Integrated fused salt heat storage semi-closed supercritical CO2-steam combined cycle zero-carbon emission combined heat and power generation system

Abstract

The invention discloses a semi-closed supercritical CO2-steam combined cycle zero-carbon emission combined heat and power generation system integrating fused salt heat storage, and belongs to the technical field of energy conversion and power systems. Comprising a semi-closed supercritical CO2 circulation subsystem, a fused salt heat storage and heat exchange subsystem and a steam circulation subsystem. Wherein the combustion chamber, the gas turbine, the fused 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 high-temperature salt tank, the high-temperature fused salt pump, the second adjusting valve, the fused salt-water heat exchanger, the low-temperature salt tank, the low-temperature fused salt pump and the fused salt-CO2 heat exchanger are sequentially connected in series to form a loop; the fused 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 set, the deaerator, the second pump and the high-pressure heater set are sequentially connected in series to form a loop. According to the invention, the stability and adaptability of system operation are improved, and reliable operation of the combined cycle power generation system in a complex power grid environment is ensured.

Description

Technical Field

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

[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 a certain degree of maturity and reliability in energy conversion, they also have limitations such as low thermal efficiency, large emissions of CO2 and other greenhouse gases, and poor load regulation capabilities. Existing combined cycle power generation systems, such as the gas-steam combined cycle, have improved power generation efficiency to a certain extent, but there are still problems such as insufficient energy cascade utilization, limited load regulation capabilities and the inability to truly achieve zero carbon emissions. Molten salt heat storage technology is an efficient way to store thermal energy. Molten salt has good thermal stability and large specific heat capacity. It can store a large amount of thermal energy at high temperature 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 solutions, which cannot fully realize its potential.

[0003] In recent years, the supercritical CO2 cycle has received widespread attention as a new type of power cycle technology. The semi-closed supercritical CO2 cycle utilizes the excellent thermophysical properties of CO2 in the supercritical state, can efficiently transfer heat under high temperature and high pressure, and has the characteristics of compact structure, high efficiency, flexibility, and zero carbon emissions, but it also faces some challenges. First, the supercritical CO2 cycle has a long startup time and a large heat capacity of the regenerator, which requires a high initial investment, limiting its large-scale promotion. Secondly, when a single supercritical CO2 cycle operates at low load or partial load, the efficiency may decrease, affecting the overall performance of the system.

[0004] Therefore, a semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage is needed to improve power generation efficiency, achieve zero carbon emissions and enhance system flexibility. Summary of the invention

[0005] The purpose of the present invention is to propose a semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage, comprising a semi-closed supercritical CO2 circulation subsystem, a molten salt heat storage and heat exchange subsystem and a steam circulation subsystem;

[0006] The semi-closed supercritical CO2 circulation subsystem includes an air separation unit, 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 includes 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 cycle subsystem includes a high-pressure cylinder, an intermediate-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] Among them, the combustion chamber, gas turbine, molten salt-CO2 heat exchanger, heat exchanger, gas-water separator, diverter, and compressor are connected in series in sequence to form a loop; the air separation unit 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 connected in series in sequence to form a loop; one end of the first regulating valve is connected between the high-temperature molten salt pump and the second regulating valve, and the other end is connected between the low-temperature salt tank and the molten salt-water heat exchanger; the molten salt-water exchanger The steam generator, the high-pressure cylinder, the intermediate-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 connected in series in sequence to form a loop; the low-pressure cylinder is connected to the second generator; the first and second stage extraction steam of the high-pressure cylinder and the first stage extraction steam of the intermediate-pressure cylinder are connected to the high-pressure heater group; the third stage extraction steam of the intermediate-pressure cylinder and the first, second, and third stage extraction steam of the low-pressure cylinder are connected to the low-pressure heater group; the second stage extraction steam of the intermediate-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 a semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage, in which natural gas and high-purity oxygen provided by an air separation unit are mixed and burned in a combustion chamber to generate high-temperature and high-pressure flue gas that mixes with the internal CO2 stream and enters the gas turbine to perform work, thereby driving a first generator to generate electricity; the exhaust gas after the gas turbine performs work enters the molten salt-CO2 heat exchanger, and at the same time, a low-temperature molten salt pump transports the molten salt in the low-temperature salt tank into the molten salt-CO2 heat exchanger, thereby absorbing the exhaust waste heat, closing the second regulating valve, and storing the heat in the high-temperature salt tank; the exhaust gas after heat exchange in the molten salt-CO2 heat exchanger is cooled by cooling water through the heat exchanger and enters a gas-water separator to remove water to obtain a pure CO2 circulating flow; the CO2 circulating flow then passes through a diverter, a part of which is captured, and the other part is pressurized by a compressor and enters the combustion chamber again to adjust the combustion chamber outlet temperature and participate in the circulation;

[0011] In the steam cycle subsystem, the high-temperature molten salt pump transports the turbine exhaust waste heat stored in the molten salt in the high-temperature salt tank into the molten salt-water heat exchanger, heats the water to superheated steam and passes through the high-pressure cylinder, medium-pressure cylinder and low-pressure cylinder in turn to perform work and drive the second generator to generate electricity; then the molten salt temperature drops and returns to the low-temperature salt tank to wait for the next cycle; the exhaust steam after performing work in the low-pressure cylinder enters the low-pressure heater group to participate in the heat recovery process after being cooled by the condenser and pressurized 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 of the medium-pressure cylinder enter the deaerator for deoxygenation together, and enters the high-pressure regenerator group again after being pressurized by the second pump to continue participating in the heat recovery process; after the heat recovery is completed, the water obtains heat from the molten salt-water heat exchanger again to become superheated steam to form a complete closed loop.

[0012] Furthermore, the molten salt heat storage and heat exchange subsystem isolates the semi-closed supercritical CO2 circulation subsystem and the steam circulation subsystem. When the electricity demand changes, the semi-closed supercritical CO2 circulation subsystem responds quickly and controls the heat release of the molten salt heat storage and heat exchange subsystem by adjusting the opening of the first regulating valve and the second regulating valve, thereby adjusting the power generation power of the steam circulation subsystem.

[0013] Furthermore, when the first regulating valve is opened widely and the second regulating valve is opened small, the power generation of the steam cycle subsystem decreases; when the first regulating valve is opened small and the second regulating valve is opened widely, the power generation of the steam cycle subsystem increases, thereby realizing efficient wide load operation and flexible response of the system.

[0014] Furthermore, the exhaust gas temperature after heat exchange in the molten salt-CO2 heat exchanger is 200°C.

[0015] Furthermore, the cooling water is heated by the heat exchanger and used to supply heat to the outside.

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

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

[0018] 2. The air separation unit creates an oxygen-rich environment for combustion, which is conducive to the full combustion of natural gas, increases the carbon dioxide content in the flue gas, and is more conducive to subsequent carbon capture and water removal recycling, achieving zero carbon emissions and playing an important role in efficient energy saving.

[0019] 3. Molten salt heat storage and heat exchange subsystem The molten salt heat storage and heat exchange subsystem is used to effectively isolate the top and bottom cycles, which can realize the flexible adjustment of the top and bottom cycles for independent or combined power generation, greatly improving the load adjustment 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 exhaust of the gas turbine, realize the cross-time and space utilization of energy, and at the same time, by adjusting the working fluid flow of the steam cycle subsystem, the system can operate stably under a lower load; when the electricity demand increases, the molten salt heat storage and heat exchange subsystem can release the stored heat in time and heat the working fluid of the steam cycle subsystem to a higher temperature, thereby supplementing the system's power generation and ensuring that the system can quickly respond to load changes and meet the needs of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic structural diagram of the semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage of the present invention. DETAILED DESCRIPTION

[0021] The present invention proposes a semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage, and the present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0022] Figure 1This is a schematic structural diagram of the semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage of the present invention. The semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage includes 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, the air separation unit 1 is connected in series with the combustion chamber 2 and the gas turbine 3, one end of the gas turbine 3 is connected to the first generator 4, and the other end is connected to the molten salt-CO2 heat exchanger 9; the molten salt-CO2 heat exchanger 9 is connected in series with the heat exchanger 8, the gas-water separator 7, the diverter 6 and the compressor 5, and finally the compressor 5 is connected to the combustion chamber 2; the molten salt heat storage and heat exchange subsystem is connected in series with a low-temperature salt tank 10, a 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 provided at the outlets of the low-temperature salt tank 10 and the high-temperature salt tank 11; a a regulating valve 25, and a second regulating valve 26 is also provided 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, the high-pressure cylinder 13, the medium-pressure cylinder 14, the low-pressure cylinder 15 and the second generator 16 are connected in sequence, the first and second stage extraction steam of the high-pressure cylinder 13 and the first stage extraction steam of the medium-pressure cylinder are connected to the high-pressure heater group 20; the third stage extraction steam of the medium-pressure cylinder 14 and the first, second and third stage extraction steam of the low-pressure cylinder 15 are connected to the low-pressure heater group 22; at the same time, the second stage extraction steam of the medium-pressure cylinder 14 and the water from the high-pressure heater group 20 and the low-pressure heater group 22 respectively enter the deaerator 17 together and are connected to the second pump 21; the outlet exhaust steam of the low-pressure cylinder 15 and the low-temperature steam after heat recovery through the low-pressure heater group 22 enter the condenser 18 together and are connected to the first pump 19 to form a steam circulation closed loop with a multi-stage heat recovery device.

[0023] The entire system realizes oxygen-enriched combustion in a semi-closed supercritical CO2 circulation subsystem. High-purity oxygen that meets the pressure requirements is obtained through the air separation unit 1. The oxygen enters the combustion chamber 2 and is mixed with natural gas for combustion. The main components of the combustion products are CO2 and water. At the cold end of the subsystem, low-energy physical separation of CO2 and water can be achieved through cooling. This combustion method makes the carbon dioxide content in the flue gas relatively high, which greatly facilitates the subsequent carbon capture work, and is also conducive to the recycling of carbon dioxide dehydration, effectively improving the environmental protection performance and resource utilization efficiency of the entire system, and providing a guarantee for achieving the goal of zero carbon emissions.

[0024] The working method of the semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage is as follows: in the semi-closed supercritical CO2 circulation subsystem, natural gas and high-purity oxygen provided by the air separation unit 1 are mixed and burned in the combustion chamber 2, and the high-temperature and high-pressure flue gas generated is mixed with the internal CO2 stream and enters the gas turbine 3 to perform work, thereby driving the first generator 4 to generate electricity; the exhaust gas after the gas turbine 3 performs work enters the molten salt-CO2 heat exchanger 9, and at the same time, the low-temperature molten salt pump 23 transports the molten salt in the low-temperature salt tank 10 into the molten salt-CO2 The heat exchanger 9 absorbs the waste heat of the exhaust gas. At this time, the second regulating valve 26 is closed and the heat is stored in the high-temperature salt tank 11. The exhaust temperature after heat exchange is 200°C. After being cooled by cooling water in the heat exchanger 8, the water is removed by the gas-water separator 7 to obtain a relatively pure CO2 circulating flow. At the same time, the cooling water can be used for external heating after being heated by the exhaust gas, thereby realizing the cascade utilization of energy. After that, a part of the CO2 circulating flow is captured by the diverter 6, and the other part is pressurized by the compressor 5 and enters the combustion chamber 2 again to adjust the combustion chamber outlet temperature and participate in the circulation.

[0025] In the steam cycle subsystem, the high-temperature molten salt pump 24 transports the turbine exhaust waste heat stored in the molten salt in the high-temperature salt tank 11 into the molten salt-water heat exchanger 12, heats the water to superheated steam, and sequentially passes through the high-pressure cylinder 13, the medium-pressure cylinder 14 and the low-pressure cylinder 15 with a steam extraction and heat recovery device to perform work and drive the second generator 16 to generate electricity; then the molten salt temperature is reduced and returns to the low-temperature salt tank 10 to wait for the next heat storage cycle. The exhaust steam after the low-pressure cylinder 15 performs work 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 heated by the low-pressure heater group 22, the water from the high-pressure heater group 20, and the second-stage extraction steam of the medium-pressure cylinder 14 enter the deaerator 17 for deoxidation, and enters the high-pressure heat recovery group 20 again after being pressurized by the second pump 21 to continue to participate in the heat recovery process; the water after the heat recovery is completed 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 circulation subsystem as the top cycle and the steam circulation subsystem as the bottom cycle, and can realize the flexible adjustment of the top and bottom cycles for independent or combined power generation. When the electricity demand changes, the semi-closed supercritical CO2 circulation subsystem responds quickly, and at the same time, by adjusting the opening of the two valves to control the heat release of the molten salt heat storage and heat exchange subsystem, the power generation of the steam circulation subsystem is adjusted. When the first regulating valve 25 is opened widely and the second regulating valve 26 is opened slightly, the power generation of the steam circulation subsystem is reduced; when the first regulating valve 25 is opened slightly and the second regulating valve 26 is opened widely, the power generation of the steam circulation subsystem is increased, thereby realizing the efficient wide load operation and flexible response of the system.

[0027] In summary, the semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage of the present invention improves power generation efficiency and achieves zero carbon emissions. In addition, the use of molten salt heat storage system to replace inefficient and backward boilers and combined operation with the semi-closed supercritical CO2 cycle can effectively transform the power station boiler unit and broaden the system's variable load range. It greatly improves the stability and adaptability of the system operation, ensures the reliable operation of the combined cycle power generation system in a complex power grid environment, enhances the competitiveness of the entire system, and provides strong support for the production of efficient and clean energy.

Claims

1. A semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage, characterized in that: It includes a semi-closed supercritical CO2 circulation subsystem, a molten salt heat storage and heat 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 heat 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 cycle 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 diverter (6), and the compressor (5) are sequentially connected in series to form a loop; the air separation device (1) is connected to the combustion chamber (2), and 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 sequentially connected in series to form a loop; one end of the first regulating valve (25) is connected between the high-temperature molten salt pump (24) and the second regulating valve (26), and the other end is connected between the low-temperature salt tank (10) and the molten salt-water heat exchanger (12); the molten salt-water heat exchanger (12), the high-temperature molten salt pump (24), the second regulating valve (26), the molten salt-water heat exchanger (12), the low-temperature 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 sequentially connected in series to form a loop; the low-pressure cylinder (15) is connected to the second generator (16); the first and second stage extraction steam of the high-pressure cylinder (13) and the first stage extraction steam of the medium-pressure cylinder are connected to the high-pressure heater group (20); the third stage extraction steam of the medium-pressure cylinder (14) and the first, second and third stage extraction steam of the low-pressure cylinder (15) are connected to the low-pressure heater group (22); the second stage extraction steam 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 for operating the semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage as claimed in claim 1, characterized in that: In the semi-closed supercritical CO2 circulation subsystem, natural gas and high-purity oxygen provided by the air separation unit (1) are mixed and burned in the combustion chamber (2), generating high-temperature and high-pressure flue gas that mixes with the internal CO2 stream and enters the gas turbine (3) to perform work, thereby driving the first generator (4) to generate electricity; the exhaust gas after the gas turbine (3) performs work enters the molten salt-CO2 heat exchanger (9), and at the same time, 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 waste heat, closing the second regulating valve (26), and the heat is stored in the high-temperature salt tank (11); the exhaust gas after heat exchange in the molten salt-CO2 heat exchanger (9) is cooled by cooling water through the heat exchanger (8) and enters the gas-water separator (7) to remove water to obtain a pure CO2 circulation flow; the CO2 circulation flow then passes through the diverter (6), a part of which is captured, and the other part is pressurized by the compressor (5) and enters the combustion chamber (2) again to adjust the combustion chamber outlet temperature and participate in the circulation; In the steam cycle subsystem, the high-temperature molten salt pump (24) transports the turbine exhaust waste heat stored in the molten salt in the high-temperature salt tank (11) into the molten salt-water heat exchanger (12), heats the water to superheated steam and sequentially passes through the high-pressure cylinder (13), the medium-pressure cylinder (14) and the low-pressure cylinder (15) to perform 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) to wait for the next cycle; the exhaust steam after performing work in the low-pressure cylinder (15) is cooled by the condenser (18) After being pressurized by the first pump (19), the water enters the low-pressure heater group (22) to participate in the heat recovery process; the water heated by the low-pressure heater group (22) and the water from the high-pressure heater group (20) and the second-stage extraction steam of the medium-pressure cylinder (14) enter the deaerator (17) for deoxygenation, and after being pressurized by the second pump (21), it enters the high-pressure regenerator group (20) again to continue participating in the heat recovery process; after the heat recovery is completed, the water obtains heat from the molten salt-water heat exchanger (12) again to become superheated steam to form a complete closed loop.

3. The working method of the semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage according to claim 2 is characterized in that: The molten salt heat storage and heat exchange subsystem isolates the semi-closed supercritical CO2 circulation subsystem and the steam circulation subsystem. When the power demand changes, the semi-closed supercritical CO2 circulation subsystem responds quickly, and at the same time, the opening of the first regulating valve (25) and the second regulating valve (26) are adjusted to control the heat release of the molten salt heat storage and heat exchange subsystem, thereby adjusting the power generation power of the steam circulation subsystem.

4. The working method of the semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage according to claim 3 is characterized in that: When the first regulating valve (25) is opened at a large degree and the second regulating valve (26) is opened at a small degree, the power generation of the steam cycle subsystem decreases; when the first regulating valve (25) is opened at a small degree and the second regulating valve (26) is opened at a large degree, the power generation of the steam cycle subsystem increases, thereby achieving efficient wide-load operation and flexible response of the system.

5. The working method of the semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage according to claim 2, 3 or 4, characterized in that: The exhaust gas temperature after heat exchange in the molten salt-CO2 heat exchanger (9) is 200°C.

6. The working method of the semi-closed supercritical CO2-steam combined cycle zero-carbon emission cogeneration system with integrated molten salt heat storage according to claim 5 is characterized in that: The cooling water is heated by the heat exchanger (8) and then used to supply heat to the outside.

Images