Compressor unit

Abstract

To prevent elimination of liquefaction of oxygen which is a combustion supporting gas and secure maintainability easily in a reciprocation compressor.SOLUTION: A compressor unit 10 includes a compression stage 12 which compresses hydrogen gas which is a boil-off gas from a liquid hydrogen tank. The compression stage 12 includes: a cylinder part 31; a piston 32; a piston rod 33 which connects the piston 32 with a crank mechanism 14; a cover part 25 disposed at the outer side of the cylinder part 31; a nitrogen gas supply part 46 which supplies nitrogen gas to a heat insulation space 28 between the cover part 25 and the cylinder part 31; and a control unit 50 which controls the nitrogen gas supply part 46 so that nitrogen gas is supplied to the heat insulation space 28 when the compression stage 12 compresses the hydrogen gas.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a reciprocating compressor unit. [Background technology]

[0002] In recent years, with consideration given to the environment, hydrogen has been considered for use as a fuel for power generation and automobiles, and the demand for hydrogen is increasing. Conventionally, low-temperature boil-off gas (BOG) from liquefied natural gas (LNG), liquid hydrogen (LH2), etc. is recovered by a compressor and supplied to users such as drive equipment and power generation equipment. In particular, the boil-off gas generated from LH2 is at an extremely low temperature. For this reason, if a configuration is adopted in which the compressor directly sucks in the boil-off gas, restrictions are imposed, such as the need to select materials suitable for extremely low temperatures, the need to adopt design conditions that take into account the amount of thermal deformation, and the need to implement strict insulation treatment. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-172870 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, Patent Document 1 points out the following problem: "In recent years, hydrogen has been attracting attention as a new energy source. When using hydrogen as an energy source, it is assumed that, like natural gas, it will be stored and transported in a liquefied state. However, hydrogen has the characteristic that its liquefaction temperature is lower than that of air. For this reason, if equipment such as reciprocating compressors intended for natural gas, etc., is directly applied to hydrogen, there is a possibility that problems will arise due to the extremely low temperature of liquid hydrogen. For example, liquefied air will be generated around the equipment to which liquid hydrogen and its boil-off gas are supplied."

[0005] Therefore, the issue of preventing problems caused by cryogenic liquid hydrogen is being studied. Specifically, a vessel part is formed around the compression part to form a vacuum region. However, to maintain the vacuum state, the vessel part requires a lid for internal inspection and sealing means at the connection part with the part where gas flows in and out of the compression part. In addition, since the inside of the vessel part is in a vacuum state, strength (plate thickness) and reinforcement are required to withstand the pressure difference between the external pressure (atmospheric pressure) and the internal pressure. This sacrifices maintainability. In addition, various measures are required, such as providing a pedestal inside the part that supports the cylinder.

[0006] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to prevent liquefaction of oxygen, which is one of the main components of air and also a combustion supporting gas, and to make it easier to deal with maintenance in a reciprocating compressor. [Means for solving the problem]

[0007] The compressor unit according to the present invention is a reciprocating compressor unit that recovers hydrogen gas, which is a boil-off gas, from a liquid hydrogen storage tank and supplies at least a portion of the recovered hydrogen gas to a demand destination including at least one of an engine, a power generation facility, and a boiler, and includes a compression stage that compresses hydrogen gas that flows out of the liquid hydrogen storage tank and flows through an intake passage, and a crank mechanism that drives the compression stage. The compression stage includes a cylinder section, a piston, a cover section that is disposed outside the cylinder section, a nitrogen gas supply section that supplies nitrogen gas to an insulation space between the cover section and the cylinder section, and a nitrogen gas discharge section that discharges nitrogen gas from the insulation space. The compressor unit further includes a control section that controls the nitrogen gas supply section so that nitrogen gas is supplied into the insulation space while the compression stage is compressing the hydrogen gas.

[0008] In the compressor unit according to the present invention, the oxygen concentration of the air in the heat-insulating space between the cover and the cylinder can be reduced as much as possible by filling the heat-insulating space between the cover and the cylinder with nitrogen gas. Therefore, it is possible to prevent the liquefaction of oxygen, which is a combustion-supporting gas, caused by the air (outside air) around the cylinder being cooled by the boil-off gas (suction gas) of liquefied hydrogen, which is a low-temperature gas.

[0009] Also, maintainability is improved compared to the compressor disclosed in Patent Document 1, which requires connecting a vacuum pump or the like to the space between the cylinder and the container to create a vacuum every time a part of the container is opened to inspect and maintain the cylinder. In other words, since there is no need to create a vacuum in the insulation space, there is no need to install equipment for creating a vacuum in the insulation space.

[0010] The compressor unit may further include a pressure equalization means for making the pressure inside the insulation space substantially equal to atmospheric pressure.

[0011] In this embodiment, the heat insulation space is always at approximately atmospheric pressure. Therefore, it is not necessary to use a plate material having a thickness required to bear the differential pressure as the cover. In addition, it is not necessary to provide a large number of bolts in the opening of the cover to confine the pressure. In addition, since a sealing function is not required, it is possible to reduce the weight and to adopt a simplified structure for bolts, seals, etc. Therefore, it is easier to maintain and can be easily adapted to larger sizes.

[0012] The cover portion may be configured by a metallic outer tube member fixed to the cylinder portion so as to maintain the formation of the heat insulating space in a predetermined shape.

[0013] In this aspect, since the cover portion is constituted by the outer tubular member fixed to the cylinder portion, the shape of the heat insulating space is maintained in a predetermined shape.

[0014] The nitrogen gas exhaust section may include an exhaust passage section having an exhaust pipe fixed to the outer tube member so as to open into the insulation space, and an exhaust valve which is a valve disposed on the exhaust pipe.

[0015] In this embodiment, while the compression stage is compressing the hydrogen gas, the nitrogen gas continues to flow through the heat insulating space, so that the nitrogen gas is prevented from being cooled and liquefied.

[0016] The compressor unit may further include a temperature sensor for detecting a temperature of the nitrogen gas in the discharge passage. In this case, the control unit may control the nitrogen gas supply unit to increase the supply amount of the nitrogen gas when the temperature detected by the temperature sensor is equal to or lower than a threshold value assumed from a liquefaction temperature of the nitrogen gas.

[0017] In this embodiment, liquefaction of the nitrogen gas can be more reliably prevented, and excess consumption of nitrogen can be suppressed.

[0018] The compressor unit may further include a cotton-like or sponge-like insulating material. In this case, the cover may be formed of a sheet member arranged to cover the insulating material, and nitrogen gas may be supplied into the insulating space inside the sheet member by the nitrogen gas supply unit.

[0019] In this embodiment, unlike the case where the cover is constituted by an outer cylinder member fixed to the cylinder, a container-shaped outer cylinder member that covers the cylinder is not required, so the burden of attaching and detaching during maintenance can be reduced, and it is easier to accommodate larger sizes. In other words, compared to the case where the cover is constituted by a metal outer cylinder member, it is possible to reduce the weight of the members that constitute the cover, improving maintainability. Note that the inside of the sheet member that covers the heat insulating material functions as a heat insulating space, but this heat insulating space is not limited to an enclosed space.

[0020] The cover portion may be breathable. In this embodiment, nitrogen gas in the heat insulating space can be appropriately discharged to the outside, thereby preventing the sheet member from expanding.

[0021] The compressor unit may further include a temperature sensor for detecting a temperature of the nitrogen gas in the insulation space. In this case, the control unit may control the nitrogen gas supply unit to increase the supply amount of the nitrogen gas when the temperature detected by the temperature sensor is equal to or lower than a threshold value assumed from a liquefaction temperature of the nitrogen gas.

[0022] In this embodiment, liquefaction of the nitrogen gas can be more reliably prevented, and excess consumption of nitrogen can be suppressed.

[0023] The compression stage may further include an adapter portion connecting the cylinder portion and a case of the crank mechanism, and the adapter portion may include at least one partition portion dividing an inner space of the adapter portion into a plurality of spaces. In this case, hydrogen gas may be present in a space closest to the compression chamber among the plurality of spaces, and nitrogen gas may be present in a space closest to the crank mechanism among the plurality of spaces, and a temperature of the hydrogen gas in the space closest to the compression chamber may be higher than a liquefaction temperature of the nitrogen gas in the space closest to the crank mechanism.

[0024] In this embodiment, since the adapter portion has a partition portion, it is possible to more reliably prevent contact between the low-temperature boil-off gas (suction gas) and the nitrogen gas. Also, since the temperature of the hydrogen gas in the space on the compression chamber side is higher than the liquefaction temperature of the nitrogen gas in the space on the crank mechanism side, it is possible to prevent the nitrogen gas from liquefying.

[0025] The compression stage may be a horizontal type in which the piston slides horizontally. In this case, the cylinder portion may include a suction valve located on an upper side in the direction of gravity and a discharge valve located on a lower side in the direction of gravity.

[0026] When the lower side is the suction side, the support part of the cylinder is provided on the suction side, which has a lower temperature, and this can cause a large effect of freezing and thermal contraction around the support part. Also, even if nitrogen liquefies on the outer surface of the cylinder, the liquid is gasified by flowing to the lower discharge side, which has a higher temperature. In contrast, in the case of a configuration in which the suction valve is located on the upper side in the direction of gravity, as in this embodiment, the support part is provided on the discharge side, which has a higher temperature, and therefore the effects of freezing and thermal contraction can be reduced. Effect of the Invention

[0027] As described above, according to the present invention, it is possible to prevent liquefaction of oxygen, which is one of the main components of air and also a combustion supporting gas, and to facilitate maintenance of a reciprocating compressor. [Brief description of the drawings]

[0028] [Figure 1] FIG. 2 is a diagram illustrating a schematic configuration of a compressor unit according to the first embodiment. [Diagram 2] FIG. 4 is a diagram illustrating a schematic configuration of a compressor unit according to a modified example of the first embodiment. [Diagram 3] FIG. 4 is a diagram illustrating a schematic configuration of a compressor unit according to a modified example of the first embodiment. [Figure 4] FIG. 6 is a diagram illustrating a schematic configuration of a compressor unit according to a second embodiment. [Diagram 5] FIG. 10 is a diagram illustrating a schematic configuration of a compressor unit according to a modified example of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0030] (First embodiment) The compressor unit according to the present embodiment is configured to recover hydrogen gas, which is boil-off gas, from a liquid hydrogen storage tank, compress the recovered hydrogen gas, and supply it to a demand destination. This allows for efficient supply of hydrogen gas. The boil-off gas, which is hydrogen gas, is about -253°C. The demand destination includes at least one of an engine, a power generation facility, or a boiler, but may also include facilities other than those that utilize gas as an energy source, such as a gas combustion facility, a flare facility, or a vent. The hydrogen gas discharged from the compressor unit does not necessarily need to be directly supplied to a demand destination, and may be supplied to a demand destination by various means, such as, for example, filling a cylinder or the like and then transporting the cylinder or a gas piping connected to the cylinder.

[0031] 1, the compressor unit 10 includes a compression stage 12 for compressing hydrogen gas, and a crank mechanism 14 for driving the compression stage 12. The hydrogen gas compressed in the compression stage 12 is discharged to a discharge passage 18. The hydrogen gas compressed in the compression stage 12 and flowing through the discharge passage 18 is supplied to a demand destination not shown in the figure.

[0032] A downstream compression stage (not shown) may be provided on the discharge side of the compression stage 12. In this case, the hydrogen gas compressed in the compression stage 12 and then compressed in the downstream compression stage is sent to a consumer.

[0033] The compression stage 12 is connected to the liquid hydrogen storage tank 23 via the suction passage 21. Therefore, boil-off gas (BOG) of the liquefied gas generated in the liquid hydrogen storage tank 23 is sucked into the compression stage 12 through the suction passage 21. Note that the suction passage 21 does not need to be directly connected to the liquid hydrogen storage tank 23, as long as the suction passage 21 is capable of allowing the boil-off gas generated in the liquid hydrogen storage tank 23 to flow therethrough.

[0034] The compression stage 12 is configured by a reciprocating compression mechanism. That is, the compression stage 12 includes a cylinder portion 31, a piston 32 arranged in the cylinder portion 31, and a piston rod 33 connected to the piston 32. The piston rod 33 is connected to the crank mechanism 14. The piston 32 reciprocates in the cylinder portion 31, whereby hydrogen gas is compressed in a compression chamber 34.

[0035] The compression stage 12 may be of a horizontal type in which the piston 32 slides in a horizontal direction. In this case, the suction valve 21a provided in the cylinder section 31 between the portion to which the suction passage 21 is connected and the compression chamber 34 is located on the upper side in the direction of gravity, and the discharge valve 18a provided in the cylinder section 31 between the portion to which the compression chamber 34 and the discharge passage 18 are connected is located on the lower side in the direction of gravity. The compression stage 12 may be of a vertical type in which the piston 32 slides in a vertical direction.

[0036] 1 shows the compression stage 12 having a double acting structure, the compression stage 12 may have a single acting structure. The compression stage 12 does not necessarily have to be composed of one cylinder, but may be composed of a plurality of parallel compression stages. That is, the compression stage 12 may be configured such that hydrogen gas is compressed and pressurized by pistons 32 in a plurality of cylinder sections 31 connected in parallel.

[0037] A cover portion 25 is disposed on the outside of the cylinder portion 31 so as to form a space between the cover portion 25 and the cylinder portion 31. In this embodiment, the cover portion 25 is configured by an outer tube member 26 that is fixed to the cylinder portion 31 to form a space between the cover portion 25 and the cylinder portion 31.

[0038] The outer cylinder member 26 is formed of a material that does not easily deform, such as a metal. When the outer cylinder member 26 is attached to the cylinder portion 31, a space of a predetermined size is formed around the cylinder portion 31. This space functions as a heat insulating space 28 for removing oxygen around the cylinder portion 31 and thermally insulating it from the outside air (atmosphere) because nitrogen gas is introduced into it as described below. That is, the heat insulating space 28 is provided around the portion that forms the compression chamber 34, and this makes it possible to prevent oxygen in the outside air from liquefying around the cylinder portion 31. Since the outer cylinder member 26 is a material that does not easily deform, the shape of the heat insulating space 28 is maintained in a predetermined shape.

[0039] The outer cylinder member 26 is attached, for example, to a rear head 31a that is a part of the cylinder portion 31. However, the outer cylinder member 26 does not need to be fixed to the rear head 31a, and may be attached anywhere in the cylinder portion 31 as long as the heat insulating space 28 can be formed.

[0040] The outer cylinder member 26 is provided with an opening through which the piping (piping connected to the cylinder portion 31) forming the discharge flow passage 18 penetrates, and also has an opening through which the piping forming the suction flow passage 21 penetrates. A gap or hole (hereinafter referred to as a "leakage portion 29") is intentionally provided between these piping and the opening. The outer cylinder member 26 is also provided with an opening (not shown) through which the support of the cylinder portion 31 penetrates. A leakage portion 29 is also intentionally provided between the support and the opening. In the compression stage 12, these leakage portions 29, together with a discharge passage portion 48 described later, serve as a nitrogen gas discharge portion that discharges the nitrogen gas inside. The outer cylinder member 26 may be provided with other leakage portions (not shown) that appropriately discharge the nitrogen gas inside.

[0041] The compression stage 12 includes a rod packing portion 36 provided in the cylinder portion 31, a hollow adapter portion 37 arranged adjacent to the cylinder portion 31 and connected to the cylinder portion 31, and a crankcase 38 that houses a crankshaft, which is part of the crank mechanism 14.

[0042] The adaptor portion 37 is formed in a cylindrical shape, and the piston rod 33 is disposed in the space inside the adaptor portion 37. One longitudinal end of the adaptor portion 37 is connected to the cylinder portion 31. The other longitudinal end of the adaptor portion 37 is connected to the crankcase 38. A partition wall 40 that separates the internal space of the adaptor portion 37 from the space inside the crankcase 38 is provided at this other end.

[0043] The rod packing portion 36 is fixed to the rear head 31a. The rod packing portion 36 is provided to prevent the hydrogen gas in the compression chamber 34 from leaking out from the cylinder portion 31 through the gap between the rear head 31a and the piston rod 33.

[0044] The adapter part 37 has a partition part 44 that divides the internal space into a space on the compression chamber 34 side (first space 37a) and a space on the crank mechanism 14 side (second space 37b). The piston rod 33 also passes through this partition part 44. A seal part 44a is provided on the periphery of the through hole in the partition part 44, through which the piston rod 33 passes.

[0045] The compression stage 12 includes a nitrogen gas supply unit 46 that supplies nitrogen gas to the heat insulation space 28. The nitrogen gas supply unit 46 has a supply passage 46a fixed to the outer tubular member 26 so as to open to the heat insulation space 28, and a supply valve 46b that is a valve disposed in the supply passage 46a. The supply passage 46a is connected to a nitrogen gas source 47, and receives a supply of nitrogen gas from the nitrogen gas source 47. The supply valve 46b is configured, for example, by an on-off valve that opens and closes based on a command from a control unit 50 described later.

[0046] The compression stage 12 includes a discharge passage 48 for discharging nitrogen gas from the heat insulation space 28. The discharge passage 48 includes a discharge pipe 48a fixed to the outer cylinder member 26 so as to open into the heat insulation space 28, and a discharge valve 48b disposed on the discharge pipe 48a. The discharge pipe 48a may be open to the atmosphere, or may be connected to a tank (not shown) having an internal pressure of about atmospheric pressure. The discharge pipe 48a also functions as a pressure equalization means for making the heat insulation space 28 substantially equal to atmospheric pressure. The leakage portion 29 is also a part of the pressure equalization means.

[0047] The exhaust valve 48b is configured, for example, by an on-off valve that opens and closes based on a command from the later-described control unit 50. It should be noted that the exhaust valve 48b may be omitted.

[0048] The compression stage 12 includes a hydrogen gas supply unit 59 that supplies hydrogen gas to the first space 37a in the adapter portion 37, and a nitrogen supply unit 60 that supplies nitrogen gas to the second space 37b in the adapter portion 37.

[0049] The hydrogen gas supply unit 59 has a hydrogen flow path 59a connected to a hydrogen gas source 61. The hydrogen gas source 61 contains hydrogen gas at room temperature. The hydrogen flow path 59a is connected to an outer peripheral wall that forms the first space 37a in the adaptor unit 37. The hydrogen gas supply unit 59 supplies hydrogen gas from the hydrogen gas source 61 through the hydrogen flow path 59a to the first space 37a in the adaptor unit 37. For this reason, it can be said that the temperature of the hydrogen gas in the first space 37a is higher than the liquefaction temperature of the nitrogen gas in the second space 37b.

[0050] The nitrogen supply unit 60 has a nitrogen flow path 60a connected to a nitrogen gas source 62. The nitrogen flow path 60a is connected to an outer peripheral wall that forms the second space 37b in the adaptor part 37. The nitrogen supply unit 60 supplies nitrogen gas from the nitrogen gas source 62 through the nitrogen flow path 60a to the second space 37b in the adaptor part 37. The nitrogen gas source 62 contains nitrogen gas at room temperature.

[0051] The hydrogen flow path 59a of the hydrogen gas supply unit 59 is provided with a hydrogen valve 59b, which is a valve that adjusts the pressure of hydrogen gas flowing through the hydrogen flow path 59a, and the nitrogen flow path 60a is provided with a nitrogen valve 60b, which is a valve that adjusts the pressure of nitrogen gas flowing through the nitrogen flow path 60a.

[0052] The hydrogen gas in the first space 37a and the nitrogen gas in the second space 37b are exhausted to the vent 70. The hydrogen gas in the first space 37a and the nitrogen gas in the second space 37b may be collected in a predetermined tank or returned to the hydrogen gas source 61 and the nitrogen gas source 62, respectively.

[0053] The supply valve 46b and the exhaust valve 48b are communicatively connected to the control unit 50. The control unit 50 controls the supply valve 46b and the exhaust valve 48b so that the supply valve 46b and the exhaust valve 48b are opened when the piston 32 is driven by the crank mechanism 14, and the supply valve 46b and the exhaust valve 48b are closed when the piston 32 is stopped. In other words, the control unit 50 performs control to open the supply valve 46b and the exhaust valve 48b based on a signal for driving the crank mechanism 14.

[0054] The hydrogen valve 59b and the nitrogen valve 60b are also communicatively connected to the control unit 50. The control unit 50 controls the hydrogen valve 59b and the nitrogen valve 60b so that the hydrogen valve 59b and the nitrogen valve 60b are opened when the piston 32 is driven, and are closed when the piston 32 is stopped.

[0055] Here, we will explain the operation of the compressor unit 10. In the compressor unit 10, when the crank mechanism 14 is operated, the piston 32 is operated, and hydrogen gas, which is boil-off gas, is sucked into the compression chamber 34 from the suction passage 21, and the hydrogen gas is compressed.

[0056] While the crank mechanism 14 is driven, the supply valve 46b, the exhaust valve 48b, the hydrogen valve 59b, and the nitrogen valve 60b are open. Therefore, while the piston 32 is operating, nitrogen gas is constantly or intermittently supplied from the nitrogen gas supply unit 46 to the heat insulation space 28. The nitrogen gas in the heat insulation space 28 is mainly discharged into the atmosphere through the exhaust passage 48, and is also discharged into the atmosphere from the leakage portion 29. In this way, while the compression stage 12 is compressing the hydrogen gas, the nitrogen gas continues to flow through the heat insulation space 28, so that the oxygen gas that was around the cylinder portion 31 before the compressor was driven is discharged and prevented from liquefying. Furthermore, the nitrogen gas is cooled and prevented from liquefying.

[0057] Furthermore, while the crank mechanism 14 is being driven, hydrogen gas is supplied to the first space 37a in the adapter part 37 by the hydrogen gas supply part 59, and nitrogen gas is supplied to the second space 37b in the adapter part 37 by the nitrogen supply part 60. This prevents the nitrogen gas in the second space 37b from mixing with the hydrogen gas in the compression chamber 34 through the rod packing part 36.

[0058] As described above, in this embodiment, the heat insulation space 28 between the cover part 25 and the cylinder part 31 is filled with nitrogen gas, so that it is possible to reduce the oxygen concentration of the air as much as possible in the heat insulation space 28. Therefore, it is possible to prevent the air (outside air) around the cylinder part 31 from being cooled by the boil-off gas (suction gas) of liquefied hydrogen, which is a low-temperature gas, and therefore it is possible to prevent oxygen, which is a combustion-supporting gas, from being liquefied.

[0059] While the compression stage 12 is compressing the hydrogen gas, nitrogen gas continues to be discharged from the insulation space 28 through the various nitrogen gas discharge parts, namely the discharge passage part 48 and the leakage part 29, thereby preventing the nitrogen gas from being cooled and liquefied.

[0060] In addition, the nitrogen gas discharge portion also functions as a pressure equalizing means, so that the pressure inside and outside the insulation space 28 is equalized. This improves maintainability compared to a configuration in which the insulation space 28 is maintained in a vacuum state. In other words, since it is not necessary to make the insulation space 28 in a vacuum state, there is no need to install equipment for making the insulation space 28 vacuum. Furthermore, as the plate material for the outer tube member 26, there is no need to adopt a plate material having a thickness required to bear the differential pressure. In the opening provided in the outer tube member 26, there is no need to provide a large number of bolts to confine the pressure. Since no sealing function is required, it is possible to reduce the weight and to adopt a simplified structure for bolts, seals, etc. Therefore, maintainability is improved and it is easier to handle larger sizes.

[0061] In this embodiment, since the adapter part 37 has the partition part 44, it is possible to more reliably prevent contact between the low-temperature boil-off gas (suction gas) and the nitrogen gas. Since the temperature of the hydrogen gas in the first space 37a, which is the space on the compression chamber 34 side, is higher than the liquefaction temperature of the nitrogen gas in the second space 37b, which is the space on the crank mechanism 14 side, it is possible to prevent the nitrogen gas from liquefying.

[0062] In this embodiment, the compression stage 12 may be horizontal. In this case, if the lower side is the suction side, the support part of the cylinder part 31 is provided on the suction side, which has a lower temperature, and this may cause a large effect of freezing and thermal contraction around the support part. In addition, even if nitrogen liquefies on the outer surface of the cylinder part 31, the liquid is gasified by flowing to the lower discharge side, which has a higher temperature. In contrast, in a configuration in which the suction valve 21a is located on the upper side in the direction of gravity, the support part is provided on the discharge side, which has a higher temperature, and this can reduce the effect of freezing and thermal contraction.

[0063] In this embodiment, the supply valve 46b is configured as an on-off valve, but is not limited thereto and may be configured as an electric valve with an adjustable opening. In this case, as shown in Fig. 2, a temperature sensor 52 may be provided to detect the temperature of the nitrogen gas in the discharge pipe 48a of the discharge passage 48 or the temperature of the nitrogen gas in the heat insulation space 28. When the temperature sensor 52 is provided to detect the temperature of the nitrogen gas in the heat insulation space 28, the temperature sensor 52 is preferably disposed in the vicinity of the suction passage 21 or the suction valve 21a so as to detect the temperature of the nitrogen gas in the heat insulation space 28 near the suction passage 21 or the suction valve 21a.

[0064] The control unit 50 may be configured to change the opening of the supply valve 46b based on the temperature detected by the temperature sensor 52. Specifically, when the temperature detected by the temperature sensor 52 is equal to or lower than a threshold value assumed from the liquefaction temperature of nitrogen gas (i.e., set based on the liquefaction temperature of nitrogen gas), the control unit 50 controls the supply valve 46b so as to increase the amount of nitrogen gas supplied to the insulation space 28. In other words, when liquefaction of the nitrogen gas in the exhaust pipe 48a or the nitrogen gas in the insulation space 28 may occur, a larger flow rate of nitrogen gas is supplied to the insulation space 28. This makes it possible to prevent liquefaction of the nitrogen gas.

[0065] In this embodiment, as shown in Fig. 1, one partition section 44 is provided in the adapter section 37, but this is not limited to this. As shown in Fig. 3, two partition sections 44 may be provided, or a greater number of partition sections 44 may be provided.

[0066] In this embodiment, if nitrogen gas is sufficiently discharged by the discharge passage portion 48, there is no need to actively provide the leakage portion 29. In addition, by adjusting the size and number of the leakage portion 29, it is possible to cause the leakage portion 29 to function as a nitrogen gas leakage portion and a pressure equalization means, and therefore it is also possible to omit the discharge passage portion 48.

[0067] Second embodiment In the first embodiment, the cover portion 25 is configured with an outer cylinder member 26 made of a material that is not easily deformed, whereas in the second embodiment, as shown in Fig. 4, the cover portion 25 is configured with a sheet member 74 that covers a heat insulating material 72 attached to the cylinder portion 31. Note that the same components as those in the first embodiment are denoted with the same reference numerals, and detailed description thereof will be omitted.

[0068] In the second embodiment, a heat insulating material 72 is provided so as to cover the cylinder portion 31. The heat insulating material 72 can be wrapped around the cylinder portion 31 as desired. The heat insulating material 72 is a cotton-like or sponge-like member such as glass wool, and is arranged so as to cover the entire outer surface of the cylinder portion 31, thereby making it difficult for heat from the outside air to be transmitted to the cylinder portion 31. The heat insulating material 72 is wrapped around the cylinder portion 31 and fixed by a band (not shown). Alternatively, a pre-formed material may be used, or a combination of these may be used.

[0069] The sheet member 74 covering the heat insulating material 72 is made of a material that is lighter and softer than the outer cylinder member 26, which is made of metal or the like. In other words, the sheet member 74 only needs to have the function of preventing the heat insulating material 72 from being exposed to the outside, and therefore does not need to be a rigid member that can form a space of a predetermined size by itself.

[0070] A moisture-proof sheet 75 may be provided on the inside of the insulating material 72. That is, the moisture-proof sheet 75 may be wrapped around the outer surface of the cylinder portion 31, and the insulating material 72 may be provided so as to cover this moisture-proof sheet 75. Alternatively, the moisture-proof sheet 75 may be provided on this insulating material 72, and another insulating material 72 may be provided on the outside of this. In this case, the sheet member 74 is provided so as to cover the outer insulating material 72. That is, the moisture-proof sheet 75 and the insulating material 72 may have a multi-layer structure.

[0071] In the second embodiment, nitrogen gas is supplied to the space inside the sheet member 74, and a heat insulating material 72 is disposed in this space. Therefore, the space inside the sheet member 74 functions as a heat insulating space 28 for thermally insulating the cylinder portion 31 from the outside air.

[0072] The sheet member 74 has waterproof properties. Furthermore, the sheet member 74 may have air permeability so that the nitrogen gas in the insulation space 28 can be discharged.

[0073] The sheet member 74 is provided with an opening through which the piping forming the discharge flow path 18 passes, and also with an opening through which the piping forming the suction flow path 21 passes. A leakage portion 29 (i.e., a hole or a gap) is intentionally provided between these piping and the opening. Note that the sheet member 74 may have a leakage portion added to a location other than the opening.

[0074] In the compressor unit 10, while the compression stage is compressing the hydrogen gas, nitrogen gas is constantly or intermittently supplied from the nitrogen gas supply unit 46 to the heat insulation space 28. The nitrogen gas in the heat insulation space 28 is released into the atmosphere from the leakage unit 29. In addition, since the sheet member 74 has breathability, the nitrogen gas can be discharged from the entire sheet member 74 (i.e., the sheet member 74 itself functions as a nitrogen gas discharge unit). In this way, the nitrogen gas continues to flow through the heat insulation space 28, and the oxygen gas that was around the cylinder unit 31 before the compressor was driven is discharged and prevented from liquefying. Furthermore, the nitrogen gas is cooled and prevented from liquefying.

[0075] In the compressor unit 10, by adjusting the size and number of the leakage parts 29 and by using a highly breathable sheet member 74, the leakage parts 29 and the sheet member 74 themselves can function not only as nitrogen gas leakage parts, but also as pressure equalization means for making the insulation space 28 approximately equal to atmospheric pressure.

[0076] In this embodiment, the cover 25 is composed of a sheet member 74 arranged to cover the heat insulating material 72. Therefore, compared to the case where the cover 25 is composed of the outer tube member 26 fixed to the cylinder 31, the burden of the attachment and detachment work during maintenance can be reduced, and it is easier to deal with larger cylinders with complex shapes. That is, compared to the case where the cover 25 is composed of the metal outer tube member 26, it is possible to reduce the weight of the members constituting the cover 25, improving maintainability. In addition, since the work of covering the heat insulating material 72 with the sheet member 74 can be performed manually, the burden of the attachment and detachment work can be reduced. Therefore, the burden of the maintenance work for the cylinder 31 can also be reduced. The sheet member 74 may be composed of a material that is not breathable as long as the nitrogen gas can be sufficiently discharged through the leakage portion 29.

[0077] In this embodiment, similarly to the first embodiment, the supply valve 46b may be configured as an electric valve whose opening degree is adjustable. In this case, as shown in FIG. 5, a temperature sensor 52 may be provided to detect the temperature of the nitrogen gas in the discharge pipe 48a of the discharge passage portion 48 or the temperature of the nitrogen gas in the heat insulation space 28. The control unit 50 is configured to change the opening degree of the supply valve 46b based on the temperature detected by the temperature sensor 52. Specifically, when the temperature detected by the temperature sensor 52 is equal to or lower than a threshold value assumed from the liquefaction temperature of the nitrogen gas (i.e., set based on the liquefaction temperature of the nitrogen gas), the control unit 50 controls the supply valve 46b so as to increase the supply amount of the nitrogen gas to the heat insulation space 28. In other words, when the nitrogen gas in the discharge pipe 48a or the nitrogen gas in the heat insulation space 28 may be liquefied, a larger flow rate of the nitrogen gas is supplied to the heat insulation space 28. This makes it possible to prevent the nitrogen gas from liquefying.

[0078] Although the description of other configurations, operations, and effects will be omitted, the description of the first embodiment can be applied to the second embodiment. Furthermore, the present invention is not limited to the above-described embodiment, and various changes, improvements, etc. can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0079] 10: Compressor unit 12: Compression stage 14: Crank mechanism 18a: Discharge valve 21: Suction passage 21a: Suction valve 23: Liquid hydrogen storage tank 25: Covering part 26: External cylinder member 28: Insulation space 31: Cylinder section 32: Piston 33: Piston rod 34: Compression chamber 37: Adapter part 44: Partition 46: Nitrogen gas supply unit 48: Discharge passage section 50: Control section 52: Temperature sensor 72: Insulation material 74: Sheet material

Claims

1. A reciprocating compressor unit that recovers boil-off gas of hydrogen gas from a liquid hydrogen storage tank and supplies at least a portion of the recovered hydrogen gas to a demand destination including at least one of an engine, a power generation facility, or a boiler, a compression stage for compressing hydrogen gas flowing out of the liquid hydrogen storage tank and through an intake passage; a crank mechanism that drives the compression stage; Equipped with The compression stage comprises: A cylinder portion; The piston and A cover portion disposed on the outside of the cylinder portion; a nitrogen gas supply unit that supplies nitrogen gas to a heat insulating space between the cover unit and the cylinder unit; a nitrogen gas exhaust section for exhausting nitrogen gas from the heat insulation space; Equipped with The compressor unit includes: The compressor unit further includes a control unit that controls the nitrogen gas supply unit so that nitrogen gas is supplied into the insulation space while the compression stage is compressing the hydrogen gas.

2. 2. The compressor unit according to claim 1, further comprising a pressure equalization means for making the pressure in said insulation space substantially equal to atmospheric pressure.

3. 3. The compressor unit according to claim 1, wherein the cover portion is configured by a metallic outer tube member fixed to the cylinder portion so that the heat insulating space is maintained in a predetermined shape.

4. The compressor unit according to claim 3, wherein the nitrogen gas discharge section comprises a discharge passage section having a discharge pipe fixed to the outer tubular member so as to open into the insulation space, and a discharge valve which is a valve arranged on the discharge pipe.

5. A temperature sensor is further provided to detect the temperature of the nitrogen gas in the exhaust passage portion. The compressor unit according to claim 4, wherein the control unit controls the nitrogen gas supply unit so as to increase the amount of nitrogen gas supplied when the temperature detected by the temperature sensor becomes equal to or lower than a threshold value assumed from the liquefaction temperature of the nitrogen gas.

6. Further comprising a cotton-like or sponge-like insulating material; The cover portion is constituted by a sheet member arranged to cover the heat insulating material, The compressor unit according to claim 1 or 2, wherein the nitrogen gas supply unit supplies nitrogen gas into the heat insulating space inside the sheet member.

7. The compressor unit according to claim 6 , wherein the cover portion has air permeability.

8. Further, a temperature sensor is provided for detecting a temperature of the nitrogen gas in the heat insulation space. The compressor unit according to claim 7, wherein the control unit controls the nitrogen gas supply unit so as to increase the amount of nitrogen gas supplied when the temperature detected by the temperature sensor is equal to or lower than a threshold value assumed from the liquefaction temperature of nitrogen gas.

9. The compression stage further includes an adapter portion that connects the cylinder portion and a case of the crank mechanism, The adapter portion includes at least one partition portion that divides an inner space of the adapter portion into a plurality of spaces, hydrogen gas is present in a space among the plurality of spaces closest to a compression chamber, and nitrogen gas is present in a space among the plurality of spaces closest to the crank mechanism, 3. The compressor unit according to claim 1, wherein a temperature of the hydrogen gas in the space closest to the compression chamber is higher than a liquefaction temperature of the nitrogen gas in the space closest to the crank mechanism.

10. The compression stage is a horizontal type in which the piston slides horizontally, The cylinder portion is A suction valve located on the upper side in the direction of gravity; A discharge valve located on the lower side in the direction of gravity; A compressor unit according to claim 1 or 2, comprising:

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