Multi-generation system coupling lng cold energy and wet flue gas waste heat and working method

Abstract

The application discloses a poly-generation system and working method for coupling LNG cold energy and wet flue gas waste heat, comprising a low-temperature Rankine power generation sub-system, a multi-stage expansion sub-system, a low-temperature carbon capture sub-system and a waste flue gas power generation sub-system, wherein the low-temperature carbon capture sub-system is the most characteristic, and is divided into preliminary low-temperature carbon capture and deep low-temperature carbon capture; the high-grade LNG cold energy is used for deep carbon capture of low-temperature flue gas, and the LNG before gasification is preheated, so that the LNG gasification heat exchange temperature difference is reduced, and the double-condensation liquefied carbon dioxide is obtained; the carbon capture degree of the flue gas is higher; meanwhile, according to different required cold energy grades, the cold energy released by the LNG in the gasification process is sequentially used in stages; the high-grade LNG cold energy is used for deep liquefied carbon dioxide; the medium-grade LNG cold energy is used for low-temperature power generation and preliminary carbon capture; and the low-grade LNG cold energy is used for condensation and dehumidification of the wet flue gas, so that the LNG cold energy utilization rate is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of LNG cold energy utilization technology, and relates to the field of combined heat and power generation, including cold energy power generation, cryogenic carbon capture, and flue gas waste heat recovery. In particular, it relates to a combined heat and power system and its working method based on LNG cold energy utilization. Background Technology

[0002] Liquefied Natural Gas (LNG) is one of the main methods of natural gas storage and transportation. At receiving terminals, LNG is typically vaporized before being transported to downstream users. This vaporization process inevitably releases a large amount of cold energy, approximately 830 kJ / kg. If all this cold energy were converted into electricity, one ton of LNG would release the equivalent of 240 kWh. Currently, my country's LNG receiving terminals have a total receiving capacity of 109.57 million tons per year, with the cold energy contained within equivalent to approximately 26.3 billion kWh per year. In traditional vaporization processes, the cold energy carried by LNG is carried away by seawater or air, resulting in extreme energy waste and severe cold pollution of nearby sea areas or the terminal area. The utilization of LNG cold energy is not only significant for energy conservation and environmental protection but also generates considerable economic and social benefits; therefore, the utilization of LNG cold energy is gradually receiving widespread attention.

[0003] The utilization of LNG cold energy is generally divided into two types: direct utilization and indirect utilization. Direct utilization includes cold energy power generation, cryogenic air separation, light hydrocarbon separation, liquid CO2 production (carbon capture), automotive air conditioning, seawater desalination, and air conditioning refrigeration; indirect utilization includes cryogenic pulverization and cryogenic medical applications. However, in industrial production processes, the cold energy of LNG has not been utilized rationally, and its utilization has not been rationally tiered according to the quality of the cold energy, resulting in a significant waste of LNG cold energy.

[0004] Currently, existing technologies, such as the one described in application number CN202311382282.1, entitled "A Low-Temperature Carbon Capture Process for Hydrogen Production from Natural Gas," require cooling capacity supplied by low-temperature purified gas and an independent vapor compression mixed refrigerant refrigeration cycle. Therefore, the system requires electrical power, resulting in energy consumption during carbon capture. Another existing technology, such as publication number CN114961899A, entitled "An Integrated Utilization System for Waste Heat and Cold Energy of LNG-Powered Ships with Carbon Capture Function," includes an air separation subsystem, a flue gas waste heat recovery and utilization subsystem, and a low-temperature carbon capture subsystem. This system recovers high-grade LNG cold energy through air separation, but the overall system has high energy consumption.

[0005] Therefore, designing efficient and energy-saving LNG cold energy utilization polygeneration systems and managing energy coordination between systems to improve LNG cold energy utilization efficiency is of great significance to the development of cascade utilization of LNG cold energy. Summary of the Invention

[0006] The purpose of this invention is to provide a combined heat and power system and operating method that couples LNG cold energy and wet flue gas waste heat, aiming to improve the problems of low cold energy utilization rate and low cold energy utilization efficiency in existing LNG cold energy utilization technologies, and to provide an effective energy utilization solution for further reducing carbon dioxide emissions from LNG power plants throughout their entire life cycle, thereby achieving energy conservation and emission reduction.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a multi-generation system coupling LNG cold energy and wet flue gas waste heat, including a low-temperature Rankine power generation system, a multi-stage expansion subsystem, a low-temperature carbon capture subsystem, and a waste flue gas power generation system;

[0008] The low-temperature Rankine electronic system includes heat exchanger I, heat exchanger II, heat exchanger III, solution pump, and expander I;

[0009] Heat exchanger I includes a hot end outlet, a hot end inlet, a cold end outlet, and a cold end inlet; heat exchanger II includes a hot end outlet, a hot end inlet, a cold end outlet, and a cold end inlet; heat exchanger III includes a hot end outlet, a hot end inlet, a cold end outlet, and a cold end inlet; the solution pump includes a solution pump inlet and a solution pump outlet; expander I includes an expander I inlet and an expander I outlet.

[0010] The hot-side outlet of heat exchanger I is connected to the inlet of water separator I via a pipe. The cold-side outlet of heat exchanger I is connected to the inlet of expander I via a pipe. The outlet of expander I is connected to the hot-side inlet of heat exchanger II via a pipe. The hot-side outlet of heat exchanger II is connected to the hot-side inlet of heat exchanger III via a pipe. The hot-side outlet of heat exchanger III is connected to the inlet of solution pump via a pipe. The outlet of solution pump is connected to the cold-side inlet of heat exchanger II via a pipe. The cold-side outlet of heat exchanger II is connected to the cold-side inlet of heat exchanger I via a pipe.

[0011] The multi-stage expansion subsystem includes water separator I, heat exchanger IV, heat exchanger V, heat exchanger VI, water separator II, compressor I, heat exchanger VII, expander II, expander III, heat exchanger VIII, compressor II, heat exchanger IX, compressor III, heat exchanger X, and heat exchanger;

[0012] Separator I includes a water separator I inlet, a water separator I gas outlet, and a water separator I liquid outlet; Heat exchanger IV includes a heat exchanger IV hot end outlet, a heat exchanger IV hot end inlet, a heat exchanger IV cold end outlet, and a heat exchanger IV cold end inlet; Heat exchanger V includes a heat exchanger V hot end outlet, a heat exchanger V hot end inlet, a heat exchanger V cold end outlet, and a heat exchanger V cold end inlet; Heat exchanger VI includes a heat exchanger VI hot end outlet, a heat exchanger VI hot end inlet, a heat exchanger VI cold end outlet, and a heat exchanger VI cold end inlet; Water separator II includes a water separator II inlet, a water separator II gas outlet, and a water separator II liquid outlet; Compressor I includes a compressor I inlet and a compressor I outlet; Heat exchanger VII includes a heat exchanger VII hot end outlet and a heat exchanger VII hot end inlet. Heat exchanger VII includes a cold end outlet and a cold end inlet; heat exchanger VIII includes a hot end outlet, a hot end inlet, a cold end outlet, and a cold end inlet; compressor II includes an inlet end and an outlet end; expander III includes an inlet end and an outlet end; heat exchanger IX includes a hot end outlet, a hot end inlet, a cold end outlet, and a cold end inlet; compressor III includes an inlet end and an outlet end; heat exchanger X includes a hot end outlet, a hot end inlet, a cold end outlet, and a cold end inlet; heat exchanger A includes a hot end outlet, a hot end inlet, a cold end outlet, and a cold end inlet.

[0013] The hot-side outlet of heat exchanger I is connected to the inlet of water separator I via a pipe. The gas outlet of water separator I is connected to the hot-side inlet of heat exchanger IV via a pipe. The hot-side outlet of heat exchanger IV is connected to the hot-side inlet of heat exchanger V via a pipe. The hot-side outlet of heat exchanger V is connected to the hot-side inlet of heat exchanger VI via a pipe. The hot-side outlet of heat exchanger VI is connected to the inlet of water separator II via a pipe. The gas outlet of water separator II is connected to the inlet of compressor I via a pipe. The outlet of compressor I is connected to the hot-side inlet of heat exchanger VII via a pipe. The hot-side outlet of heat exchanger VII is connected to compressor II via a pipe. The outlet of compressor II is connected to the hot-side inlet of heat exchanger IX via a pipe. The hot-side outlet of heat exchanger IX... The pipeline connects to the hot-side inlet of heat exchanger VIII. The hot-side outlet of heat exchanger VIII is connected to the inlet of compressor III via a pipeline. The outlet of compressor III is connected to the hot-side inlet of heat exchanger X via a pipeline. The hot-side outlet of heat exchanger X is connected to the hot-side inlet of heat exchanger A via a pipeline. The hot-side outlet of heat exchanger A is connected to the valve inlet via a pipeline. The cold-side outlet of heat exchanger A is connected to the cold-side inlet of heat exchanger VIII via a pipeline. The cold-side inlet of heat exchanger VIII is connected to the inlet of expander III via a pipeline. The outlet of expander III is connected to the cold-side inlet of heat exchanger IV via a pipeline. The cold-side outlet of heat exchanger IV is connected to the inlet of expander II via a pipeline. The outlet of expander II is connected to the cold-side inlet of heat exchanger VII via a pipeline. The cold-side outlet of heat exchanger VII is the natural gas outlet.

[0014] The cryogenic carbon capture system includes valves, gas-liquid separator I, heat exchanger B, gas-liquid separator II, cryogenic pump I, LNG storage tank, CO2 storage tank, cryogenic pump II, and mixer;

[0015] The valve includes a valve inlet and a valve outlet; gas-liquid separator I includes a gas-liquid separator I inlet, a gas outlet, and a liquid outlet; heat exchanger B includes a heat exchanger B hot end outlet, a heat exchanger B hot end inlet, a heat exchanger B cold end outlet, and a heat exchanger B cold end inlet; gas-liquid separator II includes a gas-liquid separator II inlet, a gas outlet, and a gas-liquid separator II liquid outlet; cryogenic pump I includes a cryogenic pump I inlet and a cryogenic pump I outlet; LNG storage tank includes an LNG storage tank inlet and an LNG storage tank outlet; CO2 storage tank includes a CO2 storage tank inlet and a CO2 storage tank outlet; cryogenic pump II includes a cryogenic pump II inlet and a cryogenic pump II outlet; and a mixer includes a mixer inlet a, a mixer inlet b, and a mixer outlet.

[0016] The valve outlet is connected to the inlet of gas-liquid separator I via a pipeline. The gas outlet of gas-liquid separator I is connected to the hot side inlet of heat exchanger B via a pipeline. The hot side outlet of heat exchanger B is connected to the inlet of gas-liquid separator II via a pipeline. The gas outlet of gas-liquid separator II is connected to the cold side inlet of heat exchanger VI via a pipeline. The LNG storage tank outlet is connected to the inlet of cryogenic pump I via a pipeline. The outlet of cryogenic pump I is connected to the cold side inlet of heat exchanger B via a pipeline. The cold side outlet of heat exchanger B is connected to the inlet of cryogenic pump II via a pipeline. The liquid outlet of gas-liquid separator II is connected to the inlet a of mixer via a pipeline. The liquid outlet of gas-liquid separator I is connected to the inlet b of mixer via a pipeline.

[0017] The waste gas power generation system includes heat exchanger V, heat exchanger VI, expander IV, expander V, and cooler;

[0018] Heat exchanger V includes a hot end outlet, a hot end inlet, a cold end outlet, and a cold end inlet; heat exchanger VI includes a hot end outlet, a hot end inlet, a cold end outlet, and a cold end inlet; expander IV includes an inlet end and an outlet end; expander V includes an inlet end and an outlet end; cooler includes a hot end outlet, a hot end inlet, a cold end outlet, and a cold end inlet.

[0019] The cold-side outlet of heat exchanger VI is connected to the inlet of expander IV via a pipe. The outlet of expander IV is connected to the cold-side inlet of heat exchanger V via a pipe. The cold-side outlet of heat exchanger V is connected to the inlet of expander V via a pipe. The outlet of expander V is connected to the inlet of cooler via a pipe. The outlet of cooler is the exhaust gas outlet.

[0020] As a preferred option, the hot-end inlet medium in heat exchanger I can be wet flue gas or other low-grade waste heat.

[0021] As a preferred embodiment, the cold-side inlet of heat exchanger IX is connected to the cold-side outlet of heat exchanger X, and the medium at the inlet of heat exchanger X can be cold water, coolant, etc.

[0022] As a preferred option, propane can be used as the working fluid in the low-temperature Rankine voltammetric system, and a two-component refrigerant can be selected.

[0023] As a preferred embodiment, the cooler mainly recovers the residual cold from the outlet of expander V for refrigeration, and the refrigerant can be water or other refrigerants.

[0024] As a preferred solution, the pressure of gas-liquid separator I is adjusted by regulating the outlet pressure of the valve, thereby obtaining the corresponding purity of liquid carbon dioxide.

[0025] As a preferred option, the condensate collected at the liquid outlet of water separator I and water separator II is recycled as water resources.

[0026] As a preferred embodiment, the wet flue gas of the present invention uses the wet flue gas obtained from the oxygen-enriched combustion of natural gas as the heat source.

[0027] This invention also discloses a method for coupling LNG cold energy and wet flue gas waste heat, including a two-stage wet flue gas dehumidification method, a three-stage gas compression method, and a two-stage cryogenic carbon capture method:

[0028] 1) Two-stage dehumidification method for wet flue gas:

[0029] The high-temperature and high-humidity flue gas enters two water separators for two-stage dehumidification, as follows: The high-temperature and high-humidity flue gas enters heat exchanger I1 and is cooled by a low-temperature circulating medium, reducing the temperature of the wet flue gas and causing some water vapor to condense. When the flue gas flows through water separator I, the condensate flows out from the liquid outlet of water separator I, and the dry flue gas flows out from the gas outlet of water separator I. Subsequently, it enters the hot side of heat exchangers IV, V, and VI in sequence for further cooling. The temperature of the cooled wet flue gas is reduced by less than 15°C. When the flue gas enters water separator II for further separation, the moisture content in the flue gas is reduced to the minimum.

[0030] 2) Three-stage gas compression method:

[0031] After two stages of drying, the flue gas enters compressor I for compression and pressurization, and its temperature rises. Then, it enters the hot side of heat exchanger VII and is cooled to room temperature by low-temperature natural gas. After that, it enters compressor II for compression, and its temperature rises again. Subsequently, it enters the hot side of heat exchangers IX and VIII in sequence, and is cooled to room temperature again. Then, it enters compressor III for compression, and the flue gas pressure reaches the pressure required for carbon dioxide liquefaction. Finally, it enters heat exchanger A and is cooled to room temperature again.

[0032] 3) Two-stage low-temperature carbon capture method:

[0033] After the flue gas at room temperature reaches the carbon dioxide liquefaction pressure, it flows through the valve and is throttled, causing the carbon dioxide in the flue gas to begin initial liquefaction. Subsequently, the flue gas enters gas-liquid separator I for separation. The liquefied carbon dioxide flows out from the liquid outlet of gas-liquid separator I and enters the mixer. The unliquefied flue gas flows out from the gas outlet of gas-liquid separator I and enters heat exchanger B for further cooling. The decrease in flue gas temperature causes the remaining carbon dioxide in the flue gas to liquefy again, and then enters gas-liquid separator II for separation. The liquefied carbon dioxide flows out from the liquid outlet of gas-liquid separator II and enters the mixer. The remaining flue gas in gas-liquid separator II flows out from the gas outlet of gas-liquid separator II. The liquefied carbon dioxide in the mixer flows out from the liquid outlet and enters the CO2 storage tank.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. This system combines a cryogenic Rankine power generation system, a multi-stage expansion power generation system, a cryogenic carbon capture system, and a waste gas power generation system. Among them, the cryogenic carbon capture subsystem is the most distinctive, which can be divided into preliminary cryogenic carbon capture and deep cryogenic carbon capture. It uses the high-grade cold energy of LNG to perform deep carbon capture of cryogenic flue gas, preheating the LNG before gasification and reducing the temperature difference for LNG gasification heat exchange. It uses the cold energy of medium-grade LNG to perform preliminary carbon capture of high-pressure flue gas. After double condensation and liquefaction of carbon dioxide, the carbon capture degree in the flue gas is even higher.

[0036] 2. High-grade LNG cold energy is used for liquefying carbon dioxide, thereby preheating the LNG; medium-grade LNG cold energy is used for cryogenic power generation and preliminary carbon capture; and low-grade LNG cold energy is used for condensation and dehumidification of wet flue gas. Based on the required cold energy grade, the cold energy released during LNG gasification is utilized in a tiered manner.

[0037] 3. While improving energy utilization, it also enriches the product range of the system, providing users with functions such as electricity, natural gas, liquid carbon dioxide, cooling and heating.

[0038] 3. While improving energy utilization, it also enriches the product range of the system, providing users with functions such as electricity, natural gas, liquid carbon dioxide, cooling and heating. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of a novel combined heat and power system and its operating method for coupling LNG cold energy and wet flue gas waste heat in the present invention.

[0040] Figure 2 This is a schematic diagram of the low-temperature Rankine generator system in this invention.

[0041] Figure 3 This is a schematic diagram of the multi-level expansion subsystem in this invention.

[0042] Figure 4 This is a schematic diagram of the low-temperature carbon capture subsystem in this invention.

[0043] Figure 5 This is a schematic diagram of the waste flue gas to electron system in this invention.

[0044] Figure 6 This is a schematic diagram illustrating the flow path in this invention.

[0045] In the diagram: 1. Heat exchanger I; 2. Heat exchanger II; 3. Heat exchanger III; 4. Solution pump; 5. Expander I; 6. Water separator I; 7. Heat exchanger IV; 8. Heat exchanger V; 9. Heat exchanger VI; 10. Water separator II; 11. Compressor I; 12. Heat exchanger VII; 13. Expander II; 14. Expander III; 15. Heat exchanger VIII; 16. Compressor II; 17. Heat exchanger IX; 18. Compressor III; 19. Heat exchanger X; 20. Heat exchanger A; 21. Valve; 2 2. Gas-liquid separator I; 23. Heat exchanger B; 24. Gas-liquid separator II; 25. Cryogenic pump I; 26. LNG storage tank; 27. CO2 storage tank; 28. Cryogenic pump II; 29. ​​Expander IV; 30. Expander V; 31. Cooler; 32. Mixer, a. Flow path of refrigerant; b. Flow path of flue gas; c. Flow path of heat transfer fluid; d. Flow path of liquefied natural gas; e. Flow path of liquid carbon dioxide; f. Flow path of waste flue gas. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] Please see Figures 1-6The present invention provides a technical solution: a multi-generation system coupling LNG cold energy and wet flue gas waste heat, including a low-temperature Rankine power generation system, a multi-stage expansion subsystem, a low-temperature carbon capture subsystem and a waste flue gas power generation system.

[0048] The low-temperature Rankine electronic system includes heat exchanger I1, heat exchanger II2, heat exchanger III3, solution pump 4, and expander I5.

[0049] The multi-stage expansion subsystem includes water separator I6, heat exchanger IV7, heat exchanger V8, heat exchanger VI9, water separator II10, compressor I11, heat exchanger VII12, expander II13, expander III14, heat exchanger VIII15, compressor II16, heat exchanger IX17, compressor III18, heat exchanger X19, and heat exchanger A20.

[0050] The cryogenic carbon capture system includes valve 21, gas-liquid separator I 22, heat exchanger B 23, gas-liquid separator II 24, cryogenic pump I 25, LNG storage tank 26, CO2 storage tank 27, cryogenic pump II 28, and mixer 32.

[0051] The waste gas power generation system includes heat exchanger V8, heat exchanger VI9, expander IV29, expander V30, and cooler 31.

[0052] Heat exchanger I1 is connected to expander I5, expander I5 is connected to heat exchanger II2, heat exchanger II2 is connected to heat exchanger III3, heat exchanger III3 is connected to solution pump 4, and solution pump 4 is connected to heat exchanger II2.

[0053] Heat exchanger I1 is connected to water separator I6, water separator I6 is connected to heat exchanger IV7, heat exchanger IV7 is connected to heat exchanger V8, heat exchanger V8 is connected to heat exchanger VI9, heat exchanger VI9 is ​​connected to water separator II10, water separator II10 is connected to compressor I11, compressor I11 is connected to heat exchanger VII12, heat exchanger VII12 is connected to compressor II16, compressor II16 is connected to heat exchanger IX17, heat exchanger IX17 is connected to heat exchanger VIII15, heat exchanger VIII15 is connected to compressor III18, compressor III18 is connected to heat exchanger X19, heat exchanger X19 is connected to heat exchanger A20, and heat exchanger A20 is connected to valve 21.

[0054] Valve 21 is connected to gas-liquid separator I 22, gas-liquid separator I 22 is connected to heat exchanger B 23, heat exchanger B 23 is connected to gas-liquid separator II 24, gas-liquid separator II 24 is connected to heat exchanger VI 9, heat exchanger VI 9 is connected to expander IV 29, expander IV 29 is connected to heat exchanger V 8, heat exchanger V 8 is connected to expander V 30, and expander V 30 is connected to cooler 31.

[0055] Heat exchanger VIII 15 is connected to expander III 14, expander III 14 is connected to heat exchanger IV 7, heat exchanger IV 7 is connected to expander II 13, expander II 13 is connected to heat exchanger VII 12, LNG storage tank 26 is connected to cryogenic pump I 25, cryogenic pump I 25 is connected to heat exchanger B 23, heat exchanger B 23 is connected to cryogenic pump II 28, mixer 32 is connected to gas-liquid separator I 22 and gas-liquid separator II 24, and CO2 storage tank 27 is connected to mixer 32.

[0056] in, Figures 1-5 The meanings of the lines in the text are all related to Figure 6 The lines in the text have the same meaning.

[0057] The present invention also discloses a working method for coupling LNG cold energy and wet flue gas waste heat, which includes five processes.

[0058] The first process is as follows: Low-temperature, atmospheric-pressure liquefied natural gas is drawn and pressurized by cryogenic pump I25 and transported into heat exchanger B23 for waste heat treatment. Subsequently, it is pressurized by cryogenic pump II28 and transported into heat exchanger III for gasification. The gasified cryogenic natural gas then enters heat exchanger A20 and heat exchanger VIII15 for heating and is then sent to expander III14 for expansion and power generation. After expansion, the pressure and temperature of the natural gas decrease. It then enters heat exchanger IV7 and is heated by the latent heat of vaporization of wet flue gas before flowing into expander II13 for expansion and power generation. Finally, it enters heat exchanger VII12 for reheating and is then discharged from the system.

[0059] The second process is as follows: The low-grade waste heat humid flue gas enters heat exchanger I1 for cooling, then enters water separator I6 for dehumidification. The dried flue gas then flows sequentially through heat exchangers IV7, V8, and VI9, where the water in the humid flue gas is condensed, before entering water separator II10 for further dehumidification. The dried flue gas flows out of the gas outlet of water separator II10 and enters compressor I11 for pressurization and temperature increase. It then enters heat exchanger VII12 for cooling, followed by pressurization in compressor II16. It then enters heat exchangers IX17 and VIII15 for cooling, then enters compressor III18 for further pressurization, enters heat exchanger A20 for cooling, then enters valve 21 for throttling, and enters gas-liquid separator I22 for initial carbon dioxide liquefaction. Finally, it enters heat exchanger B23 for deep cooling, and then enters gas-liquid separator II24 for further carbon dioxide liquefaction. After carbon dioxide is removed from the flue gas, the waste flue gas enters heat exchanger VI9 for heating, then enters expander IV29 for expansion and power generation, then enters heat exchanger V8 for heating, then enters expander V30 for expansion and power generation, and finally enters cooler 31 for cooling before being discharged from the system.

[0060] The third process is as follows: after the refrigerant is liquefied in heat exchanger Ⅲ3, it is pressurized by solution pump 4 and transported to heat exchanger Ⅱ2 for reheating. Then it flows into heat exchanger Ⅰ1 and is vaporized by wet flue gas. After vaporization, the refrigerant enters expander Ⅰ5 for expansion and power generation. Then it enters heat exchanger Ⅱ2 for cooling and then enters heat exchanger Ⅲ3 for liquefaction. This cycle is repeated.

[0061] The fourth process is as follows: the refrigerant enters the hot side inlet of heat exchanger X19 and heat exchanger IX17 in sequence to cool the high temperature and high pressure flue gas. Then the refrigerant temperature rises and flows out from the hot side outlet of heat exchanger IX17, which can provide heating function for users.

[0062] The fifth process is as follows: the liquid carbon dioxide flowing out of the liquid outlet of gas-liquid separator I 22 and gas-liquid separator II 24 flows into mixer 32, and then flows from the outlet of mixer 32 into CO2 storage tank 27.

[0063] The aforementioned novel combined heat and power system and operating method for LNG cold energy and wet flue gas waste heat includes a two-stage wet flue gas dehumidification method, a three-stage gas compression method, and a two-stage cryogenic carbon capture method.

[0064] 1) Two-stage dehumidification method for wet flue gas:

[0065] The high-temperature and high-humidity flue gas enters two water separators for two-stage dehumidification, as follows: The high-temperature and high-humidity flue gas enters heat exchanger I1 and is cooled by a low-temperature circulating medium, reducing the temperature of the wet flue gas and causing some water vapor to condense. When the flue gas flows through water separator I6, the condensate flows out from the liquid outlet of water separator I6, and the dry flue gas flows out from the gas outlet of water separator I6. Subsequently, it enters the hot side of heat exchangers IV7, V8, and VI9 for further cooling. The temperature of the cooled wet flue gas is reduced by less than 15°C. When the flue gas enters water separator II10 for further separation, the moisture content in the flue gas is reduced to the minimum.

[0066] 2) Three-stage gas compression method:

[0067] After two stages of drying, the flue gas enters compressor I11 for compression and pressurization, and its temperature rises. Then, it enters the hot side of heat exchanger VII12 and is cooled to room temperature by low-temperature natural gas. After that, it enters compressor II16 for compression, and its temperature rises again. Subsequently, it enters the hot side of heat exchangers IX17 and VIII15 in sequence, and is cooled to room temperature again. Then, it enters compressor III18 for compression, and the flue gas pressure reaches the pressure required for carbon dioxide liquefaction. Finally, it enters heat exchanger A20 and is cooled to room temperature again.

[0068] 3) Two-stage low-temperature carbon capture method:

[0069] After the flue gas at room temperature reaches the carbon dioxide liquefaction pressure, it flows through valve 21 and is throttled, causing the carbon dioxide in the flue gas to begin initial liquefaction. Subsequently, the flue gas enters gas-liquid separator I 22 for separation. The liquefied carbon dioxide flows out from the liquid outlet of gas-liquid separator I 22 and enters mixer 32. The unliquefied flue gas flows out from the gas outlet of gas-liquid separator I 22 and enters heat exchanger B 23 for further cooling. The decrease in flue gas temperature causes the remaining carbon dioxide in the flue gas to liquefy again, and then enters gas-liquid separator II 24 for separation. The liquefied carbon dioxide flows out from the liquid outlet of gas-liquid separator II 24 and enters mixer 32. The remaining flue gas in gas-liquid separator II 24 flows out from the gas outlet of gas-liquid separator II 24, and the liquefied carbon dioxide in the mixer flows out from the liquid outlet and enters CO2 storage tank.

[0070] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

[0071] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A combined heat and power system that couples LNG cold energy and wet flue gas waste heat, including a cryogenic Rankine power generation system, a multi-stage expansion subsystem, a cryogenic carbon capture subsystem, and a waste flue gas power generation system; Its features are, The low-temperature Rankine electronic system includes heat exchanger I (1), heat exchanger II (2), heat exchanger III (3), solution pump (4), and expander I (5); The multi-stage expansion subsystem includes water separator I (6), heat exchanger IV (7), heat exchanger V (8), heat exchanger VI (9), water separator II (10), compressor I (11), heat exchanger VII (12), expander II (13), expander III (14), heat exchanger VIII (15), compressor II (16), heat exchanger IX (17), compressor III (18), heat exchanger X (19), and heat exchanger A (20). The cryogenic carbon capture system includes valves (21), gas-liquid separator I (22), heat exchanger B (23), gas-liquid separator II (24), cryogenic pump I (25), LNG storage tank (26), CO2 storage tank (27), cryogenic pump II (28), and mixer (32). The waste flue gas power generation system includes heat exchanger V (8), heat exchanger VI (9), expander IV (29), expander V (30), and cooler (31); The heat exchanger I (1) is connected to the water separator I (6), the water separator I (6) is connected to the heat exchanger IV (7), the heat exchanger IV (7) is connected to the heat exchanger V (8), the heat exchanger V (8) is connected to the heat exchanger VI (9), the heat exchanger VI (9) is connected to the water separator II (10), the water separator II (10) is connected to the compressor I (11), and the compressor I (11) is connected to the heat exchanger VII (12). Heat exchanger VII (12) is connected to compressor II (16), compressor II (16) is connected to heat exchanger IX (17), heat exchanger IX (17) is connected to heat exchanger VIII (15), heat exchanger VIII (15) is connected to compressor III (18), compressor III (18) is connected to heat exchanger X (19), heat exchanger X (19) is connected to heat exchanger A (20), and heat exchanger A (20) is connected to valve (21). The valve (21) is connected to the gas-liquid separator I (22), the gas-liquid separator I (22) is connected to the heat exchanger B (23), the heat exchanger B (23) is connected to the gas-liquid separator II (24), the gas-liquid separator II (24) is connected to the heat exchanger VI (9), the heat exchanger VI (9) is connected to the expander IV (29), the expander IV (29) is connected to the heat exchanger V (8), the heat exchanger V (8) is connected to the expander V (30), and the expander V (30) is connected to the cooler (31). The heat exchanger VIII (15) is connected to the expander III (14), the expander III (14) is connected to the heat exchanger IV (7), the heat exchanger IV (7) is connected to the expander II (13), the expander II (13) is connected to the heat exchanger VII (12), the LNG storage tank (26) is connected to the cryogenic pump I (25), the cryogenic pump I (25) is connected to the heat exchanger B (23), the heat exchanger B (23) is connected to the cryogenic pump II (28), the mixer (32) is connected to the gas-liquid separator I (22) and the gas-liquid separator II (24), and the CO2 storage tank (27) is connected to the mixer (32). The cryogenic pump II (28) is connected to heat exchanger III (3), heat exchanger III (3) is connected to heat exchanger A (20), and heat exchanger A (20) is connected to heat exchanger VIII (15).

2. The operating method of the combined heat and power system for LNG cold energy and wet flue gas waste heat according to claim 1, characterized in that, Includes the following steps: S01: Low-temperature, atmospheric-pressure liquefied natural gas transportation process; S02: Low-grade waste heat wet flue gas conveying process; S03: Refrigerant delivery process; S04: Refrigerant delivery process; S05: Liquid carbon dioxide flowing out of the liquid outlets of gas-liquid separator I (22) and gas-liquid separator II (24) flows into mixer (32) and then flows from the outlet of mixer (32) into CO2 storage tank (27).

3. The operating method of the combined heat and power system for LNG cold energy and wet flue gas waste heat according to claim 2, characterized in that: In step S01, low-temperature, atmospheric-pressure liquefied natural gas is drawn and pressurized by cryogenic pump I (25) and transported into heat exchanger B (23) for waste heat recovery. Then, it is pressurized by cryogenic pump II (28) and transported into heat exchanger III (3) for gasification. The gasified cryogenic natural gas enters heat exchanger A (20) and heat exchanger VIII (15) in sequence for heating and then is sent to expander III (14) for expansion and power generation. The pressure and temperature of the expanded natural gas decrease. Then, it enters heat exchanger IV (7) and is heated by the latent heat of vaporization of wet flue gas. It then flows into expander II (13) for expansion and power generation. Finally, it enters heat exchanger VII (12) for reheating and is discharged from the system.

4. The operating method of the combined heat and power system for LNG cold energy and wet flue gas waste heat according to claim 2, characterized in that: In step S02, the low-grade waste heat wet flue gas enters heat exchanger I (1) and is cooled, then enters water separator I (6) for dehumidification. The dried flue gas then flows sequentially through heat exchanger IV (7), heat exchanger V (8), and heat exchanger VI (9), where the water in the wet flue gas is condensed. It then enters water separator II (10) for dehumidification. The dried flue gas flows out from the gas outlet of water separator II (10) and enters compressor I (11) for pressurization and temperature increase. It then enters heat exchanger VII (12) for cooling, and then enters compressor II (16) for pressurization. Subsequently, it enters heat exchanger IX (17) and heat exchanger VIII (15) in sequence. The gas is cooled in the compressor (18), then pressurized in the compressor (18), cooled in the heat exchanger (20), then throttled in the valve (21), and initially liquefied in the gas-liquid separator (22). After being deeply cooled in the heat exchanger (23), it is deeply liquefied in the gas-liquid separator (24). The waste gas after removing carbon dioxide from the flue gas enters the heat exchanger (9) for heating, enters the expander (29) for expansion and power generation, then enters the heat exchanger (8) for heating, enters the expander (30) for expansion and power generation, and then enters the cooler (31) for cooling before being discharged from the system.

5. The operating method for coupling LNG cold energy and wet flue gas waste heat according to claim 2, characterized in that: In step S03, the refrigerant enters heat exchanger III (3) and is liquefied. It is then pressurized by solution pump (4) and transported to heat exchanger II (2) for reheating. Then it flows into heat exchanger I (1) and is vaporized by wet flue gas. The vaporized refrigerant enters expander I (5) for expansion and power generation. After that, it enters heat exchanger II (2) for cooling. Then it enters heat exchanger III (3) for liquefaction. This cycle repeats.

6. The operating method for coupling LNG cold energy and wet flue gas waste heat according to claim 2, characterized in that: In step S04, the refrigerant enters the hot side inlet of heat exchanger X (19) and heat exchanger IX (17) in sequence to cool the high temperature and high pressure flue gas. Then the refrigerant temperature rises and flows out from the hot side outlet of heat exchanger IX (17) to provide heating function for users.

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