A natural gas power generation system and method combined with liquefied air energy storage

Abstract

The present invention discloses a natural gas power generation system and method combined with liquefied air energy storage, wherein the natural gas power generation system includes an air liquefaction subsystem, a liquefied air gasification subsystem, an LNG gasification subsystem, a gas turbine subsystem, a waste heat utilization subsystem and a carbon dioxide capture subsystem; the air liquefaction subsystem produces liquefied air; the liquefied air gasification subsystem uses liquefied air to generate electricity; the LNG gasification subsystem uses LNG cold energy for the air liquefaction subsystem and the carbon dioxide capture subsystem to gasify LNG into natural gas; the gas turbine subsystem uses part of the natural gas of the LNG gasification subsystem as fuel for power generation; the waste heat utilization subsystem uses the waste heat of flue gas for power generation; the carbon dioxide capture subsystem is coupled with the LNG gasification subsystem to condense and capture carbon dioxide in the flue gas. The present invention can solve the defects of large energy loss and low efficiency in the prior art and reduce greenhouse gas emissions.

Description

Technical Field

[0001] The present invention belongs to the field of energy storage technology and power generation, and in particular relates to a natural gas power generation system and method combined with liquefied air energy storage. Background Art

[0002] As the cleanest and most efficient fossil fuel, natural gas is one of the important energy sources in the power generation industry. Natural gas can be efficiently converted into electricity through the use of gas turbines and combined cycles.

[0003] Since the volume of natural gas can be reduced by 600 times after liquefaction, natural gas is transported across long distances across the sea in the form of LNG. At coastal receiving stations, LNG needs to be reheated and gasified into normal temperature natural gas before being transported into the gas supply network. When liquid pure methane is gasified from the standard boiling point (111.65 K) to normal temperature and pressure gas, it can release about 830 kJ / kg of cold energy. By utilizing this part of cold energy, energy conservation and efficiency improvement of the natural gas industry chain can be achieved, bringing significant environmental and economic benefits.

[0004] In addition, with the widespread application of renewable energy, its inherent volatility and intermittency make it impossible to directly integrate it into the power grid, which in turn causes serious "wind abandonment" and "light abandonment" phenomena. In order to solve these problems, combining renewable energy generation with energy storage technology can effectively balance the supply and demand of electricity and improve the stability and efficiency of the power grid. Liquid air energy storage technology has become a feasible and promising option with its advantages such as clean and pollution-free, high energy storage density, and no geographical restrictions. For example, the Chinese patent document with publication number CN111648833A discloses a liquefied air energy storage system; the Chinese patent document with publication number CN113700628A discloses a multi-supply liquefied air energy storage system and an optimization control method.

[0005] At present, natural gas power generation technology faces the problems of insufficient utilization of low-temperature waste heat and still large greenhouse gas emissions during combustion, and the integration of LNG gasification cold energy in the power generation process has not yet achieved the best effect, limiting its wider application. Liquid air energy storage technology is subject to the defects of large compression power consumption during the charging process and insufficient power generation output during the discharge process, and the energy conversion efficiency needs to be further improved. More importantly, there is a lack of effective integration and complementarity between the two technologies, and they have failed to give full play to their respective advantages to maximize energy utilization and minimize emissions. Summary of the invention

[0006] The present invention provides a natural gas power generation system and method combined with liquefied air energy storage, which can achieve low energy loss, low greenhouse gas emissions, high energy efficiency and high integration.

[0007] A natural gas power generation system combined with liquefied air energy storage, comprising an air liquefaction subsystem, a liquefied air gasification subsystem, an LNG gasification subsystem, a gas turbine subsystem, a waste heat utilization subsystem and a carbon dioxide capture subsystem;

[0008] The air liquefaction subsystem includes a compression liquefaction equipment group and a liquefied air storage tank connected in sequence;

[0009] The liquefied air gasification subsystem includes an expansion work equipment group connected to the outlet of the liquefied air storage tank;

[0010] The waste heat utilization subsystem includes a steam Rankine cycle and is coupled with an expansion work device group;

[0011] The LNG gasification subsystem includes three branches, the first branch is coupled to the compression liquefaction equipment group, the second branch is coupled to the carbon dioxide capture subsystem, and the third branch is coupled to the propane cold storage cycle;

[0012] During the period of low electricity consumption, all LNG enters the first branch, and after heat exchange through the compression and liquefaction equipment group and the recuperative Rankine cycle, the first part of natural gas obtained by gasification is all output to the gas supply network; during the period of peak electricity consumption, LNG enters the second and third branches. The LNG in the second branch is used to capture the carbon dioxide condensation of the flue gas at the outlet of the waste heat utilization subsystem, and the LNG in the third branch is used for propane cold storage cycle. The heated LNG in the second and third branches is merged and then heat exchanged through the recuperative Rankine cycle, and is gasified into the second part of natural gas and the third part of natural gas; the second part of natural gas enters the gas supply network, and the third part of natural gas is transported to the gas turbine subsystem as fuel.

[0013] Preferably, the compression liquefaction equipment group comprises a plurality of stages of multi-stream heat exchangers connected in series, and a compressor is connected between the hot flow outlet of the upper stage multi-stream heat exchanger and the hot flow inlet of the lower stage multi-stream heat exchanger;

[0014] The heat source of the compression liquefaction equipment group is air, and the cold source is the circulating medium of the LNG and propane cold storage cycle.

[0015] Preferably, the expansion work device group includes several stages of heat exchangers connected in series, and an expander is connected between the cold flow outlet of the upper stage heat exchanger and the cold flow inlet of the lower stage heat exchanger;

[0016] The heat source of the expansion working equipment group comes from the flue gas of the waste heat utilization subsystem, and the cold source is liquefied air or air.

[0017] Preferably, the propane cold storage cycle comprises a first propane storage tank, a first propane pump, a compression liquefaction equipment group, a second propane pump, a second propane storage tank and a sixth heat exchanger connected in sequence, and the sixth heat exchanger is connected to the first propane storage tank to form a cycle;

[0018] The heat source of the sixth heat exchanger is the circulating medium of the propane cold storage cycle, and the cold source is the LNG of the third branch.

[0019] Preferably, the regenerative Rankine cycle comprises a mixed working fluid pump, a first regenerator, a heating expansion unit and a seventh heat exchanger;

[0020] The hot flow outlet of the seventh heat exchanger is connected to the inlet of the mixed working fluid pump, the outlet of the mixed working fluid pump is connected to the cold flow inlet of the first heat exchanger, the cold flow outlet of the first heat exchanger is connected to the inlet of the heating expansion unit, the outlet of the heating expansion unit is connected to the hot flow inlet of the first heat exchanger, and the hot flow outlet of the first heat exchanger is connected to the hot flow inlet of the seventh heat exchanger, forming a cycle;

[0021] The heating expansion unit comprises at least one stage of heater, and an expander is connected after the cold flow outlet of each stage of heater, and work is output through the expander;

[0022] The heat source of the seventh heat exchanger is the circulating medium of the recuperative Rankine cycle, and the cold source is the LNG of the first branch, the second branch or the third branch; the heat source of the heater is process water, and the cold source is the circulating medium of the recuperative Rankine cycle.

[0023] Further preferably, the circulating medium of the regenerative Rankine cycle is a hydrocarbon mixture, preferably a hydrocarbon mixture with a molar composition of 31.61 mol % of ethane, 41.59 mol % of propane, 13.39 mol % of n-butane and 13.40 mol % of isobutane.

[0024] Preferably, the gas turbine subsystem comprises a combustion chamber, a gas turbine, a compressor and a second regenerator;

[0025] The inlet of the compressor is connected to the external environment, the outlet of the compressor is connected to the cold flow inlet of the second reheater, the cold flow outlet of the second reheater is connected to the first inlet of the combustion chamber, the second inlet of the combustion chamber is used to receive the third part of natural gas, the outlet of the combustion chamber is connected to the inlet of the gas turbine, the outlet of the gas turbine is connected to the hot flow inlet of the second reheater, and the hot flow outlet of the second reheater is connected to the waste heat utilization subsystem.

[0026] Further preferably, an oxygen-rich combustion reaction occurs in the combustion chamber, the air is excess air, and the preferred mass flow ratio of the air to the third portion of natural gas is 52.77:1.

[0027] The gas turbine and compressor are both axial flow type, and the gas turbine drives the compressor to rotate coaxially; when the gas turbine is not sufficient to drive the coaxial compressor, an additional drive device (such as an electric motor or an auxiliary gas turbine) is used to provide additional power.

[0028] Preferably, the steam Rankine cycle comprises a feedwater pump, an eighth heat exchanger, a steam turbine and a condenser;

[0029] The outlet of the feedwater pump is connected to the cold flow inlet of the eighth heat exchanger, the cold flow outlet of the eighth heat exchanger is connected to the inlet of the steam turbine, the outlet of the steam turbine is connected to the hot flow inlet of the condenser, and the hot flow outlet of the condenser is connected to the inlet of the feedwater pump, forming a cycle;

[0030] The heat source of the eighth heat exchanger is the flue gas received from the gas turbine subsystem, and the cold source of the condenser is process water, which is suitable for condensing all the exhaust steam from the turbine; the circulating medium of the steam Rankine cycle is liquid water or water vapor.

[0031] Preferably, the carbon dioxide capture subsystem comprises a gas-liquid separator, a regenerator unit, a fifth heat exchanger, a solid carbon dioxide storage tank and a second thermostat;

[0032] The gas phase outlet of the gas-liquid separator is connected to the hot flow inlet of the regenerator, the hot flow outlet of the regenerator is connected to the hot flow inlet of the fifth heat exchanger, the hot flow outlet of the fifth heat exchanger is connected to the cold flow inlet of the regenerator unit, the cold flow outlet of the regenerator unit is connected to the cold flow inlet of the second thermostat, and the cold flow outlet of the second thermostat is connected to the external environment;

[0033] The regenerator unit comprises at least one stage of regenerator, the hot flow outlet and the cold flow inlet of the previous stage of regenerator are respectively connected to the hot flow inlet and the cold flow outlet of the next stage of regenerator;

[0034] The gas-liquid separator receives the flue gas from the waste heat utilization subsystem, and the liquid phase outlet is liquid water separated from the flue gas; the cold source of the fifth heat exchanger is the LNG of the second branch, which can export the condensed solid carbon dioxide from the hot flow and store it in a solid carbon dioxide storage tank; the heat source of the second thermostat is process water, which is suitable for adjusting the exhaust gas after carbon capture to a state close to the ambient temperature.

[0035] Preferably, the natural gas power generation system further comprises a liquid air pump connected between the liquefied air storage tank and the expansion work equipment group, an LNG pump and a first flow divider connected before the propane cold storage cycle, a mixer connected between the propane cold storage cycle and the regenerative Rankine cycle, and a first thermostat and a second flow divider connected after the regenerative Rankine cycle;

[0036] The first flow splitter divides the LNG into the second branch and the third branch; the second flow splitter divides the gasified natural gas into the second part of natural gas and the third part of natural gas.

[0037] The heat source of the first thermostat is process water, which is suitable for adjusting the vaporized natural gas to a suitable gas supply temperature.

[0038] A natural gas power generation method combined with liquefied air energy storage, based on the above natural gas power generation system, includes a charging process during low power consumption and a discharging process during peak power consumption, as follows:

[0039] During the charging process when electricity consumption is low, air at normal temperature and pressure passes through the compression and liquefaction equipment group, and is compressed and liquefied into liquefied air with the energy provided by the LNG and propane cold storage cycle of the first branch and stored in the liquefied air storage tank. Subsequently, the LNG of the first branch provides energy to the regenerative Rankine cycle and is gasified into the first part of natural gas, which is all sent to the gas supply network. At this time, the circulating medium in the regenerative Rankine cycle does work in the expander and outputs electricity.

[0040] During the discharge process at peak power consumption, the liquefied air stored in the liquefied air storage tank passes through the expansion work equipment group, absorbs the energy of the flue gas, gasifies into high-pressure gaseous air, and performs work in the expander, outputs electricity, and is converted into air at normal pressure;

[0041] The LNG in the second branch provides energy to the fifth heat exchanger, so that the carbon dioxide in the flue gas condenses into solid carbon dioxide. The LNG in the third branch provides energy to the propane cold storage cycle so that the cold energy is stored in the propane cold storage cycle. Then, the LNG in the second branch and the LNG in the third branch are combined through the mixer to provide energy to the regenerative Rankine cycle and gasify into the second part of natural gas and the third part of natural gas. At this time, the circulating medium in the regenerative Rankine cycle does work in the expander, outputs electricity, and the second part of natural gas enters the gas supply network.

[0042] The third part of natural gas enters the combustion chamber and mixes with air to burn. The flue gas after combustion enters the gas turbine to generate power and drive the compressor to work. The low-pressure flue gas provides energy to the second regenerator, steam Rankine cycle and expansion work equipment group in turn. At this time, the circulating medium in the steam Rankine cycle performs work in the expander and outputs electricity.

[0043] The flue gas then enters the gas-liquid separator to separate the water, and then enters the fifth heat exchanger through the regenerator, where the solid carbon dioxide obtained by condensation is discharged and stored in a solid carbon dioxide storage tank. The remaining low-temperature decarbonized gas passes through the regenerator to provide energy for flue gas cooling, and then is discharged to the external environment.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1. The present invention combines the liquefied air energy storage system (air liquefaction subsystem + liquefied air gasification subsystem), the LNG gasification process (LNG gasification subsystem), the natural gas power generation cycle (gas turbine subsystem + waste heat utilization subsystem) and the carbon capture process (carbon dioxide capture subsystem), which can effectively smooth out the volatility of the power grid, significantly reduce greenhouse gas emissions during the power generation process, and greatly increase peak power output. During the off-peak period, the cold energy of LNG and the cold energy recovered from propane are used to produce liquefied air in the air liquefaction subsystem; during the peak period, the natural gas power generation cycle and the liquefied air gasification subsystem work together to generate electricity, which plays the role of peak shaving and valley filling in the power grid.

[0046] 2. Under different power consumption time periods, the LNG all-weather continuous gasification process has two different operating modes that can be flexibly switched. First, by using the high-grade cold energy of LNG for the charging process of the liquefied air energy storage system, the working fluid temperature of the compression process can be greatly reduced, the power consumption of the compressor can be significantly reduced, and the cycle efficiency of the system can be improved. Second, by using a small part of the high-grade cold energy of LNG for carbon dioxide condensation capture and using a propane cold storage cycle to recover the high-grade cold energy of the rest of the LNG, the greenhouse gas emissions of the power generation cycle can be effectively reduced, and the energy storage performance of the system can be improved at the same time. The medium and low-grade cold energy of LNG is used in the heat recovery Rankine cycle to achieve the cascade utilization of LNG cold energy, reduce energy losses in the LNG gasification process, and improve energy utilization efficiency.

[0047] 3. The present invention uses the high-grade energy of the flue gas discharged by the gas turbine in the natural gas power generation cycle for excess air preheating, increases the reaction temperature of the raw materials in the combustion chamber, and improves the combustion efficiency. The remaining medium and low-grade energy of the flue gas is used in the discharge process of the steam Rankine cycle and the liquefied air energy storage system in turn, increases the working fluid temperature in the expansion process, and thus greatly improves the power generation of the expander during the peak electricity consumption period, realizes the efficient cascade utilization of the flue gas heat, and fully improves the cycle efficiency and energy utilization rate of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a schematic structural diagram of a natural gas power generation system combined with liquefied air energy storage according to the present invention.

[0049] In the figure: 1-first multi-stream heat exchanger; 2-first compressor; 3-second multi-stream heat exchanger; 4-second compressor; 5-third multi-stream heat exchanger; 6-third compressor; 7-fourth multi-stream heat exchanger; 8-fourth compressor; 9-fifth multi-stream heat exchanger; 10-liquefied air storage tank; 11-liquid air pump; 12-first heat exchanger; 13-first expander; 14-second heat exchanger; 15-second expander; 16-third heat exchanger; 17-third expander; 18-fourth heat exchanger; 19-fourth expander; 20-LNG pump; 21-first splitter; 22-fifth heat exchanger; 23-sixth heat exchanger; 24-mixer; 25 -seventh heat exchanger; 26-first thermostat; 27-second diverter; 28-first propane storage tank; 29-first propane pump; 30-second propane pump; 31-second propane storage tank; 32-mixed working fluid pump; 33-first regenerator; 34-first heater; 35-fifth expander; 36-second heater; 37-sixth expander; 38-combustion chamber; 39-gas turbine; 40-compressor; 41-second regenerator; 42-eighth heat exchanger; 43-feedwater pump; 44-steam turbine; 45-condenser; 46-gas-liquid separator; 47-third regenerator; 48-fourth regenerator; 49-solid carbon dioxide storage tank; 50-second thermostat. DETAILED DESCRIPTION

[0050] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0051] like Figure 1 As shown, a natural gas power generation system combined with liquefied air energy storage includes an air liquefaction subsystem, a liquefied air gasification subsystem, an LNG gasification subsystem, a gas turbine subsystem, a waste heat utilization subsystem and a carbon dioxide capture subsystem.

[0052] The air liquefaction subsystem is connected to the liquefied air gasification subsystem; the LNG gasification subsystem is connected to the gas turbine subsystem; the gas turbine subsystem is connected to the waste heat utilization subsystem; and the waste heat utilization subsystem is connected to the carbon dioxide capture subsystem.

[0053] The air liquefaction subsystem includes a compression liquefaction equipment group and a liquefied air storage tank connected in sequence; the liquefied air gasification subsystem includes an expansion work equipment group. The waste heat utilization subsystem includes a steam Rankine cycle and is coupled with the expansion work equipment group.

[0054] The LNG gasification subsystem includes a propane cold storage cycle and a recuperative Rankine cycle connected in sequence, and has flexible operation characteristics. The LNG gasification subsystem contains three branches, which are coupled with the compression and liquefaction equipment group during the off-peak period of electricity consumption. The first part of the natural gas obtained by gasifying all the LNG in the first branch is output to the gas supply network. During the peak period of electricity consumption, it is coupled with the carbon dioxide capture subsystem. The LNG in the second branch is used for carbon dioxide condensation capture, and the LNG in the third branch is used for the propane cold storage cycle. After the heated LNG in the second branch and the third branch are combined, they are subjected to heat exchange in the recuperative Rankine cycle and are gasified into the second part of natural gas and the third part of natural gas; the second part of natural gas enters the gas supply network, and the third part of natural gas is delivered to the gas turbine subsystem as fuel.

[0055] Among them, the air liquefaction subsystem works during the off-peak period of electricity consumption (12 hours), one end of which is connected to the air of normal temperature and pressure in the external environment, and enters the liquefied air storage tank 10 for storage after heat exchange and liquefaction by the compression and liquefaction equipment group and the LNG and propane cold storage cycle of the first branch. The other end of the liquefied air storage tank 10 is connected to the liquefied air gasification subsystem. The liquefied air gasification subsystem works during the peak period of electricity consumption (12 hours), and the liquefied air stored in the liquefied air storage tank 10 exchanges heat with the flue gas of the waste heat utilization subsystem to perform gasification, output electricity, and discharge normal pressure air to the external environment. The LNG gasification subsystem operates around the clock (24 hours) and is directly connected to the coastal LNG receiving station at one end. During the off-peak period (12 hours), the LNG in the first branch exchanges heat with the air liquefaction subsystem. The heated LNG in the first branch exchanges heat with the recuperative Rankine cycle to obtain the first part of natural gas, which is all transported into the gas supply network. During the peak period (12 hours), the LNG in the second branch and the LNG in the third branch exchange heat with the carbon dioxide capture subsystem and the propane cold storage cycle respectively and then merge. The merged LNG also exchanges heat with the recuperative Rankine cycle to be gasified into the second part of natural gas and the third part of natural gas. The second part of natural gas is transported into the gas supply network, and the third part of natural gas is used as fuel in the gas turbine subsystem. The expander in the recuperative Rankine cycle continuously outputs electricity in both periods. The gas turbine subsystem, waste heat utilization subsystem and carbon dioxide capture subsystem all operate during the peak electricity consumption period (12 hours), utilizing the combustion process of the third part of the fuel, natural gas, and the resulting flue gas heat to output electricity, and capture solid carbon dioxide through heat exchange between the flue gas and the LNG in the second branch.

[0056] The compression liquefaction equipment group includes five stages of multi-stream heat exchangers connected in series. A compressor is connected between the hot flow outlet of the upper multi-stream heat exchanger and the hot flow inlet of the lower multi-stream heat exchanger, that is, the air is also pressurized and heated by the compressor between the two stages of multi-stream heat exchangers. The heat source of the compression liquefaction equipment group is air, and the cold source is the circulating medium of the LNG and propane cold storage cycle. Specifically, Figure 1As shown in , air at normal temperature and pressure enters the first multi-stream heat exchanger 1 and passes through the first compressor 2, the second multi-stream heat exchanger 3, the second compressor 4, the third multi-stream heat exchanger 5, the third compressor 6, the fourth multi-stream heat exchanger 7, the fourth compressor 8 and the fifth multi-stream heat exchanger 9 in sequence, and reaches the critical point of air liquefaction after heat exchange and compression. Then the liquefied air is sent to the liquefied air storage tank 10 for storage; the circulating medium (propane) of the LNG and propane cold storage cycle exchanges heat with the air in a countercurrent manner in each stage of the multi-stream heat exchanger. It can be seen that the high-grade cold capacity of LNG and the LNG cold energy recovered from propane are used in the process of air compression and liquefaction to reduce the temperature of the air at the compressor inlet, which can greatly reduce the power consumption of the compressor and thus improve the operating efficiency of the system.

[0057] The expansion work equipment group includes four stages of heat exchangers arranged in series. The cold flow outlet of each stage of the heat exchanger is connected to an expander, and pre-stage heating is used to improve the expansion work power generation capacity of the working medium. The heat source of the expansion work equipment group is the flue gas after the steam Rankine cycle heat exchange, and the cold source is the high-pressure liquefied air or the gaseous air at the outlet of the previous stage of the expander. Specifically, Figure 1 As shown in , the liquefied air after being pressurized by the liquid air pump 11 enters the first heat exchanger 12, and is successively heat exchanged and expanded by the first expander 13, the second heat exchanger 14, the second expander 15, the third heat exchanger 16, the third expander 17, the fourth heat exchanger 18 and the fourth expander 19 to obtain normal pressure air, and the first expander 13, the second expander 15, the third expander 17 and the fourth expander 19 output work to the outside. It can be seen that the low-grade waste heat of the flue gas is used in the process of air expansion to increase the temperature of the air at the inlet of the expander, which can greatly improve the output work of the expander, thereby improving the operating efficiency of the system.

[0058] The propane cold storage cycle includes a first propane storage tank 28, a second propane storage tank 31, a first propane pump 29, a second propane pump 30 and a sixth heat exchanger 23; the first propane storage tank 28, the first propane pump 29, the compression and liquefaction equipment group, the second propane pump 30, the second propane storage tank 31 and the sixth heat exchanger 23 are connected in sequence, and the sixth heat exchanger 23 is connected to the first propane storage tank 28 to form a cycle. Among them, the heat source of the sixth heat exchanger 23 is the circulating medium (propane) of the propane cold storage cycle, and the cold source is the LNG of the third branch.

[0059] In the propane cold storage cycle, during the off-peak period of electricity consumption (12 h), the first propane pump 29 transports the circulating medium in the low-temperature first propane storage tank 28 through the compression and liquefaction equipment group in the air liquefaction subsystem, provides cold capacity for air compression and liquefaction, and then is sent to the second propane storage tank 31 by the second propane pump 30 for storage; during the peak period of electricity consumption (12 h), the high-temperature cold storage circulating medium in the second propane storage tank 31 passes through the sixth heat exchanger 23, and is cooled by heat exchange with the LNG in the third branch through the sixth heat exchanger 23, and then re-enters the low-temperature first propane storage tank 28 for storage.

[0060] The regenerative Rankine cycle includes a mixed working fluid pump 32, a first regenerator 33, a first heater 34, a fifth expander 35, a second heater 36, a sixth expander 37 and a seventh heat exchanger 25; the hot flow outlet of the seventh heat exchanger 25 is connected to the inlet of the mixed working fluid pump 32, the outlet of the mixed working fluid pump 32 is connected to the cold flow inlet of the first regenerator 33, the cold flow outlet of the first regenerator 33 is connected to the cold flow inlet of the first heater 34, the cold flow outlet of the first heater 34 is connected to the inlet of the fifth expander 35, the outlet of the fifth expander 35 is connected to the cold flow inlet of the second heater 36, the cold flow outlet of the second heater 36 is connected to the inlet of the sixth expander 37, the outlet of the sixth expander 37 is connected to the hot flow inlet of the first regenerator 33, and the hot flow outlet of the first regenerator 33 is connected to the hot flow inlet of the seventh heat exchanger 25, forming a cycle. Among them, the heat source of the seventh heat exchanger 25 is the circulating medium of the recuperative Rankine cycle, and the cold source is the LNG of the first branch after the heat exchange of the compression and liquefaction equipment group or the LNG of the second branch after the heat exchange of the carbon dioxide capture subsystem and the LNG of the third branch after the heat exchange of the propane cold storage cycle; the heat sources of the first heater 34 and the second heater 36 are both temperature-controllable process water, and the cold source is the circulating medium of the recuperative Rankine cycle; the fifth expander 35 and the sixth expander 37 output work to the outside. The circulating medium of the recuperative Rankine cycle can be a hydrocarbon mixture, and the most preferred molar composition is a hydrocarbon mixture of 31.61 mol %, 41.59 mol % of ethane, 13.39 mol % of propane, and 13.40 mol % of isobutane. The circulating medium of the recuperative Rankine cycle uses the medium and low-grade cold energy of LNG to generate power.

[0061] The mixed working fluid pump 32 is used to pressurize the circulating medium of the recuperative Rankine cycle to the initial expansion pressure; the first regenerator 33 is used to realize heat exchange between the outlet circulating medium after expansion and the outlet circulating medium of the mixed working fluid pump 32, and precool the gaseous circulating medium after expansion; the first heater 34 uses process water to further heat and vaporize the preheated low-temperature liquid circulating medium, and then the gaseous circulating medium enters the high-pressure fifth expander 35 to do work and generate electricity; the second heater 36 is used between the two-stage expanders for reheating to improve the working capacity of the circulating medium after the initial expansion, and then enters the low-pressure sixth expander 37 to do work and generate electricity; the circulating medium after expansion enters the first regenerator 33 for precooling and then enters the seventh heat exchanger 25 for heat exchange with LNG, thereby reducing the exergy loss in the seventh heat exchanger 25.

[0062] The gas turbine subsystem includes a combustion chamber 38, a gas turbine 39, a compressor 40 and a second regenerator 41; the inlet of the compressor 40 is connected to the external environment, the outlet of the compressor 40 is connected to the cold flow inlet of the second regenerator 41, the cold flow outlet of the second regenerator 41 is connected to the first inlet of the combustion chamber 38, the second inlet of the combustion chamber 38 is used to receive the third part of natural gas, the outlet of the combustion chamber 38 is connected to the inlet of the gas turbine 39, the outlet of the gas turbine 39 is connected to the hot flow inlet of the second regenerator 41, and the hot flow outlet of the second regenerator 41 is connected to the waste heat utilization subsystem. Among them, an oxygen-rich combustion reaction occurs in the combustion chamber 38, the air is excess air, and the optimal mass flow ratio of air to the third part of natural gas is 52.77:1. The gas turbine 39 and the compressor 40 are both axial flow type, and the gas turbine 39 drives the compressor 40 to rotate coaxially, and the net work output by the gas turbine 39 is used for power generation; when the gas turbine 39 is insufficient to drive the coaxial compressor 40, an additional driving device (such as an electric motor or an auxiliary gas turbine) is used to provide supplementary power. The heat source of the second regenerator 41 is the flue gas expanded by the gas turbine 39, and the cold source is the excess air compressed by the compressor 40.

[0063] The combustion chamber 38 provides a reaction place for the combustion of excess air and the third part of natural gas, generating a large amount of high-temperature and high-pressure flue gas; the flue gas performs work in the gas turbine 39, driving the coaxial compressor 40 to operate, compressing the outside air at normal temperature and pressure to a high-pressure state, and the remaining net work output by the gas turbine 39 is used for power generation; the second recuperator 41 is used to realize the heat exchange between the normal-pressure flue gas after expansion and the air at the outlet of the compressor 40, and preheat the excess air used as reaction fuel.

[0064] The steam Rankine cycle includes a feedwater pump 43, an eighth heat exchanger 42, a steam turbine 44 and a condenser 45; the outlet of the feedwater pump 43 is connected to the cold flow inlet of the eighth heat exchanger 42, the cold flow outlet of the eighth heat exchanger 42 is connected to the inlet of the steam turbine 44, the outlet of the steam turbine 44 is connected to the hot flow inlet of the condenser 45, and the hot flow outlet of the condenser 45 is connected to the inlet of the feedwater pump 43, forming a cycle. Among them, the heat source of the eighth heat exchanger 42 is the flue gas received from the gas turbine subsystem; work is output to the outside through the steam turbine 44. The cold source of the condenser 45 is temperature-controllable process water, which is suitable for condensing all the exhaust steam discharged from the steam turbine 44. The circulating medium of the steam Rankine cycle is liquid water or water vapor. The circulating medium of the steam Rankine cycle uses the medium-grade heat in the flue gas to generate power.

[0065] The feed water pump 43 is used to pressurize the circulating medium of the steam Rankine cycle to the initial expansion pressure; the eighth heat exchanger 42 is used to realize the heat exchange between the flue gas at the hot flow outlet of the second regenerator 41 and the circulating medium of the steam Rankine cycle, so that the circulating medium of the steam Rankine cycle is heated and vaporized, and enters the steam turbine 44 to perform work and generate electricity; the condenser 45 is used to condense all the exhaust steam of the steam turbine 44 into liquid circulating medium.

[0066] The carbon dioxide capture subsystem includes a gas-liquid separator 46, a third reheater 47, a fourth reheater 48, a fifth heat exchanger 22, a solid carbon dioxide storage tank 49 and a second thermostat 50; the gas phase outlet of the gas-liquid separator 46 is connected to the hot flow inlet of the third reheater 47, the hot flow outlet of the third reheater 47 is connected to the hot flow inlet of the fourth reheater 48, the hot flow outlet of the fourth reheater 48 is connected to the hot flow inlet of the fifth heat exchanger 22, the hot flow outlet of the fifth heat exchanger 22 is connected to the cold flow inlet of the fourth reheater 48, the cold flow outlet of the fourth reheater is connected to the cold flow inlet of the third reheater 47, the cold flow outlet of the third reheater 47 is connected to the cold flow inlet of the second thermostat 50, and the cold flow outlet of the second thermostat 50 is connected to the external environment. Among them, the gas-liquid separator 46 receives the flue gas of the waste heat utilization subsystem, and the liquid phase outlet is liquid water separated from the flue gas. The cold source of the fifth heat exchanger 22 is the LNG of the second branch, which has a special structure and can extract the condensed solid carbon dioxide from the hot stream and store it in the solid carbon dioxide storage tank 49. The heat source of the second thermostat 50 is temperature-controllable process water, which is suitable for adjusting the exhaust gas after carbon capture to a state close to the ambient temperature.

[0067] The gas-liquid separator 46 is used to separate liquid water from the flue gas at the outlet of the waste heat utilization subsystem to avoid ice blockage in the pipeline under subsequent low-temperature conditions; the third regenerator 47 and the fourth regenerator 48 are used to achieve heat exchange between the low-temperature flue gas after decarbonization and the flue gas at the gas phase outlet of the gas-liquid separator 46, and pre-cool the flue gas to be captured; the fifth heat exchanger 22 is used to achieve the condensation of carbon dioxide in the flue gas, and separate the solid carbon dioxide from the heat flow and export it to the solid carbon dioxide storage tank 49 for storage; the second thermostat 50 is used to heat the decarbonized flue gas to room temperature and output it to the outside.

[0068] In addition, in addition to the above-mentioned subsystems, the liquefied air energy storage system also includes a liquid air pump 11 connected between the liquefied air storage tank 10 and the expansion work equipment group, an LNG pump 20 and a first diverter 21 connected before the propane cold storage cycle, a mixer 24 connected between the propane cold storage cycle and the recuperative Rankine cycle, and a first thermostat 26 and a second diverter 27 connected after the recuperative Rankine cycle. Among them, the first diverter 21 divides the LNG into the LNG of the second branch and the LNG of the third branch; the second diverter 27 divides the gasified natural gas into the second part of the natural gas and the third part of the natural gas. The heat source of the first thermostat 26 is temperature-controllable process water, which is suitable for adjusting the gasified natural gas to a suitable gas supply temperature.

[0069] The liquid air pump 11 is used to increase the pressure of the liquefied air output from the liquefied air storage tank 10 to a high-pressure state, so as to improve the power generation capacity of the working fluid in the expansion and gasification stage; the LNG pump 20 is used to increase the LNG from the receiving station to a reasonable pipeline transportation pressure and output high-pressure LNG; the first diverter 21 is used to divide the LNG output from the LNG pump 20 into two parts according to a certain ratio during the low-power consumption period (12 hours), and provide cooling to the carbon dioxide capture subsystem and the propane cold storage cycle respectively; the mixer 24 is used to re-combine the two heated LNG streams and continue to provide cooling to the regenerative Rankine cycle; the first thermostat 26 is used to heat the low-temperature natural gas to a normal temperature state and transport it to the gas supply network; the second diverter 27 is used to divert most of the natural gas to the gas supply network during the peak power consumption period (12 hours), and a small part of the natural gas is transported to the gas turbine subsystem.

[0070] This embodiment further combines a LNG receiving station in a coastal area to illustrate the method of natural gas power generation combined with liquefied air energy storage of the present invention. The molar composition of the LNG used is methane 91.15%, ethane 5.55%, propane 2.16%, n-butane 0.51%, isobutane 0.51%, and nitrogen 0.12%.

[0071] The above-mentioned method of natural gas power generation combined with liquefied air energy storage comprises the following steps:

[0072] S01, during the off-peak period of electricity consumption (12 h), the air from the external environment with a temperature of 298.1 K and a pressure of 1.013 bar is pretreated and has a flow rate of 104070.9 kg / h. It is compressed, cooled and liquefied to a temperature of 127.8 K and a pressure of 36.0 bar by the first multi-stream heat exchanger 1, the first compressor 2, the second multi-stream heat exchanger 3, the second compressor 4, the third multi-stream heat exchanger 5, the third compressor 6, the fourth multi-stream heat exchanger 7, the fourth compressor 8 and the fifth multi-stream heat exchanger 9, and then enters the liquefied air storage tank 10 for storage. The power consumption of the multi-stage compressor unit is 5193.4 kW. The multi-stream heat exchanger uses the high-grade cold energy of LNG and the cold energy recovered from the cold storage working medium propane as the cold source to cool the energy storage working medium air.

[0073] S02, during the peak electricity consumption period (12 h), the liquefied air stored in the liquefied air storage tank 10 has a temperature of 127.8 K and a pressure of 36.0 bar, with a flow rate of 104070.9 kg / h. It is pressurized by the liquid air pump 11 to become high-pressure air with a temperature of 155.5 K and a pressure of 201.9 bar. The power consumption of the liquid air pump 11 is 993.5 kW. Then, it passes through the first heat exchanger 12, the first expander 13, the second heat exchanger 14, the second expander 15, the third heat exchanger 16, the third expander 17, the fourth heat exchanger 18 and the fourth expander 19 in sequence, and uses the waste heat of the flue gas of the waste heat utilization subsystem to heat up and expand to the air with a temperature of 298.1 K and a pressure of 1.013 bar, which is discharged to the external environment. The total output power of the multi-stage expander is 12779.5 kW.

[0074] S03, LNG with a temperature of 111.1 K and a pressure of 1.3 bar is exported from the coastal receiving station with a flow rate of 125000.0 kg / h, and is pressurized to 70.0 bar by LNG pump 20. The power consumption of LNG pump 20 is 579.4 kW, and then it is operated in different LNG high-grade cold energy utilization modes and gas supply modes in different time periods; during the low power consumption period (12 h), the LNG of the first branch with an outlet temperature of 113.2 K and a pressure of 70.0 bar of LNG pump 20 passes through the fifth multi-stream heat exchanger 9, the fourth multi-stream heat exchanger 7, the third multi-stream heat exchanger 5, the second multi-stream heat exchanger 3 and the first multi-stream heat exchanger 1 in turn to absorb heat and heat up to 182.1 K, and then passes through the seventh heat exchanger 25 and the first thermostat 26 in turn to be gasified into the first part of natural gas products with a temperature of 298.1 K and a pressure of 70.0 bar, and all of them are transported to the gas supply network. During the peak power consumption period (12 h), the LNG of the first branch with an outlet temperature of 113.2 K and a pressure of 70.0 bar of LNG pump 20 passes through the fifth multi-stream heat exchanger 9, the fourth multi-stream heat exchanger 7, the third multi-stream heat exchanger 5, the second multi-stream heat exchanger 3 and the first multi-stream heat exchanger 1 to absorb heat and heat up to 182.1 K, and then passes through the seventh heat exchanger 25 and the first thermostat 26 in turn to be gasified into the first part of natural gas products with a temperature of 298.1 K and a pressure of 70.0 bar, and all of them are transported to the gas supply network. h), the LNG at the outlet of the LNG pump 20 passes through the first splitter 21 and is divided into the LNG of the second branch with a flow rate of 35425.8 kg / h and the LNG of the third branch with a flow rate of 89574.2 kg / h, wherein the LNG of the second branch is heat exchanged with the flue gas to be decarbonized in the fifth heat exchanger 22 and the temperature is raised to 182.1 K, and the LNG of the third branch is heat exchanged with the circulating medium propane of the propane cold storage cycle in the sixth heat exchanger 23 and the temperature is also raised to 182.1 K, then the LNG of the second branch and the LNG of the third branch are reunited through the mixer 24, and then successively pass through the seventh heat exchanger 25 and the first thermostat 26 to be gasified into a natural gas product with a flow rate of 298.1 K and a pressure of 70.0 bar, and then pass through the second splitter 27 to be divided into the second part of the natural gas with a flow rate of 121445.4 kg / h and the third part of the natural gas with a flow rate of 3554.6 kg / h of the third part of natural gas, of which the second part of natural gas is all transported to the gas supply network, and the third part of natural gas is used as fuel for the gas turbine subsystem for power generation; during the off-peak period (12h), the liquid propane with a temperature of 120.4 K and a pressure of 1.013 bar in the low-temperature first propane storage tank 28 has a flow rate of 176896.2 kg / h, which passes through the liquefied fifth multi-stream heat exchanger 9, the fourth multi-stream heat exchanger 7, the third multi-stream heat exchanger 5, the second multi-stream heat exchanger 3 in sequence, and the first multi-stream heat exchanger 1 absorbs heat and heats up to 187.4 K before entering the second propane storage tank 31 for storage. During the peak period (12h), the cold storage medium propane with a temperature of 187.4 K and a pressure of 1.013 bar in the second propane storage tank 31 passes through the sixth heat exchanger 23 to cool down to 120.4 K before entering the low-temperature first propane storage tank 28 for storage; the circulating medium flow rate of the regenerative Rankine cycle is 115296.9 kg / h, after absorbing the cold energy of LNG in the seventh heat exchanger 25, the temperature is completely reduced to a liquid state with a temperature of 186.5 K and a pressure of 1.5 bar, and then enters the mixed working fluid pump 32 to increase the pressure to a temperature of 186.7 K and a pressure of 7.3 bar, the mixed medium pump 32 consumes 32.6 kW of power, and then passes through the first regenerator 33 to pre-cool the circulating medium after expansion, and the temperature rises to 262.6 K. Then, it passes through the first heater 34, the fifth expander 35, the second heater 36, and the sixth expander 37 in sequence to expand and generate power, and the temperature becomes 272.3 K and the pressure is 1.5 bar. The total output power of the two-stage expander is 2350.8 kW. The outlet temperature of the circulating medium after passing through the heater is 298.1 K. After all gasification, it enters the expander for expansion and work. Preheating before expansion can improve the work capacity. After the expansion is completed, the circulating medium enters the first regenerator 33 to absorb the cold of the circulating medium that has not done work and cools down to 244.9 K before entering the seventh heat exchanger 25, which reduces the exergy loss caused by the direct heat exchange between the circulating medium and LNG in the regenerative Rankine cycle. .

[0075] S04, during the peak electricity consumption period (12 h), the air from the external environment with a temperature of 298.1 K and a pressure of 1.013 bar after pretreatment, with a flow rate of 187573.8 kg / h, passes through the compressor 40 and the second regenerator 41 in turn, and is compressed to absorb heat and rise to a temperature of 970.0 K and a pressure of 15.4 bar. The power consumption of the compressor 40 is 20298.4 kW. Then, it enters the combustion chamber 38 as a reaction raw material, and reacts with the third part of the natural gas with a flow rate of 3554.6 kg / h from the LNG gasification subsystem to undergo oxygen-enriched combustion, thereby improving the combustion efficiency and reducing pollutant emissions. The outlet flue gas temperature of the combustion chamber 38 is as high as 1668.7 K, the pressure is 13.9 bar, and the flow rate is 191127.7 kg / h. Subsequently, the high-temperature and high-pressure flue gas is expanded through the gas turbine 39 to generate electricity, and becomes a state of temperature 981.6 K and 1.013 bar. The total output power of the gas turbine 39 is 45685.3 kW, of which 20298.4 kW is used to drive the compressor 40 to work, and the net output work is 25386.9 kW. The normal pressure high temperature flue gas after work continues to pass through the second reheater 41 to preheat the high pressure air as the reaction raw material and cool it down to 699.0 K.

[0076] S05, during the peak electricity consumption period (12 h), the flue gas from the gas turbine subsystem has a temperature of 699.0 K and a pressure of 1.013 bar, with a flow rate of 191127.7 kg / h. It passes through the eighth heat exchanger 42, the fourth heat exchanger 18, the third heat exchanger 16, the second heat exchanger 14 and the first heat exchanger 12 in sequence to release heat and cool down to 274.1 K, realizing the step-by-step utilization of the medium and low-grade heat of the flue gas after combustion, and fully improving the working capacity by pre-heating the working medium before expansion; the circulating medium flow rate of the steam Rankine cycle is 14372.8 kg / h, which is pressurized to a temperature of 374.7 K and a pressure of 163.9 bar by the feed water pump 43, and the power consumption of the feed water pump 43 is 75.4 kW. It then passes through the eighth heat exchanger 42 to absorb the heat of the flue gas and heat it up to a temperature of 630.4 K, and then enters the steam turbine 44 to expand and generate power, becoming a temperature of 373.2 K, pressure 1.015 bar, the output power of the steam turbine 44 is 2677.6 kW, and the exhausted steam is completely condensed into liquid water with a temperature of 373.1 K and a pressure of 1.015 bar through the condenser 45, and then enters the feed water pump 43.

[0077] S06, during the peak electricity consumption period (12 h), the flue gas with a temperature of 274.1 K and a pressure of 1.013 bar from the waste heat utilization subsystem, with a flow rate of 191127.7 kg / h, enters the gas-liquid separator 46, and all the water in the flue gas is separated from the liquid phase outlet, with a corresponding flow rate of 7622.1 kg / h. The remaining water-removed flue gas with a flow rate of 183505.6 kg / h flows out from the gas phase outlet of the gas-liquid separator 46 and passes through the third regenerator 47 and the fourth regenerator 48 in sequence. After cooling to 185.3 K, it enters the fifth heat exchanger 22 for heat exchange with the LNG in the second branch, thereby cooling to 143.2 K, so that the carbon dioxide with a flow rate of 8985.6 kg / h in the flue gas is condensed and exported to the solid carbon dioxide storage tank 49 for storage. The remaining flow rate is 174520.0 The decarbonized flue gas of kg / h passes through the fourth reheater 48 and the third reheater 47 in sequence to pre-cool the flue gas to be carbon captured, and then the decarbonized flue gas heated to 236.4K passes through the second thermostat 50 to heat the temperature to 298.1K and the pressure to 1.013 bar and is discharged into the external environment.

[0078] The charging process of the liquefied air energy storage system is combined with the LNG gasification process, and the discharging process of the liquefied air energy storage system is combined with the natural gas power generation process. The LNG gasification process works around the clock (24 hours) to ensure the continuous supply of natural gas to the gas supply network. During the off-peak period of electricity consumption, the air liquefaction subsystem uses the cold energy of LNG and the cold energy recovered from propane to obtain liquefied air. During this period, the LNG gasification power generation can supplement the air compression process. During the peak period of electricity consumption, the liquefied air gasification subsystem uses the flue gas heat of the waste heat utilization subsystem to generate power. The LNG gasification subsystem uses part of the cold energy for carbon dioxide condensation capture in the carbon dioxide capture subsystem, and uses the cold storage device (propane cold storage cycle) to store most of the remaining LNG cold energy during this period to ensure system flexibility. Subsequently, part of the gasified natural gas enters the gas turbine subsystem for combustion and power generation. The flue gas heat is fully utilized through the reaction raw material preheating, steam Rankine cycle and expansion work equipment group, which plays a role in peak shaving and valley filling and smoothing the fluctuation of power grid supply and demand. Subsequently, most of the carbon dioxide is captured by low-temperature condensation to reduce the overall greenhouse gas emissions of the system.

[0079] At this LNG receiving station, the liquefied air gasification subsystem has a power output of 12779.5 kW, the recuperative Rankine cycle has a net power output of 2318.2 kW, the gas turbine subsystem has a net power output of 25386.9 kW, the steam Rankine cycle has a net power output of 2602.2 kW, and the carbon dioxide capture subsystem obtains a mass flow rate of solid carbon dioxide of 8985.6 kg / h. The system energy conversion efficiency is 78.59%, and the carbon dioxide capture rate is 91.00%.

[0080] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A natural gas power generation system combined with liquefied air energy storage, characterized in that: It includes air liquefaction subsystem, liquefied air gasification subsystem, LNG gasification subsystem, gas turbine subsystem, waste heat utilization subsystem and carbon dioxide capture subsystem; The air liquefaction subsystem comprises a compression liquefaction equipment group and a liquefied air storage tank (10) connected in sequence; the compression liquefaction equipment group comprises a plurality of stages of multi-stream heat exchangers connected in series, a compressor being connected between a hot flow outlet of an upper-stage multi-stream heat exchanger and a hot flow inlet of a lower-stage multi-stream heat exchanger; the heat source of the compression liquefaction equipment group is air, and the cold source is a circulating medium of a cold storage cycle of LNG and propane; The liquefied air gasification subsystem comprises an expansion working device group connected to the outlet of the liquefied air storage tank (10); the expansion working device group comprises a plurality of stages of heat exchangers connected in series, an expander is connected between the cold flow outlet of the upper stage heat exchanger and the cold flow inlet of the lower stage heat exchanger; the heat source of the expansion working device group comes from the flue gas of the waste heat utilization subsystem, and the cold source is liquefied air or air; The waste heat utilization subsystem includes a steam Rankine cycle and is coupled with an expansion work device group; The LNG gasification subsystem comprises three branches, wherein the first branch is coupled to the compression and liquefaction equipment group, the second branch is coupled to the carbon dioxide capture subsystem, and the third branch is coupled to the propane cold storage cycle; the propane cold storage cycle comprises a first propane storage tank (28), a first propane pump (29), a compression and liquefaction equipment group, a second propane pump (30), a second propane storage tank (31) and a sixth heat exchanger (23) which are connected in sequence, and the sixth heat exchanger (23) is connected to the first propane storage tank (28) to form a cycle; the heat source of the sixth heat exchanger (23) is the circulating medium of the propane cold storage cycle, and the cold source is the LNG in the third branch; During the off-peak period of electricity consumption, all LNG enters the first branch, and after heat exchange through the compression and liquefaction equipment group and the regenerative Rankine cycle, the first part of the gasified natural gas is all output to the gas supply network; During the peak period of electricity consumption, LNG enters the second branch and the third branch. The LNG in the second branch is used to capture the carbon dioxide condensation of the flue gas at the outlet of the waste heat utilization subsystem, and the LNG in the third branch is used for the propane cold storage cycle. The LNG heated in the second branch and the third branch are combined and then heat-exchanged by the recuperative Rankine cycle, and then gasified into the second part of natural gas and the third part of natural gas. The second part of natural gas enters the gas supply network, and the third part of natural gas is delivered to the gas turbine subsystem as fuel. The regenerative Rankine cycle comprises a mixed working fluid pump (32), a first regenerator (33), a heating expansion unit and a seventh heat exchanger (25); the hot flow outlet of the seventh heat exchanger (25) is connected to the inlet of the mixed working fluid pump (32), the outlet of the mixed working fluid pump (32) is connected to the cold flow inlet of the first regenerator (33), the cold flow outlet of the first regenerator (33) is connected to the inlet of the heating expansion unit, the outlet of the heating expansion unit is connected to the hot flow inlet of the first regenerator (33), and the hot flow outlet of the first regenerator (33) is connected to the hot flow inlet of the seventh heat exchanger (25), thereby forming a cycle; the heating expansion unit comprises at least one stage of heater, and an expander is connected after the cold flow outlet of each stage of heater, and work is output through the expander; the heat source of the seventh heat exchanger (25) is the circulating medium of the regenerative Rankine cycle, and the cold source is the LNG of the first branch, the second branch or the third branch; the heat source of the heater is process water, and the cold source is the circulating medium of the regenerative Rankine cycle; The gas turbine subsystem comprises a combustion chamber (38), a gas turbine (39), a compressor (40) and a second reheater (41); the inlet of the compressor (40) is connected to the external environment, the outlet of the compressor (40) is connected to the cold flow inlet of the second reheater (41), the cold flow outlet of the second reheater (41) is connected to the first inlet of the combustion chamber (38), the second inlet of the combustion chamber (38) is used to receive the third part of natural gas, the outlet of the combustion chamber (38) is connected to the inlet of the gas turbine (39), the outlet of the gas turbine (39) is connected to the hot flow inlet of the second reheater (41), and the hot flow outlet of the second reheater (41) is connected to the waste heat utilization subsystem; The steam Rankine cycle comprises a feed water pump (43), an eighth heat exchanger (42), a steam turbine (44) and a condenser (45); the outlet of the feed water pump (43) is connected to the cold flow inlet of the eighth heat exchanger (42), the cold flow outlet of the eighth heat exchanger (42) is connected to the inlet of the steam turbine (44), the outlet of the steam turbine (44) is connected to the hot flow inlet of the condenser (45), and the hot flow outlet of the condenser (45) is connected to the inlet of the feed water pump (43), thereby forming a cycle; the heat source of the eighth heat exchanger (42) is the flue gas received from the gas turbine subsystem, the cold source of the condenser (45) is process water, and the circulating medium of the steam Rankine cycle is liquid water or water vapor; The carbon dioxide capture subsystem comprises a gas-liquid separator (46), a regenerator unit, a fifth heat exchanger (22), a solid carbon dioxide storage tank (49) and a second thermostat (50); the gas phase outlet of the gas-liquid separator (46) is connected to the heat flow inlet of the regenerator, the heat flow outlet of the regenerator is connected to the heat flow inlet of the fifth heat exchanger (22), the heat flow outlet of the fifth heat exchanger (22) is connected to the cold flow inlet of the regenerator unit, and the cold flow outlet of the regenerator unit is connected to the cold flow inlet of the second thermostat (50). The cold flow outlet of the second thermostat (50) is connected to the external environment; the regenerator unit includes at least one stage of regenerator, and the hot flow outlet and cold flow inlet of the previous stage of regenerator are respectively connected to the hot flow inlet and cold flow outlet of the next stage of regenerator; the gas-liquid separator (46) receives the flue gas of the waste heat utilization subsystem, and the liquid phase outlet is liquid water separated from the flue gas; the cold source of the fifth heat exchanger (22) is the LNG of the second branch; the heat source of the second thermostat (50) is process water.

2. The natural gas power generation system combined with liquefied air energy storage according to claim 1 is characterized in that: The natural gas power generation system further comprises a liquid air pump (11) connected between the liquefied air storage tank (10) and the expansion work device group, an LNG pump (20) and a first flow divider (21) connected before the propane cold storage cycle, a mixer (24) connected between the propane cold storage cycle and the regenerative Rankine cycle, and a first thermostat (26) and a second flow divider (27) connected after the regenerative Rankine cycle; The first flow divider (21) divides the LNG into a second branch and a third branch of LNG; the second flow divider (27) divides the gasified natural gas into a second portion of natural gas and a third portion of natural gas.

3. A natural gas power generation method combined with liquefied air energy storage, characterized in that: The natural gas power generation system according to any one of claims 1 to 2 includes a charging process during a low power consumption period and a discharging process during a peak power consumption period, which are specifically as follows: During the charging process when electricity consumption is low, air at normal temperature and pressure passes through the compression and liquefaction equipment group, and is compressed and liquefied into liquefied air with the help of energy provided by the LNG and propane cold storage cycle of the first branch, and is stored in a liquefied air storage tank (10). Subsequently, the LNG of the first branch provides energy to the regenerative Rankine cycle and is gasified into the first part of natural gas, which is all sent to the gas supply network. At this time, the circulating medium in the regenerative Rankine cycle performs work in the expander to output electricity. During the discharge process at the peak of electricity consumption, the liquefied air stored in the liquefied air storage tank (10) passes through the expansion work device group, absorbs the energy of the flue gas, is gasified into high-pressure gaseous air, performs work in the expander, outputs electricity, and is converted into air at normal pressure; The LNG in the second branch provides energy to the fifth heat exchanger (22), so that the carbon dioxide in the flue gas is condensed into solid carbon dioxide. The LNG in the third branch provides energy to the propane cold storage cycle so that cold energy is stored in the propane cold storage cycle. Subsequently, the LNG in the second branch and the LNG in the third branch are combined through the mixer (24) to provide energy to the regenerative Rankine cycle and are gasified into the second part of natural gas and the third part of natural gas. At this time, the circulating medium in the regenerative Rankine cycle performs work in the expander to output electricity, and the second part of natural gas enters the gas supply network. The third part of the natural gas enters the combustion chamber (38) and is mixed with air to burn. The flue gas after combustion enters the gas turbine (39) to generate power and drive the compressor (40) to work. The low-pressure flue gas sequentially provides energy to the second regenerator (41), the steam Rankine cycle and the expansion work equipment group. At this time, the circulating medium in the steam Rankine cycle performs work in the expander and outputs electricity. The flue gas then enters the gas-liquid separator (46) to separate the water, and then passes through the regenerator to enter the fifth heat exchanger (22), where the solid carbon dioxide obtained by condensation is discharged and stored in the solid carbon dioxide storage tank (49). The remaining low-temperature decarbonized gas passes through the regenerator to provide energy for cooling the flue gas, and is then discharged to the external environment.

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