Compressed air energy storage system series-parallel heat exchanger thermal resistance calculation method

Abstract

The invention discloses a thermal resistance calculation method for series-parallel heat exchangers of a compressed air energy storage system, and belongs to the field of compressed air energy storage. Aiming at different arrangement modes of the heat exchangers of the whole system, a heat exchanger model is established based on standard thermal resistance of the heat exchangers of inlet temperature and pressure; a heat exchanger is simplified through a standard thermal resistance method and decomposed into a plurality of equivalent thermal resistances, and temperature distribution of different thermal resistances is calculated through a series and parallel circuit rule. According to the method, the defects of a traditional heat exchanger modeling mode can be overcome, the heat exchanger model is established based on the standard heat resistance of the heat exchanger of inlet temperature and pressure for different arrangement modes of the heat exchanger of the whole system, and the energy flow model of the heat exchanger is established, so that design calculation of the heat exchanger is simple and convenient, and consideration factors in the heat exchange process are increased; according to the mode, different energy flow models are established through different series-parallel connection modes, and the heat exchange process is simplified.

Description

Technical Field

[0001] The present invention relates to the field of compressed air energy storage, and in particular to a method for calculating the thermal resistance of series-parallel heat exchangers in a compressed air energy storage system. The method is specifically applied in a compressed air energy storage system to calculate the thermal resistance of a system heat exchanger. Background Art

[0002] As fossil energy and ecological environment problems become increasingly serious, new energy generation technologies such as wind power, solar photovoltaic / solar thermal power generation have become the backbone of future energy generation. Although the total installed capacity of wind and solar power continues to increase, there are still a lot of problems of wind and solar power abandonment, and the instability, intermittency and volatility of wind and solar power generation have brought great threats to the safe operation of the power grid, greatly limiting the safe grid connection of renewable energy.

[0003] Compressed air energy storage technology has the advantages of low cost, short construction period, relatively easy site selection, and eco-friendly environment. It has become a large-scale physical clean energy storage that has developed rapidly after pumped storage. During the energy storage process, electrical energy is converted into high-pressure air for storage. When releasing energy, the high-pressure air is released to drive the turbine to work, thereby driving the generator to output electrical energy. The system requires multiple heat exchangers for heat exchange during the recovery, storage and utilization of compression heat. The system heat exchangers are arranged in series, parallel, and series-parallel. At present, there are the following problems in the design and calculation of compressed air energy storage heat exchangers: 1) Most of the heat exchanger design calculation and modeling processes use efficiency calculations, which only consider the inlet and outlet temperatures of the hot and cold fluids and the end difference of the heat exchanger. There are few factors considered, which is not comprehensive and has large errors; 2) Secondly, there is little research on the overall heat exchanger layout of the system, and the impact of series and parallel connections on the heat exchanger outlet temperature is not considered; 3) Traditional modeling has little research on the structure, operating parameters and arrangement of fluids in heat exchangers. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for calculating the thermal resistance of series-parallel heat exchangers in a compressed air energy storage system, which can overcome the shortcomings of traditional heat exchanger modeling methods. According to the different arrangements of the heat exchangers in the overall system, a heat exchanger model is established based on the standard thermal resistance of the heat exchanger at the inlet temperature and pressure. By establishing an energy flow model of the heat exchanger, the design and calculation of the heat exchanger is simplified, and the factors to be considered in the heat exchange process are increased. Different energy flow models are established by different series and parallel modes, which simplifies the heat exchange process.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: A method for calculating the thermal resistance of series-parallel heat exchangers in a compressed air energy storage system is proposed. A heat exchanger model is established based on the standard thermal resistance of the heat exchanger at inlet temperature and pressure according to the different arrangements of the heat exchangers in the overall system. The heat exchanger is simplified and decomposed into several equivalent thermal resistances using the standard thermal resistance method, and the temperature distribution of different thermal resistances is calculated using the series and parallel circuit rules.

[0006] A further improvement of the technical solution of the present invention is that the standard thermal resistance modeling process of the heat exchanger is: When a downstream heat exchanger is used, the cold and hot fluids flow in the same direction, and the temperature changes of the cold and hot fluids are: (1) In the formula, m c is the mass flow rate of the cold fluid, m h is the mass flow rate of thermal fluid, in kg / s; c p,c is the specific heat capacity of the cold fluid, c p,h is the specific heat capacity of the thermal fluid, in kJ / (kg·k); K is the total heat transfer coefficient of the heat exchanger, in W / (m 2 K); L is the length of the heat exchange pipe, in m; A is the area of ​​the heat exchanger, in m 2 ; is the temperature of the cooling fluid in the heat exchanger, is the temperature of the hot fluid in the heat exchanger, in K; Combine equation (1) and integrate equation (1) from the fluid inlet to the outlet: (2) In the formula, T c,o is the outlet temperature of the cold fluid in the heat exchanger, T h,o is the outlet temperature of the hot fluid in the heat exchanger, in K; T c,i is the inlet temperature of the cold fluid in the heat exchanger, T h,i is the inlet temperature of the heat exchanger hot fluid, in K; is the heat capacity of the cold fluid, is the heat capacity of the thermal fluid, in W / K; According to the energy conservation equation of hot and cold fluids, the thermal resistance of the downstream heat exchanger is: (3) The thermal resistance of the downstream heat exchanger is: (4) Similarly, the thermal resistance of the counterflow heat exchanger is: (5) Where Q is the heat transfer between fluids, unit is W.

[0007] A further improvement of the technical solution of the present invention is that when the heat exchangers in the compressed air energy storage system are arranged in parallel, the cold fluid exchanges heat with each heat exchanger through the channel, and the high-temperature fluid enters the storage tank for storage after the heat exchange. Assuming that the inlet and outlet temperatures of the cold fluid are the same, the parallel heat exchanger network model is: (6) In the formula, is the inlet temperature of the hot fluid in the first heat exchanger, is the inlet temperature of the hot fluid in the second heat exchanger, is the inlet temperature of the hot fluid of the third heat exchanger, in K; is the outlet temperature of the cold fluid, in K; The heat exchange amount of the cold and hot fluids in the first heat exchanger, The heat exchanger for the hot and cold fluids in the second heat exchanger, is the heat exchange amount of the cold and hot fluids in the third heat exchanger, in W; is the thermal resistance of the first heat exchanger, is the thermal resistance of the second heat exchanger, is the thermal resistance of the third heat exchanger, in K / W; G 1 is the heat capacity of the first heat exchanger 、G 2 is the heat capacity of the second heat exchanger 、G 3 is the heat capacity of the third heat exchanger, in W / K.

[0008] A further improvement of the technical solution of the present invention is that when the heat exchangers in the compressed air energy storage system are arranged in series, the cold fluid exchanges heat with each heat exchanger in turn through the channel, and the cold fluid enters the storage tank for storage after being heated by the multi-stage heat exchanger. Assuming that the inlet and outlet temperatures of the cold fluid are the same, the network model of the series heat exchanger is: (7) (8) (9) In the formula, is the inlet temperature of the hot fluid in the first heat exchanger, is the inlet temperature of the hot fluid in the second heat exchanger, is the inlet temperature of the hot fluid of the third heat exchanger, in K; is the outlet temperature of the cold fluid, in K; The heat exchange amount of the cold and hot fluids in the first heat exchanger, The heat exchanger for the hot and cold fluids in the second heat exchanger, is the heat exchange amount of the cold and hot fluids in the third heat exchanger, in W; is the thermal resistance of the first heat exchanger, is the thermal resistance of the second heat exchanger, is the thermal resistance of the third heat exchanger, in K / W; is the heat capacity of the cold fluid, in W / K.

[0009] Due to the adoption of the above technical solution, the technical progress achieved by the present invention is: Compared with the heat exchanger modeling method in traditional compressed air energy storage technology, the present invention takes into account the layout of the overall heat exchanger of the system, builds an energy flow model for the heat exchanger layout, and treats the heat exchanger as a one-dimensional flat wall thermal or electrical resistance when analyzing and designing the performance of the heat exchanger, and uses "Fourier's Law" (Ohm's Law) to express it. At the same time, the calculation of the fluid temperature after heat exchange fully considers the structure of the heat exchanger performance, operating parameters and the layout of the fluid in the heat exchanger, and considers the mutual influence between the heat exchangers. Compared with the existing modeling method, this method improves the calculation accuracy, is more in line with the actual system operating conditions, and provides a more accurate mathematical model for related system research. At the same time, by building and connecting the energy flow model in series, the heat exchange problem is simplified to a thermal resistance problem, and the whole process is simpler and more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative labor. Figure 1 is a schematic diagram of a downstream heat exchanger in an embodiment of the present invention; Figure 2 is a schematic diagram of a parallel heat exchange network of heat exchangers in an embodiment of the present invention; Figure 3 is a schematic diagram of a heat exchange network of heat exchangers in series in an embodiment of the present invention; Figure 4 is a schematic diagram of a parallel network energy flow model in an embodiment of the present invention; Figure 5 It is a schematic diagram of a series network energy flow model in an embodiment of the present invention. DETAILED DESCRIPTION

[0011] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or apparatus.

[0012] The present invention is further described in detail below with reference to the accompanying drawings and embodiments: A method for calculating the thermal resistance of series-parallel heat exchangers in a compressed air energy storage system is proposed. A heat exchanger model is established based on the standard thermal resistance of the heat exchanger at inlet temperature and pressure according to the different arrangements of the heat exchangers in the overall system. The heat exchanger is simplified and decomposed into several equivalent thermal resistances using the standard thermal resistance method, and the temperature distribution of different thermal resistances is calculated using the series and parallel circuit rules.

[0013] When a downstream heat exchanger is used, as shown in Figure 1, the cold and hot fluids flow in the same direction, as shown in the following formula, and the temperature change of the cold and hot fluids is: (1) In the formula, m c is the mass flow rate of the cold fluid, m h is the mass flow rate of thermal fluid, in kg / s; c p,c is the specific heat capacity of the cold fluid, c p,h is the specific heat capacity of the thermal fluid, in kJ / (kg·k); K is the total heat transfer coefficient of the heat exchanger, in W / (m 2 K); L is the length of the heat exchange pipe, in m; A is the area of ​​the heat exchanger, in m 2 ; is the temperature of the cooling fluid in the heat exchanger, is the temperature of the hot fluid in the heat exchanger, in K; Combine equation (1) and integrate equation (1) from the fluid inlet to the outlet: (2) In the formula, T c,o is the outlet temperature of the cold fluid in the heat exchanger, T h,o is the outlet temperature of the hot fluid in the heat exchanger, in K; T c,i is the inlet temperature of the cold fluid in the heat exchanger, T h,i is the inlet temperature of the heat exchanger hot fluid, in K; is the heat capacity of the cold fluid, is the heat capacity of the thermal fluid, in W / K; According to the energy conservation equation of hot and cold fluids, the thermal resistance of the downstream heat exchanger can be deduced as: (3) The thermal resistance of the downstream heat exchanger is: (4) Similarly, the thermal resistance of the counterflow heat exchanger is: (5) Where Q is the heat transfer between fluids, unit is W.

[0014] The layout of the heat exchanger in the compressed air energy storage system can be divided into series, parallel and multi-circuit modes. When analyzing and designing the performance of the heat exchanger, the heat exchanger is treated as a one-dimensional flat wall thermal or electrical resistor and expressed using the "Fourier Law" (Ohm's Law). At the same time, the calculation of the fluid temperature after heat exchange fully considers the structure of the heat exchanger performance, operating parameters, and the layout of the fluid in the heat exchanger, and considers the mutual influence between the heat exchangers, thereby improving the calculation accuracy.

[0015] In common CAE systems, heat exchangers are connected in parallel, as shown in Figure 2. The cold fluid exchanges heat with each heat exchanger through channels. After the heat exchange, the high-temperature fluid enters the storage tank for storage.

[0016] In the compressed air energy storage (CAES) system, the heat exchangers are connected in parallel. The cold fluid exchanges heat with each heat exchanger through the channel. After the heat exchange, the high-temperature fluid enters the storage tank for storage. As shown in Figure 2 and Figure 4, they are the heat exchange network and energy flow model of the heat exchanger parallel connection respectively: Assuming that the inlet and outlet temperatures of the cold fluid are the same, the parallel heat exchanger network model is: (6) In addition, through multi-stage heating, the cold end temperature of the heat exchanger is connected in series, as shown in Figure 3, and the cold fluid is heated by the multi-stage heat exchanger and then enters the storage tank for storage.

[0017] like Figure 3 and Figure 5 As shown in the figure, they are the heat exchange network and energy flow model of the heat exchanger in series, and the network model of the heat exchanger in series is: (7) (8) (9) In the formula, is the hot fluid inlet temperature of the first heat exchanger, is the inlet temperature of the hot fluid in the second heat exchanger, is the inlet temperature of the hot fluid of the third heat exchanger, in K; is the outlet temperature of the cold fluid, in K; The heat exchange amount of the cold and hot fluids in the first heat exchanger, The heat exchanger for the hot and cold fluids in the second heat exchanger, is the heat exchange amount of the cold and hot fluids in the third heat exchanger, in W; is the thermal resistance of the first heat exchanger, is the thermal resistance of the second heat exchanger, is the thermal resistance of the third heat exchanger, in K / W; G 1 is the heat capacity of the first heat exchanger 、G 2 is the heat capacity of the second heat exchanger 、G 3 is the heat capacity of the third heat exchanger, in W / K.

[0018] It should also be noted that for the sake of ease of explanation, the present invention only lists the arrangement of three heat exchangers in series and parallel. If the compressed air energy storage system is purely connected in series or parallel, this thermal resistance model can be used for calculation, and only the number of heat exchangers needs to be increased. However, if the multi-circuit mode is synthesized in series and parallel, the thermal resistance remains unchanged, only the energy flow changes.

[0019] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating the thermal resistance of series-parallel heat exchangers in a compressed air energy storage system, characterized in that: According to the different arrangements of the heat exchanger in the overall system, a heat exchanger model is established based on the standard thermal resistance of the heat exchanger at the inlet temperature and pressure. The heat exchanger is simplified and decomposed into several equivalent thermal resistances using the standard thermal resistance method, and the temperature distribution of different thermal resistances is calculated using the series and parallel circuit rules.

2. A method for calculating thermal resistance of series-parallel heat exchangers in a compressed air energy storage system according to claim 1, characterized in that: The standard thermal resistance modeling process of the heat exchanger is: When a downstream heat exchanger is used, the cold and hot fluids flow in the same direction, and the temperature changes of the cold and hot fluids are: (1) In the formula, m c is the mass flow rate of the cold fluid, m h is the mass flow rate of thermal fluid, in kg / s; c p,c is the specific heat capacity of the cold fluid, c p,h is the specific heat capacity of the thermal fluid, in kJ / (kg·k); K is the total heat transfer coefficient of the heat exchanger, in W / (m 2 K); L is the length of the heat exchange pipe, in m; A is the area of ​​the heat exchanger, in m 2 ; is the temperature of the cooling fluid in the heat exchanger, is the temperature of the hot fluid in the heat exchanger, in K; Combine equation (1) and integrate equation (1) from the fluid inlet to the outlet: (2) In the formula, T c,o is the outlet temperature of the cold fluid in the heat exchanger, T h,o is the outlet temperature of the hot fluid in the heat exchanger, in K; T c,i is the inlet temperature of the cold fluid in the heat exchanger, T h,i is the inlet temperature of the heat fluid in the heat exchanger, in K; is the heat capacity of the cold fluid, is the heat capacity of the thermal fluid, in W / K; According to the energy conservation equation of hot and cold fluids, the thermal resistance of the downstream heat exchanger is: (3) The thermal resistance of the downstream heat exchanger is: (4) Similarly, the thermal resistance of the counterflow heat exchanger is: (5) Where Q is the heat transfer between fluids, unit is W.

3. A method for calculating thermal resistance of series-parallel heat exchangers in a compressed air energy storage system according to claim 2, characterized in that: When the heat exchangers in the compressed air energy storage system are arranged in parallel, the cold fluid exchanges heat with each heat exchanger through the channel. After the heat exchange, the high-temperature fluid enters the storage tank for storage. Assuming that the inlet and outlet temperatures of the cold fluid are the same, the parallel heat exchanger network model is: (6) In the formula, is the inlet temperature of the hot fluid in the first heat exchanger, is the inlet temperature of the hot fluid in the second heat exchanger, is the inlet temperature of the hot fluid of the third heat exchanger, in K; is the outlet temperature of the cold fluid, in K; The heat exchange amount of the cold and hot fluids in the first heat exchanger, The heat exchanger for the hot and cold fluids in the second heat exchanger, is the heat exchange amount of the cold and hot fluids in the third heat exchanger, in W; is the thermal resistance of the first heat exchanger, is the thermal resistance of the second heat exchanger, is the thermal resistance of the third heat exchanger, in K / W; G 1 is the heat capacity of the first heat exchanger 、G 2 is the heat capacity of the second heat exchanger 、G 3 is the heat capacity of the third heat exchanger, in W / K.

4. A method for calculating thermal resistance of series-parallel heat exchangers in a compressed air energy storage system according to claim 2, characterized in that: When the heat exchangers in the compressed air energy storage system are arranged in series, the cold fluid exchanges heat with each heat exchanger through the channel in turn. The cold fluid is heated by the multi-stage heat exchanger and then enters the storage tank for storage. Assuming that the inlet and outlet temperatures of the cold fluid are the same, the network model of the series heat exchanger is: (7) (8) (9) In the formula, is the inlet temperature of the hot fluid in the first heat exchanger, is the inlet temperature of the hot fluid in the second heat exchanger, is the inlet temperature of the hot fluid in the third heat exchanger, K; is the outlet temperature of the cold fluid, K; The heat exchange amount of the cold and hot fluids in the first heat exchanger, The heat exchanger for the hot and cold fluids in the second heat exchanger, is the heat exchange amount of the hot and cold fluids in the third heat exchanger, W; is the thermal resistance of the first heat exchanger, is the thermal resistance of the second heat exchanger, is the thermal resistance of the third heat exchanger, K / W; is the heat capacity of the cold fluid, in W / K.

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