Compressor unit and control method of the same

Abstract

To cope with pressure fluctuation of suction gas to a front-stage compression stage without providing adjustment means operated by compressed air in the front-stage compression stage.SOLUTION: A compressor unit 10 includes a first spill-back unit 18 for returning hydrogen gas delivered from a front-stage compression stage 12 to a suction flow passage, adjustment means 31 for adjusting a treatment amount of hydrogen gas by a succeeding compression stage 14, a pressure sensor 47, an upstream-side pressure sensor 45, and a control unit 50. The control unit 50 can perform first control for controlling the adjustment means 31 so that the treatment amount of the succeeding compression stage 14 is adjusted on the basis of a pressure acquired by the upstream-side pressure sensor 45, and second control for controlling a first spill-back valve 18b so that an intermediate pressure acquired by the pressure sensor 47 falls within a predetermined pressure range.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In recent years, in consideration of the environment, hydrogen has been considered for use as a fuel for power generation and automobiles, etc., and the demand for hydrogen is increasing. Conventionally, low-temperature boil-off gas (BOG) such as liquefied natural gas (LNG) and liquid hydrogen (LH2) has been recovered by a compressor and supplied to a consumer such as an engine. For example, Patent Document 1 discloses a reciprocating compressor for compressing hydrogen gas.

[0003] One of the main roles of this boil-off compressor is to maintain a constant internal pressure in the liquefied gas storage tank. In other words, the compressor is operated so that when the internal pressure of the storage tank rises, the compressor starts (or the compressor's throughput is increased), and when the internal pressure falls, the compressor stops (or the compressor's throughput is decreased).

[0004] For this reason, when the compressor that processes the boil-off gas is a reciprocating compressor, a processing amount control device such as a suction valve unloader or a clearance pocket for changing the processing amount is often installed.

[0005] On the other hand, especially in the case of a tank that stores liquid hydrogen (LH2), the boil-off gas generated from the tank is at a very low temperature. Therefore, if a configuration is adopted in which the compressor directly sucks in the boil-off gas, it is necessary to select materials suitable for extremely low temperatures and to adopt design conditions that take into account the amount of thermal deformation. This imposes various constraints, such as the need to apply strict insulation treatment to the throughput control device.

[0006] In addition, because the temperature of the intake gas at the first stage is close to absolute zero, even a slight rise in temperature causes a large volume expansion. For this reason, when boil-off gas is sucked into a reciprocating compressor, which is a volumetric compressor, operation is carried out under conditions where the throughput changes greatly. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2020-172870 A Summary of the Invention [Problem to be solved by the invention]

[0008] Incidentally, Patent Document 1 states the following: "The rod drive unit 48 of the unloader 38 provided in the suction valve 36 is disposed on the outer circumferential surface side of the housing 17. According to this configuration, the rod drive unit 48 is disposed outside the housing 17. The outside of the housing 17 is thermally insulated from the compression section 2 by the vacuum region. Therefore, the unloader 38 can operate reliably without being affected by the heat of the compression section 2. Specifically, the unloader 38 receives compressed gas for driving the diaphragm. Examples of compressed gas include compressed air and compressed nitrogen. According to the above configuration, the unloader 38 is not affected by the heat of the compression section 2, and therefore the compressed air does not liquefy. Therefore, the unloader 38 can operate reliably."

[0009] That is, since the rod drive unit of the unloader provided in the suction valve into which the extremely low temperature boil-off gas is introduced is configured to be driven by compressed gas, it is suggested that thermal treatment is necessary to prevent the rod drive unit from being affected by cold. In other words, it is suggested that unless appropriate thermal treatment is performed, the volume of the boil-off gas sucked into the compression section cannot be appropriately adjusted.

[0010] In addition, in the case of an ultra-low temperature gas such as boil-off gas of LH2, the temperature of the gas suctioned into the compressor falls below about -180°C, so in the compressor described in Patent Document 1, the cylinder is covered with a container that forms a vacuum region in order to prevent liquefaction of air on the outer surface of the device. However, in the case of such a configuration, it is necessary to take special measures to prevent cold heat from entering the air drive unit in the capacity adjustment device such as an unloader, making the structure complicated. In addition, maintenance is also complicated.

[0011] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to enable a reciprocating compressor unit that compresses boil-off gas of liquefied hydrogen, which is at an extremely low temperature, to respond to pressure fluctuations of the gas suctioned into a previous compression stage without providing an adjustment means operated by compressed gas in the previous compression stage. [Means for solving the problem]

[0012] The compressor unit of the present invention is a reciprocating compressor unit that recovers hydrogen gas, which is boil-off gas, from a liquid hydrogen storage tank and supplies at least a portion of it to a demand destination including at least one of an engine, a power generation facility, or a boiler, and is equipped with one or more front-stage compression stages that compress hydrogen gas that is at a predetermined temperature below 0°C and flows through an intake passage, one or more subsequent compression stages that further compress the hydrogen gas discharged from the front-stage compression stage, a crank mechanism that drives the front-stage compression stage and the subsequent compression stage, a first spillback section that returns the hydrogen gas discharged from the front-stage compression stage to the intake passage and includes a first spillback valve that adjusts the amount of spillback in the first spillback passage, an adjustment means that adjusts the amount of hydrogen gas processed by the subsequent compression stage, a pressure sensor that is arranged in an intermediate passage between the front-stage compression stage and the subsequent compression stage, an upstream pressure sensor that is arranged in the intake passage, and a control unit that controls the first spillback valve and the adjustment means, respectively. Each of the front compression stage and the rear compression stage includes a cylinder portion, a piston, a piston rod connecting the piston to the crank mechanism, and a rod packing sealing between the piston rod and the cylinder portion. The front compression stage is air-cooled and oil-free. The control unit is capable of executing a first control for controlling the adjustment means so that a throughput of the rear compression stage is adjusted based on a pressure acquired by the upstream pressure sensor, and a second control for controlling the first spillback valve before, after, or simultaneously with the first control, with reference to an intermediate pressure acquired by the pressure sensor, so that the intermediate pressure falls within a predetermined pressure range.

[0013] In the compressor unit according to the present invention, the spillback amount is adjusted by the first spillback section based on the intermediate pressure in the previous compression stage. Therefore, a compressor unit that can respond to pressure fluctuations of the intake gas can be configured without providing an adjustment means operated by compressed gas in the previous compression stage. In other words, since the previous compression stage that compresses the boil-off gas of liquefied hydrogen, which is at a very low temperature, is provided with the first spillback section instead of a drive unit operated by compressed gas, this compressor unit can respond to pressure fluctuations of the intake gas in combination with the adjustment of the processing amount by the adjustment means in the subsequent compression stage.

[0014] At least a part of the subsequent compression stage may have a leak gas discharge portion that returns the leak gas from the rod packing to the suction passage. In this embodiment, the leak gas can be recovered.

[0015] The adjusting means may include, in at least one subsequent compression stage, an intake valve unloader attached to a cylinder section of the subsequent compression stage. In this case, in the first control, the control unit may adjust the throughput of the cylinder section by controlling the intake valve unloader based on the pressure acquired by the upstream pressure sensor.

[0016] In this embodiment, the power required to compress the gas can be further reduced.

[0017] The adjusting means may include, in at least one subsequent compression stage, a second spillback section including a second spillback flow path for returning hydrogen gas flowing through the discharge side of the subsequent compression stage to the suction side of the subsequent compression stage and a second spillback valve for adjusting the amount of spillback in the second spillback flow path, and a suction valve unloader attached to a cylinder section of the subsequent compression stage. In this case, in the first control, the control section may adjust the throughput of the cylinder section by controlling the second spillback valve and the suction valve unloader based on the pressure acquired by the upstream pressure sensor.

[0018] In this embodiment, the power required to compress the gas can be further reduced.

[0019] The adjusting means may include a stepless capacity adjusting device having, in at least one subsequent compression stage, a suction valve unloader attached to a cylinder portion of the subsequent compression stage and a hydraulic or electric drive device for opening and closing the suction valve unloader. In this case, the control unit may drive the drive device so that the operation timing of the suction valve unloader is adjusted in conjunction with the rotational motion of a crankshaft in the crank mechanism, and in the first control, the control unit may control the drive device based on the pressure acquired by the upstream pressure sensor to adjust the throughput of the subsequent compression stage.

[0020] In this embodiment, the timing and duration of the operation of the suction valve unloader are controlled to return a portion of the hydrogen gas in the cylinder to the suction side, thereby reducing the amount of gas processed in the subsequent compression stage, thereby further reducing power consumption.

[0021] The control method of the compressor unit according to the present invention is a control method of 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. The compressor unit includes one or more front compression stages that compress hydrogen gas having a predetermined temperature below 0°C and flowing through an intake passage, one or more rear compression stages that further compress hydrogen gas discharged from the front compression stage, a crank mechanism that drives the front compression stage and the rear compression stage, a first spillback flow passage that returns hydrogen gas discharged from the front compression stage to the intake passage, and a first spillback section including a first spillback valve that adjusts the amount of spillback in the first spillback flow passage, an adjustment means that adjusts the amount of hydrogen gas processed by the rear compression stage, a pressure sensor disposed in an intermediate flow passage between the front compression stage and the rear compression stage, and an upstream pressure sensor disposed in the intake passage. The front compression stage and the rear compression stage each include a cylinder portion, a piston, a piston rod connecting the piston to the crank mechanism, and a rod packing sealing between the piston rod and the cylinder portion. The front compression stage is air-cooled and oil-free. The control method for the compressor unit includes: acquiring a pressure of hydrogen gas flowing through the suction passage by the upstream pressure sensor; acquiring a pressure of hydrogen gas flowing through the intermediate passage by the pressure sensor; performing a first control to control the adjustment means so that a throughput of the rear compression stage is adjusted based on the pressure acquired by the upstream pressure sensor; and performing a second control to control the first spillback valve before, after, or simultaneously with the first control, with reference to an intermediate pressure acquired by the pressure sensor, so that the intermediate pressure falls within a predetermined pressure range. Effect of the Invention

[0022] As described above, according to the present invention, in a reciprocating compressor unit that compresses boil-off gas of liquefied hydrogen, which is at an extremely low temperature, it is possible to respond to pressure fluctuations of the gas suctioned into the previous compression stage without providing an adjustment means that operates by compressed gas in the previous compression stage. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram illustrating a compressor unit according to a first embodiment. [Diagram 2] FIG. 2 is a schematic diagram of a pre-compression stage in the compressor unit; [Diagram 3] FIG. 4 shows a schematic diagram of a subsequent compression stage in the compressor unit. [Figure 4] 5A and 5B are diagrams for explaining an operation of the compressor unit. [Diagram 5] FIG. 6 is a diagram illustrating a compressor unit according to a second embodiment. [Figure 6] 5A and 5B are diagrams for explaining an operation of the compressor unit. [Figure 7] FIG. 11 is a diagram illustrating a compressor unit according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0025] (First embodiment) The compressor unit according to this embodiment is configured to recover hydrogen gas, which is boil-off gas, from a liquid hydrogen tank, compress the recovered hydrogen gas, and supply it to a consumer. The boil-off gas, which is hydrogen gas, has a temperature of about -253°C.

[0026] As shown in FIG. 1, the compressor unit 10 includes a front compression stage 12 that compresses hydrogen gas in an intake passage 21, a subsequent compression stage 14 connected to the front compression stage 12 via an intermediate passage 22, and a crank mechanism 16 that drives the front compression stage 12 and the subsequent compression stage 14.

[0027] The front-stage compression stage 12 is connected to the liquid hydrogen tank 23 via the suction passage 21. Therefore, boil-off gas of the liquefied gas generated in the liquid hydrogen tank 23 is sucked into the front-stage compression stage 12 through the suction passage 21. That is, hydrogen gas at a predetermined temperature or lower, i.e., hydrogen gas at a reference temperature or lower based on the liquefaction temperature of air, is introduced into the front-stage compression stage 12 through the suction passage 21. Note that this "reference temperature or lower" may be, for example, -180°C or lower.

[0028] The front compression stage 12 is configured by a reciprocating compression mechanism. That is, as shown in Fig. 2, the front compression stage 12 has a cylinder section 211, a piston 212 arranged in the cylinder section 211, a piston rod 213 connected to the piston 212, a pair of suction valves 214, and a pair of discharge valves 215. In the cylinder section 211, a compression chamber 216 is formed between a front head 211a and the piston 212, and between a rear head 211b and the piston 212. The front compression stage 12 is configured by an air-cooled, oil-free compression mechanism that does not use lubricating oil.

[0029] A rod packing 217 for preventing leakage of hydrogen gas from the compression chamber 216 is provided in the rear head 211b of the cylinder portion 211. The rod packing 217 is configured to seal between the piston rod 213 and the cylinder portion 211, and has a packing ring 217a arranged so as to surround the piston rod 213, and a case 217b that holds the packing ring 217a.

[0030] The piston 212 is connected to the crank mechanism 16 via a piston rod 213. The piston 212 reciprocates in the cylinder portion 211, thereby compressing the hydrogen gas in a compression chamber 216. Although the front compression stage 12 having a double acting structure is shown in Fig. 2, the front compression stage 12 may adopt a single acting structure in which the compression chamber 216 is provided only on the front head side or the rear head side.

[0031] 1, the front compression stage 12 is shown as a single trapezoid for convenience, but the front compression stage 12 may have a plurality of cylinder sections 211. That is, the front compression stage 12 may be configured such that hydrogen gas is compressed and pressurized by pistons 212 in a plurality of cylinder sections 211 connected in parallel. The same applies to other embodiments. The front compression stage 12 may be multiple stages.

[0032] The subsequent compression stage 14 is a compression mechanism for further compressing the hydrogen gas discharged from the previous compression stage 12. That is, hydrogen gas having a temperature higher than a predetermined temperature, that is, hydrogen gas having a temperature higher than a reference temperature based on the liquefaction temperature of air, is introduced into the subsequent compression stage 14.

[0033] The hydrogen gas compressed by the subsequent compression stage 14 is discharged to a discharge flow passage 24. The hydrogen gas flowing through the discharge flow passage 24 is sent directly or indirectly via other equipment to a consumer 26. The consumer 26 may be a power generation facility, a boiler, an engine of a ship, or the like, and may also include equipment that releases gas into the atmosphere, such as a flare facility or a vent.

[0034] As shown in Fig. 3, the subsequent compression stage 14 is configured by a reciprocating compression mechanism, similar to the preceding compression stage 12. The piston 212 of the subsequent compression stage 14 is also connected to the crank mechanism 16 via a piston rod 213. The subsequent compression stage 14 is configured similarly to the preceding compression stage 12, but is further provided with a leakage gas discharge section 29 that returns leakage gas from the rod packing 217 to the suction passage 21. The leakage gas discharge section 29 may be formed by a pipe member provided to connect the rod packing 217 and the suction passage 21 to each other.

[0035] In addition, in Fig. 1, the subsequent compression stage 14 is shown as a single trapezoid for convenience, but the subsequent compression stage 14 does not necessarily have to be a single stage type, and may have a compression mechanism of multiple compression stages. That is, the subsequent compression stage 14 may be configured such that hydrogen gas is sequentially compressed and pressurized by pistons 212 in multiple cylinder portions 211, respectively. The same applies to other embodiments. In the subsequent compression stage 14, the compression stage that discharges room temperature hydrogen gas may be of an oil-free type or a lubricated type.

[0036] As shown in FIG. 1, the compressor unit 10 includes a first spillback section 18 that returns a portion of the hydrogen gas discharged from the front compression stage 12 to the suction passage 21. The first spillback section 18 includes a first spillback passage 18a and a first spillback valve 18b that is an adjustable valve disposed in the first spillback passage 18a. One end of the first spillback passage 18a is connected to the intermediate passage 22, and the other end is connected to the suction passage 21. That is, the hydrogen gas that flows through the first spillback passage 18a merges with the hydrogen gas from the liquid hydrogen tank 23 in the suction passage 21. The first spillback valve 18b adjusts the amount of spillback in the first spillback passage 18a.

[0037] The compressor unit 10 includes an adjustment means 31 for adjusting the amount of hydrogen gas processed by the subsequent compression stage 14. The adjustment means 31 is provided in at least one of the subsequent compression stages 14. The adjustment means 31 adjusts the amount of gas processed in the subsequent compression stage 14 by a method other than adjusting the rotation speed of the crank mechanism 16. In this embodiment, the adjustment means 31 includes a suction valve unloader 32 and a drive device 33.

[0038] The suction valve unloader 32 is attached to the suction valve 214 (see FIG. 3) of the subsequent compression stage 14, and is driven in an on-off manner by a drive unit 33. When the suction valve unloader 32 is operated, the valve plate of the suction valve 214 is maintained in an open state, and the suction valve 214 cannot function as a check valve. When the unloader 32 is not operated and the piston 212 is in the suction stroke, the pressure in the compression chamber 216 becomes lower than the pressure in the intermediate flow passage 22, and the suction valve 214 is in an open state. As a result, hydrogen gas is introduced from the intermediate flow passage 22 to the compression chamber 216. When the piston 212 is in the compression stroke, the pressure in the compression chamber 216 becomes higher than the pressure in the intermediate flow passage 22, and the suction valve 214 is in a closed state.

[0039] The suction valve unloaders 32 are mounted in the front head side compression chamber 216 and the rear head side compression chamber 216 of the cylinder section 211, and can be operated independently. A state in which neither is operating is called 100% load, and a state in which either one is operating is called 50% load.

[0040] The suction valve unloader 32 is driven by a drive device 33 using compressed gas such as air or nitrogen. Driven by the drive device 33, the suction valve unloader 32 sets the suction valve 214 in a state in which the compression chamber 216 is opened or closed relative to the intermediate flow path 22 in accordance with the pressure difference between the compression chamber 216 and the intermediate flow path 22 (loaded state), or in a state in which the space between the compression chamber 216 and the intermediate flow path 22 is maintained in an open state (unloaded state). For example, by not applying pressure of a gas such as air or nitrogen to the drive device 33, the suction valve unloader 32 sets the suction valve 214 in a free state so that the compression chamber 216 can be opened or closed in accordance with the pressure difference between the compression chamber 216 and the intermediate flow path 22. On the other hand, when the pressure of a gas such as air or nitrogen acts on the drive unit 33, the compression chamber 216 would normally be closed due to the pressure difference between the compression chamber 216 and the intermediate flow path 22, but the suction valve unloader 32 forcibly keeps the suction valve 214 open.

[0041] In addition, the drive unit 33 may be constructed so that a spring is used for the drive force and the pressure of a gas such as air or nitrogen is used to release the spring force, so that by not applying gas pressure, the suction valve is forcibly maintained in an open state, and by applying gas pressure, the suction valve has the opposite effect to being in a free state.

[0042] An upstream pressure sensor 45 is provided in the suction passage 21 to detect the pressure of hydrogen gas in the suction passage 21. The upstream pressure sensor 45 is disposed in the suction passage 21 at a location upstream of the connection portion of the first spillback passage 18a. Note that the upstream pressure sensor 45 may also be disposed in the suction passage 21 at a location downstream of the connection portion of the first spillback passage 18a.

[0043] The intermediate flow passage 22 is provided with a pressure sensor 47 that detects the pressure of hydrogen gas in the intermediate flow passage 22. The pressure sensor 47 is located in the intermediate flow passage 22 between the connection part of the front compression stage 12 and the first spillback flow passage 18a. Note that the pressure sensor 47 only needs to be able to detect the pressure of hydrogen gas in the intermediate flow passage 22, so it may be located between the connection part of the first spillback flow passage 18a and the subsequent compression stage 14. The pressure sensor 47 may also be provided in a portion of the first spillback flow passage 18a upstream of the first spillback valve 18b.

[0044] The upstream pressure sensor 45 and the pressure sensor 47 output signals indicating the detected pressures. The signals from the pressure sensor 47 and the upstream pressure sensor 45 are input to the control unit 50.

[0045] The control unit 50 is a computer that controls various operations of the compressor unit 10, and the functions of the control unit 50 executed by this computer include a first control unit 50a, which is a functional unit for executing the first control, and a second control unit 50b, which is a functional unit for executing the second control.

[0046] In the first control, the adjustment means 31 is controlled based on the pressure P1 acquired by the upstream pressure sensor 45. That is, the first control unit 50a refers to the pressure (hydrogen gas pressure in the suction passage 21) P1 acquired by the upstream pressure sensor 45, and controls the drive device 33 of the suction valve unloader 32 based on this pressure P1.

[0047] In the second control, the first spillback valve 18b is controlled based on the pressure P2 acquired by the pressure sensor 47. That is, the second control unit 50b refers to the pressure (intermediate pressure which is the hydrogen gas pressure in the intermediate flow path 22) P2 acquired by the pressure sensor 47, and controls the first spillback valve 18b based on this intermediate pressure P2.

[0048] Here, the operation of the compressor unit 10 according to this embodiment will be described with reference to FIG.

[0049] By operation of the crank mechanism 16, the piston 212 reciprocates in the cylinder portion 211 in the front compression stage 12 and the subsequent compression stage 14. As a result, in the front compression stage 12, hydrogen gas in the suction passage 21 is sucked into the front compression stage 12, and in the subsequent compression stage 14, hydrogen gas in the intermediate passage 22 is sucked into the subsequent compression stage 14, thereby compressing the hydrogen gas.

[0050] When the compression stages 12, 14 are operating, pressure information of the hydrogen gas sucked into the front compression stage 12 is acquired by the upstream pressure sensor 45 (step ST11). Then, the control unit 50 compares the pressure P1 indicated by the pressure information acquired from the upstream pressure sensor 45 with a pre-stored reference range, and determines whether the pressure of the hydrogen gas in the intake passage 21 has changed to the point where it falls outside the reference range (step ST12). If it is determined that the hydrogen gas pressure P1 is within the reference range and has not changed, the process returns to step ST11, and step ST11 is executed again.

[0051] On the other hand, if it is determined that the detected pressure P1 of hydrogen gas in the suction passage 21 has changed so as to fall outside the reference range (YES in step ST12), the first control and the second control are executed (step ST13).

[0052] Specifically, the first control unit 50a refers to the pressure P1 acquired by the upstream pressure sensor 45, and when it is determined that the pressure P1 has dropped below a predetermined reference range, it uses the suction valve unloader 32 to lower the load of the subsequent compression stage 14 (e.g., from 100% load to 50% load). This reduces the amount of hydrogen gas processed in the subsequent compression stage 14. On the other hand, when it is determined that the acquired pressure P1 has risen above the predetermined reference range, it uses the suction valve unloader 32 to increase the load of the subsequent compression stage 14 (e.g., from 50% load to 100% load). This increases the amount of hydrogen gas processed in the subsequent compression stage 14.

[0053] The control unit 50 continues to acquire pressure information from the pressure sensor 47 from before the first control is executed. Therefore, the control unit 50 receives the pressure information acquired by the pressure sensor 47 even during and after the first control is executed.

[0054] The second control unit 50b executes the second control before or after the first control (i.e., before or after the first control) or simultaneously with the first control. In the first control, when the suction valve unloader 32 operates, the amount of hydrogen gas processed in the subsequent compression stage 14 changes. Therefore, the pressure (intermediate pressure) P2 acquired by the pressure sensor 47 also changes accordingly. When the intermediate pressure P2 changes, the second control unit 50b changes the opening degree of the first spillback valve 18b accordingly.

[0055] For example, when the suction valve unloader 32 is operated and the throughput of the subsequent compression stage 14 is reduced, the intermediate pressure P2 tends to increase accordingly. The second control unit 50b controls the first spillback valve 18b so that the opening degree of the first spillback valve 18b is increased by a predetermined opening degree. On the other hand, when the throughput of the subsequent compression stage 14 is increased, the intermediate pressure P2 tends to decrease accordingly. The second control unit 50b controls the first spillback valve 18b so that the opening degree of the first spillback valve 18b is decreased by a predetermined opening degree. As a result, the pressure fluctuation of the hydrogen gas in the intermediate flow passage 22 caused by the pressure fluctuation of the hydrogen gas from the liquid hydrogen storage tank 23 can be suppressed. Excessive compression operation in the subsequent compression stage 14 can also be suppressed.

[0056] As described above, in the compressor unit 10 of this embodiment, the spillback amount is adjusted by the first spillback section 18 based on the intermediate pressure P2 in the front compression stage 12. Therefore, it is possible to configure the compressor unit 10 that can handle pressure fluctuations of the intake gas without providing an adjustment means that operates with compressed gas in the front compression stage 12.

[0057] Generally, to adjust the capacity of a reciprocating compressor, a suction valve unloader operated by air is provided in the cylinder section of each compression stage. In some cases, a clearance pocket is additionally provided. In the case of a general cylinder section that compresses both the push stroke and the pull stroke, the suction valve unloader allows for 100%, 50%, and 0% capacity adjustment, and if a clearance pocket is added, it becomes possible to further adjust the capacity by 75% and 25%. Following this general method, these capacity adjustment devices are installed in the cylinder sections of all compression stages according to the capacity adjustment request from the liquid hydrogen storage tank. In the case of a multi-stage reciprocating compressor, the gas processed in the first compression stage is usually processed in its entirety in the second compression stage, and further, the gas processed in the second compression stage (after further processing if there are three or more subsequent stages) is sent to the entire discharge flow path. Therefore, when it is desired to reduce the amount of suction from the liquid hydrogen storage tank to the compressor unit, the amount of suction into the cylinder section of the first compression stage is reduced by the suction valve unloader, and similarly, the suction amounts of the second and subsequent compression stages are also reduced accordingly by suction valve unloaders.

[0058] However, when a suction valve unloader operated by compressed air is provided in the cylinder of the first compression stage, thermal treatment using cryogenic hydrogen gas from the liquid hydrogen tank is required. If appropriate thermal treatment is not performed, there is a risk that the pressure fluctuations in the liquid hydrogen tank will not be properly handled.

[0059] In contrast, in the compressor unit 10 according to the present embodiment, the adjustment of the throughput in the front compression stage 12 is performed by the first spillback section 18, so that it is possible to respond to pressure fluctuations of the intake gas without providing an intake valve unloader operated by compressed gas in the front compression stage 12. That is, the front compression stage 12, which compresses the boil-off gas of liquefied hydrogen, which is at a very low temperature, is provided with the first spillback section 18, rather than a drive section operated by compressed gas. Therefore, in combination with the adjustment of the throughput by the adjustment means 31 in the subsequent compression stage 14, the compressor unit 10 can respond to pressure fluctuations of the intake gas. In addition, stable recovery of hydrogen gas is possible.

[0060] Second embodiment In the second embodiment, as shown in Fig. 5, a second spillback section 35 is added to the adjustment means 31. That is, the adjustment means 31 includes a suction valve unloader 32 and a second spillback section 35. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0061] The second spillback section 35 has a second spillback flow path 35a and a second spillback valve 35b, which is an adjustable valve arranged in the second spillback flow path 35a. One end of the second spillback flow path 35a is connected to the discharge flow path 24, and the other end is connected to the intermediate flow path 22. Therefore, by opening the second spillback valve 35b, a part of the hydrogen gas discharged from the subsequent compression stage 14 is returned to the intermediate flow path 22. The second spillback valve 35b adjusts the amount of spillback in the second spillback flow path 35a. The second spillback section 35 adjusts the flow rate of hydrogen gas sent from the subsequent compression stage 14 to the demand destination 26 by performing a process of returning a part of the hydrogen gas discharged from the subsequent compression stage 14 to the intermediate flow path 22.

[0062] The suction valve unloader 32 adjusts the flow rate of hydrogen gas sucked into the compression chamber 216, thereby adjusting the amount of hydrogen gas processed in the subsequent compression stage 14. In this manner, in the compressor unit 10, the suction valve unloader 32 and the second spillback section 35 are controlled to adjust the amount of hydrogen gas processed in the subsequent compression stage 14.

[0063] 6, in the first control, the first control unit 50a refers to the pressure P1 (hydrogen gas pressure in the suction passage 21) acquired by the upstream pressure sensor 45 (step ST11). If it is determined that the acquired pressure P1 has dropped below a predetermined reference range (YES in step ST12), the first control including the control of the suction valve unloader 32 and the second control are performed (step ST14).

[0064] In the first control, the second spillback valve 35b is controlled so that the opening degree of the second spillback valve 35b becomes larger by a predetermined opening degree.

[0065] The second control is performed before, after, or simultaneously with the first control. In the second control, the second control unit 50b controls the first spillback valve 18b so that the opening degree is increased by a predetermined opening degree based on the pressure (intermediate pressure) P2 acquired by the pressure sensor 47. This suppresses a pressure increase of the hydrogen gas in the intermediate flow path 22 that is caused by increasing the opening degree of the second spillback valve 35b.

[0066] Thereafter, when the opening degree of the second spillback valve 35b exceeds the threshold value, the first control unit 50a further performs the following operation as the first control. That is, the first control unit 50a reduces the load of the subsequent compression stage 14 by the suction valve unloader 32 (for example, from 100% load to 50% load). At the same time, the first control unit 50a controls the second spillback valve 35b so that the opening degree of the second spillback valve 35b is minimized. This makes it possible to suppress excessive compression operation in the subsequent compression stage 14.

[0067] On the other hand, when it is determined that the acquired pressure P1 has increased above the predetermined reference range (YES in step ST12), the first control and the second control are also performed (step ST14).

[0068] In the first control, the second spillback valve 35b is controlled so that the opening degree of the second spillback valve 35b becomes smaller than a predetermined opening degree.

[0069] In the second control, the second control unit 50b controls the first spillback valve 18b so that the opening degree is reduced to a predetermined opening degree based on the pressure (intermediate pressure) P2 measured by the pressure sensor 47. This suppresses a pressure drop of the hydrogen gas in the intermediate flow path 22 that is caused by reducing the opening degree of the second spillback valve 35b.

[0070] Thereafter, when the opening degree of the second spillback valve 35b is at the minimum value and the load of the subsequent compression stage 14 is 50% load, the first control unit 50a further performs the following operation as the first control. That is, the first control unit 50a increases the load of the subsequent compression stage 14 by the suction valve unloader 32 (e.g., from 50% to 100% load). At the same time, the first control unit 50a controls the second spillback valve 35b so that the opening degree of the second spillback valve 35b becomes the threshold value.

[0071] As described above, in the compressor unit 10, by executing the first control and the second control, it is possible to more precisely suppress the pressure fluctuations of the hydrogen gas in the intermediate flow path 22 caused by the pressure fluctuations of the hydrogen gas from the liquid hydrogen storage tank 23.

[0072] In this embodiment, the adjustment means 31 includes the suction valve unloader 32 and the second spillback portion 35, but the suction valve unloader 32 may be omitted. That is, the adjustment means 31 may be composed of only the second spillback portion 35. In this case, step ST23 is omitted. The description of the other configurations, actions, and effects will be omitted, but the description of the first embodiment can be applied to the second embodiment.

[0073] Third embodiment 7, in the third embodiment, the adjustment means 31 includes a stepless capacity adjustment device 37. The adjustment means 31 does not include a second spill-back portion 35. Here, the same components as those in the first and second embodiments are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0074] The stepless capacity adjusting device 37 has a suction valve unloader 32b, a hydraulic or electric drive device 33b, and a detector 34b that detects the rotation of the crankshaft in the crank mechanism 16. The suction valve unloader 32b is driven by the hydraulic or electric drive device 33b, and can maintain or release the open state of the valve plate of the suction valve 214 faster than the time it takes for the piston 212 to reciprocate. In addition, the control unit 50 performs a calculation process to estimate the position of the piston 212 based on a signal sent from the detector 34b installed in the crank mechanism 16.

[0075] The suction valve 214 (see FIG. 3) attached to the cylinder portion 211 of the subsequent compression stage 14 is composed of a valve plate that opens and closes the intermediate flow passage 22, which is the flow passage on the suction side, and a valve body that houses it. Similar to a check valve, the suction valve 214 is structured so that when the upstream pressure is higher than the downstream pressure, the valve plate opens due to the pressure difference, and gas does not flow when the downstream pressure is higher.

[0076] When the suction valve unloader 32b operates, the valve plate of the suction valve 214 is maintained in an open state and does not function as a check valve. When the piston 212 goes through a suction stroke with the unloader 32b not operating, if the pressure in the compression chamber 216 falls below the pressure in the intermediate passage 22, which is the passage on the suction side, the suction valve 214 opens. This allows gas to be introduced into the compression chamber 216. When the piston 212 goes through a compression stroke, the pressure in the compression chamber 216 rises above the pressure in the intermediate passage 22, and the suction valve 214 closes.

[0077] In the first control, the first control unit 50a of the control unit 50 refers to the pressure P1 acquired by the upstream pressure sensor 45, and controls the drive device 33b that operates the suction valve unloader 32b when the pressure P1 falls outside a predetermined standard range or when the pressure P1 fluctuates beyond a predetermined value.

[0078] When the fluctuation of the pressure P1 is detected, the first control unit 50a controls the drive device 33b so that the operation timing of the intake valve unloader 32b is adjusted in conjunction with the rotational motion of the crankshaft in the crank mechanism 16. Specifically, the first control unit 50a operates the intake valve unloader 32b to maintain the open state of the intake valve 214 at the beginning of the compression stroke. As a result, a part of the gas in the compression chamber 216 is returned to the intermediate flow path 22. Then, in the middle of the compression stroke, the first control unit 50a controls the drive device 33 so that the operation of the intake valve unloader 32b is released. As a result, the open state of the intake valve 214 is released, and the intake valve 214 is closed. At that time, the gas remaining in the compression chamber 216 is compressed and sent from the compression chamber 216 to the discharge flow path 24. At the time of the next suction stroke, the first control unit 50a controls the drive device 33b to operate the suction valve unloader 32b again, and controls the drive device 33b to release the open state after the start of the compression stroke of the piston 212. Such operation and release of the suction valve unloader 32b are repeated in accordance with the reciprocating motion of the piston 212.

[0079] If the release timing of the suction valve unloader 32b is made earlier, the discharge amount increases, and if it is made later, the discharge amount decreases, so that the suction valve unloader 32b can fulfill the same function as the second spillback section 35. In other words, by adjusting the throughput of the subsequent compression stage 14 in response to the pressure fluctuation in the intermediate flow path 22 caused by the first control, it is possible to further reduce power.

[0080] It should be noted that the explanation of the other configurations, operations and effects will be omitted, but the explanations of the first and second embodiments can be applied to the third embodiment.

[0081] (Other embodiments) It should be noted that the embodiments disclosed herein are illustrative in all respects and should not be construed as limiting. The present invention is not limited to the above-described embodiments, and various modifications and improvements can be made without departing from the spirit and scope of the present invention.

[0082] For example, in the first and third embodiments, when two or more subsequent compression stages 14 are provided, at least one of the subsequent compression stages 14 may be provided with the suction valve unloader 32, 32b.

[0083] In the first embodiment, as the adjustment means 31, a clearance pocket may be provided instead of the suction valve unloader 32.

[0084] In the second embodiment, when two or more subsequent compression stages 14 are provided, it is sufficient that at least one subsequent compression stage 14 is provided with the suction valve unloader 32 and the second spillback section 35. In addition, the second spillback section 35 may be configured such that the second spillback flow path 35a spans the multiple subsequent compression stages 14.

[0085] In the above embodiment, when two or more front compression stages 12 are provided, the first spillback section 18 may be configured such that one end of the first spillback flow passage 18a is connected to a flow passage between adjacent front compression stages 12, and the other end is connected to the suction flow passage 21. Also, two or more first spillback sections 18 may be provided. [Explanation of symbols]

[0086] 10: Compressor unit 12: Pre-compression stage 14: Subsequent compression stage 16: Crank mechanism 18: First spillback section 18a: First spillback channel 18b: First spillback valve 21: Suction passage 22: Intermediate flow path 23: Liquid hydrogen storage tank 26: Demand destination 29: Leak gas exhaust section 31: Adjustment means 32: Suction valve unloader 32b: Suction valve unloader 33: Drive unit 33b: Drive unit 35: Second spillback section 35a: Second spillback channel 35b: Second spillback valve 37: Capacity adjustment device 45: Upstream pressure sensor 47: Pressure sensor 50: Control section 50a: First control section 50b: Second control section 211: Cylinder section 212: Piston 213: Piston rod 214: Suction valve 217: Rod packing

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, one or more pre-compression stages for compressing hydrogen gas flowing through an intake passage at a temperature below a predetermined temperature of less than 0° C.; one or more subsequent compression stages for further compressing the hydrogen gas discharged from the first compression stage; a crank mechanism that drives the front compression stage and the rear compression stage; A first spillback section including a first spillback flow path that returns hydrogen gas discharged from the previous compression stage to the suction flow path, and a first spillback valve that adjusts the amount of spillback in the first spillback flow path; an adjusting means for adjusting the throughput of hydrogen gas through the subsequent compression stage; a pressure sensor disposed in an intermediate flow path between the first compression stage and the second compression stage; an upstream pressure sensor disposed in the intake passage; A control unit that controls the first spillback valve and the adjustment means, Equipped with The front compression stage and the rear compression stage each include A cylinder portion; The piston and a piston rod connecting the piston to the crank mechanism; a rod packing that seals between the piston rod and the cylinder portion; Equipped with The pre-compression stage is air-cooled and oil-free; The control unit is a first control for controlling the adjusting means so that a throughput of the subsequent compression stage is adjusted based on a pressure acquired by the upstream pressure sensor; A second control that controls the first spillback valve before, after, or simultaneously with the first control by referring to the intermediate pressure acquired by the pressure sensor so that the intermediate pressure is within a predetermined pressure range; A compressor unit capable of

2. The compressor unit according to claim 1 , wherein at least a portion of the subsequent compression stage includes a leakage gas discharge portion that returns leakage gas from a rod packing to the suction passage.

3. The adjustment means is In at least one subsequent compression stage, a suction valve unloader is provided in a cylinder portion of the subsequent compression stage, 3. The compressor unit according to claim 1, wherein in the first control, the control unit adjusts the throughput of the cylinder unit by controlling the suction valve unloader based on the pressure acquired by the upstream pressure sensor.

4. The adjustment means is In at least one subsequent compression stage, A second spillback section including a second spillback flow path that returns hydrogen gas flowing through the discharge side of the subsequent compression stage to the suction side of the subsequent compression stage, and a second spillback valve that adjusts the amount of spillback in the second spillback flow path; a suction valve unloader attached to a cylinder portion of the subsequent compression stage; Equipped with The compressor unit according to claim 1 or 2, wherein in the first control, the control unit adjusts the throughput of the cylinder section by controlling the second spillback valve and the suction valve unloader based on the pressure acquired by the upstream pressure sensor.

5. The adjustment means is In at least one subsequent compression stage, a suction valve unloader attached to a cylinder portion of the subsequent compression stage; a hydraulic or electric drive device for opening and closing the suction valve unloader; A stepless capacity adjusting device having the control unit drives the drive device so that an operation timing of the suction valve unloader is adjusted in conjunction with a rotational motion of a crankshaft in the crank mechanism, The compressor unit according to claim 1 or 2, wherein in the first control, the control unit controls the drive device based on the pressure acquired by the upstream pressure sensor to adjust a throughput of the subsequent compression stage.

6. A control method for 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, comprising: The compressor unit includes: one or more pre-compression stages for compressing hydrogen gas flowing through an intake passage at a temperature below a predetermined temperature of less than 0° C.; one or more subsequent compression stages for further compressing the hydrogen gas discharged from the first compression stage; a crank mechanism that drives the front compression stage and the rear compression stage; A first spillback section including a first spillback flow path that returns hydrogen gas discharged from the previous compression stage to the suction flow path, and a first spillback valve that adjusts the amount of spillback in the first spillback flow path; an adjusting means for adjusting the throughput of hydrogen gas through the subsequent compression stage; a pressure sensor disposed in an intermediate flow path between the first compression stage and the second compression stage; an upstream pressure sensor disposed in the suction passage; The front compression stage and the rear compression stage each include A cylinder portion; The piston and a piston rod connecting the piston to the crank mechanism; a rod packing that seals between the piston rod and the cylinder portion; Equipped with The pre-compression stage is air-cooled and oil-free; The control method of the compressor unit includes: The upstream pressure sensor acquires a pressure of the hydrogen gas flowing through the intake passage, The pressure sensor acquires the pressure of the hydrogen gas flowing through the intermediate flow path; performing a first control for controlling the adjusting means so as to adjust a throughput of the subsequent compression stage based on the pressure acquired by the upstream pressure sensor; A control method for a compressor unit, comprising: referring to an intermediate pressure acquired by the pressure sensor; and performing a second control to control the first spillback valve before, after, or simultaneously with the first control so that the intermediate pressure falls within a predetermined pressure range.

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