Integrated molten-salt thermal storage semi-closed supercritical co2-steam combined cycle zero-carbon emission cogeneration system

Abstract

The application discloses a semi-closed supercritical CO2-steam combined cycle zero carbon emission cogeneration system integrated with molten salt heat storage, belonging to the technical field of energy conversion and power system, and comprising a semi-closed supercritical CO2 circulation subsystem, a molten salt heat storage and heat exchange subsystem and a steam circulation subsystem; wherein, a combustion chamber, a gas turbine, a molten salt-CO2 heat exchanger, a heat exchanger, a gas-water separator, a flow divider and a compressor are connected in series to form a loop; a high-temperature salt tank, a high-temperature molten salt pump, a second regulating valve, a molten salt-water heat exchanger, a low-temperature salt tank, a low-temperature molten salt pump and a molten salt-CO2 heat exchanger are connected in series to form a loop; and the molten salt-water heat exchanger, a high-pressure cylinder, a medium-pressure cylinder, a low-pressure cylinder, a condenser, a first pump, a low-pressure heater group, a deaerator, a second pump and a high-pressure heater group are connected in series to form a loop. The application improves the stability and adaptability of system operation, and guarantees reliable operation of the combined cycle power generation system under a complex power grid environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy conversion and power systems, and particularly relates to a semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system integrated with molten salt heat storage. BACKGROUND

[0002] Traditional thermal power generation systems, such as coal-fired, gas-fired and oil-fired power plants, mainly rely on the steam Rankine cycle. Although these systems have certain maturity and reliability in energy conversion, they also have the limitations of low thermal efficiency, large CO2 and other greenhouse gas emissions, and poor load regulation capability. Existing combined cycle power generation systems, such as gas-steam combined cycles, have improved power generation efficiency to some extent, but still have problems such as insufficient energy cascade utilization, limited load regulation capability, and inability to truly achieve zero carbon emissions. Molten salt heat storage technology is a highly efficient way of storing thermal energy. Molten salt has good thermal stability and large specific heat capacity, and can store a large amount of heat at high temperatures and release it to the power generation system when needed. However, the application of molten salt heat storage technology in traditional power generation systems is relatively small, and there is a lack of effective integration schemes, which cannot fully realize its potential.

[0003] In recent years, supercritical CO2 cycle has received widespread attention as a new type of power cycle technology. Semi-closed supercritical CO2 cycle utilizes the excellent thermophysical properties of CO2 in supercritical state, can efficiently transfer heat at high temperature and high pressure, and has the characteristics of compact structure, high efficiency, flexibility and zero carbon emission, but also faces some challenges. First, the start-up time of supercritical CO2 cycle is long, the heat capacity of regenerator is large, and high initial investment is required, which limits its wide application. Second, the single supercritical CO2 cycle may have lower efficiency when running at low or partial load, affecting the overall performance of the system.

[0004] Therefore, there is a need for a semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system integrated with molten salt heat storage, which aims to improve power generation efficiency, achieve zero carbon emission and enhance the flexibility of the system. SUMMARY

[0005] The purpose of the present application is to provide a semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system integrated with molten salt heat storage, which includes a semi-closed supercritical CO2 cycle subsystem, a molten salt heat storage and heat exchange subsystem, and a steam cycle subsystem.

[0006] The semi-closed supercritical CO2 cycle subsystem includes an air separation device, a combustion chamber, a gas turbine, a first generator, a compressor, a flow divider, a gas-water separator, and a heat exchanger.

[0007] The molten salt heat storage and heat exchange subsystem comprises a molten salt-CO2 heat exchanger, a low-temperature salt tank, a high-temperature salt tank, a molten salt-water heat exchanger, a low-temperature molten salt pump, a high-temperature molten salt pump, a first regulating valve and a second regulating valve;

[0008] The steam circulation subsystem comprises a high-pressure cylinder, a medium-pressure cylinder, a low-pressure cylinder, a second generator, a deaerator, a condenser, a first pump, a high-pressure heater group, a second pump and a low-pressure heater group.

[0009] The combustion chamber, the gas turbine, the molten salt-CO2 heat exchanger, the heat exchanger, the gas-water separator, the flow divider and the compressor are sequentially connected in series to form a loop; the air separation device is connected to the combustion chamber, and the gas turbine is connected to the first generator; the high-temperature salt tank, the high-temperature molten salt pump, the second regulating valve, the molten salt-water heat exchanger, the low-temperature salt tank, the low-temperature molten salt pump and the molten salt-CO2 heat exchanger are sequentially connected in series to form a loop; one end of the first regulating valve is connected to the middle of the high-temperature molten salt pump and the second regulating valve, and the other end is connected to the middle of the low-temperature salt tank and the molten salt-water heat exchanger; the molten salt-water heat exchanger, the high-pressure cylinder, the medium-pressure cylinder, the low-pressure cylinder, the condenser, the first pump, the low-pressure heater group, the deaerator, the second pump and the high-pressure heater group are sequentially connected in series to form a loop; the low-pressure cylinder is connected to the second generator; the first and second stage steam extraction of the high-pressure cylinder and the first stage steam extraction of the medium-pressure cylinder are connected to the high-pressure heater group; the third stage steam extraction of the medium-pressure cylinder and the first, second and third stage steam extraction of the low-pressure cylinder are connected to the low-pressure heater group; the second stage steam extraction of the medium-pressure cylinder, the high-pressure heater group and the low-pressure heater group are connected to the deaerator; the low-pressure heater group is connected to the condenser and forms a closed loop with the first pump.

[0010] A working method of an integrated molten salt heat storage semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system, in the semi-closed supercritical CO2 circulation subsystem, natural gas is mixed and combusted with high-purity oxygen provided by an air separation device in a combustion chamber to produce high-temperature and high-pressure flue gas mixed with an internal CO2 stream to enter a gas turbine to do work and in turn drive a first generator to generate electricity; the exhaust gas after doing work in the gas turbine enters a molten salt-CO2 heat exchanger, and a low-temperature molten salt pump delivers molten salt in a low-temperature salt tank into the molten salt-CO2 heat exchanger to absorb the exhaust heat, and a second regulating valve is closed, so that the heat is stored in a high-temperature salt tank; the exhaust gas after heat exchange in the molten salt-CO2 heat exchanger is cooled by cooling water in a heat exchanger and then enters a gas-water separator to remove water to obtain a pure CO2 circulation stream; then the CO2 circulation stream passes through a flow divider, part of which is captured, and the other part is pressurized by a compressor and then enters the combustion chamber to adjust the outlet temperature of the combustion chamber and participate in the cycle;

[0011] In the steam cycle subsystem, the high-temperature molten salt pump delivers the turbine exhaust waste heat stored in the high-temperature molten salt tank into the molten salt-water heat exchanger, heats the water to superheated steam, and sequentially passes through the high-pressure cylinder, the medium-pressure cylinder and the low-pressure cylinder to do work and drive the second generator to generate electricity; then the molten salt temperature is reduced and returned to the low-temperature molten salt tank for the next cycle; the exhaust steam after the low-pressure cylinder does work enters the low-pressure heater group to participate in the regenerative process after cooling by the condenser and pressurization by the first pump; the water heated by the low-pressure heater group and the water from the high-pressure heater group and the second stage extraction steam from the medium-pressure cylinder enter the deaerator together for deaeration, and then enter the high-pressure regenerator group again to continue participating in the regenerative process after pressurization by the second pump; the water after the completion of the regenerative process obtains heat from the molten salt-water heat exchanger again to become superheated steam to form a complete closed loop.

[0012] Further, the molten salt heat storage and heat exchange subsystem isolates the semi-closed supercritical CO2 cycle subsystem and the steam cycle subsystem, when the electricity demand changes, the semi-closed supercritical CO2 cycle subsystem responds quickly, and at the same time, the heat release amount of the molten salt heat storage and heat exchange subsystem is controlled by adjusting the opening degree of the first regulating valve and the second regulating valve, so as to adjust the power generation of the steam cycle subsystem.

[0013] Further, when the opening degree of the first regulating valve is large and the opening degree of the second regulating valve is small, the power generation of the steam cycle subsystem is reduced; when the opening degree of the first regulating valve is small and the opening degree of the second regulating valve is large, the power generation of the steam cycle subsystem is increased, so as to realize efficient wide load operation and flexible response of the system.

[0014] Further, the exhaust gas temperature after heat exchange by the molten salt-CO2 heat exchanger is 200 DEG C.

[0015] Further, the cooling water heated by the heat exchanger is used for external heat supply.

[0016] The beneficial effects of the present application are:

[0017] 1、The system of the present application uses semi-closed supercritical CO2 as the top cycle and conventional steam Rankine cycle as the bottom cycle, realizing the synergy of energy cascade utilization and zero carbon emission.

[0018] 2、The air separation device creates an oxygen-rich environment for combustion, which is conducive to the complete combustion of natural gas and improves the carbon dioxide content in the flue gas, which is more conducive to subsequent carbon capture and water removal and recycling, realizes zero carbon emission, and plays an important role in efficient energy saving.

[0019] 3、The molten salt heat storage and heat exchange subsystem effectively isolates the top and bottom cycles, can realize independent or combined power generation of the top and bottom cycles, and greatly improves the load regulation range of the combined cycle. When the electricity demand is small, the molten salt heat storage and heat exchange subsystem can effectively store the excess heat in the gas turbine exhaust, realize the cross-time and space utilization of energy, and through the adjustment of the working fluid flow of the steam cycle subsystem, the system can stably operate at a lower load; when the electricity demand increases, the molten salt heat storage and heat exchange subsystem can release the stored heat in time, heat the working fluid of the steam cycle subsystem to a higher temperature, thereby supplementing the power generation of the system, ensuring that the system can quickly respond to load changes and meet the demand of the power grid. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The structure diagram of the integrated molten salt heat storage semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system of the application. DETAILED DESCRIPTION

[0021] The application proposes an integrated molten salt heat storage semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system, which is further described below in combination with the drawings and specific embodiments.

[0022] Figure 1The application discloses a structure schematic diagram of a semi-closed supercritical CO2-steam combined cycle zero-carbon emission combined heat and power system integrated with molten salt heat storage. The semi-closed supercritical CO2-steam combined cycle zero-carbon emission combined heat and power system integrated with molten salt heat storage comprises a semi-closed supercritical CO2 circulation subsystem, a molten salt heat storage and heat exchange subsystem and a steam circulation subsystem; in the semi-closed supercritical CO2 circulation subsystem, an air separation device 1 is connected in series with a combustion chamber 2 and a gas turbine 3, one end of the gas turbine 3 is connected with a first generator 4, and one end of the gas turbine 3 is connected with a molten salt-CO2 heat exchanger 9; the molten salt-CO2 heat exchanger 9 is connected in series with a heat exchanger 8, a gas-water separator 7, a flow divider 6 and a compressor 5, and finally the compressor 5 is connected with the combustion chamber 2; the molten salt heat storage and heat exchange subsystem is connected in series with a low-temperature salt tank 10, the molten salt-CO2 heat exchanger 9, a high-temperature salt tank 11 and a molten salt-water heat exchanger 12; a low-temperature molten salt pump 23 and a high-temperature molten salt pump 24 are respectively arranged at outlets of the low-temperature salt tank 10 and the high-temperature salt tank 11; a first regulating valve 25 is arranged between the high-temperature salt tank 11 and the low-temperature salt tank 10, and a second regulating valve 26 is arranged between the high-temperature salt tank 11 and the molten salt-water heat exchanger 12; finally, in the steam circulation subsystem, the molten salt-water heat exchanger 12, a high-pressure cylinder 13, a medium-pressure cylinder 14, a low-pressure cylinder 15 and a second generator 16 are sequentially connected, first and second stage steam extraction of the high-pressure cylinder 13 and first stage steam extraction of the medium-pressure cylinder are connected with a high-pressure heater group 20; third stage steam extraction of the medium-pressure cylinder 14 and first, second and third stage steam extraction of the low-pressure cylinder 15 are connected with a low-pressure heater group 22; meanwhile, second stage steam extraction of the medium-pressure cylinder 14 is connected with water from the high-pressure heater group 20 and the low-pressure heater group 22, and the water enters a deaerator 17 and is connected with a second pump 21; exhaust steam of the low-pressure cylinder 15 and low-temperature steam after heat recovery of the low-pressure heater group 22 enter a condenser 18 and are connected with a first pump 19, thereby forming a steam circulation closed loop with a multi-stage heat recovery device.

[0023] The whole system realizes oxygen-rich combustion in the semi-closed supercritical CO2 circulation subsystem, high-purity oxygen meeting pressure requirements is obtained through the air separation device 1, the oxygen enters the combustion chamber 2 and is mixed and combusted with natural gas, main components of combustion products are CO2 and water, and the CO2 and water can be physically separated at a low energy consumption through cooling at a cold end of the subsystem. The combustion mode makes the content of carbon dioxide in flue gas relatively high, which provides great convenience for subsequent carbon capture work, is also beneficial to carbon dioxide water removal and recycling, effectively improves the environmental protection performance and resource utilization efficiency of the whole system, and provides guarantee for realizing the zero-carbon emission target.

[0024] The working method of the integrated molten salt heat storage semi-closed supercritical CO2-steam combined cycle zero carbon emission cogeneration system, in the semi-closed supercritical CO2 cycle subsystem, natural gas is mixed and combusted with high-purity oxygen provided by an air separation device 1 in a combustion chamber 2, high-temperature and high-pressure flue gas is mixed with an internal CO2 stream to enter a gas turbine 3 to do work, and then drive a first generator 4 to generate electricity; the exhaust gas after doing work in the gas turbine 3 enters a molten salt-CO2 heat exchanger 9, and a low-temperature molten salt pump 23 transports molten salt in a low-temperature salt tank 10 into the molten salt-CO2 heat exchanger 9, so as to absorb the exhaust gas waste heat, at this time, a second regulating valve 26 is closed, and the heat is stored in a high-temperature salt tank 11; the temperature of the exhaust gas after heat exchange is 200 DEG C, after being cooled by a cooler 8, water is removed by a gas-water separator 7, a relatively pure CO2 circulating stream is obtained, and the cooling water heated by the exhaust gas can be used for external heat supply, so that the energy is used in stages; then the CO2 circulating stream passes through a flow divider 6, part of which is captured, and the other part is pressurized by a compressor 5 and then enters the combustion chamber 2 again to adjust the outlet temperature of the combustion chamber and participate in the circulation.

[0025] In the steam cycle subsystem, a high-temperature molten salt pump 24 transports the turbine exhaust waste heat stored in the high-temperature salt tank 11 into a molten salt-water heat exchanger 12, heats the water to superheated steam, and then sequentially passes through a high-pressure cylinder 13, a medium-pressure cylinder 14 and a low-pressure cylinder 15 with steam extraction and heat recovery devices to do work and drive a second generator 16 to generate electricity; then the molten salt temperature is reduced and returned to the low-temperature salt tank 10 for the next heat storage cycle. The exhaust steam after doing work in the low-pressure cylinder 15 passes through a condenser 18, a first pump 19, a low-pressure heater group 22, a deaerator 17, a second pump 21 and a high-pressure heater group 20 in sequence to participate in the heat recovery process; the water after being heated by the low-pressure heater group 22, the water from the high-pressure heater group 20 and the second stage exhaust steam from the medium-pressure cylinder 14 enter the deaerator 17 together, are pressurized by the second pump 21 and then enter the high-pressure heater group 20 again to continue participating in the heat recovery process; the water after heat recovery obtains heat from the molten salt-water heat exchanger 12 again to become superheated steam to form a complete closed loop.

[0026] The molten salt heat storage and heat exchange subsystem effectively isolates the semi-closed supercritical CO2 cycle subsystem as the top cycle and the steam cycle subsystem as the bottom cycle, and can realize independent or combined power generation of the top and bottom cycles for flexible adjustment. When the electricity demand changes, the semi-closed supercritical CO2 cycle subsystem responds quickly, and the heat release amount of the molten salt heat storage and heat exchange subsystem is controlled by adjusting the opening degrees of the two valves, so as to adjust the power generation capacity of the steam cycle subsystem; when the opening degree of the first regulating valve 25 is large and the opening degree of the second regulating valve 26 is small, the power generation capacity of the steam cycle subsystem is reduced; when the opening degree of the first regulating valve 25 is small and the opening degree of the second regulating valve 26 is large, the power generation capacity of the steam cycle subsystem is increased, so that the system realizes efficient wide load operation and flexible response.

[0027] In summary, the integrated molten salt heat storage semi-closed supercritical CO2-steam combined cycle zero carbon emission cogeneration system of the application improves the power generation efficiency and realizes zero carbon emission.In addition, the molten salt heat storage system is used to replace the low-efficiency and backward boiler, and is combined with the semi-closed supercritical CO2 cycle to run, so that the power station boiler unit can be effectively transformed, and the variable load range of the system is widened.The stability and adaptability of the system operation are greatly improved, the reliable operation of the combined cycle power generation system in the complex power grid environment is ensured, the competitiveness of the whole system is enhanced, and strong support is provided for the production of efficient and clean energy.

Claims

1. A semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system integrated with molten salt thermal storage, characterized in that, The system comprises a semi-closed supercritical CO2 circulation subsystem, a molten salt heat storage and exchange subsystem and a steam circulation subsystem. The semi-closed supercritical CO2 circulation subsystem comprises an air separation device (1), a combustion chamber (2), a gas turbine (3), a first generator (4), a compressor (5), a flow divider (6), a gas-water separator (7) and a heat exchanger (8). The molten salt heat storage and exchange subsystem comprises a molten salt-CO2 heat exchanger (9), a low-temperature salt tank (10), a high-temperature salt tank (11), a molten salt-water heat exchanger (12), a low-temperature molten salt pump (23), a high-temperature molten salt pump (24), a first regulating valve (25) and a second regulating valve (26). The steam circulation subsystem comprises a high-pressure cylinder (13), a medium-pressure cylinder (14), a low-pressure cylinder (15), a second generator (16), a deaerator (17), a condenser (18), a first pump (19), a high-pressure heater group (20), a second pump (21) and a low-pressure heater group (22). The combustion chamber (2), the gas turbine (3), the molten salt-CO2 heat exchanger (9), the heat exchanger (8), the gas-water separator (7), the flow divider (6) and the compressor (5) are connected in series to form a loop; the air separation device (1) is connected to the combustion chamber (2), the gas turbine (3) is connected to the first generator (4); the high-temperature salt tank (11), the high-temperature molten salt pump (24), the second regulating valve (26), the molten salt-water heat exchanger (12), the low-temperature salt tank (10), the low-temperature molten salt pump (23) and the molten salt-CO2 heat exchanger (9) are connected in series to form a loop; one end of the first regulating valve (25) is connected to the high-temperature molten salt pump (24) and the second regulating valve (26), and the other end is connected to the low-temperature salt tank (10) and the molten salt-water heat exchanger (12); the molten salt-water heat exchanger (12), the high-pressure cylinder (13), the medium-pressure cylinder (14), the low-pressure cylinder (15), the condenser (18), the first pump (19), the low-pressure heater group (22), the deaerator (17), the second pump (21) and the high-pressure heater group (20) are connected in series to form a loop; the low-pressure cylinder (15) is connected to the second generator (16); the first and second stage steam extraction of the high-pressure cylinder (13) and the first stage steam extraction of the medium-pressure cylinder (14) are connected to the high-pressure heater group (20); the third stage steam extraction of the medium-pressure cylinder (14) and the first, second and third stage steam extraction of the low-pressure cylinder (15) are connected to the low-pressure heater group (22); the second stage steam extraction of the medium-pressure cylinder (14), the high-pressure heater group (20) and the low-pressure heater group (22) are connected to the deaerator (17); the low-pressure heater group (22) is connected to the condenser (18) and forms a closed loop with the first pump (19).

2. A method of operating the integrated molten-salt thermal energy storage, semi-closed supercritical CO2-steam combined cycle, zero-carbon emission, combined heat and power system of claim 1, wherein, In the semi-closed supercritical CO2 cycle subsystem, natural gas is mixed with high-purity oxygen provided by the air separation device (1) in the combustion chamber (2) to produce high-temperature and high-pressure flue gas, which is mixed with the internal CO2 stream to enter the gas turbine (3) to do work and drive the first generator (4) to generate electricity; the exhaust gas after the work of the gas turbine (3) enters the molten salt-CO2 heat exchanger (9), and the low-temperature molten salt pump (23) transports the molten salt in the low-temperature salt tank (10) into the molten salt-CO2 heat exchanger (9), thereby absorbing the exhaust heat, closing the second regulating valve (26), and storing the heat in the high-temperature salt tank (11); the exhaust gas after the heat exchange in the molten salt-CO2 heat exchanger (9) is cooled by the cooling water in the heat exchanger (8) and then enters the gas-water separator (7) to remove water, obtaining pure CO2 circulating stream; then the CO2 circulating stream passes through the flow divider (6), part of which is captured, and the other part is pressurized by the compressor (5) and then enters the combustion chamber (2) again to adjust the outlet temperature of the combustion chamber and participate in the cycle; In the steam cycle subsystem, the high-temperature molten salt pump (24) transports the turbine exhaust heat stored in the high-temperature salt tank (11) into the molten salt-water heat exchanger (12) to heat the water to superheated steam, which successively passes through the high-pressure cylinder (13), the medium-pressure cylinder (14), and the low-pressure cylinder (15) to do work and drive the second generator (16) to generate electricity; then the molten salt temperature decreases and returns to the low-temperature salt tank (10) for the next cycle; the exhaust steam after the work of the low-pressure cylinder (15) enters the low-pressure heater group (22) to participate in the heat recovery process after being cooled by the condenser (18) and pressurized by the first pump (19); the water after the heat recovery in the low-pressure heater group (22) and the water from the high-pressure heater group (20) and the second-stage extraction steam from the medium-pressure cylinder (14) enter the deaerator (17) together to remove oxygen, and then enter the high-pressure heater group (20) again to continue participating in the heat recovery process after being pressurized by the second pump (21); the water after the heat recovery obtains heat from the molten salt-water heat exchanger (12) again to become superheated steam to form a complete closed loop.

3. The method of operating an integrated molten-salt thermal energy storage half- closed supercritical CO2 -steam combined cycle zero-carbon emission cogeneration system of claim 2, wherein, The molten salt heat storage and heat exchange subsystem isolates the semi-closed supercritical CO2 cycle subsystem and the steam cycle subsystem, and when the electricity demand changes, the semi-closed supercritical CO2 cycle subsystem responds quickly, and at the same time, the heat release of the molten salt heat storage and heat exchange subsystem is controlled by adjusting the opening of the first regulating valve (25) and the second regulating valve (26), thereby adjusting the power generation of the steam cycle subsystem.

4. The method of operating an integrated molten-salt thermal energy storage half- closed supercritical CO2 -steam combined cycle zero-carbon emission cogeneration system of claim 3, wherein, When the opening of the first regulating valve (25) is large and the opening of the second regulating valve (26) is small, the power generation of the steam cycle subsystem decreases; when the opening of the first regulating valve (25) is small and the opening of the second regulating valve (26) is large, the power generation of the steam cycle subsystem increases, thereby realizing efficient wide-load operation and flexible response of the system.

5. The method of operating an integrated molten-salt thermal energy storage- semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system of claim 2, 3 or 4, wherein, The temperature of the exhaust gas after the heat exchange in the molten salt-CO2 heat exchanger (9) is 200℃.

6. The method of operating an integrated molten-salt thermal energy storage half- closed supercritical CO2 -steam combined cycle zero-carbon emission cogeneration system of claim 5, wherein, The cooling water heated by the heat exchanger (8) is used for external heat supply.

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