CN114687821A - A high-efficiency power generation system based on liquid natural gas and its working method - Google Patents

Abstract

The invention discloses a high-efficiency power generation system based on liquid natural gas and a working method thereof, belonging to the technical field of power generation systems. The system mainly includes natural gas boiler, carbon dioxide gas turbine, primary carbon dioxide heat exchanger, secondary carbon dioxide heat exchanger, air heat exchanger, flue gas heat exchanger, organic working fluid turbine, organic working fluid heat exchanger, liquid natural gas Tanks, motor cooling fluid heat exchangers and ultra-low temperature motors. The invention uses the liquid natural gas fuel as the cold source, utilizes the cooling capacity of the liquid natural gas in steps, reduces the lower limit of the working temperature of the carbon dioxide cycle and the organic working medium cycle, and at the same time couples the low-temperature organic working medium cycle to absorb the exothermic heat of the carbon dioxide cycle and the air in the atmospheric environment. reduce the working temperature of the motor, save cooling equipment and reduce energy consumption; improve the overall cycle efficiency and simplify the cycle structure, greatly reduce the investment and operation and maintenance costs of the system, and meet the current overall requirements for energy conservation and emission reduction.

Description

A high-efficiency power generation system based on liquid natural gas and its working method

technical field

The invention belongs to the technical field of power generation systems, and in particular relates to a high-efficiency power generation system based on liquid natural gas and a working method thereof.

Background technique

With the promotion of market demand and the continuous development of energy utilization and equipment manufacturing technology, in the past few decades, the large-scale power generation technology of the Rankine cycle using water vapor as the working fluid and the Brayton cycle using gas as the working fluid has always been Towards the direction of high parameters and high power. The analysis found that this development of large-scale power generation technology has improved the energy conversion efficiency and reduced the construction and power generation costs per unit of power. However, high parameters also make the volume of the generator set very large and the circulation system extremely complex, which brings challenges to material strength, equipment manufacturing and operation control. Therefore, the development of high-parameter and high-power large-scale generator sets faces a major technical bottleneck.

In recent years, academia and industry have generally paid attention to a closed Brayton cycle power generation technology using supercritical carbon dioxide as the working fluid. The gaseous carbon dioxide is heated to reach the working pressure, and then enters the supercritical carbon dioxide gas turbine to do work, and the exhaust gas is reheated through multiple gas-gas heat exchangers to improve the cycle efficiency.

Although it has been proved in practice that the turbomachinery of supercritical carbon dioxide Brayton cycle is more compact than that of water vapor Rankine cycle, it still has the following disadvantages: (1) In order to improve the cycle efficiency, recompression or triple compression is used. The gas turbine also adopts the secondary reheating scheme, which is very complicated in structure, which brings difficulties to the system control; (2) In order to achieve multiple compression, multiple reheating and multi-stage reheating, it is necessary to set up multiple boilers in coordination with Heat transfer in the temperature range to improve boiler efficiency; (3) Due to compression near the critical point, there is a liquid state of the working fluid at the compressor inlet, which causes water erosion to the blades and brings difficulties to the stable control of the compressor; (4) The minimum pressure of the cycle is 7.38MPa, which causes the enthalpy drop in the gas turbine to be about 160kJ/kg, which is much lower than that of the water vapor cycle. In this way, to increase the output power of the cycle, it is necessary to increase the flow rate of the working fluid, which is the reason why the working fluid is in the boiler. The pressure loss has a fatal impact.

SUMMARY OF THE INVENTION

In order to solve the above problems, the purpose of the present invention is to provide a high-efficiency power generation system based on liquefied natural gas and a working method thereof, which can fully utilize the cold energy of liquefied natural gas and fully release the energy of the carbon dioxide circulating working fluid, thereby highly simplifying boilers and impeller machinery. , Improve the compactness of large motors and realize efficient conversion of thermal energy to electric energy.

The present invention is achieved through the following technical solutions:

The invention discloses a high-efficiency power generation system based on liquid natural gas, comprising a natural gas boiler, a carbon dioxide gas turbine, a first-stage carbon dioxide heat exchanger, a second-stage carbon dioxide heat exchanger, an air heat exchanger, a flue gas heat exchanger, and an organic working medium. Gas turbines, organic working fluid heat exchangers, liquid natural gas tanks, motor cooling working fluid heat exchangers and ultra-low temperature motors;

The working fluid outlet of the natural gas boiler is connected to the inlet of the carbon dioxide gas turbine, the outlet of the carbon dioxide gas turbine is connected to the high temperature side inlet of the first-stage carbon dioxide heat exchanger, and the high temperature side outlet of the first-stage carbon dioxide heat exchanger is connected to the second-stage carbon dioxide heat exchanger. The high temperature side inlet is connected, the high temperature side outlet of the secondary carbon dioxide heat exchanger is connected with the inlet of the air heat exchanger, the outlet of the air heat exchanger is connected with the inlet of the flue gas heat exchanger, and the outlet of the flue gas heat exchanger is connected with the natural gas boiler The low temperature side outlet of the first-stage carbon dioxide heat exchanger is connected with the inlet of the organic working medium gas turbine, and the outlet of the organic working medium gas turbine is connected with the high temperature side inlet of the organic working medium heat exchanger, and the organic working medium exchange The high temperature side outlet of the heat exchanger is connected with the second low temperature side inlet of the secondary carbon dioxide heat exchanger, the second low temperature side outlet of the secondary carbon dioxide heat exchanger is connected with the low temperature side inlet of the carbon dioxide heat exchanger; the outlet of the liquid natural gas tank is connected to the low temperature side inlet of the carbon dioxide heat exchanger. The low temperature side inlet of the organic working fluid heat exchanger is connected, the low temperature side outlet of the organic working fluid heat exchanger is connected with the first low temperature side inlet of the secondary carbon dioxide heat exchanger, and the first low temperature side outlet of the secondary carbon dioxide heat exchanger is connected to The low temperature side inlet of the motor cooling working fluid heat exchanger is connected, the low temperature side outlet of the motor cooling working fluid heat exchanger is connected with the fuel inlet of the natural gas boiler; the high temperature side outlet of the motor cooling working fluid heat exchanger is connected with the motor cooling working fluid pump inlet The outlet of the motor cooling working fluid pump is connected to the cooling working fluid inlet of the ultra-low temperature motor, and the cooling working fluid outlet of the ultra-low temperature motor is connected to the high temperature side inlet of the motor cooling working fluid heat exchanger; the rotor of the ultra-low temperature motor is connected to the carbon dioxide gas turbine through the coupling. The rotor of the carbon dioxide gas turbine is connected with the rotor of the organic working medium gas turbine through a coupling.

Preferably, a carbon dioxide pump is provided between the high temperature side outlet of the secondary carbon dioxide heat exchanger and the inlet of the air heat exchanger; the high temperature side outlet of the organic working fluid heat exchanger and the second low temperature side inlet of the secondary carbon dioxide heat exchanger There is an organic working fluid pump between them; a liquefied natural gas pump is arranged between the outlet of the liquid natural gas tank and the low temperature side inlet of the organic working fluid heat exchanger; the high temperature side outlet of the motor cooling working fluid heat exchanger and the cooling unit of the ultra-low temperature motor There is a motor cooling working medium pump between the quality inlets.

Preferably, the ultra-low temperature motor, the carbon dioxide gas turbine and the organic working medium gas turbine are arranged coaxially.

Preferably, the primary carbon dioxide heat exchanger is a printed circuit board heat exchanger, the secondary carbon dioxide heat exchanger is a multi-stream printed circuit board heat exchanger, the air heat exchanger is a printed circuit board heat exchanger, and the flue gas heat exchanger The heat exchanger is a printed circuit board heat exchanger, the organic working fluid heat exchanger is a plate-fin heat exchanger, and the motor cooling working fluid heat exchanger is a plate-fin heat exchanger.

The working method of the above-mentioned high-efficiency power generation system based on liquid natural gas disclosed in the present invention includes:

The exhaust gas of the carbon dioxide gas turbine transfers heat to the organic working medium and liquid natural gas in the first-stage carbon dioxide heat exchanger and the second-stage carbon dioxide heat exchanger in turn. In the flue gas heat exchanger, the heat contained in the exhaust gas of the natural gas boiler is absorbed and gasified; the gaseous carbon dioxide is heated and heated to the maximum working temperature by the heat energy released by the combustion of natural gas and air in the natural gas boiler; the gaseous carbon dioxide enters the carbon dioxide wheel gas The expansion in the turbine does work, and the shaft work drives the ultra-low temperature motor to convert the mechanical work into electrical energy;

The organic working medium gas turbine exhaust gas transfers heat to liquid natural gas in the organic working medium heat exchanger, and the gaseous organic working medium changes into liquid phase, and then absorbs carbon dioxide in the second-stage carbon dioxide heat exchanger and the first-stage carbon dioxide heat exchanger in turn. The heat released by the exhaust gas is converted into a gaseous state and heated up to the highest working temperature; the gaseous organic working medium enters the organic working medium gas turbine to expand and do work, and the shaft work drives the ultra-low temperature motor to convert the mechanical work into electrical energy;

The liquid natural gas in the liquid natural gas storage tank enters the organic working medium heat exchanger, absorbs the heat released by the organic working medium circulating exhaust gas, and then enters the secondary carbon dioxide heat exchanger to continue to absorb the heat released by the carbon dioxide circulating exhaust gas. The mass heat exchanger absorbs the heat in the ultra-low temperature motor, converts it into gaseous natural gas, and sends it into the natural gas boiler as a fuel to have a chemical reaction with the air and release heat energy;

The motor cooling medium absorbs the heat generated by copper loss, iron loss and eddy current loss in the ultra-low temperature motor, and is released to natural gas in the motor cooling medium heat exchanger to change from liquid to gaseous state, and the motor cooling medium enters the ultra-low temperature motor. .

Preferably, the high temperature side outlet pressure of the secondary carbon dioxide heat exchanger is 0.55-7.00 MPa.

Preferably, the exhaust pressure of the carbon dioxide gas turbine is below the critical pressure of carbon dioxide.

Preferably, the working temperature of the ultra-low temperature motor is lower than 0°C.

Compared with the prior art, the present invention has the following beneficial technical effects:

The invention discloses a high-efficiency power generation system based on liquid natural gas, which combines the power cycle of carbon dioxide and the cold energy utilization of liquid natural gas, and absorbs and utilizes the heat originally required to be discharged to the outside in the power cycle of carbon dioxide by using liquid natural gas, thereby further reducing The lowest pressure of carbon dioxide power cycle, improve the working capacity of working fluid per unit mass, reduce carbon dioxide flow, reduce boiler pressure loss, and improve carbon dioxide cycle efficiency; use the heat of carbon dioxide cycle exhaust to heat the organic working fluid and enter the organic working fluid gas turbine. Doing work, the heat of the exhaust gas is absorbed by the liquid natural gas, forming a low-temperature organic working fluid power cycle, making full use of the exhaust heat of the carbon dioxide cycle, and further improving the overall cycle efficiency.

Both the carbon dioxide power cycle and the low-temperature organic working fluid power cycle use the Rankine cycle form, that is, the working fluid is cooled into a liquid, and when the working fluid is pressurized, more mechanical work can be saved than during gaseous compression, and the cycle is improved. efficiency. After the liquid carbon dioxide is pressurized by the pump, it first absorbs the heat of the atmospheric environment in the air heat exchanger, making full use of the heat in the natural environment, and then absorbs the heat contained in the boiler exhaust in the flue gas heat exchanger. The cooling of liquid natural gas expands the temperature limit between the high temperature heat source and the low temperature heat source, and improves the efficiency of the carbon dioxide cycle.

The exhaust heat of the organic working medium gas turbine is absorbed by the liquid natural gas, and the exhaust gas temperature is reduced to about -150 °C, which expands the temperature limit between the high temperature heat source and the low temperature heat source of the organic working medium circulation, and improves the efficiency of the organic working medium circulation. . Liquefied natural gas absorbs the heat of the ultra-low temperature motor, reduces the operating temperature of the motor to below 0°C, reduces the resistance of the coil, reduces the heat generated by the motor, improves the efficiency of the motor, or increases the current and magnetic flux in the coil, reducing the size of the motor , reduce material and processing costs. At the same time, the minimum pressure of the carbon dioxide cycle of the present invention can be reduced to 0.55MPa. Compared with the traditional 7.38MPa, the shaft end seal of the carbon dioxide gas turbine greatly reduces the sealing pressure difference, greatly reduces the difficulty of sealing technology, and reduces the cost of sealing.

The working method of the above-mentioned high-efficiency power generation system based on liquefied natural gas disclosed in the present invention uses liquefied natural gas fuel as the cooling source, utilizes the cooling capacity of the liquefied natural gas in steps, reduces the lower limit of the working temperature of the carbon dioxide cycle and the organic working medium cycle, and simultaneously couples with low temperature The organic working fluid cycle absorbs the heat released by the carbon dioxide cycle and the heat in the atmospheric environment; reduces the working temperature of the motor, saves cooling equipment, and reduces energy consumption; improves the overall cycle efficiency and simplifies the cycle structure, greatly reducing the investment and operation of the system The maintenance cost is in line with the current overall requirements for energy conservation and emission reduction.

Description of drawings

FIG. 1 is a schematic diagram of a high-efficiency power generation system based on liquid natural gas according to the present invention.

In the figure: 1 is a natural gas boiler, 2 is a carbon dioxide gas turbine, 3 is a primary carbon dioxide heat exchanger, 4 is a secondary carbon dioxide heat exchanger, 5 is a carbon dioxide pump, 6 is an air heat exchanger, and 7 is a flue gas heat exchange 8 is an organic working medium gas turbine, 9 is an organic working medium heat exchanger, 10 is an organic working medium pump, 11 is a liquid natural gas tank, 12 is a liquid natural gas pump, 13 is a motor cooling working medium heat exchanger, and 14 is a Ultra-low temperature motor, 15 is the motor cooling working fluid pump.

Detailed ways

The present invention is described in further detail below in conjunction with the accompanying drawings and examples, and its content is to explain rather than limit the present invention:

Liquid natural gas contains cold energy, which cannot be used well at present; the current cycle efficiency of supercritical carbon dioxide is not high, and the system is complicated. The high-efficiency power generation system based on liquefied natural gas of the present invention combines the power cycle of carbon dioxide with the utilization of cold energy of liquefied natural gas, and solves the current technical problems.

As shown in Figure 1, it is a high-efficiency power generation system based on liquid natural gas of the present invention, including a natural gas boiler 1, a carbon dioxide gas turbine 2, a first-stage carbon dioxide heat exchanger 3, a second-stage carbon dioxide heat exchanger 4, a carbon dioxide pump 5, and an air heat exchanger. 6. Flue gas heat exchanger 7, organic working fluid turbine 8, organic working fluid heat exchanger 9, organic working fluid pump 10, liquid natural gas tank 11, liquefied natural gas pump 12, motor cooling working fluid heat exchanger 13, ultra-low temperature The motor 14 and the motor cooling working fluid pump 15 .

The outlet of the working fluid of the natural gas boiler 1 is connected to the inlet of the carbon dioxide gas turbine 2, the outlet of the carbon dioxide gas turbine 2 is connected to the high temperature side inlet of the primary carbon dioxide heat exchanger 3, and the high temperature side outlet of the primary carbon dioxide heat exchanger 3 is connected to the secondary carbon dioxide heat exchanger 4 The high temperature side inlet is connected, the high temperature side outlet of the secondary carbon dioxide heat exchanger 4 is connected to the inlet of the carbon dioxide pump 5, the outlet of the carbon dioxide pump 5 is connected to the inlet of the air heat exchanger 6, and the outlet of the air heat exchanger 6 is connected to the inlet of the flue gas heat exchanger 7 , the outlet of the flue gas heat exchanger 7 is connected to the inlet of the working medium of the natural gas boiler 1, the outlet of the low temperature side of the primary carbon dioxide heat exchanger 3 is connected to the inlet of the organic working medium gas turbine 8, and the outlet of the organic working medium gas turbine 8 exchanges heat with the organic working medium The high temperature side inlet of the heat exchanger 9 is connected, the high temperature side outlet of the organic working fluid heat exchanger 9 is connected with the organic working fluid pump 10 inlet, the organic working fluid pump 10 outlet is connected with the second low temperature side inlet of the secondary carbon dioxide heat exchanger 4, and the secondary carbon dioxide The outlet of the second low temperature side of the heat exchanger 4 is connected to the inlet of the low temperature side of the first-stage carbon dioxide heat exchanger 3, the outlet of the liquid natural gas tank 11 is connected to the inlet of the liquid natural gas pump 12, and the outlet of the liquid natural gas pump 12 is connected to the low temperature side of the organic working fluid heat exchanger 9 The inlet is connected, the low temperature side outlet of the organic working fluid heat exchanger 9 is connected to the first low temperature side inlet of the secondary carbon dioxide heat exchanger 4, and the first low temperature side outlet of the secondary carbon dioxide heat exchanger 4 is connected to the low temperature of the motor cooling working fluid heat exchanger 13 The side inlet is connected, the low temperature side outlet of the motor cooling working fluid heat exchanger 13 is connected with the fuel inlet of the natural gas boiler 1, the high temperature side outlet of the motor cooling working fluid heat exchanger 13 is connected with the inlet of the motor cooling working fluid pump 15, and the motor cooling working fluid pump The outlet 15 is connected to the cooling medium inlet of the ultra-low temperature motor 14, the cooling medium outlet of the ultra-low temperature motor 14 is connected to the high temperature side inlet of the motor cooling medium heat exchanger 13, the rotor of the ultra-low temperature motor 14 is connected to the rotor of the carbon dioxide gas turbine 2 through a coupling, and the carbon dioxide The rotor of the gas turbine 2 is connected to the organic working medium gas turbine 8 through a coupling.

After the carbon dioxide is pressurized by the carbon dioxide pump 5, it is heated from a liquid state to a gas state through the three-stage heating of the air heat exchanger 6, the flue gas heat exchanger 7 and the natural gas boiler 1.

The heat of the cooling working fluid of the ultra-low temperature motor 14 is absorbed by the natural gas in the motor cooling working fluid heat exchanger 13 .

The heat of the exhaust gas of the carbon dioxide gas turbine 2 is absorbed by the organic working medium on the cold side in the primary carbon dioxide heat exchanger 3 and the secondary carbon dioxide heat exchanger 4 .

The secondary carbon dioxide heat exchanger 4 has two cold-side working fluids, natural gas and organic working fluid.

The heat of the organic working medium in the organic working medium heat exchanger 9 is absorbed by the liquid natural gas on the cold side.

The air heat exchanger 6 absorbs heat from the atmosphere to raise the temperature of the liquid carbon dioxide.

In a preferred embodiment of the present invention, the ultra-low temperature motor 14 , the carbon dioxide gas turbine 2 and the organic working medium gas turbine 8 are arranged coaxially.

In a preferred embodiment of the present invention, the first-stage carbon dioxide heat exchanger 3, the second-stage carbon dioxide heat exchanger 4, the air heat exchanger 6 and the flue gas heat exchanger 7 are printed circuit board heat exchangers, two of which are printed circuit board heat exchangers. The stage carbon dioxide heat exchanger 4 is a multi-stream printed circuit board heat exchanger; the organic working fluid heat exchanger 9 and the motor cooling working fluid heat exchanger 13 are plate-fin heat exchangers.

The working method of the above-mentioned high-efficiency power generation system based on liquid natural gas:

The exhaust gas of the carbon dioxide gas turbine 2 transfers heat to the organic working medium and the liquid natural gas in the first-stage carbon dioxide heat exchanger 3 and the second-stage carbon dioxide heat exchanger 4 in turn, and the gaseous carbon dioxide changes into liquid phase, and is added by the carbon dioxide pump 5. to the maximum working pressure of the carbon dioxide cycle. Subsequently, the heat of the atmospheric environment is absorbed in the air heat exchanger 6 to increase temperature, and the heat contained in the exhaust gas of the natural gas boiler 1 is absorbed in the flue gas heat exchanger 7 for gasification. Then the gaseous carbon dioxide is heated in the natural gas boiler 1 by the heat energy released by the combustion of natural gas and air, and the temperature is raised to the maximum working temperature of the carbon dioxide cycle. Finally, the gaseous carbon dioxide with a certain temperature and pressure enters the carbon dioxide gas turbine 2 for expansion and work, and the shaft work drives the ultra-low temperature motor 14 to convert the mechanical work into electrical energy.

The exhaust gas of the organic working medium gas turbine 8 transfers heat to the liquid natural gas in the organic working medium heat exchanger 9, and the gaseous organic working medium changes into a liquid state, and is pressurized by the organic working medium pump 10 to the maximum working pressure of the organic working medium circulation. Subsequently, the organic working fluid sequentially absorbs the heat released by the carbon dioxide circulating exhaust in the secondary carbon dioxide heat exchanger 4 and the primary carbon dioxide heat exchanger 3, transforms into a gaseous state, and is heated to the maximum working temperature of the organic working fluid cycle. Then the gaseous organic working medium with a certain temperature and pressure enters the organic working medium gas turbine 8 to expand and do work, and the shaft work drives the ultra-low temperature motor 14 to convert the mechanical work into electrical energy.

The liquid natural gas in the liquid natural gas storage tank 11 is transported to the organic working medium heat exchanger 9 through the liquid natural gas pump 12 to absorb the heat released by the circulating exhaust gas of the organic working medium. Then enter the secondary carbon dioxide heat exchanger 4 to continue to absorb the heat released by the carbon dioxide circulating exhaust gas. Finally, the heat in the ultra-low temperature motor 14 is absorbed in the motor cooling working fluid heat exchanger 13, converted into gaseous natural gas, and sent to the natural gas boiler 1 as a fuel to chemically react with the air and release heat energy.

The motor cooling medium absorbs the heat generated by copper loss, iron loss and eddy current loss in the ultra-low temperature motor 14, and is released to natural gas in the motor cooling medium heat exchanger 13, so that it undergoes a phase change from liquid to gas. Then, the motor cooling working fluid enters the ultra-low temperature motor 14 under the pressurized delivery of the motor cooling working fluid pump 15 .

The exhaust pressure of the carbon dioxide gas turbine 2 is lower than the critical pressure of carbon dioxide, which is 7.38 MPa.

The operating temperature of the ultra-low temperature motor 14 is lower than 0°C.

The intake air temperature of the carbon dioxide gas turbine 2 is about 630°C.

The inlet temperature of the organic working medium gas turbine 8 is about 150°C, and the outlet temperature is about -150°C.

The outlet pressure of the high temperature side of the secondary carbon dioxide heat exchanger 4 can be reduced to a minimum of 0.55MPa, and the temperature is about -55°C.

The above descriptions are only part of the embodiments of the present invention. Although some terms are used in the present invention, the possibility of using other terms is not excluded. These terms are used only for convenience in describing and explaining the essence of the present invention, and it is contrary to the spirit of the present invention to interpret them as any kind of additional limitation. The above is only to further illustrate the content of the present invention with examples, so as to facilitate easier understanding, but it does not mean that the embodiments of the present invention are limited to this. Any technical extension or re-creation made according to the present invention is subject to the protection of.

Claims (8)

1. A high-efficiency power generation system based on liquid natural gas, characterized in that, comprising a natural gas boiler (1), a carbon dioxide gas turbine (2), a primary carbon dioxide heat exchanger (3), a secondary carbon dioxide heat exchanger (4), Air heat exchanger (6), flue gas heat exchanger (7), organic working medium gas turbine (8), organic working medium heat exchanger (9), liquid natural gas tank (11), motor cooling working medium heat exchanger (13) and an ultra-low temperature motor (14); The outlet of the working fluid of the natural gas boiler (1) is connected to the inlet of the carbon dioxide gas turbine (2), and the outlet of the carbon dioxide gas turbine (2) is connected to the high temperature side inlet of the first-stage carbon dioxide heat exchanger (3), and the first-stage carbon dioxide heat exchanger The high temperature side outlet of (3) is connected to the high temperature side inlet of the secondary carbon dioxide heat exchanger (4), the high temperature side outlet of the secondary carbon dioxide heat exchanger (4) is connected to the inlet of the air heat exchanger (6), and the air exchange The outlet of the heat exchanger (6) is connected with the inlet of the flue gas heat exchanger (7), and the outlet of the flue gas heat exchanger (7) is connected with the working medium inlet of the natural gas boiler (1); the first-stage carbon dioxide heat exchanger (3) ) is connected with the inlet of the organic working medium gas turbine (8), the outlet of the organic working medium gas turbine (8) is connected with the high temperature side inlet of the organic working medium heat exchanger (9), and the organic working medium heat exchanger The high temperature side outlet of (9) is connected to the second low temperature side inlet of the secondary carbon dioxide heat exchanger (4), and the second low temperature side outlet of the secondary carbon dioxide heat exchanger (4) is connected to the low temperature side of the carbon dioxide heat exchanger (3). The side inlet is connected; the outlet of the liquid natural gas tank (11) is connected with the low temperature side inlet of the organic working fluid heat exchanger (9), and the low temperature side outlet of the organic working fluid heat exchanger (9) is connected with the secondary carbon dioxide heat exchanger (4). ) is connected to the first low temperature side inlet of the secondary carbon dioxide heat exchanger (4), the first low temperature side outlet of the secondary carbon dioxide heat exchanger (4) is connected to the low temperature side inlet of the motor cooling working fluid heat exchanger (13), and the motor cooling working fluid heat exchanger (13) ) of the low temperature side outlet is connected to the fuel inlet of the natural gas boiler (1); the high temperature side outlet of the motor cooling working fluid heat exchanger (13) is connected to the inlet of the motor cooling working fluid pump (15), and the motor cooling working fluid pump (15) The outlet is connected with the cooling medium inlet of the ultra-low temperature motor (14), and the cooling medium outlet of the ultra-low temperature motor (14) is connected with the high temperature side inlet of the motor cooling medium heat exchanger (13); the rotor of the ultra-low temperature motor (14) is connected through the coupling shaft The device is connected with the rotor of the carbon dioxide gas turbine (2), and the rotor of the carbon dioxide gas turbine (2) is connected with the rotor of the organic working medium gas turbine (8) through a coupling. 2. The high-efficiency power generation system based on liquid natural gas according to claim 1, wherein a carbon dioxide pump is provided between the high temperature side outlet of the secondary carbon dioxide heat exchanger (4) and the inlet of the air heat exchanger (6). (5); an organic working fluid pump (10) is provided between the high temperature side outlet of the organic working fluid heat exchanger (9) and the second low temperature side inlet of the secondary carbon dioxide heat exchanger (4); a liquid natural gas tank (11) ) and the low temperature side inlet of the organic working medium heat exchanger (9) is provided with a liquid natural gas pump (12); the high temperature side outlet of the motor cooling working medium heat exchanger (13) and the cooling of the ultra-low temperature motor (14) A motor cooling working medium pump (15) is arranged between the working medium inlets. 3 . The high-efficiency power generation system based on liquid natural gas according to claim 1 , wherein the ultra-low temperature motor ( 14 ), the carbon dioxide gas turbine ( 2 ) and the organic working medium gas turbine ( 8 ) are coaxially arranged. 4 . 4. The high-efficiency power generation system based on liquid natural gas according to claim 1, characterized in that, the first-stage carbon dioxide heat exchanger (3) is a printed circuit board heat exchanger, and the second-stage carbon dioxide heat exchanger (4) is a multi-strand heat exchanger. The flow printed circuit board heat exchanger, the air heat exchanger (6) is a printed circuit board heat exchanger, the flue gas heat exchanger (7) is a printed circuit board heat exchanger, and the organic working fluid heat exchanger (9) is a plate heat exchanger The fin heat exchanger, the motor cooling working medium heat exchanger (13) is a plate fin heat exchanger. 5. The working method of the high-efficiency power generation system based on liquid natural gas according to any one of claims 1 to 4, characterized in that, comprising: The exhaust gas of the carbon dioxide gas turbine (2) transfers heat to the organic working medium and the liquid natural gas in the first-stage carbon dioxide heat exchanger (3) and the second-stage carbon dioxide heat exchanger (4) in turn, and the gaseous carbon dioxide phase changes into a liquid state, and then sequentially The heat of the atmospheric environment is absorbed in the air heat exchanger (6) to heat up, and the heat contained in the exhaust gas of the natural gas boiler (1) is absorbed in the flue gas heat exchanger (7) for gasification; gaseous carbon dioxide is evaporated in the natural gas boiler (1) It is heated by the heat energy released by the combustion of natural gas and air, and the temperature rises to the highest working temperature; the gaseous carbon dioxide enters the carbon dioxide gas turbine (2) to expand and perform work, and the shaft work drives the ultra-low temperature motor (14) to convert the mechanical work into electrical energy; The exhaust gas of the organic working medium gas turbine (8) transfers heat to the liquid natural gas in the organic working medium heat exchanger (9), and the gaseous organic working medium changes into a liquid state, and then sequentially absorbs the secondary carbon dioxide heat exchanger (4) and The heat released by the carbon dioxide circulating exhaust in the first-stage carbon dioxide heat exchanger (3) is converted into a gaseous state and heated to the highest working temperature; the gaseous organic working medium enters the organic working medium gas turbine (8) to expand and do work, and the shaft work drives the ultra-low temperature The motor (14) converts mechanical work into electrical energy; The liquid natural gas in the liquid natural gas storage tank (11) enters the organic working medium heat exchanger (9), absorbs the heat released by the organic working medium circulating exhaust gas, and then enters the secondary carbon dioxide heat exchanger (4) to continue to absorb the carbon dioxide circulating exhaust gas The released heat finally absorbs the heat in the ultra-low temperature motor (14) in the motor cooling working medium heat exchanger (13), converts it into gaseous natural gas, and sends it into the natural gas boiler (1) as fuel to react with the air and release heat energy ; The motor cooling working medium absorbs heat generated by copper loss, iron loss and eddy current loss in the ultra-low temperature motor (14), and is released to natural gas in the motor cooling working medium heat exchanger (13) to change from liquid to gaseous state. The cooling medium enters the ultra-low temperature motor (14). 6 . The working method of the high-efficiency power generation system based on liquid natural gas according to claim 5 , wherein the outlet pressure of the high temperature side of the secondary carbon dioxide heat exchanger ( 4 ) is 0.55-7.00 MPa. 7 . 7. The working method of the high-efficiency power generation system based on liquid natural gas according to claim 5, characterized in that the exhaust pressure of the carbon dioxide gas turbine (2) is lower than the critical pressure of carbon dioxide. 8 . The working method of the high-efficiency power generation system based on liquid natural gas according to claim 5 , wherein the working temperature of the ultra-low temperature motor ( 14 ) is lower than 0° C. 9 .

Images