WO2008069778A1

WO2008069778A1 - Regenerable ammonia scrubber system for a fuel cell

Info

Publication number: WO2008069778A1
Application number: PCT/US2006/046184
Authority: WO
Inventors: Richard D. Breault
Original assignee: UTC Fuel Cells LLC
Current assignee: UTC Power Corp
Priority date: 2006-12-04
Filing date: 2006-12-04
Publication date: 2008-06-12
Anticipated expiration: 2009-06-04

Abstract

A regenerable ammonia scrubber system (10) for removing ammonia from a fuel stream for a fuel cell (18) includes a first regenerable scrubber (12) and a second regenerable scrubber (22). Each scrubber (12, 22) is secured in fluid communication with a fuel distribution valve (28) configured to selectively direct the fuel stream to one of the first scrubber (12) or the second scrubber (22), and is also secured in fluid communication with an oxidant distribution valve (38) configured to selectively direct flow of the oxidant to the other of the first or the second scrubbers (12, 22). The first and second regenerable scrubbers (12, 22) contain an acid solution (60), a porous support material (62) within the acid solution (60), and a noble metal catalyst uniformly dispersed through the porous support material (62). The noble metal catalyst is preferably platinum.

Description

Description REGENERABLE AMMONIA SCRUBBER SYSTEM FOR A FUEL CELL

Technical Field [0001] The present disclosure relates to fuel cells that are suited for usage in transportation vehicles, portable power plants, or as stationary power plants, and the disclosure especially relates to a system for removing ammonia from a fuel stream flowing into a fuel cell.

Background Art

[0002] Fuel cells are well known and are commonly used to produce electrical current from hydrogen containing reducing fluid fuel and oxygen containing oxidant reactant streams to power electrical apparatus such as transportation vehicles. In fuel cells of the prior art, it is well known that fuel is often produced by a reformer and the resulting fuel flows from the reformer through a fuel inlet line into an anode flow field of the fuel cell. As is well known an oxygen rich reactant simultaneously flows through a cathode flow field of the fuel cell to produce electricity. Unfortunately, known fuels for fuel cells, such as reformate fuels from reformers, frequently contain contaminants especially ammonia. The presence of ammonia in the fuel stream is detrimental to the performance of the fuel cell.

[0003] It is understood that ammonia is a common byproduct of the reforming process and although the reforming process is designed to minimize formation of ammonia, it is common that low levels of ammonia are present in the reformate fuel. Nitrogen present in a hydrogen rich fuel reacts with hydrogen in common steam reformers, which typically utilize conventional nickel catalysts, to form ammonia in a concentration range of parts per million. The ammonia causes performance degradation of the fuel cell when introduced to either a proton exchange membrane fuel cell ("PEMFC") or a phosphoric acid fuel cell ("PAFC") . Fuel specifications for a known PAFC power plant require a maximum allowable nitrogen concentration in the natural gas of 4% to prevent degradation of the fuel cell due to ammonia formation. This fuel specification places a serious limitation on the use of fuel cells in areas of the world where natural gas includes a nitrogen content in excess of the fuel specification. Additionally, in the case of auto thermal or partial oxidation reformers, nitrogen can also be introduced when air is used as the oxygen source for the reforming process.

[0004] Many efforts have been undertaken to remove ammonia and other contaminants from fuel streams of fuel cells. For example, U.S. Patent No. 4,259,302 to Katz et al . discloses use of a regenerable scrubber for removing ammonia from a fuel cell fuel stream. Ammonia gas is scrubbed from the fuel stream in a bed of support material soaked with acid. Thereafter, oxygen containing gas is passed through the scrubber to oxidize the captured ammonia and vent it out of the scrubber as nitrogen gas. In Katz et al., the preferred acid is phosphoric acid and the preferred support material is carbon in the form of porous carbon particles or pellets. Katz et al . also shows dual scrubbers, wherein the scrubbers alternately scrub ammonia from the fuel stream and are subsequently regenerated with a flow of oxygen containing gas in order to provide the fuel cell with an uninterrupted flow of a substantially ammonia free fuel stream. As disclosed in Katz, when an ammonia contaminant passes through a scrubber having phosphoric acid, the ammonia is absorbed on the support material and reacts with the phosphoric acid as follows:

H₃PO₄+NH₃→ (NH₄) H₂PO₄ (Equation 1)

[0005] Prior to using all of the phosphoric acid, the scrubber is regenerated by passing an oxygen containing gas through the scrubber. The effect of the oxygen is to convert the ammonium dyhydrogen phosphate back to phosphoric acid according to the following equation:

2(NH₄)H₂PO₄ +3/2O₂ →2H₃PO₄+N₂ +3H₂O (Equation 2)

Unfortunately however, protracted testing has established that the regeneration of the Katz et al. scrubbers is poorer than anticipated.

[0006] U.S. Patent 5,792,572 to Foley et al . shows a further effort at minimizing ammonia contamination wherein a scrubber contains phosphoric acid absorbed onto porous carbon pellets. This scrubber of Foley et al. is utilized to both remove ammonia from the fuel stream and also to add acid to the fuel cell in a controlled manner. However, in the Foley et al. system, a scrubber capable of providing acceptable ammonia removal for five to ten years without replacement must be unacceptably large, bulky and excessively costly.

[0007] More recently U.S. Patent No. 6,376,114, that issued on April 23, 2002 to Bonville, Jr. et al . , discloses another elaborate system for removing ammonia and other contaminants from reformate fuel. The system of Bonville, Jr. et al., includes alternatively a disposable ammonia scrubber, an ammonia scrubbing cool water bed and an ammonia stripping warm water bed, a pair of first and second regenerable scrubbers, or a single regenerable scrubber. Again, while effective the Bonville, Jr. et al. system includes elaborate and costly components that require a high level of maintenance to operate the system. The aforesaid three patents are owned by the assignee of all rights in the present disclosure. Other ammonia and related contaminant removal systems for fuel cells are known in the art. However, none of these provide for efficiently removing ammonia with minimal costs and minimal maintenance requirements . Most known ammonia contaminant removal systems require large components for processing a high volume of fluids, or require high frequency removal and replacement of expensive, contaminated filters and/or ion beds, etc. [0008] Consequently, there is a need for a ammonia removal system for a fuel stream of a fuel stream that may be operated efficiently for long periods of time without high-frequency maintenance.

Summary

[0009] The disclosure is a regenerable ammonia scrubber system for removing ammonia from a fuel stream for a fuel cell. The system includes a first regenerable scrubber secured in fluid communication with a fuel inlet line that is configured to selectively direct flow of the fuel stream from the first scrubber into the fuel cell. The first regenerable scrubber is also secured in fluid communication with a first oxidant exhaust valve that is configured to permit or prohibit flow of an oxidant out of the first scrubber. The system also includes a second regenerable scrubber secured in fluid communication with the fuel inlet line, and in fluid communication with a second oxidant exhaust valve configured to permit or prohibit flow of the oxidant out of the second scrubber. A fuel distribution valve is secured in fluid communication with a fuel source and with the first and second regenerable scrubbers and is configured to selectively direct flow of the fuel stream from the fuel source to either the first regenerable scrubber or the second regenerable scrubber. An oxidant distribution valve is also secured in fluid communication with an oxidant source and is configured to selectively direct flow of the oxidant from the oxidant source to whichever of the first regenerable scrubber or the second regenerable scrubber that is not receiving the fuel stream.

[0010] The first and second regenerable scrubbers contain a porous support material, an acid solution absorbed within the support material, wherein the porous support material is compatible with the acid solution, and a noble metal catalyst uniformly dispersed through the porous support material. The noble metal catalyst is preferably platinum, and a preferable concentration of the noble metal catalyst is about 0.1 to about 1.0 weight percent P^λwt%") of the weight of the porous support material. A preferred porous support material includes carbon in the form of cylindrical pellets. Use of pellets minimizes a pressure drop of gaseous fuel passing through the scrubber. In known scrubbers that utilize oxygen containing gas for regeneration to oxidize accumulated ammonia, a rate of oxidation of the contaminants within the scrubbers is determined by an effective electrochemical potential which is a function of the oxidation of the support material. Where carbon is the support material, the potential for oxidation of carbon is about 0.60 volts. By catalyzing the porous support material, such as catalyzed carbon having a noble metal such as platinum, the potential is increased to about 0.90 volts, which provides for an oxidation rate that is effectively about two-hundred times greater than an oxidation rate based upon non-catalyzed carbon support material .

[0011] Additionally, during the regeneration cycle wherein the oxygen containing gas is passing through either of the regenerable scrubbers, some of the noble metal will be dissolved into solution within the acid. However, in the absorption cycle, the gaseous hydrogen fuel present and passing through the scrubber will reduce the noble metal ions back to a metal form and they are thereafter re-deposited as metal crystals upon the porous support material. Therefore, the present system provides for maintenance of an initial system concentration condition of the noble metal upon the support material through repeated absorption-regeneration cycles, rather than a slow deterioration or loss of the valuable noble metal catalyst.

[0012] By catalyzing the porous support material with a noble metal, the present system provides for a dramatic increase in a rate of regeneration of the regenerable scrubbers through use of a relatively small amount of expensive noble metal that is maintained in a stable concentration within the regenerable scrubbers . Therefore, the scrubbers may be sized considerably smaller than would be required to achieve the same high proportion of contaminant removal achieved by prior art scrubbers that are much larger and much more costly. The disclosure also includes an embodiment of the system having one of the regenerable scrubbers with the described acid, noble metal catalyzed porous support material, and selective fuel and oxygen feed and exhaust lines .

[0013] Accordingly, it is a general purpose of the present disclosure to provide a regenerable ammonia scrubber system for a fuel cell that overcomes deficiencies of the prior art. [0014] It is a more specific purpose to provide a regenerable ammonia scrubber system for a fuel cell that enhances removal of ammonia from a fuel stream for a fuel cell while also reducing costs and sizes of components of the system.

[0015] These and other purposes and advantages of the present regenerable ammonia scrubber system for a fuel cell will become more readily apparent when the following description is read in conjunction with the accompanying drawing.

Brief Description of Drawing

[0016] Figure 1 is a simplified schematic representation of a regenerable ammonia scrubber system for a fuel cell constructed in accordance with the present disclosure.

Description of the Preferred Embodiments [0017] Referring to the drawings in detail, a regenerable ammonia scrubber system for a fuel cell is shown in FIG. 1, and is generally designated by the reference numeral 10. The system 10 includes a first regenerable scrubber 12 secured in fluid communication with a fuel inlet line 14 through a first extension 15 of the fuel inlet line 14. The fuel inlet line 14 includes a fuel inlet valve 16 that is configured to selectively direct flow of a fuel stream from the first regenerable scrubber 12 and a first extension 15 of the fuel inlet line 14 to a fuel cell 18. By the word "selectively," it is meant that the fuel inlet valve 16 may be selected to permit or restrict flow of the fuel stream from the first regenerable scrubber 12 to the fuel cell 18. The fuel inlet line 14 may include any control means 16 known in the art that can achieve that function. The first regenerable scrubber 12 is also secured in fluid communication with a first oxidant exhaust line 20 that is configured to direct flow of an oxidant out of the first regenerable scrubber 12.

[0018] The system 10 also includes a second regenerable scrubber 22 that is secured in fluid communication with the fuel inlet line 14 through a second extension 24 of the fuel inlet line 14. As shown in FIG. 1, the second extension 24 of the fuel inlet line 14 is also secured in fluid communication with the fuel inlet valve 16. The fuel inlet valve 16 may be a three- way valve known in the art that may selectively direct the fuel stream from either the first regenerable scrubber 12 or the second regenerable scrubber 22 into the fuel cell 18, or any control means 16 known in art that can achieve this described function. The second regenerable scrubber 22 is also secured in fluid communication with a second oxidant exhaust line 26 that is configured to direct flow of an oxidant out of the second regenerable scrubber 22. [0019] A fuel distribution valve 28 is secured in fluid communication with a fuel source 30 and with the first and second regenerable scrubbers 12, 22 through a fuel feed line 32. A first extension 34 of the fuel feed line 32 directs flow of the fuel stream from the fuel distribution valve 28 into the first regenerable scrubber 12. A second extension 36 of the fuel feed line 32 directs flow of fuel from the valve 28 into the second regenerable scrubber 22. The fuel distribution valve 28 is configured to selectively direct flow of the fuel stream from the fuel source 30 into one of the first regenerable scrubber 12 or second regenerable scrubber 22. The fuel distribution valve 28 may also be any fuel distribution control means 28 known in art that is capable of performing the described function, such as two separate fuel distribution valves (not shown) on two separate fuel feed lines (not shown) , etc.

[0020] An oxidant distribution valve 38 is secured in fluid communication with an oxidant source 40 and is configured to selectively direct flow of an oxidant from the oxidant source 40 to 'the other of the first regenerable scrubber 12 or the second regenerable scrubber 22 through an oxidant feed line 42. A first extension 44 of the oxidant feed line 42 is secured in fluid communication between the oxidant distribution valve 38 and the first regenerable scrubber 12, and a second extension 46 of the oxidant feed line 42 is secured in fluid communication between the valve 38 and the second regenerable scrubber 22. As with the fuel distribution valve 28, the oxidant distribution valve 38 may be an oxidant distribution control means 38 for selectively directing flow of the oxidant from the oxidant source 40 to whichever of the first regenerable scrubber 12 or the second regenerable scrubber 22 that is not receiving flow of the fuel stream. [0021] For purposes herein, by the above characterization of the fuel distribution valve 28 being configured to selectively direct flow of the fuel stream to "one of the" first regenerable scrubber 12 or second regenerable scrubber 22, and the characterization of the oxidant distribution valve 38 being configured to selectively direct flow of the oxidant to "the other of the" first regenerable scrubber 12 or second regenerable scrubber 22, it is meant that if the fuel distribution valve 28 is configured to direct flow of the fuel stream through the first regenerable scrubber 12, then, responsive to that setting of the fuel distribution valve 28, the oxidant distribution valve 38 would be configured to direct flow of the oxidant through the second regenerable scrubber 22. Similarly, whenever the fuel distribution valve 28 directs flow of the fuel through the second regenerable scrubber 22, then, responsive to that setting of the fuel distribution valve 28, the oxidant distribution valve 38 would be configured to direct flow of the oxidant through the first regenerable scrubber 12.

[0022] Whenever the oxidant is flowing through either the first regenerable scrubber 12 or the second regenerable scrubber 22, the scrubber receiving the oxidant is referred to as being in a regeneration portion of an absorption-regeneration cycle. Similarly, whenever a scrubber 12, 22, is receiving the fuel stream, it is referred to as being in an absorption portion of the absorption-regeneration cycle. It is pointed out however, that while the distribution valves 28, 38, are configured as described above, a regeneration portion of the absorption-regeneration cycle does not have to be the same duration as the absorption portion of the cycle. In other words, satisfactory regeneration of a scrubber 12, 22, may occur long before the scrubber 12, 22, in the absorption portion of the cycle needs to be regenerated. In such circumstances, the oxidant distribution valve 38 or oxidant distribution control means 38 would be configured to terminate flow of the oxidant to the scrubber 12, 22, in the regeneration portion of the cycle.

[0023] The first oxidant exhaust line 20 also includes a first oxidant exhaust valve 48 for selectively permitting or prohibiting flow through the first oxidant exhaust line 20. The second oxidant exhaust line 26 similarly includes a second oxidant exhaust valve 50 for selectively permitting or prohibiting flow through the second oxidant exhaust line 26. The first and second oxidant exhaust line 20, 26, may simply vent oxidant out of the system 10 down stream from the valves 48, 50, or, as shown in FIG. 1, the lines 20, 26, may direct flow to exhaust through a fuel cell exhaust line 52 down stream from a fuel cell exhaust valve 54. In alternative embodiments of the system 10, the first and second oxidant exhaust valves 48, 50 may be secured in direct fluid communication with the first and second regenerable scrubbers 12, 22 to selectively exhaust the oxidant directly out of the scrubbers 12, 22.

[0024] The system 10 may also include a controller means 56 for controlling the fuel inlet valve 16, the fuel distribution valve 28, the oxidant distribution valve 38, the first oxidant exhaust valve 48, and the second oxidant exhaust valve 50, to perform the functions described herein. The controller means 56 may be any controller known in the art capable of performing the functions described herein such as a computer, a electro-mechanical controls, a human operator (not shown) manually operating the valves, etc. The controller means 56 may also receive sensed information signals from the valves 16, 28, 38, 48, 50 and/or transmits control signals through communication lines 58 shown as hatched lines in FIG. 1.

[0025] The first regenerable scrubber 12 and the second regenerable scrubber 22 contain an acid solution 60 and a porous support material 62, wherein the acid solution 60 is absorbed within the porous support material 62. The porous support material 62 is selected to be compatible with the acid solution 60. By the phrase "compatible with", it is meant that the porous support material 62 is not corroded by or otherwise degraded by the particular acid contained within the scrubbers 12, 22. A preferred acid is phosphoric acid. A noble metal catalyst is uniformly dispersed through the porous support material 62. The porous support material 62 may be any porous material known in the art capable of supporting the selected noble metal. A preferred porous support material 62 includes carbon in the form of cylindrical pellets 62. Use of such cylindrical carbon pellets minimizes a pressure drop of gaseous fuel passing through the scrubbers 12, 22. The support material 62 may be a carbon or activated carbon material, preferably in the form of a porous pellet. Such porous carbon pellets are available from the CALGON CARBON CORPORATION, of Pittsburgh, Pennsylvania, U.S.A., under the brand name "WSC470 Pellet Activated Carbon". Carbon pellets that have a 3-4 millimeter diameter are preferred.

[0026] The noble metal catalyst is preferably platinum, and a preferable concentration of the noble metal catalyst is about 0.1 to about 1.0 weight percent

("wt%") of the weight of the porous support material 62. The noble metal catalyst platinum may be deposited by techniques known in the art. For example, 99 grams of carbon pellets are made into a slurry with a solution of 50% deionized water and 50% isopropanol. An aqueous solution of chloroplatinic acid containing one gram of platinum is added to the slurry with constant stirring. The slurry is heated to 90⁰C with continuous stirring to evaporate the water and isopropanol and to deposit the chloroplatinic acid within the carbon pellets . Hydrogen gas is flowed over the dried pellets at 90⁰C to reduce the chloroplatinic acid to platinum and to remove the chloride as hydrochloric acid. This results in a catalyzed pellet containing 1 weight percent platinum.

[0027] In a printed publication by Szymanski et al. published in J. Electrochemical Society, Vol. 127, No. 7 in July 1980, and entitled "The Effect of Ammonia on Hydrogen-Air Phosphoric Acid Fuel Cell Performance", the authors showed that ammonia can be oxidized to gaseous nitrogen and that a rate of oxidation of the ammonia is a strong function of a potential to which the oxygen and ammonia are exposed. In a known scrubber that utilizes oxygen for regeneration to oxidize accumulated ammonia, a rate of oxidation of the contaminants within the scrubbers is determined by an effective electrochemical potential of the porous support material. Where carbon is the support material, the potential for oxidation of carbon is about 0.60 volts for a form of carbon particles such as utilized in the aforesaid Patent to Katz et al. In the present system 10, by catalyzing the porous cylindrical carbon pellet support material 62 with platinum, the electrochemical potential of the carbon support material 62 is increased to about 0.90 volts. That increase provides an oxidation rate that is effectively about two-hundred times greater than an oxidation rate based upon non-catalyzed porous carbon support material. (For purposes herein, the word "about" means plus or minus ten percent.)

[0028] During the regeneration portion of the absorption-regeneration cycle wherein the oxidant is passing through either of the regenerable scrubbers 12, 22, some of the noble metal will be dissolved into solution within the acid 60. However, In the absorption portion of the cycle, the gaseous hydrogen fuel stream present and passing through the scrubber 12, 22 will reduce the noble metal ions back to a metal form and they thereafter re-deposit as metal crystals upon the porous support material 62. Therefore, the present system 10 provides for maintenance of an initial system concentration condition of the noble metal upon the support material 62 through repeated absorption- regeneration cycles, instead of the system 10 experiencing a slow deterioration or loss of the valuable noble metal catalyst.

[0029] In operation of the regenerable ammonia scrubber system 10 for a fuel cell 18, the first regenerable scrubber 12 may be first controlled to be in the absorption portion of the absorption-regeneration cycle and to thereby supply a de-contaminated fuel stream to the fuel cell through closing the first oxidant exhaust valve 48, directing flow of the fuel stream from the fuel source 32 through the fuel feed line 32, first regenerable scrubber 12, fuel inlet line 14 into the fuel cell 18. Simultaneously, or for a predetermined regeneration duration, the fuel distribution valve 32 is controlled to prohibit flow of the fuel stream into the second regenerable scrubber 22, while the oxidant distribution valve 38 is controlled to direct flow of the oxidant from the oxidant source 40 (which may also be from the fuel cell exhaust 52, or a cathode exhaust (not shown) or power plant exhaust (not shown) of the fuel cell 18, or ambient air, or pure oxygen, etc.) into the second regenerable scrubber 22, while the second oxidant exhaust valve 50 is controlled to be open to discharge the oxidant out of the second regenerable scrubber 22. [0030] Whenever accumulated ammonia within the first regenerable scrubber 12 has reached a predetermined upper limit, or whenever ammonia within the fuel stream within the fuel inlet line 14 has reached a pre-determined upper limit, the system 10 is controlled to place the first regenerable scrubber 12 in the regeneration portion of the cycle by terminating flow of the fuel stream into the scrubber 12, and instead directing flow of the oxidant through the first regenerable scrubber 12. That may be achieved by controlling the fuel distribution valve 28 to terminate flow of fuel to the scrubber 12, while controlling the oxidant distribution valve 38 to direct the oxidant to pass through the first regenerable scrubber 12, while also opening the first oxidant exhaust valve 48 and terminating flow from the scrubber 12 into the fuel cell 18 through the fuel inlet line 14. While the first regenerable scrubber 12 is being regenerated as just described, to provide an uninterrupted flow of the fuel stream into the fuel cell 18, the fuel stream is directed by the fuel distribution means 28 to flow into and through the second regenerable scrubber 22 and fuel inlet line 14 into the fuel cell, while the second oxidant exhaust valve 50 is closed, and the oxidant distribution control means 38 is controlled to terminate flow of the oxidant into the second regenerable scrubber 22. In the event it is desired to stop the regeneration of one of the scrubbers 12, 22 while the other scrubber 12, 22 is in the absorption portion of the cycle because the scrubber has achieved a satisfactory level of regeneration, the oxidant distribution valve 38 is controlled to terminate flow of the oxidant to the scrubber 12, 22 in the regeneration portion of the cycle and the oxidant exhaust valve 48, 50 of that scrubber is closed. In the event that the regeneration portion of the cycle is shorter than the absorption portion of the cycle, fuel should be admitted to the regenerated scrubber 12, 22 upon completion of the oxidation to minimize degradation of the catalyst.

[0031] During operation of the system 10 and in particular while a regenerable scrubber 12, 22 is in the absorption portion of the absorption-regeneration cycle so that fuel is flowing through the scrubber 12, 22, the temperature of the regenerable scrubber 12, 22 must be above a dew point of the fuel to prevent water accumulation within the scrubber 12, 22. The dew point of a reformate fuel stream is typically about 60 degrees Celsius ("⁰C") to about 70⁰C. The temperature of the regenerable scrubber 12, 22 must also be less than an exhaust temperature of a fuel cell reactants being exhausted from the fuel cell 18 in order to prevent acid accumulation within the fuel cell. The temperature of the exhaust stream from the fuel cell 18 is typically between 140⁰C to 170°C. Scrubber 12, 22 temperatures in excess of 120⁰C will probably require periodic acid replenishment to the scrubbers 12, 22 due to acid evaporation into fuel stream entering the fuel cell 12. Considering these limitations, an optimum temperature range of operation of the regenerable scrubbers during the absorption portion of the absorption-regeneration cycle is between about 80⁰C and 12O⁰C.

[0032] An embodiment of the system 10 includes one of the regenerable scrubbers 12 with the described acid 60, noble metal catalyzed porous support material 62, the fuel distribution control means 28 and oxygen distribution control means 38 so that the regenerable scrubber 12 may be operated in the absorption- regeneration cycle. Such a use of only one regenerable scrubber may 12 may be appropriate in circumstances wherein the scrubber 12 is used for a fuel cell 18 that is used intermittently and has predetermined periods of inactivity. During such periods of inactivity, the regenerable scrubber 12 may be controlled to be in the regeneration portion of the absorption-regeneration cycle in the manner described above. When the fuel cell 18 is to be operated again, the regenerable scrubber 12 would then be controlled to be in the absorption portion of the cycle .

[0033] By catalyzing the porous support material 62 with a noble metal, the present regenerable ammonia scrubber system 10 provides for a dramatic increase in a rate of regeneration of the regenerable scrubbers 12, 22 through use of a relatively small amount of expensive noble metal that is maintained in a stable concentration within the regenerable scrubbers 12, 22. Consequently, the scrubbers 12, 22 may be sized considerably smaller than would be required to achieve the same high proportion of contaminant removal achieved by known scrubbers.

[0034] While the present disclosure has been disclosed with respect to the described and illustrated regenerable ammonia scrubber system 10, it is to be understood the disclosure is not to be limited to those alternatives and described embodiments. For example, while control of the system 10 has been described as effected through changing the fuel and oxidant distribution valves 28, 38, oxidant exhaust valves 48, 50 and fuel inlet valve 16, it is to be understood that the system may be controlled to achieve the same operational functions through application of different control means for directing flow of the fuel stream and oxidant through the system as described above. Additionally, the system 10 may be utilized with any fuel cells including phosphoric acid fuel cells, proton exchange membrane fuel cells, etc. Accordingly, reference should be made primarily to the following claims rather than the forgoing description to determine the scope of the disclosure .

Claims

What is claimed is:

1. A regenerable ammonia scrubber system (10) for removing ammonia from a fuel stream for a fuel cell (18), the system comprising: a. a regenerable scrubber (12) secured in fluid communication with a fuel inlet line (16) configured to selectively direct flow of the fuel stream from the regenerable scrubber (12) into the fuel cell (18), and secured in fluid communication with an oxidant exhaust valve (48) configured to permit or prohibit flow of an oxidant out of the regenerable scrubber (12); b. a fuel distribution control means (28) secured in fluid communication with a fuel source (30) and with the regenerable scrubber (12) and configured to selectively permit or prohibit flow of the fuel stream from the fuel source to the regenerable scrubber (12); c. an oxidant distribution control means (38) secured in fluid communication with an oxidant source (40) and configured to selectively permit or prohibit flow of the oxidant from the oxidant source (40) to the regenerable scrubber (12), and configured to permit flow of the oxidant to the regenerable scrubber (12) responsive to the fuel distribution control means (38) prohibiting flow of the fuel stream to the regenerable scrubber (12) ; and, d. wherein the regenerable scrubber (12) contains a porous support material (62) , an acid solution (60) absorbed within the support material (62), and a noble metal catalyst dispersed through the porous support material (62) .

2. The regenerable ammonia scrubber system (10) of claim 1, wherein the acid solution is phosphoric acid.

3. The regenerable ammonia scrubber system (10) of claim 1, wherein the porous support material comprises a plurality of cylindrical shaped carbon pellets.

4. The regenerable ammonia scrubber system (10) of claim 1, wherein the noble metal catalyst is platinum dispersed through the porous support material (62) at a concentration of between about 0.1 weight percent and 1.0 weight percent of the weight of the porous support material (62) .

6. A regenerable ammonia scrubber system (10) for removing ammonia from a fuel stream for a fuel cell (18), the system comprising: a. a first regenerable scrubber (12) secured in fluid communication with a fuel inlet line (14) configured to selectively direct flow of the fuel stream from the first scrubber (12) into the fuel cell (18), and secured in fluid communication with a first oxidant exhaust valve (48) configured to permit or prohibit flow of an oxidant out of the first scrubber (12); b. a second regenerable scrubber secured (22) in fluid communication with the fuel inlet line (14), and in fluid communication with a second oxidant exhaust valve (50) configured to permit or prohibit flow of the oxidant out of the second scrubber (22); c. a fuel distribution valve (28) secured in fluid communication with a fuel source (30) and with the first and second regenerable scrubbers (12, 22) for selectively directing flow of the fuel stream from the fuel source (30) to one of the first regenerable scrubber (12) or the second regenerable scrubber (22); d. an oxidant distribution valve (38) secured in fluid communication with an oxidant source (40) for selectively directing flow of the oxidant from the oxidant source (38) to the other of the first regenerable scrubber (12) or the second regenerable scrubber (22); and, e. wherein the first regenerable scrubber (12) and the second regenerable scrubber (22) contain a porous support material (62) , an acid solution (60) within the porous support material (62), and a noble metal catalyst uniformly dispersed through the support material (62).

7. The regenerable ammonia scrubber system (10) of claim 6, wherein the acid solution is phosphoric acid.

8. The regenerable ammonia scrubber system (10) of claim 6, wherein the porous support material (62) comprises a plurality of cylindrical shaped carbon pellets .

9. The regenerable ammonia scrubber system (10) of claim 6, wherein the noble metal catalyst is platinum dispersed through the porous support material (62) at a concentration of between about 0.1 weight percent and 1.0 weight percent of the weight of the porous support material (62) .

10. A method of removing ammonia from a fuel stream for a fuel cell (18), comprising the steps of: a. dispersing a noble metal catalyst through a porous support material (62); b. dispersing an acid solution (60) throughout the porous support material (62), and securing the support material (62) and dispersed acid solution (60) within a regenerable scrubber

(12); c. then directing flow of a fuel stream through the regenerable scrubber (12) and then into the fuel cell (18) ; d. terminating flow of the fuel stream through the regenerable scrubber (12); e. then directing flow of an oxidant through the regenerable scrubber (12) and through an oxidant exhaust valve (48) out of the scrubber

(12) .

11. The method of removing ammonia of claim 10, wherein the step of dispersing a noble metal catalyst further comprises dispersing a platinum noble metal catalyst through the porous support material (62) at a concentration of between about 0.1 weight percent and 1.0 weight percent of the weight of the porous support material (62) .

12. The method of removing ammonia of claim 11, wherein the step of dispersing further comprises dispersing the platinum noble metal catalyst through a porous carbon pellet support material (62).

13. The method of removing ammonia of claim 11, wherein the step of directing the fuel stream through the regenerable scrubber (12) comprises the further step of simultaneously controlling a temperature of the regenerable scrubber to be between about 80⁰C and 12O⁰C.