Compressor unit and method for controlling compressor unit

Abstract

This compressor unit includes: a first spill-back part for returning hydrogen gas discharged from a first compression stage to an intake passage; an adjustment means for adjusting the amount of treatment performed on the hydrogen gas in a subsequent compression stage; a pressure sensor; an upstream-side pressure sensor; and a control unit. The control unit can execute: first control for controlling the adjustment means so that the amount of treatment in the subsequent compression stage is adjusted on the basis of the pressure acquired by the upstream-side pressure sensor; and second control for controlling a first spill-back valve so that an intermediate pressure acquired by the pressure sensor is within a predetermined pressure range.

Description

Compressor unit and control method for compressor unit

[0001] The present invention relates to a reciprocating compressor unit and a method for controlling the compressor unit.

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

[0003] One of the main roles of this boil-off gas compressor is to maintain a constant internal pressure in the liquefied gas storage tank. That is, the compressor is operated so that it starts (or increases the compressor's throughput) when the internal pressure of the storage tank rises, and stops (or decreases the compressor's throughput) when the internal pressure drops.

[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 clearance pocket for changing the processing amount is often installed.

[0005] On the other hand, particularly in the case of a storage tank for storing liquid hydrogen (LH2), the boil-off gas generated from the storage tank is at an extremely 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 even to the throughput control device.

[0006] In addition, because the intake gas temperature of the first compression stage is close to absolute zero, even a slight increase in temperature causes a large volume expansion. For this reason, when a reciprocating compressor, which is a positive displacement compressor, sucks in boil-off gas, it operates under conditions where the throughput fluctuates greatly.

[0007] Incidentally, the following description is found in Patent Document 1: "The rod drive unit 48 of the unloader 38 provided in the suction valve 36 is disposed on the outer peripheral surface side of the housing 17. With 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. With 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."

[0008] That is, since the rod drive unit of the unloader provided in the intake valve into which the cryogenic 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 boil-off gas taken into the compression section cannot be appropriately adjusted.

[0009] Furthermore, 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 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 liquefaction of the air on the outer surface of the device. However, this configuration requires special measures to prevent cold heat from entering the air drive unit of the capacity adjustment device such as an unloader, making the structure complicated. Furthermore, maintenance is also complicated.

[0010] Japanese Patent Application Laid-Open No. 2020-172870

[0011] An object of the present invention is to enable a reciprocating compressor unit that compresses boil-off gas of liquefied hydrogen, which is at a very low temperature, to respond to pressure fluctuations of gas suctioned into a previous compression stage without providing an adjustment means in the previous compression stage that operates using compressed gas.

[0012] a first spillback section including a first spillback valve that adjusts the amount of spillback in the first spillback section; a pressure sensor disposed in an intermediate flow path between the upstream compression stage and the downstream compression stage; an upstream pressure sensor disposed in the upstream flow path; and a control section that controls the first spillback valve and the adjustment section. The upstream compression stage and the downstream compression stage each include a cylinder, a piston, a piston rod connecting the piston to the crank mechanism, and a rod packing sealing between the piston rod and the cylinder. The upstream compression stage is air-cooled and oil-free. The control unit is configured to execute a first control that controls the adjustment means to adjust the throughput of the downstream compression stage based on the pressure acquired by the upstream pressure sensor, and a second control that controls 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] According to one aspect of the present invention, there is provided a control method for a reciprocating compressor unit that recovers hydrogen gas (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 upstream compression stages that compress hydrogen gas flowing through an intake passage at a predetermined temperature below 0°C, one or more downstream compression stages that further compress the hydrogen gas discharged from the upstream compression stage, a crank mechanism that drives the upstream compression stage and the downstream compression stage, a first spillback flow path that returns the hydrogen gas discharged from the upstream compression stage to the intake passage and a first spillback unit including a first spillback valve that adjusts the amount of spillback in the first spillback flow path, adjustment means for adjusting the amount of hydrogen gas processed by the downstream compression stage, a pressure sensor disposed in an intermediate flow path between the upstream compression stage and the downstream compression stage, and an upstream pressure sensor disposed in the intake passage. The upstream compression stage and the subsequent compression stage each include a cylinder portion, a piston, a piston rod connecting the piston to the crank mechanism, and a rod packing that seals between the piston rod and the cylinder portion. The upstream 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 using the upstream pressure sensor; acquiring a pressure of hydrogen gas flowing through the intermediate passage using the pressure sensor; performing a first control that controls the adjustment means so that a throughput of the subsequent compression stage is adjusted based on the pressure acquired by the upstream pressure sensor; and performing a second control that refers to an intermediate pressure acquired by the pressure sensor and controls the first spillback valve before, after, or simultaneously with the first control so that the intermediate pressure is within a predetermined pressure range.

[0014] FIG. 1 is a diagram schematically showing a compressor unit according to a first embodiment; FIG. 2 is a diagram schematically showing a front compression stage in the compressor unit; FIG. 3 is a diagram schematically showing a rear compression stage in the compressor unit; FIG. 4 is a diagram for explaining the operation of the compressor unit; FIG. 5 is a diagram schematically showing a compressor unit according to a second embodiment; FIG. 6 is a diagram for explaining the operation of the compressor unit; and FIG. 7 is a diagram schematically showing a compressor unit according to a third embodiment.

[0015] Hereinafter, embodiments will be described with reference to the accompanying drawings. Note that the following embodiments are examples of specific embodiments of the present invention and are not intended to limit the technical scope of the present invention.

[0016] (First embodiment) The compressor unit according to this embodiment is configured to recover hydrogen gas, which is boil-off gas, from a liquid hydrogen storage tank, compress the recovered hydrogen gas, and supply it to a consumer. The boil-off gas, which is hydrogen gas, has a temperature of approximately -253°C.

[0017] 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 rear compression stage 14 that is 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 rear compression stage 14.

[0018] The pre-compression stage 12 is connected to a liquid hydrogen storage tank 23 via an intake passage 21. Therefore, boil-off gas of the liquefied gas generated in the liquid hydrogen storage tank 23 is drawn into the pre-compression stage 12 through the intake passage 21. That is, hydrogen gas at a predetermined temperature or below, i.e., hydrogen gas at a temperature below a reference temperature based on the liquefaction temperature of air, is introduced into the pre-compression stage 12 through the intake passage 21. Note that this "temperature below the reference temperature" may be, for example, -180°C or below.

[0019] 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 portion 211, a piston 212 arranged in the cylinder portion 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 portion 211, compression chambers 216 are 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.

[0020] A rod packing 217 is provided in the rear head 211b of the cylinder section 211 to prevent leakage of hydrogen gas from the compression chamber 216. The rod packing 217 is configured to seal the gap between the piston rod 213 and the cylinder section 211, and includes a packing ring 217a arranged to surround the piston rod 213, and a case 217b that holds the packing ring 217a.

[0021] The piston 212 is connected to the crank mechanism 16 via a piston rod 213. The reciprocating movement of the piston 212 within the cylinder portion 211 compresses the hydrogen gas within a compression chamber 216. While the front compression stage 12 has a double-acting structure in FIG. 2, the front compression stage 12 may have a single-acting structure in which the compression chamber 216 is located only on the front head side or the rear head side.

[0022] 1, for convenience, the front-stage compression stage 12 is shown as a single trapezoid, but the front-stage compression stage 12 may have a plurality of cylinder sections 211. In other words, the front-stage 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-stage compression stage 12 may also be configured as a plurality of stages.

[0023] The subsequent compression stage 14 is a compression mechanism for further compressing the hydrogen gas discharged from the preceding compression stage 12. That is, hydrogen gas having a temperature higher than a predetermined temperature, i.e., 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.

[0024] The hydrogen gas compressed by the subsequent compression stage 14 is discharged to a discharge flow path 24. The hydrogen gas flowing through the discharge flow path 24 is sent to a consumer 26 directly or indirectly via other equipment. The consumer 26 may include a power generation facility, a boiler, an engine of a ship, etc., but may also include equipment that releases gas into the atmosphere, such as a flare facility or a vent.

[0025] 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.

[0026] 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 multiple cylinder portions 211. The same applies to other embodiments. In the subsequent compression stage 14, the compression stage that discharges room temperature hydrogen gas may be either oil-free or lubricated.

[0027] 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 previous 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, which is an adjustable valve disposed in the first spillback passage 18a. The first spillback passage 18a has one end connected to the intermediate passage 22 and the other end connected to the suction passage 21. In other words, the hydrogen gas that flows through the first spillback passage 18a merges with hydrogen gas from the liquid hydrogen storage tank 23 in the suction passage 21. The first spillback valve 18b adjusts the amount of spillback in the first spillback passage 18a.

[0028] The compressor unit 10 includes an adjusting means 31 for adjusting the amount of hydrogen gas processed by the subsequent compression stage 14. The adjusting means 31 is provided in at least one subsequent compression stage 14. The adjusting 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 adjusting means 31 includes an intake valve unloader 32 and a drive device 33.

[0029] 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 activated, the valve plate of the suction valve 214 is maintained in an open state, preventing it from functioning as a check valve (unloaded state). When the piston 212 is in the suction stroke with the unloader 32 not activated (loaded state), the pressure in the compression chamber 216 drops below the pressure in the intermediate flow path 22, causing the suction valve 214 to open. This allows hydrogen gas to be introduced from the intermediate flow path 22 into the compression chamber 216. When the piston 212 is in the compression stroke, the pressure in the compression chamber 216 rises above the pressure in the intermediate flow path 22, causing the suction valve 214 to close.

[0030] The intake 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 intake valve unloader 32 is operating is called 100% load, and a state in which either one is operating is called 50% load.

[0031] 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 opens and closes relative to the intermediate flow path 22 depending on the pressure difference between the compression chamber 216 and the intermediate flow path 22 (loaded state), or in a state in which the compression chamber 216 and the intermediate flow path 22 are maintained open (unloaded state). For example, by not applying gas pressure 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 open and close depending on the pressure difference between the compression chamber 216 and the intermediate flow path 22. On the other hand, when gas pressure such as air or nitrogen is applied to the drive device 33, the suction valve unloader 32 forcibly maintains the suction valve 214 in an open state, even though the compression chamber 216 would normally be closed due to the pressure difference between the compression chamber 216 and the intermediate flow path 22.

[0032] Alternatively, the drive unit 33 may be configured to use a spring for driving force and utilize gas pressure, such as air or nitrogen, to release the spring force. In this configuration, the intake valve can be forcibly maintained in an open state by not applying gas pressure to the drive unit 33. On the other hand, applying gas pressure to the drive unit 33 can cause the intake valve to be in the opposite state to be free.

[0033] 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 with 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 with the first spillback passage 18a.

[0034] The intermediate flow path 22 is provided with a pressure sensor 47 that detects the pressure of hydrogen gas in the intermediate flow path 22. The pressure sensor 47 is located in the intermediate flow path 22 between the connection portion of the previous compression stage 12 and the first spillback flow path 18a. Note that the pressure sensor 47 only needs to be able to detect the pressure of hydrogen gas in the intermediate flow path 22, so it may be located between the connection portion of the first spillback flow path 18a and the subsequent compression stage 14. The pressure sensor 47 may also be provided in the first spillback flow path 18a at a location upstream of the first spillback valve 18b.

[0035] 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.

[0036] 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.

[0037] In the first control, the adjusting 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 P1 acquired by the upstream pressure sensor 45 (the hydrogen gas pressure in the suction flow path 21), and controls the drive device 33 of the suction valve unloader 32 based on this pressure P1.

[0038] 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 (the 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.

[0039] Here, the operation of the compressor unit 10 according to this embodiment will be described with reference to FIG.

[0040] Operation of the crank mechanism 16 causes the piston 212 to reciprocate within the cylinder portion 211 in the front compression stage 12 and the rear compression stage 14. As a result, in the front compression stage 12, hydrogen gas in the intake passage 21 is sucked into the front compression stage 12, and in the rear compression stage 14, hydrogen gas in the intermediate passage 22 is sucked into the rear compression stage 14, thereby compressing the hydrogen gas.

[0041] During operation of the compression stages 12, 14, pressure information of the hydrogen gas sucked into the first 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 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.

[0042] On the other hand, if it is determined that the detected pressure P1 of hydrogen gas in the intake 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).

[0043] Specifically, the first control unit 50a references the pressure P1 acquired by the upstream pressure sensor 45, and if it determines 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, if it determines 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.

[0044] 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 during and after the first control is executed.

[0045] 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 operates in the first control, 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 fluctuates accordingly. When the intermediate pressure P2 fluctuates, the second control unit 50b changes the opening degree of the first spillback valve 18b accordingly.

[0046] For example, if the suction valve unloader 32 is activated and the throughput of the subsequent compression stage 14 decreases, the intermediate pressure P2 tends to increase accordingly. In this case, the second control unit 50b controls the first spillback valve 18b so that the opening degree of the first spillback valve 18b increases by a predetermined amount. On the other hand, if the throughput of the subsequent compression stage 14 increases, the intermediate pressure P2 tends to decrease accordingly. In this case, the second control unit 50b controls the first spillback valve 18b so that the opening degree of the first spillback valve 18b decreases by a predetermined amount. As a result, pressure fluctuations of hydrogen gas in the intermediate flow path 22 caused by pressure fluctuations of hydrogen gas from the liquid hydrogen storage tank 23 can be suppressed. In addition, excessive compression operation in the subsequent compression stage 14 can also be suppressed.

[0047] 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 pre-compression stage 12. Therefore, the compressor unit 10 can be configured to respond to pressure fluctuations of the intake gas without providing an adjustment means that operates on compressed gas in the pre-compression stage 12.

[0048] Generally, to adjust the capacity of a reciprocating compressor, a pneumatically operated suction valve unloader is provided in the cylinder of each compression stage. A clearance pocket may also be added. In a typical cylinder that compresses both the push stroke and the pull stroke, the suction valve unloader allows for capacity adjustment of 100%, 50%, or 0%, and adding a clearance pocket further enables capacity adjustment of 75% or 25%. Following this general approach, these capacity adjustment devices are installed in the cylinder of all compression stages in response to the capacity adjustment request from the liquid hydrogen storage tank. In a multi-stage reciprocating compressor, typically, all of the gas processed in the first compression stage is processed in the second compression stage, and the gas processed in the second compression stage (or, if there are three or more subsequent stages, after further processing) is sent to the discharge flow path. 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 into the cylinder section of the first compression stage is reduced by the suction valve unloader, and similarly, the amount of suction in the second compression stage and thereafter is reduced accordingly by the suction valve unloader.

[0049] However, if 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 a liquid hydrogen storage tank is required. If appropriate thermal treatment is not performed, there is a risk that the system will not be able to properly respond to pressure fluctuations in the liquid hydrogen storage tank.

[0050] In contrast, in the compressor unit 10 according to this embodiment, the adjustment of the throughput in the upstream compression stage 12 is performed by the first spillback section 18, so that pressure fluctuations of the intake gas can be accommodated without providing an intake valve unloader operated by compressed gas in the upstream compression stage 12. That is, the upstream compression stage 12, which compresses the boil-off gas of cryogenic liquefied hydrogen, is not provided with a drive unit operated by compressed gas, but is provided with the first spillback section 18 that adjusts the spillback amount of gas discharged from the upstream compression stage 12. 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 accommodate pressure fluctuations of the intake gas. Furthermore, stable recovery of hydrogen gas is possible.

[0051] Second Embodiment In a second embodiment, as shown in Fig. 5, a second spillback portion 35 is added to the adjusting means 31. That is, the adjusting means 31 includes a suction valve unloader 32 and the second spillback portion 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.

[0052] The second spillback unit 35 has a second spillback flow path 35a and a second spillback valve 35b, which is an adjustable valve disposed in the second spillback flow path 35a. The second spillback flow path 35a has one end connected to the discharge flow path 24 and the other end connected to the intermediate flow path 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 flow path 22. The second spillback valve 35b adjusts the amount of spillback in the second spillback flow path 35a. The second spillback unit 35 performs a process of returning a portion of the hydrogen gas discharged from the subsequent compression stage 14 to the intermediate flow path 22. This adjusts the flow rate of hydrogen gas sent from the subsequent compression stage 14 to the demand destination 26.

[0053] 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 way, 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.

[0054] 6, during the first control, the first control unit 50a refers to the pressure P1 (the 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, which includes control of the suction valve unloader 32, and the second control are performed (step ST14).

[0055] In the first control, the second spillback valve 35b is controlled so that the opening degree of the second spillback valve 35b increases by a predetermined opening degree.

[0056] 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 occurs when the opening degree of the second spillback valve 35b is increased.

[0057] Thereafter, if 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 using the suction valve unloader 32 (e.g., from 100% load to 50% load). This reduces the amount of hydrogen gas processed in the subsequent compression stage 14. 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 suppresses excessive compression in the subsequent compression stage 14.

[0058] 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).

[0059] In the first control, the second spillback valve 35b is controlled so that the opening degree of the second spillback valve 35b is reduced to a predetermined opening degree.

[0060] In the second control, the second control unit 50b controls the first spillback valve 18b so that the opening degree is reduced by a predetermined amount based on the pressure (intermediate pressure) P2 measured by the pressure sensor 47. This suppresses a decrease in the pressure of the hydrogen gas in the intermediate flow path 22 that occurs when the opening degree of the second spillback valve 35b is reduced.

[0061] Thereafter, when the opening degree of the second spillback valve 35b is at its 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 using the suction valve unloader 32 (e.g., from 50% to 100% load). This increases the amount of hydrogen gas processed in the subsequent compression stage 14. 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.

[0062] As described above, by performing the first control and the second control, the compressor unit 10 can more precisely suppress pressure fluctuations of the hydrogen gas in the intermediate flow path 22 that are caused by pressure fluctuations of the hydrogen gas from the liquid hydrogen storage tank 23.

[0063] 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 configured only by the second spillback portion 35. In this case, the step of controlling the suction valve unloader 32 is omitted. Although a description of the other configurations, actions, and effects will be omitted, the description of the first embodiment can be applied to the second embodiment.

[0064] 7, in the third embodiment, the adjusting means 31 includes a stepless capacity adjusting device 37. The adjusting means 31 does not include the second spillback 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.

[0065] The stepless capacity adjuster 37 has an intake valve unloader 32b, a hydraulic or electric drive unit 33b, and a detector 34b that detects the rotation of the crankshaft in the crank mechanism 16. The intake valve unloader 32b is driven by the hydraulic or electric drive unit 33b, and can maintain or release the open state of the valve plate of the intake valve 214 faster than the time it takes for the piston 212 to reciprocate. In addition, the control unit 50 performs calculations to estimate the position of the piston 212 based on a signal sent from the detector 34b installed in the crank mechanism 16.

[0066] The intake 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 path 22, which is the flow path on the intake side, and a valve body that houses the valve plate. Similar to a check valve, the intake 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.

[0067] When the suction valve unloader 32b is activated, the valve plate of the suction valve 214 is maintained in an open state, and the suction valve 214 does not function as a check valve. When the piston 212 is on its suction stroke with the unloader 32b not activated, if the pressure in the compression chamber 216 drops below the pressure in the intermediate flow path 22, which is the suction-side passage, the suction valve 214 opens. This allows gas to be introduced into the compression chamber 216. When the piston 212 is on its compression stroke, the pressure in the compression chamber 216 rises above the pressure in the intermediate flow path 22, and the suction valve 214 closes.

[0068] 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 this pressure P1 falls outside a predetermined standard range or when this pressure P1 fluctuates by more than a predetermined value.

[0069] When a fluctuation in pressure P1 is detected, the first control unit 50a controls the drive device 33b to adjust the operation timing of the intake valve unloader 32b in conjunction with the rotational movement 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. This causes a portion of the gas in the compression chamber 216 to return to the intermediate flow path 22. Then, midway through the compression stroke, the first control unit 50a controls the drive device 33 to deactivate the intake valve unloader 32b. This releases the open state of the intake valve 214, causing the intake valve 214 to close. The gas remaining in the compression chamber 216 at this time 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 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 activation and release of the suction valve unloader 32b is repeated in accordance with the reciprocating motion of the piston 212.

[0070] If the timing of releasing the suction valve unloader 32b is advanced, the amount of refrigerant delivered to the discharge flow path 24 increases, and if the timing is delayed, the amount of refrigerant delivered to the discharge flow path 24 decreases, so that the suction valve unloader 32b can perform the same function as the second spillback section 35. In other words, the throughput of the subsequent compression stage 14 can be adjusted in accordance with the pressure fluctuations in the intermediate flow path 22 caused by the first control, thereby further reducing power consumption.

[0071] Although the description of other configurations, actions, and effects will be omitted, the descriptions of the first and second embodiments can be applied to the third embodiment.

[0072] (Other Embodiments) It should be noted that the embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The present invention is not limited to the above-described embodiments, and various modifications and improvements are possible without departing from the spirit and scope of the present invention.

[0073] For example, in the first and third embodiments, 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 intake valve unloader 32, 32b.

[0074] In the first embodiment, a clearance pocket may be provided as the adjusting means 31 instead of the suction valve unloader 32 .

[0075] 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 portion 35. Furthermore, the second spillback portion 35 may be configured such that the second spillback flow path 35a spans multiple subsequent compression stages 14.

[0076] In the above embodiment, when two or more previous compression stages 12 are provided, the first spillback section 18 may be configured so that one end of the first spillback flow path 18a is connected to a flow path between adjacent previous compression stages 12, and the other end is connected to the suction flow path 21. Furthermore, two or more first spillback sections 18 may be provided.

[0077] Here, the above embodiment will be outlined.

[0078] (1) The compressor unit according to the above embodiment 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 the recovered hydrogen gas to a demand destination including at least one of an engine, a power generation facility, or a boiler. The compressor unit includes one or more upstream compression stages that compress hydrogen gas that is at a predetermined temperature below 0°C and flows through an intake passage; one or more downstream compression stages that further compress the hydrogen gas discharged from the upstream compression stage; a crank mechanism that drives the upstream compression stage and the downstream compression stage; a first spillback flow path that returns the hydrogen gas discharged from the upstream compression stage to the intake passage, and a first spillback unit that includes a first spillback valve that adjusts the amount of spillback in the first spillback flow path; adjustment means that adjusts the amount of hydrogen gas processed by the downstream compression stage; a pressure sensor that is arranged in an intermediate flow path between the upstream compression stage and the downstream 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. The upstream compression stage and the downstream compression stage each include a cylinder, a piston, a piston rod connecting the piston to the crank mechanism, and a rod packing sealing between the piston rod and the cylinder. The upstream compression stage is air-cooled and oil-free. The control unit is configured to execute a first control that controls the adjustment means to adjust the throughput of the downstream compression stage based on the pressure acquired by the upstream pressure sensor, and a second control that controls 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.

[0079] In the compressor unit, the spillback amount is adjusted by the first spillback section in the upstream compression stage based on the intermediate pressure. Therefore, a compressor unit that can accommodate pressure fluctuations of the intake gas can be configured without installing an adjustment device operated by compressed gas in the upstream compression stage. That is, since the upstream compression stage that compresses the cryogenic liquefied hydrogen boil-off gas does not have a drive device operated by compressed gas but has a first spillback section, this compressor unit can accommodate pressure fluctuations of the intake gas, in combination with adjustment of the gas throughput by the adjustment device in the subsequent compression stage. That is, the gas throughput in the subsequent compression stage is adjusted based on the pressure acquired by the upstream pressure sensor, and the spillback amount is adjusted by the first spillback section based on the intermediate pressure, which can fluctuate due to adjustment of the gas throughput in the subsequent compression stage. Therefore, a compressor unit that can accommodate pressure fluctuations of the intake gas can be configured.

[0080] (2) At least one of the one or more subsequent compression stages may have a leak gas discharge portion that returns leak gas from the rod packing to the suction passage. In this aspect, the leak gas can be recovered.

[0081] (3) The adjusting means may include an intake valve unloader attached to a cylinder portion of at least one of the one or more subsequent compression stages. In this case, in the first control, the control unit may be configured to control the intake valve unloader based on the pressure acquired by the upstream pressure sensor so as to adjust the throughput of the cylinder portion.

[0082] In this embodiment, it is possible to further reduce the power required to compress the gas.

[0083] (4) The adjusting means may include, in at least one of the one or more subsequent compression stages, a second spillback section including a second spillback flow path that returns hydrogen gas flowing through a discharge side of the subsequent compression stage to a suction side of the subsequent compression stage, and a second spillback valve that adjusts 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 unit may be configured to control the second spillback valve and the suction valve unloader based on the pressure acquired by the upstream pressure sensor so as to adjust the throughput of the cylinder section.

[0084] In this embodiment, it is possible to further reduce the power required to compress the gas.

[0085] (5) The adjusting means may include a stepless capacity adjusting device in at least one of the one or more subsequent compression stages, the stepless capacity adjusting device having 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 movement of a crankshaft in the crank mechanism. In the first control, the control unit may be configured to control the drive device based on the pressure acquired by the upstream pressure sensor so that the throughput of the subsequent compression stage is adjusted.

[0086] In this embodiment, the operation timing and operation time of the intake valve unloader are controlled to return a portion of the hydrogen gas in the cylinder to the intake side, thereby reducing the gas throughput in the subsequent compression stage and thereby further reducing power consumption.

[0087] (6) A control method for a compressor unit according to the above embodiment is a control method for 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 the recovered hydrogen gas to a demand destination including at least one of an engine, a power generation facility, or a boiler. The compressor unit includes one or more upstream compression stages that compress hydrogen gas at a predetermined temperature below 0°C and flowing through an intake passage, one or more downstream compression stages that further compress the hydrogen gas discharged from the upstream compression stage, a crank mechanism that drives the upstream compression stage and the downstream compression stage, a first spillback flow path that returns the hydrogen gas discharged from the upstream compression stage to the intake passage and a first spillback unit that includes a first spillback valve that adjusts the amount of spillback in the first spillback flow path, adjustment means for adjusting the amount of hydrogen gas processed by the downstream compression stage, a pressure sensor disposed in an intermediate flow path between the upstream compression stage and the downstream compression stage, and an upstream pressure sensor disposed in the intake passage. The upstream compression stage and the subsequent compression stage each include a cylinder portion, a piston, a piston rod connecting the piston to the crank mechanism, and a rod packing that seals between the piston rod and the cylinder portion. The upstream 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 using the upstream pressure sensor; acquiring a pressure of hydrogen gas flowing through the intermediate passage using the pressure sensor; performing a first control that controls the adjustment means so that a throughput of the subsequent compression stage is adjusted based on the pressure acquired by the upstream pressure sensor; and performing a second control that refers to an intermediate pressure acquired by the pressure sensor and controls the first spillback valve before, after, or simultaneously with the first control so that the intermediate pressure is within a predetermined pressure range.

[0088] As described above, 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 in the gas suctioned into the preceding compression stage without providing an adjustment means that operates using compressed gas in the preceding compression stage.

[0089] This application is based on Japanese Patent Application No. 2023-138329 filed with the Japan Patent Office on August 28, 2023, the contents of which are incorporated herein by reference.

Claims

1. A reciprocating compressor unit which 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, comprising: one or more front compression stages which compress hydrogen gas at a predetermined temperature below 0°C and flowing through an intake passage; one or more rear compression stages which further compress the hydrogen gas discharged from the front compression stage; a crank mechanism which drives the front compression stage and the rear compression stage; a first spillback section which includes a first spillback passage which returns hydrogen gas discharged from the front compression stage to the intake passage and a first spillback valve which adjusts the amount of spillback in the first spillback passage; adjustment means which adjusts the amount of hydrogen gas processed by the rear compression stage; a pressure sensor which is disposed in an intermediate passage between the front compression stage and the rear compression stage; an upstream pressure sensor which is disposed in the intake passage; and a control section which controls the first spillback valve and the adjustment means, the upstream compression stage and the subsequent compression stage each include a cylinder portion, a piston, a piston rod connecting the piston to the crank mechanism, and a rod packing that seals between the piston rod and the cylinder portion, the upstream compression stage being air-cooled and oil-free, and the control unit being configured to be able to execute a first control that controls the adjustment means so that a throughput of the subsequent compression stage is adjusted based on a pressure acquired by the upstream pressure sensor, and a second control that refers to an intermediate pressure acquired by the pressure sensor and controls the first spillback valve before, after, or simultaneously with the first control so that the intermediate pressure is within a predetermined pressure range.

2. The compressor unit according to claim 1, wherein at least one of said one or more subsequent compression stages has a leakage gas discharge portion that returns leakage gas from said rod packing to said suction passage.

3. A compressor unit as described in claim 1 or 2, wherein the adjustment means comprises an intake valve unloader attached to a cylinder section of at least one of the one or more subsequent compression stages, and in the first control, the control section is configured to control the intake valve unloader based on the pressure acquired by the upstream pressure sensor so that the processing volume of the cylinder section is adjusted.

4. A compressor unit as described in claim 1 or 2, wherein the adjustment means comprises: a second spillback section, in at least one of the one or more subsequent compression stages, 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; and a suction valve unloader attached to the cylinder section of the subsequent compression stage, and wherein in the first control, the control section is configured to control the second spillback valve and the suction valve unloader based on the pressure obtained by the upstream pressure sensor so that the processing volume of the cylinder section is adjusted.

5. A compressor unit as described in claim 1 or 2, wherein the adjustment means comprises a stepless capacity adjustment device having, in at least one of the one or more subsequent compression stages, a suction valve unloader attached to a cylinder portion of the subsequent compression stage, and a hydraulic or electric drive unit for opening and closing the suction valve unloader, and the control unit drives the drive unit 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 is configured to control the drive unit based on the pressure obtained by the upstream pressure sensor in the first control so that the processing volume of the subsequent compression stage is adjusted.

6. A control method for a reciprocating compressor unit which recovers hydrogen gas, which is 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, or a boiler, the compressor unit comprising: one or more upstream compression stages which compress hydrogen gas at a predetermined temperature below 0°C and flowing through an intake passage; one or more subsequent compression stages which further compress the hydrogen gas discharged from the upstream compression stage; a crank mechanism which drives the upstream compression stage and the subsequent compression stage; a first spillback section including a first spillback flow passage which returns hydrogen gas discharged from the upstream compression stage to the intake passage and a first spillback valve which adjusts the amount of spillback in the first spillback flow passage; adjustment means for adjusting the amount of hydrogen gas processed by the subsequent compression stage; a pressure sensor disposed in an intermediate flow passage between the upstream compression stage and the subsequent compression stage; and an upstream pressure sensor disposed in the intake passage, the upstream compression stage and the subsequent compression stage each comprising: a cylinder portion, a piston, a piston rod connecting the piston to the crank mechanism, and a rod packing that seals between the piston rod and the cylinder portion, wherein the previous compression stage is air-cooled and oil-free, and the control method for the compressor unit comprises: 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 subsequent 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, by referring to an intermediate pressure acquired by the pressure sensor, so that the intermediate pressure falls within a predetermined pressure range.

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