Wet Oxidation Hydrogen Purification

Abstract

The invention is directed to a process for the purification of a raw hydrogen gas stream comprising hydrogen gas in an amount of 85-99%, said process comprising the step of contacting said raw hydrogen gas stream with an oxidized bed comprising an oxidized metal resulting in a waste gas stream comprising water and less than 5% hydrogen gas, and in a reduction of said oxidized metal; and a step of contacting a bed comprising a reduced metal with water to produce a purified hydrogen gas stream comprising more than 99% hydrogen gas, preferably comprising 99.97% or more hydrogen gas, and the oxidized metal. In a further aspect, the invention is directed to an apparatus suitable to carry out said process.

Claims

1. A process for the purification of a raw hydrogen gas stream comprising hydrogen gas in an amount of 85-99 mol %, said process comprising the steps of: a) contacting said raw hydrogen gas stream with an oxidized bed comprising an oxidized metal at least resulting in a waste gas stream comprising water and less than 5 mol % hydrogen gas, and in a reduction of said oxidized metal; and b) contacting a bed comprising a reduced metal with water to at least produce a purified hydrogen gas stream comprising more than 99 mol % hydrogen gas, and the oxidized metal.

2. The process according to claim 1, wherein said raw hydrogen gas stream further comprises one or more further reducing gases, and wherein step a) includes oxidizing said reducing gas to a higher oxidation state utilizing the oxidized bed.

3. The process according to claim 1, said process further comprising a step c) that comprises compressing the purified hydrogen gas stream to a pressure in the range of 200 to 1000 bar.

4. The process according to claim 3, wherein said compressed purified hydrogen is stored in a hydrogen gas storage container.

5. The process according to claim 1, wherein said purified hydrogen gas stream is fed to and stored in a fuel container that is connected to a hydrogen fuel cell.

6. The process according to claim 1, wherein steps a) and b) are carried out simultaneously.

7. The process according to claim 1, wherein heat is generated in step b) and which heat is at least partially used in step a).

8. The process according to claim 1, wherein step a) is carried out at a temperature in the range of 200 to 900° C. and wherein the waste gas stream has an elevated temperature, and wherein heat is extracted from the waste gas stream, which heat is at least partially used in step a).

9. The process according to claim 1, wherein the raw hydrogen gas stream comprises hydrogen gas in an amount of 90 to 98 mol %.

10. The process according to claim 1, wherein the oxidized metal comprises iron oxides and wherein the reduced metal particles comprise metallic iron.

11. The process according to claim 1, wherein the waste gas stream comprises less than 1 mol % hydrogen gas.

12. An apparatus for the purification of a raw hydrogen gas stream in accordance with claim 1, said apparatus comprising at least a first reactor comprising an oxidized bed comprising an oxidized metal or a reduced bed comprising a reduced metal, said first reactor further comprising a gas inlet and a gas outlet, which gas outlet is connected to a hydrogen gas storage container via a compressor that is suitable for compressing hydrogen gas.

13. The apparatus according to claim 12, wherein the inlet is connected to a hydrogen gas supply pipe line.

14. The apparatus according to claim 12, said apparatus comprising at least a further second reactor that comprises an oxidized bed comprising the oxidized metal or a reduced bed comprising the reduced metal, wherein said first reactor is connected to said second reactor via a heat exchanger such that during operation heat that is generated in the first reactor can be exchanged to the second reactor and vise-versa.

15. The process according to claim 1 wherein the purified hydrogen gas stream comprises 99.97 mol % or more hydrogen gas.

16. The process according to claim 1 wherein the one or more further reducing gases comprises carbon monoxide or methane.

17. The process according to claim 1 wherein the purified hydrogen gas is compressed.

18. The process according to claim 1 wherein the purified hydrogen gas is compressed and stored in a fuel container that is located in a vehicle.

19. The process according to claim 1 wherein the waste gas stream has an elevated temperature in the range at which step a) is carried out.

Description

[0027] In a particularly preferred embodiment of the present invention, steps a) and b) are carried out simultaneously. As such, it appears that the raw hydrogen gas stream that is processed is directly converted into a purified hydrogen gas stream. It may be appreciated however that in this embodiment, step a) and b) are carried out with at least two different particles beds. Thus, although the reduced bed is converted into an oxidized bed in step a), step b) is carried out with another oxidized bed at that moment. This embodiment can for instance be carried out in an apparatus comprising at least two reactors, each containing a bed, as is described in more detail herein below. The advantage of this embodiment is that there is not required to store a large amount of purified hydrogen gas in order to be able to meet high purified gas demands. If a high gas demand presents itself, the raw hydrogen gas stream can be purified at that moment. The maximum flow capacity can readily be increased by using more than two reactors or by increasing the flow capacity of the individual reactors. For instance, if the present process is carried out at a hydrogen refueling station, it can be ensured that the flow capacity of the purification process is at least equal to the flow capacity which with it is possible to fuel the vehicles. As such, even if a longer period of a high demand presents itself, delivery of the purified hydrogen gas stream can be guaranteed, provided there is sufficient raw hydrogen gas. However, if the process is connected to a large raw hydrogen gas pipeline infrastructure (which is preferred), the pipeline infrastructure can serve as a buffer or reservoir providing sufficient raw hydrogen gas. The storage container may however still be preferred to absorb small fluctuation in in- and output of the raw and purified hydrogen gas stream respectively.

[0028] In yet further preferred embodiments of the present invention, heat that is generated is at least partially recycled into a part of the process where heat is required. As such, the overall efficiency of the process is increased. Heat may be generated in several parts of the process. For example, the reduction of the oxidized metal in step a) is possibly an endothermic reaction requiring the input of heat. Accordingly, in a preferred embodiment, heat that is generated in step b) is at least partially used for said reduction of the oxidized metal in step a).

[0029] Another exchange of heat can take place between the waste gas stream and the reduction of the oxidized metal in step a). Generally, step a) is carried out at a temperature in the range of 200 to 900° C., preferably in the range of 300 to 700° C. such as about 500° C. As such, the waste gas stream has an elevated temperature, typically in the range at which step a) is carried out. In a typical embodiment of the invention, the waste gas stream is emitted into the air. However, emitting the waste gas stream at an elevated temperature would mean an undesirable loss of heat from the process. Accordingly, in a preferred embodiment of the invention, heat is extracted from the waste gas stream and at least partially used in said reduction in step a). This can be carried out using one or more heat exchangers.

[0030] Compressing the purified hydrogen gas stream generally requires the input of heat, albeit that the inherent inefficiency of the compressor may already produce sufficient heat to heat the compression process. However, depending on the pressure and temperature to which the purified hydrogen gas is compressed, the compression may also coincide with the generation of heat, which heat can be at least partially led to and used in step a). Therefore, there may be a heat exchange between the compression process steps of the purified gas stream and other process steps to optimize the efficiency of the process. For instance, if the compression and gas storage require or may benefit from additional heat input, said heat can at least partially be provided by using the heat generated in step b) (in case of an exothermic oxidation of the reduced metal).

[0031] In the embodiments wherein compressing the purified hydrogen gas stream result in cooling of the purified hydrogen gas, it may however actually be preferred to maintain this cooling and to not provide additional heat from other process steps. For instance, if the purified hydrogen gas is stored at a pressure of more than 700 bar (e.g. 900 bar), fueling a vehicle with the gas to a lower pressure (e.g. 700 bar) will typically result in a temperature increase of the gas (due to the Joule-Thomson effect). As such, the hydrogen gas in the fuel gas container of the vehicle will initially be of a high temperature an the gas will inherently be cooled by the environment (which will continue also after the fueling has been finished), due to which the pressure in the fuel container of the vehicle will drop. The result is that the vehicle contains less gas (i.e. gas at a lower pressure) than it could have been charged with and thus that it has been fueled to a sub-optimal driving range. This principle may be prevented by cooling the hydrogen gas upon fueling, such that the hydrogen gas entering the fueling container is of a lower temperature which will lead to no, or at least less, pressure decrease. This cooling may however make the overall process less energy efficient. Advantageously, by compressing the purified hydrogen gas and thereby cooling the purified gas stream, less or no additional cooling may be required when the vehicle is fueled. As such, compressing the purified hydrogen gas stream in step c) preferably coincides with cooling the purified hydrogen gas stream. This may enable more efficient and/or more rapid fueling of vehicles.

[0032] As for step a), step b) is preferably also carried out at a temperature in the range of 200 to 900° C., preferably in the range of 300 to 700° C. such as about 500° C. It is possible that steps a) and b) are carried out at about the same temperature, or at different temperatures. A consequence of carrying out step b) at an elevated temperature is that the temperature of the pure hydrogen gas that is generated is also elevated. In fact, the temperature of the gas is typically the same as the temperature at which step b) is carried out.

[0033] An advantage of carrying out steps a) and b) simultaneously, as described above, is that this facilitates the heat exchange between these steps. It removes or reduces the requirement to intermediately store heat obtained from one part of the process before it can be provided to the other part of the process. Simultaneously carrying out steps a) and b) thus also facilitates the heat integration of these steps.

[0034] In the embodiments wherein step b) is carried out at elevated temperatures, it is particularly preferred to pre-heat or pre-pressurize the water that is used in this step. The water used in this step is preferably steam. A suitable pressure to which the water can be pressurized is in the range of 20 to 50 bar such as about 30 bar. Pre-heating the water can efficiently be done out by using the heat generated in step b) (in case of an exothermic oxidation of the reduced metal) and/or by the heat of the water in the waste gas stream.

[0035] In a further aspect, the present invention is directed to an apparatus for the purification and supply of the raw hydrogen gas stream. The apparatus is particularly suitable to carry out the process as described herein-above. The apparatus comprises at least a first reactor comprising an oxidized material bed comprising oxidized metal material (e.g. particles) or a reduced material bed comprising reduced metal material (e.g. particles), said first reactor further comprising a gas inlet and a gas outlet, which gas outlet is connected to a hydrogen gas storage container via a compressor that suitable for compressing hydrogen gas. The inlet of the reactor is preferably connected to a hydrogen gas supply pipe line infrastructure.

[0036] In a preferred embodiment, the apparatus further comprises at least a further second reactor that comprises an oxidized bed comprising an oxidized metal or a reduced bed comprising a reduced metal, wherein said first reactor is connected to said second reactor via a heat exchanger such that during operation heat that is generated in the first reactor can be exchanged to the second reactor and vise-versa.

[0037] FIG. 1 illustrates a setup of the apparatus in accordance with a preferred embodiment. The first reactor (2) comprises the bed 1. When reactor 2 is in the state to process raw hydrogen gas, the bed 1 is at least partially the oxidized bed as described above. The raw hydrogen gas (indicated in FIG. 1 as containing H.sub.2, CO and CO.sub.2) can flow through the reactor entering in gas inlet (5). Then, upon full conversion of the hydrogen, the waste gas stream (indicated in FIG. 1 as containing H.sub.2O and CO.sub.2) can leave the first reactor (2) through outlet 6. In a particularly preferred embodiment, the heat from the waste gas stream can be recycled into the first reactor (2) or parts thereof (indicated in FIG. 1 with Q.sub.2). A preferred part of the first reactor to which the heat (Q.sub.2) is led is the gas inlet (5), which allows the heating the raw hydrogen gas when or just before this gas stream enters the first reactor (2). The second reactor 4 comprises the bed 3. When reactor 4 is in the state to convert water to the purified hydrogen gas, the bed 3 is at least partially the reduced bed as described above. The water (indicated in FIG. 1 as H.sub.2O) can flow through the reactor entering in gas inlet (7). Then, upon full conversion of the water, the purified hydrogen gas stream (indicated in FIG. 1 as containing H.sub.2) can leave the reactor 4. In a particularly preferred embodiment, the heat from the oxidation of the reduced metal is recycled into the first reactor (2) or parts thereof (indicated in FIG. 1 with Q.sub.1). A preferred part of the first reactor to which the heat (Q.sub.1) is led is the gas inlet (5), which allows the heating the raw hydrogen gas when or just before this gas stream enters the first reactor (2). The purified hydrogen gas stream can leave reactor 4 through outlet 8 and be led to the storage tank (10) after it has been compressed by a compressor (9). Thus, reactor 4 is preferably connected to the storage tank (10) via the compressor (9).

[0038] As described herein-above in more detail for the process, the process for which the apparatus is dedicated may comprise various heat exchanges to optimize the process. In FIG. 1 as described above, some of these heat exchanges have explicitly been described. It may be appreciated that for other embodiments the apparatus may comprise alternative or additional means to facilitate the exchange of heat in the apparatus. For instance, the heat from the waste gas stream can also be recycled to the gas inlet (7), which allows the pre-heating the water (e.g. to form steam) before it enters the second reactor (4). Also, the heat from the oxidation of the reduced metal in the second reactor (4) may be recycled to the gas inlet (7) for this reason.

[0039] In another particularly preferred embodiment, e.g. the heat from the compression of the purified hydrogen gas stream is recycled into first reactor (2).

[0040] In particularly preferred embodiment, the particle beds are included in the reactors in cartridges for an easy replacement of the particle beds.

[0041] It may be appreciated that the role of reactors 2 and 4 can be alternated. As such, reactor 4 can be used to purify the raw hydrogen gas stream and reactor 2 can be used to reduce the water to the purified hydrogen gas stream. Accordingly, both reactor 2 and 4 are preferably connected to the storage tank (10) via outlets 6 and 8 respectively and which reactor is actually used to lead the hydrogen gas stream to the compressor can be regulated by one or more valve systems (not illustrated). Similarly, both reactor 2 and 4 are preferably connected to the hydrogen supply pipe line via inlets 5 and 7 respectively. Moreover, the apparatus according to the invention can be controlled such that reactors 2 and 4 can be run simultaneously for an improved heat integration (Q.sub.1 and Q.sub.3 in particular). An additional advantage of simultaneously running the reactors and timely alternating their functions, is that the apparatus can effectively be run continuously. To this end, it may also be preferred that the apparatus comprises more than two reactors, for instance 4 or 5, or even more reactors. If the apparatus comprises more than two reactors, this would allow a preparation time between two cycles (i.e. steps a) and b)) while still operating the apparatus continuously (i.e. letting in a continuous flow of raw hydrogen gas and yielding a continuous flow of purified hydrogen gas). This preparation time can for example be used to purse the reactor or to bring it to a desired temperature and/or pressure.

[0042] In an alternative embodiment to alternating the role of reactors 2 and 4, a fluidized bed of particles can be circulated, similarly to a chemical looping combustion process. In a process and apparatus according this embodiment, the oxidized bed in reactor 2 can be reduced and after reduction be transferred to reactor 4, wherein it is again oxidized by the water. After its oxidation, the particles can again be transferred to reactor 2. As such, the process can also be carried out continuously.

[0043] The process and apparatus described herein are not necessarily limited to providing a purified hydrogen gas stream for application in hydrogen fuel cells. Other application that use or may benefit from the pure hydrogen gas stream can also be linked to the present process and apparatus. For instance, the raw hydrogen gas stream may also be purified by the process and the apparatus described herein to provide the purified hydrogen gas stream for use of the hydrogen gas as a reducing agent in chemical industry, for applications requiring a very clean hydrogen gas flame, for applications utilizing hydrogen plasma of a very high purity, and the like.

[0044] As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term “and/or” includes any and all combinations of one or more of the associated listed items. It will be understood that the terms “comprises” and/or “comprising” specify the presence of stated features but do not preclude the presence or addition of one or more other features.

[0045] For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.