A compressed air energy storage system design method

Abstract

The present disclosure provides a compressed air energy storage system design method, which selects the number of compressor stages and the number of expander stages, determines the compression ratio of each stage of compressor and the expansion ratio of each stage of expander; the number of compressor stages, the number of expander stages, the compression ratio of each stage and the expansion ratio of each stage constitute a comparison scheme. For each comparison scheme, the temperature and pressure distribution of each stage of compressor and expander are calculated; based on the enthalpy corresponding to the temperature and pressure, the unit mass air electric power and unit mass air heat power of the compressor part, and the unit mass air expansion power and unit mass air heat absorption of the expander part are calculated. Using the four unit mass parameters, the design indexes of each comparison scheme are calculated, and the scheme whose design indexes meet the design requirements is screened out. Using the present application, the number of system compression stages and expansion stages with high efficiency and the corresponding parameter configuration can be quickly determined in the system conceptual design stage, guiding the accurate and rapid design of the compressed air energy storage system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage, in particular to a compressed air energy storage system design method. BACKGROUND

[0002] As a new type of energy storage technology, compressed air energy storage technology has the advantages of large scale, low cost, long service life, cleanliness, unlimited energy storage period, and heat transfer and storage during energy storage and release. It is a new type of physical energy storage technology suitable for large-scale promotion. The compressed air energy storage system usually adopts the form of advanced adiabatic compressed air energy storage, and the system generally adopts a multi-stage compression and intermediate cooling method. The compression heat is stored in the heat storage tank after heat exchange with air and water or heat-conducting oil, and the gas with high pressure potential is stored in the gas storage. In the expansion and release process, the high-pressure air from the gas storage absorbs the compression heat from the heat storage tank to drive the expander to do work.

[0003] The operation of the compressed air energy storage system involves energy decoupling, heat and work conversion, and efficient heat exchange. It contains multiple large thermal equipment such as compressors, expanders, heat exchangers, and heat storage tanks. The system design has the difficulties of multiple design variables, wide parameter selection range, high variable coupling degree, and strong nonlinearity of the calculation model. An efficient design method is needed to avoid a large amount of repeated and tedious calculation and checking work in the design process.

[0004] However, the existing compressed air energy storage system design method mostly performs thermal calculation and simulation on a single device, and cannot achieve efficient coupled calculation and iterative optimization. Some schemes use simulation software to hope to design the system, rather than a single device. However, because the parameters related to the system process scheme cannot be effectively decoupled, the calculation process is complex, increasing the design calculation cost and workload. Therefore, a systematic and multi-dimensional efficient design calculation method is needed. SUMMARY

[0005] Therefore, the present application provides a compressed air energy storage system design method. The method proposes the concepts of unit mass air electric power and unit mass air thermal power, effectively decouples the parameters related to the system process scheme, optimizes the scheme with system constraints, forms a system scheme rapid design method, and improves the design efficiency and effect of the compressed air energy storage system.

[0006] To solve the above technical problems, the present application is implemented as follows.

[0007] A compressed air energy storage system design method, the compressed air energy storage system comprising a multi-stage compressor and a multi-stage expander; the method comprising:

[0008] Step 1: set initial values of parameters to be optimized, including the number of compressor stages n c and the number of expander stages n e , n c ≥ n e ;

[0009] Step 2: based on the selected number of compressor stages n c and the number of expander stages n e , determine the compression ratio of each stage of compressor and the expansion ratio of each stage of expander by using the compressor thermodynamic model and the expander thermodynamic model; a set of the number of compressor stages n c , the number of expander stages n e , the compression ratio of each stage and the expansion ratio of each stage constitute a comparison scheme;

[0010] Step 3: for each comparison scheme, calculate the temperature and pressure distribution of each stage of compressor and expander; based on the enthalpy value corresponding to the temperature and pressure distribution, calculate the unit mass air electric power p c and the unit mass air heat power q c of the compressor part, calculate the unit mass air expansion power p e and the unit mass air heat absorption q e of the expander part; wherein p c is the sum of enthalpy difference between outlet and inlet of each stage of compressor, q c is the sum of air enthalpy difference between stages of each stage of compressor, p e is the sum of enthalpy difference between outlet and inlet of each stage of expander, q e is the sum of air enthalpy difference between stages of each stage of expander;

[0011] Step 4: for each comparison scheme, obtain each design index; wherein the electric-to-electric efficiency η ee is the ratio of p e to p c , and the thermal energy utilization rate η q is the ratio of q e to q c ;

[0012] Step 5: screen out the scheme that meets the design requirements.

[0013] Preferably, the method further comprises: changing the number of compressor stages n c and the number of expander stages n e , repeating steps 2-5 to obtain a set of schemes that meet the design requirements under different numbers of compression stages and expansion stages.

[0014] Preferably, the method further comprises: after obtaining the scheme satisfying the design requirements, further calculating scheme parameters for use in engineering scheme selection; the scheme parameters include: air expansion working condition flow, air compression working condition flow, air reservoir volume, heat storage medium expansion working condition flow, heat storage medium compression working condition flow, heat storage system volume, compression working condition heat exchange area, and expansion working condition heat exchange area; and outputting a heat balance diagram according to the determined scheme parameters to determine the pressure, temperature, flow, and enthalpy value of the air side and the water side at various positions.

[0015] Preferably, in step 2, the compression ratio of each stage of compressor is determined in the following manner:

[0016] The compression ratio of each stage of compressor is determined using a compressor thermodynamic model, including the following steps: c - the compression ratio of the first stage of compressor is β c , and the compression ratio of the last stage of compressor is β c_last .

[0017] The compressor thermodynamic model is expressed by formula (1):

[0018]

[0019] where ΔP gasin is the pressure loss from the outlet of the last stage of compressor to the inlet of the air reservoir; ΔP c_i is the pressure loss of air passing through the pipeline and the intermediate heat exchanger between the i-th stage of compressor and the i+1-th stage of compressor, i is an integer ranging from 1 to n c -1; P0 is the inlet pressure of the first stage of compressor; P back is the maximum pressure of the air reservoir;

[0020] When β c and β c_last are determined using formula (1), there are multiple solutions, and different β c and β c_last correspond to different comparison schemes.

[0021] Preferably, when the compression ratio of each stage of compressor is determined using the compressor thermodynamic model, β c = β c_last is first set, a temporary value of β c is solved using formula (1), then β c_last is set to a value greater than 1 and less than the temporary value, and β c is set to a value greater than the temporary value, so that β c and β c_last satisfy formula (1).

[0022] Preferably, in step 2, the expansion ratio of each stage of expander is determined in the following manner:

[0023] determining the expansion ratio β of each stage of the expander using an expander thermodynamic model e ; the expander thermodynamic model is expressed by equation (2):

[0024]

[0025] where ΔP gasout is the pressure loss from the outlet of the gas storage to the first stage of the expander, ΔP e_j is the pressure loss of the air passing through the pipeline and the intermediate heat exchanger between the i-th stage and the i+1-th stage of the expander, j is in the range of 1 to n e -1; P eo_last is the exhaust pressure of the last stage of the expander, P back is the maximum pressure of the gas storage.

[0026] Preferably, in step 3, the unit mass air electric power p c and the unit mass air heat power q c of the compressor part are calculated as follows:

[0027] Setting the intake temperature of each stage of the compressor, the exhaust temperature, the exhaust pressure and the intake pressure of each stage of the compressor are calculated; using the intake temperature and the intake pressure of each stage of the compressor, the inlet air enthalpy of each stage of the compressor is determined; using the exhaust temperature and the exhaust pressure of each stage of the compressor, the outlet air enthalpy of each stage of the compressor is determined;

[0028] calculating the unit mass air compression electric power consumption where h co,i and h ci,i are the air enthalpy at the outlet and the inlet of the i-th stage of the compressor, respectively;

[0029] calculating the unit mass air heat release where h co,i is the air enthalpy at the outlet of the i-th stage of the compressor, and h ci,i+1 is the air enthalpy at the inlet of the i+1-th stage of the compressor.

[0030] Preferably, in step 3, the unit mass air expansion power p e and the unit mass air heat absorption q e are calculated as follows:

[0031] calculating the intake temperature and the exhaust temperature of each stage of the expander; calculating the intake pressure and the exhaust pressure of each stage of the expander; using the intake temperature and the intake pressure of each stage of the expander, the inlet air enthalpy of each stage of the expander is determined; using the exhaust temperature and the exhaust pressure of each stage of the expander, the outlet air enthalpy of each stage of the expander is determined;

[0032] calculating the unit mass air expansion power where heo,j and h ei,j are the air enthalpy at the outlet and the inlet of the jth expander, respectively;

[0033] Calculate the heat release of unit mass air wherein, h ei,j+1 is the air enthalpy at the inlet of the j+1th expander, and h eo,j is the air enthalpy at the outlet of the jth expander.

[0034] Preferably, in step 4, the design indicators are obtained as follows:

[0035] Calculate the electric efficiency η ee and the thermal energy utilization rate η q .

[0036] Solve the heat storage temperature and the heat storage pressure;

[0037] Obtain the exhaust temperature of the first n c -1 stage compressor and the exhaust temperature of the last stage expander.

[0038] Preferably, the scheme screening criteria meeting the design requirements are as follows:

[0039] The electric efficiency η ee is greater than or equal to the design electric efficiency;

[0040] The thermal energy utilization rate η q is greater than or equal to the design thermal energy utilization rate;

[0041] The heat storage temperature is within the economic heat storage temperature interval range;

[0042] The heat storage pressure is within the economic heat storage pressure interval range;

[0043] The exhaust temperature of the first n c -1 stage compressor is less than the upper limit of the exhaust temperature;

[0044] The exhaust temperature of the last stage expander is within the economic exhaust temperature interval range.

[0045] Beneficial effects:

[0046] (1) The compressed air energy storage system design method of the present application can quickly determine the system compression stage number and expansion stage number with high efficiency and the corresponding parameter configuration in the system conceptual design stage, and guide the precise design of the compressed air energy storage system. The thermodynamic model of the compressor and the expander is constructed, and the system parameters such as the compression ratio distribution, the expansion ratio distribution, the heat storage and exchange system scheme, and the throttling scheme are considered. The system design indicators are used as the guide, and the method of partial modeling + overall coupling is used to realize the systematized design of the compressed air energy storage power station.

[0047] (2) The method proposes the concepts of unit mass air electric power and unit mass air thermal power, uses the ratio of unit mass data to represent the electric-electric efficiency and thermal energy utilization rate, thereby effectively decoupling the parameters related to the system process scheme.

[0048] (3) The present application takes the number of compressor stages and the number of expander stages as optimization parameters, determines the compression ratio of each stage of compressor and the expansion ratio of each stage of expander based on the determined number of stages combined with the model, and then determines the temperature and pressure distribution of each stage of compressor and expander, thereby realizing the calculation of the above-mentioned unit mass data, and forming a comparison scheme. Through index comparison, the scheme meeting the design requirements is selected.

[0049] (4) In addition, the present method improves the calculation ability and efficiency through reasonable simplifying assumptions and efficient coupling of each sub-model, has the advantages of high accuracy, fast calculation speed and strong applicability, and can not only be used for system design, but also be used for sensitivity analysis research with heat storage temperature, compression stage number and the like as variables. The calculation method has strong expandability and wider application range.

[0050] (5) In a preferred embodiment, when determining the compression ratio of the compressor, one equation relationship requires solving two unknown parameters. In order to avoid generating more difference solutions, the present application first makes the compression ratios of all stages of compressor the same, uses a unique formula to calculate the compression ratio as a temporary value, and then determines the compression ratio of the front stage of compressor and the last stage of compression ratio according to the temporary value, so that the selection of the compression ratio is more reasonable, and the overall design efficiency is improved. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 The schematic diagram of the compressed air energy storage system designed by the present application;

[0052] Figure 2 The schematic diagram of the compressed air energy storage method designed by the present application;

[0053] Figure 3 The process scheme parameter comparison diagram under different design schemes in the embodiment;

[0054] Figure 4 The T-s diagram curve of the 4-stage compression-3-stage expansion compressed air energy storage system scheme in the embodiment;

[0055] Figure 5 The compression ratio distribution of the 4-stage compression-3-stage expansion scheme in the embodiment;

[0056] Figure 6 The compressor exhaust temperature change curve of the 4-stage compression-3-stage expansion scheme in the embodiment;

[0057] Figure 7The variation curves of the heat storage pressure and the heat storage temperature for the 4-stage compression-3-stage expansion scheme in the example;

[0058] Figure 8 The variation curves of the compression power and the heat storage amount for the 4-stage compression-3-stage expansion scheme in the example. DETAILED DESCRIPTION

[0059] The present application provides a compressed air energy storage system design method, which proposes the concepts of unit mass air electric power and unit mass air thermal power, uses the ratio of unit mass data to represent the electric-electric efficiency and the thermal energy utilization rate, thereby effectively decoupling the parameters related to the system process scheme. Meanwhile, the present application takes the number of compressor stages and the number of expander stages as optimization parameters, determines the compression ratio of each stage of compressor and the expansion ratio of each stage of expander based on the determined number of stages and the model, and then determines the temperature and pressure distribution of each stage of compressor and expander, thereby realizing the calculation of the above-mentioned unit mass data, and then forming a comparison scheme. Through index comparison, the scheme meeting the design requirements is selected. The present application quickly determines the system compression stage number and expansion stage number with high efficiency and the corresponding parameter configuration in the system conceptual design stage, guides the precise design of the compressed air energy storage system, and improves the design efficiency and effect of the compressed air energy storage system.

[0060] The present application will be described in detail below with reference to the accompanying drawings and examples.

[0061] Figure 1 The design object of the design method of the present application, i.e. the compressed air energy storage system, is shown. As shown in the figure, the compressed air energy storage system comprises a compressor, an expander, a heat exchanger, a high-temperature heat storage tank, a low-temperature heat storage tank, a gas storage and a cooling tower. The compressor part comprises a plurality of compressors arranged in series, and an intermediate heat exchanger is arranged between the compressors, the air side pipeline inlet and outlet of the intermediate heat exchanger are connected to the upper and lower compressors respectively, and the heat storage medium side pipeline inlet and outlet are connected to the high-temperature heat storage tank and the low-temperature heat storage tank respectively. The expander part comprises a plurality of expanders arranged in series, and an intermediate heat exchanger is arranged between the expanders, the air side pipeline inlet and outlet of the intermediate heat exchanger are connected to the upper and lower expanders respectively, and the heat storage medium side pipeline inlet and outlet are connected to the high-temperature heat storage tank and the low-temperature heat storage tank respectively. Since the compression process and the expansion process generally do not occur at the same time, the intermediate heat exchanger is shared by the compression side and the expansion side.

[0062] The compressed air energy storage system comprises two working conditions of compression and expansion:

[0063] In compression mode, air enters through the inlet of the first-stage compressor, is compressed stage by stage, and then discharged. The high-temperature air is cooled by an intermediate heat exchanger before entering the next stage compressor and finally flowing into the storage tank. The intermediate heat exchanger is where the low-temperature heat storage medium exchanges heat with the air; the high-temperature heat storage medium after heat exchange flows into the high-temperature heat storage device. The first three stages of compressors typically operate at industrial frequency. The last stage compressor needs to adjust its speed and compression ratio according to pressure changes in the storage tank, resulting in a lower exhaust temperature than the first three stages. Cooling towers and circulating water are typically used to cool the exhaust from the last stage compressor; therefore, this portion of heat is not recovered to the high-temperature heat storage device.

[0064] During expansion, after the air from the storage tank flows out, it passes through a throttling device and enters the intermediate heat exchanger 3. There, it absorbs heat from the high-temperature storage medium before entering the first-stage expander. After performing work, its temperature decreases, and it is then heated by the intermediate heat exchanger 2 before flowing into the next-stage expander and finally into the atmosphere. The intermediate heat exchanger is where the high-temperature storage medium exchanges heat with the air; the cooled storage medium, after heat exchange, flows into the low-temperature storage device. To ensure the power generation and flow capacity of the expander throughout the energy release process, a suitable main gas pressure must be selected. Therefore, a suitable throttling valve needs to be placed at the inlet of the first-stage expander.

[0065] Figure 1 This is a schematic diagram of the design object of the present invention, illustrating an example of four-stage compression + three-stage expansion. Prior to design, the number of stages and compression / expansion ratio of the compressor and expander, as well as further parameters, are unknown. The present invention aims to design the system using appropriate sequence and decoupling parameters to obtain one or more feasible solutions that meet the design requirements.

[0066] The compressed air energy storage system design provided by this invention has three characteristics:

[0067] First, four indicators were proposed, including the electrical power per unit mass of air and the power consumption per unit mass of air compression p. e Power generation per unit mass of air expansion p c Thermal power per unit mass of air includes the heat released per unit mass of air, q. c Heat absorbed per unit mass of air q e The above four indicators are calculated from the enthalpy difference (the difference in thermodynamic enthalpy at different spatial locations), and the unit is kJ / kg. Furthermore, the system's electro-electric efficiency and thermal energy utilization rate can be directly calculated from the above four indicators.

[0068] Secondly, this invention designs a decoupling method for multiple parameters. The parameters of a compressed air energy storage system are divided into known parameters, design parameters, and calculated parameters. "Known parameters" are essential parameters required during the system design phase, typically provided by the demand side of the compressed air energy storage power station, and represent the design requirements that the compressed air energy storage system must meet. "Design parameters" are parameters necessary for calculating the electrical power and thermal power per unit mass of air; they are independent parameters that directly reflect the system's work capacity and electrical efficiency. "Calculated parameters" are parameters that can be determined after the design parameters are obtained, based on mutual calculations between the design parameters and known conditions. Both design parameters and calculated parameters are parameters to be solved. The classification of compressed air energy storage system parameters is shown in Table 1.

[0069] Table 1 Classification of Compressed Air Energy Storage System Scheme Parameters

[0070]

[0071] Third, this invention proposes an index system for screening and comparing different design schemes. The design indices for compressed air energy storage systems refer to the criteria used to judge the technical merits and engineering feasibility of different design schemes. The design indices adopted in this invention mainly consist of the following eight indices:

[0072] ① Electrical efficiency η ee The existing technology defines it as total power generation / compression power consumption × 100%. This invention defines it as... The condition is satisfied by η ee ≥Design electrical efficiency, such as 65%.

[0073] ② Thermal energy utilization rate η q The existing technology defines it as the ratio of heat absorbed during expansion to heat stored during compression.

[0074] 100%. This invention is defined as... The condition is satisfied by η q ≥Design thermal energy utilization rate

[0075] For example, 70%

[0076] ③ Thermal storage temperature T hs The condition is T. hs ∈ Economic thermal storage temperature range; if water is used as the medium, it can be selected

[0077] [100, 250] (°C); oil as medium, [250, 350] (°C) can be selected; molten salt as medium,

[0078] [290, 570] (°C) can be selected.

[0079] ④ Thermal storage pressure P hs The condition is P. hsEconomic heat storage pressure range; for water medium, can be selected

[0080] [1, 3] (MPa), and oil and molten salt are set according to the operating pressure of the selected medium.

[0081] V. Compressor discharge temperature T co , satisfying the condition T co <Upper limit of discharge temperature, which can be selected as 360

[0082] (℃).

[0083] VI. Expander discharge temperature T eo , satisfying the condition T eo Economic discharge temperature range, which can be selected as [30,

[0084] 50] (℃).

[0085] VII. Air consumption rate = total mass of circulating air / total power generation (kg / kWh).

[0086] VIII. Heat consumption rate = Q eh / P ch (MW / kWh).

[0087] Generally, ① and ② are index requirements specified by the demand side of the compressed air energy storage power station; ③-⑥ are important considerations for designers when comparing and selecting system schemes, and are important evaluation parameters related to the economic performance, safety, manufacturability and the like of the compressed air energy storage system; and ⑦ and ⑧ are other reference indexes, which can be selected for auxiliary evaluation of the performance of the system.

[0088] Figure 2 A flowchart of the design method of the compressed air energy storage system is shown. As shown in the figure, the method comprises the following steps:

[0089] Step 1: Set initial values of parameters to be optimized, including the number of compressor stages n c and the number of expander stages n e , n c ≥ n e .

[0090] In this step, a set of values of the number of compressor stages n c and the number of expander stages n e is given according to the limiting condition n c ≥ n e , or multiple sets of values can be given. Each set of (n c , n e ) will generate multiple comparison schemes in the subsequent steps.

[0091] Step 2: Based on the selected number of compressor stages n c and the number of expander stages n eGiven the known maximum pressure of the gas storage tank, the compression ratio of each stage of the compressor and the expansion ratio of each stage of the expander are determined using the thermodynamic models of the compressor and expander.

[0092] ① The method for determining the compression ratio of each stage of the compressor in this step is as follows:

[0093] During compression, the first n c The -1 stage compressor operates at industrial frequency, while the final stage compressor operates at variable frequency. Its compression ratio needs to change with the back pressure of the gas storage tank; therefore, the first n stage compressor is set during the design phase. c -1 stage compression ratio β per stage c The final stage compression ratio β is a constant value. c_last It is a variable value, and β c_last Typically less than β c When the preset compression level n c At that time, the distribution of compression ratio and the compression ratio of each stage of the compressor can be determined based on the thermodynamic model of the compressor.

[0094] The thermodynamic model of the compressor is expressed by equation (1):

[0095]

[0096] Wherein, ΔP gasin The pressure loss from the outlet of the final stage compressor to the inlet of the gas storage tank; ΔP c_1 ΔP c_2 ...ΔP c_(nc-1) The pressure loss of air passing through the pipes between the two-stage compressor and the intermediate heat exchanger can also be expressed as ΔP. c_i ΔP c_i This refers to the pressure loss of air passing through the pipes and intermediate heat exchangers between the i-th and i+1-th stage compressors, where i ranges from 1 to n. c -1; P0 is the inlet pressure of the first-stage compressor, which is also the ambient pressure; P back This is the highest pressure of the gas storage facility, also known as the rated pressure. ΔP gasin ΔP c_i P0, P back Both are considered known.

[0097] β is determined using equation (1) c and β c_last There are multiple solutions, with different β values. c and β c_last Different comparison schemes are available.

[0098] Because β c and β c_last Since there are two unknowns, formula (1) has only one equation relationship. In practice, different β values ​​can be chosen. c and βc_last The combination is acceptable as long as the relationship of formula (1) is satisfied, but this will generate more options.

[0099] In order to speed up the design effect, in a preferred embodiment, β c = β c_last , a temporary value of β c is calculated by formula (1), and then β c_last is taken in the range greater than 1 and less than the temporary value, and β c is taken in the range greater than the temporary value, so that β c and β c_last satisfy formula (1).

[0100] ②The way to determine the expansion ratio of each stage expander in this step is:

[0101] In the expansion process, the expansion ratios β e of each stage expander are set to be equal, and the expansion stage number n e is given, and then the expansion ratio β e can be calculated by using the thermodynamic model of the expander.

[0102] The thermodynamic model of the expander is expressed by formula (2):

[0103]

[0104] Where ΔP gasout is the pressure loss from the outlet of the gas storage to the first stage expander; ΔP e_1 , ΔP e_2 , are the pressure losses of the air passing through the pipeline and the intermediate heat exchanger between the two expanders, which can be expressed as ΔP e_j , ΔP e_j is the pressure loss of the air passing through the pipeline and the intermediate heat exchanger between the i-th stage and the i+1-th stage expander, and j takes the value range of 1-n e -1; P eo_last is the exhaust pressure of the last stage expander, and P back is the highest pressure of the gas storage. ΔP gasout , ΔP e_j , P eo_last , P back are all considered to be known. In particular, when the throttling intake scheme is used before the first stage expander, P back should take the intake pressure value after the throttle valve for calculation, so that the system design process and the actual operation process are better matched, and the pressure value after the throttle valve is usually slightly lower than the highest pressure of the gas storage.

[0105] After the above calculation, a set of compressor stage numbers nc , the number of expansion machine stages n e , the compression ratio of each stage, and the expansion ratio of each stage constitute a comparison scheme.

[0106] Step 3: For each comparison scheme, calculate the temperature and pressure distribution of each stage of the compressor and the expander; based on the enthalpy value corresponding to the temperature and pressure distribution, calculate the unit mass air electric power p c and the unit mass air heat power q c of the compressor part, and calculate the unit mass air expansion power p e and the unit mass air heat absorption q e of the expander part.

[0107] In this step, for the compressor part, the unit mass air electric power p c and the unit mass air heat power q c include the following steps S301-S304:

[0108] S301: Set the inlet temperature of each stage of the compressor, and calculate the outlet temperature, outlet pressure and inlet pressure of each stage of the compressor.

[0109] The calculation process in this step is as follows:

[0110] Calculate the inlet pressure P ci,i of each stage of the compressor = P ci,i-1 -ΔP c_i . The first stage compressor inlet pressure P ci,1 is the above-mentioned ambient pressure P0.

[0111] Calculate the outlet pressure of each stage of the compressor; wherein the outlet pressure of the first n c -1 stage is P co,i = P ci,i ×β c , i takes the value range of 1-n c -1; the outlet pressure of the last stage of the compressor is

[0112] Set the inlet temperature T ci,i of each stage of the compressor, T ci,i represents the inlet temperature of the i-th stage of the compressor. Among them, the inlet temperature of the first stage of the compressor takes the average ambient temperature, and the range of other stages can be taken as [30℃-50℃].

[0113] The outlet temperature of each stage of the compressor is calculated as T co,i :

[0114]

[0115] In the above formula, η c is the isentropic efficiency of the compressor, which is provided by the compressor manufacturer, and k takes 1.4.

[0116] Since the first n c The inlet temperatures of the -1 stage compressors are not significantly different and the first n c The compression ratio is the same for stage -1 compressors, and the first n... c The discharge temperature of the -1 stage compressor is basically the same, which is higher than that of the final stage compressor.

[0117] S302: Determine the inlet air enthalpy of each compressor stage using the inlet air temperature and pressure of each compressor stage; determine the outlet air enthalpy of each compressor stage using the exhaust air temperature and pressure of each compressor stage.

[0118] In this step, based on the discharge temperature of each stage of the compressor... and compressor discharge pressure The outlet air enthalpy values ​​of each stage of the compressor can be obtained by referring to tables or directly using air property parameter software.

[0119] Based on the intake temperature of each level of compressor and compressor intake pressure The inlet air enthalpy values ​​for each stage of the compressor can be obtained by referring to tables or directly using air property parameter software.

[0120] S303: Calculate the power consumption per unit mass of compressed air Among them, h co,i and h ci,i Let p be the air enthalpy values ​​at the outlet and inlet of the i-th stage compressor, respectively. Therefore, p c This is the summation of the enthalpy differences between the outlet and inlet of each compressor stage.

[0121] S304: Calculation of heat release per unit mass of air Among them, h co,i h is the enthalpy of the air at the outlet of the i-th stage compressor. ci,i+1 Let q be the enthalpy of the air at the inlet of the (i+1)th stage compressor. Therefore, q c This is the summation of the air enthalpy differences between each stage of the compressor.

[0122] In this step, for the expander section, the power generation p per unit mass of air expanded is calculated. e Heat absorbed per unit mass of air q e This includes the following steps S311-S314:

[0123] S311: Calculate the inlet and outlet temperatures, inlet and outlet pressures of each stage of the expander.

[0124] The calculation process for this step is as follows:

[0125] Calculate the inlet temperature T of each stage expanderei =T hs -ΔT eh Among them, T ei ΔT represents the inlet temperature of each stage of the expander. Since the inlet temperature of each stage of the expander is the same, no distinction is made here; eh For the difference in high-temperature heat exchange at the expansion side, T hs T represents the temperature of the heat storage medium inside the high-temperature heat storage tank. hs =T co -ΔT ch , where ΔT ch Due to the temperature difference at the high-temperature heat transfer end on the compression side, T co For the first n c -1 stage compressor discharge temperature, first n c -1 stage compressor discharge temperature The same, therefore it is abbreviated as T here. co ;

[0126] The exhaust temperatures of each stage of the expander are calculated as follows:

[0127]

[0128] Where, η e This represents the isentropic efficiency of the expander.

[0129] Calculate the inlet pressure P of each stage of the expander ei,j =P ei,j-1 -ΔP e_j .

[0130] Calculate the exhaust pressure P of each stage of the expander eo,j =P ei,j / β e The value of j ranges from 1 to n. e .

[0131] S312: Determine the inlet air enthalpy of each stage of the expander by using the inlet air temperature and pressure of each stage of the expander; determine the outlet air enthalpy of each stage of the expander by using the exhaust air temperature and pressure of each stage of the expander.

[0132] In this step, the outlet air enthalpy values ​​of each expander are obtained by referring to tables or directly calling air property parameter software based on the exhaust temperatures and pressures of each expander stage.

[0133] The inlet air enthalpy values ​​for each stage of the expander can be obtained by referring to tables or directly using air property parameter software based on the inlet air temperature and pressure of each stage of the expander.

[0134] S313: Calculation of electricity generated per unit mass of air expansion Among them, h eo,j and hei,j Air enthalpy at the outlet and inlet of the jth expander, respectively. Thus, p e is the summation of the enthalpy difference of the outlet and inlet of each expander.

[0135] S314: Calculate the heat release per unit mass of air where h ei,j+1 is the air enthalpy at the inlet of the j+1th expander, h eo,j is the air enthalpy at the outlet of the jth expander. Thus, q e is the summation of the enthalpy difference of the outlet and inlet of each expander.

[0136] Step 4: Obtain each design index for each comparison scheme.

[0137] In this step, first determine the high-temperature heat storage temperature T hs and heat storage pressure P hs :

[0138] T hs = T co - ΔT ch , where T co is the exhaust temperature of the first n c -1 compressors, and the first n c -1 compressors are the same.

[0139] When water is selected as the heat storage medium, the heat storage pressure is the saturation pressure corresponding to the heat storage temperature plus a design margin ΔP hs :

[0140] P hs = f(T hs ) + ΔP hs , where f(T hs ) is the saturation pressure corresponding to the high-temperature heat storage temperature T hs ; when other media are selected, the heat storage pressure needs to be designed according to the allowable use pressure of other media.

[0141] Then calculate each design index: select a suitable system scheme according to one or more indexes, as described above, since ①-⑤ are important indexes affecting system performance, they should be considered and evaluated. The gas consumption rate and heat consumption rate indexes can be calculated and evaluated after all relevant parameters are completely determined.

[0142] ① Electrical-to-electrical efficiency η ee ≥ design electrical-to-electrical efficiency, such as 65%.

[0143] ② Thermal energy utilization rate η q ≥ design thermal energy utilization rate, such as 70%

[0144] ③Thermal storage temperature T hs ∈ Economic thermal storage temperature range, such as water as medium, can be selected [100, 250] (℃);

[0145] Oil as medium, can be selected [250, 350] (℃); molten salt as medium, can be selected [290, 570]

[0146] (℃)

[0147] ④Thermal storage pressure P hs ∈ Economic thermal storage pressure range, such as water as medium, can be selected [1, 3] (MPa),

[0148] When heat conducting oil and molten salt are used as thermal storage medium, the operating pressure is set according to the selected medium.

[0149] ⑤n c -1st stage compressor discharge temperature T co <Upper limit of discharge temperature, which can be selected as 360 (℃);

[0150] ⑥Last stage expander discharge temperature T eo ∈ Economic discharge temperature range, which can be selected as [30, 50] (℃).

[0151] The discharge temperature of each stage of expander is the same, and the last stage expander discharge temperature can be selected.

[0152] Step 5: Select the scheme that meets the design requirements of the design index.

[0153] According to the above calculation index, it can be judged whether the index requirement in the design requirement is met. If it is not met, the compression stage number n c -1st stage compression ratio, and the expansion stage number can be adjusted in step 6, so as to obtain a set of feasible solutions that meet the electric and thermal efficiency.

[0154] Step 6: Change the compression stage number n c And the expansion stage number n e , repeat steps 2-5 to obtain a set of schemes that meet the design requirements under different compression stage number and expansion stage number.

[0155] Step 7: After obtaining the scheme that meets the design requirements, further calculate the scheme parameters for engineering scheme selection.

[0156] After the above steps, the scheme has been designed and calculated under different design parameter combinations, and the calculation parameters have not been solved. The calculation method is as follows:

[0157] (1) Air flow calculation: expansion working condition flow m ea And compression working condition flow mca Computing

[0158] According to the power generation (MW) requirements, m ea = power generation / p e ;

[0159] According to the mass conservation of air in a cycle, m ca = t e × m ea / t c , where t e and t c are the expansion and compression power generation durations, respectively.

[0160] (2) Calculation of the gas storage volume

[0161] According to the thermodynamic model of the gas storage, by solving the following differential equations, the gas storage operating pressure range is obtained, and it is determined whether the minimum pressure of the gas storage meets the requirement of the lower limit of the gas storage pressure in the known parameters. If not, it indicates that the gas storage volume is too small or the operating pressure range is too small, and the gas storage needs to be reselected.

[0162]

[0163] where m is the mass of air in the gas storage, kg; mu is the thermodynamic energy of all air in the gas storage, kJ; m in and m out are the mass flow rates during charging and discharging of the gas storage, kg / s; h in and h out are the specific enthalpies during charging and discharging of the gas storage, u is the specific internal energy of air, kJ / kg; k w is the overall heat transfer coefficient between the gas storage and air, W / (m 2 ·K); A w is the heat exchange surface area of the gas storage, m 2 ; T and T amb are the temperatures of the air in the gas storage and the environment, respectively, K; p is the pressure in the gas storage, MPa; T in is the temperature of air entering the gas storage, ℃; T out is the temperature of air flowing out of the gas storage, ℃; c p and c v are the specific heat capacities at constant pressure and constant volume of air, respectively, kJ / (kg·K); R is the universal gas constant, 287 kJ / (kg·K); V is the volume of the gas storage, m 3 .

[0164] (3) Calculation of the heat storage medium flow rate, including the expansion condition flow rate m ew and the compression condition flow rate m cw

[0165] m ew =q e ×m ea / η hx / c pw / △T we

[0166] m cw =q c ×m ca ×η hx / c pw / △T wc

[0167] wherein, △T wc and △T we are the temperature difference between the inlet and outlet of the heat storage medium under compression and expansion conditions, respectively, which can be solved according to the temperature difference between the inlet and outlet of the compressed air and the heat transfer end difference; c pw is the specific heat capacity of the heat storage medium at constant pressure, and η hx is the efficiency of the heat exchanger.

[0168] (4) Volume calculation of heat storage system

[0169] The volume V h of each heat storage tank = max(m cw ×t c , m ew ×t e ) × ε v , ε v is the volume allowance coefficient.

[0170] (5) Area calculation of heat exchanger

[0171] The heat exchange area A c under compression condition = Q ch / t c × η hx / K c / △T lmc , η hx is the efficiency of the heat exchanger, K c is the total heat transfer coefficient of the heat exchanger under compression condition, and △T lmc is the logarithmic mean temperature difference of heat transfer under compression condition. Q ch is the total heat storage amount of the compressed air, and Q ch = q c × m ca × t c .

[0172] The heat exchange area Ae under expansion condition = Q eh / t e / η hx / K e / △T lme , K e is the total heat transfer coefficient of the heat exchanger in the expansion condition, △T lme is the logarithmic mean temperature difference of the heat transfer in the expansion condition. Q eh is the total heat storage of the air in the expansion process, Q eh = q e × m ea × t e .

[0173] Heat exchanger area A = max(A c , A e )

[0174] Finally, according to the determined scheme, a heat balance diagram is output, and the pressure, temperature, flow rate and enthalpy value of the air side and the water side at each position are determined, so that the design of the entire compressed air energy storage system is completed.

[0175] The different stage number technical schemes of the design scheme of the application will be described below in combination with a specific example 1.

[0176] According to the compressed air energy storage system scheme comparison method proposed in the application, Table 2 is the design parameters of a certain compressed air energy storage project, and Table 3 is the design indexes of the project. Before calculation, the performance parameters of the main equipment such as the compressor and the expander at the rated operating condition and the maximum operating pressure of the air storage reservoir need to be selected according to the design parameters. Before the technical scheme comparison, the technical indexes of the project need to be determined, and in this embodiment, the design electric-to-electric efficiency, the design thermal energy utilization rate, the compressor exhaust temperature, the expander exhaust temperature, the heat storage pressure and the rated power generation power are selected as the design indexes, and the technical schemes that meet all the design indexes are selected and compared.

[0177] Table 2 Design parameters of a certain compressed air energy storage project

[0178]

[0179] Table 3 Design indexes of a certain compressed air energy storage project

[0180]

[0181] According to the above known conditions and design indexes, since the heat of the last stage compressor in the compression process is not recovered, the compression stage number is usually slightly more than the expansion stage number to ensure the heat absorption requirement of the expansion process. In addition, the expansion stage number cannot be too small, and if the expansion stage number is too small, the expander outlet exhaust temperature will be too low, resulting in waste of cold energy . Therefore, from the scientificity of system design, this embodiment selects a design scheme with one less expansion stage number than compression stage number for comparison, and the comparison of other design schemes can be carried out according to the design method of the application.

[0182] According to the design method given in the case, taking the 4-stage compression-3-stage expansion as an example, the system process scheme under different compression ratio distribution is comprehensively considered during the design, and the scheme with the heat storage temperature of 191℃ is finally optimized as the best scheme. Under this scheme, the compression ratio of the first three compressors is 4.114, the compression ratio of the last compressor is 2.374, the expansion ratio is 6.558, and other main parameters are as follows:

[0183] Table 4 Inlet and outlet parameters of each stage compressor under the 4-stage compression-3-stage expansion scheme

[0184] Temperature Pressure Entropy Enthalpy Specific volume pe or pc qe or qc Units ℃ MPa kJ / kg K kJ / kg m3 / kg kJ / kg kJ / kg Pressure in 30.00 0.09 6.90 303.50 0.94 / / Pressure out 201.56 0.38 6.95 477.29 0.36 173.8 / Pressure in 30.00 0.30 6.56 303.03 0.29 / 174.3 Pressure out 201.56 1.25 6.61 476.75 0.11 173.7 / Pressure in 30.00 1.18 6.17 301.12 0.07 / 175.6 Pressure out 201.56 4.84 6.21 474.76 0.03 173.6 / Pressure in 30.00 4.76 5.74 293.59 0.02 / 181.2 Pressure out 126.51 11.29 5.77 390.40 0.01 96.8 / Gas reservoir 50.00 11.19 5.53 304.94 0.01 / 85.5 Expansion in 181.56 11.09 5.91 450.42 0.01 / 145.5 Expansion out 41.13 2.40 5.99 310.08 0.04 140.3 / Expansion in 181.56 2.35 6.38 455.38 0.06 / 145.3 Expansion out 41.13 0.51 6.45 313.85 0.18 141.5 / Expansion in 181.56 0.46 6.85 456.72 0.29 / 142.9 Expansion out 41.13 0.10 6.92 314.69 0.91 142.0 /

[0185] The p e , p c , q e and q c given in the above table are the unit mass air electric power and unit mass air heat power of each stage compressor or expander. Further summation is needed to obtain the unit mass air electric power and unit mass air heat power of the whole compression side or expansion side. By referring to the similar method for design comparison, the 3-stage compression-2-stage expansion scheme and the 5-stage compression-4-stage expansion scheme can be solved again, and the calculation results are shown in Table 5 and Figure 3 .

[0186] Table 5 Capacity comparison under different schemes

[0187]

[0188] By continuing to compare the above three schemes, it can be seen that the electric-to-electric efficiency of scheme ① is the highest, but since the heat storage temperature is very high, only the double heat storage medium scheme of heat conducting oil + water can be selected at this temperature, which will inevitably increase the investment cost and control complexity of the system heat exchanger, water pump, etc. Therefore, from the operation and maintenance aspect, this scheme is not the best choice. Scheme ② and scheme ③ can both meet the various indicators, and the system running and maintenance cost is lower with water as the medium, but scheme ③ needs to add one expander, one compressor and one set of inter-stage heat exchanger compared with scheme ②. By further comparing the differences of other indicators of the three schemes, it is calculated that the average electric-to-electric efficiency in the operation temperature range of scheme ② is 68.6%, and the average electric-to-electric efficiency in the operation temperature range of scheme ③ is 68.2%. In summary, the comprehensive advantage of scheme ② is more obvious. It needs to be noted that this scheme is only the ideal electric-to-electric efficiency without considering the plant power consumption. During the design stage, the difference of the real electric-to-electric efficiency and the increased investment cost after considering the equipment power consumption need to be comprehensively evaluated, so as to select the most suitable thermal system scheme.

[0189] After selecting this scheme, the design parameters can be calculated, in which m ea= 708 kg / s, according to the design requirements of the compression process 8h, the expansion power generation time 5h, the air flow rate m of the compression process can be calculated ca = 442.5 kg / s, and in the given gas storage volume 280,000 m 3 Under the condition, the model of the gas storage using the method can calculate the pressure interval of the gas storage to meet the design requirement of 5.2-11.3 MPa. Therefore, the design of the 4-stage compression-3-stage expansion scheme selected in the scheme is reasonable. The temperature-entropy diagram (T-s diagram) of the scheme is shown in Figure 4 , the solid line is the compression process, the left side is the last stage compressor, and the dashed line is the expansion process.

[0190] Under the 4-stage compression-3-stage expansion scheme described in embodiment 1, when the air flow rate is 708 kg / s, the influence of the heat storage temperature on the compressor stage distribution, the compressor discharge temperature, and the power generation power can be further studied. Engineers can design appropriate heat storage temperature and system scheme according to the sensitivity analysis characteristics. In formula (1), since there are two variables of the compression ratio β c of the first n-1 compressors and the compression ratio β clast of the last stage compressor, therefore, a set of infinite solutions can be formed. Considering that β clast is usually less than β c , and each solution of (β clast , β c ) corresponds to a heat storage temperature, a heat storage pressure, and a power generation power, the set of solutions formed under the 4-stage compression-3-stage expansion scheme of embodiment 1 can form Figure 5 .

[0191] Sensitivity analysis of compression ratio distribution with heat storage temperature: as the heat storage temperature rises from 174.8°C to 229.2°C, the compression ratio of the first three stages of compressors changes in the range of 3.664-5.264, and the compression ratio of the fourth stage of compressors changes in the range of 3.632-1.009. The higher the heat storage temperature, the greater the difference between β c_last and β c .

[0192] Sensitivity analysis of compression discharge temperature with heat storage temperature: as shown in Figure 6 , as the heat storage temperature rises from 174.8°C to 229.2°C, the discharge temperature of the first three stages of compressors increases, and the discharge temperature of the last stage of compressors decreases, but the decrease of the last stage of compressors is more obvious.

[0193] Sensitivity analysis of heat storage pressure with heat storage temperature: as shown in Figure 7 , as the heat storage temperature rises from 174.8°C to 229.2°C, the heat storage pressure shows an accelerating growth trend, and the highest reaches 2.856 MPa.

[0194] The analysis of the compression power and the heat storage capacity with the heat storage temperature sensitivity: the compression power and the heat storage capacity with the heat storage temperature are shown in FIG. 2 and FIG. 3, respectively. Figure 8 As shown in FIG. 2 and FIG. 3, with the heat storage temperature increasing from 174.8℃ to 229.2℃, the compression power shows a trend of first decreasing and then increasing, while the heat storage capacity continues to increase.

[0195] The compression air energy storage system design method can quickly determine the system compression stage number and expansion stage number with higher efficiency and corresponding parameter configuration in the system conceptual design stage, and guide the precise design of the compression air energy storage system. The compression air energy storage system design method is characterized in that the concepts of unit mass air electric power and unit mass air thermal power are innovatively proposed, so as to effectively decouple the parameters related to the system process scheme, and cooperate with the system constraint conditions to revise the scheme, form the system scheme rapid design and method. In addition, the method improves the calculation ability and efficiency through reasonable simplification assumptions and efficient coupling of each sub-model, has the advantages of high accuracy, fast calculation speed and strong applicability, and can not only be used for system design, but also be used for sensitivity analysis research with heat storage temperature, compression stage number and other variables, which is convenient for engineers to make more comprehensive and detailed scheme comparison and system design. The calculation method has strong scalability and wider application range.

[0196] The above specific embodiments only describe the design principles of the present application, and the shapes and names of the components in the description can be different and are not limited. Therefore, the person skilled in the art of the present application can modify or equivalently replace the technical solutions described in the foregoing embodiments; and these modifications and replacements do not deviate from the purpose and technical solutions of the present application, and should all belong to the protection scope of the present application.

Claims

1. A compressed air energy storage system design method, the compressed air energy storage system comprising a multi-stage compressor and a multi-stage expander; characterized by, The method comprises: Step 1: Set initial values of parameters to be optimized, including the number of compressor stages n c and the number of expander stages n e , n c ≥ n e ; Step 2: Based on the selected number of compressor stages n c Number of expander stages n e Using the thermodynamic models of the compressor and expander, the compression ratios of each stage of the compressor and the expansion ratios of each stage of the expander are determined; a set of compressor stages n c Number of expander stages n e Compression ratios and expansion ratios at each stage constitute a selection scheme; Step 3: For each comparative scheme, calculate the temperature and pressure distribution of each stage of the compressor and expander; based on the enthalpy values ​​corresponding to the temperature and pressure distribution, calculate the unit mass air electrical power p of the compressor section. c Thermal power per unit mass of air q c Calculate the power generation p per unit mass of air expanded in the expander section. e Heat absorbed per unit mass of air q e ; where p c q is the sum of the inlet and outlet enthalpy differences of each stage of the compressor. c p is the sum of the air enthalpy differences between each stage of the compressor. e q is the sum of the enthalpy differences at the inlet and outlet of each expander stage. e This is the sum of the air enthalpy differences between each stage of the expander; Step 4: obtaining design indexes for each comparison scheme; the electric-electric efficiency η ee is p e , the ratio of p c to q q , the thermal energy utilization rate η e is q c , the ratio of q Step 5: screening out a scheme meeting the design requirements of the design index; Step 6: change the number of compressor stages n c and the number of expander stages n e Repeat steps 2-5 to obtain a set of schemes that meet the design requirements under different numbers of compressor stages and expander stages. Step 7: after obtaining the scheme meeting the design requirements, further calculating scheme parameters for use in engineering scheme selection; the scheme parameters comprise air expansion working condition flow, air compression working condition flow, air reservoir volume, heat storage medium expansion working condition flow, heat storage medium compression working condition flow, heat storage system volume, compression working condition heat exchange area, expansion working condition heat exchange area; and outputting a heat balance diagram according to the determined scheme parameters to determine the pressure, temperature, flow and enthalpy of the air side and the water side at various positions.

2. The method of claim 1, wherein, In step 2, the manner of determining the compression ratio of each stage compressor is as follows: The compression ratio of each stage of compressor is determined using a compressor thermodynamic model, including the same compression ratio β c for the first stage compressor c and the compression ratio β c_last for the last stage of compression. The compressor thermodynamic model is expressed by formula (1): where ΔP gasin is the pressure loss from the outlet of the last compressor to the inlet of the reservoir; ΔP c_i is the pressure loss of air through the pipe between the i-th and i+1-th compressor and the intercooler, i ranging from 1 to n c - 1 ; P0is the inlet pressure of the first compressor; P back is the maximum pressure of the reservoir; β is determined using equation (1) c and β c_last There are multiple solutions for different β c and β c_last corresponding to different options.

3. The method of claim 2, wherein, When determining the compression ratio of each stage compressor by using the compressor thermodynamic model, first let β c =β c_last , solve the temporary value of β c by using formula (1), then take the value of β c_last in the range greater than 1 and less than the temporary value, take the value of β c in the range greater than the temporary value, so that β c and β c_last satisfy formula (1).

4. The method of claim 1, wherein, In step 2, the manner of determining the expansion ratio of each stage expander is as follows: determining the expansion ratio β of each stage of the expander using an expander thermodynamic model e ; the expander thermodynamic model is expressed by equation (2): where ΔP gasout is the pressure loss from the storage to the first stage expander, ΔP e_j is the pressure loss of air through the pipe and intercooler between the i-th and i+1-th stage expanders, j is in the range of 1 to n e -1; P eo_last is the exhaust pressure of the last stage expander, P back is the maximum pressure of the storage.

5. The method of claim 1, wherein, In step 3, the specific electric power p of the compressor section is calculated c and the specific thermal power q of the air is calculated c as: Set the air inlet temperature of each stage compressor, and calculate the air outlet temperature, air outlet pressure and air inlet pressure of each stage compressor; determine the inlet air enthalpy of each stage compressor by using the air inlet temperature and air inlet pressure of each stage compressor; determine the outlet air enthalpy of each stage compressor by using the air outlet temperature and air outlet pressure of each stage compressor; Computing the power consumption for compressing a unit mass of air where h co,i and h ci,i are the enthalpy of air at the outlet and inlet of the i-th compressor, respectively. Computing the heat release of a unit mass of air where h co,i is the air enthalpy at the outlet of the i-th compressor, h ci,i+1 is the air enthalpy at the inlet of the i+1-th compressor.

6. The method of claim 1, wherein, In Step 3, the calculated power generated per unit mass of air expanded p e and the heat absorbed per unit mass of air q e are: Calculate the air inlet temperature and air outlet temperature of each stage expander; calculate the air inlet pressure and air outlet pressure of each stage expander; determine the inlet air enthalpy of each stage expander by using the air inlet temperature and air inlet pressure of each stage expander; determine the outlet air enthalpy of each stage expander by using the air outlet temperature and air outlet pressure of each stage expander; Power generation amount of expansion of a unit mass of air where h eo,j and h ei,j are the enthalpy of air at the outlet and the inlet of the jth expander, respectively; Heat released per unit mass of air where h ei,j+1 is the air enthalpy at the inlet of the j+1th expander, h eo,j is the air enthalpy at the outlet of the jth expander.

7. The method according to any one of claims 1 to 6, characterized in that, In step 4, the design index is obtained as follows: Computing the electrical efficiency η ee , the thermal energy utilization η q ; Solve the heat storage temperature and the heat storage pressure; acquisition of the previous n c - exhaust temperature of the last compressor stage, exhaust temperature of the last expander stage.

8. The method of claim 7, wherein, The scheme meeting the design requirements is screened according to the following standards: Electrical efficiency η ee Greater than or equal to the design electrical efficiency; Heat energy utilization rate η q greater than or equal to the design heat energy utilization rate; The heat storage temperature is within the economic heat storage temperature interval range; The heat storage pressure is within the economic heat storage pressure interval range; n c - the discharge temperature of the stage 1 compressor is less than the discharge temperature upper limit; The air outlet temperature of the last stage expander is within the economic air outlet temperature interval range.

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