A method for storing energy in full sliding pressure operation of compressed air energy storage system

Abstract

The present invention relates to a method for storing energy in a compressed air energy storage system in full sliding pressure operation, wherein the compressed air energy storage system comprises a compressor unit, an expansion unit, a heat exchanger, an air storage chamber, a heat storage tank and a cold storage tank; in the compressed air energy storage process, electric energy drives the compressor unit to work, and the air is compressed to a high-temperature and high-pressure state by means of multi-stage compression, and the compression heat is recovered and stored by means of a heat exchange medium, the air enters the air storage chamber for storage while maintaining a low-temperature and high-pressure state, and the heat exchange medium enters the high-temperature heat storage tank; in the compressed air energy release process, the high-pressure air is heated by the heat exchanger, and then enters the expansion machine to perform work, and the expansion work is achieved by means of step-by-step expansion and step-by-step heating, and during the compression process, the valve opening at the compressor inlet is controlled to adjust the compression ratio of the compressor, thereby realizing the sliding pressure operation of the compressor unit, and during the expansion process, the valve opening at the air storage chamber outlet is controlled to adjust the expansion ratio of the expansion machine, thereby realizing the sliding pressure operation of the expansion machine unit.

Description

Technical Field

[0001] The invention relates to the technical field of compressed air energy storage, and in particular to a full sliding pressure operation energy storage method for a compressed air energy storage system. Background Art

[0002] Traditional compressed air energy storage technology generally adopts full constant pressure operation or partial sliding pressure operation, but in actual application, sliding pressure operation in the expansion stage will bring higher output power to better meet the load end requirements. Since the utilization rate of thermal oil is often maximized during the system design process, not only the air mass flow rate changes during the sliding pressure operation, but also the expander inlet temperature changes. The outlet pressure of the system expansion stage cannot be guaranteed to be greater than the atmospheric pressure, and the expander operating environment is unstable. Patent application document CN116608113A provides a compressed air energy storage operation system and energy storage method, which uses a cold tank to preheat air with a temperature lower than the design temperature to ensure that the air temperature is near the set value. Patent application document CN116537905A provides a distributed power adjustable two-stage compressed air energy storage system and its operation method, which separates the two-stage compression and expansion by adding an intermediate air storage chamber to achieve power adjustment. Patent CN116591791A proposes coupling the compressed air energy storage system with a thermal power plant, using the high-parameter steam of the thermal power plant to heat the compressed air to do work, thereby eliminating the heat storage device. Patent application document CN116576092A proposes using flue gas from thermal power plants to heat the compressed air in compressed air energy storage to improve energy utilization. Therefore, how to improve the efficiency and operation method of compressed air energy storage systems is one of the keys to realizing the application of compressed air energy storage technology.

[0003] The expansion process in the existing compressed air energy storage technology mainly adopts the design condition operation or semi-sliding pressure operation, and does not consider the full sliding pressure operation of the two-stage expander by reducing the expansion ratio by a certain amount during the expansion process. Therefore, this application adopts the method of controlling the mass flow rate and reducing the expansion ratio to realize the sliding pressure operation of the expansion process, thereby improving the system circulation efficiency and the utilization rate of the heat exchange medium in the heat storage tank. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a full sliding pressure operation energy storage method for a compressed air energy storage system, wherein the compressed air energy storage system comprises a compressor unit, an expansion unit, a heat exchanger, an air storage chamber, a heat storage tank and a cold storage tank; during the compressed air energy storage process, electric energy drives the compressor unit to work, and the air is compressed to a high temperature and high pressure state by a multi-stage compression method, and at the same time, the heat of compression is recovered and stored by a heat exchange medium, and the air enters the air storage chamber for storage while maintaining a low temperature and high pressure state, and the heat exchange medium enters the high temperature heat storage tank; during the compressed air energy release process, the high-pressure air is heated by the heat exchanger, and then enters the expander to perform work, and the expansion work is achieved by a step-by-step expansion and heating method; the energy storage method comprises the following steps:

[0005] The compression process uses the following steps to control the compressor unit to perform sliding pressure operation:

[0006] S1: fitting curve of total pressure ratio of simulated compressor unit changing with mass flow rate;

[0007] S2: Measure the pressure in the air storage chamber, calculate the air mass flow rate by fitting the curve of the total pressure ratio of the compressor unit with the mass flow rate, and adjust the air mass flow rate by changing the valve opening at the compressor inlet;

[0008] S3: Measure the air pressure at the inlet of the air storage chamber. If it is greater than the pressure of the air storage chamber, increase the valve opening at the inlet of the compressor. If it is less than the pressure of the air storage chamber, reduce the valve opening at the inlet of the compressor.

[0009] S4: Calculate the heat exchange medium flow rate required by the heat exchanger under the air mass flow rate;

[0010] S5: Measure the air flow rate at the heat exchanger inlet, and adjust the opening of the heat exchange medium inlet valve to the calculated opening according to the air flow rate;

[0011] S6: Measure the outlet air temperature of the heat exchanger. If the outlet air temperature is greater than the set temperature, increase the opening of the heat exchange medium inlet valve. If it is less than the set temperature, reduce the opening of the heat exchange medium inlet valve until the outlet air temperature of the heat exchanger reaches the design temperature.

[0012] S7: Measure whether the pressure in the air storage chamber reaches the maximum pressure of the air storage chamber. If so, the control process ends; if not, return to S2 and repeat the above S2-S6;

[0013] The expansion process uses the following steps to control the expansion unit to perform sliding pressure operation:

[0014] S8: Simulate the curve of total expansion ratio of the expander unit changing with mass flow rate;

[0015] S9: Measure the pressure in the gas storage chamber, calculate the total expansion ratio of the expansion unit, calculate the outlet flow of the gas storage chamber through the curve of the total expansion ratio of the expansion unit versus the mass flow rate, and adjust the opening of the outlet valve of the gas storage chamber;

[0016] S10: Measure the outlet pressure of the final expansion unit. If it is higher than atmospheric pressure and relatively close to atmospheric pressure, there is no need to adjust the opening of the gas storage chamber outlet valve. If it is lower than atmospheric pressure, the opening of the gas storage chamber outlet valve needs to be reduced. If it is significantly higher than atmospheric pressure, the opening of the gas storage chamber outlet valve needs to be increased.

[0017] S11: Calculate the air mass flow rate at the outlet of the air storage chamber and the heat exchange medium usage of the heat exchanger during the expansion process; determine whether the ratio of the air mass flow rate at the outlet of the air storage chamber to the heat exchange medium usage of the heat exchanger during the expansion process is the design value; if not, adjust the opening of the heat exchange medium inlet valve of the heat exchanger so that the ratio of the air mass flow rate at the outlet of the air storage chamber to the heat exchange medium usage of the heat exchanger reaches the design value; if so, measure the pressure of the air storage chamber;

[0018] S12: Determine whether the pressure in the air storage chamber has reached the minimum pressure. If so, the control process ends; if not, return to S9 and repeat the above S9-S11.

[0019] Furthermore, the fitting curve of the total pressure ratio of the compressor unit in S1 changing with the mass flow rate is simulated using the following formula:

[0020] P out，c =π c P in，c (1)

[0021]

[0022] η c =(h c，out，is -h c，in ) / h c，out -h c，in ) (3)

[0023] Among them, P out,c , P in,c , π c , are respectively the compressor outlet pressure, compressor inlet pressure, compressor pressure ratio, and compressor inlet air mass flow rate; h c,out 、h c,in They represent the specific enthalpy of the air at the compressor outlet and the specific enthalpy of the air at the compressor inlet, respectively. c,out,is It represents the outlet air specific enthalpy when the compressor is compressed to the same back pressure in an isentropic process; is the power consumed by air passing through the compressor, η c is the isentropic efficiency of the compressor.

[0024] When the compressor is running under variable conditions, the compressor characteristic diagram can be used to calculate:

[0025]

[0026]

[0027] Among them, π c , π c0 are respectively the compressor pressure ratio and the compressor design point pressure ratio. are the relative flow rate and relative speed of the compressor, η c0 is the isentropic efficiency of the compressor design point, parameter c 1 、c 2 、c 3 Calculate as follows:

[0028]

[0029]

[0030]

[0031] Where p and q are parameters.

[0032] Furthermore, the total expansion ratio of the expansion unit in S8 is simulated with the mass flow rate using the following formula, and the characteristic formula of the expansion unit is obtained according to the Flugel formula:

[0033]

[0034]

[0035] In the formula, π t , π t0 They are working point expansion ratio and design point expansion ratio respectively; is the relative flow rate of the expander; is the relative speed of the expander; is the relative isentropic efficiency of the expander.

[0036] Furthermore, the calculation formula used in S4 is as follows:

[0037] According to the law of conservation of mass, the heat released by the air is equal to the heat absorbed by the heat transfer medium.

[0038]

[0039] is the air mass flow rate, is the mass flow rate of heat transfer medium, h in,hot 、h out,hot are the enthalpy of air inlet and outlet in the heat exchanger, respectively. in,cold 、h out,cold are the inlet enthalpy of the heat exchanger and the outlet enthalpy of the heat exchanger, respectively. Indicates heat absorption;

[0040] The heat exchanger adopts a shell and tube heat exchanger. The air flows on the tube side and the heat transfer medium flows on the shell side. The convection heat transfer coefficient and the total heat transfer coefficient of the heat exchanger can be expressed as:

[0041]

[0042]

[0043] Where, T hot,in , T hot,out are the air inlet temperature and the air outlet temperature of the heat exchanger respectively; T cold,in , T cold,out are the inlet temperature of the heat exchange medium in the heat exchanger and the outlet temperature of the heat exchange medium in the heat exchanger respectively; U is the heat transfer coefficient; A is the heat transfer area of ​​the heat exchanger; h s and h t are the heat transfer coefficients on the shell side and the tube side, respectively, 0 and d i are the outer and inner diameters of the tube, R fs and R ft are the fouling resistance on the shell side and tube side, respectively;

[0044] The heat transfer rate of the heat exchanger can be calculated by the following formula:

[0045]

[0046] Beneficial effects of the present invention:

[0047] (1) During the compression process, the compressed air energy storage system controls the valve opening at the compressor inlet to achieve flow control during the compression process, thereby adjusting the compressor compression ratio and achieving sliding pressure operation of the compressor unit.

[0048] (2) During the compression process of the compressed air energy storage system, the heat exchanger measures the air outlet temperature through a temperature measuring device and controls the valve opening at the heat exchange medium inlet to keep the air outlet temperature constant.

[0049] (3) During the expansion process, the compressed air energy storage system controls the flow rate by controlling the valve opening at the outlet of the air storage chamber, thereby adjusting the expansion ratio of the expander and realizing sliding pressure operation of the expander unit.

[0050] (4) In order to make full use of the heat storage medium in the heat storage tank, the gas storage volume and the amount of heat exchange medium used in the gas storage process are calculated, and the flow control method is used to pass the heat exchange medium and compressed air into the heat exchanger in proportion for heat exchange; the expansion ratio is appropriately reduced to ensure the normal operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of compressed air energy storage system;

[0052] Figure 2 This is the flow chart of the compressor compression process control;

[0053] Figure 3 This is the control flow chart of the expander expansion process. DETAILED DESCRIPTION

[0054] The present invention will be further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0055] Figure 1 This is a schematic diagram of a compressed air energy storage system. The system includes a compressor unit, an expansion unit, a heat exchanger, an air storage chamber, a heat storage tank, and a cold storage tank. In the compressed air energy storage process, the remaining electricity in the power grid or the new energy electricity drives the compressor unit to work. Through multi-stage compression, the air is compressed to a high temperature and high pressure state. At the same time, the heat exchange medium is used to recover and store the compression heat. The air is kept in a low temperature and high pressure state and enters the air storage chamber for storage. The heat exchange medium enters the high temperature heat storage tank to achieve the storage of electricity. In the compressed air energy release process, the high-pressure air is heated by the first-stage heat exchanger and then enters the first-stage expander to perform work. The expansion work is achieved through step-by-step expansion and heating, which drives the generator to generate electricity and complete the release of electricity.

[0056] like Figure 2-3 As shown, this embodiment also provides a method for storing energy in a compressed air energy storage system in full sliding pressure operation, which uses the above compressed air energy storage operation system to store energy, including the following steps:

[0057] The compression process uses the following steps to control the compressor unit to perform sliding pressure operation:

[0058] S1: fitting curve of total pressure ratio of simulated compressor unit changing with mass flow rate;

[0059] The fitting curve of the total pressure ratio of the compressor unit changing with mass flow rate is simulated using the following formula:

[0060] P out，c =π C P in,c (1)

[0061]

[0062] η c =(h c，our，is -h c，in ) / (h c，our -h c，in ) (3)

[0063] Among them, Pout,c , P in,c , π c , are respectively the compressor outlet pressure, compressor inlet pressure, compressor pressure ratio, and compressor inlet air mass flow rate; h c,out 、h c,in They represent the specific enthalpy of the air at the compressor outlet and the specific enthalpy of the air at the compressor inlet, respectively. c,out,is It represents the outlet air specific enthalpy when the compressor is compressed to the same back pressure in an isentropic process; is the power consumed by air passing through the compressor, η c is the isentropic efficiency of the compressor.

[0064] When the compressor is running under variable conditions, the compressor characteristic diagram can be used for calculation. The compressor characteristic diagram is fitted based on physics and a large amount of experimental data. The formula is:

[0065]

[0066]

[0067] Among them, π c , π c0 are respectively the compressor pressure ratio and the compressor design point pressure ratio. are the relative flow rate and relative speed of the compressor, η c0 is the isentropic efficiency of the compressor design point, parameter c 1 、c 2 、c 3 Calculate as follows:

[0068]

[0069]

[0070]

[0071] In the formula, p, q are parameters;

[0072] S2: Measure the pressure in the air storage chamber, calculate the air mass flow rate by fitting the curve of the total pressure ratio of the compressor unit with the mass flow rate, and adjust the air mass flow rate by changing the valve opening at the compressor inlet;

[0073] S3: Measure the air pressure at the inlet of the air storage chamber. If it is greater than the pressure of the air storage chamber, increase the valve opening at the inlet of the compressor. If it is less than the pressure of the air storage chamber, reduce the valve opening at the inlet of the compressor.

[0074] S4: Calculate the heat exchange medium flow rate required by the heat exchanger under the air mass flow rate;

[0075] S5: Measure the air flow rate at the heat exchanger inlet, and adjust the opening of the heat exchange medium inlet valve to the calculated opening according to the air flow rate;

[0076] S6: Measure the outlet air temperature of the heat exchanger. If the outlet air temperature is greater than the set temperature, increase the opening of the heat exchange medium inlet valve. If it is less than the set temperature, reduce the opening of the heat exchange medium inlet valve until the outlet air temperature of the heat exchanger reaches the design temperature.

[0077] S7: Measure whether the pressure in the air storage chamber reaches the maximum pressure of the air storage chamber. If so, the control process ends; if not, return to S2 and repeat the above S2-S6.

[0078] The expansion process uses the following steps to control the expansion unit to perform sliding pressure operation:

[0079] S8: Simulate the curve of total expansion ratio of the expander unit changing with mass flow rate;

[0080] S9: Measure the pressure in the gas storage chamber, calculate the total expansion ratio of the expansion unit, calculate the outlet flow of the gas storage chamber through the curve of the total expansion ratio of the expansion unit versus the mass flow rate, and adjust the opening of the outlet valve of the gas storage chamber;

[0081] S10: Measure the outlet pressure of the final expansion unit. If it is higher than atmospheric pressure and relatively close to atmospheric pressure, there is no need to adjust the opening of the gas storage chamber outlet valve. If it is lower than atmospheric pressure, the opening of the gas storage chamber outlet valve needs to be reduced. If it is significantly higher than atmospheric pressure, the opening of the gas storage chamber outlet valve needs to be increased.

[0082] S11: Calculate the air mass flow rate at the outlet of the air storage chamber and the heat exchange medium usage of the heat exchanger during the expansion process; determine whether the ratio of the air mass flow rate at the outlet of the air storage chamber to the heat exchange medium usage of the heat exchanger during the expansion process is the design value; if not, adjust the opening of the heat exchange medium inlet valve of the heat exchanger so that the ratio of the air mass flow rate at the outlet of the air storage chamber to the heat exchange medium usage of the heat exchanger reaches the design value; if so, measure the pressure of the air storage chamber;

[0083] S12: Determine whether the pressure in the air storage chamber has reached the minimum pressure. If so, the control process ends; if not, return to S9 and repeat the above S9-S11.

[0084] The expansion process can achieve efficient utilization of the heat storage capacity of the heat exchange medium through this regulation method, and also realize the full sliding pressure process of the expansion process.

[0085] Although this specification is described according to implementation modes, not every implementation mode includes only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for storing energy in full sliding pressure operation of a compressed air energy storage system, characterized in that: The compressed air energy storage system comprises a compressor unit, an expansion unit, a heat exchanger, an air storage chamber, a heat storage tank and a cold storage tank; in the compressed air energy storage process, electric energy drives the compressor unit to work, and the air is compressed to a high temperature and high pressure state through a multi-stage compression method, and the compression heat is recovered and stored by a heat exchange medium. The air is kept in a low temperature and high pressure state and enters the air storage chamber for storage, and the heat exchange medium enters the high temperature heat storage tank; in the compressed air energy release process, the high pressure air is heated by the heat exchanger, and then enters the expander to do work, and the expansion work is achieved by a step-by-step expansion and heating method; the energy storage method comprises the following steps: The compression process uses the following steps to control the compressor unit to perform sliding pressure operation: S1: fitting curve of total pressure ratio of simulated compressor unit changing with mass flow rate; S2: Measure the pressure in the air storage chamber, calculate the air mass flow rate by fitting the curve of the total pressure ratio of the compressor unit with the mass flow rate, and adjust the air mass flow rate by changing the valve opening at the compressor inlet; S3: Measure the air pressure at the inlet of the air storage chamber. If it is greater than the pressure of the air storage chamber, increase the valve opening at the inlet of the compressor. If it is less than the pressure of the air storage chamber, reduce the valve opening at the inlet of the compressor. S4: Calculate the heat exchange medium flow rate required by the heat exchanger under the air mass flow rate; S5: Measure the air flow rate at the heat exchanger inlet, and adjust the opening of the heat exchange medium inlet valve to the calculated opening according to the air flow rate; S6: Measure the outlet air temperature of the heat exchanger. If the outlet air temperature is greater than the set temperature, increase the opening of the heat exchange medium inlet valve. If it is less than the set temperature, reduce the opening of the heat exchange medium inlet valve until the outlet air temperature of the heat exchanger reaches the design temperature. S7: Measure whether the pressure in the air storage chamber reaches the maximum pressure of the air storage chamber. If so, the control process ends; if not, return to S2 and repeat the above S2-S6; The expansion process uses the following steps to control the expansion unit to perform sliding pressure operation: S8: Simulate the curve of total expansion ratio of the expander unit changing with mass flow rate; S9: Measure the pressure in the gas storage chamber, calculate the total expansion ratio of the expansion unit, calculate the outlet flow of the gas storage chamber through the curve of the total expansion ratio of the expansion unit versus the mass flow rate, and adjust the opening of the outlet valve of the gas storage chamber; S10: Measure the outlet pressure of the final expansion unit. If it is higher than atmospheric pressure and relatively close to atmospheric pressure, there is no need to adjust the opening of the gas storage chamber outlet valve. If it is lower than atmospheric pressure, the opening of the gas storage chamber outlet valve needs to be reduced. If it is significantly higher than atmospheric pressure, the opening of the gas storage chamber outlet valve needs to be increased. S11: Calculate the air mass flow rate at the outlet of the air storage chamber and the heat exchange medium usage of the heat exchanger during the expansion process; determine whether the ratio of the air mass flow rate at the outlet of the air storage chamber to the heat exchange medium usage of the heat exchanger during the expansion process is the design value; if not, adjust the opening of the heat exchange medium inlet valve of the heat exchanger so that the ratio of the air mass flow rate at the outlet of the air storage chamber to the heat exchange medium usage of the heat exchanger reaches the design value; if so, measure the pressure of the air storage chamber; S12: Determine whether the pressure in the air storage chamber has reached the minimum pressure. If so, the control process ends; if not, return to S9 and repeat the above S9-S11.

2. A method for storing energy in a compressed air energy storage system in full sliding pressure operation according to claim 1, characterized in that , the fitting curve of the total pressure ratio of the compressor unit in S1 changing with the mass flow rate is simulated using the following formula: P out,c =π c P in,c (1) η c =(h c,out,is -h c,in ) / (h c,out -h c,in ) (3) Among them, P out,c , P in,c , π c , are respectively the compressor outlet pressure, compressor inlet pressure, compressor pressure ratio, and compressor inlet air mass flow rate; h c,out 、h c,in They represent the specific enthalpy of the air at the compressor outlet and the specific enthalpy of the air at the compressor inlet, respectively. c,out,is It represents the outlet air specific enthalpy when the compressor is compressed to the same back pressure in an isentropic process; is the power consumed by air passing through the compressor, η c is the isentropic efficiency of the compressor; When the compressor is running under variable conditions, the compressor characteristic diagram is used to calculate: Among them, π c , π c0 are respectively the compressor pressure ratio and the compressor design point pressure ratio. are the relative flow rate and relative speed of the compressor, η c0 is the isentropic efficiency of the compressor design point, and the parameters c1, c2, and c3 are calculated as follows: Where p and q are parameters.

3. A method for storing energy in a compressed air energy storage system in full sliding pressure operation according to claim 1, characterized in that The total expansion ratio of the expansion unit in S8 is simulated with the mass flow rate using the following formula, and the characteristic formula of the expansion unit is obtained according to the Flugel formula: In the formula, π t , π t0 They are working point expansion ratio and design point expansion ratio respectively; is the relative flow rate of the expander; is the relative speed of the expander; is the relative isentropic efficiency of the expander.

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