A method for predicting temperature-limited output of compressed air energy storage system

Abstract

The invention discloses a method for predicting the temperature-limited output of a compressed air energy storage system, which comprises: step 1, collecting the air pressure, air temperature, air flow rate at the outlet of the air tank and the current power generation value of the air storage tank; step 2, determining the minimum allowable temperature Ts of the air storage tank; step 3, calculating the mass of compressed air in the air storage tank; step 4, calculating the remaining power generation time of the air storage tank; step 5, calculating the remaining power generation amount of the air storage tank according to the remaining power generation time of the air storage tank and the power generation power of the expander; the problem that the prior art cannot calculate the remaining power generation time according to the limited temperature of the air storage tank, and cannot grasp the remaining power generation amount limited by the temperature, is not conducive to performing the operation of related units and the arrangement of the power grid operation mode according to the power generation capacity in advance.

Description

Technical Field

[0001] The present invention belongs to the technical field of compressed air energy storage, and in particular relates to a method for predicting temperature-limited output of a compressed air energy storage system. Background Art

[0002] In recent years, with the continuous acceleration of the process of clean and low-carbon energy, the installed capacity of new energy power generation such as wind power generation and photovoltaic power generation has become larger and larger. However, the output of new energy has strong intermittent, volatile and random characteristics, which leads to prominent problems of peak and frequency regulation of the power grid, affecting the power quality and safe and stable operation of the power grid. Large-scale power storage technology is one of the effective ways to solve the above problems. Among them, the compressed air energy storage system is environmentally friendly, has the advantages of large energy storage capacity, low pollution, rotational inertia, and long storage period. It is considered to be one of the most promising large-scale clean power storage technologies.

[0003] The compressed air energy storage system includes an energy storage power consumption system and an energy release power generation system. In the energy storage stage, electric energy is used to drive the compressor to compress air and convert the electric energy into pressure potential energy. In the energy release stage, the stored high-pressure compressed air is used to drive the turbine to generate electricity. The energy storage stage and the energy release stage of the compressed air energy storage system cannot be performed at the same time. Therefore, the available working medium (i.e., the remaining stored gas in the gas tank) in the energy release stage is limited, and its power generation time is limited by the gas storage energy of the gas tank. At the same time, as the working air in the gas tank flows out, the temperature of the gas tank gas decreases monotonically after the expansion. If the temperature reaches the gas tank temperature limit during the operation of the unit, the minimum allowable temperature of the gas tank design, and the minimum allowable temperature of the pipe design between the gas tank and the heat exchanger, the unit will stop generating electricity. At present, the compressed air energy storage system only monitors the temperature and pressure of the gas tank. The existing technology cannot calculate the remaining power generation time according to the gas tank limit temperature, and it is even more impossible to grasp the remaining power generation amount limited by the temperature, which is not conducive to the operation of the relevant units and the arrangement of the grid operation mode according to the power generation capacity in advance. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for predicting the temperature-limited output of a compressed air energy storage system, so as to solve the problem that the prior art cannot calculate the remaining power generation time according to the temperature limit of the gas tank, and cannot grasp the remaining power generation amount limited by the temperature, which is not conducive to arranging the operation of related units and the operation mode of the power grid in advance according to the power generation capacity.

[0005] The technical solution of the present invention is:

[0006] A method for predicting temperature-limited output of a compressed air energy storage system, comprising:

[0007] Step 1, collecting the air pressure of the gas tank, the air temperature of the gas tank, the air flow rate at the gas tank outlet and the current power generation value;

[0008] Step 2, determine the minimum allowable temperature Ts of the gas storage tank;

[0009] Step 3, calculate the mass of compressed air in the gas tank;

[0010] Step 4, calculate the remaining power generation time of the gas storage tank;

[0011] Step 5: Calculate the remaining power generation capacity of the gas storage tank according to the remaining power generation time of the gas storage tank and the power generation power of the expander.

[0012] The air temperature measurement method of the gas tank is as follows: if there is one gas tank, the air temperature is measured at no less than 3 points, which are located at the bottom, middle and upper part of the gas tank, and the mathematical average is finally taken; if there are more than one gas tank, each gas tank is provided with an air temperature measurement point, and the mathematical average is finally taken; a contact PT100 thermal resistor temperature sensor is used, and the probe is vertically inserted into 1 / 3 of the diameter of the gas tank.

[0013] The method for measuring the air pressure and air density of the gas tank is as follows: if there is one gas tank, the measuring point is at the outlet of the gas tank pipeline; if there are more than one gas tank, each gas tank is set with a measuring point, and the mathematical average is finally taken; the pressure uses a resistive strain gauge pressure sensor, and the flow measurement uses an inserted vortex gas flow sensor, which are installed in the straight pipe section of the pipeline.

[0014] The method for determining the minimum allowable temperature Ts of the gas storage tank is as follows: based on the temperature limit T1 of the gas storage tank during unit operation, the minimum allowable temperature T2 of the gas storage tank design, and the minimum allowable operating temperature T3 of the pipe design between the gas storage tank and the heat exchanger, the minimum allowable temperature Ts of the gas storage tank is obtained as max(T1, T2, T3);

[0015] Method for determining the gas tank temperature limit T1 during unit operation: The initial states of the gas tank and the heat storage tank are both the designed full states, and they operate at rated conditions on this basis. When the unit is finally shut down due to failure to meet operating conditions, the temperature of the gas tank during unit operation is the gas tank temperature limit T1.

[0016] The method for determining the quality of compressed air in the gas tank is:

[0017] Qu=(Pg*V*M) / (8.314*(273.15+Tg))

[0018] Qu is the mass of compressed air in the gas tank;

[0019] V is the volume of the gas tank;

[0020] M is the molar mass of the gas.

[0021] The method for calculating the remaining power generation time of the gas tank is:

[0022] According to the formula:

[0023] dT / dt=Tg*(γ-1)*m / Qu-h*A*(Tg-Tam) / (Qu*Cv)

[0024] h is the heat transfer coefficient between the environment and the outer wall of the gas tank;

[0025] A is the surface area of ​​the gas tank;

[0026] Tam is the ambient temperature;

[0027] Cv is the specific heat capacity of the gas at constant volume in the gas tank;

[0028] γ is Cp / Cv,

[0029] The above formula can be simplified to

[0030] dT / dt=Tg*(γ-1)*m / Qu

[0031] Get the real-time drop rate of the gas tank temperature dT / dt;

[0032] Based on the lowest allowable temperature Ts of the gas tank, the calculation formula for the remaining power generation time of the gas tank is obtained:

[0033] tu=Qu*(Tg-Ts) / ((273.15+Tg)*m*(γ-1))

[0034] tu is the remaining power generation time of the gas tank.

[0035] The method for calculating the remaining power generation capacity of the gas storage tank based on the remaining power generation time of the gas storage tank and the power generation power of the expander is:

[0036] Apu=tu*Wn

[0037] Apu is the remaining power generation capacity of the gas tank; tu is the remaining power generation time of the gas tank; Wn is the current power generation value.

[0038] Beneficial effects of the present invention:

[0039] The present invention selects the maximum value of the gas tank temperature limit during unit operation, the minimum allowable temperature of the gas tank design, and the minimum allowable temperature of the pipe design between the gas tank and the heat exchanger as the restriction condition, monitors the gas tank temperature parameters during the operation of the energy storage power generation system, and calculates the remaining power generation time of the expansion power generation system subject to temperature restrictions in real time through the derived formula, calculates the remaining power generation of the power generation system according to the current power generation, and arranges the operation of related units and the operation mode of the power grid in advance according to the power generation capacity prediction.

[0040] Advantages of the present invention:

[0041] The relationship between the temperature parameters of the gas tank and the remaining power generation time and remaining power generation amount of the expansion power generation system is revealed, and the time and amount of power generated by the gas tank are calculated in real time, making the power generation capacity of the expansion generator measurable and observable.

[0042] Arrange the unit operation in advance and in an orderly manner according to the unit's remaining power output and operating time.

[0043] Provide sufficient time to process the grid operation mode to prevent the impact of sudden load reduction on the grid.

[0044] The problem that the prior art cannot calculate the remaining power generation time according to the temperature limit of the gas tank, and cannot grasp the remaining power generation amount subject to temperature limit, is not conducive to arranging the operation of related units and the operation mode of the power grid in advance according to the power generation capacity, is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic diagram of the process of the present invention;

[0046] Figure 2 It is a schematic diagram of the hardware system composition of the present invention. DETAILED DESCRIPTION

[0047] The invention discloses a compressed air energy storage system for expansion and power generation. Figure 1 , including: an air storage tank (1), an air intake regulating valve (2), a multi-stage expansion machine (3), a generator (4), a heat storage tank (5), a heat pump (6), a multi-stage heat exchanger (7), and a cold storage tank (8). The air storage tank 1 stores high-pressure compressed air, which is connected to the first-stage heat exchanger 701 through a pipeline for heating and then goes to the first-stage expansion machine 301 of the multi-stage expansion machine. The compressed air is discharged from the first-stage expansion machine 301 after doing work, and enters the second-stage expansion machine after being heated by the second-stage heater, and so on, until it is discharged from the last-stage expansion machine 303. The heat storage tank 5 stores heat through a heat exchange medium, which enters each stage of the heat exchanger to heat the compressed air after being pressurized by a heat pump 6, and enters the cold storage tank 8 after the heat exchange medium is cooled. The number of multi-stage heaters 7 is equal to the number of multi-stage expansion machines 3, and they are arranged at the corresponding expansion machine inlets. The high-temperature and high-pressure compressed air enters the expansion machine to drive the expansion machine to rotate, and the expansion machine drives the generator 4 to rotate through the shaft to generate electricity.

[0048] The first step is to collect Pg, Tg, m, and Wn through the real-time monitoring system, the pressure and temperature sensors of the gas storage tank, and the flow sensor at the outlet.

[0049] Pg-air pressure of gas tank, Tg-air temperature of gas tank, m-air flow rate at gas tank outlet, Wn-current power generation value.

[0050] Air temperature measurement requirements for gas tanks: If there is one gas tank, the air temperature should be measured at no less than 3 points, covering the bottom, middle and top of the gas tank, and the mathematical average should be taken for calculation. Because the air in the gas tank does not flow out stably during operation, the temperature at different heights in the gas tank is different. If there are multiple gas tanks, each gas tank has an air temperature measurement point, and the mathematical average should be taken for calculation.

[0051] Requirements for measuring air pressure and air density of gas tanks: If there is only one gas tank, the measuring point is at the outlet of the gas tank pipeline. If there are multiple gas tanks, each gas tank has a measuring point, and the mathematical average is finally calculated.

[0052] The temperature adopts contact PT100 thermal resistance temperature sensor, the probe is vertically inserted into 1 / 3 of the diameter of the gas tank, and outputs 4~20mA signal.

[0053] The pressure uses a resistive strain gauge pressure sensor with a measuring range of 0-25MPa and an output signal of 4-20mA.

[0054] The flow measurement uses an inserted vortex gas flow sensor installed in the straight section of the pipeline. Because the pipeline will produce unstable flow during the adjustment process, the amplifier is separated from the sensor. The sensor uses an interference cancellation circuit and an anti-vibration sensor head, has anti-environmental vibration performance, and outputs 4-20mA signals.

[0055] The second step is to determine the minimum allowable temperature of the gas tank (Ts): the temperature limit of the gas tank during unit operation T1, the designed minimum allowable temperature of the gas tank T2, and the designed minimum allowable operating temperature of the pipe between the gas tank and the heat exchanger T3, and the minimum allowable temperature of the gas tank Ts = max (T1, T2, T3).

[0056] Method for determining the temperature limit T1 of the gas tank during unit operation: the initial states of the gas tank and the heat storage tank are both designed to be full, and they operate at rated conditions on this basis. The temperature of the gas tank is determined when the unit is shut down due to failure to meet operating conditions (insufficient gas storage pressure or insufficient heat storage).

[0057] Method for determining the minimum allowable temperature T2 of the gas tank design: determined based on the gas tank material and operating rated pressure.

[0058] The method for determining the minimum allowable operating temperature T3 of the pipe design between the gas tank and the heat exchanger is determined based on the pipe material and operating rated pressure between the gas tank and the heat exchanger.

[0059] The third step is to calculate the mass of compressed air in the gas tank:

[0060] Qu=(Pg*V*M) / (8.314*(273.15+Tg))

[0061] Qu-mass of compressed air in the gas tank, kg

[0062] V-gas tank volume, m 3

[0063] M- gas molar mass, take 0.02896kg / mol

[0064] The fourth step is to calculate the remaining power generation time of the gas tank:

[0065] According to the existing technical formula:

[0066] dT / dt=Tg*(γ-1)*m / Qu-h*A*(Tg-Tam) / (Qu*Cv)

[0067] h – heat transfer coefficient between the environment and the outer wall of the gas tank, W / (m 2 ·K)

[0068] A – Surface area of ​​gas tank, m 2

[0069] Tam – ambient temperature, °C

[0070] Cv – specific heat capacity of gas at constant volume in the gas tank, taken as 0.717 kJ / (kg·K)

[0071] γ is Cp / Cv, take 1.4

[0072] It is known that the gas tanks are all installed with insulation layers on site, so the heat dissipation of the gas tanks is ignored, and the above formula can be simplified to

[0073] dT / dt=Tg*(γ-1)*m / Qu

[0074] From the above, the real-time drop rate dT / dt of the gas storage tank temperature can be obtained.

[0075] Based on the lowest allowable temperature Ts of the gas tank, the calculation formula for the remaining power generation time of the gas tank is finally derived:

[0076] tu=Qu*(Tg-Ts) / ((273.15+Tg)*m*(γ-1))

[0077] tu-Gas tank remaining power generation time

[0078] The fifth step is to calculate the remaining power generation capacity of the gas tank according to the remaining power generation time of the gas tank and the power generation power of the expander:

[0079] Apu=tu*Wn

[0080] Apu - Remaining power generation capacity of the gas tank.

[0081] Case: The system power generation capacity is 10MW and the gas storage capacity of the gas tank is 6000m 3 The initial pressure and temperature are set to 10MPa and 30℃ respectively. The temperature of the gas tank is 0℃ when the unit suddenly stops during the power generation process of the initial full state of gas and heat storage. The minimum allowable design temperature of the gas tank is -4℃. The minimum allowable operating temperature of the pipe between the gas tank and the heat exchanger is designed to be -20℃.

[0082] Step 1: Collect data through real-time monitoring system: Pg = 8.531MPa, Tg = 16.45℃, ρ = 102.18kg / m 3 , m=36.51kg / s, Wn=9.992MW.

[0083] The second step is to determine the minimum allowable temperature of the gas tank (Ts): Ts = max (T1, T2, T3) = max (0, -4, -20) = 0 °C.

[0084] The third step is to calculate the mass of compressed air in the gas tank: Qu = (Pg*V*M) / (8.314*(273.15+Tg)) = (8.531*10^6*6000*0.02896) / (8.314*(273.15+16.45)) = 615660.33 kg

[0085] Step 4: Calculate the remaining power generation time of the gas tank: tu = (Tg-Ts) / (dT / dt) = Qu*(Tg-Ts) / ((273.15+Tg)*m*(γ-1)) = 615660.33*(16.45-0) / ((273.15+16.45)*36.51*(1.4-1)) = 2394.62s = 39.91min

[0086] The fifth step is to calculate the remaining power generation of the gas tank Apu = tu * Wn = 2394.62 * 9.992 * 10 3 =23927043kJ=6646.4kW·h.

Claims

1. A method for predicting temperature-limited output of a compressed air energy storage system, comprising: Step 1, collecting the air pressure of the gas tank, the air temperature of the gas tank, the air flow rate at the gas tank outlet and the current power generation value; Step 2, determine the minimum allowable temperature Ts of the gas storage tank; The method for determining the minimum allowable temperature Ts of the gas storage tank is as follows: based on the temperature limit T1 of the gas storage tank during unit operation, the minimum allowable temperature T2 of the gas storage tank design, and the minimum allowable operating temperature T3 of the pipe design between the gas storage tank and the heat exchanger, the minimum allowable temperature Ts of the gas storage tank is obtained as max(T1, T2, T3); Step 3, calculate the mass of compressed air in the gas tank; Step 4, calculate the remaining power generation time of the gas storage tank; The method for calculating the remaining power generation time of the gas tank is: According to the formula: dT / dt=Tg*(γ-1)*m / Qu-h*A*(Tg-Tam) / (Qu*Cv) h is the heat transfer coefficient between the environment and the outer wall of the gas tank; A is the surface area of ​​the gas tank; Tam is the ambient temperature; Cv is the specific heat capacity of the gas at constant volume in the gas tank; γ is Cp / Cv, The above formula is simplified to dT / dt=Tg*(γ-1)*m / Qu Get the real-time drop rate of the gas tank temperature dT / dt; The calculation formula of the remaining power generation time of the gas tank is obtained from the lowest allowable temperature Ts of the gas tank: tu = Qu*(Tg-Ts) / ((273.15+Tg)*m*(γ-1)) tu is the remaining power generation time of the gas tank; Step 5, calculating the remaining power generation capacity of the gas storage tank according to the remaining power generation time of the gas storage tank and the power generation power of the expander; The method for calculating the remaining power generation capacity of the gas storage tank based on the remaining power generation time of the gas storage tank and the power generation power of the expander is: Apu=tu*Wn Apu is the remaining power generation capacity of the gas tank; tu is the remaining power generation time of the gas tank; Wn is the current power generation value.

2. A method for predicting temperature-limited output of a compressed air energy storage system according to claim 1, characterized in that: The air temperature measurement method of the gas tank is as follows: if there is one gas tank, the air temperature is measured at no less than 3 points, which are located at the bottom, middle and upper part of the gas tank, and the mathematical average is finally taken; if there are more than one gas tank, each gas tank is provided with an air temperature measurement point, and the mathematical average is finally taken; a contact PT100 thermal resistor temperature sensor is used, and the probe is vertically inserted into 1 / 3 of the diameter of the gas tank.

3. A method for predicting temperature-limited output of a compressed air energy storage system according to claim 1, characterized in that: The method for measuring the air pressure and air density of the gas tank is as follows: if there is one gas tank, the measuring point is at the outlet of the gas tank pipeline; if there are more than one gas tank, each gas tank is set with a measuring point, and the mathematical average is finally taken; the pressure uses a resistive strain gauge pressure sensor, and the flow measurement uses an inserted vortex gas flow sensor, which are installed in the straight pipe section of the pipeline.

4. A method for predicting temperature-limited output of a compressed air energy storage system according to claim 1, characterized in that: Method for determining the gas tank temperature limit T1 during unit operation: The initial states of the gas tank and the heat storage tank are both the designed full states, and they operate at rated conditions on this basis. When the unit is finally shut down due to failure to meet operating conditions, the temperature of the gas tank during unit operation is the gas tank temperature limit T1.

5. A method for predicting temperature-limited output of a compressed air energy storage system according to claim 1, characterized in that: The method for determining the quality of compressed air in the gas tank is: Qu=(Pg*V*M) / (8.314*(273.15+Tg)) Qu is the mass of compressed air in the gas tank; V is the volume of the gas tank; M is the molar mass of the gas.

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