Thermal power generating unit, supercritical carbon dioxide and compressed air combined cycle energy storage system and operation method

Abstract

The invention discloses a thermal power generating unit, supercritical carbon dioxide and compressed air combined cycle energy storage system and an operation method, and belongs to the technical field of peak and frequency regulation and waste heat utilization of energy systems. The system comprises a compressed air energy storage subsystem, a supercritical CO2 Brayton cycle subsystem, a thermal power collaborative heat exchange subsystem, a coupling heat exchange device and an intelligent control system. In the energy storage stage, efficient compression is achieved through multi-stage compression and intermediate cooling, and air and CO2 are stored separately; in the energy release stage, compressed air drives an air expansion machine to generate power after being subjected to steam extraction and flue gas preheating of the thermal power plant, and meanwhile supercritical CO2 circularly utilizes waste heat of boiler tail gas of the thermal power plant and system tail gas to be preheated and expanded to serve as a second heat source channel to improve the output power. The intelligent control system coordinates the operation conditions of all the subsystems, and flexible switching of the system under various load and heat source boundaries is achieved. The system has high energy efficiency, high response speed and high integration level, and the peak regulation capacity and the clean operation level of the thermal power generating unit are remarkably improved.

Description

Technical Field

[0001] The present invention relates to multiple technical fields, including compressed air energy storage systems (CAES), supercritical carbon dioxide Brayton cycles (sCO2-Brayton), and utilization of waste heat from thermal power plants. The present invention particularly relates to an energy system and a control method that integrates a supercritical CO2 auxiliary cycle with a compressed air energy storage system and operates in deep coupling with a thermal power unit. The system falls within the cross-innovation technology category of peak and frequency regulation of power systems and development of flexible resources. Background Art

[0002] With the large-scale integration of renewable energy sources (such as wind and solar energy) into the power grid, the power system is becoming increasingly dependent on flexible regulation resources. Compressed Air Energy Storage (CAES), as a physical energy storage technology with large-scale and long-term energy storage capabilities, has received widespread attention in recent years. The supercritical carbon dioxide Brayton cycle (sCO2-Brayton) has the advantages of strong compactness, high specific power, fast start and stop, and suitability for medium and high temperature heat source drive. In recent years, it has been widely studied for use in new energy systems such as nuclear power and solar tower power generation. Its low expansion ratio and high efficiency make it an ideal choice for waste heat recovery from thermal power plants and short-term energy storage power generation.

[0003] However, existing technologies have yet to systematically integrate supercritical CO2 cycles with CAES. The two have significantly different thermodynamic characteristics, making matching pressure, temperature, and specific heat difficult. Furthermore, technical challenges such as heat exchange coupling, start-stop synchronization, and complex control strategies hinder their engineering applications in multi-source energy storage and frequency modulation scenarios.

[0004] Therefore, there is an urgent need to propose an integrated solution that can organically integrate the supercritical CO2 cycle with the CAES system and achieve dynamic multi-heat source collaboration with thermal power plants, so as to improve the overall efficiency, adjustment flexibility and response speed of the system and meet the higher requirements of modern power systems for flexibility, stability and efficiency. Summary of the Invention

[0005] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to propose a combined cycle energy storage system and operation method of a thermal power unit, supercritical carbon dioxide and compressed air. By constructing a dual-cycle coordinated energy storage-release system, efficient energy conversion, deep recovery of waste heat and rapid frequency regulation response are achieved, thereby significantly improving the flexibility of the thermal power unit and the overall energy efficiency of the system.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A combined cycle energy storage system for a thermal power unit, supercritical carbon dioxide, and compressed air, comprising a compressed air energy storage subsystem, a supercritical carbon dioxide Brayton cycle subsystem, a thermal power coordinated heat exchange subsystem, a coupled heat exchange device 13, and an intelligent control system 14;

[0008] The compressed air energy storage subsystem includes a multi-stage compressor 1, an intercooler 2, an air storage tank 3 and an air expander 4;

[0009] The supercritical carbon dioxide Brayton cycle subsystem includes a CO2 main compressor 5, a cooler 6, a main heat exchanger 7, a CO2 expander 8 and a recompression unit 9;

[0010] The thermal power cooperative sub-heat exchange system includes a steam extraction interface 10, a flue gas heat exchanger 11, and a condensate heat exchanger 12. The steam extraction interface 10 is connected between the intermediate pressure section and the reheater of the steam turbine. The flue gas heat exchanger 11 is located in front of the boiler economizer. The condensate heat exchanger 12 is arranged in front of the condensate pump inlet for auxiliary heating and waste heat recovery.

[0011] The coupled heat exchange device 13 is connected to the steam extraction interface 10, the flue gas heat exchanger 11 and the condensate heat exchanger 12 of the thermal power coordinated heat exchange subsystem, and is used to transfer the waste heat of thermal power to the compressed air and CO2 fluid respectively;

[0012] The intelligent control system 14 is used to coordinate the operating status of the above-mentioned subsystems; in the energy storage mode, the compressed air is compressed by the compressor 1 and cooled by the intermediate cooler 2 before entering the gas tank 3 for storage, and the CO2 circulates through the cooler 6 to enter the standby state; in the energy release mode, the high-pressure air in the gas tank 3 is heated by the steam extraction interface 10 and the flue gas heat exchanger 11 to drive the air expander 4 to generate electricity, and the CO2 fluid absorbs heat through the main heat exchanger 7 and enters the CO2 expander 8 to generate electricity; the control system 14 adjusts the flow and temperature of the air and CO2 sides according to the AGC signal to realize the system's joint frequency modulation and dynamic switching operation.

[0013] The multi-stage compressor 1 is a two-stage or three-stage series structure, and an intercooler 2 is provided between each stage to achieve a near-isothermal compression process, thereby improving the compression efficiency and recovering part of the compression heat for subsequent heat exchange.

[0014] An air-to-fired power heat exchange path is provided between the gas storage tank 3 and the air expander 4. The air is sequentially heat-exchanged through the steam extraction interface 10 and the flue gas heat exchanger 11, thereby achieving multi-heat source coordinated heating and raising the initial expansion temperature to no less than 500°C.

[0015] The supercritical carbon dioxide Brayton cycle subsystem is a closed Brayton cycle structure. A recompression unit 9 is provided after the CO2 main compressor 5. By controlling the compression ratio and the outlet temperature of the cooler 6, the CO2 is kept in a supercritical state at 35-40°C.

[0016] The main heat exchanger 7 is connected to the flue gas heat exchanger 11 and the exhaust end of the air expander 4 at the same time, forming a three-level thermal coupling network, which can realize multi-path conduction and reuse of heat from flue gas-CO2-air exhaust.

[0017] The intelligent control system 14 includes an AGC frequency modulation interface module, an energy storage status monitoring module, and a heat source priority judgment module. It can automatically select the air or CO2 channel for priority response based on the grid frequency modulation signal, the pressure of the gas storage tank 3, and the temperature difference of the heat exchanger, and adjust the valve opening of the steam extraction interface 10 and the inlet and outlet temperature difference of the flue gas heat exchanger in real time.

[0018] The condensate heat exchanger 12 is located at the end of the exhaust channel of the air expander 4, which can reduce the exhaust temperature to 90-120°C. At the same time, it heats the condensate heating network of the thermal power plant or preheats the boiler make-up water, realizing the cascade utilization of the exhaust waste heat.

[0019] The operating method of the combined cycle energy storage system of the present invention is as follows:

[0020] During the energy storage phase, the intelligent control system 14 activates compressor 1, performing multi-stage compression on ambient air. The compressed air is cooled by intercooler 2 and then stored in air storage tank 3. A portion of the heat from the compression process is transferred via the main heat exchanger 7 to the CO2 side or the heat storage tank for backup. During the energy release phase, high-pressure air is released from air storage tank 3, passing through steam extraction interface 10 and flue gas heat exchanger 11 for heat exchange before entering air expander 4 to generate electricity. Simultaneously, CO2 circulates through the main heat exchanger 7, absorbing waste heat from the thermal power system and CAES exhaust, expanding in CO2 expander 8 to produce work, and partially recovering the fluid in the recompression unit 9, achieving efficient closed-loop operation.

[0021] The entire system uses the intelligent control system 14 to achieve intelligent management of air flow, CO2 pressure ratio, heat source flow direction and power output, ensuring that the system has good response performance and thermal efficiency in the AGC frequency regulation scenario.

[0022] The combined cycle energy storage system of the present invention is divided into three main operating modes during operation: energy storage mode, energy release mode and combined frequency regulation mode. The specific operation process is as follows:

[0023] 1). Energy storage mode

[0024] On the air side, intelligent control system 14 activates compressor 1, compressing ambient air to a high pressure (8-20 MPa) in stages. This air is then cooled in stages by intercooler 2, reducing compression power consumption in a near-isothermal manner. Part of the compression heat is recovered by coupling heat exchanger 13 or supplied to main heat exchanger 7 for subsequent heating. The compressed air is ultimately stored in air storage tank 3, to be released for use during peak grid load periods.

[0025] CO2 side: CO2 circulates under the impetus of the main compressor 5 and the recompression unit 9. After being cooled to a supercritical state (about 35-40°C) by the cooler 6, it is placed in a standby insulation state to maintain the pressure balance and thermal inertia inside the system.

[0026] 2). Energy release mode

[0027] The intelligent control system 14 automatically switches to the energy release mode according to the grid AGC frequency modulation signal and starts the compressed air and CO2 dual-channel joint energy release process:

[0028] Air energy release path: After the high-pressure air in the gas storage tank 3 is released, it first enters the steam extraction interface 10, exchanges heat with the medium-pressure extraction steam of the thermal power plant turbine, and performs primary temperature increase; then the air flows through the flue gas heat exchanger 11, and performs deep heat exchange with the high-temperature flue gas at the tail of the boiler, so that the air temperature is further increased to above 550°C; the fully heated air enters the air expander 4 to expand and perform work, driving the generator to output electrical energy; the expanded exhaust gas finally flows into the condensate heat exchanger 12, exchanges heat with the condensate of the thermal power plant to recover the cold end heat, and realizes the cascade utilization of thermal energy.

[0029] CO2 energy release path: After being pressurized by the main compressor 5 and the recompression unit 9, CO2 is cooled by the cooler 6 and then enters the main heat exchanger 7, where it exchanges heat with heat source fluids such as the flue gas heat exchanger 11 and the exhaust of the air expander 4 to increase its temperature; the heated CO2 flows into the CO2 expander 8 to expand, perform work and generate electricity; the expanded CO2 forms a complete closed-loop cycle through the recompression unit 9 and the cooler 6.

[0030] Reuse of exhaust heat: The exhaust gas after the air and CO2 release energy is recycled through the condensate heat exchanger 12 and the main heat exchanger 7 respectively to improve the overall energy efficiency of the system.

[0031] 3). Joint frequency modulation mode

[0032] The intelligent control system 14 receives the AGC frequency modulation instruction, and determines the priority response path based on the status of the gas tank 3, the CO2 temperature and the availability of waste heat from thermal power generation; if the load changes suddenly, the CO2 path is activated first, and the CO2 expander 8 responds quickly; if the load changes continuously, the intelligent control system 14 synchronously opens the compressed air channel, controls the compressor 1 and the air expander 4 to dynamically adjust the air flow; the intelligent control system 14 adjusts the valve opening of the steam extraction interface 10 and the flue gas heat exchanger 11 in real time to achieve dynamic output control of multiple heat sources in coordination.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] The present invention couples a traditional thermal power system with a supercritical carbon dioxide system and a compressed air energy storage system. By constructing a dual-circulation coordinated energy storage-release system, it achieves efficient energy conversion, deep recovery of waste heat and rapid frequency regulation response, significantly improving the flexibility of thermal power units and the overall energy efficiency of the system, and can meet the requirements of modern power systems for flexibility, stability and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of the overall structure of a supercritical carbon dioxide compressed air combined cycle energy storage system and its integrated operation method with a thermal power unit according to the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] like Figure 1 As shown, the present invention provides a combined cycle energy storage system of a thermal power unit and supercritical carbon dioxide compressed air, which includes the following structural units:

[0038] The compressed air energy storage subsystem includes a multi-stage compressor 1, an intercooler 2, an air storage tank 3 and an air expander 4, which are used to complete air compression, heat recovery and energy release expansion; among them, the intercooler 2 is set between the compressor stages, the outlet of the last-stage compressor is connected to the air storage tank 3, and the compressed air between the outlet of the air storage tank 3 and the first-stage air expander is heated by using the compression heat recovered by the intercooler 2. The outlet of the last-stage air expander is connected to the atmosphere, and the normal-pressure gas is directly discharged into the atmosphere.

[0039] The supercritical carbon dioxide Brayton cycle subsystem includes a CO2 main compressor 5, a cooler 6, a main heat exchanger 7, a CO2 expander 8 and a recompression unit 9, forming a closed cycle path; when storing energy, the CO2 main compressor 5 is connected to the cooler 6, and the cooled CO2 is stored in a pressure vessel; when releasing energy, the CO2 is heated by the main heat exchanger 7 and then enters the CO2 expander 8. After expansion and work, it enters the recompression unit 9 for secondary compression, and the compressed CO2 enters the CO2 main compressor 5 again.

[0040] The thermal power coordinated heat exchange subsystem includes a steam extraction interface 10, a flue gas heat exchanger 11 and a condensate heat exchanger 12, which realize the injection of waste heat from the thermal power system's steam extraction, boiler flue gas and condensate; wherein, the condensate heat exchanger 12, the flue gas heat exchanger 11 and the steam extraction interface 10 are connected to a coupling heat exchange device 13, which is used to distribute the multi-source waste heat of the thermal power plant to the compressed air path or the CO2 path as needed, and input the waste heat into the main heat exchanger 7 after the coupled heat exchange, so as to realize the cascade utilization of energy and improve the utilization efficiency of the heat source.

[0041] The intelligent control system 14 is used to coordinate the operating status of each unit and realize functions such as operating mode switching, power output adjustment, heat source priority determination and power grid AGC signal response. Specific embodiments

[0043] In a 600MW thermal power plant demonstration project, a combined cycle energy storage system was deployed. The project setting conditions are as follows: the volume of gas tank 3 is 40000Nm 3 , working pressure is 15MPa; compressor 1 has an output power of approximately 30MW and adopts a three-stage compression with intermediate cooling structure; air expander 4 is a double-cylinder structure, with a designed inlet temperature of 550℃ and a maximum power output of approximately 35MW; CO2 expander 8 has a designed inlet pressure of 20MPa, a temperature of 550℃, and a single-unit output power of 12MW; flue gas heat exchanger 11 is installed at the tail of the boiler, with a flue gas inlet temperature of 600℃ and a thermal power capacity of 50MW; the control system 14 is connected to the power plant DCS and power grid dispatching platform, and has a frequency tracking capability in seconds.

[0044] The operation process is as follows:

[0045] During the nighttime off-peak period, or the energy storage phase, control system 14 activates compressor 1, compressing air into air storage tank 3. Simultaneously, intercooler 2 directs the exhaust heat into main heat exchanger 7. After energy storage is complete, the system enters energy release mode, with control system 14 issuing a frequency modulation command to release the air from air storage tank 3. The air then flows sequentially through steam extraction port 10 and flue gas heat exchanger 11, achieving combined heating from multiple heat sources. The heated air then enters air expander 4, generating power. Simultaneously, its exhaust enters condensate heat exchanger 12, preheating boiler feed water.

[0046] The CO2 system is started synchronously. After being pressurized by the main compressor 5 and recompression unit 9, the CO2 is cooled by the cooler 6 before entering the main heat exchanger 7. After absorbing heat, it enters the CO2 expander 8 to generate electricity. The control system 14 collects the pressure, temperature, and heat source flow of each subsystem in real time and adjusts the gas source ratio and valve opening according to the AGC power command, achieving compound frequency modulation control.

[0047] Measured data show that the combined cycle efficiency reaches over 63%, which is more than 15% higher than the peak-shaving efficiency of traditional thermal power plants, and the frequency regulation response time is shortened from minutes to within 10 seconds, verifying the advancement and engineering feasibility of the scheme of the present invention.

Claims

1. A combined cycle energy storage system of a thermal power unit, supercritical carbon dioxide and compressed air, characterized in that: The system includes a compressed air energy storage subsystem, a supercritical carbon dioxide Brayton cycle subsystem, a thermal power coordinated heat exchange subsystem, a coupled heat exchange device (13) and an intelligent control system (14); The compressed air energy storage subsystem includes a multi-stage compressor (1), an intercooler (2), an air storage tank (3) and an air expander (4); The supercritical carbon dioxide Brayton cycle subsystem includes a CO2 main compressor (5), a cooler (6), a main heat exchanger (7), a CO2 expander (8) and a recompression unit (9); The thermal power coordinated heat exchange subsystem includes a steam extraction interface (10), a flue gas heat exchanger (11) and a condensate heat exchanger (12); the steam extraction interface (10) is connected between the intermediate pressure section and the reheater of the steam turbine, the flue gas heat exchanger (11) is located in the front section of the boiler economizer, and the condensate heat exchanger (12) is arranged in front of the condensate pump inlet for auxiliary heating and waste heat recovery; A coupled heat exchange device (13) is connected to the steam extraction interface (10), the flue gas heat exchanger (11) and the condensate heat exchanger (12) of the thermal power coordinated heat exchange subsystem, and is used to transfer the thermal power waste heat to the compressed air and the CO2 fluid respectively; An intelligent control system (14) is used to coordinate the operating states of the above-mentioned subsystems; wherein, in the energy storage mode, the compressed air is compressed by the compressor (1) and cooled by the intermediate cooler (2) before entering the gas storage tank (3) for storage, and the CO2 circulates through the cooler (6) and enters the standby state; in the energy release mode, the high-pressure air in the gas storage tank (3) is heated by the steam extraction interface (10) and the flue gas heat exchanger (11) and then drives the air expander (4) to generate electricity, and the CO2 fluid absorbs heat through the main heat exchanger (7) and then enters the CO2 expander (8) to generate electricity; the control system (14) adjusts the flow and temperature of the air and CO2 sides according to the AGC signal to realize the system joint frequency modulation and dynamic switching operation.

2. The system according to claim 1, wherein: The multi-stage compressor (1) is a two-stage or three-stage series structure, and an intercooler (2) is provided between each stage to achieve a near-isothermal compression process, thereby improving compression efficiency and recovering part of the compression heat for subsequent heat exchange.

3. The system according to claim 1, wherein: An air-fired power heat exchange path is provided between the gas storage tank (3) and the air expander (4), and the air is sequentially heat-exchanged through the steam extraction interface (10) and the flue gas heat exchanger (11), thereby achieving multi-heat source coordinated temperature increase and raising the initial expansion temperature to no less than 500°C.

4. The system according to claim 1, wherein: The supercritical carbon dioxide Brayton cycle subsystem is a closed Brayton cycle structure, wherein a recompression unit (9) is provided after the CO2 main compressor (5), and the CO2 is kept in a supercritical state at 35-40°C by controlling the compression ratio and the outlet temperature of the cooler (6).

5. The system according to claim 1, wherein: The main heat exchanger (7) is simultaneously connected to the flue gas heat exchanger (11) and the exhaust end of the air expander (4), forming a three-level thermal coupling network, thereby realizing multi-path conduction and reuse of heat from flue gas → CO2 → exhaust air.

6. The system according to claim 1, wherein: The intelligent control system (14) includes an AGC frequency modulation interface module, an energy storage state monitoring module and a heat source priority judgment module. According to the grid frequency modulation signal, the pressure of the gas storage tank (3) and the temperature difference of the heat exchanger, it automatically selects the air or CO2 channel for priority response and adjusts the valve opening of the steam extraction interface (10) and the inlet and outlet temperature difference of the flue gas heat exchanger in real time.

7. The system according to claim 1, wherein: The condensate heat exchanger (12) is located at the end of the exhaust channel of the air expander (4), reducing the exhaust temperature to 90-120°C and simultaneously heating the condensate heating pipe network of the thermal power plant or preheating the boiler feed water, thereby realizing the cascade utilization of the exhaust waste heat.

8. The method for operating the system according to any one of claims 1 to 7, characterized in that: In the energy storage stage, the intelligent control system (14) starts the compressor (1) and performs multi-stage compression on the ambient air. The compressed air is cooled by the intercooler (2) and then enters the gas storage tank (3) for storage. Part of the heat during the compression process is introduced into the CO2 side or the heat storage tank through the main heat exchanger (7) for standby. In the energy release stage, the high-pressure air is released from the gas storage tank (3), and is heated by the steam extraction interface (10) and the flue gas heat exchanger (11) before entering the air expander (4) to generate electricity. At the same time, the CO2 circulates through the main heat exchanger (7) to absorb the waste heat of the thermal power system and the CAES exhaust, expands and performs work through the CO2 expander (8), and recovers part of the fluid by the recompression unit (9), thereby achieving efficient closed operation. The entire system realizes intelligent management of air flow, CO2 pressure ratio, heat source flow direction and power output through an intelligent control system (14), ensuring that the system has good response performance and thermal efficiency in the AGC frequency regulation scenario.

9. The operating method according to claim 8, characterized in that: The specific operation process is as follows: 1). Energy storage mode On the air side: the intelligent control system (14) starts the compressor (1), compresses the ambient air to high pressure in stages, and cools it step by step through the intercooler (2), reducing the compression power consumption in a nearly isothermal manner; part of the compression heat is recovered to the coupled heat exchange device (13) or supplied to the main heat exchanger (7) for subsequent heating; the compressed air is finally stored in the air storage tank (3) to be released and used during the peak load period of the power grid; CO2 side: CO2 circulates under the impetus of the main compressor (5) and the recompression unit (9), and is cooled to a supercritical state by the cooler (6) and then placed in a standby heat preservation state to maintain the pressure balance and thermal inertia inside the system; 2). Energy release mode The intelligent control system (14) automatically switches to the energy release mode according to the grid AGC frequency modulation signal and starts the compressed air and CO2 dual-channel combined energy release process: Air energy release path: After the high-pressure air in the gas storage tank (3) is released, it first enters the steam extraction interface (10) and exchanges heat with the medium-pressure extraction steam of the thermal power plant turbine to perform primary temperature increase; then the air flows through the flue gas heat exchanger (11) and performs deep heat exchange with the high-temperature flue gas at the tail of the boiler, so that the air temperature is further increased to above 550°C; the fully heated air enters the air expander (4) to expand and perform work, driving the generator to output electrical energy; the expanded tail gas finally flows into the condensate heat exchanger (12), exchanges heat with the condensate of the thermal power plant to recover the cold end heat, thereby realizing the cascade utilization of thermal energy; CO2 energy release path: After being pressurized by the main compressor (5) and the recompression unit (9), CO2 is cooled by the cooler (6) and then enters the main heat exchanger (7), where it exchanges heat with the heat source fluid such as the flue gas heat exchanger (11) and the exhaust of the air expander (4) to increase its temperature; the heated CO2 flows into the CO2 expander (8) to expand and generate electricity; the expanded CO2 passes through the recompression unit (9) and the cooler (6) to form a complete closed loop cycle; Reuse of exhaust heat: The exhaust gas after the air and CO2 release energy is respectively recycled through the condensate heat exchanger (12) and the main heat exchanger (7), thereby improving the overall energy efficiency of the system; 3). Joint frequency modulation mode The intelligent control system (14) receives the AGC frequency modulation instruction and determines the priority response path based on the status of the gas storage tank (3), the CO2 temperature and the availability of the waste heat of the thermal power plant; if the load changes suddenly, the CO2 path is activated first, and the CO2 expander (8) responds quickly; if the load changes continuously, the intelligent control system (14) synchronously opens the compressed air channel and controls the compressor (1) and the air expander (4) to dynamically adjust the air flow; the intelligent control system (14) adjusts the valve opening of the steam extraction interface (10) and the flue gas heat exchanger (11) in real time to achieve multi-heat source coordinated dynamic output control.

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