Carbon dioxide energy storage system and method for low-pressure side cold supplement

Abstract

The invention provides a carbon dioxide energy storage system and method for low-pressure side cold supplement. The carbon dioxide energy storage system comprises a low-pressure storage tank, a multi-layer sleeve type energy storage heat exchange module, an energy charging and releasing module and a high-pressure storage tank which are connected in sequence. The multi-layer sleeve type energy storage heat exchange module comprises an inner pipe, a sleeve and an outer pipe which are coaxial and sequentially arranged in a sleeved mode from inside to outside, and inner-layer flow channels which are sequentially arranged from inside to outside are formed. And an energy storage chamber and an outer layer flow channel. And the energy storage chamber is filled with a phase change material. The multi-layer sleeve type energy storage heat exchange module corresponds to a refrigerating machine. A multi-layer sleeve type energy storage heat exchange module with a three-layer nested structure is introduced to the low-pressure side of the carbon dioxide energy storage system; in the energy releasing process, when the conditions of carbon dioxide flow fluctuation, insufficient cooling capacity of the phase-change material of the middle layer and the like occur, cold is supplemented to the phase-change material and carbon dioxide of the inner layer through the outer-layer flow channel, and it can be ensured that carbon dioxide can be fully liquefied and enter the low-pressure storage tank.

Description

Technical Field

[0001] The present invention relates to the field of physical energy storage technology, and in particular to a carbon dioxide energy storage system and method for low-pressure side cooling supplementation. Background Art

[0002] Building a new power system with renewable energy as the main body will help reduce coal-fired power generation and carbon dioxide emissions. However, renewable energy is subject to natural conditions and has great volatility and intermittency. Large-scale grid connection will affect the safe and stable operation of the power grid, and the utilization rate is low, making development difficult. Therefore, it is necessary to develop energy storage technology to facilitate peak load shifting and valley filling of new power system power generation. Traditional physical energy storage methods mainly include pumped storage, compressed air storage, flywheel storage, etc. The dual liquid compressed carbon dioxide energy storage system can use natural cold sources and natural heat sources to liquefy and gasify carbon dioxide, thereby improving the overall power-to-power conversion efficiency of the system.

[0003] At present, the liquefaction of carbon dioxide on the low-pressure side of the dual-liquid compressed carbon dioxide energy storage system adopts phase change cold storage, and carbon dioxide liquefaction is achieved by absorbing the evaporative cold released during the compression process of carbon dioxide stored in the phase change material. In order to avoid the waste of cold energy, the phase change material can be pre-cooled to near the phase change point before the carbon dioxide system is started. However, since the evaporation and liquefaction of carbon dioxide will absorb and release huge amounts of heat, the mass of the phase change material required for cold and heat storage is large, which requires a large amount of cold energy for pre-cooling the phase change material. In addition, during the liquefaction process, carbon dioxide can only absorb the cold energy stored in the phase change material. If the flow rate of carbon dioxide is too large or there is a problem with the phase change material during the cold storage process, resulting in insufficient storage of cold energy, it will lead to incomplete liquefaction of carbon dioxide, causing excessive system pressure and safety risks. Summary of the invention

[0004] In order to solve the technical problems existing in the prior art, the present invention provides a multi-layer sleeve type energy storage and heat exchange module for liquefaction on the low-pressure side of a carbon dioxide energy storage system. The present invention can realize pre-cooling of phase change materials before starting the carbon dioxide energy storage system and supplementary cooling during carbon dioxide liquefaction, thereby improving the economy and stability of the operation of the carbon dioxide energy storage system.

[0005] In the first aspect, the present invention provides a carbon dioxide energy storage system with supplementary cooling on the low-pressure side, which comprises a low-pressure storage tank, a multi-layer sleeve-type energy storage heat exchange module, an energy charging and releasing module and a high-pressure storage tank connected in sequence. The multi-layer sleeve-type energy storage heat exchange module comprises an inner tube, a sleeve and an outer tube which are coaxial and sequentially sleeved from the inside to the outside; the inner cavity of the inner tube is an inner layer flow channel; a circular energy storage chamber is formed between the inner wall of the sleeve and the outer wall of the inner tube; and a circular outer layer flow channel is formed between the outer wall of the sleeve and the inner wall of the outer tube. The energy storage chamber is filled with phase change material.

[0006] The multi-layer tube-type energy storage heat exchange module corresponds to a refrigerator. The refrigerator is connected to the outer flow channel to form a cold supplement circulation loop. The charging and releasing module includes a charging branch and a releasing branch connected in parallel. The charging branch is used to compress the gaseous carbon dioxide output by the multi-layer tube-type energy storage heat exchange module to perform work and liquefy the carbon dioxide; the releasing branch is used to gasify the liquid carbon dioxide output by the high-pressure storage tank and expand the carbon dioxide to perform work externally.

[0007] During the energy storage process, the liquid carbon dioxide in the low-pressure storage tank passes through the multi-layer shell-and-tube energy storage and heat exchange module and the charging branch in turn, and is stored in the high-pressure storage tank.

[0008] During the energy release process, the liquid carbon dioxide in the high-pressure storage tank passes through the energy release branch and the multi-layer sleeve-type energy storage and heat exchange module in turn, and is stored in the low-pressure storage tank.

[0009] Preferably, the thickness of the energy storage chamber (7-5) is Less than or equal to the upper limit of thickness . Upper limit of thickness . is the upper limit of the inner diameter of the casing, and its expression is:

[0010]

[0011] in, is the thermal conductivity of the phase change material; h o is the heat transfer coefficient between the phase change material in the energy storage chamber (7-5) and the heat transfer medium in the outer flow channel.

[0012] Preferably, the thickness of the energy storage chamber (7-5) is Greater than or equal to the lower limit of thickness . Upper limit of thickness . is the lower limit of the casing inner diameter, and its expression is:

[0013]

[0014] Wherein, k and ΔT are respectively the heat exchange coefficient and the heat exchange temperature difference between the phase change material in the energy storage chamber (7-5) and the carbon dioxide in the inner flow channel (7-4); t is the energy storage operation time (specifically, the time for the carbon dioxide energy storage system to perform a complete energy storage process); is the minimum phase change material mass; is the density of the phase change material; is the target cooling capacity.

[0015] Preferably, the length L of the sleeve (7-2) satisfies the following relationship:

[0016]

[0017] in, is the cross-sectional area of ​​the energy storage chamber (7-5).

[0018] Minimum phase change material mass The following relationship is satisfied:

[0019]

[0020] in, is the latent heat of phase change of phase change material.

[0021] Preferably, the energy storage system further comprises a low-pressure inlet and outlet module connected between the low-pressure storage tank and the inner flow channel of the multi-layer sleeve-type energy storage and heat exchange module. The low-pressure inlet and outlet module comprises a throttle valve and a switch valve connected in parallel.

[0022] Preferably, the charging branch includes a low-pressure energy storage heat exchanger, a compressor, a high-pressure energy storage heat exchanger, and a high-pressure liquefaction heat exchanger. The energy release branch includes a high-pressure gasification heat exchanger, an energy release high-pressure heat exchanger, a turbine, and an energy release low-pressure heat exchanger. The first heat exchange flow path in the low-pressure energy storage heat exchanger, the compressor, the first heat exchange flow path in the high-pressure energy storage heat exchanger, the first heat exchange flow path in the high-pressure liquefaction heat exchanger, and the high-pressure storage tank are connected in sequence along the flow direction of carbon dioxide. The first heat exchange flow path in the high-pressure gasification heat exchanger, the first heat exchange flow path in the high-pressure energy release heat exchanger, the turbine, and the first heat exchange flow path in the low-pressure energy release heat exchanger are connected in sequence along the flow direction of carbon dioxide.

[0023] Preferably, a cold storage device and a heat storage device for transferring heat or cold are respectively provided between the energy storage low-pressure heat exchanger and the energy release low-pressure heat exchanger, between the energy storage high-pressure heat exchanger and the energy release high-pressure heat exchanger, and between the high-pressure liquefaction heat exchanger and the high-pressure gasification heat exchanger.

[0024] Preferably, the phase change material needs to be selected according to the temperature range required by the system process, and the phase change temperature is generally -50-0°C.

[0025] Preferably, the difference between the inner and outer diameters of the outer layer flow channel is 2-10 mm.

[0026] In a second aspect, the present invention provides a carbon dioxide energy storage method with low-pressure side supplementary cooling, which uses the aforementioned carbon dioxide energy storage system. The carbon dioxide energy storage method comprises the following steps: including an energy storage process and an energy release process.

[0027] The energy storage process is as follows: the liquid carbon dioxide output from the low-pressure storage tank is partially vaporized in the throttle valve, absorbs heat and vaporizes in the multi-layer shell-and-tube energy storage heat exchange module, absorbs heat and heats up in the energy storage low-pressure heat exchanger, is compressed to a supercritical state in the compressor transcritical state, releases heat and cools down in the energy storage high-pressure heat exchanger, releases heat and liquefies in the high-pressure liquefaction heat exchanger, and is stored in the high-pressure storage tank.

[0028] The energy release process is as follows: the liquid carbon dioxide output from the high-pressure storage tank absorbs heat and vaporizes in the high-pressure gasification heat exchanger, absorbs heat and heats up in the energy-release high-pressure heat exchanger, expands and works in the turbine unit, releases heat and cools down in the energy-release low-pressure heat exchanger, releases heat and liquefies in the multi-layer sleeve-type energy storage heat exchange module, and is stored in the low-pressure storage tank through the switch valve. In the process of gaseous carbon dioxide passing through the multi-layer sleeve-type energy storage heat exchange module, if the cold capacity or heat exchange power of the phase change material stored in the multi-layer sleeve-type energy storage heat exchange module is insufficient, the refrigerator will transport the cooled heat exchange medium to the outer flow channel of the multi-layer sleeve-type energy storage heat exchange module for supplementary cooling.

[0029] Preferably, before the low-pressure storage tank outputs liquid carbon dioxide during the energy storage process, the refrigerator transports cooled heat exchange medium to the outer flow channel of the multi-layer shell-and-tube energy storage heat exchange module, so that the phase change material in the energy storage chamber is cooled to near the phase change point and remains in liquid state.

[0030] This enables the phase change material to undergo phase change and release heat as quickly as possible when carbon dioxide enters the multi-layer tube-type energy storage heat exchange module, thereby improving the efficiency of carbon dioxide absorption and gasification.

[0031] The present invention has the following beneficial effects.

[0032] 1. The present invention introduces a multi-layer sleeve-type energy storage heat exchange module with a three-layer nested structure on the low-pressure side of the carbon dioxide energy storage system; during the energy release process, when the carbon dioxide flow fluctuates or the cooling capacity of the phase change material in the middle layer is insufficient, the outer flow channel is used to supply cooling to the phase change material and the inner layer of carbon dioxide, thereby ensuring that the carbon dioxide can be fully liquefied and enter the low-pressure storage tank.

[0033] 2. The multi-layer sleeve-type energy storage heat exchange module in the present invention can cool the liquid phase change material in the middle layer to a temperature close to the phase change point before energy storage by introducing a low-temperature heat exchange medium into the outer flow channel, so as to ensure that the carbon dioxide can quickly absorb heat and gasify when passing through the inner flow channel during the energy storage process.

[0034] 3. The present invention provides a parameter optimization design scheme for the inner and middle layer structures of a multi-layer sleeve-type energy storage and heat exchange module, which can effectively take into account the energy storage capacity of the phase change material, the cooling efficiency of the outer layer flow channel to the inner layer flow channel, and the flow resistance of carbon dioxide in the inner layer pipeline, thereby improving the overall efficiency of the carbon dioxide energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] 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 will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 It is a system block diagram of an embodiment of the present invention.

[0037] Figure 2 It is a structural schematic diagram of the multi-layer sleeve type energy storage heat exchange module in the present invention.

[0038] Figure numerals: 1. low-pressure storage tank; 2. high-pressure storage tank; 3. compressor; 4. turbine; 5. throttle valve; 6. switch valve; 7. multi-layer shell-and-tube energy storage and heat exchange module; 7-1. inner tube; 7-2 shell; 7-3. outer tube; 7-4. inner flow channel; 7-5. energy storage chamber; 7-6. outer flow channel; 8. refrigerator; 9. energy storage low-pressure heat exchanger; 10. energy release low-pressure heat exchanger; 11. low-pressure cold storage device; 12. low-pressure heat storage device; 13. energy storage high-pressure heat exchanger; 14. energy release high-pressure heat exchanger; 15. high-pressure heat storage device; 16. high-pressure cold storage device; 17. high-pressure liquefaction heat exchanger; 18. high-pressure vaporization heat exchanger; 19. vaporization heat storage device; 20. liquefaction cold storage device. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] like Figure 1 As shown, a carbon dioxide energy storage system with supplementary cooling on the low-pressure side includes a low-pressure storage tank 1, a low-pressure inlet and outlet module, a multi-layer tube-type energy storage and heat exchange module 7, a charging and releasing module, and a high-pressure storage tank 2 connected in sequence. The multi-layer tube-type energy storage and heat exchange module 7 is used to perform gasification output and liquefaction input of carbon dioxide on the low-pressure side of the carbon dioxide energy storage system.

[0041] like Figure 2As shown, the multi-layer sleeve-type energy storage heat exchange module 7 includes an inner tube 7-1, a sleeve 7-2 and an outer tube 7-3 which are coaxial and sequentially sleeved from the inside to the outside; the inner cavity of the inner tube 7-1 is an inner layer flow channel 7-4; a circular energy storage chamber 7-5 is formed between the inner wall of the sleeve 7-2 and the outer wall of the inner tube 7-1; and a circular outer layer flow channel 7-6 is formed between the outer wall of the sleeve 7-2 and the inner wall of the outer tube 7-3. The inner layer flow channel 7-4 is used for the flow of carbon dioxide and for providing heat exchange of carbon dioxide, so as to completely gasify the gas-liquid two-phase carbon dioxide or liquefy the gaseous carbon dioxide; the outer side wall of the outer tube 7-3 is provided with a supplementary cooling input port and a supplementary cooling output port connected to the outer layer flow channel 7-6 at both ends. The energy storage chamber 7-5 is filled with phase change material.

[0042] The multi-layer sleeve-type energy storage heat exchange module 7 corresponds to a refrigerator 8. The input port and output port of the refrigerator 8 are respectively connected to the supplementary cooling output port and supplementary cooling input port of the outer tube 7-3 of the multi-layer sleeve-type energy storage heat exchange module 7 to form a supplementary cooling circuit. During the supplementary cooling process, the refrigerator 8 outputs a supplementary cooling heat exchange medium with a reduced temperature. The supplementary cooling heat exchange medium provides coldness to the phase change material in the energy storage chamber 7-5 through the outer layer flow channel 7-6, so that the temperature of the phase change material is close to the phase change temperature.

[0043] like Figure 1 As shown, the low-pressure inlet and outlet module includes a throttle valve 5 and a switch valve 6. The throttle valve 5 and the switch valve 6 are connected in parallel between the low-pressure storage tank 1 and one end of the inner flow channel 7-4 of the multi-layer sleeve type energy storage heat exchange module 7.

[0044] like Figure 1 As shown, the energy charging and releasing module includes a cold storage tank group, a heat storage tank group, and a parallel charging branch and an energy releasing branch. The charging branch includes an energy storage low-pressure heat exchanger 9, a compressor 3, an energy storage high-pressure heat exchanger 13, and a high-pressure liquefaction heat exchanger 17. The energy releasing branch includes a high-pressure vaporization heat exchanger 18, an energy releasing high-pressure heat exchanger 14, a turbine 4, and an energy releasing low-pressure heat exchanger 10. The energy storage low-pressure heat exchanger 9, the energy storage high-pressure heat exchanger 13, the high-pressure liquefaction heat exchanger 17, the high-pressure vaporization heat exchanger 18, the energy releasing high-pressure heat exchanger 14, and the energy releasing low-pressure heat exchanger 10 all use internal double-flow heat exchangers.

[0045] The inlet and outlet of the low-pressure storage tank 1, the inner flow channel 7-4 of the multi-layer sleeve-type energy storage heat exchange module 7, the first heat exchange flow path in the energy storage low-pressure heat exchanger 9, the compressor 3, the first heat exchange flow path in the energy storage high-pressure heat exchanger 13, the first heat exchange flow path in the high-pressure liquefaction heat exchanger 17, and the inlet and outlet of the high-pressure storage tank 2 are connected in sequence along the flow direction of carbon dioxide to form a complete carbon dioxide charging and pressure-boosting flow path.

[0046] The inlet and outlet of the high-pressure storage tank 2, the first heat exchange path in the high-pressure gasification heat exchanger 18, the first heat exchange path in the energy-releasing high-pressure heat exchanger 14, the turbine 4, the first heat exchange path in the energy-releasing low-pressure heat exchanger 10, the inner flow channel 7-4 of the multi-layer shell-and-tube energy storage heat exchange module 7, and the inlet and outlet of the low-pressure storage tank 1 are connected in sequence along the flow direction of carbon dioxide to form a complete carbon dioxide energy-releasing and pressure-reducing path.

[0047] The cold storage tank group includes a low-pressure cold storage device 11, a high-pressure cold storage device 16 and a liquefied cold storage device 20; the heat storage tank group includes a low-pressure heat storage device 12, a high-pressure heat storage device 15 and a gasification heat storage device 19.

[0048] The second heat exchange path of the energy storage low-pressure heat exchanger 9, the low-pressure cold storage device 11, the second heat exchange path of the energy release low-pressure heat exchanger 10, and the low-pressure heat storage device 12 are connected in sequence along the flow direction of the heat exchange medium to form a first heat exchange circulation loop.

[0049] The second heat exchange path of the energy storage high-pressure heat exchanger 13, the high-pressure heat storage device 15, the second heat exchange path of the energy release high-pressure heat exchanger 14, and the high-pressure cold storage device 16 are sequentially connected along the flow direction of the heat exchange medium to form a second heat exchange circulation loop.

[0050] The second heat exchange path of the high-pressure liquefaction heat exchanger 17, the vaporization heat storage device 19, the second heat exchange path of the high-pressure vaporization heat exchanger 18, and the liquefaction cold storage device 20 are sequentially connected along the flow direction of the heat exchange medium to form a third heat exchange circulation loop.

[0051] In some embodiments, the compressor unit 3 and the turbine unit 4 both use a multi-stage series structure.

[0052] In this embodiment, the storage temperature of carbon dioxide on the low temperature side is -50 to -40°C; the temperature on the high temperature side is selected according to the actual process pressure, and the selection range is relatively large, for example, 200°C to 800°C.

[0053] The working method of the carbon dioxide energy storage system includes an energy storage process and an energy release process.

[0054] The energy storage process is as follows: before the energy storage starts, the refrigerator 8 passes the low-temperature heat exchange medium (the temperature in this embodiment is -50℃~-40℃) into the outer flow channel 7-6 of the multi-layer sleeve type energy storage heat exchange module 7, and the low-temperature heat exchange medium entering the outer flow channel 7-6 exchanges heat with the phase change material in the energy storage chamber 7-5, cooling the phase change material in the energy storage chamber 7-5 to near its phase change point (2-5℃ higher than the phase change point temperature) and maintaining the liquid state. After that, the liquid carbon dioxide passes through the throttle valve 5, the multi-layer sleeve type energy storage heat exchange module 7, and the energy storage low-pressure heat exchanger 9 from the low-pressure storage tank 1, and enters the compressor 3; the liquid carbon dioxide is throttled and cooled in the throttle valve 5 and partially gasified to form gas-liquid two-phase carbon dioxide. The liquid phase change material in the multi-layer sleeve type energy storage heat exchange module 7 absorbs the cold of the gas-liquid two-phase carbon dioxide and solidifies, and the gas-liquid two-phase carbon dioxide absorbs heat and completely gasifies to form gaseous carbon dioxide. The gaseous carbon dioxide absorbs heat and heats up in the energy storage low-pressure heat exchanger 9. The compressor 3 performs transcritical compression on the gaseous carbon dioxide to obtain supercritical carbon dioxide; the supercritical carbon dioxide releases heat in the energy storage high-pressure heat exchanger 13 to reduce its temperature, and further releases heat to cool and liquefy after entering the high-pressure liquefied heat exchanger 17; the liquid carbon dioxide output by the high-pressure liquefied heat exchanger 17 enters the high-pressure storage tank 2 for storage. Transcritical compression is the compression of carbon dioxide from a subcritical state at normal temperature and pressure to a supercritical state at high temperature and pressure.

[0055] The energy release process is as follows: the high-pressure storage tank 2 outputs liquid carbon dioxide, and the liquid carbon dioxide enters the high-pressure gasification heat exchanger 18 to absorb heat and vaporize; the gaseous carbon dioxide output by the high-pressure gasification heat exchanger 18 enters the energy-releasing high-pressure heat exchanger 13 to further absorb heat and heat up before entering the turbine unit 4; the gaseous carbon dioxide expands and does work in the turbine unit 4, driving the generator to generate electricity; after releasing energy in the turbine 4, the gaseous carbon dioxide enters the energy-releasing low-pressure heat exchanger 10 to release heat and cool down; the gaseous carbon dioxide output by the energy-releasing low-pressure heat exchanger 10 enters the multi-layer sleeve-type energy storage heat exchange module 7; the gaseous carbon dioxide absorbs the cold of the solid phase change material in the energy storage chamber 7-5 of the multi-layer sleeve-type energy storage heat exchange module 7, thereby cooling down and liquefying; at the same time, the solid phase change material absorbs heat and liquefies; the liquefied carbon dioxide finally enters the low-pressure storage tank 1 for storage. In the process of gaseous carbon dioxide passing through the multi-layer sleeve type energy storage heat exchange module 7, if the cooling capacity or heat exchange power of the phase change material is insufficient, the refrigerator will pass the low-temperature heat exchange medium into the outer flow channel 7-6 of the multi-layer sleeve type energy storage heat exchange module to supplement the cooling of the phase change material in the energy storage chamber 7-5, thereby ensuring the complete liquefaction of carbon dioxide.

[0056] In the multi-layer sleeve type energy storage heat exchange module 7 provided in this embodiment, it is necessary to supplement the cooling of the inner layer flow channel 7-4 of the inner ring through the heat exchange material in the outer layer flow channel 7-6 of the outer ring when necessary; therefore, the heat exchange power between the outer layer flow channel 7-6 of the outer ring and the inner layer flow channel 7-4 of the inner ring needs to meet the requirements to ensure that the cold input into the outer layer flow channel 7-6 can be exchanged to the inner layer flow channel 7-4 in time.

[0057] The diameter of the casing must meet the actual cooling capacity requirements. The target cooling capacity of the phase change material is known. , then according to the formula, the required phase change material mass can be calculated :

[0058]

[0059] in, is the latent heat of phase change of phase change material.

[0060] The calculation formula of casing length L is:

[0061]

[0062]

[0063] in, is the density of phase change material; is the flow cross-sectional area of ​​the energy storage chamber 7-5; is the inner diameter of the casing 7-2; is the diameter of the inner tube 7 - 1 (specifically refers to the outer diameter in this embodiment).

[0064] Inner pipe diameter The preferred diameter in this embodiment is 2.5 mm, which is selected based on the pressure-bearing requirements of the system process design and the processing technology.

[0065] Given the length of the casing L, the overall heat exchange area between the phase change material in the energy storage chamber 7-5 and the carbon dioxide in the inner tube 7-1 is :

[0066]

[0067] Constructing the heat exchange power between the phase change material in the energy storage chamber 7-5 and the carbon dioxide in the inner tube 7-1 The expression is as follows:

[0068]

[0069] Where k is the total heat transfer coefficient; ΔT is the heat transfer temperature difference.

[0070] According to the law of conservation of energy, to achieve the cold storage requirement, the total heat exchange of the system during the operating time must reach the set cold storage capacity, so the energy relationship for the cold storage requirement is established:

[0071]

[0072] in, is the target cold storage capacity, and its value is set according to the storage capacity of the energy storage system; t is the energy storage operation time, specifically the time it takes for the carbon dioxide energy storage system to complete a complete energy storage process.

[0073] The heat exchange power between the phase change material and carbon dioxide obtained previously is , and the overall heat exchange area between the phase change material and carbon dioxide Substituting the above energy conservation equation into the equation, we can get:

[0074]

[0075] Solving the above equation, we can establish the lower limit of the casing inner diameter: The expression is as follows:

[0076]

[0077] If the inner diameter of the casing 7-2 Less than , the cold storage capacity will not meet the requirements, that is, the minimum thickness of the energy storage chamber 7-5 :

[0078]

[0079] It is worth noting that in the present invention, the inner diameter of the casing The bigger the better. If the diameter of the sleeve becomes larger and the thickness of the phase change material is too large, the heat transfer resistance of carbon dioxide will increase. Therefore, the device has an optimal sleeve diameter for different phase change materials. The design method is as follows:

[0080] The heat transfer formula for the cylinder is established as follows:

[0081]

[0082] in, For heat exchange; is the tube length; t fi is the fluid temperature of the inner channel; t fo is the fluid temperature of the outer flow channel; h i is the heat transfer coefficient between the phase change material in the energy storage chamber 7-5 and the carbon dioxide in the inner flow channel; d i is the inner diameter of the energy storage chamber 7-5 (i.e. the diameter of the inner tube); is the thermal conductivity of the phase change material; ho is the heat transfer coefficient between the phase change material in the energy storage chamber 7-5 and the heat transfer medium in the outer flow channel; d o It is the outer diameter of the energy storage chamber 7-5 (i.e. the inner diameter of the casing).

[0083] For the increase of the outer diameter do of the tube, the thermal resistance of the second term in the denominator increases, while the convection heat transfer resistance of the third term decreases, so the derivative of do is taken and set to 0:

[0084]

[0085] Therefore, the optimal casing diameter for different phase change materials is obtained under the condition of maximum heat transfer coefficient. for:

[0086]

[0087] Then the maximum thickness of the energy storage chamber 7-5 is :

[0088]

[0089] Therefore, in actual design, the selection of the thickness δ of the energy storage chamber 7-5 needs to comprehensively consider factors such as pipeline pressure bearing and equipment cost, and select an appropriate value within the range:

[0090]

[0091] When selecting the appropriate casing middle channel thickness δ, casing diameter You can determine:

[0092]

[0093] After knowing the diameters of the inner tube and the shell, the total length L of the shell-and-tube heat exchanger can be calculated based on the total cold storage capacity.

[0094]

[0095]

[0096] 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 make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A carbon dioxide energy storage system with low-pressure side cooling, characterized in that: The invention comprises a low-pressure storage tank (1), a multi-layer sleeve-type energy storage heat exchange module (7), an energy charging and releasing module and a high-pressure storage tank (2) which are connected in sequence; the multi-layer sleeve-type energy storage heat exchange module (7) comprises an inner tube (7-1), a sleeve (7-2) and an outer tube (7-3) which are coaxial and sleeved in sequence from the inside to the outside; the inner cavity of the inner tube (7-1) is an inner flow channel (7-4); a circular space is formed between the inner wall of the sleeve (7-2) and the outer wall of the inner tube (7-1); An annular energy storage chamber (7-5); an annular outer flow channel (7-6) is formed between the outer wall of the sleeve (7-2) and the inner wall of the outer tube (7-3); the energy storage chamber (7-5) is filled with a phase change material; the multi-layer sleeve type energy storage heat exchange module (7) corresponds to a refrigerator (8); the refrigerator (8) is connected to the outer flow channel (7-6) to form a cooling circulation loop; the energy charging and releasing module includes a parallel charging branch and an energy releasing branch; During the energy storage process, the liquid carbon dioxide in the low-pressure storage tank (1) passes through the multi-layer tube-type energy storage heat exchange module (7) and the charging branch in sequence, and is then stored in the high-pressure storage tank (2); During the energy release process, the liquid carbon dioxide in the high-pressure storage tank (2) passes through the energy release branch and the multi-layer sleeve-type energy storage heat exchange module (7) in sequence before being stored in the low-pressure storage tank (1).

2. A low-pressure side supplementary cooling carbon dioxide energy storage system according to claim 1, characterized in that: The thickness of the energy storage chamber (7-5) Less than or equal to the upper limit of thickness ; Upper limit of thickness ; is the upper limit of the inner diameter of the casing, and its expression is: ； in, is the thermal conductivity of the phase change material; h o is the heat transfer coefficient between the phase change material in the energy storage chamber (7-5) and the heat transfer medium in the outer flow channel.

3. A carbon dioxide energy storage system with low-pressure side cooling according to claim 2, characterized in that: The thickness of the energy storage chamber (7-5) Less than or equal to the lower limit of thickness ; Upper limit of thickness ; is the lower limit of the casing inner diameter, and its expression is: ； Wherein, k and ΔT are respectively the heat transfer coefficient and the heat transfer temperature difference between the phase change material in the energy storage chamber (7-5) and the carbon dioxide in the inner flow channel (7-4); t is the energy storage operation time; is the minimum phase change material mass; is the density of the phase change material; is the target cooling capacity.

4. A low-pressure side supplementary cooling carbon dioxide energy storage system according to claim 3, characterized in that: The length L of the sleeve (7-2) satisfies the following relationship: ； in, is the cross-sectional area of ​​the energy storage chamber (7-5).

5. A carbon dioxide energy storage system with low-pressure side cooling according to claim 1, characterized in that: It also includes a low-pressure inlet and outlet module connected between the low-pressure storage tank (1) and the inner flow channel (7-4) of the multi-layer sleeve-type energy storage heat exchange module (7); the low-pressure inlet and outlet module includes a throttle valve (5) and a switch valve (6) connected in parallel.

6. A carbon dioxide energy storage system with low-pressure side cooling according to claim 5, characterized in that: The energy charging branch includes an energy storage low-pressure heat exchanger (9), a compressor (3), an energy storage high-pressure heat exchanger (13) and a high-pressure liquefaction heat exchanger (17); the energy release branch includes a high-pressure gasification heat exchanger (18), an energy release high-pressure heat exchanger (14), a turbine (4) and an energy release low-pressure heat exchanger (10); the first heat exchange flow path in the energy storage low-pressure heat exchanger (9), the compressor (3), the first heat exchange flow path in the energy storage high-pressure heat exchanger (13), the first heat exchange flow path in the high-pressure liquefaction heat exchanger (17), and the high-pressure storage tank (2) are connected in sequence along the flow direction of carbon dioxide; the first heat exchange flow path in the high-pressure gasification heat exchanger (18), the first heat exchange flow path in the energy release high-pressure heat exchanger (14), the turbine (4), and the first heat exchange flow path in the energy release low-pressure heat exchanger (10) are connected in sequence along the flow direction of carbon dioxide.

7. A carbon dioxide energy storage system with low-pressure side cooling according to claim 6, characterized in that: A cold storage device and a heat storage device for transferring heat or cold are respectively provided between the energy storage low-pressure heat exchanger (9) and the energy release low-pressure heat exchanger (10), between the energy storage high-pressure heat exchanger (13) and the energy release high-pressure heat exchanger (14), and between the high-pressure liquefaction heat exchanger (17) and the high-pressure gasification heat exchanger (18).

8. A carbon dioxide energy storage system with low-pressure side cooling according to claim 1, characterized in that: The difference between the inner and outer diameters of the outer layer flow channel (7-6) is 2 mm to 10 mm.

9. A carbon dioxide energy storage method with low-pressure side cooling, characterized in that: Using the carbon dioxide energy storage system as claimed in claim 6; the carbon dioxide energy storage method comprises the following steps: including an energy storage process and an energy release process; The energy storage process is as follows: the liquid carbon dioxide output from the low-pressure storage tank (1) is partially gasified in the throttle valve (5), absorbs heat and gasifies in the multi-layer sleeve-type energy storage heat exchange module (7), absorbs heat and heats up in the energy storage low-pressure heat exchanger (9), is transcritically compressed to a supercritical state in the compressor (3), releases heat and cools down in the energy storage high-pressure heat exchanger (13), releases heat and liquefies in the high-pressure liquefaction heat exchanger (17), and is stored in the high-pressure storage tank (2); The energy release process is as follows: the liquid carbon dioxide output from the high-pressure storage tank (2) absorbs heat and vaporizes in the high-pressure vaporization heat exchanger (18), absorbs heat and heats up in the energy-releasing high-pressure heat exchanger (14), expands and performs work in the turbine unit (4), releases heat and cools down in the energy-releasing low-pressure heat exchanger (10), releases heat and liquefies in the multi-layer sleeve-type energy storage heat exchange module (7), and is stored in the low-pressure storage tank (1) through the switch valve (6); in the process of the gaseous carbon dioxide passing through the multi-layer sleeve-type energy storage heat exchange module (7), if the cold capacity or heat exchange power of the phase change material stored in the multi-layer sleeve-type energy storage heat exchange module (7) is insufficient, the refrigerator will transport the cooled heat exchange medium to the outer flow channel (7-6) of the multi-layer sleeve-type energy storage heat exchange module (7) for supplementary cooling.

10. A carbon dioxide energy storage method with low-pressure side cooling according to claim 9, characterized in that: Before the low-pressure storage tank (1) outputs liquid carbon dioxide during the energy storage process, the refrigerator (8) transports cooled heat exchange medium to the outer flow channel (7-6) of the multi-layer tube-in-tube energy storage heat exchange module (7), so that the phase change material in the energy storage chamber (7-5) is cooled to a point close to the phase change point and remains in a liquid state.

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