Compressor unit and method for controlling the compressor unit

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 Art

[0002] In recent years, in consideration of the environment, it has been considered to use hydrogen as a fuel for power generation, 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 demand destination such as an engine. For example, Patent Document 1 discloses a reciprocating compressor for compressing hydrogen gas.

[0003] One of the major roles of this boil-off gas compressor is to keep the internal pressure of the liquefied gas storage tank constant. That is, when the internal pressure of the storage tank rises, the compressor is started (or the throughput of the compressor is increased), and when the internal pressure drops, the compressor is stopped (or the throughput of the compressor is decreased).

[0004] Therefore, when the compressor for treating boil-off gas is a reciprocating compressor, a throughput control device such as a suction valve unloader or a clearance pocket for changing the throughput is often installed.

[0005] On the other hand, especially in the case of a storage tank storing liquid hydrogen (LH2), the boil-off gas generated from the storage tank is very low temperature. Therefore, when the compressor is configured to directly inhale the boil-off gas, it is necessary to select a material suitable for extremely low temperatures or to adopt design conditions considering the amount of thermal deformation. For this reason, various restrictions are imposed, such as the need to perform strict heat insulation treatment on the throughput control device.

[0006] In addition, since the temperature of the suction gas in the first stage is close to absolute zero, it has the characteristic that the volume expands greatly even with a slight temperature rise. Therefore, when a reciprocating compressor, which is a positive displacement compressor, inhales boil-off gas, the operation is performed in a state where the change in throughput is large. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-172870 [Overview of the project] [Problems that the invention aims to solve]

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

[0009] In other words, since the rod drive unit of the unloader, which is installed in the intake valve into which cryogenic boil-off gas is introduced, is driven by compressed gas, it is suggested that thermal treatment is necessary to prevent the rod drive unit from being affected by cold. To put it another way, it is suggested that if thermal treatment is not properly carried out, the volume adjustment of the boil-off gas drawn into the compression unit cannot be properly handled.

[0010] Furthermore, in the case of ultra-low temperature gases such as LH2 boil-off gas, the temperature of the gas drawn into the compressor falls below approximately -180°C. Therefore, in the compressor described in Patent Document 1, the cylinder is covered with a container that forms a vacuum region to prevent the liquefaction of air on the outer surface of the device. However, in such a configuration, special measures are required to block the intrusion of cold air into the air-driven parts of capacity adjustment devices such as unloaders, making the structure complex. Maintenance also becomes complex.

[0011] Therefore, the present invention has been made in view of the above problems, and its objective is to enable a reciprocating compressor unit that compresses boil-off gas of liquefied hydrogen at extremely low temperatures to respond to pressure fluctuations of the intake gas to the preceding compression stage without providing an adjustment means that operates with compressed gas in the preceding compression stage. [Means for solving the problem]

[0012] 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 it to a customer including at least one of an engine, power generation equipment, or boiler. Standards based on the liquefaction temperature of airThe device comprises one or more pre-compression stages that compress hydrogen gas flowing through an intake channel, which is hydrogen gas below a certain temperature; one or more subsequent compression stages that further compress the hydrogen gas discharged from the pre-compression stages; a crank mechanism that drives the pre-compression stages and the subsequent compression stages; a first spillback channel that returns the hydrogen gas discharged from the pre-compression stages back to the intake channel; a first spillback section including a first spillback valve that adjusts the amount of spillback in the first spillback channel; an adjustment means for adjusting the amount of hydrogen gas processed by the subsequent compression stages; a pressure sensor disposed in an intermediate channel between the pre-compression stages and the subsequent compression stages; an upstream pressure sensor disposed in the intake channel; and a control unit that controls the first spillback valve and the adjustment means, respectively. The pre-compression stages and the subsequent compression stages each comprise a cylinder section, a piston, a piston rod connecting the piston to the crank mechanism, and a rod packing that seals the space between the piston rod and the cylinder section. The aforementioned pre-compression stage is air-cooled and oil-free. Furthermore, it does not have an adjustment mechanism that operates with compressed gas to adjust the amount of hydrogen gas processed. The control unit controls the adjustment means so that the processing amount of the subsequent compression stage is adjusted based on the pressure acquired by the upstream pressure sensor. First control unit that executes Then, referring to the intermediate pressure obtained by the pressure sensor, a second control controls the first spillback valve before, during, or simultaneously with, the first control, so that the intermediate pressure falls within a predetermined pressure range. The second control unit that executes and, including a single device That is the case.

[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 preceding compression stage. Therefore, a compressor unit that can respond to pressure fluctuations of the intake gas can be configured without installing an adjustment means that operates with compressed gas in the preceding compression stage. In other words, since the preceding compression stage, which compresses the boil-off gas of liquefied hydrogen at an extremely low temperature, is provided with a first spillback section instead of an adjustment unit that operates with compressed gas, it becomes a compressor unit that can respond to pressure fluctuations of the intake gas in conjunction with the adjustment of the processing amount by the adjustment means in the subsequent compression stage.

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

[0015] The adjustment means may include, in at least one subsequent compression stage, a suction valve unloader mounted on the cylinder portion of the subsequent compression stage. In this case, in the first control, the control unit may adjust the processing amount of the cylinder portion by controlling the suction valve unloader based on the pressure obtained by the upstream pressure sensor.

[0016] In this embodiment, it becomes possible to further reduce the power required to compress the gas.

[0017] The adjustment means may include, in at least one subsequent compression stage, a second spillback section including a second spillback passage that returns hydrogen gas flowing on the discharge side of the subsequent compression stage back to the suction side of the subsequent compression stage, and a second spillback valve that adjusts the amount of spillback in the second spillback passage, and a suction valve unloader mounted on the cylinder section of the subsequent compression stage. In this case, in the first control, the control unit may adjust the processing amount of the cylinder section by controlling the second spillback valve and the suction valve unloader based on the pressure obtained by the upstream pressure sensor.

[0018] In this embodiment, it becomes possible to further reduce the power required to compress the gas.

[0019] The adjustment means may include a stepless capacity adjustment device having, in at least one subsequent compression stage, a suction valve unloader mounted on the 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 in conjunction with the rotational movement of the crankshaft in the crank mechanism to adjust the operating timing of the suction valve unloader, and in the first control, the control unit may control the drive device based on the pressure obtained by the upstream pressure sensor to adjust the processing amount of the subsequent compression stage.

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

[0021] The compressor unit control method according to the present invention is a control method for 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 it to a customer including at least one of an engine, power generation equipment, or boiler. The compressor unit is Standards based on the liquefaction temperature of air One or more pre-compression stages that compress hydrogen gas flowing through an intake channel, which is hydrogen gas below a certain temperature, and hydrogen gas discharged from the pre-compression stages hydrogen gas at a temperature higher than the aforementioned reference temperatureOne or more subsequent compression stages for further compressing, a crank mechanism for driving the previous compression stage and the subsequent compression stages, a first spillback flow path for returning the hydrogen gas after being discharged from the previous compression stage to the suction flow path, and a first spillback part including a first spillback valve for adjusting the spillback amount in the first spillback flow path, an adjusting means for adjusting the processing amount of hydrogen gas by the subsequent compression stage, a pressure sensor disposed in an intermediate flow path between the previous compression stage and the subsequent compression stage, and an upstream pressure sensor disposed in the suction flow path. The previous compression stage and the subsequent compression stages each include a cylinder part, a piston, a piston rod connecting the piston to the crank mechanism, and a rod packing for sealing between the piston rod and the cylinder part. The previous compression stage is air-cooled and oil-free. Furthermore, it does not have an adjustment mechanism that operates with compressed gas to adjust the amount of hydrogen gas processed. The control method of the compressor unit acquires the pressure of the hydrogen gas flowing through the suction flow path by the upstream pressure sensor, acquires the pressure of the hydrogen gas flowing through the intermediate flow path by the pressure sensor, and performs a first control for controlling the adjusting means so that the processing amount of the subsequent compression stage is adjusted based on the pressure acquired by the upstream pressure sensor. Referring to the intermediate pressure acquired by the pressure sensor, a second control for controlling the first spillback valve is performed before or after or simultaneously with the first control so that the intermediate pressure is within a predetermined pressure range. The first control and the second control are performed by a control unit, which is a single device.

Advantages of the Invention

[0022] As described above, according to the present invention, in a reciprocating compressor unit for compressing boil-off gas of liquefied hydrogen which is at an extremely low temperature, even if an adjusting means operated by compressed gas is not provided in the previous compression stage, it is possible to cope with pressure fluctuations of the suction gas to the previous compression stage.

Brief Description of the Drawings

[0023] [Figure 1] It is a diagram schematically showing a compressor unit according to a first embodiment. [Figure 2]This diagram schematically shows the pre-compression stage in the aforementioned compressor unit. [Figure 3] This diagram schematically shows the subsequent compression stage in the aforementioned compressor unit. [Figure 4] This is a diagram illustrating the operation of the compressor unit. [Figure 5] This diagram schematically shows a compressor unit according to the second embodiment. [Figure 6] This is a diagram illustrating the operation of the compressor unit. [Figure 7] This diagram schematically shows a compressor unit according to the third embodiment. [Modes for carrying out the invention]

[0024] Hereinafter, embodiments for carrying out 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 a boil-off gas, from a liquid hydrogen storage tank, compress the recovered hydrogen gas, and supply it to the customer. The boil-off gas, which is hydrogen gas, is at approximately -253°C.

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

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

[0028] The pre-compression stage 12 is composed of a reciprocating compression mechanism. Specifically, as shown in Figure 2, the pre-compression stage 12 includes a cylinder section 211, a piston 212 positioned within 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. Within the cylinder section 211, compression chambers 216 are formed between the front head 211a and the piston 212, and between the rear head 211b and the piston 212. The pre-compression stage 12 is air-cooled and consists of an oil-free compression mechanism that does not use lubricating oil.

[0029] The rear head 211b of the cylinder section 211 is provided with a rod packing 217 to prevent hydrogen gas leakage from the compression chamber 216. The rod packing 217 is configured to seal the space between the piston rod 213 and the cylinder section 211 and includes a packing ring 217a positioned 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 the piston rod 213. The piston 212 reciprocates within the cylinder section 211, compressing hydrogen gas in the compression chamber 216. Figure 2 shows a double-acting pre-compression stage 12; however, the pre-compression stage 12 may employ a single-acting structure with the compression chamber 216 located only on the front head side or the rear head side.

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

[0032] The subsequent compression stage 14 is a compression mechanism for further compressing the hydrogen gas discharged from the preceding compression stage 12. Specifically, hydrogen gas at a temperature higher than a predetermined temperature, i.e., hydrogen gas at 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 into the discharge channel 24. The hydrogen gas flowing through the discharge channel 24 is sent directly or indirectly through other equipment to the consumer 26. Examples of consumer 26 include power generation equipment, boilers, engines of ships, etc., and may also include equipment that releases gas into the atmosphere, such as flare equipment and vents.

[0034] As shown in Figure 3, the subsequent compression stage 14 is configured with 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 the subsequent compression stage 14 is further provided with a leak gas discharge section 29 that returns leak gas from the rod packing 217 to the suction passage 21. The leak gas discharge section 29 may be configured with a pipe member that connects the rod packing 217 and the suction passage 21 to each other.

[0035] In Figure 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 and may have a compression mechanism with 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 each of the multiple cylinder sections 211. The same applies to other embodiments. In the subsequent compression stage 14, the compression stage that discharges hydrogen gas at room temperature may be either oil-free or lubricated.

[0036] As shown in Figure 1, the compressor unit 10 is equipped with a first spillback section 18 that returns a portion of the hydrogen gas discharged from the preceding compression stage 12 to the suction channel 21. The first spillback section 18 has a first spillback channel 18a and a first spillback valve 18b, which is a valve with an adjustable opening that is located in the first spillback channel 18a. One end of the first spillback channel 18a is connected to the intermediate channel 22, and the other end is connected to the suction channel 21. In other words, the hydrogen gas that flows through the first spillback channel 18a merges with the hydrogen gas from the liquid hydrogen storage tank 23 in the suction channel 21. The first spillback valve 18b adjusts the amount of spillback in the first spillback channel 18a.

[0037] The compressor unit 10 is equipped with 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 means other than adjusting the rotational speed of the crank mechanism 16. In this embodiment, the adjustment means 31 comprises a suction valve unloader 32 and a drive device 33.

[0038] The suction valve unloader 32 is attached to the suction valve 214 (see Figure 3) of the subsequent compression stage 14 and is driven on / off by the drive unit 33. When the suction valve unloader 32 is activated, the valve plate of the suction valve 214 is kept open and unable to function as a check valve. When the piston 212 enters the suction stroke while the unloader 32 is not activated, the pressure in the compression chamber 216 falls below the pressure in the intermediate passage 22, so the suction valve 214 opens. As a result, hydrogen gas is introduced from the intermediate passage 22 into the compression chamber 216. When the piston 212 enters the compression stroke, the pressure in the compression chamber 216 rises above the pressure in the intermediate passage 22, so the suction valve 214 closes.

[0039] The suction valve unloaders 32 are installed in the front head side compression chamber 216 and the rear head side compression chamber 216 of the cylinder section 211, and each can operate independently. The state in which neither is operating is referred to as 100% load, and the state in which either one is operating is referred to as 50% load.

[0040] The suction valve unloader 32 is driven by a drive unit 33 using compressed gas such as air or nitrogen. Driven by the drive unit 33, the suction valve unloader 32 causes the suction valve 214 to either open or close relative to the intermediate passage 22 (loaded state) or to maintain an open state between the compression chamber 216 and the intermediate passage 22 in accordance with the differential pressure between the two (unloaded state). For example, by not applying pressure of air or a gas such as nitrogen to the drive unit 33, the suction valve unloader 32 frees the suction valve 214 so that the compression chamber 216 can be opened or closed in accordance with the differential pressure between the compression chamber 216 and the intermediate passage 22. On the other hand, when the drive unit 33 is subjected to the pressure of a gas such as air or nitrogen, the suction valve unloader 32 forcibly keeps the suction valve 214 open, whereas the compression chamber 216 would normally be closed by the pressure difference between the compression chamber 216 and the intermediate flow path 22.

[0041] Furthermore, the drive unit 33 may be structured to use a spring for driving force and utilize the pressure of a gas such as air or nitrogen to release the spring force. By not applying gas pressure, the suction valve can be forcibly kept open, and by applying gas pressure, the opposite effect occurs, causing the suction valve to be in a free state.

[0042] The suction channel 21 is equipped with an upstream pressure sensor 45 for detecting the pressure of hydrogen gas within the suction channel 21. The upstream pressure sensor 45 is located in the suction channel 21 upstream of the connection point of the first spillback channel 18a. Alternatively, the upstream pressure sensor 45 may be located in the suction channel 21 downstream of the connection point of the first spillback channel 18a.

[0043] The intermediate flow path 22 is equipped with a pressure sensor 47 for detecting the pressure of hydrogen gas within the intermediate flow path 22. The pressure sensor 47 is located in the intermediate flow path 22 between the connection between the preceding compression stage 12 and the first spillback flow path 18a. The pressure sensor 47 only needs to be able to detect the pressure of hydrogen gas within the intermediate flow path 22, so it may also be located between the connection between the first spillback flow path 18a and the subsequent compression stage 14. Furthermore, the pressure sensor 47 may be located upstream of the first spillback valve 18b in the first spillback flow path 18a.

[0044] The upstream pressure sensor 45 and the pressure sensor 47 output signals indicating the detected pressure. 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. The functions of the control unit 50 performed by this computer include a first control unit 50a, which is a functional unit for performing first control, and a second control unit 50b, which is a functional unit for performing 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. Specifically, 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 P2 acquired by the pressure sensor 47 (intermediate pressure, which is the hydrogen gas pressure in the intermediate flow path 22) 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 explained with reference to Figure 4.

[0049] The crank mechanism 16 operates, causing the piston 212 to reciprocate within the cylinder section 211 in the preceding compression stage 12 and the succeeding compression stage 14. As a result, hydrogen gas from the intake passage 21 is drawn into the preceding compression stage 12, and hydrogen gas from the intermediate passage 22 is drawn into the succeeding compression stage 14, thereby compressing the hydrogen gas.

[0050] During the operation of the compression stages 12 and 14, the pressure information of the hydrogen gas drawn into the preceding compression stage 12 is acquired by the upstream pressure sensor 45 (step ST11). The control unit 50 then 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 suction channel 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 hydrogen gas pressure P1 in the suction channel 21 has changed to fall outside the reference range (if the answer is 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 obtained by the upstream pressure sensor 45, and if it determines that this pressure P1 has fallen below a predetermined reference range, it reduces the load of the subsequent compression stage 14 using the suction valve unloader 32 (for example, from 100% load to 50% load). This reduces the amount of hydrogen gas processed in the subsequent compression stage 14. On the other hand, if it determines that the obtained pressure P1 has risen above a predetermined reference range, it increases the load of the subsequent compression stage 14 using the suction valve unloader 32 (for example, 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 even before the first control is executed. Therefore, the control unit 50 receives pressure information acquired by the pressure sensor 47 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. When the suction valve unloader 32 is activated in the first control, the amount of hydrogen gas processed in the subsequent compression stage 14 changes. Accordingly, the pressure (intermediate pressure) P2 acquired by the pressure sensor 47 also changes. 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, if the suction valve unloader 32 is activated and the processing rate of the subsequent compression stage 14 decreases, the intermediate pressure P2 will try to rise accordingly. The second control unit 50b controls the first spillback valve 18b so that its opening degree increases by a predetermined amount. On the other hand, if the processing rate of the subsequent compression stage 14 increases, the intermediate pressure P2 will try to decrease accordingly. The second control unit 50b controls the first spillback valve 18b so that its opening degree decreases by a predetermined amount. As a result, pressure fluctuations of hydrogen gas in the intermediate flow path 22 due to pressure fluctuations of 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 unit 18 based on the intermediate pressure P2 in the pre-compression stage 12. Therefore, the compressor unit 10 that responds to pressure fluctuations of the suction gas can be configured without installing an adjustment means that operates with compressed gas in the pre-compression stage 12.

[0057] Generally, to adjust the capacity of a reciprocating compressor, an air-operated suction valve unloader is installed in the cylinder section of each compression stage. In some cases, a clearance pocket may also be added. In the case of a cylinder section that compresses in both the pushing and pulling strokes, the suction valve unloader allows for capacity adjustments of 100%, 50%, and 0%, and with the addition of a clearance pocket, further adjustments of 75% and 25% are possible. Following this general method, these capacity adjustment devices are installed in the cylinder sections of all compression stages in response to capacity adjustment requests from the liquid hydrogen storage tank. In the case of a multi-stage reciprocating compressor, typically, all the gas processed in the first compression stage is processed in the second compression stage, and then the gas processed in the second compression stage (after further processing if there are three or more subsequent stages) is sent entirely to the discharge channel. Therefore, if it is desired to reduce the amount of suction from the liquid hydrogen storage tank to the compressor unit, the amount of suction to the cylinder section of the first compression stage is reduced by the suction valve unloader, and similarly, the amount of suction for the second compression stage and subsequent stages is reduced accordingly by the suction valve unloader.

[0058] However, if a suction valve unloader operated by compressed air is provided in the cylinder section of the first compression stage, thermal treatment with cryogenic hydrogen gas from the liquid hydrogen storage tank is required. If proper thermal treatment is not performed, there is a risk that the system will not be able to adequately respond to pressure fluctuations in the liquid hydrogen storage tank.

[0059] In contrast, in the compressor unit 10 according to this embodiment, the processing amount in the preceding compression stage 12 is adjusted by the first spillback unit 18. Therefore, it is possible to respond to pressure fluctuations of the intake gas without providing a suction valve unloader that operates with compressed gas in the preceding compression stage 12. That is, instead of providing a drive unit that operates with compressed gas in the preceding compression stage 12, which compresses the boil-off gas of liquefied hydrogen, which is at an extremely low temperature, a first spillback unit 18 is provided. As a result, in combination with the adjustment of the processing amount by the adjustment means 31 in the subsequent compression stage 14, the compressor unit 10 can respond to pressure fluctuations of the intake gas. Furthermore, stable recovery of hydrogen gas becomes possible.

[0060] (Second Embodiment) In the second embodiment, as shown in Figure 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. Here, the same reference numerals are used for the same components as in the first embodiment, and their detailed descriptions are omitted.

[0061] The second spillback section 35 includes a second spillback passage 35a and a second spillback valve 35b, which is a valve with an adjustable opening that is located in the second spillback passage 35a. One end of the second spillback passage 35a is connected to the discharge passage 24, and the other end is connected to the intermediate passage 22. Therefore, when the second spillback valve 35b is opened, a portion of the hydrogen gas discharged from the subsequent compression stage 14 is returned to the intermediate passage 22. The second spillback valve 35b adjusts the amount of spillback in the second spillback passage 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 returning a portion of the hydrogen gas discharged from the subsequent compression stage 14 to the intermediate passage 22.

[0062] The suction valve unloader 32 adjusts the amount of hydrogen gas processed in the subsequent compression stage 14 by adjusting the flow rate of hydrogen gas drawn into the compression chamber 216. In this way, the amount of hydrogen gas processed in the subsequent compression stage 14 is adjusted in the compressor unit 10 by controlling the suction valve unloader 32 and the second spillback section 35.

[0063] When the compressor unit 10 is driven, in the first control, as shown in Figure 6, the first control unit 50a refers to the pressure P1 (hydrogen gas pressure in the suction passage 21) obtained by the upstream pressure sensor 45 (step ST11). If it is determined that the obtained pressure P1 has fallen 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 its opening degree increases by a predetermined amount.

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

[0066] Subsequently, if the opening of the second spillback valve 35b exceeds a threshold, the first control unit 50a performs the following operation as a first control. That is, the first control unit 50a reduces the load of the subsequent compression stage 14 using 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 its opening is minimized. This suppresses excessive compression operation in the subsequent compression stage 14.

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

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

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

[0070] Subsequently, if the opening of the second spillback valve 35b is at its minimum value and the load of the subsequent compression stage 14 is at 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 using the suction valve unloader 32 (for example, from 50% to 100% load). At the same time, the first control unit 50a controls the second spillback valve 35b so that its opening becomes a threshold value.

[0071] As described above, by performing the first and second controls, the compressor unit 10 can more precisely suppress the pressure fluctuations of the hydrogen gas in the intermediate flow path 22 that occur due to pressure fluctuations of the hydrogen gas from the liquid hydrogen storage tank 23.

[0072] In this embodiment, the adjustment means 31 includes a suction valve unloader 32 and a second spillback section 35, but the suction valve unloader 32 may be omitted. That is, the adjustment means 31 may consist only of the second spillback section 35. In this case, step ST23 will be omitted. The other configurations, operations, and effects will not be described here, but the description of the first embodiment can be applied to the second embodiment.

[0073] (Third embodiment) As shown in Figure 7, in the third embodiment, the adjustment means 31 is equipped with a stepless capacity adjustment device 37. The adjustment means 31 does not include a second spillback section 35. Here, the same reference numerals are used for components identical to those in the first and second embodiments, and their detailed descriptions are omitted.

[0074] The stepless capacity adjustment device 37 includes 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 at a speed faster than the time it takes for the piston 212 to reciprocate. In addition, the control unit 50 performs calculation processing to estimate the position of the piston 212 based on the signal sent from the detector 34b installed in the crank mechanism 16.

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

[0076] When the suction valve unloader 32b is activated, the valve plate of the suction valve 214 is kept open and does not function as a check valve. When the piston 212 is in the suction stroke while the unloader 32b is not activated, if the pressure in the compression chamber 216 falls below the pressure in the intermediate passage 22, which is the suction side passage, the suction valve 214 opens. As a result, gas is introduced into the compression chamber 216. Then, when the piston 212 is in the compression stroke, the pressure in the compression chamber 216 rises above the pressure in the intermediate passage 22, so 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 obtained by the upstream pressure sensor 45 and controls the drive device 33b that operates the suction valve unloader 32b if this pressure P1 falls outside a predetermined reference range or if this pressure P1 fluctuates to a value greater than or equal to a predetermined value.

[0078] When a fluctuation in pressure P1 is detected, the first control unit 50a controls the drive unit 33b so that the operating timing of the suction valve unloader 32b is adjusted in conjunction with the rotational movement of the crankshaft in the crank mechanism 16. Specifically, in the initial stages of the compression stroke, the first control unit 50a operates the suction valve unloader 32b to maintain the open state of the suction valve 214. This returns a portion of the gas in the compression chamber 216 to the intermediate flow path 22. Then, at some point during the compression stroke, the first control unit 50a controls the drive unit 33 so that the operation of the suction valve unloader 32b is released. As a result, the open state of the suction valve 214 is released, and the suction valve 214 closes. 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. During the next suction stroke, the first control unit 50a controls the drive unit 33b so that the suction valve unloader 32b operates again, and controls the drive unit 33b so that the open state is released after the compression stroke of the piston 212 begins. This operation and release of the suction valve unloader 32b is repeated in accordance with the reciprocating motion of the piston 212.

[0079] By releasing the suction valve unloader 32b earlier, the discharge volume increases, and by delaying its release, the discharge volume decreases. Therefore, the suction valve unloader 32b can perform the same function as the second spillback section 35. In other words, by adjusting the processing volume of the subsequent compression stage 14 in accordance with the pressure fluctuations in the intermediate flow path 22 caused by the first control, power consumption can be reduced even further.

[0080] The other configurations, functions, and effects will not be described here, but the descriptions 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 and not restrictive in all respects. The present invention is not limited to the embodiments described above, and various modifications and improvements are possible without departing from its spirit.

[0082] For example, in the first and third embodiments, if two or more subsequent compression stages 14 are provided, it is sufficient that at least one of the subsequent compression stages 14 is provided with a suction valve unloader 32, 32b.

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

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

[0085] In the above embodiment, if two or more pre-compression stages 12 are provided, the first spillback section 18 may be configured such that one end of the first spillback passage 18a is connected to the passage between adjacent pre-compression stages 12, and the other end is connected to the suction passage 21. Alternatively, 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 channel 22: Intermediate channel 23: Liquid hydrogen storage tank 26: Demand destination 29: Leak gas discharge 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 Unit 50a: First control unit 50b: Second control unit 211: Cylinder section 212: Piston 213: Piston rod 214: Suction valve 217: Rod packing

Claims

1. 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 it to a customer including at least one of an engine, power generation equipment, or boiler, One or more pre-compression stages that compress hydrogen gas flowing through an intake channel, which is hydrogen gas at a temperature below a reference temperature based on the liquefaction temperature of air, One or more subsequent compression stages that further compress hydrogen gas discharged from the preceding compression stage and having a temperature higher than the reference temperature, A crank mechanism that drives the preceding compression stage and the succeeding compression stage, A first spillback section includes a first spillback passage that returns the hydrogen gas discharged from the preceding compression stage back to the suction passage, and a first spillback valve that adjusts the amount of spillback in the first spillback passage. An adjustment means for adjusting the amount of hydrogen gas processed by the subsequent compression stage, A pressure sensor is positioned in the intermediate flow path between the preceding compression stage and the succeeding compression stage. An upstream pressure sensor is positioned in the aforementioned suction passage, A control unit that controls the first spillback valve and the adjustment means, respectively, Equipped with, The preceding compression stage and the subsequent compression stage are, respectively, Cylinder section and Piston and, A piston rod connecting the piston to the crank mechanism, A rod packing that seals the space between the piston rod and the cylinder portion, Equipped with, The aforementioned pre-compression stage is air-cooled and oil-free, and operates with compressed gas and does not have an adjustment means for adjusting the amount of hydrogen gas processed. The control unit, A first control unit that performs first control to control the adjustment means so that the processing amount of the subsequent compression stage is adjusted based on the pressure obtained by the upstream pressure sensor, A second control unit performs a second control that controls the first spillback valve before, during, or simultaneously with, the first control, by referring to the intermediate pressure obtained by the pressure sensor, so that the intermediate pressure falls within a predetermined pressure range. A compressor unit, which is a single piece of equipment including the compressor.

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

3. The adjustment means, In at least one subsequent compression stage, a suction valve unloader is mounted on the cylinder portion of the subsequent compression stage, The compressor unit according to claim 1 or 2, wherein in the first control, the control unit adjusts the processing amount of the cylinder section by controlling the suction valve unloader based on the pressure obtained by the upstream pressure sensor.

4. The adjustment means, In at least one subsequent compression stage, A second spillback section includes a second spillback passage that returns hydrogen gas flowing on the discharge side of the subsequent compression stage back to the suction side of the subsequent compression stage, and a second spillback valve that adjusts the amount of spillback in the second spillback passage. A suction valve unloader attached to the cylinder section 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 processing amount of the cylinder section by controlling the second spillback valve and the suction valve unloader based on the pressure obtained by the upstream pressure sensor.

5. The adjustment means, In at least one subsequent compression stage, A suction valve unloader is mounted on the cylinder portion of the subsequent compression stage, A hydraulic or electric drive device for opening and closing the aforementioned suction valve unloader, It is equipped with a stepless capacity adjustment device having The control unit drives the drive device so that the operating timing of the suction valve unloader is adjusted in conjunction with the rotational movement of the 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 obtained by the upstream pressure sensor and adjusts the processing amount of the subsequent compression stage.

6. A control method for 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 it to a customer including at least one of an engine, power generation equipment, or boiler, The aforementioned compressor unit is One or more pre-compression stages that compress hydrogen gas flowing through an intake channel, which is hydrogen gas at a temperature below a reference temperature based on the liquefaction temperature of air, One or more subsequent compression stages that further compress hydrogen gas discharged from the preceding compression stage and having a temperature higher than the reference temperature, A crank mechanism that drives the preceding compression stage and the succeeding compression stage, A first spillback section includes a first spillback passage that returns the hydrogen gas discharged from the preceding compression stage back to the suction passage, and a first spillback valve that adjusts the amount of spillback in the first spillback passage. An adjustment means for adjusting the amount of hydrogen gas processed by the subsequent compression stage, A pressure sensor is positioned in the intermediate flow path between the preceding compression stage and the succeeding compression stage. The system includes an upstream pressure sensor positioned in the aforementioned suction passage, The preceding compression stage and the subsequent compression stage are, respectively, Cylinder section and Piston and, A piston rod connecting the piston to the crank mechanism, A rod packing that seals the space between the piston rod and the cylinder portion, Equipped with, The aforementioned pre-compression stage is air-cooled and oil-free, and operates with compressed gas and does not have an adjustment means for adjusting the amount of hydrogen gas processed. The control method for the compressor unit is as follows: The upstream pressure sensor obtains the pressure of the hydrogen gas flowing through the suction channel. The pressure sensor obtains the pressure of the hydrogen gas flowing through the intermediate channel. Based on the pressure obtained by the upstream pressure sensor, a first control is performed to control the adjustment means so that the processing amount of the subsequent compression stage is adjusted. Referencing the intermediate pressure obtained by the pressure sensor, a second control is performed to control the first spillback valve before, during, or simultaneously with, the first control, such that the intermediate pressure falls within a predetermined pressure range. The first control and the second control are performed by a control unit which is a single device. Control method for the compressor unit.

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