Dry ice production system

Abstract

To provide a dry ice production system that achieves both simplification and compactness of equipment and minimization of carbon dioxide loss.SOLUTION: A dry ice production system 1 according to the present invention comprises a liquefied carbon dioxide drum 10, a liquefied carbon dioxide circulation line that includes the liquefied carbon dioxide drum 10 and forms a circulation path for liquefied carbon dioxide, an ejector 40 that uses liquefied carbon dioxide flowing through the liquefied carbon dioxide circulation line as a driving fluid and uses carbon dioxide gas as a suction fluid, a liquefied carbon dioxide discharge line 81 that discharges liquefied carbon dioxide for dry ice generation from the liquefied carbon dioxide stored in the liquefied carbon dioxide drum 10 and depressurizes the same by a liquefied carbon dioxide pressure reducing valve 82 to a pressure accompanied by solidification to generate dry ice, a dry ice storage tank 50 that stores the generated dry ice, and a carbon dioxide gas recycling line 83 that supplies carbon dioxide gas generated by depressurization from the dry ice storage tank 50 to the ejector 40.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a dry ice production system for producing dry ice. [Background technology]

[0002] Generally, dry ice is produced by reducing the pressure of liquid CO2 to atmospheric pressure, and as the liquid CO2 evaporates, it removes the latent heat of vaporization, cooling the remaining liquid to produce dry ice. As a result, some of the liquid CO2 evaporates and becomes carbon dioxide gas at atmospheric pressure, leaving a certain percentage of carbon dioxide gas that does not become dry ice.

[0003] In this regard, Patent Document 1 discloses a technology in which carbon dioxide gas generated during decompression is compressed and cooled by a compressor, and then decompressed by an expansion turbine to recover a portion of the gas as dry ice. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-117458 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the inclusion of a compressor and turbine makes the equipment complex and large-scale, increasing the equipment and maintenance costs. In addition, some of the heat is released outside as exhaust, resulting in a loss of carbon dioxide.

[0006] The present invention has been made to solve such problems, and aims to provide a dry ice production system that achieves both simplification and compactness of the equipment and minimization of carbon dioxide loss. [Means for solving the problem]

[0007] (1) The dry ice production system of the present invention comprises: a liquefied carbon dioxide drum for storing liquefied carbon dioxide; a liquefied carbon dioxide circulation line that includes the liquefied carbon dioxide drum and forms a circulation path for liquefied carbon dioxide; an ejector disposed in the liquefied carbon dioxide circulation line, using the liquefied carbon dioxide flowing through the liquefied carbon dioxide circulation line as a driving fluid and carbon dioxide gas as a suction fluid; a liquefied carbon dioxide discharge line that discharges liquefied carbon dioxide for producing dry ice from the liquefied carbon dioxide stored in the liquefied carbon dioxide drum and reduces the pressure of the discharged liquefied carbon dioxide to a pressure that will solidify the liquefied carbon dioxide using a liquefied carbon dioxide pressure reducing valve to produce dry ice; a dry ice storage tank that receives and stores the generated dry ice; and a carbon dioxide gas recycle line that supplies the carbon dioxide gas generated by the pressure reduction using the liquefied carbon dioxide pressure reducing valve from the dry ice storage tank to the ejector.

[0008] (2) In addition, in the device described in (1) above, the ejector further includes a gas receiving line for receiving carbon dioxide gas from the outside. [Effects of the Invention]

[0009] According to the dry ice production system of the present invention, dry ice can be produced while achieving both simplification and compactness of the equipment and minimization of carbon dioxide loss. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing a dry ice production system according to a first embodiment of the present invention. [Figure 2] FIG. 10 is a schematic diagram showing a dry ice production system according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Embodiment 1] First, the configuration and functions of the first embodiment of the present invention will be described with reference to FIG. The dry ice production system 1 of this embodiment has a liquefied carbon dioxide drum 10, a liquefied carbon dioxide pump 20, a liquefied carbon dioxide cooler 30, an ejector 40, a dry ice storage tank 50, a liquefied carbon dioxide discharge line 81, a liquefied carbon dioxide pressure reducing valve 82, a carbon dioxide gas recycle line 83, a carbon dioxide gas recycle flow control valve 84, and a dry ice discharge line 85.

[0012] The liquefied carbon dioxide drum 10 is a vertical cylindrical drum that temporarily stores the liquefied carbon dioxide received from the ejector outlet line 74 .

[0013] The liquefied carbon dioxide pump 20 is a centrifugal pump that receives liquefied carbon dioxide temporarily stored in the liquefied carbon dioxide drum 10 from a liquefied carbon dioxide pump inlet line 71, pressurizes the liquefied carbon dioxide, and discharges it to a liquefied carbon dioxide pump outlet line 72. The amount of pressure increase by the liquefied carbon dioxide pump 20 corresponds to the pressure loss in the system including the liquefied carbon dioxide cooler 30 and the ejector 40.

[0014] The liquefied carbon dioxide cooler 30 is a typical shell-and-tube heat exchanger, and cools the liquefied carbon dioxide received from the liquefied carbon dioxide pump outlet line 72 with a low-temperature refrigerant. The refrigerant is supplied from a refrigerant supply line 76, and is discharged to a refrigerant discharge line 77 after heat exchange.

[0015] The ejector 40 is a general ejector that creates a reduced pressure state using liquefied carbon dioxide supplied from an ejector inlet line 73 as a driving fluid, and receives carbon dioxide gas from a gas receiving line 75. At this time, the receiving flow rate of the carbon dioxide gas is adjusted by a gas receiving flow rate adjustment valve 78. After the ejector 40, the liquefied carbon dioxide flows through an ejector outlet line 74 toward the liquefied carbon dioxide drum 10.

[0016] <Dry ice storage tank> The dry ice storage tank 50 is a vertical cylindrical container with a conical bottom, and temporarily stores the dry ice generated by flashing downstream of the liquefied carbon dioxide pressure reducing valve 82.

[0017] <Liquefied carbon dioxide delivery line> The liquefied carbon dioxide discharge line 81 is a pipe connected to the liquefied carbon dioxide drum 10 and the dry ice storage tank 50, and discharges the liquefied carbon dioxide stored in the liquefied carbon dioxide drum 10 for use in producing dry ice into the dry ice storage tank 50.

[0018] <Liquid carbon dioxide pressure reducing valve> The liquefied carbon dioxide pressure reducing valve 82 is a remotely controlled globe valve arranged in the liquefied carbon dioxide discharge line 81, and reduces the pressure of the liquefied carbon dioxide flowing through the liquefied carbon dioxide discharge line 81 to a pressure that will cause solidification.

[0019] <Carbon dioxide gas recycling line> The carbon dioxide gas recycle line 83 is a pipe connecting the dry ice storage tank 50 and the gas receiving line 75, and sends the carbon dioxide gas generated by pressure reduction using the liquefied carbon dioxide pressure reducing valve 82 from the dry ice storage tank 50 to the gas receiving line 75.

[0020] <Carbon dioxide gas recycle flow control valve> The carbon dioxide gas recycle flow rate adjustment valve 84 is a remotely controlled butterfly valve disposed in the carbon dioxide gas recycle line 83 and adjusts the flow rate of the low-temperature carbon dioxide gas flowing through the carbon dioxide gas recycle line 83 .

[0021] Next, the operation of the dry ice production system 1 of this embodiment will be described. Liquefied carbon dioxide is circulated within the system by operating the liquefied carbon dioxide pump 20. Specifically, the liquefied carbon dioxide in the liquefied carbon dioxide drum 10 is sent to a liquefied carbon dioxide pump inlet line 71, passes through the liquefied carbon dioxide pump 20, a liquefied carbon dioxide pump outlet line 72, the liquefied carbon dioxide cooler 30, an ejector inlet line 73, the ejector 40, and an ejector outlet line 74, and is then refluxed to the liquefied carbon dioxide drum 10. As described above, the liquefied carbon dioxide drum 10, the liquefied carbon dioxide pump inlet line 71, the liquefied carbon dioxide pump outlet line 72, the ejector inlet line 73 and the ejector outlet line 74 form a circulation path for the liquefied carbon dioxide, and therefore these constitute the liquefied carbon dioxide circulation line of the present invention.

[0022] In the liquefied carbon dioxide drum 10, the liquefied carbon dioxide is stored at, for example, 0.6 MPaG and −50° C., and is pressurized by the liquefied carbon dioxide pump 20 to, for example, 1.3 MPaG.

[0023] The liquefied carbon dioxide pressurized by the liquefied carbon dioxide pump 20 is cooled in the liquefied carbon dioxide cooler 30 to a temperature range where it will not solidify, for example, -53°C, by a refrigerant supplied by cold heat generation equipment (e.g., a refrigerator) not shown.

[0024] The liquefied carbon dioxide cooled by the liquefied carbon dioxide cooler 30 is supplied to the ejector 40, and a reduced pressure state is created by flowing at high speed through the small diameter portion inside the ejector 40 using Bernoulli's principle. Carbon dioxide gas at atmospheric pressure or low pressure is supplied from the gas receiving line 75 to the inside of the ejector 40 in a reduced pressure state.

[0025] Inside the ejector 40, the carbon dioxide gas supplied from the gas receiving line 75 mixes with the liquefied carbon dioxide, which is flowing at a high speed. As the diameter inside the ejector 40 expands and the flow rate decreases, the pressure of the mixed fluid that has passed through the small diameter portion of the ejector 40 recovers to, for example, 0.6 MPaG, and the carbon dioxide gas in the mixed fluid is compressed and cooled, causing it to condense. At this time, the carbon dioxide gas is compressed while coming into contact with the liquefied carbon dioxide and being cooled, so the compression process of the carbon dioxide gas is close to isothermal compression, and therefore the carbon dioxide gas is compressed with high compression efficiency.

[0026] In the downstream of the ejector 40, the liquefied carbon dioxide flows through the ejector outlet line 74 towards the liquefied carbon dioxide drum 10, but if carbon dioxide gas that has not been completely condensed remains inside the ejector 40, it becomes a multiphase flow.

[0027] The liquefied carbon dioxide that flows into the liquefied carbon dioxide drum 10 becomes saturated at 0.6 MPaG and separates into a gas layer and a liquid layer. The amount of carbon dioxide held in the system increases as carbon dioxide gas is supplied from the gas receiving line 75. Therefore, an amount of liquefied carbon dioxide equal to the amount of carbon dioxide gas that has been supplied is discharged from the liquefied carbon dioxide drum 10 via the liquefied carbon dioxide discharge line 81 and discharged to the outside as dry ice.

[0028] The liquefied carbon dioxide discharged from the liquefied carbon dioxide drum 10 is supplied to the dry ice storage tank 50 via the liquefied carbon dioxide discharge line 81. At this time, the liquefied carbon dioxide is flashed by being reduced in pressure to a low pressure (for example, 10 kPaG) by the liquefied carbon dioxide pressure reducing valve 82, and the latent heat of vaporization is removed. As a result, a low-temperature (approximately -79°C) multiphase fluid containing dry ice is blown out from the secondary side of the carbon dioxide pressure reducing valve 82, and the dry ice and low-temperature carbon dioxide gas are supplied to the dry ice storage tank 50.

[0029] Dry ice supplied to the dry ice storage tank 50 accumulates in the lower conical portion by gravity and is discharged to the outside through the dry ice dispensing line 85.

[0030] The low-temperature carbon dioxide gas supplied to the dry ice storage tank 50 is supplied to the gas receiving line 75 via the carbon dioxide gas recycle line 83 and the carbon dioxide gas recycle flow rate control valve 84, and is then supplied to the ejector 40 again.

[0031] According to the dry ice production system 1 of this embodiment, carbon dioxide gas is received through the gas receiving line 75, and dry ice can be dispensed through the dry ice dispensing line 85. Therefore, if equipment for recovering carbon dioxide as a low-pressure gas is placed upstream, the liquefaction process can be completed within the system and the dry ice can be dispensed, making it easy to reuse the recovered carbon dioxide.

[0032] Furthermore, since the system does not have large rotating machines such as compressors or expanders, the equipment can be simplified and made compact, and maintainability can also be improved. Furthermore, since the carbon dioxide gas generated in the dry ice storage tank 50 is collected and re-liquefied in the ejector 40, the loss of carbon dioxide in the dry ice production process can be minimized.

[0033] Furthermore, by utilizing the reduced pressure created by the ejector 40, atmospheric or low pressure carbon dioxide can be received and liquefied, so the compressor power required to pressurize the carbon dioxide can be reduced to zero or significantly reduced. Furthermore, the pressure recovery process downstream of the ejector 40 described above is carried out while in contact with low-temperature liquefied carbon dioxide, so that the compression is close to isothermal compression, enabling efficient compression.

[0034] In this embodiment, the dry ice storage tank 50 has been described as a vertical cylindrical container with a conical bottom, but any container with a shape that allows the dry ice to be deposited at the bottom by gravity, such as a vertical pipe, may be used. Furthermore, the types of components such as pumps, coolers, and valves described in this embodiment are merely examples, and may be selected appropriately within the scope of design.

[0035] Furthermore, in the above description, carbon dioxide is received by the ejector 40, but it is not limited to carbon dioxide, and gases containing carbon dioxide, such as the atmosphere or a gas obtained by increasing the carbon dioxide concentration from the atmosphere, or a product gas from the steam reforming of a hydrocarbon gas, can also be used. In this case, non-condensable gases other than carbon dioxide will accumulate in the liquefied carbon dioxide drum 10, so a line is provided to discharge the non-condensable gases from the liquefied carbon dioxide drum 10 to the outside.

[0036] [Embodiment 2] Next, the configuration and functions of the second embodiment will be described with reference to FIG. The same numbers are used for components having the same configurations and functions as those in the first embodiment. The dry ice production system 200 according to the second embodiment includes a liquefied carbon dioxide receiving line 271 and a liquefied carbon dioxide receiving flow rate adjustment valve 272.

[0037] The liquefied carbon dioxide receiving line 271 is a pipe whose starting end is connected to a carbon dioxide liquefaction device not shown and whose end is connected to the liquefied carbon dioxide drum 10, and supplies the liquefied carbon dioxide produced in the carbon dioxide liquefaction device to the liquefied carbon dioxide drum 10.

[0038] The liquefied carbon dioxide receiving flow rate adjustment valve 272 is a remotely controlled butterfly valve arranged in the liquefied carbon dioxide receiving line 271 and adjusts the flow rate of the liquefied carbon dioxide flowing through the liquefied carbon dioxide receiving line 271 .

[0039] Next, the operation of the dry ice production system 200 according to this embodiment will be described. The explanation of the same functions as those in the first embodiment will be omitted.

[0040] The amount of liquefied carbon dioxide supplied to the liquefied carbon dioxide drum 10 is discharged from the liquefied carbon dioxide discharge line 81 to the dry ice storage tank 50 and discharged to the outside as dry ice. Therefore, the amount of carbon dioxide discharged to the outside as dry ice is received into the liquefied carbon dioxide drum 10 from the liquefied carbon dioxide receiving line 271.

[0041] The low-temperature carbon dioxide gas supplied to the dry ice storage tank 50 is supplied to the ejector 40 via the carbon dioxide gas recycle line 83 and the carbon dioxide gas recycle flow rate control valve 84, and is liquefied again.

[0042] According to the dry ice production system 200 of this embodiment, liquefied carbon dioxide is accepted instead of carbon dioxide gas, and therefore there is no need for the ability to liquefy carbon dioxide gas accepted from outside the system. This allows the carbon dioxide liquefaction device to be made smaller, making the equipment even more compact compared to the dry ice production system 1. [Industrial Applicability]

[0043] The present invention can utilize a dry ice production system that achieves both simplification and compactness of equipment and minimization of carbon dioxide loss. [Explanation of symbols]

[0044] 1. Dry ice production system 10 liquefied carbon dioxide drums 20 Liquefied carbon dioxide pump 30 Liquid carbon dioxide cooler 40 Ejector 50 Dry Ice Storage Tank 71 Liquefied carbon dioxide pump inlet line 72 Liquefied carbon dioxide pump outlet line 73 Ejector inlet line 74 Ejector outlet line 75 Gas receiving line 76 Refrigerant supply line 77 Refrigerant discharge line 78 Gas receiving flow control valve 81 Liquefied carbon dioxide delivery line 82 Liquefied carbon dioxide pressure reducing valve 83 Carbon dioxide gas recycling line 84 Carbon dioxide gas recycle flow control valve 85 Dry ice delivery line 200 Dry ice production system (embodiment 2) 271 Liquefied carbon dioxide receiving line 272 Liquefied carbon dioxide receiving flow control valve

Claims

1. a liquefied carbon dioxide drum for storing the liquefied carbon dioxide; a liquefied carbon dioxide circulation line that includes the liquefied carbon dioxide drum and forms a circulation path for liquefied carbon dioxide; an ejector disposed in the liquefied carbon dioxide circulation line, using the liquefied carbon dioxide flowing through the liquefied carbon dioxide circulation line as a driving fluid and carbon dioxide gas as a suction fluid; a liquefied carbon dioxide discharge line that discharges liquefied carbon dioxide for producing dry ice from the liquefied carbon dioxide stored in the liquefied carbon dioxide drum and reduces the pressure of the discharged liquefied carbon dioxide to a pressure that will solidify the liquefied carbon dioxide using a liquefied carbon dioxide pressure reducing valve to produce dry ice; a dry ice storage tank that receives and stores the produced dry ice; a carbon dioxide gas recycle line that supplies the carbon dioxide gas generated by the pressure reduction using the liquefied carbon dioxide pressure reducing valve from the dry ice storage tank to the ejector.

2. 2. The dry ice production system according to claim 1, further comprising a gas receiving line for receiving carbon dioxide gas from the outside of the ejector.

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