A calculation method for the gas storage volume of an underground cavern for compressed air energy storage

Abstract

The present invention relates to a method for calculating the gas storage volume of an underground cavern for compressed air energy storage, which includes obtaining the exhaust temperature, pressure, flow rate of the compressor and the duration of each working condition; setting parameters such as the initial air temperature, pressure, and initial rock mass temperature of each working condition of the gas storage cavern; calculating the initial gas storage volume of the gas storage cavern; successively calculating the change curves of the air temperature, pressure, and rock mass temperature in the gas storage cavern over time under each working condition, and judging whether the errors between the air temperature and pressure in the gas storage cavern at the end of the storage working condition and the air temperature and pressure in the gas storage cavern at the start of the charging working condition; calculating the final gas storage volume of the gas storage cavern. By using the thermodynamic principles of the air and rock mass in the gas storage cavern, a reasonable cavern volume can be quickly calculated, and a relatively accurate gas storage cavern volume can be obtained. During the calculation process, the air temperature change curve and air pressure change curve are updated according to the gas storage cavern volume, accurately reflecting the temperature change and pressure change in the gas storage cavern, making the calculation result more accurate.

Description

Technical Field

[0001] The invention relates to a method for calculating the gas storage volume of a compressed air energy storage underground cavern, belonging to the technical field of energy storage. Background Art

[0002] It is well known that energy storage technology is a means to alleviate the impact of renewable energy on the power grid, and it is also capable of frequency and peak regulation, and has been a hot topic of research in recent years. Compressed air energy storage, as a form of energy storage, has the characteristics of cleanliness, efficiency, and scalability, and is one of the most promising energy storage technologies. The thermal system of the compressed air system includes system components such as the compressor system, heat exchange system, heat storage system, turbine system, and air storage chamber. The capacity of the air storage chamber is closely related to the design and operation of the compressed air energy storage system. Compressors and turbines are always operating under variable operating conditions, and a reasonable air storage volume plays a key role in the operating conditions of compressors and turbines.

[0003] According to preliminary estimates, for artificial caverns as gas storage chambers, when the gas storage space is 250,000 m 3 The unit cost of large tank is about 1200 yuan / m 3 The cost of tunnel unit is about RMB 2400 / m 3 When the gas storage space is 350,000 m 3 The unit cost of large tank is about 1000 yuan / m 3 The cost of tunnel unit is about 2000 yuan / m 3 The deviation of gas storage space will inevitably lead to the deviation of investment.

[0004] For example, in the authorization announcement number “CN109543214B”, the air storage chamber capacity estimation method and device of the compressed air energy storage system is used in the process S1 step of the process to obtain the air temperature change curve and the air pressure change curve of the air storage chamber. The air storage chamber capacity is used in the process S2 and S3 steps. The air storage chamber capacity is calculated based on the storage capacity. In step S1, the air storage chamber capacity is still unknown and can only be estimated. Therefore, the obtained air temperature and air pressure change curves are only estimates and cannot accurately reflect the temperature and pressure changes in the air storage chamber. The calculation process has no feedback mechanism, and the air temperature and air pressure change curves are updated according to the air storage chamber capacity. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for calculating the gas storage volume of a compressed air energy storage underground cavern to solve the problems raised in the above background technology.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for calculating the gas storage volume of a compressed air energy storage underground cavern comprises the following steps:

[0008] Step 1: Obtain the compressor exhaust temperature, pressure, flow rate, and the duration of each working condition based on the operating status of the compressed air energy storage system;

[0009] Step 2: Set the initial air temperature, pressure, and initial rock mass temperature parameters before the air storage cavern charging condition, after the air storage cavern charging condition, after the air storage condition, after the air discharging condition, and after the waiting-to-store condition;

[0010] Step 3: Calculate the initial air storage volume of the air storage cavern;

[0011] Step 4: Calculate the curves of the air temperature, pressure, and rock mass temperature in the air storage cavern over time under each working condition successively according to the air principle in the air storage cavern and the rock mass thermodynamics principle;

[0012] After one cycle of the compressed air energy storage system, determine whether the air temperature and pressure in the air storage cavern at the end of the waiting-to-store condition and the air temperature and pressure in the air storage cavern at the start of the charging condition are within the error range; if within the error range, proceed to Step 5; if outside the error range, return to Step 2, and assign the parameters obtained at the end of the current waiting-to-store condition calculation to the parameters before the charging condition as the initial values for the calculation in Step 2;

[0013] Step 5: Calculate the final air storage volume of the air storage cavern, and determine whether the final air storage volume of the air storage cavern and the initial air storage volume of the air storage cavern are within the error range; if outside the error range, return to Step 3 and assign the calculated final air storage volume of the air storage cavern to the initial air storage volume of the air storage cavern.

[0014] Preferably, in Step 4, calculate the control equations for the charging condition, air storage condition, air discharging condition, and waiting-to-store condition successively according to the initial air storage volume, and use the air temperature, pressure, and rock mass temperature parameters at the end of the previous working condition obtained by solving as the initial conditions at the start of the next working condition.

[0015] Preferably, Step 3 calculates the initial air storage volume of the air storage cavern according to the following formula:

[0016]

[0017] where, V represents the initial air storage volume of the air storage cavern, m(t) represents the compressor exhaust flow rate during the charging process, t0 represents the start time of the charging condition, t1 represents the end time of the charging condition, P0 represents the air pressure in the air storage cavern at the start of the charging condition, P1 represents the air pressure in the air storage cavern at the end of the charging condition, T0 represents the air temperature in the air storage cavern at the start of the charging condition, T1 represents the air temperature in the air storage cavern at the end of the charging condition, and R represents the gas constant;

[0018] The initial inner diameter of the air storage cavern and the initial heat exchange area of the air storage cavern can be calculated according to the following formula:

[0019]

[0020] A = 4πr in 2

[0021] where r in represents the inner diameter of the gas storage cavern, and A represents the heat exchange area of the gas storage cavern.

[0022] Preferably, the control equations include the air differential equation of the gas storage cavern, the air state equation of the gas storage cavern, and the rock mass heat conduction differential equation.

[0023] Preferably, the air differential equation of the gas storage cavern:

[0024] Vd(ρc p T) + Ah(T - T w )dt = amc p T in dt

[0025] where V represents the volume of the gas storage cavern calculated according to step two, ρ represents the air density in the gas storage cavern, c p represents the specific heat capacity at constant pressure of the air in the gas storage cavern, T represents the air temperature in the gas storage cavern, T in represents the air temperature entering the cavern, A represents the heat exchange area of the gas storage cavern, h represents the heat transfer coefficient between the air and the surface of the gas storage cavern, T w represents the temperature of the wall of the gas storage cavern, m represents the air flow rate entering the gas storage cavern, and a represents the operating state of the compressed air energy storage system; a = 1 under the charging condition, a = -1 under the discharging condition, and a = 0 under the gas storage condition and the waiting-to-store condition;

[0026] The air state equation of the gas storage cavern:

[0027] P = ρRT

[0028] where P represents the air pressure in the gas storage cavern, ρ represents the air density in the gas storage cavern, R represents the gas constant, and T represents the air temperature in the gas storage cavern;

[0029] The rock mass heat conduction differential equation:

[0030]

[0031] where T R represents the temperature of the rock mass of the gas storage cavern, λ R represents the thermal conductivity of the rock mass of the gas storage cavern, ρ R represents the density of the rock mass of the gas storage cavern, c R represents the specific heat capacity of the rock mass of the gas storage cavern, and r represents the radius of the rock mass of the gas storage cavern.

[0032] Preferably, it includes:

[0033] Boundary conditions:

[0034]

[0035]

[0036] Where, T R represents the temperature of the rock mass in the gas storage cavern, T represents the air temperature in the gas storage cavern, T out represents the temperature of the outer surface of the rock mass in the gas storage cavern, h represents the heat transfer coefficient between the air and the surface of the gas storage cavern, T w represents the temperature of the wall surface of the gas storage cavern, λ R represents the thermal conductivity of the rock mass in the gas storage cavern, r out represents the outer diameter of the rock mass in the gas storage cavern, r in represents the inner diameter of the rock mass in the gas storage cavern;

[0037] Initial conditions:

[0038] T(0) = T0

[0039] T R (0) = T R0

[0040] T(0) represents the initial condition of the air temperature in the gas storage cavern, T R (0) represents the initial condition of the temperature of the rock mass in the gas storage cavern, T0 represents the air temperature in the gas storage cavern before the gas filling operation, T R0 represents the temperature of the rock mass in the gas storage cavern before the gas filling operation.

[0041] The present invention has the following beneficial effects:

[0042] By using the thermodynamic principles of the air and rock mass in the gas storage cavern, a reasonable cavern volume can be quickly calculated, and a relatively accurate gas storage cavern volume can be obtained, providing a reliable basis for the design and operation of the compressed air energy storage system.

[0043] Save the investment in the compressed air energy storage system and improve the energy utilization efficiency.

[0044] During the calculation process, the air temperature change curve and the air pressure change curve are updated according to the gas storage chamber capacity, accurately reflecting the temperature change and pressure change in the gas storage chamber, making the calculated initial gas storage volume of the gas storage cavern more accurate. Description of the drawings

[0045] Figure 1 It is a schematic flow chart of the calculation method of the present invention;

[0046] Figure 2 It is a schematic flow chart of the compressed air energy storage system of the present invention;

[0047] Figure 3 is the curve of the air pressure change in the chamber of the present invention;

[0048] Figure 4 is the curve of the air temperature change in the chamber of the present invention;

[0049] Figure 5 are the specific indicators of the compressor of the present invention. Specific Embodiments

[0050] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0051] During the low valley of the power grid load, the compressed air energy storage system absorbs the excess electricity of the power grid, drives the compressor to do work, compresses the air into high-pressure air and stores it in the gas storage chamber. Heat is generated during the compression process, and the heat is exchanged out through the heat exchange system and stored in the heat storage system. During the peak of the power grid load, the compressed air energy storage system releases high-pressure air from the gas storage chamber, enters the turbine to expand and do work to generate electricity and send it to the power grid, and absorbs the heat stored in the heat storage system through the heat exchange system during the work process.

[0052] As Figure 2 shown, the compressed air energy storage system includes: a compressor, a turbine, a heat exchange unit, a heat storage unit, a gas storage unit, etc.

[0053] The compressor includes several compression cylinders. The compression cylinders are connected in series with the heat exchanger through air pipelines. The inlet of the first-stage compression cylinder is connected to the atmospheric environment, and the final exhaust outlet of the compression cylinder is connected to the inlet of the gas storage unit through an air pipeline. The turbine includes several turbine cylinders. The turbine cylinders are connected in series with the heat exchanger through air pipelines. The inlet of the first-stage turbine cylinder is connected to the outlet of the gas storage unit through an air pipeline, and the final exhaust outlet of the turbine cylinder is connected to the atmospheric environment. The heat exchange unit includes several heat exchangers. The heat exchanger includes a water side and an air side. The air side is respectively connected to the compression cylinders of the compressor and the turbine cylinders of the turbine, and the water side is respectively connected to the high-temperature water storage tank and the low-temperature water storage tank in the heat storage unit through water pipelines. The heat storage unit includes a high-temperature water storage tank and a low-temperature water storage tank, which are respectively connected to the water side of the heat exchanger in the heat exchange unit through water pipelines. The gas storage unit includes a gas storage chamber, which is connected to the inlet of the turbine and the outlet of the compressor through air pipelines.

[0054] During the charging condition, the compressor receives the electric energy from the power system, does work through several compression cylinders, compresses the air from the atmospheric pressure to a certain pressure and stores it in the gas storage chamber. Heat is generated during the compression process, and the heat is transferred to the water through the heat exchanger and stored in the high-temperature water storage tank.

[0055] During the air release condition, the compressed air in the gas storage chamber enters the turbine to do work and generate electric energy. During the air expansion process, the temperature drops. The air is heated by the heat in the high-temperature water storage tank, and the heated air enters the turbine. The water cooled by the air enters the low-temperature water storage tank.

[0056] Generally, in a complete charge-discharge cycle of compressed air energy storage, there are the following four processes in the gas storage space: 1. Charging condition: The compressor does work to charge the gas storage chamber; 2. Gas storage condition: The charging stops, and the gas storage chamber is in a static state; 3. Air release condition: The gas storage chamber releases gas to drive the turbine to do work; 4. Waiting-to-store condition: The air release stops, and the gas storage chamber is in a static state.

[0057] As Figure 1 、 3 shown in Figure 4:

[0058] Step 1: Set the operating state parameters of the compressed air energy storage system, including the temperature, pressure, flow rate of the compressor exhaust entering the chamber, and the duration of each condition, etc.

[0059] The compressor operates with variable frequency according to the charging process. According to the calculation of the operating conditions of the compressor, the exhaust outlet temperature of each stage of the compression cylinder is 190°C, the temperature of the compressor exhaust entering the gas storage chamber after heat exchange is 60°C, the air flow rate at the compressor outlet is approximately 1600 t / h, and the pressure change range at the compressor outlet during the charging process is 13.3 - 17.3 MPa, and the change curve is approximately linear.

[0060] The specific indicators of the compressor are as Figure 5 shown;

[0061] According to the material balance calculation of the compressed air energy storage system, the charging process lasts about 9 hours, the gas storage process lasts 3 hours, the air release process lasts 6 hours, and the waiting-to-store time lasts 6 hours.

[0062] Step 2: Set parameters such as the initial air temperature, pressure, and initial rock mass temperature of the gas storage chamber.

[0063] Set the air temperature of the gas storage chamber before the charging condition as T0, the pressure as P0, and the rock mass temperature as T R0 ; the air temperature of the gas storage chamber after the charging condition (before the gas storage condition) as T1, the pressure as P1, and the rock mass temperature as T R1 ; the air temperature of the gas storage chamber after the gas storage condition (before the air release condition) as T2, the pressure as P2, and the rock mass temperature as T R2 ; the air temperature of the gas storage chamber after the air release condition (before the waiting-to-store condition) as T3, the pressure as P3, and the rock mass temperature as T R3 ; the air temperature of the gas storage chamber after the waiting-to-store condition as T4, the pressure as P4, and the rock mass temperature as T R4 .

[0064] In the first cycle of calculation, set the initial temperature values as T0 = T1 = T2 = T3 = T4 = 50 °C, and T R0 = 30 °C; set the initial pressure values as P0 = 12.8 MPa, P1 = 16.8 MPa, P2 = 16.8 MPa, P3 = 12.8 MPa, P4 = 12.8 MPa. In subsequent calculations, update the temperature and pressure values according to the calculation results.

[0065] Step 3: Calculate the initial gas storage volume of the gas storage cavern.

[0066]

[0067] The initial gas storage volume of the gas storage cavern obtained from the first cycle of calculation is 357,400 m 3 .

[0068] Estimate the inner diameter r in of the cavern and the heat exchange area A. The calculation formula is:

[0069]

[0070] A = 4πr in 2

[0071] The inner diameter of the gas storage cavern obtained from the first cycle of calculation is approximately 44 m, and the heat exchange area is approximately 24,300 m 2 . Step 4: Calculate the thermodynamic processes of the air and rock mass in the gas storage cavern.

[0072] Control equations:

[0073] Differential equation of air in the gas storage cavern:

[0074] Vd(ρc p T) + Ah(T - T w )dt = amc p T in dt

[0075] State equation of air in the gas storage cavern:

[0076] P = ρRT

[0077] Differential equation of heat conduction in the rock mass:

[0078]

[0079] Boundary conditions:

[0080]

[0081]

[0082] Initial conditions:

[0083] T(0) = T0

[0084] T R (0) = T R0

[0085] Solution sequence: 1) Solve the control equations for the gas charging condition to obtain the curves of the air temperature, pressure, and rock mass temperature in the gas storage cavern over time during the gas charging condition, and use the temperature, pressure, and other state parameters at the end of the gas charging condition as the boundary conditions and initial conditions for the gas storage condition; 2) Solve the control equations for the gas storage condition to obtain the curves of the air temperature, pressure, and rock mass temperature in the gas storage cavern over time during the gas storage condition, and use the temperature, pressure, and other state parameters at the end of the gas storage condition as the boundary conditions and initial conditions for the gas discharging condition; 3) Solve the control equations for the gas discharging condition to obtain the curves of the air temperature, pressure, and rock mass temperature in the gas storage cavern over time during the gas discharging condition, and use the temperature, pressure, and other state parameters at the end of the gas discharging condition as the boundary conditions and initial conditions for the waiting-to-store condition; 4) Solve the control equations for the waiting-to-store condition to obtain the curves of the air temperature, pressure, and rock mass temperature in the gas storage cavern over time during the waiting-to-store condition.

[0086] The curves of the air temperature and pressure in the gas storage cavern are obtained as Figure 3 、 4 shown.

[0087] It can be seen from the figure that at the start of gas charging, the air temperature in the gas storage cavern is 50 °C and the pressure is 12.8 MPa, and at the end of the waiting-to-store condition, the air temperature in the gas storage cavern is 49.5 °C and the pressure is 12.79 MPa.

[0088] Judge whether the air temperature and pressure in the gas storage cavern at the end of the waiting-to-store condition are within the error range of the air temperature and pressure in the gas storage cavern at the start of the gas charging condition; the error range is set to 1.5%.

[0089] Calculate the first and second indicators E1 and E2:

[0090] The first cycle of calculation gives

[0091]

[0092]

[0093] E1, E2 < 1.5% meets the requirements, proceed to step five

[0094] Step five:

[0095] Calculate the final gas storage volume of the gas storage cavern, the calculation formula is:

[0096]

[0097] The gas storage volume calculated in the first cycle is 401,800 m³ 3 . Among them, the temperatures T0 and T1, and the pressures P0 and P1 are the temperatures and pressures calculated in Step 4.

[0098] Judge whether V1 and V in Step 3 are within a reasonable error range.

[0099] The error range is set to 1.5%, and the third index E3 is calculated:

[0100] Calculated in the first cycle

[0101] If it exceeds the error range, return to Step 3, and assign the V1 calculated this time to the gas storage chamber volume V in Step 3 for the next cycle of calculation.

[0102] After multiple iterative calculations, the final gas storage volume is approximately 400,000 m³ 3 . The calculation is completed.

[0103] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A method for calculating the gas storage volume of a compressed air energy storage underground cavern, characterized by: The following steps are involved: Step 1: Obtain the compressor exhaust temperature, pressure, flow rate, and duration of each operating condition based on the operating status of the compressed air energy storage system; Step 2: Set the initial air temperature, pressure, and initial rock temperature parameters before the gas storage chamber is filled, after the gas filling, after the gas storage, after the gas discharge, and after the waiting storage condition; Step 3: Calculate the initial gas storage volume of the gas storage chamber; Step 4: Based on the air principle of the gas storage chamber and the thermodynamic principle of rock mass, the time-varying curves of the air temperature, pressure and rock mass temperature of the gas storage chamber under various working conditions are calculated in sequence; After the compressed air energy storage system cycles once, determine whether the air temperature and pressure of the gas storage tank at the end of the waiting state and the air temperature and pressure of the gas storage tank at the beginning of the filling state are within the error range; if they are within the error range, proceed to step 5; if they are outside the error range, return to step 2, and assign the parameters at the end of the waiting state obtained in this calculation to the parameters before the filling state as the initial values calculated in step 2; Step 5: Calculate the final gas storage volume of the gas storage chamber, and determine whether the final gas storage volume and the initial gas storage volume of the gas storage chamber are within the error range; if they are outside the error range, return to step 3 and assign the calculated final gas storage volume to the initial gas storage volume of the gas storage chamber; Step 3: Calculate the initial gas storage volume of the gas storage chamber according to the following formula: in, Indicates the initial gas storage volume of the gas storage chamber, Indicates the exhaust flow of the compressor during the charging process. Indicates the start time of the inflation condition. Indicates the end time of the inflation condition. Indicates the air pressure of the gas storage tank when the inflation condition begins. Indicates the air pressure of the gas storage tank at the end of the inflation condition. Indicates the air temperature of the gas storage tank when the inflation condition begins. Indicates the air temperature of the gas storage tank at the end of the inflation condition. represents the gas constant; The initial gas storage chamber inner diameter and initial gas storage chamber heat exchange area are calculated according to the following formula: in, Indicates the inner diameter of the gas storage chamber. Indicates the heat exchange area of the gas storage chamber.

2. The method for calculating the gas storage volume of a compressed air energy storage underground cavern according to claim 1, characterized in that: In step 4, the control equations of the inflation condition, gas storage condition, gas release condition and waiting-for-storage condition are calculated in sequence according to the initial gas storage volume, and the air temperature, pressure and rock temperature parameters of the gas storage chamber at the end of the previous condition are used as the initial conditions at the beginning of the next condition.

3. The method for calculating the gas storage volume of a compressed air energy storage underground cavern as claimed in claim 2, characterized in that: The control equations include the air differential equation of the gas storage chamber, the state equation of the air of the gas storage chamber, and the rock heat conduction differential equation.

4. The method for calculating the gas storage volume of a compressed air energy storage underground cavern as claimed in claim 3, characterized in that: Differential equation of air in gas storage tank: in, represents the volume of the gas storage chamber calculated according to step 2, Indicates the air density of the gas storage chamber, It represents the specific heat capacity of the air in the gas storage tank at constant pressure. Indicates the air temperature of the gas storage tank. Indicates the temperature of the air entering the cavern. represents the heat exchange area of the gas storage chamber, Indicates the heat transfer coefficient between air and gas storage chamber surface, Indicates the wall temperature of the gas storage chamber, Indicates the air flow entering the gas storage tank, Indicates the operating status of the compressed air energy storage system; under the inflation condition , under deflation conditions , gas storage conditions and waiting for storage conditions ; The state equation of air in the gas storage tank is: in, Indicates the air pressure of the gas storage tank. Indicates the air density of the gas storage chamber, represents the gas constant, Indicates the air temperature of the gas storage chamber; Differential equation for heat conduction in rock mass: in, represents the rock temperature of the gas storage chamber, represents the thermal conductivity of the gas storage rock mass, represents the rock density of the gas storage chamber, represents the specific heat capacity of the gas storage rock mass, Indicates the rock mass radius of the gas storage chamber.

5. The method for calculating the gas storage volume of a compressed air energy storage underground cavern as claimed in claim 4, characterized in that: include: Boundary conditions: in, represents the rock temperature of the gas storage chamber, Indicates the air temperature of the gas storage tank. Indicates the surface temperature of the rock body outside the gas storage chamber, Indicates the heat transfer coefficient between air and gas storage chamber surface, Indicates the wall temperature of the gas storage chamber, represents the thermal conductivity of the gas storage rock mass, Indicates the outer diameter of the rock body of the gas storage chamber. Indicates the inner diameter of the rock mass of the gas storage chamber; Initial conditions: represents the initial condition of the air temperature in the gas storage chamber, represents the initial temperature condition of the gas storage rock mass, Indicates the air temperature of the gas storage chamber before the inflation condition. Indicates the rock temperature of the gas storage chamber before inflation.

Images