Pressure regulating system for liquid carbon dioxide and method for controlling the same

Abstract

This invention provides a pressure regulation system and control method for liquid carbon dioxide. The system includes a carbon dioxide storage tank, a pressure regulation unit, and a liquid supply unit. The pressure regulation unit includes a refrigerant storage tank, an electric valve, a heat exchanger, and a cooler connected in sequence. The heat exchanger is located inside the carbon dioxide storage tank. The refrigerant in the refrigerant storage tank flows through the heat exchanger to cool the gaseous carbon dioxide in the carbon dioxide storage tank and convert it into liquid carbon dioxide, ultimately reducing the internal pressure of the carbon dioxide storage tank. The liquid supply unit includes a liquid supply pipeline, a liquid return pipeline, and a gas return pipeline. The liquid supply pipeline supplies liquid carbon dioxide to external working pipelines. The liquid return pipeline and the gas return pipeline are connected to the gas phase interface of the carbon dioxide storage tank, respectively. Before supplying liquid to the external working pipeline, the liquid return pipeline and the gas return pipeline are opened to pre-cool the external working pipeline to reach the controlled temperature of liquid carbon dioxide before starting the liquid supply process, so as to meet the pure liquid phase operation requirements of the external working pipeline.

Description

Technical Field

[0001] This invention relates to the field of liquid carbon dioxide storage and supply technology, and further to a pressure regulation system and control method for liquid carbon dioxide. Background Technology

[0002] Carbon dioxide is gaseous at room temperature and pressure. To reduce the cost of transporting and storing carbon dioxide, the most effective current technology is to liquefy it under pressure before transportation and storage. During storage, the liquefied carbon dioxide must be kept at a pressure within the equilibrium pressure range of the liquid phase. If the pressure exceeds the maximum pressure required to maintain the liquid phase, the carbon dioxide will solidify into dry ice; if the pressure falls below the minimum pressure required to maintain the liquid phase, the carbon dioxide will vaporize, leading to a significant increase in pressure inside the storage container.

[0003] To ensure the safety of the storage container, carbon dioxide gas needs to be released to reduce the pressure and keep the tank pressure within the equilibrium pressure range for the liquid phase. Currently, mainstream carbon dioxide storage tanks use the vaporization of liquid carbon dioxide to pressurize the tank and maintain the pressure within the carbon dioxide liquid phase equilibrium pressure range. However, using liquid carbon dioxide in the storage tank for vaporization and self-pressurization to maintain the liquid phase equilibrium pressure has certain drawbacks for systems operating with pure liquid carbon dioxide: First, because the liquid carbon dioxide is introduced into the pressurization pipeline for vaporization, it needs to absorb external heat to heat and vaporize the carbon dioxide. The high-pressure gas after vaporization then flows back to the storage tank for pressurization. During this process, the pressure may exceed the working pressure of the storage tank, which requires the removal of excess high-pressure gas to bring the tank pressure back down to within the working pressure. This results in a waste of carbon dioxide and increases operating costs. Second, when the storage tank is connected to the pure liquid phase working pipeline, the pipeline is relatively long because the storage tank needs to be located at a safe distance from the building. External heat inevitably enters through the working pipeline, further intensifying the carbon dioxide vaporization. This results in the liquid carbon dioxide containing gaseous carbon dioxide, which cannot meet the requirements of pure liquid phase operation and exacerbates the discharge of gaseous carbon dioxide, leading to waste. Summary of the Invention

[0004] To address the problems of waste caused by gas emissions during pressure regulation and the inability to meet the pure liquid phase supply requirements in existing technologies, the present invention aims to provide a liquid carbon dioxide pressure regulation system and its control method. A heat exchanger is installed inside the carbon dioxide storage tank. The refrigerant flowing through the heat exchanger cools the gaseous carbon dioxide inside the tank, converting it into liquid carbon dioxide, thus reducing the internal pressure of the tank. The internal pressure is monitored and automatically adjusted in real time, maintaining it at 13-22 bar in both non-supply and supply operation states. The pressure regulation process eliminates the need to emit gaseous carbon dioxide, reducing waste and increasing economic efficiency. Before supplying liquid, the external working pipeline is pre-cooled to the controlled temperature of the liquid carbon dioxide before the supply process begins, ensuring that the liquid carbon dioxide flowing in the external working pipeline does not contain gas, meeting the pure liquid phase operation requirements.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A pressure regulating system for liquid carbon dioxide includes: a carbon dioxide storage tank, a pressure regulating unit, and a liquid supply unit. The carbon dioxide storage tank is provided with a gas phase interface and a liquid phase interface. The pressure regulating unit includes a refrigerant storage tank, an electric valve, a heat exchanger, and a cooler connected in sequence. The heat exchanger is disposed inside the carbon dioxide storage tank, and the refrigerant in the refrigerant storage tank flows through the heat exchanger to cool the gaseous carbon dioxide in the carbon dioxide storage tank and convert it into liquid carbon dioxide. The liquid supply unit includes a liquid supply pipeline, a liquid return pipeline, and a gas return pipeline. The two ends of the liquid supply pipeline are respectively connected to the liquid phase interface and an external working pipeline, and the liquid supply pipeline is used to supply liquid carbon dioxide to the external working pipeline. The two ends of the liquid return pipeline are respectively connected to the gas phase interface and the external working pipeline, and the two ends of the gas return pipeline are respectively connected to the gas phase interface and the external working pipeline. Both the liquid return pipeline and the gas return pipeline are used to pre-cool the external working pipeline.

[0007] In some technical solutions, the pressure regulating unit further includes: a liquid phase pipeline, a gas phase pipeline, a balancing valve, a level gauge, and a pressure gauge. The liquid inlet of the liquid phase pipeline is connected to the liquid phase interface, the gas inlet of the gas phase pipeline is connected to the gas phase interface, and the two sides of the balancing valve are respectively connected to the liquid outlet of the liquid phase pipeline and the gas outlet of the gas phase pipeline. The level gauge is installed on the liquid phase pipeline, and the pressure gauge is installed on the gas phase pipeline.

[0008] In some technical solutions, the pressure regulating unit further includes a thermal expansion valve and a temperature sensor. The thermal expansion valve is disposed on the pipeline between the electric valve and the inlet of the heat exchanger, and the temperature sensor is disposed on the pipeline between the outlet of the heat exchanger and the inlet of the cooler.

[0009] In some technical solutions, the pressure regulating unit further includes a controller, which is electrically connected to the pressure gauge and the electric valve respectively.

[0010] In some technical solutions, the carbon dioxide storage tank includes a tank shell, a vacuum jacket, and an inner storage tank. The vacuum jacket is equipped with a vacuum pipeline, and the vacuum pipeline is equipped with a vacuum valve and a vacuum measuring gauge. The vacuum valve is used to evacuate the vacuum jacket, and the vacuum measuring gauge is used to measure the vacuum level in the vacuum jacket.

[0011] In some technical solutions, the pressure regulating system further includes a safety device, which includes a first safety valve group installed on the carbon dioxide storage tank and a second safety valve group connected to the gas phase interface.

[0012] In some technical solutions, the pressure regulating system further includes a compressor and a filter, wherein the compressor is disposed on a pipeline between the outlet of the heat exchanger and the inlet of the cooler; and the filter is disposed on a pipeline between the outlet of the refrigerant storage tank and the inlet of the heat exchanger.

[0013] The present invention also provides a control method for the pressure regulating system using the above-mentioned liquid carbon dioxide, comprising:

[0014] The internal pressure of the carbon dioxide storage tank is monitored in real time. When the internal pressure rises to the maximum preset pressure, a pressure reduction process is initiated. The pressure reduction process includes: the electric valve drives the refrigerant in the refrigerant storage tank to circulate through the heat exchanger, and the gaseous carbon dioxide in the carbon dioxide storage tank is cooled and converted into liquid carbon dioxide to reduce the internal pressure of the carbon dioxide storage tank. When the internal pressure drops to the minimum preset pressure, the pressure reduction process is shut down. The maximum preset pressure is 22 bar, and the minimum preset pressure is 13 bar.

[0015] In some technical solutions, before the carbon dioxide storage tank supplies liquid to the external working pipeline, the supply pipeline and the return pipeline are opened, driving the liquid carbon dioxide in the carbon dioxide storage tank to flow sequentially through the supply pipeline, the external working pipeline and the return pipeline, so as to pre-cool the external working pipeline.

[0016] In some technical solutions, before opening the liquid supply line and the liquid return line, the method further includes: opening the gas return line to drive low-temperature gaseous carbon dioxide to pre-cool the external working line.

[0017] Compared with the prior art, the liquid carbon dioxide pressure regulation system and control method provided by the present invention have the following beneficial effects:

[0018] 1. This invention places a heat exchanger inside a carbon dioxide storage tank. Whether in liquid supply or non-liquid supply mode, when the internal pressure of the carbon dioxide storage tank increases, a pressure reduction process is initiated. The refrigerant flowing through the heat exchanger cools the gaseous carbon dioxide inside the carbon dioxide storage tank and converts it into liquid carbon dioxide, thereby reducing the internal pressure of the carbon dioxide storage tank. During the pressure reduction process, the gaseous carbon dioxide is not discharged from the storage tank, reducing carbon dioxide waste and increasing economic benefits.

[0019] 2. Before starting the liquid supply operation, the present invention first opens the return gas pipeline and uses low-temperature gaseous carbon dioxide to preliminarily cool the external working pipeline. Then, the liquid supply pipeline and the return liquid pipeline are opened, and low-temperature liquid carbon dioxide is used to circulate and cool the external working pipeline. When the temperature in the external working pipeline reaches the controlled temperature of the liquid carbon dioxide, the liquid carbon dioxide in the external working pipeline can be taken out. The second pre-cooling process can ensure that the liquid carbon dioxide flowing through the external working pipeline does not contain gas, thus meeting the requirements for pure liquid phase liquid supply.

[0020] 3. This invention monitors the internal pressure of the carbon dioxide storage tank in real time using a pressure gauge and controls the start, stop, and opening degree of the electric valve through a controller, thereby realizing the automatic regulation of the internal pressure of the carbon dioxide storage tank. This keeps the internal pressure of the carbon dioxide storage tank at 13-22 bar, improving the accuracy of pressure regulation and reducing the labor intensity of operators. Attached Figure Description

[0021] The preferred embodiments will now be described in a clear and easy-to-understand manner, in conjunction with the accompanying drawings, to further explain the above-mentioned characteristics, technical features, advantages, and implementation methods of the present invention.

[0022] Figure 1 A schematic diagram of the overall structure of the liquid carbon dioxide parameter adjustment system provided by the present invention.

[0023] Explanation of icon numbers:

[0024] 1—Carbon dioxide storage tank; 1-1 Tank outer shell; 1-2 Vacuum jacket; 1-3 Inner tank;

[0025] 2—First safety valve assembly; 3—Full gauge valve; 4—Vacuum valve; 5—Vacuum measuring gauge tube; 6—Heat exchanger; 7—Thermal expansion valve; 8—Temperature sensor; 9—Electric valve; 10—Filter; 11—Refrigerant storage tank; 12—Cooler; 13—Compressor; 14—Level gauge; 15—Pressure gauge; 16—Gas phase valve; 17—Pressure gauge valve; 18—Balancing valve; 19—Liquid phase valve; 20—Discharge valve; 21—Filling valve; 22—Filling gas valve; 23—First safety valve; 24—First rupture disc; 25—Second safety valve; 26—Second rupture disc; 27—Three-way valve; 28—Exhaust valve; 29—Return valve; 30—Return gas valve; 31—Ventilation valve. Detailed Implementation

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0027] To keep the drawings concise, each figure only schematically shows the parts relevant to the invention, and these do not represent the actual structure of the product. Furthermore, to facilitate understanding, in some figures, only one of components with the same structure or function is schematically depicted, or only one is labeled. In this document, "one" not only means "only one," but can also mean "more than one."

[0028] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0029] In this document, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections 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 based on the specific circumstances.

[0030] Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0031] Example 1

[0032] like Figure 1As shown, this embodiment provides a pressure regulating system for liquid carbon dioxide, including a carbon dioxide storage tank 1, a pressure regulating unit and a liquid supply unit, wherein the carbon dioxide storage tank 1 is provided with a gas phase interface and a liquid phase interface.

[0033] Specifically, since both gaseous and liquid carbon dioxide exist inside the carbon dioxide storage tank 1, the gas phase interface is preferably located at the top of the carbon dioxide storage tank 1, and the liquid phase interface is preferably located at the bottom of the carbon dioxide storage tank 1.

[0034] In some embodiments, the carbon dioxide storage tank 1 is a double-walled vacuum insulated storage tank, including a tank shell 1-1, a vacuum interlayer 1-2 and an inner tank 1-3. The gas phase interface is located at the top of the inner tank 1-3, while the liquid phase interface is located at the bottom of the inner tank 1-3.

[0035] The inner storage tank 1-3 is made of 16MnDr alloy steel or 304 stainless steel, the outer shell 1-1 is made of Q235B carbon steel or 16MnDr alloy steel, and the vacuum interlayer 1-2 is filled with high-vacuum perlite.

[0036] Furthermore, a vacuum pipeline is provided inside the vacuum jacket 1-2, and the outlet of the vacuum pipeline extends to the outside of the tank shell 1-1. A vacuum valve 4 and a vacuum measuring gauge 5 are provided on the vacuum pipeline extending outside the tank shell 1-1. The vacuum valve 5 is used to evacuate the vacuum jacket 1-2 and control the vacuum pressure of the vacuum jacket 1-2 at 5-10 Pa. The vacuum measuring gauge 5 is used to measure the vacuum degree inside the vacuum jacket 1-2. During use, the vacuum degree can be measured periodically through the vacuum measuring gauge 5, and the vacuum valve 4 is used to maintain the vacuum degree of the vacuum jacket 1-2 to ensure the heat insulation capacity of the carbon dioxide storage tank 1.

[0037] More preferably, considering that in actual application scenarios, carbon dioxide storage tank 1 is connected to multiple delivery pipelines, multiple gas phase interfaces and liquid phase interfaces can be set up to connect different delivery pipelines to different interfaces one by one, so that the messy multiple delivery pipelines can be distributed and managed in an orderly manner.

[0038] The pressure regulating unit described above includes a refrigerant storage tank 11, an electric valve 9, a heat exchanger 6, and a cooler 12 connected in sequence. The heat exchanger 6 is located inside the carbon dioxide storage tank 1, preferably at the top of the inner cavity of the carbon dioxide storage tank 1, and more preferably at the top of the inner cavity of the inner storage tank 1-3.

[0039] When the liquid carbon dioxide in carbon dioxide storage tank 1 is heated and vaporized, causing the internal pressure to rise, the pressure reduction process is initiated: the electric valve 9 is opened, and the refrigerant in the refrigerant storage tank 11 flows into the heat exchanger 6. The gaseous carbon dioxide in carbon dioxide storage tank 1 exchanges heat with the refrigerant, and after the gaseous carbon dioxide cools down and turns into liquid carbon dioxide, the internal pressure of carbon dioxide storage tank 1 is reduced. The heated refrigerant flows from the outlet of heat exchanger 6 into cooler 12, cools down, and returns to refrigerant storage tank 11 to continue the next round of pressure reduction process. When the internal pressure of carbon dioxide storage tank 1 drops to the minimum preset pressure of liquid carbon dioxide, the electric valve 9 is closed, and the pressure reduction process ends.

[0040] The minimum preset pressure mentioned above is 13 bar.

[0041] In some embodiments, the cooler 12 is used to reduce the temperature of the refrigerant, preferably an air-cooled heat exchanger, but commercially available coolers can also be used.

[0042] In some embodiments, the pressure regulating unit further includes a thermal expansion valve 7 and a temperature sensor 8, wherein the thermal expansion valve 7 is disposed on the pipeline between the electric valve 9 and the inlet of the heat exchanger 6, and the temperature sensor 8 is disposed on the pipeline between the outlet of the heat exchanger 6 and the inlet of the cooler 12.

[0043] In some embodiments, the pressure regulating unit further includes a liquid phase pipeline, a gas phase pipeline, a balance valve 18, a level gauge 14, and a pressure gauge 15. The liquid phase pipeline and the gas phase pipeline are respectively connected to the liquid phase interface and the gas phase interface of the carbon dioxide storage tank 1. More specifically, the liquid inlet of the liquid phase pipeline is connected to the liquid phase interface of the inner storage tank 1-3, and the gas inlet of the gas phase pipeline is connected to the gas phase interface of the inner storage tank 1-3. The two sides of the balance valve 18 are respectively connected to the liquid outlet of the liquid phase pipeline and the gas outlet of the gas phase pipeline. A liquid phase valve 19 is provided on the liquid phase pipeline, and a gas phase valve 16 is provided on the gas phase pipeline.

[0044] Furthermore, the level gauge 14 is installed on the liquid phase pipeline. More specifically, one end of the level gauge 14 is connected to the pipeline between the outlet of the liquid phase valve 19 and the balance valve 18, and the other end is connected to the pipeline between the balance valve 18 and the gas phase valve 16.

[0045] Pressure gauge 15 is installed on the gas phase pipeline to detect the pressure inside carbon dioxide storage tank 1. Furthermore, pressure gauge 15 is used to detect the pressure inside inner storage tanks 1-3.

[0046] Specifically, a pressure gauge valve 17 is also installed on the pipeline between the balance valve 18 and the gas phase valve 16, and the pressure gauge 15 is connected to the pressure gauge valve 17.

[0047] In some embodiments, the pressure regulation system also includes a controller that is electrically connected to the pressure gauge 15, the temperature sensor 8, the electric valve 9, and the thermal expansion valve 7, respectively.

[0048] Specifically, pressure gauge 15 detects the pressure inside the inner storage tank 1-3 in real time and transmits the pressure signal to the controller. The controller converts the pressure signal into a control signal for electric valve 9 and transmits it to electric valve 9 to control the opening and closing and the degree of opening of electric valve 9.

[0049] The maximum preset pressure in the inner storage tanks 1-3 is set to 22 bar, and the minimum preset pressure is set to 13 bar. Correspondingly, the controlled temperature of liquid carbon dioxide is between -30℃ and -24℃.

[0050] When pressure gauge 15 detects that the pressure inside the inner storage tank 1-3 has reached the maximum preset pressure, the pressure reduction process is initiated: the controller controls the electric valve 9 to open, and the refrigerant flows from the refrigerant storage tank 11 through the heat exchanger 6 to cool the gaseous carbon dioxide at the top of the inner storage tank 1-3, converting it into liquid carbon dioxide. When pressure gauge 15 detects that the pressure inside the inner storage tank 1-3 has dropped to the minimum preset pressure, the controller controls the electric valve 9 to close, and the cooling and pressure reduction process of the carbon dioxide storage tank is completed.

[0051] Temperature sensor 8 detects the temperature of the refrigerant flowing out of heat exchanger 6 in real time and transmits the temperature signal to controller. Controller converts the temperature signal into a control signal for thermal expansion valve 7 and transmits it to thermal expansion valve 7 to control the opening degree of thermal expansion valve 7, thereby realizing automatic control of refrigerant flow.

[0052] In some embodiments, the pressure regulating unit further includes a compressor 13 and a filter 10. The compressor 13 is installed on the pipeline between the outlet of the heat exchanger 6 and the inlet of the cooler 12. The refrigerant flows through the heat exchanger 6, absorbs heat and is converted into gas. After being compressed by the compressor 13, it becomes a high-pressure refrigerant low-temperature gas-liquid mixture that flows into the cooler 12. The refrigerant cooled by the cooler 12 is converted into a lower-temperature refrigerant liquid and flows into the refrigerant storage tank 11, and then enters the next round of cooling and heat exchange process.

[0053] The filter 10 is installed on the pipeline between the refrigerant storage tank 11 and the inlet of the heat exchanger 6. More preferably, the filter 10 is installed on the pipeline between the refrigerant storage tank 11 and the electric valve 9. The refrigerant enters the heat exchanger 6 for cooling and heat exchange after being filtered by the filter 10.

[0054] The aforementioned liquid supply unit includes a liquid supply pipeline, a liquid return pipeline, and a gas return pipeline. The two ends of the liquid supply pipeline are connected to the liquid phase interface of the carbon dioxide storage tank 1 and the external working pipeline, respectively, to supply liquid carbon dioxide to the external working pipeline. Specifically, the inlet of the liquid supply pipeline is connected to the liquid phase interface of the inner storage tank 1-3, and the outlet of the liquid supply pipeline extends to the outer shell 1-1 of the storage tank and is connected to the external working pipeline. An outlet valve 20 is provided on the liquid supply pipeline.

[0055] The two ends of the above-mentioned return liquid pipeline are connected to the gas phase interface of carbon dioxide storage tank 1 and the external working pipeline, respectively. The two ends of the return gas pipeline are connected to the gas phase interface of carbon dioxide storage tank 1 and the external working pipeline, respectively. Both the return liquid pipeline and the return gas pipeline are used to pre-cool the external working pipeline.

[0056] More specifically, one end of the return gas pipeline is connected to the gas phase interface of the inner storage tank 1-3, and the other end of the return gas pipeline extends to the outer shell 1-1 of the storage tank and is connected to the external working pipeline. The return gas pipeline is equipped with a return gas valve 30. Before the carbon dioxide storage tank 1 supplies liquid to the external working pipeline, the return gas pipeline is opened to use the gaseous carbon dioxide in the carbon dioxide storage tank 1 to perform preliminary cooling of the external working pipeline.

[0057] One end of the return liquid pipeline is connected to the gas phase interface of the inner storage tank 1-3, and the other end of the return liquid pipeline extends to the outer shell 1-1 of the storage tank and connects to the external working pipeline. The return liquid pipeline is equipped with a return liquid valve 29. After the external working pipeline is initially cooled, the temperature inside the external working pipeline is still higher than the controlled temperature of liquid carbon dioxide. At this time, the outlet valve 30 and the return liquid valve 29 are opened at the same time. Liquid carbon dioxide flows into the external working pipeline through the supply liquid pipeline and returns to the carbon dioxide storage tank 1 through the return liquid pipeline to cool the external working pipeline again. After a period of cyclic cooling and pre-cooling, when the temperature inside the external working pipeline is cooled to the controlled temperature of liquid carbon dioxide, it is considered that the external working pipeline is full of liquid carbon dioxide. At this time, the liquid carbon dioxide in the external working pipeline can be taken out.

[0058] It should be noted that when the return liquid pipeline and the supply liquid pipeline are opened to pre-cool the external working pipeline, the excess gas-liquid mixture or liquid in the external working pipeline can also be returned to the inner storage tank 1-3 through the return gas pipeline.

[0059] When the outlet valve 30 and return valve 29 are first opened, the liquid carbon dioxide in the external working pipeline absorbs heat and is converted into gaseous carbon dioxide because the temperature of the external working pipeline is higher than the controlled temperature of the liquid carbon dioxide. It then returns to the inner storage tank 1-3 from the gas phase interface through the return pipeline. At this time, the pressure in the inner storage tank 1-3 increases, and the pressure regulating unit starts to operate. The refrigerant flows from the refrigerant storage tank 11 into the heat exchanger 6 to cool the gaseous carbon dioxide at the top of the inner storage tank 1-3, converting it into liquid and reducing the pressure in the inner storage tank 1-3, so that the pressure in the inner storage tank 1-3 is always maintained within 13 bar-22 bar.

[0060] In some embodiments, the pressure regulating system further includes a safety device comprising a first safety valve assembly 2 disposed on the carbon dioxide storage tank 1 and a second safety valve assembly connected to the gas phase interface, the second safety valve assembly comprising a first safety valve 23 and a first rupture disc 24.

[0061] Preferably, the first safety valve assembly 2 is installed on the outer shell 1-1 of the storage tank. When a leak occurs in the inner storage tank 1-3, the first safety valve 2 can burst to release pressure and ensure the safety of equipment and personnel.

[0062] More preferably, it also includes a third safety valve assembly, which includes a second safety valve 25 and a second rupture disc 26. The gas phase interface on the inner storage tank 1-3 is connected to the inlet of a three-way valve 27 via a pipeline. One outlet of the three-way valve 27 is connected to the first safety valve 23 and the first rupture disc 24 via a pipeline, and the other outlet of the three-way valve 27 is connected to the second safety valve 25 and the second rupture disc 26 via a pipeline.

[0063] Furthermore, the bursting pressure of the first rupture disc 24 and the second rupture disc 26 is set to be slightly higher than the opening pressure of the first safety valve 23 and the second safety valve 25. When the safety valve is damaged or fails, the rupture disc can ensure the safety of the equipment and personnel.

[0064] This safety device has two sets of safety valve assemblies, one in use and one on standby during normal operation. When one set of safety valves is damaged or requires maintenance, the three-way valve 27 can be switched to the other set of safety valves, and the safety valve requiring maintenance can be removed for repair. The same applies to the rupture disc, which will not be described in detail here.

[0065] It should be noted that there is no limit to the number of safety valves and rupture discs; the number can be set according to actual needs.

[0066] In some embodiments, the pressure regulating system is further provided with a filling pipeline for replenishing liquid carbon dioxide into the carbon dioxide storage tank 1. The two ends of the filling pipeline are connected to the liquid phase interface of the carbon dioxide storage tank 1 and an external liquid carbon dioxide supply vehicle (liquid carbon dioxide tank truck), respectively. A filling valve 21 is provided on the filling pipeline.

[0067] In some embodiments, the pressure regulating system is also provided with a liquid-filling gas pipeline. The two ends of the liquid-filling gas pipeline are connected to the gas phase interface of the carbon dioxide storage tank 1 and the external liquid carbon dioxide supply vehicle, respectively. The liquid-filling gas valve 22 on the liquid-filling gas pipeline is used to prevent the pressure from dropping suddenly when filling the carbon dioxide storage tank 1 with liquid carbon dioxide. If the pressure drops too quickly, the liquid carbon dioxide will easily form dry ice. In order to prevent this from happening, before filling the liquid carbon dioxide, the pressure in the space to be filled (carbon dioxide storage tank 1) must be balanced with the storage pressure of the external liquid carbon dioxide supply vehicle. The liquid-filling gas valve 22 is opened first to make the pressure equalize, and then the liquid-filling valve 21 can be opened to fill.

[0068] In some embodiments, the pressure regulating system is equipped with a level-side full pipe connected to the carbon dioxide storage tank 1. Specifically, the highest liquid level of liquid carbon dioxide stored in the inner storage tank 1-3 is determined by calibration, and a full-level measuring port is set on the outer wall of the inner storage tank 1-3 corresponding to the highest liquid level. The inlet of the level-side full pipe is connected to the full-level measuring port, and the outlet of the level-side full pipe extends outside the outer shell 1-1 of the storage tank. A level-side full valve 3 is provided on the level-side full pipe. During the process of filling the inner storage tank 1-3 with liquid carbon dioxide through the filling pipeline, when the filling liquid level approaches the highest liquid level, the full-level measuring valve 3 is slightly opened to continue filling. When liquid flows out of the outlet of the level-side full pipe, the full-level measuring valve 3, the filling valve 21, and the filling gas valve 22 can be closed to stop filling.

[0069] In some implementations, vent valves 31 are provided on the liquid supply line, liquid filling line, liquid return line, and liquid filling gas line. Specifically, taking the liquid supply line as an example, a matching vent valve 31 is provided for each relatively closed section formed on the liquid supply line. When the liquid supply line stops working, the liquid carbon dioxide remaining inside the line will slowly vaporize in the closed section. As the carbon dioxide vaporizes, the pressure inside the line increases, which will cause the safety valve to open to release the pressure. Under normal circumstances, frequent opening and pressure release of the safety valve is extremely detrimental to the sealing of the safety valve and is very likely to cause leakage of the sealing surface. At this time, the liquid carbon dioxide or gas-liquid mixture remaining in the line can be vented by opening the vent valve 31.

[0070] The vent valves installed on the filling line, return line, and filling gas line serve the same function as the vent valve on the supply line, and will not be described again here.

[0071] In some embodiments, the pressure regulating system is further provided with an exhaust pipe connected to the gas phase interface of the carbon dioxide storage tank 1. The exhaust pipe is used to discharge some carbon dioxide gas when the internal pressure of the carbon dioxide storage tank 1 is overpressured, thereby reducing the internal pressure of the carbon dioxide storage tank 1 and protecting the safety of the carbon dioxide storage tank 1.

[0072] Specifically, one end of the exhaust pipe is connected to the gas phase interface of the inner storage tank 1-3, and the other end extends to the outside of the outer shell 1-1 of the storage tank. An exhaust valve 28 is provided on the exhaust pipe.

[0073] Example 2

[0074] This embodiment provides a control method for a pressure system using liquid carbon dioxide as described in Embodiment 1. The control method includes a liquid supply precooling process and a pressure reduction process.

[0075] The specific steps of the liquid supply precooling process include:

[0076] When carbon dioxide storage tank 1 needs to supply liquid carbon dioxide to the outside, first open the return gas valve 30 on the return gas pipeline. Use the gaseous carbon dioxide in carbon dioxide storage tank 1 to pre-cool the external working pipeline. After the pump in the external working pipeline is cooled, open the liquid outlet valve 20 on the liquid supply pipeline and the liquid return valve 29 on the liquid return pipeline to allow the low-temperature liquid carbon dioxide to flow through the external working pipeline and return to the carbon dioxide storage tank 1. At this time, the pump body on the external working pipeline can be turned on to make the liquid carbon dioxide circulate in the external working pipeline, so as to achieve the circulating cooling and pre-cooling of the external working pipeline.

[0077] When liquid carbon dioxide enters the external supply pipeline and begins to cool, the temperature of the external working pipeline is still higher than the controlled temperature of the liquid carbon dioxide. Heat will still be input into the external working pipeline, and the liquid carbon dioxide in the external working pipeline will absorb heat and convert into vaporized carbon dioxide. It takes a period of time to circulate and cool down the external working pipeline to the controlled temperature of the liquid carbon dioxide. When the temperature of the external working pipeline reaches the controlled temperature of the liquid carbon dioxide, it can be determined that the external working pipeline is full of liquid carbon dioxide. At this time, the liquid supply working state can be started, that is, the liquid carbon dioxide in the external working pipeline can be used to meet the pure liquid phase working requirements.

[0078] The aforementioned liquid carbon dioxide pressure system experiences external heat input in both non-supply and supply modes. When external heat is input, the liquid carbon dioxide absorbs heat and vaporizes, causing the internal pressure of carbon dioxide storage tank 1 to rise. To prevent the internal pressure of carbon dioxide storage tank 1 from exceeding the maximum preset pressure (22 bar), a pressure reduction process can be implemented through a pressure regulating unit.

[0079] The specific steps of the pressure reduction process are as follows: The internal pressure of the inner storage tank 1-3 is detected in real time by the pressure gauge 15. When the pressure gauge 15 detects that the internal pressure of the inner storage tank 1-3 exceeds the maximum preset pressure of 22 bar, the controller sends an opening control signal to the electric valve 9. The refrigerant stored in the refrigerant storage tank 11 flows through the filter 10, the electric valve 9, and the thermal expansion valve 7 in sequence before entering the heat exchanger 6. Under the action of the refrigerant, the gaseous carbon dioxide in the inner storage tank 1-3 is converted into liquid carbon dioxide. The temperature of the refrigerant rises after heat exchange and flows into the compressor 13 from the outlet of the heat exchanger 6. After being compressed by the compressor 13, it becomes high-pressure refrigerant and enters the cooler 12. After cooling, it returns to the refrigerant storage tank 11 to start the next round of pressure reduction process.

[0080] As the depressurization process proceeds, gaseous carbon dioxide is converted into liquid carbon dioxide, and the internal pressure of the inner storage tank 1-3 gradually decreases. When the pressure gauge 15 detects that the internal pressure of the inner storage tank 1-3 has dropped to the minimum preset pressure of 13 bar, the controller sends a closing control signal to the electric valve 9, and the depressurization process ends.

[0081] It should be noted that during actual operation, when the pressure gauge 15 detects that the internal pressure of the inner tank 1-3 has risen to near the maximum preset pressure of 22 bar, the pressure reduction process can be started. When the internal pressure of the inner tank 1-3 drops to near the minimum preset pressure of 13 bar, the pressure reduction process can be stopped, so that the internal pressure of the inner tank 1-3 is always maintained between 13 bar and 22 bar.

[0082] Meanwhile, temperature sensor 8 detects the temperature of the refrigerant flowing out of heat exchanger 6 in real time and transmits the temperature signal to controller. At this time, controller converts the temperature signal into a thermal signal and transmits it to thermal expansion valve 7 to control the opening of thermal expansion valve 7 and realize the control of refrigerant flow.

[0083] For example, in the initial stage of the depressurization process, the internal pressure of the inner storage tanks 1-3 is relatively high, and there is a large amount of gaseous carbon dioxide that needs to be cooled. After the refrigerant undergoes heat exchange in the heat exchanger 6, the temperature sensor detects a significant increase in the refrigerant temperature. At this point, the opening of the thermal expansion valve 7 can be increased to increase the refrigerant flow into the heat exchanger 6, causing the gaseous carbon dioxide to cool down rapidly and convert into liquid carbon dioxide. As the depressurization process continues, the amount of gaseous carbon dioxide in the inner storage tanks 1-3 gradually decreases. At this point, the temperature sensor detects a decrease in the refrigerant temperature increase, and the opening of the thermal expansion valve 7 can be decreased to reduce the refrigerant flow into the heat exchanger 6.

[0084] In summary, the aforementioned depressurization process ensures that the carbon dioxide vaporized due to external heat input during the storage and supply process is not discharged from the storage tank, reducing waste caused by carbon dioxide gas emissions. Furthermore, this circulating cooling depressurization process guarantees that the pressure inside carbon dioxide storage tank 1 remains between 13-22 bar, corresponding to a liquid carbon dioxide temperature controlled between -30°C and -24°C. After the pre-cooling process is completed and the external working pipeline temperature reaches the liquid carbon dioxide temperature (-30°C), the medium flowing in the external working pipeline remains pure liquid carbon dioxide.

[0085] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A pressure regulating system for liquid carbon dioxide, characterized in that, include: Carbon dioxide storage tank, pressure regulating unit, and liquid supply unit. The carbon dioxide storage tank is equipped with a gas phase interface and a liquid phase interface; The pressure regulating unit includes a refrigerant storage tank, an electric valve, a heat exchanger, and a cooler connected in sequence. The heat exchanger is installed inside the carbon dioxide storage tank. The refrigerant in the refrigerant storage tank flows through the heat exchanger to cool the gaseous carbon dioxide in the carbon dioxide storage tank and convert it into liquid carbon dioxide. The liquid supply unit includes a liquid supply pipeline, a liquid return pipeline, and a gas return pipeline. The two ends of the liquid supply pipeline are connected to the liquid phase interface and an external working pipeline, respectively. The liquid supply pipeline is used to supply liquid carbon dioxide to the external working pipeline. The two ends of the return liquid pipeline are respectively connected to the gas phase interface and the external working pipeline, and the two ends of the return gas pipeline are respectively connected to the gas phase interface and the external working pipeline. The return gas pipeline is equipped with a return gas valve, the return liquid pipeline is equipped with a return liquid valve, and the supply liquid pipeline is equipped with a liquid outlet valve. Before the carbon dioxide storage tank supplies liquid to the external working pipeline, the return gas valve is opened to allow the gaseous carbon dioxide in the carbon dioxide storage tank to pre-cool the external working pipeline through the return gas pipeline. After the pre-cooling, the liquid outlet valve and the return liquid valve are opened simultaneously to allow the liquid carbon dioxide to flow into the external working pipeline through the supply liquid pipeline and return to the carbon dioxide storage tank through the return liquid pipeline, thereby circulating and pre-cooling the external working pipeline until the temperature in the external working pipeline is cooled to the controlled temperature of the liquid carbon dioxide before it is used. The pressure regulating unit also includes a pressure gauge and a controller. The pressure gauge is used to detect the internal pressure of the carbon dioxide storage tank. The controller is electrically connected to the pressure gauge and the electric valve. The controller is configured to start a pressure reduction process and drive the refrigerant to circulate through the heat exchanger to reduce the internal pressure when the internal pressure rises to the highest preset pressure, and to shut down the pressure reduction process when the internal pressure drops to the lowest preset pressure.

2. The pressure regulating system for liquid carbon dioxide according to claim 1, characterized in that, The pressure regulating unit further includes: The system includes a liquid phase pipeline, a gas phase pipeline, a balancing valve, a level gauge, and a pressure gauge. The inlet of the liquid phase pipeline is connected to the liquid phase interface, the inlet of the gas phase pipeline is connected to the gas phase interface, and the two sides of the balancing valve are connected to the outlet of the liquid phase pipeline and the outlet of the gas phase pipeline, respectively. The level gauge is installed on the liquid phase pipeline, and the pressure gauge is installed on the gas phase pipeline.

3. The pressure regulating system for liquid carbon dioxide according to claim 1, characterized in that, The pressure regulating unit further includes: A thermal expansion valve and a temperature sensor are provided, wherein the thermal expansion valve is disposed on the pipeline between the electric valve and the inlet of the heat exchanger, and the temperature sensor is disposed on the pipeline between the outlet of the heat exchanger and the inlet of the cooler.

4. The pressure regulating system for liquid carbon dioxide according to claim 1, characterized in that, The carbon dioxide storage tank includes a tank shell, a vacuum jacket, and an inner tank. The vacuum jacket is equipped with a vacuum pipeline, and the vacuum pipeline is equipped with a vacuum valve and a vacuum measuring gauge. The vacuum valve is used to evacuate the vacuum interlayer, and the vacuum measuring gauge is used to measure the vacuum level inside the vacuum interlayer.

5. The pressure regulating system for liquid carbon dioxide according to claim 1, characterized in that, Also includes: The safety device includes a first safety valve assembly installed on the carbon dioxide storage tank and a second safety valve assembly connected to the gas phase interface.

6. The pressure regulating system for liquid carbon dioxide according to claim 1, characterized in that, Also includes: A compressor and a filter, wherein the compressor is disposed on a pipeline between the outlet of the heat exchanger and the inlet of the cooler; The filter is installed on the pipeline between the outlet of the refrigerant storage tank and the inlet of the heat exchanger.

7. A control method for a liquid carbon dioxide pressure regulation system, characterized in that, The pressure regulating system for liquid carbon dioxide according to any one of claims 1-6 comprises: Real-time monitoring of the internal pressure of the carbon dioxide storage tank; When the internal pressure rises to the maximum preset pressure, the pressure reduction process is initiated; The pressure reduction process includes: the electric valve drives the refrigerant in the refrigerant storage tank to circulate through the heat exchanger, and the gaseous carbon dioxide in the carbon dioxide storage tank is cooled and converted into liquid carbon dioxide to reduce the internal pressure of the carbon dioxide storage tank. When the internal pressure drops to the minimum preset pressure, the pressure reduction process is shut down; The maximum preset pressure is 22 bar, and the minimum preset pressure is 13 bar.

8. The control method according to claim 7, characterized in that, Also includes: Before the carbon dioxide storage tank supplies liquid to the external working pipeline, the supply pipeline and the return pipeline are opened, driving the liquid carbon dioxide in the carbon dioxide storage tank to flow sequentially through the supply pipeline, the external working pipeline and the return pipeline, so as to pre-cool the external working pipeline.

9. The control method according to claim 8, characterized in that, Before opening the supply line and the return line, the procedure further includes: The return gas line is opened, and low-temperature gaseous carbon dioxide is used to pre-cool the external working line.

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