanger three 12 in turn to heat the SOFCs intake raw material for heat recovery and then enter the subsequent dehumidification and dehydration, and carbon capture unit. Similarly, the cathode tail gas passes through the heat exchanger two 11, the heat exchanger one 10, and the heat exchanger six 27 in turn to heat the SOFCs intake raw material for heat recovery. Since the main component of the cathode tail gas is air, it enters the heating unit 26 after heat recovery to provide heat for plant use, etc.

[0036] The dehumidification system part includes a fifth control valve 5 , a first separator 6 , a second NG heat exchanger 7 , a circulating water storage tank 30 , a liquid level sensor 31 , a second separator 32 , a first NG heat exchanger 33 , and an air compressor 34 .

[0037] The dehumidification system is to dehumidify and dry the inlet air entering SOFCs, reduce the heat required for air to enter SOFCs to heat up, and improve system efficiency. Secondly, it cools, dehydrates and dehumidifies the anode tail gas passing through the heat exchanger 3 12, increases the CO2 concentration in the anode tail gas, provides conditions for the subsequent carbon capture process, and completes the complete gasification of LNG. Its working principle is that the wet air is compressed by the air compressor 34 and enters the first NG heat exchanger 33 for cooling and dehumidification, and then enters the second separator 32. The second separator 32 separates the liquid water and the dehumidified air. The low-water content air is directly heated by the heat exchanger 2 11 and the heat exchanger 3 12 and then enters the SOFCs reaction. After the SOFCs anode tail gas passes through the heat exchanger 3 12 for heat exchange and dehumidification, it enters the second NG heat exchanger 7 and enters the first separator 6. The first separator 6 separates the liquid water and CO2. The separated CO2 enters the subsequent CO2 liquefaction process and is then connected to a dry ice machine. The liquid water separated by the first separator 6 and the second separator 32 are all collected in the circulating water storage tank 30 as the system circulating water. A liquid level sensor 31 is provided in the circulating water storage tank. Although the natural gas reforming reaction and the CO water vapor shift reaction consume water, the liquid water generated by the system is higher than the water consumption. When the liquid level in the water storage tank 30 exceeds 2 / 3, the liquid level sensor transmits an electrical signal to open the fifth control valve 5 to lower the water level.

[0038] The carbon capture system and emergency fire fighting system include a CO2 gas storage unit 1, a sixth control valve 2, a check valve 3, a CO2 compressor 4, a first control valve 8, an N2 sensor 17, an LNG heat exchanger 35, and a dry ice machine 36.

[0039] The carbon capture system and emergency fire fighting system utilize the LNG cryogenic section to cool and liquefy CO2, and realize functions such as storage and emergency fire fighting. Its working principle is that the CO2 separated by the first separator 6 is compressed by the CO2 compressor, and then enters the LNG heat exchanger 35 for cooling and heat exchange with the LNG cryogenic section. The liquid carbon dioxide is used to make dry ice in the dry ice machine 36. A part of the liquid carbon dioxide is gasified into low-temperature gaseous CO2, and then enters the CO2 gas storage unit 1 for storage as a fire emergency extinguishing agent, and the other part of the liquid carbon dioxide is converted into dry ice for commercial transportation; when the CO2 in the CO2 gas storage unit 1 exceeds the rated value, it is merged into the anode tail gas before compression through the check valve 3 for pre-cooling and recirculation. After heat exchange in the LNG heat exchanger 35, the LNG passes through the first NG heat exchanger 33 and the second NG heat exchanger 7 in turn to meet the pipeline transportation standard. A part of it enters the SOFCs fuel gas pipeline through the first control valve 8, enters the SOFCs anode after reforming, and a part of it passes through the pipeline network to transport natural gas to the outside. When SOFCs are damaged by high temperature or the seal fails and the anode and cathode gases come into contact and catch fire, the N2 sensor 17 detects nitrogen at the anode, transmits an electrical signal to close the first control valve 8, cuts off the fuel source, opens the sixth control valve 2, and directly passes the low-temperature gaseous CO2 in the CO2 storage unit 1 into the cathode, thereby achieving rapid cooling and fire extinguishing.

[0040] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A system for improving efficiency and reducing carbon emissions of a SOFCs power generation system by using LNG cold energy, comprising a SOFCs power generation system, wherein the SOFCs power generation system comprises an LNG pipeline, an air pipeline, and SOFCs, wherein the SOFCs comprises a SOFCs cathode (15) and a SOFCs anode (19), and wherein: A branch is provided downstream of the LNG pipeline network, on which a first control valve (8), an NG compressor (9), a natural gas reforming reaction tower (14), and an SOFCs anode (19) are sequentially connected in series. The gasified NG enters the NG compressor (9) through the first control valve (8) for compression and then enters the natural gas reforming reaction tower (14). After reforming reaction with steam, the NG is converted into H2 and CO. The H2 and CO are used as fuel and then enter the SOFCs anode. The air pipeline comprises an air compressor (34) and a second separator (32) which are connected in series in sequence. The air outlet of the second separator (32) is connected to the SOFCs cathode (15). The air is compressed by the air compressor (34) and then enters the SOFCs cathode (15). The anode fuel and the cathode air undergo an electrochemical reaction to generate direct current. The first channel of the LNG heat exchanger (35), the first channel of the first NG heat exchanger (33), and the first channel of the second NG heat exchanger (7) are sequentially connected in series upstream of the LNG pipeline network; A first channel of a heat exchanger 1 (10) and a heat exchanger 4 (13) are sequentially connected in series between the NG compressor (9) and the natural gas reforming reaction tower (14); The second channel of the first NG heat exchanger (33) is connected in series with the air outlet of the second separator (32), the first channel of the second heat exchanger (11), the first channel of the third heat exchanger (12) and the cathode (15) of the SOFCs; It also includes a circulating water storage tank (30), and a water supply pump (29), a steam generator (28), a first channel of a heat exchanger six (27), a first channel of a heat exchanger five (25), and a second control valve (22) are sequentially connected in series between the circulating water storage tank (30) and the natural gas reforming reaction tower (14); The anode outlet of SOFCs is connected in series with a third control valve (20), a CO water vapor shift reaction tower (23), a second channel of a heat exchanger five (25), a second channel of a heat exchanger four (13), a second channel of a heat exchanger three (12), a second channel of a second NG heat exchanger (7), and a first separator (6); the anode tail gas enters the CO water vapor shift reaction tower (23), undergoes a water vapor shift reaction, and converts the remaining carbon monoxide in the anode tail gas into CO2; since the water vapor shift reaction is an exothermic reaction, the temperature of the anode tail gas is further increased, and then enters the heat exchanger five (25), the heat exchanger four (13), and the heat exchanger three (12) in sequence for heat recovery, thereby increasing the temperature of the fuel and air entering the SOFCs; The gas outlet of the first separator (6) is connected in series with the CO2 compressor (4) and the second channel of the LNG heat exchanger (35). The CO2 separated by the first separator (6) is compressed by the CO2 compressor (4) and then enters the LNG heat exchanger (35) for heat exchange and absorption of cold energy to produce liquid carbon dioxide, thereby forming a carbon capture system. The cathode outlet of SOFCs is connected in series with the second channel of heat exchanger 2 (11), the second channel of heat exchanger 1 (10), the second channel of heat exchanger 6 (27), and the heating unit (26); the cathode tail gas is sequentially passed through heat exchanger 2 (11), heat exchanger 1 (10), and heat exchanger 6 (27) for heat recovery, thereby increasing the temperature of the fuel and air entering the SOFCs, and then enters the heating unit (26) after heat recovery; The first separator (6), the circulating water storage tank (30), the second separator (32), the air compressor (34), the first NG heat exchanger (33), and the second NG heat exchanger (7) form a dehumidification system. The wet air is compressed by the air compressor (34) and then enters the first NG heat exchanger (33). After cooling and dehumidification, it enters the second separator (32). The second separator (32) separates liquid water and dehumidified air. The air is heated by the second heat exchanger (11) and the third heat exchanger (12) and then enters the SOFCs reaction. The SOFCs anode tail gas enters the second NG heat exchanger (7) for heat exchange and dehumidification and then enters the first separator (6). The first separator (6) separates liquid water and CO2. The liquid water separated by the first separator (6) and the second separator (32) are both collected in the circulating water storage tank (30) as system circulating water.

2. According to claim 1, a system for improving efficiency and reducing carbon emissions of SOFCs power generation system by using LNG cold energy, characterized in that: The SOFCs anode outlet is respectively connected to the fourth control valve (21) and the third control valve (20); the downstream end of the fourth control valve (21) is connected to the natural gas reforming reaction tower (14); an NG sensor (18) is arranged at the SOFCs anode outlet; when the NG sensor detects unreacted natural gas, the third control valve (20) is closed, the fourth control valve (21) is opened, and the anode tail gas passes through the fourth control valve (21) into the natural gas reforming reaction tower for secondary reforming; when the NG sensor does not detect natural gas, the fourth control valve (21) is closed, and the third control valve (20) is opened.

3. The system for improving efficiency and reducing carbon emissions of SOFCs power generation system by utilizing LNG cold energy according to claim 1, characterized in that: A liquid level sensor (31) is provided in the circulating water storage tank (30). When the liquid level in the circulating water storage tank (30) exceeds 2 / 3, the fifth control valve (5) opens to lower the water level.

4. The system for improving efficiency and reducing carbon emissions of SOFCs power generation system by utilizing LNG cold energy according to claim 1, characterized in that: The CO water vapor shift reaction tower (23) is connected to the fuel storage unit (24), and the H2 generated by the water vapor shift reaction tower (23) enters the fuel storage unit (24) as a system backup fuel.

5. The system for improving efficiency and reducing carbon emissions of SOFCs power generation system by utilizing LNG cold energy according to claim 1, characterized in that: The downstream end of the second channel of the LNG heat exchanger (35) is connected to a dry ice machine (36), and liquid carbon dioxide is used to produce dry ice in the dry ice machine (36) through an internal heat rejection method; An N2 sensor (17) is arranged at the SOFCs anode outlet, and the gas outlet of the dry ice machine (36) is connected in series with a CO2 gas storage unit (1), a sixth control valve (2), and an SOFCs cathode (15) to form an emergency fire fighting system; In the dry ice machine, part of the liquid carbon dioxide is gasified into low-temperature gaseous CO2 through an internal heat removal method, and then enters the CO2 gas storage unit (1) for storage as an emergency fire extinguishing agent. When SOFCs are damaged by high temperature or the seal fails, the anode fuel and cathode air come into contact and catch fire. The N2 sensor (17) detects nitrogen at the anode outlet, closes the first control valve (8), cuts off the fuel source, opens the sixth control valve (2), and directly passes the low-temperature gaseous CO2 in the CO2 gas storage unit (1) into the cathode to achieve cooling and fire extinguishing.

6. The system for improving efficiency and reducing carbon emissions of SOFCs power generation system using LNG cold energy according to claim 5, characterized in that: The CO2 gas storage unit (1) is connected to the gas inlet end of the CO2 compressor (4) via a check valve (3). When the CO2 in the CO2 gas storage unit (1) exceeds a set value, the CO2 is introduced into the anode tail gas before compression via the check valve (3) for pre-cooling and recirculation.

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