Compressor unit

Abstract

This compressor unit (10) is used for compressing hydrogen gas generated by means of a water electrolysis system (25). The compressor unit (10) comprises: a screw compressor (12) configured to suck in moisture-containing hydrogen gas generated from the water electrolysis system (25); a dryer (14) disposed downstream from the screw compressor (12) and configured to dry the hydrogen gas; and a reciprocating compressor (16) configured to further compress the hydrogen flowing out from the dryer (14).

Description

Compressor Unit

[0001] The present invention relates to a compressor unit for compressing hydrogen gas.

[0002] In recent years, with environmental considerations in mind, hydrogen has been considered for use as a fuel for power generation and automobiles, etc., leading to an increasing demand for hydrogen. A compressor unit for compressing hydrogen gas is disclosed, for example, in Patent Document 1 below. Patent Document 1 discloses that a stable discharge pressure of compressed hydrogen gas generated by water electrolysis is achieved at the outlet of a multi-stage compression system. This multi-stage compression system achieves this by using a reciprocating compressor as the second section, which is the latter stage. Meanwhile, a centrifugal compressor is used in the first section, which is the former stage. As described in paragraph 0064 of Patent Document 1, centrifugal compressors are used because they can compress large amounts of hydrogen gas at lower cost than reciprocating compressors. However, as described in paragraph 0019 of Patent Document 1, centrifugal compressors cannot generate sufficient centrifugal force for low-molecular-weight gases such as hydrogen. For this reason, centrifugal compressors are not suitable for compressing low-molecular-weight gases. Despite this, the invention disclosed in Patent Document 1 uses a centrifugal compressor in the first section, which is the former stage, as explained in paragraph 0065. This is because the hydrogen gas produced by the electrolysis of water is saturated with water vapor, and its apparent molecular weight is much larger than that of dry hydrogen gas.

[0003] Although centrifugal compressors are not suitable for compressing low-molecular-weight hydrogen gas, it is believed that a compressor unit combining a centrifugal compressor and a reciprocating compressor can achieve a large throughput with a low-cost structure, as disclosed in Patent Document 1. However, there is room for improvement as a compressor unit having multiple compressor stages for compressing hydrogen gas generated by a water electrolysis system.

[0004] US Patent Application Publication No. 2022 / 0397118

[0005] The present invention has been made in view of the above-described problems, and has an object to provide a compressor unit including multiple compressor stages and suitable for compressing hydrogen gas generated by a water electrolysis system.

[0006] A compressor unit according to one aspect of the present invention is a compressor unit that compresses hydrogen gas generated by a water electrolysis system, and includes: a screw compressor configured to take in moisture-containing hydrogen gas generated by the water electrolysis system; a dryer disposed downstream of the screw compressor and configured to remove moisture from the hydrogen gas; and a reciprocating compressor configured to further compress hydrogen flowing out from the dryer.

[0007] FIG. 1 is a diagram for explaining a compressor unit according to a first embodiment. FIG. 2 is a diagram for explaining a reciprocating compressor provided in the compressor unit. FIG. 3 is a diagram for explaining a compressor unit according to a modified example of the first embodiment. FIG. 4 is a diagram for explaining a compressor unit according to a second embodiment. FIG. 5 is a diagram for explaining control of the rotation speed of a screw rotor by a variable speed drive. FIG. 6 is a diagram for explaining a compressor unit according to a third embodiment. FIG. 7 is a diagram for explaining a compressor unit according to a fourth embodiment.

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the following embodiment is an example of a specific embodiment of the present invention and is not intended to limit the technical scope of the present invention.

[0009] (First Embodiment) A compressor unit according to this embodiment is configured to receive hydrogen gas produced by a water electrolysis system, pressurize the received hydrogen gas to a predetermined pressure, and supply the pressurized hydrogen gas to a consumer. The water electrolysis system is configured to produce hydrogen gas using, for example, electric power generated using renewable energy. Examples of renewable energy include solar light, wind power, hydroelectric power, wave power, tidal power, geothermal power, solar heat, atmospheric heat, other heat present in nature, and biomass. Note that the water electrolysis system is not limited to one that produces hydrogen gas using electric power obtained using renewable energy.

[0010] The suction volume of the compressor unit is, for example, 1,000 Nm ３ / h or more. The suction volume of the compressor unit is 10,000 Nm ３ / h or more, or 100,000 Nm ３ That is, the compressor unit of this embodiment is configured to be used for processing a large flow rate of hydrogen gas.

[0011] 1, the compressor unit 10 includes a screw compressor 12, a dryer 14, and a reciprocating compressor 16. The screw compressor 12 constitutes a front compression stage, and the reciprocating compressor 16 constitutes a rear compression stage that further compresses the hydrogen gas compressed in the front compression stage.

[0012] The screw compressor 12 is connected to the water electrolysis system 25 through the suction pipe 21. Therefore, the screw compressor 12 compresses the hydrogen gas obtained in the water electrolysis system 25.

[0013] The screw compressor 12 includes a casing 12a, a pair of screw rotors 12b housed in the casing 12a, and a drive source (or motor) 12c. One of the pair of screw rotors 12b is connected to the drive source 12c. The pair of screw rotors 12b is driven by driving this one screw rotor 12b by the drive source 12c. As a result, hydrogen gas is compressed in a compression chamber formed between the screw rotors 12b. The screw compressor 12 may include one compression stage or multiple compression stages.

[0014] The hydrogen gas obtained in the water electrolysis system 25 also contains moisture. Therefore, the moisture contained in the hydrogen gas provides a seal between the screw rotors 12b and between the screw rotors 12b and the casing 12a. As a result, even when a low-molecular-weight gas such as hydrogen gas is compressed in the preceding compression stage, the volumetric efficiency can be improved compared to when dry hydrogen gas is compressed. Note that the gas produced in the water electrolysis system 25 may contain gases other than hydrogen gas.

[0015] While using a centrifugal compressor in the upstream compression stage, as in the past, is advantageous in terms of ensuring a sufficient air throughput, it is difficult to ensure a high compression ratio. This issue is particularly pronounced when using hydrogen gas, which has a small molecular weight. To achieve a high discharge pressure using a centrifugal compressor requires an increased number of stages, resulting in an increase in the size of the compressor unit. Furthermore, operating a centrifugal compressor at a high peripheral speed places restrictions on the impeller material and requires a complex design to ensure stable operation. Furthermore, because the hydrogen gas obtained by water electrolysis contains moisture, the efficiency of a reciprocating compressor used in the upstream compression stage is reduced.

[0016] A first connecting pipe 27 is connected to the gas discharge port of the screw compressor 12, and the first connecting pipe 27 is connected to the dryer 14. In other words, the first connecting pipe 27 connects the screw compressor 12 and the dryer 14 to each other. On the other hand, no dryer is provided in the suction pipe 21. Because the dryer 14 is disposed downstream of the screw compressor 12, it is not necessary to design the screw compressor 12 in consideration of the pressure loss caused by the installation of the dryer 14. In addition, because the pressure on the suction side of the screw compressor 12 is not reduced by the dryer 14, the compression ratio can be reduced accordingly. Therefore, the size of the screw compressor 12 can be reduced.

[0017] The dryer 14 is configured as an adsorption dryer having a desiccant. That is, the dryer 14 includes a housing and a desiccant accommodated in the housing, and the desiccant adsorbs moisture contained in the hydrogen gas introduced into the housing through the first connecting pipe 27. The hydrogen gas with a reduced moisture content inside the housing is discharged from the housing of the dryer 14. The adsorption dryer 14 makes it possible to obtain hydrogen gas with a low dew point temperature.

[0018] The dryer 14 may include a regeneration means configured to regenerate the desiccant. The regeneration means may have a heater (not shown) that heats the desiccant, or may be configured to regenerate the desiccant by expanding hydrogen gas and bringing it into contact with the desiccant. Other adsorption-type dryers, such as those equipped with a PSA (Pressure Swing Adsorption) device or a TSA (Thermal Swing Adsorption) device, may also be used as the dryer 14. A membrane-type dryer equipped with a hollow fiber membrane may also be used. A refrigeration-type dryer (also called a cooling-type dryer) equipped with a cooling means and a heating means may also be used. In a refrigeration-type dryer, the gas is cooled by the cooling means to condense the moisture, and the gas that has passed through the cooling means is then heated by the heating means. The dryer 14 may also be configured with other types of dryers. The first connecting pipe 27 may be provided with a deoxygenator (not shown) that removes oxygen from the hydrogen gas flowing into the dryer 14. In this case, the hydrogen purity of the hydrogen gas can be further increased.

[0019] A second connecting pipe 28 is connected to the dryer 14. The hydrogen gas whose moisture content has been reduced by the dryer 14 is introduced into the reciprocating compressor 16 through the second connecting pipe 28. The first connecting pipe 27 and the second connecting pipe 28 form a connecting pipe 30 that connects the screw compressor 12 and the reciprocating compressor 16 to each other. The dryer 14 is disposed in the connecting pipe 30.

[0020] 2, the reciprocating compressor 16 includes a cylinder portion 211, a piston 212 disposed 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, respectively.

[0021] 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. The rod packing 2117 has a plurality of packing rings 217a arranged to surround the piston rod 213, and a case 217b that holds the packing rings 217a.

[0022] The piston 212 is connected to the crank mechanism 32 (see FIG. 6 ) 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. Although FIG. 2 shows the reciprocating compressor 16 having a double-acting structure, the reciprocating compressor 16 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.

[0023] In the reciprocating compressor 16, a rod packing 217 is provided to prevent hydrogen gas from leaking from the compression chamber 216 to the crank mechanism 32. However, since hydrogen gas may leak as far as the rod packing 217, a leak gas return flow path 34 is connected to the rod packing 217. More specifically, a leak gas collection section is provided between adjacent packing rings 217a, and the return flow path 34 is connected to this leak gas collection section. It is more preferable to provide the leak gas collection section between the packing ring 217a provided at a position farthest from the compression chamber 216 and the packing ring 217a adjacent to this packing ring 217a.

[0024] As shown in FIG. 1 , the return flow path 34 is connected to the suction pipe 21 and returns leak gas from the reciprocating compressor 16 to the suction side (e.g., the suction pipe 21) of the screw compressor 12. Therefore, even if leak gas occurs in the reciprocating compressor 16, this leak gas can be utilized in the screw compressor 12. Furthermore, since the leak gas recovery unit is connected to the space on the suction side of the screw compressor 12, which is at approximately atmospheric pressure, via the return flow path 34, it is possible to suppress a pressure increase in the leak gas recovery unit. As a result, it is possible to reduce the load on the packing ring 217a near the leak gas recovery unit.

[0025] A check valve 35 is disposed in the return flow path 34. The check valve 35 prevents backflow of hydrogen gas to the reciprocating compressor 16. In other words, by providing the check valve 35, even if pressure fluctuations occur in the suction pipe 21, it is possible to prevent leak gas or hydrogen gas from the suction pipe 21 from returning to the reciprocating compressor 16.

[0026] One end (inlet end) of the return flow passage 34 may be connected to the rear head 211 b at a position closer to the compression chamber 216 than the rod packing 217 is, rather than being connected to the rod packing 217 .

[0027] 3, the other end (outlet end) of the return flow path 34 may be connected to the casing 12a of the screw compressor 12 instead of being connected to the suction pipe 21. In this case, the leak gas is introduced through the return flow path 34 into the interior of the screw compressor 12 (for example, the space within the casing 12a where the gas exists before compression begins). It is possible to appropriately select whether the return flow path 34 is connected to the suction pipe 21 or the screw compressor 12. The return flow path 34 may be omitted.

[0028] For convenience, FIG. 1 illustrates the reciprocating compressor 16 as a single trapezoid, but the reciprocating compressor 16 may have multiple cylinder sections 211. That is, the reciprocating compressor 16 may be configured such that hydrogen gas is compressed and pressurized by pistons 212 in multiple cylinder sections 211 connected in parallel. Also, while FIG. 1 illustrates one reciprocating compressor 16, multiple reciprocating compressors 16 may be provided. The multiple reciprocating compressors 16 may be connected in parallel or in series to the second connecting pipe 28. The multiple reciprocating compressors 16 may be installed on a single base plate (not shown). In this case, the multiple reciprocating compressors 16 can be transported to the installation site in a unitized state, thereby reducing the amount of work required for piping work or testing on site.

[0029] A discharge pipe 38 is connected to the pair of discharge valves 215 of the reciprocating compressor 16. The hydrogen gas compressed in the reciprocating compressor 16 is supplied to a demand destination of the hydrogen gas through the discharge pipe 38.

[0030] In the compressor unit 10 of this embodiment, hydrogen gas obtained from the water electrolysis system 25 is drawn into the screw compressor 12. The hydrogen gas compressed by the screw compressor 12 contains moisture and has a large molecular weight. This improves the volumetric efficiency of the screw compressor 12. In other words, in the screw compressor 12, hydrogen gas is compressed in a moisture-containing state, so leakage of hydrogen gas during compression is reduced. This leads to improved compression efficiency.

[0031] Meanwhile, hydrogen gas whose moisture content has been reduced by the dryer 14 is introduced into the reciprocating compressor 16. In the reciprocating compressor 16, since there is no correlation between molecular weight and volumetric efficiency, it is more efficient to compress hydrogen gas from which moisture has been removed. For this reason, by providing the dryer 14 between the screw compressor 12 and the reciprocating compressor 16, the performance of the compressor unit 10 can be improved, contributing to the efficient supply of hydrogen gas.

[0032] Furthermore, in the compressor unit 10 of this embodiment, the return flow path 34 is provided, so that the hydrogen gas can be prevented from being wasted.

[0033] Second Embodiment In the first embodiment, the screw compressor 12 may be operated without changing the rotation speed. In contrast, in the second embodiment, the screw compressor 12 can be operated while changing the rotation speed. 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.

[0034] As shown in FIG. 4 , the compressor unit 10 according to the second embodiment includes a pressure detector 41 that detects the pressure of hydrogen gas drawn into the screw compressor 12, and a variable speed drive 43 that can adjust the rotation speed of the screw compressor 12. The pressure detector 41 is provided in the intake pipe 21. Alternatively, the pressure detector 41 may be attached to the hydrogen gas inlet of the casing 12a of the screw compressor 12. The pressure detector 41 outputs a signal indicative of the detected pressure. The variable speed drive 43 reduces the rotation speed of the screw compressor 12 as the pressure detected by the pressure detector 41 decreases, i.e., as the pressure of the hydrogen gas drawn into the screw compressor 12 decreases. In other words, the variable speed drive 43 reduces the rotation speed of the screw compressor 12 as the flow rate of hydrogen gas drawn into the screw compressor 12 decreases.

[0035] The variable speed drive 43 is connected to the drive source 12c (or motor) of the pair of screw rotors 12b so as to change the rotation speed of the pair of screw rotors 12b. The variable speed drive 43 may be configured, for example, by an inverter. The variable speed drive 43 is configured to refer to the signal output from the pressure detector 41 and change the rotation speed of the screw compressor 12 in accordance with the pressure of the hydrogen gas sucked into the screw compressor 12. In other words, the rotation speed of the screw compressor 12 is controlled in accordance with the suction pressure.

[0036] Specifically, referring to FIG. 5 , in the control of the rotation speed of the screw rotor 12b (screw compressor 12) by the variable speed drive 43, first, the pressure detector 41 detects the pressure of the hydrogen gas sucked into the screw compressor 12 (step ST11). It is determined whether the detected pressure is within a preset pressure range (step ST12). If the detected pressure is within the preset range, the rotation speed of the screw rotor 12b (screw compressor 12) is maintained (step ST13). On the other hand, if the detected pressure is below the preset range, the variable speed drive 43 reduces the rotation speed of the screw rotor 12b (screw compressor 12) (step ST14). If the detected pressure is above the preset range, the variable speed drive 43 increases the rotation speed of the screw rotor 12b (screw compressor 12) (step ST15). At this time, the rotation speed of the drive source 12c (motor) is adjusted, thereby adjusting the rotation speed of the screw rotor 12b (screw compressor 12). As a result, the screw compressor 12 can process a hydrogen gas amount corresponding to the flow rate of the hydrogen gas obtained in the water electrolysis system 25 .

[0037] 4, a spillback valve 44 may be added in addition to the variable speed drive 43 in order to adjust the gas processing rate of the screw compressor 12. In this case, when the rotation speed of the drive source 12c (motor) may be equal to or lower than a predetermined value, the spillback valve 44 may control the capacity instead of controlling the rotation speed of the drive source 12c with the variable speed drive 43. By controlling the spillback valve 44, the flow rate of hydrogen gas returned from the connecting pipe 30 to the suction pipe 21 is adjusted, thereby adjusting the gas pressure in the connecting pipe 30. For example, when the rotation speed of the drive source 12c (motor) may be equal to or lower than a predetermined value, the gas processing rate of the screw compressor 12 is adjusted by increasing the opening of the spillback valve 44 rather than reducing the rotation speed of the drive source 12c.

[0038] Therefore, in this embodiment, the processing amount by the screw compressor 12 can be adjusted in accordance with fluctuations in the amount of hydrogen gas generated in the renewable energy-based water electrolysis system 25, which is easily affected by weather, time of day, etc.

[0039] Although the description of other configurations, actions, and effects will be omitted, the description of the first embodiment can be applied to the second embodiment.

[0040] 6, in the third embodiment, a control mechanism 45 for a suction valve 214 provided in a reciprocating compressor 16 is added to the compressor unit 10 of the second embodiment to which a variable speed drive 43 has been added. Note that 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.

[0041] When the throughput of the screw compressor 12 is adjusted according to the supply flow rate of hydrogen gas from the water electrolysis system 25, as in the second embodiment, the pressure of the hydrogen gas that passes through the dryer 14 and is sucked into the reciprocating compressor 16 fluctuates. Meanwhile, the reciprocating compressor 16 is set to a rotational speed that provides a discharge flow rate appropriate for the discharge flow rate from the screw compressor 12 when the screw compressor 12 is driven at a predetermined rotational speed. That is, the rotational speed of the reciprocating compressor 16 is set to a rotational speed that provides a discharge flow rate corresponding to the discharge flow rate (predetermined flow rate) that is obtained when the screw compressor 12 is driven at a predetermined rotational speed. Therefore, if the rotational speed of the reciprocating compressor 16 is maintained even when the discharge flow rate from the screw compressor 12 decreases, the reciprocating compressor 16 will suck in too much hydrogen gas. This will result in a decrease in the suction pressure of the reciprocating compressor 16. Therefore, a control mechanism 45 is provided that reduces the discharge flow rate from the reciprocating compressor 16 while maintaining the rotational speed of the reciprocating compressor 16 in response to the rotational speed of the screw compressor 12 decreasing from a predetermined rotational speed or the pressure on the discharge side of the screw compressor 12 dropping below a predetermined pressure.

[0042] The control mechanism 45 includes a pressure detection unit 45a that detects the pressure of the hydrogen gas flowing inside the connecting pipe 30, a rotation detection unit 45b that detects the rotation of the crankshaft in the crank mechanism 32, and an unloader 45c that controls the suction valve 214 while referring to signals from the pressure detection unit 45a and the rotation detection unit 45b. In Fig. 6, the pressure detection unit 45a is provided in the second connecting pipe 28 downstream of the dryer 14, but instead, the pressure detection unit 45a may be provided in the first connecting pipe 27 upstream of the dryer 14.

[0043] The suction valve 214 has a valve plate (not shown), and when the pressure upstream of the suction valve 214 is higher than the pressure downstream, the valve plate opens due to the pressure difference. On the other hand, when the pressure downstream is higher, the valve plate of the suction valve 214 closes, preventing the flow of hydrogen gas. The unloader 45c is a functional part for changing the opening and closing timing of the suction valve 214, and when the unloader 45c is activated, the valve plate of the suction valve 214 temporarily becomes inactive regardless of the pressure difference.

[0044] For example, when it is determined based on the signal from the rotation detection unit 45b that the piston 212 is in the intake stroke, the unloader 45c does not operate. At this time, the valve plate of the intake valve 214 opens in response to the pressure difference between the pressure of the hydrogen gas in the connecting pipe 30 and the pressure in the compression chamber 216. On the other hand, when it is determined based on the signal from the rotation detection unit 45b that the piston 212 is in the compression stroke, the intake valve 214 would normally close in response to the increase in pressure in the compression chamber 216. However, by operating the unloader 45c while referring to the signal from the pressure detection unit 45a, the control mechanism 45 can delay the timing at which the intake valve 214 closes relative to its original timing. If the timing at which the intake valve 214 closes is delayed, some of the hydrogen gas in the compression chamber 216 returns to the connecting pipe 30, thereby reducing the flow rate of hydrogen gas discharged from the compression chamber 216 of the reciprocating compressor 16 to the discharge pipe 38 through the discharge valve 215. That is, by operating the unloader 45c in accordance with the rotation angle of the crankshaft, the opening and closing timing of the suction valve 214 of the reciprocating compressor 16 is adjusted so that the amount of hydrogen gas compressed by the reciprocating compressor 16 is reduced.

[0045] Therefore, according to this embodiment, the throughput of the reciprocating compressor 16 can be made to follow the throughput of the screw compressor 12, so that the compression ratio of the reciprocating compressor 16 can be prevented from becoming excessive.

[0046] When a plurality of reciprocating compressors 16 are provided, the unloader 45c of the control mechanism 45 may be provided for each reciprocating compressor 16. In this case, the signal output from the pressure detection unit 45a and the signal output from the rotation detection unit 45b are provided to each unloader 45c.

[0047] 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.

[0048] 7, in a compressor unit 10 of a fourth embodiment, a screw compressor 12 is provided with a water injection section 51. Note that the same components as those in the first to third embodiments are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0049] The water injection unit 51 is configured to inject water into the compression chamber or the casing 12a of the screw compressor 12. The hydrogen gas generated by the water electrolysis system 25 contains moisture, but in the fourth embodiment, by providing the water injection unit 51, it is possible to more easily obtain a seal between the screw rotors 12b and a seal between the screw rotor 12b and the casing 12a.

[0050] When the water injection section 51 is added, the amount of water introduced into the screw compressor 12 increases, and there is a possibility that the moisture cannot be sufficiently removed by the dryer 14 alone. For this reason, in the fourth embodiment, a gas-liquid separator 53 is further added. The gas-liquid separator 53 is disposed in the first connecting pipe 27. That is, the gas-liquid separator 53 is disposed upstream of the dryer 14 in the connecting pipe 30.

[0051] The gas-liquid separator 53 separates moisture from the hydrogen gas discharged from the screw compressor 12 and has a container 53a equipped with a demister (not shown). The moisture separated from the hydrogen gas by the demister is stored in the container 53a. An outlet for discharging the hydrogen gas is provided in the ceiling of the container 53a. The gas-liquid separator 53 discharges the hydrogen gas with a reduced moisture content through the outlet into the first connecting pipe 27. A gas cooler (not shown) for cooling the hydrogen gas may be provided in the first connecting pipe 27 between the screw compressor 12 and the gas-liquid separator 53. The provision of a gas cooler makes it easier to remove moisture in the gas-liquid separator 53. Furthermore, in a configuration in which the water injection unit 51 is provided, the gas-liquid separator 53 may be omitted.

[0052] Therefore, according to this embodiment, the hydrogen gas sucked into the screw compressor 12 also contains water from the water injection section 51, so the volumetric efficiency of the screw compressor 12 can be further improved.

[0053] Furthermore, since the gas-liquid separator 53 is provided, even if water from the water injection section 51 is drawn into the screw compressor 12, the moisture can be removed to a certain extent before the hydrogen gas flows into the dryer 14. This makes it possible to prevent moisture from being contained in the hydrogen gas drawn into the reciprocating compressor 16.

[0054] Although the description of other configurations, actions, and effects will be omitted, the descriptions of the first to third embodiments can be applied to the fourth embodiment.

[0055] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The present invention is not limited to the above-described embodiments, and various modifications and improvements can be made without departing from the spirit of the present invention.

[0056] The above-described specific embodiments mainly include inventions having the following configurations.

[0057] (1) The compressor unit according to the above embodiment is a compressor unit that compresses hydrogen gas generated by a water electrolysis system, and includes: a screw compressor configured to take in moisture-containing hydrogen gas generated by the water electrolysis system; a dryer disposed downstream of the screw compressor and configured to remove moisture from the hydrogen gas; and a reciprocating compressor configured to further compress hydrogen flowing out from the dryer.

[0058] In the compressor unit, when hydrogen gas is compressed using a screw compressor, the molecular weight increases and volumetric efficiency improves if the gas contains moisture. On the other hand, in the case of a reciprocating compressor, there is no correlation between molecular weight and volumetric efficiency, so it is more efficient to compress hydrogen gas from which moisture has been removed. For this reason, by installing a dryer between the screw compressor and the reciprocating compressor, the performance of the compressor unit can be improved.

[0059] (2) The compressor unit may further include a variable speed drive configured to reduce the rotation speed of the screw compressor in accordance with a decrease in the amount of hydrogen gas generated from the water electrolysis system.

[0060] In this embodiment, the processing amount by the screw compressor can be adjusted in accordance with fluctuations in the amount of hydrogen gas generated in the water electrolysis system using renewable energy, which is easily affected by weather, time of day, and the like.

[0061] (3) The reciprocating compressor may have an intake valve. In this case, the compressor unit may further include a control mechanism configured to control the opening and closing timing of the intake valve of the reciprocating compressor so as to reduce the discharge flow rate of hydrogen gas from the reciprocating compressor in accordance with a reduction in the discharge flow rate of the screw compressor.

[0062] In this embodiment, the throughput of the reciprocating compressor can be made to follow the throughput of the screw compressor.

[0063] (4) The screw compressor may include a compression chamber and a water injection unit configured to inject water into the compression chamber.

[0064] In this embodiment, the hydrogen gas sucked into the screw compressor also contains water from the water injection section, so that the volumetric efficiency of the screw compressor can be further improved.

[0065] (5) The compressor unit may further include a gas-liquid separator between the screw compressor and the dryer, the gas-liquid separator being configured to separate moisture from the hydrogen gas discharged from the screw compressor.

[0066] In this embodiment, even if water from the water injection section is drawn into the screw compressor, some of the moisture is removed before the hydrogen gas flows into the dryer, thereby preventing moisture from being contained in the hydrogen gas drawn into the reciprocating compressor.

[0067] (6) The compressor unit may further include a return flow path configured to return leak gas from the reciprocating compressor to the suction side of the screw compressor or to the inside of the screw compressor.

[0068] In this embodiment, it is possible to prevent the hydrogen gas from being wasted.

[0069] (7) The compressor unit may further include a check valve in the return passage that prevents backflow of hydrogen gas to the reciprocating compressor.

[0070] In this embodiment, unintentional leakage of hydrogen gas can be prevented.

[0071] As described above, it is possible to provide a compressor unit that includes multiple compressor stages and is suitable for compressing hydrogen gas produced by a water electrolysis system.

Claims

1. A compressor unit that compresses hydrogen gas produced by a water electrolysis system, comprising: a screw compressor configured to take in hydrogen gas containing moisture produced by the water electrolysis system; a dryer disposed downstream of the screw compressor and configured to remove moisture from the hydrogen gas; and a reciprocating compressor configured to further compress the hydrogen flowing out from the dryer.

2. The compressor unit according to claim 1, further comprising a variable speed drive configured to reduce the rotational speed of the screw compressor in accordance with a decrease in the amount of hydrogen gas generated from the water electrolysis system.

3. The compressor unit according to claim 2, wherein the reciprocating compressor has an inlet valve, and further comprising a control mechanism configured to control the opening and closing timing of the inlet valve of the reciprocating compressor so as to reduce the discharge flow rate of hydrogen gas from the reciprocating compressor in accordance with the reduction in the discharge flow rate of the screw compressor.

4. A compressor unit according to any one of claims 1 to 3, wherein the screw compressor comprises a compression chamber and a water injection section configured to inject water into the compression chamber.

5. The compressor unit according to claim 4, further comprising a gas-liquid separator between the screw compressor and the dryer, the gas-liquid separator being configured to separate moisture from the hydrogen gas discharged from the screw compressor.

6. A compressor unit according to any one of claims 1 to 3, further comprising a return flow path configured to return leak gas from the reciprocating compressor to the suction side of the screw compressor or to the interior of the screw compressor.

7. The compressor unit according to claim 6, further comprising a check valve on the return line for preventing backflow of hydrogen gas to the reciprocating compressor.

Images