Wall surface and surrounding rock temperature prediction method for underground air storage device of compressed air energy storage power station

Abstract

The invention provides a wall surface and surrounding rock temperature prediction method for an underground air storage device of a compressed air energy storage power station. The method comprises the following steps: firstly, collecting preliminary design parameters of the compressed air energy storage power station; then, assuming adiabatic conditions to preliminarily estimate the possible temperature range of the gas storage device in the cycle working process; then, according to the obtained initial temperature range, the maximum characteristic length influencing the distribution of the temperature field in the surrounding rock is determined by adopting the distribution characteristics of the temperature field in a semi-infinite object, and then a discretized meshing heat conduction equation set in the surrounding rock is coupled into an unsteady state flow energy equation in a gas storage device; constructing a fluid-wall surface-rock stratum temperature field solving model in the gas storage device coupled with unsteady state heat transfer; and finally, according to the preliminary design parameters, seeking help for the temperature field model through an iterative calculation method, and obtaining distribution characteristics of the wall surface and surrounding rock temperature fields of the gas storage device. The method is used for predicting upper and lower temperature limits of the wall surface and surrounding rock strata of the underground gas storage device in the operation process of the compressed air energy storage power station, and determining temperature change characteristics under different working conditions as a reference basis for design, construction and operation maintenance of the underground gas storage device.

Description

Technical Field

[0001] This invention relates to the field of compressed air energy storage technology, specifically to a method for predicting the temperature of the wall surface and surrounding rock of an underground gas storage device in a compressed air energy storage power station. Background Technology

[0002] Compressed air energy storage power plants typically use natural salt caverns, abandoned mines, rock caverns, and artificial chambers as storage devices. During the energy storage-release cycle of the power plant, the temperature of the high-pressure air inside the underground storage device changes periodically with the system's operating conditions. During energy storage, high-pressure air enters the storage device, causing the pressure to gradually rise. Simultaneously, the temperature of the gas inside the storage device also gradually rises due to the pushing work of the compressor. During energy release, high-pressure air flows out of the storage device, causing the pressure inside to decrease. Simultaneously, the pushing work of the exhaust gas causes the internal temperature to gradually decrease. The energy storage-release cycle subjectes the walls of the storage device and the surrounding rock to alternating temperature loads, resulting in alternating stress. Long-term operation may cause fatigue deformation and damage to the walls and surrounding rock structures of the underground storage device, affecting system safety and lifespan, and ultimately leading to the instability and failure of the underground storage device. Summary of the Invention

[0003] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for predicting the temperature of the wall surface and surrounding rock of the underground gas storage device in a compressed air energy storage power station. This method is used to predict the upper and lower limits of the temperature of the wall surface and surrounding rock strata of the underground gas storage device during the operation of the compressed air energy storage power station, and to determine the temperature change characteristics under different operating conditions, serving as a reference for the design, construction, operation and maintenance of the underground gas storage device.

[0004] To achieve the above and other related objectives, the present invention provides a method for predicting the wall surface and surrounding rock temperature of an underground gas storage device in a compressed air energy storage power station, comprising the following steps:

[0005] S1. Collect preliminary design parameters of the compressed air energy storage power station. The preliminary design parameters include the energy storage duration, air intake parameters, resting time, energy release time, exhaust flow rate, air storage pressure limit, volume of underground air storage device, inner wall surface area, wall material thickness and thermal conductivity, and far-end temperature and thermal conductivity of surrounding rock.

[0006] S2. Assuming the underground gas storage device is under adiabatic conditions, based on the first law of thermodynamics, construct the energy balance equation for the energy storage-release process per unit time step, and calculate the temperature range of the gas in the underground gas storage device under adiabatic conditions.

[0007] S3. Based on the temperature range of the gas in the underground gas storage device under adiabatic conditions, and combined with the temperature field distribution characteristics of the semi-infinite object of the fluid heat transfer boundary, determine the maximum characteristic length of the upper and lower limits of temperature that affect the temperature in the surrounding rock according to the energy storage time, the static time and the energy release time, respectively.

[0008] S4. Based on the maximum characteristic length, construct a set of discretized heat conduction equations within the surrounding rock strata, and combine them with the unsteady flow energy equations for the energy storage time, static time, and energy release time segments, respectively, to establish a solution model for the fluid-wall-rock strata temperature field within the gas storage device coupled with unsteady heat transfer.

[0009] S5. Based on the relevant parameters determined in step S1, construct a matrix of time-varying parameters, and then substitute them into the fluid-wall-rock temperature field solution model in step S4 to obtain the fluid-wall-rock temperature under different spatiotemporal distributions.

[0010] Further, the energy storage duration in step S1 is the charging duration under rated operating conditions in a single cycle of the compressed air energy storage power station; the air intake parameters are the temperature, pressure, and mass flow rate of the high-pressure gas at the inlet of the gas storage device during energy storage; the settling time is the time from the end of the energy storage or release phase of the compressed air energy storage power station to the start of the energy release or storage phase; the energy release duration is the rated power generation duration in a single cycle of the compressed air energy storage power station; and the gas storage pressure limit is the minimum and maximum gas pressure values ​​during the cyclic operation of the gas storage device.

[0011] Furthermore, in step S2, the energy equation for the energy storage-release process under adiabatic conditions is adopted as follows:

[0012] u τ+dτ =(m τ ·u τ +q m ·h τ ·dτ) / (m τ +q m ·dτ) (1)

[0013] Among them, u τ+dτ dτ is the specific thermodynamic energy of the air inside the gas storage device at time τ+dτ; dτ is the time step; m τ The mass of air inside the gas storage device at time τ; u τ q is the specific thermodynamic energy of the air inside the gas storage device at time τ; m h is the intake / exhaust flow rate during the energy storage phase at time τ. τ It is the specific enthalpy of intake / exhaust during the energy storage phase at time τ;

[0014] Equation (1) is solved using a time discretization method. Based on the specific thermodynamic energy and specific volume of the air in the gas storage device at time τ+dτ, the temperature of the air in the gas storage device at time τ+dτ is obtained from the REFPROP property database. Iterative calculations are performed starting from the initial time. The temperature remains unchanged in the static state, gradually decreases during exhaust, and reaches its lowest point at the end of exhaust. The highest temperature is T. a,max The lowest temperature is T a,min The temperature range of the gas storage device under adiabatic conditions is obtained as [T]. a,min ,T a,max ].

[0015] Furthermore, in step S3, the temperature field distribution characteristics within the semi-infinite object at the fluid heat transfer boundary are defined by the following formula:

[0016] Where T(x,τ) is the temperature of the surrounding rock at a distance x from the inner wall of the gas storage device at time τ; T0 is the temperature of the far end of the surrounding rock; T a is the gas temperature inside the gas storage device; erfc is the residual error function; exp is the natural exponential function; λ is the thermal conductivity of the surrounding rock; ρ is the density of the surrounding rock; c is the specific heat capacity of the surrounding rock; h is the forced convection heat transfer coefficient of the air.

[0017] The maximum characteristic length is the maximum range of influence on the temperature distribution of the surrounding rock during the operation of a compressed air energy storage power station, and is calculated using the following formula:

[0018] Where, x cl α is the maximum feature length, and α is the margin coefficient, which is taken as 1.1 to 1.2. and These are the characteristic lengths for the highest and lowest temperatures, respectively.

[0019] Furthermore, in step S4, the discretized set of heat conduction equations within the surrounding rock strata is constructed using the following formula:

[0020]

[0021] Among them, T i,j T is the temperature of grid i at time step j. i,j+1 T is the temperature of grid i at time step j+1. i-1,j T is the temperature of grid i-1 at the j-th time step. i+1,j ΔΦ is the temperature of grid i+1 at time step j, ΔΦ is the net heat transfer power of grid i at time step j, d is the grid width, Δτ is the time step, and r is the temperature of grid i+1 at time step j. i-1 It is the equivalent thermal resistance between mesh i and mesh i-1, r i+1It is the equivalent thermal resistance between mesh i and mesh i+1, d k and λ k These are the thickness and thermal conductivity of the k-th layer of wall material;

[0022] The following formula is used to establish a solution model for the fluid-wall-rock temperature field within a gas storage device with coupled unsteady heat transfer:

[0023]

[0024] m j+1 =m j +q m,j ·Δτ (8)

[0025] v j+1 =V / m j+1 (9)

[0026] Where, q m,j It is the gas mass flow rate, positive for filling and negative for releasing, which can be determined by the specific thermodynamic energy u of the air in the gas storage device at time step j+1. j+1 and specific volume v j+1 Other state parameters of air, including temperature and pressure, are determined based on data from the REFPROP physical property database. i＝1,j The temperature of the first layer of surrounding rock grid in contact with the wall of the gas storage device at time step j is given by formulas (4), (5), and (6). The temperature of each grid in the surrounding rock at time step j+1 can be determined by formulas (4), (5), and (6).

[0027] Furthermore, the temperature of the gas inside the gas storage device at the (j+1)th time step is calculated according to formulas (7), (8), and (9), and then used as a boundary condition to calculate the temperature distribution of the surrounding rock grid at the (j+1)th time step. The temperature field distribution of the wall material and the surrounding rock at different times is obtained through iterative calculation.

[0028] Furthermore, in step S5, constructing time-varying parameters in matrix form specifically includes obtaining the state parameters of air, convective heat transfer coefficient, thermal conductivity of wall material, and thermal properties of surrounding rock through linear interpolation based on the REFPROP physical property database at different temperatures.

[0029] As described above, the method for predicting the wall surface and surrounding rock temperature of the underground gas storage device in a compressed air energy storage power station according to the present invention has the following beneficial effects:

[0030] (1) The proposed modeling method of coupling the heat conduction of the surrounding rock with the energy storage-release thermodynamic process in the gas storage device can more accurately predict the temperature field distribution of the gas storage device wall and surrounding rock compared with the adiabatic model and the constant wall temperature model.

[0031] (2) By assuming adiabatic boundary conditions, the maximum possible distance (maximum characteristic length) of the gas temperature change inside the gas storage device affecting the temperature of the surrounding rock strata was determined, which reduced the dimension of the discretized heat conduction equations in the surrounding rock strata in the coupled model and reduced the computational cost.

[0032] (3) The operating temperature range of the gas storage device can be preliminarily determined in the early preliminary design stage, without the need to measure the temperature range by sensors during the power plant construction and trial operation stage. This can provide support for design material selection and process optimization in the early preliminary design stage. Attached Figure Description

[0033] Figure 1 The diagram shown is a flowchart of the method for predicting the wall surface and surrounding rock temperature of the underground gas storage device in a compressed air energy storage power station provided by the present invention.

[0034] Figure 2 The diagram shows the surrounding rock temperature distribution at various moments during the complete working cycle in the specific embodiment provided by the present invention. Detailed Implementation

[0035] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0036] In the description of this invention, it should be noted that, unless otherwise specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or a connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0037] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., used to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] Please see Figures 1 to 2 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0039] This invention provides a method for predicting the wall surface and surrounding rock temperature of an underground gas storage device in a compressed air energy storage power station, specifically including the following steps:

[0040] S1. Collect preliminary design parameters of the compressed air energy storage power station. The preliminary design parameters include the energy storage duration, air intake parameters, resting time, energy release time, exhaust flow rate, air storage pressure limit, volume of underground air storage device, inner wall surface area, wall material thickness and thermal conductivity, and far-end temperature and thermal conductivity of surrounding rock.

[0041] Specifically, the energy storage duration mentioned in step S1 is the charging duration under rated operating conditions in a single cycle of the compressed air energy storage power station; the air intake parameters are the temperature, pressure, and mass flow rate of the high-pressure gas at the inlet of the gas storage device during energy storage; the settling time is the time from the end of the energy storage or energy release phase of the compressed air energy storage power station to the start of the energy release or energy storage phase; the energy release duration is the rated power generation duration in a single cycle of the compressed air energy storage power station; and the gas storage pressure limit is the minimum and maximum gas pressure values ​​during the cyclic operation of the gas storage device.

[0042] Specifically, the wall material can be determined according to the actual design scheme of the underground gas storage device. The wall material of natural caves is the rock inside the cave, while the wall material of abandoned mines and artificial chambers is steel lining and backfill concrete.

[0043] Depending on the type of underground gas storage device, the wall material needs to be determined based on the actual design scheme. For example, the wall material of natural underground gas storage devices such as salt caverns and depleted oil and gas reservoirs is the rock inside the cave. The wall material of waste gas mines and artificial chambers needs to be considered based on the actual situation. In order to meet the gas storage requirements of compressed air energy storage power stations, these types of gas storage devices need to be reinforced and sealed, and their wall materials include steel linings and backfill concrete.

[0044] Specifically, the temperature of the surrounding rock at its far end is the temperature of the rock strata at the depth of the underground gas storage device obtained through geological surveys, and this rock strata temperature remains constant year after year.

[0045] S2. Assuming the underground gas storage device is under adiabatic conditions, based on the first law of thermodynamics, construct the energy balance equation for the energy storage-release process per unit time step, and calculate the temperature range of the gas in the underground gas storage device under adiabatic conditions.

[0046] Specifically, the adiabatic conditions in step S2 refer to the following: the gas storage device does not transfer heat to the outside world; the energy entering the gas storage device during the energy storage process is equal to the change in the internal thermodynamic energy of the gas storage device; the gas storage device reaches thermodynamic equilibrium during the static period, and the gas temperature and pressure do not change with time; and the energy flowing out of the gas storage device during the energy release process is equal to the change in the internal thermodynamic energy of the gas storage device. The energy equation is as follows:

[0047]

[0048] Where dU is the change in thermodynamic energy within the gas storage device at a certain moment under adiabatic conditions, and h i It is the specific enthalpy of the gas exchanged between the i-th gas storage device and the outside at that moment, dm i This represents the flow rate of the i-th gas stream at that moment. Typically, the compressed air energy storage power station has only one channel for exchanging gas with the outside environment. This simplifies the energy equation, and subsequent embodiments will be shown using the simplified version.

[0049] Furthermore, the energy equation for the energy storage-release process under adiabatic conditions is adopted as follows:

[0050] u τ+dτ =(m τ ·u τ +q m ·h τ ·dτ) / (m τ +q m ·dτ) (1)

[0051] Among them, u τ+dτ dτ is the specific thermodynamic energy of the air inside the gas storage device at time τ+dτ; dτ is the time step; m τ The mass of air inside the gas storage device at time τ; u τ q is the specific thermodynamic energy of the air inside the gas storage device at time τ; m h is the intake / exhaust flow rate during the energy storage phase at time τ. τ It is the specific enthalpy of the intake / exhaust air during the energy storage phase at time τ; the specific thermodynamic energy and specific enthalpy of the air are obtained from the REFPROP property database.

[0052] Based on the state parameters of the air inside the gas storage device at time τ, and combined with the air intake / static / exhaust status of the gas storage device at that time, the state parameters of the air inside the gas storage device at time τ+dτ under adiabatic conditions can be calculated.

[0053] The energy equation (1) for the energy storage-release process is essentially a set of differential equations about time at a series of moments. The operating pressure of the compressed air energy storage power station is relatively high, and the air is in a high-pressure state. If the ideal gas law is used directly, it will lead to a large error. Therefore, the air state parameters under different states are obtained using REFPROP property database data as input to the differential equation set. The air state parameters in the differential equation set change with temperature and pressure, and the state of the gas storage device also changes with time. It is impossible to obtain an analytical solution directly. A discretization method is used to obtain a numerical solution. In order to improve the accuracy of the numerical solution, the time step dτ is taken as small as possible. Iterative calculation starts from the initial moment. The temperature is the highest when the gas filling ends. The temperature does not change when the gas is in a static state. The temperature gradually decreases when the gas is discharged. The temperature reaches the lowest point when the gas is discharged. The highest temperature is T. a,max The lowest temperature is T a,min The temperature range of the gas storage device under adiabatic conditions is obtained as [T]. a,min ,T a,max ].

[0054] S3. Based on the temperature range of the gas in the underground gas storage device under adiabatic conditions, and combined with the temperature field distribution characteristics of the semi-infinite object of the fluid heat transfer boundary, determine the maximum characteristic length of the upper and lower limits of temperature that affect the temperature in the surrounding rock according to the energy storage time, the static time and the energy release time, respectively.

[0055] Furthermore, to improve computational accuracy, a larger surrounding rock thickness should be used in the model construction to determine the impact of temperature changes within the gas storage device on the surrounding rock temperature field. However, increasing the surrounding rock thickness within the computational domain will increase computational overhead. Without increasing the mesh width, increasing the surrounding rock thickness will lead to an increase in unknowns in the subsequent unsteady heat transfer equations. Therefore, it is necessary to determine the maximum possible range of influence of extreme temperatures within the gas storage device on the surrounding rock temperature field through adiabatic condition calculations, and to minimize computational overhead while ensuring accuracy.

[0056] Furthermore, based on the temperature range under adiabatic conditions obtained in S2, the maximum distance affecting the temperature field distribution of the surrounding rock under the energy storage and energy release states is calculated based on the minimum and maximum temperatures, respectively. The characteristic formula of the temperature field distribution within a semi-infinite object of the fluid heat transfer boundary is adopted:

[0057]

[0058] Where T(x,τ) is the temperature of the surrounding rock at a distance x from the inner wall of the gas storage device at time τ; T0 is the temperature of the far end of the surrounding rock; T a is the gas temperature inside the gas storage device; erfc is the residual error function; exp is the natural exponential function; λ is the thermal conductivity of the surrounding rock; ρ is the density of the surrounding rock; c is the specific heat capacity of the surrounding rock; h is the forced convection heat transfer coefficient of the air.

[0059] Substituting the storage duration and maximum temperature into formula (2), we obtain the temperature field distribution function T(x) inside the surrounding rock under adiabatic conditions and at the maximum temperature of the fluid. This function is a function of the distance x between the inside of the surrounding rock and the wall of the gas storage device. The maximum characteristic length is determined based on the temperature field distribution function T(x). That is, when T(x) approaches the temperature T0 at the far end of the surrounding rock, the distance x at that point is the characteristic length at the maximum temperature. Similarly, the characteristic length at the minimum temperature can be obtained, and then the maximum characteristic length can be further calculated. This can be obtained by plotting the function graph of T(x), or by obtaining the inverse function of T(x) and calculating using the following formula:

[0060]

[0061] Where, x cl α is the maximum feature length, and α is the margin coefficient, which is taken as 1.1 to 1.2. and These are the characteristic lengths for the highest and lowest temperatures, respectively.

[0062] S4. Based on the maximum characteristic length, construct a set of discretized heat conduction equations within the surrounding rock strata, and combine them with the unsteady flow energy equations for the energy storage time, static time, and energy release time segments, respectively, to establish a solution model for the fluid-wall-rock strata temperature field within the gas storage device coupled with unsteady heat transfer.

[0063] Furthermore, in step S4, the temperature field distribution within the surrounding rock is between the gas storage device and the surrounding rock. The boundary condition is the temperature of the gas within the gas storage device, which is also affected by the operating state of the gas storage device and the heat transfer state between it and the surrounding rock. Therefore, it is necessary to construct discretized unsteady-state heat transfer equations and unsteady-state energy equations within the gas storage device, respectively, and further construct a coupled model. Based on the maximum characteristic length, a grid is divided within the surrounding rock strata with a grid width of 1 cm.

[0064] The following formula is used to construct the discretized set of heat conduction equations within the surrounding rock strata:

[0065]

[0066] Among them, T i,j T is the temperature of grid i at time step j. i,j+1 T is the temperature of grid i at time step j+1. i-1,j T is the temperature of grid i-1 at the j-th time step. i+1,j ΔΦ is the temperature of grid i+1 at time step j, ΔΦ is the net heat transfer power of grid i at time step j, d is the grid width, Δτ is the time step, and r is the temperature of grid i+1 at time step j. i-1 It is the equivalent thermal resistance between mesh i and mesh i-1, r i+1It is the equivalent thermal resistance between mesh i and mesh i+1, d k and λ k These are the thickness and thermal conductivity of the k-th layer of wall material;

[0067] The following formula is used to establish a solution model for the fluid-wall-rock temperature field within a gas storage device with coupled unsteady heat transfer:

[0068]

[0069] m j+1 =m j +q m,j ·Δτ (8)

[0070] v j+1 =V / m j+1 (9)

[0071] Where, q m,j It is the gas mass flow rate, positive for filling and negative for releasing, which can be determined by the specific thermodynamic energy u of the air in the gas storage device at time step j+1. j+1 and specific volume v j+1 Other state parameters of air, including temperature and pressure, are determined based on data from the REFPROP physical property database. i＝1,j The temperature of the first layer of surrounding rock grid in contact with the wall of the gas storage device at time step j is given by formulas (4), (5), and (6). The temperature of each grid in the surrounding rock at time step j+1 can be determined by formulas (4), (5), and (6).

[0072] Furthermore, this coupled model is a discretized time-space model. Within each time step, the temperature field of the grid from the inside of the gas storage device to the outermost layer of the surrounding rock needs to be solved and updated. From the j-th time step to the (j+1)-th time step, the temperature of the gas inside the gas storage device at the (j+1)-th time step is solved according to formulas (7), (8), and (9). Then, as the boundary condition, it is substituted into formulas (4), (5), and (6) to solve the temperature distribution of the surrounding rock grid at the (j+1)-th time step. The temperature field distribution of the wall material and the surrounding rock at different times is obtained through iterative calculation.

[0073] S5. Based on the relevant parameters determined in step S1, construct a matrix of time-varying parameters, and then substitute them into the fluid-wall-rock temperature field solution model in step S4 to obtain the fluid-wall-rock temperature under different spatiotemporal distributions.

[0074] Considering that the physical and state parameters of the air in the gas storage device are not only functions of time but also affected by pressure and temperature, a matrix of time-varying parameters is constructed. Specifically, based on the REFPROP physical property database at different temperatures, the state parameters of the air, the convective heat transfer coefficient, the thermal conductivity of the wall material, and the thermal physical parameters of the surrounding rock are obtained by linear interpolation.

[0075] Specifically, in this embodiment, the results are presented using the preliminary design parameters of an actual compressed air energy storage power station project.

[0076] Table 1 shows some of the basic parameters collected according to step S1 in this embodiment of the application. Other air state parameters are imported from the REFPROP database during iterative calculation.

[0077] Table 1 Preliminary Design Parameters for Compressed Air Energy Storage Power Station

[0078] project numerical values unit Gas storage pressure range 6～12 MPa Surface area of ​​the inner wall of the gas storage 23000 square meters Energy storage time 10 Hour Release time 6 Hour resting time 4 Hour Inflation flow 360 t / h inflation pressure 12.2 MPa venting flow rate 600 t / h inflation temperature 50 ℃ Temperature at the far end of the surrounding rock 10 ℃ Surrounding rock density 2000 <![CDATA[kg / m 3 ]]> Specific heat capacity of surrounding rock 800 J / kg / K thermal conductivity of surrounding rock 4 W / m / K Initial forced air convection heat transfer coefficient 160 <![CDATA[W / m 2 / K]]>

[0079] like Figure 2 As shown in the figure, the distribution of the surrounding rock temperature field changes over time in a complete (24h) energy storage-release cycle in this embodiment of the application. As can be seen from the figure (from left to right), the energy storage lasts for ten hours, followed by a four-hour rest period, and the energy release lasts for six hours, followed by a four-hour rest period.

[0080] Temperature field distribution characteristics of the surrounding rock: Air undergoes intense mixing and movement within the gas storage device. The forced convection heat transfer rate between the air and the inner wall surface is much higher than that within the surrounding rock. Therefore, at the end of the previous cycle, due to the cooling effect of the exhaust gas, the temperature of the inner rock layer (the part of the surrounding rock closest to the inner wall of the gas storage device) is relatively low. However, the temperature of the outer rock layer (the part of the rock layer far from the inner wall of the gas storage device) remains relatively high due to the heating effect of the gas filling in the previous cycle. After the start of a new energy storage-release cycle, the gas temperature inside the gas storage device rises rapidly, simultaneously transferring heat to the inner rock layer. Because the air temperature rises faster and the forced convection heat transfer rate is higher than that of the surrounding rock, the temperature of the inner rock layer begins to rise rapidly until... Beyond the outer rock layer; after the energy storage phase ends, the gas storage device is in a static phase, and the air temperature no longer rises. Since the air temperature is still higher than the inner rock layer temperature at this time, the inner rock layer temperature continues to rise slowly until the static phase ends; after the energy release phase begins, the air temperature inside the gas storage device drops rapidly, and the inner rock layer transfers heat to the air inside the gas storage device, causing its temperature to drop rapidly as well. Meanwhile, the hotter rock layers in the outer rock layer not only transfer heat to the distant end but also to the inner rock layer, so the temperature curve gradually flattens out; in the static phase after the energy release phase ends, the inner rock layer transfers heat to the air inside the gas storage device on one hand and receives heat from the outer rock layer on the other. Overall, the temperature curve flattens out further.

[0081] Other components and operations of the method for predicting the wall surface and surrounding rock temperature of an underground gas storage device in a compressed air energy storage power station according to an embodiment of the present invention are known to those skilled in the art and will not be described in detail here.

[0082] In summary, the method for predicting the wall surface and surrounding rock temperature of the underground gas storage device in a compressed air energy storage power station, as proposed in this invention, employs a coupled modeling approach that integrates surrounding rock heat conduction with the energy storage-release thermodynamic process within the gas storage device. Compared to adiabatic and constant wall temperature models, this method can more accurately predict the temperature field distribution of the gas storage device wall and surrounding rock. By assuming adiabatic boundary conditions, the maximum possible distance (maximum characteristic length) by which changes in the gas temperature inside the gas storage device affect the temperature of the surrounding rock strata is determined, reducing the dimensionality of the discretized heat conduction equations within the surrounding rock strata in the coupled model and lowering computational costs. Furthermore, the operating temperature range of the gas storage device can be preliminarily determined in the early preliminary design stage, eliminating the need for temperature range measurement via sensors during the power station's construction and commissioning phase. This provides support for material selection and process optimization during the early preliminary design stage. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and possesses high industrial applicability.

[0083] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for predicting the wall surface and surrounding rock temperature of an underground gas storage device in a compressed air energy storage power station, characterized in that, Includes the following steps: S1. Collect preliminary design parameters of the compressed air energy storage power station. The preliminary design parameters include the energy storage duration, air intake parameters, resting time, energy release time, exhaust flow rate, air storage pressure limit, volume of underground air storage device, inner wall surface area, wall material thickness and thermal conductivity, and far-end temperature and thermal conductivity of surrounding rock. S2. Assuming the underground gas storage device is under adiabatic conditions, based on the first law of thermodynamics, construct the energy balance equation for the energy storage-release process per unit time step, and calculate the temperature range of the gas in the underground gas storage device under adiabatic conditions. S3. Based on the temperature range of the gas in the underground gas storage device under adiabatic conditions, and combined with the temperature field distribution characteristics of the semi-infinite object of the fluid heat transfer boundary, determine the maximum characteristic length of the upper and lower limits of temperature that affect the temperature in the surrounding rock according to the energy storage time, the static time and the energy release time, respectively. S4. Based on the maximum characteristic length, construct a set of discretized heat conduction equations within the surrounding rock strata, and combine them with the unsteady flow energy equations for the energy storage time, static time, and energy release time segments, respectively, to establish a solution model for the fluid-wall-rock strata temperature field within the gas storage device coupled with unsteady heat transfer. S5. Based on the relevant parameters determined in step S1, construct a matrix of time-varying parameters, and then substitute them into the fluid-wall-rock temperature field solution model in step S4 to obtain the fluid-wall-rock temperature under different spatiotemporal distributions.

2. The method for predicting the wall surface and surrounding rock temperature of the underground gas storage device in a compressed air energy storage power station according to claim 1, characterized in that, The energy storage duration in step S1 is the charging duration under rated operating conditions in a single cycle of the compressed air energy storage power station. The inlet parameters are the temperature, pressure, and mass flow rate of the high-pressure gas at the inlet of the gas storage device during energy storage. The settling time is the time from the end of the energy storage or release phase of the compressed air energy storage power station to the start of the energy release or storage phase. The energy release duration is the rated power generation duration in a single cycle of the compressed air energy storage power station. The gas storage pressure limit is the minimum and maximum gas pressure during the cyclic operation of the gas storage device.

3. The method for predicting the wall surface and surrounding rock temperature of the underground gas storage device in a compressed air energy storage power station according to claim 1, characterized in that, In step S2, the energy equation for the energy storage-release process under adiabatic conditions is as follows: u τ+dτ =(m τ ·u τ +q m ·h τ ·dτ) / (m τ +q m ·dτ) (1) Among them, u τ+dτ dτ is the specific thermodynamic energy of the air inside the gas storage device at time τ+dτ; dτ is the time step; m τ The mass of air inside the gas storage device at time τ; u τ q is the specific thermodynamic energy of the air inside the gas storage device at time τ; m h is the intake / exhaust flow rate during the energy storage phase at time τ. τ It is the specific enthalpy of intake / exhaust during the energy storage phase at time τ; Equation (1) is solved using a time discretization method. Based on the specific thermodynamic energy and specific volume of the air in the gas storage device at time τ+dτ, the temperature of the air in the gas storage device at time τ+dτ is obtained from the REFPROP property database. Iterative calculations are performed starting from the initial time. The temperature remains unchanged in the static state, gradually decreases during exhaust, and reaches its lowest point at the end of exhaust. The highest temperature is T. a,max The lowest temperature is T a,min The temperature range of the gas storage device under adiabatic conditions is obtained as [T]. a,min ,T a,max ].

4. The method for predicting the wall surface and surrounding rock temperature of the underground gas storage device in a compressed air energy storage power station according to claim 1, characterized in that, In step S3, the temperature field distribution characteristics within the semi-infinite object at the fluid heat transfer boundary are defined by the following formula: Where T(x,τ) is the temperature of the surrounding rock at a distance x from the inner wall of the gas storage device at time τ; T0 is the temperature of the far end of the surrounding rock; T a is the gas temperature inside the gas storage device; erfc is the residual error function; exp is the natural exponential function; λ is the thermal conductivity of the surrounding rock; ρ is the density of the surrounding rock; c is the specific heat capacity of the surrounding rock; h is the forced convection heat transfer coefficient of the air. The maximum characteristic length is the maximum range of influence on the temperature distribution of the surrounding rock during the operation of a compressed air energy storage power station, and is calculated using the following formula: Where, x cl α is the maximum feature length, and α is the margin coefficient, which is taken as 1.1 to 1.

2. and These are the characteristic lengths for the highest and lowest temperatures, respectively.

5. The method for predicting the wall surface and surrounding rock temperature of the underground gas storage device in a compressed air energy storage power station according to claim 1, characterized in that, In step S4, the discretized set of heat conduction equations within the surrounding rock strata is constructed using the following formulas: Among them, T i,j T is the temperature of grid i at time step j. i,j+1 T is the temperature of grid i at time step j+1. i-1,j T is the temperature of grid i-1 at the j-th time step. i+1,j ΔΦ is the temperature of grid i+1 at time step j, ΔΦ is the net heat transfer power of grid i at time step j, d is the grid width, Δτ is the time step, and r is the temperature of grid i+1 at time step j. i-1 It is the equivalent thermal resistance between mesh i and mesh i-1, r i+1 It is the equivalent thermal resistance between mesh i and mesh i+1, d k and λ k These are the thickness and thermal conductivity of the k-th layer of wall material; The following formula is used to establish a solution model for the fluid-wall-rock temperature field within a gas storage device with coupled unsteady heat transfer: m j+1 =m j +q m,j ·Δτ (8) in j+1 =V / m j+1 (9) Where, q m,j It is the gas mass flow rate, positive for filling and negative for releasing, which can be determined by the specific thermodynamic energy u of the air in the gas storage device at time step j+1. j+1 and specific volume v j+1 Other state parameters of air, including temperature and pressure, are determined based on data from the REFPROP physical property database. i＝1,j The temperature of the first layer of surrounding rock grid in contact with the wall of the gas storage device at time step j is given by formulas (4), (5), and (6). The temperature of each grid in the surrounding rock at time step j+1 can be determined by formulas (4), (5), and (6).

6. The method for predicting the wall surface and surrounding rock temperature of the underground gas storage device in a compressed air energy storage power station according to claim 5, characterized in that, The temperature of the gas inside the gas storage device at the (j+1)th time step is calculated using formulas (7), (8), and (9). Then, it is used as a boundary condition and substituted into formulas (4), (5), and (6) to calculate the temperature distribution of the surrounding rock grid at the (j+1)th time step. The temperature field distribution of the wall material and the surrounding rock at different times is obtained through iterative calculation.

7. The method for predicting the wall surface and surrounding rock temperature of the underground gas storage device in a compressed air energy storage power station according to claim 1, characterized in that, In step S5, constructing time-varying parameters in matrix form specifically includes obtaining the state parameters of air, convective heat transfer coefficient, thermal conductivity of wall material, and thermal properties of surrounding rock through linear interpolation based on the REFPROP physical property database at different temperatures.

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