System and method for generating dried compressed hydrogen gas

Abstract

System and method for generating dried compressed hydrogen gas, comprising: - A compressor (E01), configured for: • receiving the hydrogen gas with water vapor under atmospheric or near atmospheric pressure, in particular from a storage space; • compressing the hydrogen gas; and • delivering compressed hydrogen gas with water vapor to a separator; and - Said separator (E02), configured for: • receiving the compressed hydrogen gas with the water vapor and the condensed liquid water from the compressor (E01); • separating the compressed hydrogen gas with the water vapor from the condensed liquid water; • delivering the compressed hydrogen gas to at least one adsorber (E08); and • delivering the condensed water to a drain (SUMP), - Said at least one adsorber (E08), configured for: • receiving hydrogen with the water vapor under pressure from the separator; • drying the hydrogen gas by adsorbing the water vapor; and • releasing the hydrogen under pressure.

Description

[0001] System and method for generating dried compressed hydrogen gas

[0002] The present invention relates to a system and method for generating compressed, purified and dried hydrogen gas.

[0003] Depending on its production method, hydrogen gas may be generated under atmospheric or under high pressure. When generated under atmospheric pressure, the gas may contain relatively more water vapor than when pressurised. Figure 1 of this application shows the maximum absolute humidity expressed in grams of water vapor per actual m3of gas volume as function of temperature and pressure. This water vapor, as well as trace oxygen gas, is considered as an impurity, and needs to be removed from the hydrogen gas before it can be used. Throughout this application, the term atmospheric is used to indicate a pressure of about 1000 mbar(a), in particular between 500 mbar(a) and 1500 mbar(a).

[0004] Both for purifying and for pressurizing hydrogen, there are systems known in the prior art.

[0005] The German patent application DE 102022127312 A1 concerns a dryer / purifier that is intended to function after one of the compressors, although the option of placement before it is mentioned. Reciprocating compressors that are oil-lubricated are mentioned. In addition to water, it is therefore also necessary to remove traces of the lubricant from the hydrogen. The system is a combination of a water adsorber and an oil adsorber in series. The need of hydrogen for regeneration of the water adsorption material is not mentioned and it does not follow that a two-vessel drying system is described where one vessel is regenerated while the other dries.

[0006] The American patent US 6402809 does describe energy optimization of such classic two- vessel drying installation. However, it is not mentioned what happens to the regeneration gas that is needed for continuous operation of the system, i.e. regenerate one vessel while the other adsorbs.

[0007] Most prior art systems are configured to blow off hydrogen used as regeneration gas and / or oxygen under circumstances. Not only does this lead to a reduced efficiency, but it also implies safety risks. When a system is foreseen wherein hydrogen is blown off into the open air, the blowoff point is qualified as an ATEX 0 or 1 zone depending on the frequency, which implies that safety precautions may be legally prescribed.

[0008] Since these precautions are generally costly and labour intensive to implement and to obey, it is a goal of the present invention to propose a system and method for generating dried compressed hydrogen gas that does not require hydrogen gas to be blown off. The invention relates to hydrogen that is for instance generated by an electrolyzer system at near atmospheric pressure, which implies that more water vapor needs to be separated compared to a higher-pressure hydrogen gas.

[0009] For this purpose, the invention proposes a system for generating dried compressed hydrogen gas, comprising a compressor, configured for receiving a hydrogen gas comprising or in particular containingwater vapor at near atmospheric pressure from a storage space or directly from the electrolyzer, compressing the hydrogen gas and delivering compressed hydrogen gas with lowerwatervapor content to a separator, and delivering liquid water condensed by the compression to a drain. The separator is configured for receiving the compressed hydrogen gas with the water vapor and the condensed liquid water from the compressor and separating the compressed hydrogen gas with the water vapor from the condensed liquid water, delivering the compressed hydrogen gas to at least one adsorber and delivering the condensed water to a drain. The at least one adsorber is configured for receiving hydrogen with the water vapor under pressure from the separator drying the hydrogen gas byadsorbingthe watervapor and allow the hydrogen to pass under pressure.

[0010] As can be seen in figure 1 , at a dewpoint of 3-5C, the atmospheric hydrogen gas will contain approximately 10 grams of water per m3 of gas. When this is compressed more or less adiabatically the compressed gas can only contain 10 grams of water per m3as well. For example, when compressing from 1 bar to 13 bar, the volume is reduced by a factor 13 which means that 92% of the water in vapor form in the feed gas will be condensed and only 8% of the water in the feed gas will pass the compressor in vapor form.

[0011] The condensation and formation of liquid water may also occur internally in diaphragm and piston compressors which cannot handle liquid water well as it impedes the functioning of the inlet and outlet valves in the compressor.

[0012] The separator tank preferably has a liquid level control which discharges the collected condensed water. Compressed hydrogen gas according to the invention has a pressure of 2 to 20 bar, and in particular between 10 to 13 bar.

[0013] In a preferred embodiment, the compressor is a so-called liquid ring compressor, wherein the separator is configured to deliver at least part of the liquid water to the liquid ring compressor, in particular via a pump. As the amount of condensed water from the feed gas exceeds the water lost in vapor form exiting the separator tank to the subsequent processing steps, no make-up water system needs to be in place which simplifies the balance of plant.

[0014] By controlling the temperature of the cooling water injected into the compressor, which indirectly controls the temperature in the gas / liquid separator, the ratio of condensed water in the controller can be optimized. Maintaining a temperature as low as possible, but not below 5 Celsius will give an optimal ratio as the lowest possible temperature without danger of freezing the water will result in the lowest amount of water vapor exiting the separator tank to the next processing steps. The temperature may be maintained at 5 degrees Celsius.

[0015] The separator may further be configured to deliver the liquid water to the liquid ring compressor via a heat exchanger, wherein the heat exchanger is configured to cool the liquid water to a temperature between 1 and 30 and more in particular between 0 and 20 degrees Celsius.

[0016] The separator may be configured to deliver the compressed hydrogen gas via a de-oxerto the adsorber, wherein the de-oxer is configured to allow the oxygen gas present in the hydrogen gas to react with the hydrogen gas to form water, and wherein the system is particularly configured to extract the water thus formed from the compressed hydrogen gas via a condenser and / or water knock-out unit before delivering the compressed hydrogen gas to the adsorber.

[0017] In the de-oxer the trace oxygen is removed by allowing it to catalytically react with the hydrogen to form water. Each oxygen molecule will thus consume two hydrogen molecules and form two molecules of water:

[0018] 2H2+ O2-> 2 H2O

[0019] The output of the de-oxer unit has an increased temperature as the catalytic ‘burning’ of the trace oxygen generates heat, and also a higher water vapor concentration due to the water formed by the reaction mentioned above.

[0020] The de-oxer unit (optionally with the condenser unit and water knock-out unit) can also be situated at the inlet of the compressor. Therefore, the invention also relates to a system wherein the compressor is configured to receive the compressed hydrogen gas from the storage space or electrolyzer via a de-oxer, wherein the de-oxer is configured to allow the oxygen gas present in the hydrogen gas to react with the hydrogen gas to form water, and wherein the system optionally may be configured to separate the water thus formed from the compressed hydrogen gas via a condenser and / or water knock-out unit before the compressed hydrogen gas is delivered to the compressor. However, by positioning it in the high-pressure part after the separator, the superficial flow rates are reduced allowing a smaller catalytic reactor bed in the de-oxer while maintaining sufficient contact time.

[0021] In order notto waste any watertoo, the drain may be configured to return the condensed pure water to the hydrogen gas generating device (electrolyzer) or other process.

[0022] The at least one adsorber may be a temperature swing adsorption or a pressure swing adsorption type of adsorber. There is difference between pressure swing adsorption (PSA) and temperature swing adsorption (TSA), but both methods can be combined to achieve a more optimized process depending on the process particulars.

[0023] Generally, PSA is more energy efficient and faster than TSA. In both cases however, the saturated adsorption bed(s) when saturated with water need to be regenerated to prepare them for the next adsorption cycle.

[0024] The drying unit may therefore be based on an adsorption process in which a minimum of two beds are used, but three, four or more beds can also be applied.

[0025] Preferably however, the system comprises at least two adsorbers, wherein each of the adsorbers can be selectively switched on and off, in particular by an inlet and / or outlet valve, wherein a switched-on adsorber is configured for adsorbing water vapor from hydrogen gas and a switched-off adsorber is configured for being regenerated, by discharging water vapor and / or discharging hydrogen gas under low pressure.

[0026] For this regeneration a part of the dried gas is used. For example, if a first adsorber is the bed in which the adsorption takes place, then a part of the dried hydrogen gas exiting from the first adsorber may be fed via a flow controlling valve to the second adsorber. This occurs at the lowest possible pressure (and optionally highest possible temperature if heaters are installed) in order to reduce the percentage of gas used for regeneration as much as possible. This regeneration gas stream will exit the second adsorber at atmospheric pressure and possibly high temperature in order to transport as much water vapor as possible (see figure 1 for temperature and pressure effects) with as Iow a gas flow as possible.

[0027] In conventional systems which are not designed to operate with an atmospheric gas feed, this atmospheric humid gas cannot be reused without processing and compressing it. Mostly, the regeneration gas is flared or blown off, resulting in a loss of the hydrogen gas of 5%-15% depending on process conditions. Both these methods may also introduce safety issues around the compression and purification as flaring introduces an ignition point and a blow-off introduces an ATEX zone of 0 or 1 , which in turn requires other stringent safety measures around the compression and purification.

[0028] Due to the fact that this system may specifically be designed to operate with a feed gas at atmospheric pressure, all regeneration gas can be recycled to the inlet of the compressor. The extra condensation water in the regeneration gas is easily absorbed into the water cycle of the compressor (similar to the condensation water originating from the feed gas) and is discharged from the separator via a valve without requiring other equipment.

[0029] The system according to the invention may be configured for alternately switching on one of the two adsorbers, wherein the switched-on adsorber is configured to regenerate the switched off adsorber, by passing a fraction of the dried hydrogen gas under atmospheric pressure through the switched off adsorber.

[0030] It is noted that according to the present invention, the regeneration of an absorber goes faster than the absorption, so that a regenerated absorber is ready for use before the other absorber is satisfied and must be regenerated. The regenerated absorber is then ready for used and an entrance and exit are closed (by a valve or the like) to keep the absorber in its regenerated state until the other absorber must be regenerated.

[0031] In a further embodiment, the at least one or the at least two adsorbers are configured for returning hydrogen gas under atmospheric pressure to the compressor during regeneration of the adsorbers and thus forming a closed hydrogen system.

[0032] It is yet unknown according to the prior art to recycle (regeneration) hydrogen gas to the inlet of the compressor. In most prior art systems this is even impossible. The system according to the invention allows to do so because the compressor is able to operates at atmospheric inlet pressure (and is preferably configured to do so). According to the invention, an adsorption vessel may be regenerated with atmospheric (hot) gas because then a minimum amount (or weight) of gas is then needed to be able to evaporate all the adsorbed water.

[0033] The gas is then atmospheric and may become completely saturated with water. In prior art, in order to be able to reuse it, it must first be pressurized and dried to a large extent by e.g. condensation and water knock-out. Otherwise, as much water is introduced at the inlet of the process as was taken out and the system eventually becomes "full" or “floods with water”.

[0034] By taking advantage of the fact that the compressor will accept atmospheric humid hydrogen and condense most water out during the low-temperature compression and separating it off in the gas-liquid separator similar to the feed gas, instead of simply blowing off the atmospheric water vapour saturated gas to the atmosphere in order to get rid of the water as it is done in the prior art, is one of the inventive aspects of the present invention.

[0035] An alternative is to regenerate such an adsorption vessel (to make the adsorption material dry again) with another gas such as nitrogen or even air. However, before that vessel can be used again, it has to be flushed with hydrogen to get rid of the contamination. Otherwise, contaminated hydrogen gas will be produced for a while, which defeats the purpose of the equipment. For this, normally the hydrogen gas that has just been purified and comes out of the other vessel under pressure is used as pure regeneration gas. This gas mixes with the remaining gas in the vessel and the contaminated gas then becomes useless and may be blown off to the outside air. This flushing therefore also wastes a percentage of the hydrogen gas that is taken in at the front of the purification.

[0036] In practice, regenerating an adsorption vessel with hydrogen gas, or with another gas and then flushing, costs 7-15% of the hydrogen that was available at the entrance. This of course affects the production cost price of the hydrogen from a plant and makes it 7-15% less efficient and thus more expensive.

[0037] The system may further comprise a purity measurement device for receiving and measuring a fraction of the compressed hydrogen gas, and returning hydrogen gas under atmospheric pressure to the compressor.

[0038] If the purity measurement measures that the gas is not up to specification (for example when the system is starting up and the drying unit is not yet at its optimal working point) the gas may be recycled back to the inlet of the compressor as well until all units in the system have arrived at their optimal working points before directing the gas to the exit of the system.

[0039] This recycling of bleed streams, regeneration gas streams, and process gas stream to the inlet of the LRC result in zero loss of the hydrogen gas as opposed to the 5%-15% loss of hydrogen gas in conventional systems.

[0040] Finally, the system according to the invention may comprise a return line for returning a fraction of the compressed hydrogen gas under atmospheric pressure to the compressor or returning hydrogen gas under atmospheric pressure to the compressor when the compressor is not or not fully operational.

[0041] As there is no frequent hydrogen being emitted from the system which results in an ATEX zone category 1 or 0, fewer measures need to be taken around the system which facilitates employing this system in a plant.

[0042] The invention also relates to a method for generating dried compressed hydrogen gas, comprising generating, such as by electrolysis, of hydrogen gas under atmospheric pressure; wherein the hydrogen gas comprises water vapor, compressing the thus obtained hydrogen gas and releasing liquid water condensed by compression separating the compressed hydrogen gas with the water vapor from the condensed liquid water drying the hydrogen gas byadsorbingthe watervapor and dispensingthe hydrogen under pressure.

[0043] The invention will now be elucidated into more detail with reference to the following figures, wherein:

[0044] Figure 1 shows a graph of absolute humidity in H2gas as function of temperature and pressure;

[0045] Figure 2 shows a detailed overview of a system according to the invention.

[0046] Figure 1 shows a graph of absolute humidity in H2gas as function of temperature and pressure. When compressing and purifying hydrogen produced by an electrolyserthe trace oxygen must be removed, but specifically a very large amount of water vapor needs to be separated off. The maximum saturated water concentration expressed in gr H2O / actual m3of volume is given in figure 1 . This figure illustrates that the saturated water concentration is strongly a function of the temperature, and much less a function of the pressure.

[0047] Figure 2 shows a system for generating compressed purified and dried hydrogen gas, comprising a source of this hydrogen gas at near atmospheric pressure which can be a generator (not shown), such as an electrolyser, for generating hydrogen gas under atmospheric pressure, or a near atmospheric storage space, such as a gasholder, for storing the hydrogen gas (not shown), a compressor (E01 ), configured for: receiving the hydrogen gas with water vapor under near atmospheric pressure, compressing the hydrogen gas; and delivering compressed hydrogen gas with water vapor to a separator (E02), and delivering liquid water condensed by compression to a drain (SUMP), the separator (E02), configured for receiving the compressed hydrogen gas with the water vapor and the condensed liquid water from the compressor (E01) separating the compressed hydrogen gas with the water vapor from the condensed liquid water delivering the compressed hydrogen gas to at least one adsorber (E08); and delivering the condensed waterto a drain (SUMP), said at least one adsorber (E08), configured for receiving hydrogen with the water vapor under pressure from the separator (E02) drying the hydrogen gas by adsorbing the water vapor; and releasing the hydrogen under pressure. The compressor (E01) is a single or multi-stage liquid ring compressor, wherein the separator (E02) is configured to deliver at least part of the liquid water to the liquid ring compressor (E01), via a pump (E04). The separator (E02) is configured to deliver the liquid water to the liquid ring compressor (E01) via a heat exchanger, wherein the heat exchanger is configured to cool the liquid water to a temperature between 3 and 30 degrees Celsius, and in particular between 5-20 degrees Celsius. The separator (E02) is configured to deliver the compressed hydrogen gas via a de-oxer (E05) to the adsorber (E08), wherein the de-oxer is configured to allow the oxygen gas present in the hydrogen gas to react with the hydrogen gas to form water, and wherein the system is particularly configured to extract the water thus formed from the compressed hydrogen gas via a condenser (E06) and / or water knock-out unit (E07) before delivering the compressed and cooled hydrogen gas to the adsorber (E08). The compressor (E01 ) may also be configured to receive the compressed hydrogen gas from a generator or from the storage space via a de-oxer (E05), wherein the de-oxer is configured to allow the oxygen gas present in the hydrogen gas to react with the hydrogen gas to form water, and wherein the system is in particular configured to separate the water thus formed from the compressed hydrogen gas via a condenser (E06) and / or water knock-out unit (E07) before the compressed hydrogen gas is delivered to the compressor (E01 ). The drain (SUMP) may be configured to return the condensed water to the hydrogen gas generating device. The system in this example comprises two adsorbers (E08a, E08b), wherein each of the adsorbers (E08a, E08b) can be selectively switched on and off, in particular by an inlet and / or outlet valve (V03, V04, V05, V06), wherein a switched-on adsorber is configured for adsorbingwatervapor from hydrogen gas and a switched-off adsorber is configured for discharging hydrogen gas under low pressure. The system is configured for alternately switching on one of the two adsorbers (E08a, E08b), wherein the switched-on adsorber (E08a / E08b) is configured to regenerate the switched off adsorber (E08b / E08a), by passing a fraction of the dried hydrogen gas at atmospheric pressure and optionally higher temperature through the switched off adsorber (E08b / E08a).

[0048] The adsorbers (E08a / E08b) are configured for returning hydrogen gas under atmospheric pressure to the compressor (E01 ) during regeneration of the adsorbers and thus forming a closed hydrogen system. The system further comprises a purity measurement device (E10) for receiving and measuring a fraction of the compressed hydrogen gas, and returning hydrogen gas under atmospheric pressure to the compressor (E01) as well as a return line for returning a fraction of the compressed hydrogen gas under atmospheric pressure to the compressor (E01), or returning hydrogen gas under atmospheric pressure to the compressor (E01 ) when the compressor (E01 ) is not or not fully operational.

Claims

Claims1 . System for generating dried compressed hydrogen gas, comprising:A compressor (E01 ), configured for: o receivingthe hydrogen gas with water vapor under atmospheric or near atmospheric pressure, in particular from a storage space or electrolyzer; o compressing the hydrogen gas; and o delivering compressed hydrogen gas with water vapor to a separator; andSaid separator (E02), configured for: o receivingthe compressed hydrogen gas with the water vapor and the condensed liquid water from the compressor (E01 ); o separating the compressed hydrogen gas with the water vapor from the condensed liquid water; o delivering the compressed hydrogen gas to at least one adsorber (E08); and o delivering the condensed water to a drain (SUMP),Said at least one adsorber (E08), configured for: o receiving hydrogen with the water vapor under pressure from the separator; o drying the hydrogen gas by adsorbing the water vapor; and o releasing the hydrogen under pressure.

2. System according to claim 1 , wherein the compressor (E01 ) is a liquid ring compressor, wherein the separator (E02) is configured to deliver at least part of the liquid water to the liquid ring compressor (E01), in particular via a pump (E04).

3. System according to claim 2, wherein the separator (E02) is configured to deliver the liquid water to the liquid ring compressor (E01) via a heat exchanger, wherein the heat exchanger is configured to cool the liquid water to a temperature between 1 and 30 degrees Celsius, and in particular between 5 and 20 degrees Celsius.

4. System according to any of the preceding claims, wherein the separator (E02) is configured to deliver the compressed hydrogen gas via a de-oxer (E05) to the adsorber (E08), wherein the de-oxer is configured to allow the oxygen gas present in the hydrogen gas to reactwith the hydrogen gas to form water, and wherein the system is particularly configured to extractthe water thus formed from the compressed hydrogen gas via a condenser (E06) and / or water knock-out unit (E07) before delivering the compressed hydrogen gas to the adsorber (E08).

5. System according to any of the preceding claims, wherein the compressor (E01) is configured to receive the compressed hydrogen gas from a source (generator or storage) via a de-oxer (E05), wherein the de-oxer is configured to allow the oxygen gas present in the hydrogen gas to react with the hydrogen gas to form water, and wherein the system is in particular configured to separate the water thus formed from the compressed hydrogen gas via a condenser (E06) and / or water knock-out unit (E07) before the compressed hydrogen gas is delivered to the separator (E02).

6. System according to any of the preceding claims, wherein the drain is configured to return the condensed water to the hydrogen gas generating device or other process.

7. System according to any of the preceding claims, wherein the at least one adsorber is a temperature swing adsorption or a pressure swing adsorption type of adsorber, or a combination thereof.

8. System according to any of the preceding claims, comprising at least two adsorbers (E08a, E08b), wherein each of the adsorbers (E08a, E08b) can be selectively switched on and off, in particular by an inlet and / or outlet valve, wherein a switched-on adsorber is configured for adsorbingwater vapor from hydrogen gas and a switched-off adsorber is configured for discharging hydrogen gas under low pressure.

9. System according to claim 8, configured for alternately switching on one of the two adsorbers (E08a, E08b), wherein the switched-on adsorber (E08a / E08b) is configured to regenerate the switched off adsorber (E08b / E08a), by passing a fraction of the dried hydrogen gas under atmospheric pressure through the switched off adsorber (E08b / E08a).

10. System according to any of the preceding claims, wherein the at least one or the at least two adsorbers are configured for returning hydrogen gas under atmospheric pressure to the compressor (E01) during regeneration of the adsorbers and thus forming a closed hydrogen system preventing discharge of the return stream(s) to the environment.11 . System according to any of the preceding claims, comprising a purity measurement device (E10) for receiving and measuring a fraction of the compressed hydrogen gas, and returning hydrogen gas under atmospheric pressure to the compressor (E01 ).

12. System according to any one of the preceding claims, comprising a return line for returning a fraction of the compressed hydrogen gas under atmospheric pressure to the compressor (E01), or returning hydrogen gas under atmospheric pressure to the compressor (E01 ) when the compressor (E01 ) is not or not fully operational.

13. Method for generating dried compressed hydrogen gas, comprising: generating, such as by electrolysis, of hydrogen gas under atmospheric or near- atmospheric pressure; wherein the hydrogen gas comprises water vapor; compressing the thus obtained hydrogen gas; and releasing liquid water condensed by compression; separating the compressed hydrogen gas with the water vapor from the condensed liquid water; drying the hydrogen gas by adsorbing the water vapor; and dispensing the dried hydrogen under pressure.

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