Low-pressure liquid CO2 storage tank and method for preventing dry ice formation

Abstract

The invention belongs to the technical field of CO2 energy storage systems, and particularly provides a low-pressure liquid CO2 storage tank and method for preventing dry ice.The low-pressure liquid CO2 storage tank comprises a tank body, a liquid inlet valve is arranged at an injection port of the tank body, an outlet valve is arranged at an exhaust port of the tank body, a safety valve is arranged on the side wall of the storage tank, and a plurality of phase change coil pipes are arranged in the tank body at intervals in the axial direction of the tank body; and the phase change coil pipe is filled with a phase change material. According to the low-pressure liquid CO2 storage tank and the method, the temperature of CO2 in the storage tank is kept stable as far as possible, so that the liquid CO2 is prevented from forming dry ice.

Description

Technical Field

[0001] The present invention belongs to the technical field of CO2 energy storage systems, and in particular, relates to a low-pressure liquid CO2 storage tank and method for preventing dry ice from forming. Background Art

[0002] In the energy storage system, off-peak electricity is stored as gas pressure energy and thermal energy, and then converted into electricity during peak hours. One of the key components is the gas storage. At present, in order to reduce the construction cost of the energy storage system, waste gas mines and salt caverns are mostly used for storage, which limits the site selection of the energy storage system and may conflict with the energy distribution of the power grid. Therefore, it is imperative to develop above-ground storage tanks. However, in existing compressed gas energy storage projects, the cost of gas storage, which is mainly gas tanks, accounts for as much as 50% of the total cost. How to further reduce the cost of storage tanks needs to be solved urgently.

[0003] The cost of a storage tank is directly related to its volume. Minimizing the volume of the storage tank under a given energy storage capacity will help reduce the cost of the storage tank. Therefore, compressed CO2 energy storage systems usually choose to store liquid CO2. However, the critical temperature of CO2 is 31.0°C, the critical pressure is 7.38Mpa, the triple point temperature is -56.6°C, and the triple point pressure is 0.52MPa. This means that if compressed CO2 energy storage chooses liquid storage, the pressure of its high-pressure tank will not exceed 7.38MPa at most, and 7MPa is generally selected, while the pressure of the low-pressure tank will not be less than 0.52MPa, and it is generally 0.7MPa to prevent freezing. The pressure of the liquid CO2 energy storage system is relatively low, which causes the amount of CO2 required for the same capacity to rise sharply. At the same time, during the energy storage and release process, the CO2 in the tank will undergo a gas-liquid phase change conversion process, which will cause a certain fluctuation in the temperature in the tank, which may cause dry ice to form in the low-pressure liquid tank, thereby blocking the pipeline and affecting the circulation of CO2. Therefore, for liquid CO2 energy storage systems, effective measures must be proposed to prevent the condensation of dry ice in low-pressure liquid tanks.

[0004] In the existing literature, patent CN113843226A discloses a method for preventing and clearing dry ice in a liquid CO2 pipeline. The patent provides an external heating pipe on the outside of the liquid CO2 pipeline. By introducing hot steam into the external heating pipe, the frozen liquid CO2 pipeline can be heated and cleared. An ice-breaking mechanism is further used to break the ice on the inner wall of the liquid CO2 pipeline, thereby improving its heating efficiency and speeding up clearing.

[0005] During the energy storage process, the liquid CO2 in the low-pressure tank continuously flows out, causing part of the liquid CO2 in the tank to evaporate and absorb heat, causing the tank temperature to drop. The liquid CO2 may solidify into dry ice, causing the valve to be frozen. However, there are few methods in the existing literature for preventing dry ice from forming in liquid CO2 storage tanks. Although the ice-breaking mechanism can break the ice on the inner wall of the liquid CO2 pipeline, it cannot completely process the dry ice, and there will still be residual dry ice that affects the CO2 circulation efficiency. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a low-pressure liquid CO2 storage tank and method for preventing dry ice from forming, so that the temperature of CO2 in the storage tank can be kept as stable as possible, thereby preventing the liquid CO2 from forming dry ice.

[0007] The technical solution adopted by the present invention is: a low-pressure liquid CO2 storage tank for preventing dry ice formation, including a tank body, an injection port of the tank body is provided with a liquid inlet valve, a discharge port is provided with an outlet valve, and a side wall of the tank is provided with a safety valve. A plurality of groups of phase change coils are arranged in the tank body along the axial direction, and the phase change coils are filled with phase change materials.

[0008] In a preferred embodiment, the phase change coils are arranged transversely or longitudinally.

[0009] In a preferred solution, an electric heating wire is wound around the outer side of the phase change coil, and a temperature sensor is provided inside the tank.

[0010] In a preferred embodiment, the outer side of the outer wall of the tank body is covered with a sealing structure layer, and the sealing structure layer includes a low-pressure tank shell and a flexible phase change material modular prefabricated product from the outside to the inside. The flexible phase change material modular prefabricated product includes a prefabricated shell and a phase change material arranged in the prefabricated shell.

[0011] In a preferred solution, a thermal insulation layer is provided between the low-pressure tank shell and the flexible phase change material modular preform.

[0012] In a preferred solution, an insulating layer is provided between the low-pressure tank shell and the thermal insulation layer.

[0013] In a preferred embodiment, the phase change temperature range of the phase change material is -50°C to -20°C.

[0014] In a preferred solution, a plurality of pillars are arranged at the bottom of the tank body, and the lower ends of the pillars are arranged on piers.

[0015] The present invention also provides an operating method for a low-pressure liquid CO2 storage tank to prevent dry ice from forming. When CO2 is filled, the temperature of the storage tank gradually rises, and the phase change material absorbs heat and changes from solid to liquid to prevent the temperature of the storage tank from rising; when discharging, the temperature of the storage tank drops, and the phase change material releases heat and changes from liquid to solid to prevent the temperature of the storage tank from dropping and keep the temperature of the storage tank constant.

[0016] In a preferred solution, when the temperature sensor detects that the temperature of the storage tank is lower than the triple point temperature, the electric heating wire is activated to increase the temperature of the storage tank, and the dry ice absorbs heat and melts.

[0017] The present invention provides a low-pressure liquid CO2 storage tank and method for preventing dry ice from forming, which has the following beneficial effects: 1. Coils filled with phase change materials are arranged at intervals along the axial direction in the storage tank to achieve a near-isothermal effect during energy storage and release to prevent dry ice from forming.

[0018] 2. Use flexible phase change material modular prefabricated products to absorb the heat inside the tank or transfer the heat to the tank, so as to keep the tank temperature as constant as possible and prevent liquid CO2 from freezing.

[0019] 3. An electric heating wire is spirally wound around the coil inside the low-pressure liquid CO2 storage tank. When dry ice may appear in the tank, the electric heating wire is started to increase the temperature of CO2 to prevent dry ice from forming or melt the existing dry ice, and keep the tank temperature constant. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Figure 1 It is a schematic diagram of the overall structure of the present invention; Figure 2 Schematic diagram of the arrangement structure of the phase change coil; Figure 3 is a schematic diagram of another arrangement structure of a phase change coil; In the figure: tank body 1, tank outer wall 101, gas inlet valve 2, outlet valve 3, safety valve 4, phase change coil 5, electric heating wire 6, sealing structure layer 7, low-pressure tank shell 701, insulation layer 702, thermal insulation layer 703, flexible phase change material modular prefabricated product 704, pillar 8, pier 9, temperature sensor 10. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] Embodiment 1: Combination Figure 1~Figure 3 The specific embodiments of the present invention are described in further detail.

[0023] A low-pressure liquid CO2 storage tank to prevent dry ice formation, such as Figure 1As shown, it includes a tank body 1, a gas inlet valve 2 and an outlet valve 3 are arranged on the side wall of the tank body 1, a safety valve 4 is arranged on the side wall of the storage tank 1, and a plurality of pillars 8 are arranged at the bottom of the tank body 1, and the lower ends of the pillars 8 are arranged on piers 9.

[0024] A plurality of phase change coils 5 are arranged in the tank body 1 along the axial direction thereof at intervals. The phase change coils 5 are filled with phase change materials. The phase change coils 5 are arranged transversely or longitudinally.

[0025] like Figure 2 As shown, the phase change coil 5 is arranged horizontally. Figure 3 As shown, the phase change coil 5 is arranged longitudinally.

[0026] In a specific implementation, the phase change coils 5 arranged transversely and the phase change coils 5 arranged longitudinally are arranged at intervals.

[0027] The phase change temperature of the phase change material should be in the range of -50°C to -20°C to match the temperature change of the low-pressure liquid CO2 storage tank. For example, in this embodiment, an organic eutectic mixture or hydrated salt or nanocomposite phase change material with a phase change temperature of about -30°C is selected.

[0028] The phase change coil 5 is filled with solid-liquid phase change material to absorb the heat of the liquid CO2 filling process, and releases heat to maintain the tank temperature during the CO2 discharge process. During filling, the tank temperature gradually rises, and the phase change material absorbs heat and changes from solid to liquid to prevent the tank temperature from rising; during discharge, the tank temperature drops, and the phase change material releases heat and changes from liquid to solid to prevent the tank temperature from dropping, and finally the tank temperature can be kept constant as much as possible. Based on the average temperature of the tank throughout the year, a solid-liquid phase change material with large heat capacity and good economic benefits is selected to minimize the temperature fluctuation of the tank and prevent the low-pressure liquid CO2 tank from freezing the valve.

[0029] Preferably, the outer side of the tank outer wall 101 of the tank body 1 is coated with a sealing structure layer 7, and the sealing structure layer 7 includes a low-pressure tank shell 701 and a flexible phase change material modular preform 704 from the outside to the inside, and the flexible phase change material modular preform 704 includes a prefabricated shell and a phase change material arranged in the prefabricated shell.

[0030] The phase change material filled in the flexible phase change material modular preform 704 can be selected from phase change materials with a phase change temperature in the range of 30°C to 0°C, so as to store phase change energy between the ambient temperature and the temperature of the CO2 storage tank.

[0031] The flexible phase change material modular preform 704 is used to absorb the heat inside the storage tank or transfer the heat to the storage tank, so as to keep the temperature of the storage tank as constant as possible and prevent the liquid CO2 from freezing.

[0032] Preferably, a heat-insulating layer 703 is provided between the low-pressure tank shell 701 and the flexible phase-change material modular preform 704. By providing the heat-insulating layer 703, it is possible to effectively prevent heat from being lost to the environment during the CO2 filling and discharge process. Embodiment 2: Different from the first embodiment, the phase change coil 5 is wound with an electric heating wire 6, and the tank body 1 is provided with a temperature sensor 10. When the temperature sensor detects that the temperature of the storage tank is low, the pressure sensor arranged on the inner wall of the storage tank measures the pressure of the liquid CO2. If the low-pressure liquid CO2 storage tank may freeze dry ice, the electric heating wire 6 is activated to increase the temperature of the storage tank, and the dry ice absorbs heat and melts. Specifically, the temperature sensor 10 is used to detect the temperature of the storage tank. If the CO2 temperature is lower than the freezing point, the electric heating wire 6 is activated to increase the temperature of the storage tank to prevent dry ice from forming or to melt the existing dry ice.

[0033] Preferably, an insulating layer 702 is provided between the low-pressure tank shell 701 and the insulation layer 703. By providing the insulating layer 702, leakage can be prevented and safety can be ensured.

[0034] Embodiment 3: A method for operating a low-pressure liquid CO2 storage tank to prevent dry ice from forming. When CO2 is filled, the tank temperature gradually rises, and a phase change material absorbs heat and changes from a solid state to a liquid state to prevent the tank temperature from rising. When CO2 is discharged, the tank temperature drops, and the phase change material releases heat and changes from a liquid state to a solid state to prevent the tank temperature from dropping and keep the tank temperature constant.

[0035] When the temperature sensor 10 detects that the temperature of the storage tank is lower than the triple point, the electric heating wire 6 is started to increase the temperature of the storage tank, and the dry ice absorbs heat and melts.

[0036] The above-mentioned embodiments are only preferred technical solutions of the present invention and should not be regarded as limitations of the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to list all the implementation methods here, that is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A low-pressure liquid CO2 storage tank for preventing dry ice formation, comprising a tank body (1), the injection port of the tank body (1) is provided with a liquid inlet valve (2), the discharge port is provided with an outlet valve (3), and the side wall of the storage tank (1) is provided with a safety valve (4), characterized in that: A plurality of groups of phase change coils (5) are arranged in the tank body (1) at intervals along its axial direction, and the phase change coils (5) are filled with phase change material.

2. A low-pressure liquid CO2 storage tank for preventing dry ice formation according to claim 1, characterized in that: The phase change coils (5) are arranged transversely or longitudinally.

3. A low-pressure liquid CO2 storage tank for preventing dry ice formation according to claim 1, characterized in that: An electric heating wire (6) is wound around the outer side of the phase change coil (5), and a temperature sensor (10) is provided in the tank body (1).

4. A low-pressure liquid CO2 storage tank for preventing dry ice formation according to claim 1, characterized in that: The outer side of the storage tank outer wall (101) of the tank body (1) is coated with a sealing structure layer (7), the sealing structure layer (7) comprising, from the outside to the inside, a low-pressure tank shell (701) and a flexible phase change material modular prefabricated product (704), the flexible phase change material modular prefabricated product (704) comprising a prefabricated shell and a phase change material arranged in the prefabricated shell.

5. A low-pressure liquid CO2 storage tank for preventing dry ice formation according to claim 4, characterized in that: A thermal insulation layer (703) is provided between the low-pressure tank shell (701) and the flexible phase change material modular preform (704).

6. A low-pressure liquid CO2 storage tank for preventing dry ice formation according to claim 5, characterized in that: An insulating layer (702) is provided between the low-pressure tank shell (701) and the thermal insulation layer (703).

7. A low-pressure liquid CO2 storage tank for preventing dry ice formation according to claim 1, characterized in that: The phase change temperature range of the phase change material is -50°C to -20°C.

8. A low-pressure liquid CO2 storage tank for preventing dry ice formation according to claim 1, characterized in that: A plurality of pillars (8) are arranged at the bottom of the tank body (1), and the lower ends of the pillars (8) are arranged on buttresses (9).

9. The method for operating a low-pressure liquid CO2 storage tank for preventing dry ice formation according to any one of claims 1 to 8, characterized in that: When CO2 is filled, the tank temperature gradually rises, and the phase change material absorbs heat and changes from solid to liquid to prevent the tank temperature from rising; when discharging, the tank temperature drops, and the phase change material releases heat and changes from liquid to solid to prevent the tank temperature from dropping and keep the tank temperature constant.

10. The method for operating a low-pressure liquid CO2 storage tank for preventing dry ice formation according to claim 9, characterized in that: When the temperature sensor (10) detects that the temperature of the storage tank is lower than the triple point temperature, the electric heating wire (6) is activated to increase the temperature of the storage tank, causing the dry ice to absorb heat and melt.

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