System and method for compression of gas

Abstract

There is disclosed a system (1) for compression of hydrogen from a hydrogen source (2), the system (1) comprising: a compression vessel (6) having an upper portion (60) with an upper end (62) and a low- er portion (64) with a lower end (66), the compression vessel (6) being provided with a first inlet (8) for receiving hydrogen from a hydrogen source (2), a second inlet (12) for receiving pressurized water from a water reservoir (4), a first outlet (18) for compressed hydrogen and a second outlet (20) for draining of water; and a water supply pump (22), upstream of the second inlet (12), for pressurizing water from the water reservoir (4), wherein the compression vessel (6) further is provided with a third inlet (14) for water, the third inlet (14) being in fluid connection with one or more nozzles (16) inside the compression vessel (6); and the first inlet (8), the second inlet (12), the third inlet (14), the first outlet (18), and the second outlet (20) each occupy a different position on the compression vessel (6) There is also disclosed a hydrogen compression assembly (10) including such a system (1) as well as a method for compression of hydrogen by means of the compression assem- bly (10).

Description

[0001] SYSTEM AND METHOD FOR COMPRESSION OF GAS

[0002] The invention relates to a system for compression of hydrogen. More particularly, the invention relates to a system for compression of hydrogen using one or more compression vessels with water or another pressurizing fluid. The invention also relates to a hydrogen compression assembly comprising such a system as well as to a method of operating the hydrogen compression assembly.

[0003] Use of hydrogen as an energy carrier is expected to be a key enabler for replacement of fossil fuels in the shift towards more environmentally friendly energy solutions. Today, hydrogen is used i.a. for powering vehicles, generating electricity, powering industrial processes, heating and much more. Hydrogen from electrolysis of water is usually produced at relative low pressures, in order of 4-30 bar, and should preferably be compressed before transport and / or storage.

[0004] Known systems for compression of hydrogen are relatively large and complex with significant auxiliary equipment and also suffer from low efficiency. Many typical gas compressors are also less suitable for compression of hydrogen because of its low molecular weight compared to other gasses.

[0005] US 2013 / 0315818 Al discloses a high pressure hydrogen gas compressor comprising a source of high pressure fluid and a pressure vessel having a gas inlet for the gas to be compressed, a gas outlet for the compressed gas and a fluid inlet for the high pressure fluid. The compressor is arranged to introduce the high pressure fluid into the pressure vessel via the fluid inlet whereby to compress a volume of gas in the pressure vessel.

[0006] US 2006 / 0144229 Al discloses a biogas pressurization apparatus comprising a biogas inlet pipe having at least a biogas feeding element, a biogas outlet pipe having at least a cut-off element, a washing water inlet pipe having at least a washing water pressurization device, a washing water outlet pipe having at least a cut-off valve, the apparatus being controlled either manually or automatically.

[0007] US 2010 / 0139777 Al discloses a compressed gas transfer system comprising at least one first pressure vessel able to hold a volume of gas; and a first gas line to allow gas to pass out of the at least one first pressure vessel wherein the volume of the first pressure vessel is able to be varied to maintain the gas within the pressure vessel at a constant pressure.

[0008] WO 2023 / 114228 Al discloses a high-pressure gas compression, storage, and dispensing system including a storage vessel, a liquid sump tank, and a separation system. The pressure in the storage vessel can be controlled by partially filling or draining the storage vessel with the liquid. The stored gas can become partially saturated with the liquid, and the separation system can reduce the saturation.

[0009] US 2012 / 0130549 Al discloses a plant for storing and supplying compressed gas comprises a storage tank for gas, at least one pressurization tank for gas and a buffer tank for a pressure support fluid to be filled into or evacuated from lower portions of the storage and pressurization tanks. The lower portions of the storage and pressurization tanks are communicating with the buffer tank via fluid flow lines to fill fluid during supplying from and pressurizing gas in the plant, and a flow line for evacuating fluid during refilling of the pressurization tank.

[0010] The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to the prior art.

[0011] The object is achieved through features, which are specified in the description below and in the claims that follow.

[0012] The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.

[0013] In a first aspect, the invention relates to a system for compression of hydrogen from a hydrogen source, the system comprising: - a compression vessel having an upper portion with an upper end and a lower portion with a lower end, the compression vessel being provided with a first inlet for receiving hydrogen from a hydrogen source, a second inlet for receiving pressurized water from a water reservoir, a first outlet for compressed hydrogen and a second outlet for draining of water; and

[0014] - a water supply pump, upstream of the second inlet, for pressurizing water from the water reservoir, wherein

[0015] - the compression vessel further is provided with a third inlet for water, the third inlet being in fluid connection with one or more nozzles inside the compression vessel; and

[0016] - the first inlet, the second inlet, the third inlet, the first outlet, and the second outlet each occupy a different position on the compression vessel.

[0017] The purpose of the nozzles is to spray a cooling fluid, such as water, over the hydrogen as it is being compressed in order to approach isothermal compression. Preferably, the cooling water (or other fluid) is supplied to the compression vessel through the third inlet with an overpressure compared to the water supplied through the second inlet.

[0018] It should also be noted that the system for compression for hydrogen may also be suitable for compressing other types of gasses, in addition to H2, such as CO2, NH3, N2 or any noble gas, and that it is not limited to compression of H2 only.

[0019] In one embodiment the second inlet for pressurised water may be provided at the lower portion of the compression vessel, the third inlet for water may be provided at the upper portion of the compression vessel, and the first inlet for hydrogen may be provided between the second and third inlets.

[0020] The water supply pump, upstream of the second inlet, may in one embodiment supply water to both the second and third inlets. Additionally, the second and third inlets may be directly connected to the water supply pump.

[0021] In a second aspect the invention relates to a hydrogen compression assembly, the hydrogen compression assembly comprising:

[0022] - a system according to the first aspect of the invention; - a hydrogen source connected to the first inlet of the compression vessel;

[0023] - a water reservoir connected to the second and third inlets of the compression vessel; and

[0024] - a receiver for compressed hydrogen connected to the first outlet.

[0025] In one embodiment the water reservoir may also be connected to the second outlet of the compression vessel for receiving water and any residual hydrogen dissolved in the water drained from the compression vessel.

[0026] Additionally, the water reservoir may have an inlet for water and residual hydrogen, a first outlet connected to the inlet of the water supply pump, optionally via a cooler, and a second outlet for hydrogen. Separation of water from hydrogen may simply be enabled by gravitation.

[0027] Further additionally, the compression vessel may be provided with a fourth inlet for water and residual hydrogen, wherein the second outlet of the water reservoir is connected to the fourth inlet of the compression vessel via a residual ejector connected to the outlet discharge of the water supply pump.

[0028] In one embodiment, the hydrogen source may be directly connected to the first inlet of the compression vessel, i.e. without an intermediate ejector.

[0029] Alternatively, the hydrogen source may be connected to the first inlet of the compression vessel via one or more supply ejectors for increasing the pressure of hydrogen prior to its supply to the compression vessel.

[0030] When the hydrogen source is connected to the first inlet of the compression vessel via one or more ejectors, the hydrogen compression assembly may further comprise an ejector supply pump with an inlet connected to the water reservoir and an outlet connected to the supply ejector, the outlet of the supply ejector being directly connected to the first inlet of the compression vessel.

[0031] In one embodiment the compression vessel may be a first compression vessel among a plurality of compression vessels. In a practical embodiment, the hydrogen compression assembly may comprise two pairs of compression vessels, a first compression vessel pair including the first compression vessel and a second compression vessel, and a second compression vessel pair, including a third compression vessel and a fourth compression vessel.

[0032] In one embodiment, the hydrogen compression assembly may comprise two water supply pumps, where the first pair of compression vessels is connected to the first water supply pump and where the second pair of compression vessels is connected to the second water supply pump. As an alternative to using two water supply pumps, a single water supply pump with a suitable valve arrangement may achieve a similar distribution of water. As a further alternative, the number of water supply pumps may be equal to the number of compression vessels.

[0033] In one embodiment, a high-pressure accumulator may be added downstream of one or more of the water supply pumps, e.g. downstream of each water supply pump, in order to minimize the variable discharge head of one or more (e.g. each) pump during compression of the gas.

[0034] The first compression vessel may preferably comprise first and second level switches for sensing first and second liquid filling levels, respectively, and wherein the second, third and fourth compression vessels each comprises a level switch for sensing a liquid filling level corresponding to the second filling level. In one embodiment one or more, preferably each of, the compression vessels may comprise a low-level switch indicating that the compression vessel is empty or substantially empty after draining of water and dissolved hydrogen. The low-level switch may be connected to a drain valve, typically via a control unit, so that the drain valve closes when a liquid level corresponding to the low level is sensed.

[0035] In one embodiment one or more, e.g. each, on-off and control valves connected to the pressure vessels may be pressure balanced axial flow valves providing low energy demand to operate and low fluid pressure loss when in open position. In one embodiment one or more, e.g. each, check valve(s) connected to the pressure vessels may be spring-balanced nozzle check valves in order to provide low pressure loss when open and smooth closing.

[0036] In a third aspect the invention relates to method of operating a hydrogen compression assembly including two pairs of compression vessels, wherein the method includes the steps of:

[0037] - supplying hydrogen to each of the compression vessels from the hydrogen source;

[0038] - start supplying pressurized water to the first compression vessel to pressurize the hydrogen therein;

[0039] - sensing, by means of the first level switch, that the liquid level in the first compression vessel has reached a first filling level (Hl); and then

[0040] - start supplying pressurised water to the third compression vessel to pressurise the hydrogen therein;

[0041] - cooling the hydrogen during compression by supplying cooling water through the nozzles to each of the first and third compression vessels during its respective hydrogen compression phase; and

[0042] - opening the first outlet for compressed hydrogen in the first compression vessel when the pressure in the first compression vessel has reached a pre-determined pressure.

[0043] It should be noted that opening the first outlet for compressed hydrogen may be fully automatic in the sense that the outlet opens through a check valve when the pressure inside the compression vessel is larger than in the supply line downstream of the outlet. This may also be the case for feeding hydrogen into the first inlet of the compression vessel, which may also be through a check valve that opens into the compression vessel when the pressure on the inside is lower than that on the outside in the supply line upstream of the first inlet.

[0044] In one embodiment, the method may further comprise the steps of:

[0045] - sensing, by means of the second level switch, that the liquid level in the first compression vessel has reached the second filling level; and then

[0046] - start supplying pressurised water to the second compression vessel through its second inlet and start draining water and any residual hydrogen from the first compression vessel through the second outlet;

[0047] - opening the first outlet for compressed hydrogen from the third compression vessel when the pressure in the third compression vessel has reached a pre-determined pressure,

[0048] - sensing, by means of the level switch, that the liquid level in third compression vessel has reached the second filling level; and then

[0049] -start supplying pressurised water to the fourth compression vessel through its second inlet and start draining water and any residual hydrogen from the third compression vessel through the second outlet; and

[0050] - cooling the hydrogen during compression by supplying cooling water through the nozzles to each of the second and fourth compression vessels during its respective hydrogen compression phase.

[0051] In one embodiment, the method may further comprise the steps of:

[0052] - opening the first outlet for compressed hydrogen from the second compression vessel when the pressure in the second compression vessel has reached a pre-determined pressure;

[0053] - sensing, by means of the level switch, that the liquid level in second compression vessel has reached the second filling level; and then

[0054] - again start supplying pressurised water to the first compression vessel through its second inlet and start draining water and any residual hydrogen from the second compression vessel through the second outlet, and

[0055] - cooling the hydrogen during compression by supplying cooling water through the nozzles to the first compression vessel during its hydrogen compression phase.

[0056] In one embodiment, the method may further comprise the steps of:

[0057] - opening the first outlet for compressed hydrogen from the fourth compression vessel when the pressure in the fourth compression vessel has reached a pre-determined pressure

[0058] - sensing, by means of the level switch, that the liquid level in fourth compression vessel has reached the second filling level; and then - again start supplying pressurised water to the third compression vessel through its second inlet and start draining water and any residual hydrogen from the fourth compression vessel through the second outlet; and

[0059] - cooling the hydrogen during compression by supplying cooling water through the nozzles to the third compression vessel during its hydrogen compression phase.

[0060] The cycle of filling and emptying the compressions vessels may be repeated as necessary.

[0061] In one embodiment, the method may include, for each compression vessel, supplying a volume of water for cooling through the nozzles through the third inlet that is 5% or less, preferably 2% or less, of the total supply of water to the compression vessel, i.e. more than 95%, preferably more than 98%, of the water being supplied through the second inlet for compressing the hydrogen therein.

[0062] In one embodiment, the system for compression of hydrogen and the hydrogen compression assembly may comprise a plurality of check valves at the hydrogen inlet(s) and outlet^) which will provide gas supply to the compression vessel(s) as long as the pressure inside the compression vessels is lower than the upstream pressure, and gas will leave the compression vessel as long as the pressure inside the compression vessel is higher than the gas export pressure. During liquid draining of a compression vessel, hydrogen (or other gas) will enter the compression vessel as soon as the pressure in the supply line to the first inlet is higher than the pressure inside the compression vessel. Hydrogen entering the compression vessel during draining will assist in "pushing out" the remaining water from the compression vessel. In alternative embodiment, a similar filling and supply cycle may be enabled by means of "on-off" valves with suitable logic and pressure sensors.

[0063] In the following is described examples of preferred embodiments illustrated in the accompanying drawings, wherein:

[0064] Fig. 1 shows a first embodiment of a system according to the invention;

[0065] Fig. 2 shows a second embodiment of a system according to the invention;

[0066] Fig. 3 shows a third embodiment of a system according to the invention; Fig. 4 shows a fourth embodiment of a system according to the invention;

[0067] Fig. 5 shows a fifth embodiment of a system according to the invention;

[0068] Fig. 6 shows liquid level as a function of time in a system according to the invention; and

[0069] Fig. 7 shows pressure as a function of time in a system according to invention.

[0070] Any positional indications refer to the position shown in the figures.

[0071] In the figures, same or corresponding elements are indicated by same reference numerals. For clarity reasons, some elements may in some of the figures be with-out reference numerals. A person skilled in the art will understand that the figures are just principal drawings and that relative proportions of individual elements may also be distorted.

[0072] In the figures, reference numeral 1 will be used to denote a system for compression of hydrogen according to the first aspect of the invention, whereas reference numeral 10 denotes a hydrogen compression assembly according to the second aspect of the invention.

[0073] It should be noted that the embodiments of the invention shown in Figs. 1-5 are drawn highly schematic and simplified.

[0074] In Fig.l a first embodiment of a system for compression of hydrogen 1 is shown. The system 1 is connected to a hydrogen source 2, a water reservoir 4 and a not shown receiv- er / consumer of compressed hydrogen to define a hydrogen compression assembly 10. The source of hydrogen 2 may e.g. be hydrogen that is produced by means of electrolysis of water or, as alternative, hydrogen produced by reforming of hydrocarbons. The system 1 comprises a compression vessel 6, the compression vessel having an upper portion 60 with an upper end 62 and a lower portion 64 with a lower end 66. The compression vessel 6 is provided with a first inlet 8 for receiving hydrogen from the hydrogen source 2, a second inlet 12 for receiving pressurized water from the water reservoir 4 and a third inlet 14 for water, where the third inlet is in fluid connection with one or more nozzle outlets 16 on the inside of the compression vessel 6. In Fig. 1 three nozzle outlets 16 are highly schematically indicated in the closed circle, showing an enlarged view into the interior of the compression vessel 6. However, it should be understood that the number of nozzles 16 may differ depending on the size and type of nozzles as well as the size of the compression vessel 6 as such. The nozzle outlets 16, arranged near the upper end 62 of the compression vessel, create a water mist efficiently cooling the hydrogen during compression to establish an isothermal or close to isothermal compression. The compression vessel 6 is further provided with a first outlet 18 for compressed hydrogen and second outlet 20 for draining of water and, optionally, residual / dissolved hydrogen.

[0075] As shown in Fig. 1, the first inlet 8, second inlet 12, third inlet 14, first outlet 18, and second outlet 20 may each occupy a different position on the compression vessel 6. For example, the first outlet 18 for compressed hydrogen may be positioned in the upper end 62 of the compression vessel 6 and the second outlet 20 for draining water may be positioned in the lower end 66 of the compression vessel 6. The first inlet 8, second inlet 12, and third inlet 14 may be positioned between the first outlet 18 and the second outlet 20. In one example, the second inlet 12 for pressurised water is provided at the lower portion 64 of the compression vessel 6, the third inlet 14 for water is provided at the upper portion 60 of the compression vessel 6, and the first inlet 8 for hydrogen is provided between the second inlet 12 and the third inlet 14. However, it should be understood that this is merely one example arrangement of the inlets and outlets, and the relative positions of the inlets and outlets may differ depending on the compression vessel and the system environment.

[0076] The system 10 further comprises a water supply pump 22 for pressurizing water from the water reservoir 4 from a first outlet 26 on the water reservoir and supplying the pressurized water to the compression vessel through the second inlet 12. A water cooler 24 is provided upstream of the water supply pump 22, downstream of the water reservoir 4 for optionally removing excess heat in the compression cycle to maintain isothermal or close to isothermal compression. The cooler 24 may in a non-limiting embodiment be a water tube heat exchanger, a plate heat exchanger, or any other type of liquid or air cooler. In the shown one-vessel embodiment, one and the same water supply pump 22 both pressurizes water into the second inlet 12 and supplies water through the third inlet 14 to the nozzle outlets 16. Distribution of water between the second and third inlets may be adjusted by means of one or more not shown control valves and / or by using different diameter supply pipes. The one or more valves may be controlled by a not shown control unit. Through testing and experiments, the present applicant has surprisingly found that only 5% or less, preferably 2% or less, of the water supplied to the compression vessel 6 need to be supplied to the nozzle outlets 16 for efficient cooling, the remaining water being supplied through the second inlet 12 where pressurized water acts as a piston / cushion for pressurizing hydrogen received from the hydrogen source 2. The embodiment according to the first embodiment of Fig.l, will not be able to deliver a constant supply of pressurized hydrogen since compression and subsequent draining of water take place sequentially.

[0077] The embodiments shown in Figs. 2-5, each comprises four compression vessels, where the second, third and fourth compression vessels will be denoted 6', 6” and 6''' respectively. With careful control of pressure and liquid levels the four-vessel set-ups may be able to deliver a substantially constant supply of pressurized hydrogen if desirable, as will be explained below.

[0078] Fig. 2 shows a second embodiment of a system for compression of hydrogen 1 and hydrogen compression assembly 10 according to the invention. The system 1 in the shown embodiment comprises four compression vessels 6, 6', 6” and 6'” arranged in two pairs, 6, 6' and 6”, 6'''. The system 1 comprises two water supply pumps 22, 22', the first water supply pump 22 supplying water to the first pair of compression vessels 6, 6' and the second water supply pump 22' supplying water to the second pair of compression vessels 6'', 6'''. In addition to the first outlet 26 for water to the water supply pumps 22, 22', the water reservoir 4 in the shown embodiment is provided with a second outlet 28 for supply of residual hydrogen back to the compression vessels 6, 6', 6'', 6'''. It should be noted that each of the compression vessels 6, 6', 6'', 6''' comprises nozzle outlets 16, as indicated in Fig.l. It should also be noted that by using two pumps, it will always be possible to provide a higher pressure to the nozzle outlets 16 than to the simultaneous pressure inside the compression vessel due to the filling and discharging cycle disclosed below. While e.g. hydrogen is being compressed in the third compression vessel 6'' by the second water supply pump 22', the discharge pressure of the first water supply pump 22 is at its maximum pressure level (see Fig. 7). At the same time as the first water supply pump 22 is supplying maximum pressure to first compression vessel 6, the high-pressure water supply may also be "branched" to supply high pressure cooling water to the third compression vessel 6” during compression of hydrogen. The branching may be enabled by providing a first check valve 70 downstream of the first water supply pump 22 and upstream of the third inlets 14 and similarly a second check valve 70' downstream of the second water supply pump and upstream of the third inlets 14. The check valves 70, 70' open when maximum pressure level is reached. Similarly, when the second water supply pump 22' is operating at maximum pressure, the second check valve 70' will open so that cooling water at high pressure may be delivered to the first or second compression vessels 6, 6', depending on stage in the cycle. Since, in the cycle disclosed in more detail below, one of the water supply pumps 22, 22' will always be supplying water through one of the second inlets at maximum pressure, cooling water to the nozzles 16 in one of the third inlets 14 (for the compression vessel that is in the compression phase) will always be available through the mentioned branching. It should also be noted that each third inlet 14 to the compression vessels 6, 6', 6'', and 6''' will normally contain an on-off valve, which may in certain embodiments close just before discharge of hydrogen starts from the compression vessel through first outlet 18. This will be beneficial to prevent water droplets in discharged hydrogen. In an alternative embodiment, the supply of water to the third inlets 14 may be provided by means of a designated, independent not shown water supply pump, where this water supply pump may be significantly smaller than the shown first and second water supply pumps 22, 22' due the reduced flow requirements. In some embodiments, water drained from the compression vessels 6, 6', 6'', 6''' through second outlets 20, may include residual hydrogen that should preferably be fed back to the compression vessels 6, 6', 6'', 6'''. In the shown embodiment, residual hydrogen from the water reservoir 4 is led into a fourth inlet 30 in each of the compression vessels 6, 6', 6'', 6'''. However, tests and experiments performed by the present applicant have shown that the level of residual hydrogen in drained water may be negligible in certain set-ups and that the second outlet 28 from the water reservoir should be regarded as optional. Where the second outlet 28 from the water reservoir 4 is indeed present, hydrogen is led through the second outlet 28 of the water reservoir 4 into residual ejector 36, where the residual hydrogen is entrained with water, as motive fluid, from the water supply pumps 22, 22'. In the embodiment of Fig. 2, each of the water supply pumps 22, 22' supplies water through three different inlets for each of the compression vessels 6, 6', 6'', 6'''; the second inlet 12 for pressurized water for compressing hydrogen, the third inlet 14 for cooling through the nozzle outlets 16 and the fourth inlet 30 for water and residual hydrogen via residual ejector 36. The water supply pumps 22, 22' are directly connected to the compression vessels 6, 6', 6'', 6''' through the second inlet 12 and third inlet 14, where "directly" in this regard means that there is no ejector between the water supply pumps 22, 22' and the respective inlet, which is in contrast to the third inlet 30. The distribution of water may be enabled by a selection of not shown valves and / or pipe arrangements, where the valves may be controlled by means of the not shown control unit. In the embodiment of Fig. 2 the source of hydrogen 2 has a sufficient pressure for the hydrogen to be lifted into the compression vessels 6, 6', 6'', 6''' without additional assistance from pumps, ejectors etc. As mentioned above, the first inlet 8 for hydrogen may be provided with a not shown check valve ensuring a flow of hydrogen into the respective compression vessel 6, 6', 6'', 6''' when the pressure inside the vessel is lower than in the supply line into the first inlet 8. Similarly, the first outlet 18 may also be provided with a checkvalve ensuring supply of hydrogen when the pressure inside a compression vessel 6, 6', 6'', 6''' is higher than in the supply line.

[0079] Fig. 3 shows an embodiment of a system for hydrogen compression 1 and a hydrogen compression assembly 10 similar to the one in Fig. 2, with the difference that hydrogen is pressure-assisted before being supplied to the compression vessels 6, 6', 6'', 6'''. This may be necessary or preferred if the hydrogen source 2 does not have sufficient pressure. Pressure assistance is enabled by means of a pair of ejector supply pumps 32, 32' connected to the water reservoir 4, downstream of the water reservoir 4. A first ejector supply pump 32 is connected to a supply ejector 34 to pump water, as a motive fluid, therethrough to entrain hydrogen from the hydrogen source 2 so as to increase its pressure for supply to the first inlet 8 of the compression vessels 6, 6', 6'', 6'''. A second ejector supply pump 32' is used to pump the residual hydrogen from the water reservoir 4 into the compression vessels 6, 6', 6'', 6''' through the first inlet 8, i.e. the residual hydro- gen is mixed with "fresh" hydrogen from the hydrogen source upstream of the first inlet 8, downstream of the supply ejector 34 and residual ejector 36, implying that the water supply pumps 22, 22' in the embodiment of Fig. 3 "only" supplies water directly to the compression vessels 6, 6', 6”, 6''' through the second and third inlets 12, 14.

[0080] Fig. 4 shows yet another embodiment of a system for hydrogen compression 1 and a hydrogen compression assembly 10. The embodiment resembles the one in Fig. 3, but with some differences, as will now be explained. In this embodiment, the supply pressure of hydrogen from the hydrogen source 2 is so low that pressure-assistance is provided by two supply ejectors, the first supply ejector 34 and a second supply ejector 34'. Similar to the embodiment in Fig. 3, the first supply ejector 34 receives hydrogen from the hydrogen source 2, where the hydrogen is entrained with water supplied from the first water supply pump 32. However, instead of thereafter being supplied directly to the compression vessels 6, 6', 6'', 6''' through the first inlet 8, hydrogen undergoes one more pressurization stage before being supplied to the compression vessels 6, 6', 6'', 6'''. From the first supply ejector 34, water and entrained hydrogen flow into a suction tank 38 through a suction tank inlet 40. From the suction tank 38 hydrogen flows into the second supply ejector 34' through a first outlet 42 of the suction tank 38. The second supply ejector 34' is driven by water as motive fluid from the second ejector supply pump 32'. Water is pumped out from a second outlet 44 of the suction tank 38 back to the water reservoir 4, implying that the water reservoir 4, in the shown embodiment, has two inlets for water and residual hydrogen, one from the compression vessels 6, 6', 6'', 6''' as before, and an additional one from the second outlet 44 of the suction tank 38. The pumping of water to the water reservoir 4 from the suction tank 38 is provided by a water drain pump 46, the pressure in the suction tank 38 being lower than that in the water reservoir 4. . Further, in the shown embodiment, the water reservoir 4 has a separate outlet 48 for residual hydrogen connected to an inlet 50 of the hydrogen source, implying that instead of feeding the residual hydrogen back into the compression vessels through a residual ejector 36, residual / dissolved hydrogen is fed back to the hydrogen source 2.

[0081] Fig. 5 shows another embodiment where pressure from the hydrogen source 2 is increased in two stages, as in Fig. 4. In addition, the system for compression of hydrogen 1 also includes the residual ejector 36 for supply of residual hydrogen from the water reservoir 4, similar to the embodiments of Figs. 1 and 2. The residual ejector 36 is driven by water from the water supply pumps 22, 22' as motive fluid. In contrast to the embodiment shown in Fig. 4, there is no hydrogen inlet 50 to the hydrogen source 2 and corresponding outlet 48 from the water reservoir.

[0082] Desired output pressure for hydrogen from the first outlet 18 may typically be around 100 bar. However, for certain recipients, the output pressure may be higher, such as around 200 bar or higher. To ensure sufficient compression, the input pressure from the hydrogen source may preferably be in the order of 20 bar. In case of insufficient supply pressure, the supply of hydrogen may be pressure-assisted in one or more pressure-increasing stages by ejectors as explained above. In one embodiment, where the pressure from the hydrogen source 2 is in the order of 10 bar, the first supply ejector 34 may increase the hydrogen pressure from 10 bar to 20 bar upstream of the compression vessels 6, 6', 6”, 6''', which corresponds to the embodiment of Fig. 3. In another embodiment, where the hydrogen supply pressure at the hydrogen source 2 is in the order of 4 bar, the first supply ejector may be used to increase the pressure from 4 bar to 10 bar, whereas the second supply ejector is used to increase the hydrogen pressure from 10 bar to 20 bar upstream of the compression vessels 6, 6', 6” , 6'”, corresponding to the embodiment of Figs. 4 and 5. It should of course be noted that the pressures and pressure increases presented above are indicative only, and that other desired pressures and pressure increases are achievable by use of ejector technology.

[0083] Fig. 6 is a graph showing simulated liquid level (mm) as a function of time (min) for each of the compression vessels 6, 6', 6”, 6"' in a four-vessel set-up, similar to the one in Fig. 2. Fig. 7 is a graph showing pressure (bara) as a function of time (min) contemporaneous with Fig. 6. The compression vessels 6, 6', 6”, 6''' are also denoted CCVl, CCV2, CCV3 and CCV4, respectively, in the graphs. As mentioned above, the compression vessels 6, 6', 6”, 6''' are arranged in pairs, each pair 6, 6' and 6”, 6'” being connected to one of the water supply pumps 22, 22' each. As can be seen in Fig. 6, filling of the second compression vessel 6' / CCV2 starts when the liquid level in the first compression vessel 6 reaches a predetermined maximum filling level H2, herein also referred to as a second filling level. Draining of the first compression vessel 6 starts when (water) filling of the second compression vessel 6' starts. The supply switch from the first compression vessel 6 to the second compression vessel 6' is typically enabled by means of operating one or more not shown valves controlled by means of a not shown control unit. The not shown drain valve may be operated in a similar way and closes when the liquid level reaches a low-level LI. In an alternative embodiment, each compression vessel 6, 6', 6”, 6”’ could be supplied with pressurised water from a designated water supply pump. In yet another embodiment, all of the compression vessels 6, 6', 6”, 6” may be supplied with water from a single water supply pump. However, this may be undesirable in certain embodiments, due to a substantial loss of pressure energy when two compression vessels would have been supplied from the pump at the same time. Reaching of the second / maximum filling level in the first compression vessel 6 is sensed by a not shown level switch for sensing the second filling level, the level switch communicating with the control unit, thus receiving information that the second filling level H2 is reached in first compression vessel 6. Draining of the first compression vessel 6 starts at the same time filling of the second compression vessel 6' commences. Filling of the third compression vessel 6” is triggered by the filling level in the first compression level 6 reaches a first level Hl. In the shown embodiment, the first filling level Hl is approximately 75% of the second filling level H2. The first filling level Hl, which is sensed by a separate, not shown level switch is communicated to the control unit, is chosen to establish start of filling of the third compression vessel 6”. The time / delay between reaching of the second filling levels for the various compression vessels is substantially constant as can be seen in Fig. 6. Filling of the fourth compression vessels 6'” starts when the third compression vessels 6” reaches it second filling level H2 and draining of its water content commences. This leads to an order of filling of the compression vessels 6, 6', 6”, 6'” which is 1 (6 / CCVI), 3 (6" / CCV3), 2 (6' / CCV2), and 4 (6"' / CCV4) before the cycle is repeated. The substantially constant time interval between when the various compression vessels 6, 6', 6”, 6'” reaches their respective second filling level H2, also leads to a substantially constant output pressure, and stable supply of hydrogen to the not shown recipient, as can be seen in Fig. 7. In the exemplary embodiment, the desired pressure level / output pressure Pl is approximately 200 bara. As described above, the flow of hydrogen into and out from the compression vessels may be enabled by check valves operating on pressure differences, i.e. so that a compression vessel starts filling if the pressure inside the compression vessel is lower than the pressure in the supply line to the first inlet 8. Similarly, supply of hydrogen to the first outlet 18 may start if the pressure inside the compression vessel is higher than the pressure in the supply line from the first outlet 18. Selected check valves may be set to operate with a very small delta P.

[0084] In an alternative embodiment, each of the compression vessels 6, 6', 6”, 6'” may also comprises a respective not shown pressure sensor, each of the pressure sensors also communicating with the not shown control unit and being adapted to send pressure data to the control unit. When the pressure in each of the compression vessels reaches a predetermined pressure value Pl, corresponding to the desired supply pressure, a not shown outlet valve opens so that compressed hydrogen starts flowing out the first outlet 18 of the respective compression vessel 6, 6', 6”, 6'”. However, as mentioned above, the supply of hydrogen may also start without any use of "on-off valves", but instead with mechanical check vales. By comparing the graphs in Figs. 6 and 7 it can be observed that the desired pressure level Pl in the first compression vessel 6, at which the not shown outlet valve opens (either by delta P or electronic signal), is reached at approximately the onset of start of filling of third compression vessel 6”. The supply pressure Pl from the first compression vessel 6 is then maintained until the first compression vessel 6 reaches its second filling level H2 and a not shown drain valve opens and the pressure immediately falls below the supply pressure Pl and the supply valve closes. The drain valve remains open until a low / substantially empty liquid filling level is sensed by a not shown low- level switch. Due to the delay in filling of the third compression vessel 6”, the pressure in the third compression vessel 6” reaches the pre-determined pressure level Pl when the pressure in the first compression vessel 6 drops below the supply pressure Pl (in the shown graph, it can be seen that pressure level in the third compression vessel 6” reaches the supply pressure Pl immediately before draining of the first compression vessel 6 starts). With the substantially constant time-offset between filling and draining of the compression vessels 6, 6', 6”, 6'” one of the compression vessels 6, 6', 6”, 6'” will always be able to supply hydrogen with a substantially constant pressure and flow. With the four-vessel set-up the supply, filling and draining cycle presented above, there is always only one compression vessel discharging hydrogen at any time, and another compression vessel draining water at any time.

[0085] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embod- iments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

C l a i m s1. System (1) for compression of hydrogen from a hydrogen source (2), the system (1) comprising:- a compression vessel (6, 6', 6", 6"') having an upper portion (60) with an upper end (62) and a lower portion (64) with a lower end (66), the compression vessel (6, 6', 6", 6"') being provided with a first inlet (8) for receiving hydrogen from a hydrogen source (2), a second inlet (12) for receiving pressurized water from a water reservoir (4), a first outlet (18) for compressed hydrogen and a second outlet (20) for draining of water; and- a water supply pump (22, 22'), upstream of the second inlet (12), for pressurizing water from the water reservoir (4), characterised in that- the compression vessel (6, 6', 6", 6"') further is provided with a third inlet (14) for water, the third inlet (14) being in fluid connection with one or more nozzles (16) inside the compression vessel (6, 6', 6", 6"'); and- the first inlet (8), the second inlet (12), the third inlet (14), the first outlet (18), and the second outlet (20) each occupy a different position on the compression vessel (6, 6', 6", 6"').

2. System (1) according to claim 1, wherein the second inlet (12) for pressurised water is provided at the lower portion (64) of the compression vessel (6, 6', 6", 6"'), the third inlet (14) for water is provided at the upper portion (60) of the compression vessel (6, 6', 6", 6"'), and the first inlet (8) for hydrogen is provided between the second (12) and third (14) inlets.

3. System (1) according to claim 1 or 2, wherein the water supply pump (22, 22'), upstream of the second inlet (12), supplies water to both the second (12) and third (14) inlets.

4. System (1) according to claim 3, wherein the second (12) and third (14) inlets are directly connected to the water supply pump (22, 22').

5. Hydrogen compression assembly (10), the hydrogen compression assembly (10) comprising:- a system (1) according to any one of the preceding claims;- a hydrogen source (2) connected to the first inlet (8) of the compression vessel (6, 6', 6", 6"');- a water reservoir (4) connected to the second (12) and third (14) inlets of the compression vessel (6, 6', 6", 6"'); and- a receiver for compressed hydrogen connected to the first outlet (18).

6. Hydrogen compression assembly (10) according to claim 5, wherein the water reservoir (4) is also connected to the second outlet (20) of the compression vessel (6, 6', 6", 6"') for receiving water and any residual hydrogen drained from the compression vessel (6, 6', 6", 6"').

7. Hydrogen compression assembly (10) according to claim 6, wherein the water reservoir (4) has an inlet for water and residual hydrogen, a first outlet (26) connected to the inlet of the water supply pump, optionally via a cooler (24) and a second outlet (28) for hydrogen.

8. Hydrogen compression assembly (10) according to claim 7, wherein the compression vessel (6, 6', 6", 6"') is provided with a fourth inlet (30) for water and residual hydrogen, the second outlet (28) of the water reservoir being connected to the fourth inlet (30) of the compression vessel (6, 6', 6", 6"') via a residual ejector (36) connected to the water supply pump (22, 22').

9. Hydrogen compression assembly (10) according to any one of the claims 5-8, wherein the hydrogen source (2) is directly connected to the first inlet (8) of the compression vessel (6, 6', 6", 6"').

10. Hydrogen compression assembly (10) according to any one of the claims 5-8, wherein the hydrogen source (2) is connected to the first inlet (8) of the compression vessel (6, 6', 6", 6"') via one or more supply ejectors (34, 34').

11. Hydrogen compression assembly (10) according to claim 10, wherein the hydrogen compression assembly (10) further comprises an ejector supply pump (32, 32') with an inlet connected to the water reservoir and an outlet connected to a supply ejector (34, 34'), the outlet of the supply ejector (34, 34') being directly connected to the first inlet (8) of the compression vessel (6, 6', 6", 6'").

12. Hydrogen compression assembly (10) according to any one of the claims 5- 11, wherein the compression vessel (6, 6', 6", 6'") is a first compression vessel (6) among a plurality of compression vessels (6, 6', 6", 6'").

13. Hydrogen compression assembly (10) according to claim 12, wherein the hydrogen compression assembly (10) comprises two pairs of compression vessels (6, 6' and 6", 6'"), a first compression vessel pair (6, 6') including the first compression vessel (6) and a second compression vessel (6') and a second compression vessel pair (6", 6'"), including a third compression vessel (6") and a fourth compression vessel (6'").

14. Hydrogen compression assembly (10) according to claim 13, wherein the water supply pump (22, 22') is a first water supply pump (22), and wherein hydrogen compression assembly (10) further comprises a second water supply pump (22'), the first water supply pump (22) being connected to the first (6) and second (6') compression vessels and the second water supply pump (22') connected to the third and fourth compression vessels (6", 6'").

15. Hydrogen compression assembly (10) according to claim 13 or 14, wherein the first compression vessel (6) comprises first and second level switches for sensing first and second liquid filling levels, respectively, and wherein the second (6'), third (6") and fourth (6'") compression vessels each comprises a level switch for sensing a liquid filling level corresponding to the second filling level.

16. Method of operating a hydrogen compression assembly (10) according to claim 15, wherein the method includes the steps of:- supplying hydrogen to each of the compression vessels (6, 6', 6", 6'") from thehydrogen source (2);- start supplying pressurized water to the first compression vessel (6) to pressurize the hydrogen therein;- sensing, by means of the first level switch, that the liquid level in the first compression vessel has reached a first filling level (Hl); and then- start supplying pressurised water to the third compression vessel (6") to pressurise the hydrogen therein;- cooling the hydrogen during compression by supplying cooling water through the nozzles (16) to each of the first (6) and third (6") compression vessels during its respective hydrogen compression phase;- opening the first outlet (18) for compressed hydrogen from the first compression vessel (6) when the pressure in the first compression vessel (6) has reached a pre-determined pressure17. Method according to claim 16, wherein the method further comprises the steps of:- sensing, by means of the second level switch, that the liquid level in the first compression vessel (6) has reached the second filling level; and then- start supplying pressurised water to the second compression vessel (6') and start draining water and any residual hydrogen from the first compression vessel (6) through the second outlet (20);- opening the first outlet (18) for compressed hydrogen from the third compression vessel (6") when the pressure in the third compression vessel (6") has reached a pre-determined pressure;- sensing, by means of the level switch, that the liquid level in the third compression vessel (6") has reached the second filling level; and then-start supplying pressurised water to the fourth compression vessel (6"') and start draining water and any residual hydrogen from the third compression vessel (6") through the second outlet (20); and- cooling the hydrogen during compression by supplying cooling water through the nozzles (16) to each of the second (6') and fourth (6"') compression vessels duringits respective hydrogen compression phase.

18. Method according to claim 17, wherein the method further comprises the steps of:- opening the first outlet (18) for compressed hydrogen from the second compression vessel (6') when the pressure in the second compression vessel (6') has reached a pre-determined pressure;- sensing, by means of the level switch, that the liquid level in the second compression vessel (6') has reached the second filling level; and then- again start supplying pressurised water to the first compression vessel (6) and start draining water and any residual hydrogen from the second compression vessel (6') through the second outlet (20), and- cooling the hydrogen during compression by supplying cooling water through the nozzles (16) to the first compression vessel (6) during its hydrogen compression phase.

19. Method according to claim 18, wherein the method further comprises the steps of:- opening the first outlet (18) for compressed hydrogen from the fourth compression vessel (6"') when the pressure in the fourth compression vessel (6"') has reached a pre-determined pressure;- sensing, by means of the level switch, that the liquid level in the fourth compression vessel (6"') has reached the second filling level; and then- again start supplying pressurised water to the third compression vessel (6") and start draining water and any residual hydrogen from the fourth compression vessel (6"') through the second outlet (20); and- cooling the hydrogen during compression by supplying cooling water through the nozzles (16) to the third compression vessel (6") during its hydrogen compression phase.

20. Repeating the steps of claims 16 - 19 as necessary.

21. Method according to any one of the claims 16-20, wherein method includes the step, for each compression vessel (6, 6', 6", 6"'), supplying a volume of water for cooling through the nozzles (16) through the third inlet (14) that is 5% or less, preferably 2% or less, of the total supply of water to the compression vessel (6, 6',6", 6"'), the rest of the water being supplied through the second inlet (12) for compressing the hydrogen therein.

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