SYSTEM FOR THE REMOVAL OF HYDROGEN/OXYGEN IN A GASEOUS STREAM

Abstract

According to one embodiment of the present invention there is provided a combiner for the removal of hydrogen/oxygen gas in a gaseous stream, said combiner comprising: a pipe capable of accommodating the flow of a gaseous stream, wherein the pipe is adapted to transmit the gaseous stream to a catalytically active structure (CAS), the CAS having: contact with the substantial majority of the gaseous stream, a housing, and an inlet, said inlet being connected to the pipe, and an outlet, for the removal of the gaseous stream post recombination, and a second pipe connected to the outlet of the CAS for the transmission of the gaseous stream away from the combiner. A second embodiment of the invention sees the CAS housed within an electrochemical cell directly.

Claims

1. A combiner device for, in use, removing a hydrogen contaminant in a principal gas stream comprising predominantly oxygen, or vice versa, with said combiner device comprising: a catalytically active structure (CAS) comprising a housing having an inlet and an outlet; a first pipe coupled to the inlet for conveying said principal gas stream into the housing such that it flows from the inlet to the outlet, and an exhaust pipe for conveying said principal gas stream away from said housing; the CAS further comprising a structural element comprising or including a catalytic material operable to combine hydrogen and oxygen to form water, the structural element being located within the housing, part way between the inlet and the outlet, and extending across a substantial majority of a cross-section thereof, such that, in use, the principal gas stream flows therethrough.

2. The combiner device of claim 1, wherein the CAS is configured to combine hydrogen and oxygen to form water when the quantity of the contaminant gas in the principal gas stream is above a predetermined amount, the device further comprising supplementing means for increasing an amount of the contaminant gas in the principal gas stream to above said predetermined threshold so as to ensure that combination by the CAS of hydrogen and oxygen in said principal gas stream occurs.

3. The combiner device of claim 2, wherein said supplementing means comprises either: means for recirculating the principal gas stream from downstream of the CAS back to upstream thereof, or a reservoir containing the contaminant gas, the reservoir being adapted to release said contaminant gas under a predetermined condition.

4. The combiner device of claim 3, wherein the reservoir is a metal hydride.

5. The combiner device of claim 1, configured to simultaneously recombine the contaminant gas with the principal gas to form water, and detect the presence of said contaminant gas.

6. The combiner device of claim 5, further comprising one or more of the following sensors is used for the detection of the contaminant gas: a humidity sensor, a temperature sensor, a thermal conductivity sensor.

7. The combiner device of claim 6, wherein the one or more sensors is coupled to computing means for determining the amount of a contaminant gas present in the principal gas stream.

8. The combiner device of claim 1 coupled with a demister, the CAS being either: upstream of a demister pad, downstream of a demister pad, or combined with a demister pad.

9. The combiner device of claim 8, wherein the demister additionally acts as a flame arrestor, preferably wherein the demister is attached to the inlet.

10. The combiner device of claim 8, wherein the demister is a microporous material, preferably one of: a foam or sintered material, preferably a foam or sintered metal; a ceramic, preferably a sintered ceramic; or a carbon based material.

11. The combiner device of claim 1, further comprising means for the removal and optional recycling of the generated liquid.

12. The combiner device of claim 1, wherein the structural element comprises a backbone of: carbon black, metal oxides including ceramics, a polymeric film, metal foam, zeolitic structures, or metal organic frameworks.

13. The combiner device of claim 1, further comprising means for the introduction of ambient air to the principal gas stream.

14. The combiner device of claim 1, wherein the catalytic material is platinum, palladium or an alloy thereof.

15. The combiner device of claim 1, wherein the catalytic material is a non-PGM material including metal alloys, ceramics, chalcogenides, pnictogenides, organometallics, or other metal complexes.

16. An electrochemical cell comprising: a membrane electrode assembly (MEA) wherein the MEA comprises: an anode layer, a cathode layer and an ion exchange membrane situated therebetween; an anodic compartment adapted to operate at a first pressure, a cathodic compartment adapted to operate at a second pressure, and an electrically insulated catalytically active structure (CAS), wherein the CAS is: situated in the compartment with a relatively lower pressure, and extending across a substantial majority of the cross-section said compartment, such that, in use, the principal gas stream flows therethrough.

17. The electrochemical cell of claim 16, comprising any one of: an electrolyser, AEM or PEM, a fuel cell, reversible fuel cell, electrochemical compressor, or an AEM electrolyser with a dry cathode preferably wherein the AEM electrolyser with the dry cathode is configured to operate with the dry cathode at an elevated pressure.

18-19. (canceled)

20. The electrochemical cell of claim 16, wherein the CAS is insulated from other components of the electrochemical cell by an ionomer thin film or ultra-thin membrane on one or both sides, or a combination thereof.

21. A method, in a system that utilizes a principal gas stream comprising hydrogen and oxygen, for removing contaminant hydrogen from a principal gas stream comprising predominantly oxygen, or vice versa, the method comprising providing, in said system, a combiner device according to claim 1 such that said principal gas stream flows through the housing from the inlet to the outlet.

22. A method according to claim 21, wherein: said system comprises an electrochemical cell; and/or said principal gas stream comprises between 0.4 and 20% contaminant gas; and/or the operating temperature is between 20 and 100° C.

23-24. (canceled)

Description

[0087] To help understanding of the invention, a specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which:

[0088] FIG. 1A and FIG. 1B each illustrate schematically a combiner in accordance with a first embodiment of the present invention;

[0089] FIG. 2 illustrates schematically a combiner in accordance with an embodiment of the present invention, coupled with a demister;

[0090] FIG. 3 illustrates schematically a combiner in accordance with a second embodiment of the present invention;

[0091] FIG. 4A and FIG. 4B each illustrate schematically a respective alternative embodiment of the present invention;

[0092] FIG. 5 illustrates schematically a combiner in accordance with an embodiment of the present invention, utilising a recycle loop; and

[0093] FIG. 6 illustrates schematically a combiner in accordance with an embodiment of the present invention.

[0094] FIG. 7A and FIG. 7B Illustrates schematically a combiner in accordance with the present invention

[0095] Referring to FIG. 1A there can be seen the housing 3a, a pipe 1 introducing the gas to be purified via inlet 1a. Within the housing 3a there is present the CAS 4. At the CAS 4, the recombination reaction occurs, thereby removing the hydrogen in the predominantly oxygen stream, or oxygen in the predominantly hydrogen stream. The purified gas can leave via outlet 2a to pipe 2. Means for causing the flow of gas are not shown herein and should be known to the individual of ordinary skill in the art.

[0096] In the embodiment depicted by FIG. 1A, a stream of gas comprising predominantly oxygen with some contaminant hydrogen enters the inlet 1a where it contacts the CAS 4. At the CAS, recombination occurs combining hydrogen with oxygen to form water. Means for the removal of said water are not shown. Also not shown are an optional sensor, temperature and/or humidity, for the detection of concentration of the contaminant hydrogen. One or more temperature sensors would typically be coupled to the CAS, whereas one or more humidity sensors would typically be located shortly after (i.e. down stream of) the CAS.

[0097] The embodiment illustrated in FIG. 1B of the drawings is similar in many respects to that of FIG. 1A, but differs in the geometry of housing 3b. More generally, the geometry of the housing may be dictated by various characteristics and parameters of the system, including, for example, the pressure at the inlet and/or a desired pressure at the outlet.

[0098] As referenced above, the embodiment depicted in FIG. 1B is similar in most other respects to that of FIG. 1A, and operation thereof would occur in a similar manner to that described above in respect of FIG. 1A.

[0099] FIG. 2A illustrates an embodiment of the present invention in combination with a water tank 6. Such a water tank is commonly used with an electrolyser. In a typical such electrolyser arrangement, and as will be well understood by a person skilled in the art, the electrolyte flows from the electrolytic stack to the water tank 6 where it is recirculated. With AEM electrolysers, and other types, the dissolved gas leaving the liquid in the water tank 6 may contain a combination of oxygen and hydrogen. A demister housing 3c houses both the CAS 4, and a demister pad 5. The gas enters the housing 3c, from the water tank 6, via inlet 7a. The CAS 4 is shown by dashed lines denoting it can be above or below (i.e. upstream or downstream of) the demister pad 5, depending on whether the catalyst used is hydrophobic or hydrophilic respectively. A hydrophilic catalyst may require further drying means after recombination (not shown) if a dry outlet is needed. After combination, the gas leaves the housing 3c via outlet 7b.

[0100] A demister may be used to conserve the liquid levels within the electrolyser to reduce the frequency of maintenance such as refilling. The connections to and from the water tank not related to the outward flow of gas have not been shown here, and should be known to an individual of ordinary skill in the art.

[0101] The embodiment illustrated in FIG. 2B differs from that of FIG. 2Ain that ambient air is introduced to the CAS via a second inlet 8. A fan may be used for the introduction of ambient air, or other gas. If operating at pressure, a compressor may be used instead of a fan to allow the introduction of air to the CAS 4.

[0102] In the arrangements of both FIGS. 2A and 2B, liquid containing dissolved gases, predominantly oxygen with some hydrogen, enters the water tank 6, preferably configured as a liquid degassing tank. The dissolved gases are removed from the liquid, and travel to the demister 3c. Within this housing 3C, the demister pad 5 can retain liquid levels, and the CAS 4 ensures that only a safe gas mixture is vented from the outlet 7b.

[0103] FIGS. 2A and 2B may also combine the demister and CAS such that they are a single component. Additionally, the device may be adapted to include a recombiner as seen in FIG. 7 before and/or after a demister, with the demister in this embodiment not having a CAS. The water in FIG. 2 not shown.

[0104] In FIGS. 2A and 2B the water in the tank 6 degases, the gas and water vapour enter the housing 3c via inlet 7a before crossing the demister pad 4 then CAS 5, or the CAS 5 then demister pad 4, the order depending upon the embodiment. The demister and CAS may also be combined. The water vapour coalesced by the demister flows back down to the water tank back through the inlet 7a. For embodiments with the demister after the CAS a bypass (not shown) may be provided to allow for flow of coalesced water vapour (bypassing the CAS) back into the tank 6, or to drainage, to prevent flooding. The housing 3c may also be rotated to prevent flooding of the CAS.

[0105] Referring to FIG. 3 of the drawings, an embodiment of the invention in the form of an electrolytic cell is illustrated schematically, having a housing 3d. In this embodiment, water or an electrolyte enters the anode 9 of the cell, via inlet 13. The MEA 11 is illustrated as being electrically isolated (at 12) from the CAS 4. In operation, hydrogen is generated in the cathode 10 of the cell and leaves via outlet 15. When operating at pressure, hydrogen can crossover from the cathode 10 to the anode 9, hence the need for hydrogen removal. The CAS 4 acts to combine the crossed-over hydrogen with the oxygen generated via electrolysis of water. The relatively pure oxygen stream then leaves the anode 9 via the outlet 14. The electrolytic cell depicted in FIG. 3 is configured to operate with a dry cathode.

[0106] FIG. 4A shows, like FIG. 3, an electrolytic cell configured to operate with a dry cathode. The difference can be found in the MEA 11. In this embodiment, the an-ion exchange membrane 15 is in close contact with the CAS 4, and an ionomer layer (or thin cast membrane)16, normally an ultra-thin film, wherein the film is normally polymeric, separates the CAS 4 from the anode layer 17. The cathode layer 18 can be seen on the other side of the an-ion exchange membrane. In the embodiment illustrated in FIG. 4B of the drawings, the ionomer layer 16 separates the CAS from the ion-exchange membrane.

[0107] The electrolytic cells illustrated in FIGS. 3, 4A and 4B of the drawings work as follows. Electrolyte enters the anodic compartment via inlet 13. Electrolysis occurs with hydrogen being generated in the cathodic compartment 10 to a pressure higher than in the anodic compartment 9. As a result, some hydrogen may crossover to the anodic compartment 9 (wherein oxygen is being generated). This mixture of oxygen and hydrogen is present in the anodic compartment only, and/or downstream from the anodic compartment. The CAS 4 being in said anodic compartment causes recombination of oxygen and hydrogen to form water, thereby removing the minority contaminant gas.

[0108] FIG. 5 depicts an embodiment of the present invention similar in many respects to that depicted in FIG. 1a. in that the housing 3a has a pipe 1 entering via inlet 1a; and, after (i.e. downstream of) the CAS 4, there is the outlet 2a to pipe 2. In this case. branching from pipe 2, there is a recycle loop comprising a feed 20a to a valve 21, wherein the recycle loop enters the housing via pipe 20b. Alternatively the recycle loop could be further upstream of the CAS 4. Other embodiments may be envisaged by a person skilled in the art, and modifications and variations can be made to the described embodiments without departing from the spirit of the present invention as defined by the appended claims. Control means for the valve 21 are not shown. Also not shown is the BOP in pipe 2 for ensuring a full recycle occurs.

[0109] FIG. 6 depicts an alternative embodiment of the present invention similar to those described with reference to FIGS. 1A and 1B, wherein a hydrogen reservoir 22 is employed. In general, the hydrogen reservoir is typically a metal hydride, with options and alternatives disclosed above. The hydrogen reservoir is located, in this embodiment, prior to (i.e. upstream of) the CAS 4. Means for triggering the release of reserved hydrogen in the reservoir 22 are not shown in FIG. 6, but are disclosed above.

[0110] An embodiment combining those of FIGS. 5 and 6 could result in the reservoir 22 being downstream of the housing but before the recycle begins at 20a. This would ensure any contaminant gas not recombined is not vented or passed further downstream where issues may arise.

[0111] Any of the embodiments may be adapted to operate as a detector and not just a combiner, by the introduction of temperature sensing means, and computing means to calibrate the temperature detected to that expected at different ratios of contaminant gases. Such means are not depicted herein. Alternatively, or in addition, humidity sensors and similar computing means may be employed. The important thing here is that a sensor of a variety of types may be configured to allow for the calculation of the ratio of gases present, and any variant utilising such an approach in combination with a combiner as claimed herein should be considered within the scope of the invention.

[0112] According to FIG. 7A there is shown a combiner in accordance with the present invention. A gaseous stream from a device such as an electrolyser comprising predominantly hydrogen with some oxygen and water/water vapour enter the inlet 1. Structure 50 is a standalone, or in an alternative embodiment combined flame arrestor/demister/sintered metal filter. The water/water vapour coalescing and draining via water outlet 19, valves etc. not shown with the water going to drainage or water tank or other destination. The gas enters the housing 3 comprising the CAS 4. Within the housing the exothermic recombination occurs. Attached to the housing is a heater 30 with means for measuring temperature. Also not shown is the connection to an option PID or other controller adapted to run the heater to ensure the CAS maintains a desired temperature, heating during start up and shut down where crossover/contaminant levels are low ensures good operation of the recombiner. Additional computing means are not shown which are adapted to alert the user if the temperature is too high indicating excessive contaminant gases. After the CAS 4 the treated gas leaves the recombiner via outlet 2. Also not shown is the optional insulation and/or polymeric coating of the component.

[0113] FIG. 7B largely reflects FIG. 7A with the only difference being the demister/flame arrestor is downstream of the CAS 4. Not shown is an embodiment with demister/flame arrestor both up and down stream of the CAS 4. The water outlet 19 in FIG. 7B is optional as the coalesced water may be allowed to exit the vent line 2.

[0114] For reasons of practicality, it is not preferred but is possible that the electrolytic stack or cells thereof may be provided with a recombiner before and/or after a demister as seen in FIG. 7 or another in accordance with the present invention. In the pref3erred embodiment the demister and recombiner are situated on the water tank to which electrolyte and generated gases with contaminant are transferred.

[0115] The embodiments depicted may be amended or combined to include any of the features described in the document, such as the demister pad being the CAS, or the addition of a hydrogen or oxygen reservoir, or recycle loop for the downstream gases.

[0116] The invention is not intended to be restricted to the details of the above described embodiment. For instance, the language used refers to the removal of hydrogen in a stream containing oxygen. Conversely the device could be used and recalibrated for the removal of oxygen in a predominantly hydrogen-based stream.

[0117] The invention is not intended to be limited to the field of electrolysers. In fact, it could be utilised to detect and remove either hydrogen or oxygen from a stream comprising both gases in any application. It is envisaged that the present invention could be adapted for use in a variety of applications where two gases are in a stream and can be recombined. When such reactions are exothermic, the concentrations/ratio may be adapted in the same way. Other means may be provided to remove other contaminants, such as CO.sub.2 scrubbers, for example.

[0118] It is noted that other contaminants may be present, and other means of removal, scrubbing or detecting may also be provided in such instances.

[0119] The invention is not necessarily intended to be limited to the support upon which the catalyst is held.

[0120] For the embodiment wherein the CAS is within the electrochemical cell, the cell itself should be construed as the housing.

[0121] The present invention is not intended to be limited by the location of either the anode or cathode catalyst in embodiments claimed within an electrochemical cell.

[0122] In any embodiment the recombiner with CAS is intended to be placed between a device such as, but not necessarily limited to, an electrolyser and a vent line.