Temperature-based breakthrough detection and pressure swing adsorption systems and fuel processing systems including the same Number:7,393,382 from the United States Patent and Trademark Office (PTO) owispatent Pressure swing adsorption (PSA) assemblies with temperature-based breakthrough detection systems, as well as to hydrogen-generation assemblies and/or fuel cell systems containing the same, and to methods of operating the same. The detection systems are adapted to detect a measured temperature associated with adsorbent in an adsorbent bed of a PSA assembly and to control the operation of at least the PSA assembly responsive at least in part thereto, such as responsive to the relationship between the measured temperature and at least one reference temperature. The reference temperature may include a stored value, a previously measured temperature and/or a temperature measured elsewhere in the PSA assembly. In some embodiments, the reference temperature is associated with adsorbent downstream from the adsorbent from which the measured temperature is detected. In some embodiments, the PSA cycle and/or components thereof are determined at least in part by the relationship between the measured and reference temperatures.<H breakthrough, Temperature, Temperature, bas, 7393382.html, Patent, pto, 7393382

Title: Temperature-based breakthrough detection and pressure swing adsorption systems and fuel processing systems including the same

Abstract: Pressure swing adsorption (PSA) assemblies with temperature-based breakthrough detection systems, as well as to hydrogen-generation assemblies and/or fuel cell systems containing the same, and to methods of operating the same. The detection systems are adapted to detect a measured temperature associated with adsorbent in an adsorbent bed of a PSA assembly and to control the operation of at least the PSA assembly responsive at least in part thereto, such as responsive to the relationship between the measured temperature and at least one reference temperature. The reference temperature may include a stored value, a previously measured temperature and/or a temperature measured elsewhere in the PSA assembly. In some embodiments, the reference temperature is associated with adsorbent downstream from the adsorbent from which the measured temperature is detected. In some embodiments, the PSA cycle and/or components thereof are determined at least in part by the relationship between the measured and reference temperatures.

Patent Number: 7,393,382 Issued on 07/01/2008 to Givens

Inventors: Givens; James A. (Bend, OR)
Assignee: IDATECH LLC (Bend, OR)

Appl. No.: 11/055,843

Filed: February 10, 2005

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
60638086	Dec., 2004

Current U.S. Class: 95/14 ; 95/100; 95/103; 95/105; 95/96; 95/99; 96/112; 96/130; 96/144

Current International Class: B01D 53/02 (20060101)

Field of Search: 95/14,96,97,98,99,100,105,130,103 96/112,130,143,144

References Cited [Referenced By]

U.S. Patent Documents


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Primary Examiner: Hopkins; Robert A
Attorney, Agent or Firm: Dascenzo Intellectual Property Law, P.C.

Parent Case Text

RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application Ser. No. 60/638,086, which was filed on Dec. 20, 2004, and the complete disclosure of which is hereby incorporated by reference for all purposes.

Claims

What is claimed is:

1. A hydrogen-generation assembly, comprising: a hydrogen-producing fuel processing system adapted to produce a mixed gas stream containing hydrogen gas and other gases from at least one feedstock; and a pressure swing adsorption assembly adapted to receive at least a portion of the mixed gas stream and to remove impurities therefrom to produce a product hydrogen stream having greater hydrogen purity than the mixed gas stream, the pressure swing adsorption assembly comprising: a plurality of adsorbent beds, each bed including an adsorbent region containing adsorbent adapted to adsorb at least one of the other gases; and a temperature-based detection system, comprising: at least one temperature sensor adapted to measure a temperature associated with a portion of the adsorbent region; and a controller adapted to compare the temperature associated with a portion of the adsorbent region with at least one reference temperature that includes a temperature associated with a second portion of the adsorbent region and to selectively control the operation of at least the pressure swing adsorption assembly responsive at least in part thereto.

2. The assembly of claim 1, in combination with a fuel cell stack adapted to produce an electric current from an oxidant and at least a portion of the product hydrogen stream.

3. The assembly of claim 2, wherein the temperature-based detection system is further adapted to control the operation of the fuel processing system responsive at least in part to the relationship of the measured temperature and a reference temperature.

4. The assembly of claim 1, wherein the adsorbent region includes a feed end and a product end, and further wherein the second portion of the adsorbent region is spaced away from the product end.

5. The assembly of claim 1, wherein the second portion of the adsorbent region is located downstream from the portion of the adsorbent region, as measured in the direction of mixed gas flow through the adsorbent region during the adsorption process.

6. The assembly of claim 1, wherein the at least one reference temperature includes at least one of a previously measured temperature, a stored value, and a predetermined threshold value.

7. The assembly of claim 1, wherein the controller is adapted to detect whether or not a breakthrough condition exists in the adsorbent region responsive at least in part to the measured temperature.

8. The assembly of claim 1, wherein the at least one temperature sensor includes at least a first temperature sensor adapted to measure the temperature associated with a portion of the adsorbent region and a second temperature sensor adapted to measure a temperature associated with the adsorbent bed.

9. The assembly of claim 1, wherein the pressure swing adsorption assembly is adapted to reduce the concentration of the other gases in the mixed gas stream through a PSA cycle that includes at least pressurization, adsorption, depressurization, and purge steps and which has a cycle time.

10. The assembly of claim 9, wherein the PSA cycle further includes at least one equalization step in which at least two of the plurality of adsorbent beds are fluidly interconnected for gas flow between the beds.

11. The assembly of claim 9, wherein the temperature-based detection system is adapted to stop the adsorption step in the PSA cycle responsive to the relationship between the measured temperature and a reference temperature.

12. The assembly of claim 9, wherein the temperature-based detection system is adapted to stop the purge step in the PSA cycle responsive to the relationship between the measured temperature and the reference temperature.

13. The assembly of claim 9, wherein the temperature-based detection system is adapted to transition to at least one of the depressurization and the purge steps of the PSA cycle responsive to the relationship between the measured temperature and a reference temperature.

14. The assembly of claim 9, wherein the temperature-based detection system is adapted to reduce the cycle time of the PSA cycle by a predetermined increment responsive to the relationship between the measured temperature and a reference temperature.

15. The assembly of claim 9, wherein the cycle time includes a time period associated with each of the steps in the PSA cycle, and further wherein the temperature-based detection system is adapted to reduce the time period associated with the adsorption step of the PSA cycle by a predetermined increment responsive to the relationship between the measured temperature and a reference temperature.

16. The assembly of claim 9, wherein the cycle time includes a time period associated with each of the steps in the PSA cycle, and further wherein the temperature-based detection system is adapted to increase the time period associated with the purge step of the PSA cycle responsive to the relationship between the measured temperature and a reference temperature.

17. The assembly of claim 9, wherein the cycle time includes a time period associated with each of the steps in the PSA cycle, and further wherein the temperature-based detection system is adapted to increase the time period associated with the purge step of the PSA cycle by a predetermined increment responsive to the relationship between the measured temperature and a reference temperature.

18. The assembly of claim 1, wherein the temperature-based detection system is adapted to shutdown at least the pressure swing adsorption assembly responsive to the relationship between the measured temperature and a reference temperature.

19. The assembly of claim 1, wherein the temperature-based detection system is further adapted to control the operation of the fuel processing system responsive at least in part to the relationship of the measured temperature and a reference temperature.

20. A method for preventing breakthrough in a pressure swing adsorption assembly comprising at least one adsorbent bed having an adsorbent region containing at least one adsorbent adapted to adsorb impurities in an impure hydrogen stream to produce a purified hydrogen stream therefrom, the method comprising: detecting a measured temperature associated with a portion of the adsorbent region; detecting a reference temperature associated with a second portion of the adsorbent region downstream from the portion of the adsorbent region from which the measured temperature is detected; comparing the measured temperature and the reference temperature; and automatically adjusting the operation of the pressure swing adsorption assembly responsive to the measured temperature exceeding the reference temperature by more than a threshold value.

21. The method of claim 20, wherein the threshold value is at least 2.degree. C.

22. The method of claim 20, wherein the adsorbent region includes a feed end and a product end, and further wherein the second portion of the adsorbent region is spaced away from the product end.

23. The method of claim 20, wherein the automatically adjusting includes adjusting at least one operating parameter of the pressure swing adsorption assembly.

24. The method of claim 23, wherein the at least one operating parameter includes a time period in which the impure hydrogen stream flows through the adsorbent region in which the measured temperature is detected.

25. The method of claim 20, wherein the pressure swing adsorption assembly is adapted to reduce the concentration of the impurities in the impure hydrogen stream through a PSA cycle that includes at least pressurization, adsorption, depressurization, and purge steps and which has a cycle time, and further wherein the automatically adjusting includes changing a time period associated with at least one of the steps in the PSA cycle.

26. The method of claim 20, wherein the automatically adjusting includes shutting down the pressure swing adsorption assembly.

27. The method of claim 20, wherein the automatically adjusting includes reducing the pressure in the adsorbent bed in which the measured temperature is detected and withdrawing a stream containing desorbed gases from the bed.

28. A method for operating a pressure swing adsorption assembly comprising at least one adsorbent bed having an adsorbent region containing at least one adsorbent adapted to adsorb impurities in an impure hydrogen stream to produce a purified hydrogen stream therefrom, the method comprising: delivering under pressure a mixed gas stream containing hydrogen gas and other gases to an adsorbent bed having an adsorbent region containing adsorbent adapted to adsorb at least one of the other gases from the mixed gas stream; detecting a measured temperature associated with adsorbent in a portion of the adsorbent region; and continuing the delivering step until the measured temperature exceeds a reference temperature associated with adsorbent in another portion of the adsorbent region.

29. The method of claim 28, wherein the method further includes producing the mixed gas stream in a fuel processing assembly adapted to produce the mixed gas stream from at least one feed stream.

30. The method of claim 28, wherein the method further includes detecting the reference temperature.

31. The method of claim 30, wherein the reference temperature is associated with adsorbent in a downstream portion of the adsorbent region.

32. The method of claim 30, wherein the reference temperature includes at least one of a previously measured temperature and a threshold value.

33. The method of claim 28, wherein the continuing step is maintained until the measured temperature exceeds the reference temperature by more than a predetermined value.

34. A hydrogen-generation assembly, comprising: a hydrogen-producing fuel processing system adapted to produce a mixed gas stream containing hydrogen gas and other gases from at least one feedstock; and a pressure swing adsorption assembly adapted to receive at least a portion of the mixed gas stream and to remove impurities therefrom to produce a product hydrogen stream having greater hydrogen purity than the mixed gas stream, the pressure swing adsorption assembly comprising: a plurality of adsorbent beds, each bed including an adsorbent region containing adsorbent adapted to adsorb at least one of the other gases; and a temperature-based detection system, comprising: a first temperature sensor adapted to measure a temperature associated with a portion of the adsorbent region and a second temperature sensor adapted to measure a temperature associated with the adsorbent bed; and a controller adapted to compare the temperature associated with a portion of the adsorbent region with the temperature associated with the adsorbent bed and to selectively control the operation of at least the pressure swing adsorption assembly responsive at least in part thereto.

Description

FIELD OF THE DISCLOSURE

The present disclosure is directed generally to pressure swing adsorption systems and hydrogen-generation and/or cell systems incorporating the same, and more particularly to such systems that utilize a temperature-based breakthrough detection system.

BACKGROUND OF THE DISCLOSURE

A hydrogen-generation assembly is an assembly that converts one or more feedstocks into a product stream containing hydrogen gas as a majority component. The produced hydrogen gas may be used in a variety of applications. One such application is energy production, such as in electrochemical fuel cells. An electrochemical fuel cell is a device that converts a fuel and an oxidant to electricity, a reaction product, and heat. For example, fuel cells may convert hydrogen and oxygen into water and electricity. In such fuel cells, the hydrogen is the fuel, the oxygen is the oxidant, and the water is the reaction product. Fuel cells typically require high purity hydrogen gas to prevent the fuel cells from being damaged during use. The product stream from a hydrogen-generation assembly may contain impurities, illustrative examples of which include one or more of carbon monoxide, carbon dioxide, methane, unreacted feedstock, and water. Therefore, there is a need in many conventional fuel cell systems to include suitable structure for removing impurities from the product hydrogen stream.

A pressure swing adsorption (PSA) process is an example of a mechanism that may be used to remove impurities from an impure hydrogen gas stream by selective adsorption of one or more of the impurities present in the impure hydrogen stream. The adsorbed impurities can be subsequently desorbed and removed from the PSA assembly. PSA is a pressure-driven separation process that utilizes a plurality of adsorbent beds. The beds are cycled through a series of steps, such as pressurization, separation (adsorption), depressurization (desorption), and purge steps to selectively remove impurities from the hydrogen gas and then desorb the impurities. A concern when using a PSA assembly is preventing breakthrough, which refers to when the adsorbent in a bed has been sufficiently saturated in adsorbed impurities that the impurities pass through the bed and thereby remain with the hydrogen gas instead of being retained in the bed. Conventionally, breakthrough prevention requires either expensive composition-based detectors, such as carbon monoxide detectors, to determine when even a few parts per million (ppm) of carbon monoxide have passed through a bed, or intentional underperfornance of the PSA assembly. By this it is meant that the PSA assembly is operated inefficiently, with each bed being used for impurity adsorption for only a subset of its capacity to provide a potentially wide margin of unused adsorbent and thereby hopefully prevent breakthrough. An advantage of such a process is that the cost and equipment required is reduced; however, the lack of actual breakthrough detection and the inefficient operation of the system may outweigh the cost and equipment savings, especially when it is realized that the composition of the stream to be purified may fluctuate due to malfunctions or other causes elsewhere in the hydrogen-generation assembly.

SUMMARY OF THE DISCLOSURE

The present disclosure is directed to PSA assemblies with temperature-based breakthrough detection systems, as well as to hydrogen-generation assemblies and/or fuel cell systems containing the same, and to methods of operating the same. The PSA assemblies include at least one adsorbent bed, and typically a plurality of adsorbent beds, that include an adsorbent region including adsorbent adapted to remove impurities from a mixed gas stream containing hydrogen gas as a majority component and other gases. The mixed gas stream may be produced by a hydrogen-producing region of a fuel processing system, and the PSA assembly may produce a product hydrogen stream that is consumed by a fuel cell stack to provide a fuel cell system that produces electrical power. The PSA assembly includes a temperature-based breakthrough detection system that is adapted to monitor at least one temperature associated with the adsorbent in each bed and responsive at least in part to the measured temperature to control the operation of at least the PSA assembly, and optionally other components of the hydrogen-generation assembly and/or fuel cell system utilized therewith. The breakthrough detection system may be implemented to control the operation of at least the PSA assembly to prevent actual breakthrough from occurring. Responsive at least in part to the measured temperature, the system may be adapted, in some embodiments, to shutdown the PSA assembly and/or generate at least one alert or other notification. In some embodiments, the detection system is adapted to determine at least the time of the adsorption step utilized by the PSA assembly, if not the total PSA cycle time. In some embodiments, the detection system is adapted to regulate the total PSA cycle time and/or components thereof responsive at least in part to the measured temperature and/or the detection of a breakthrough condition. In some embodiments, the measured temperature is compared to a reference temperature. In some embodiments, the reference temperature is another measured temperature of the adsorbent or other portion of the PSA assembly. In some embodiments, the reference temperature is a previously measured or selected temperature, including a stored temperature or threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an illustrative example of an energy producing and consuming assembly that includes a hydrogen-generation assembly with an associated feedstock delivery system and a fuel processing system, as well as a fuel cell stack, and an energy-consuming device.

FIG. 2 is a schematic view of a hydrogen-producing assembly in the form of a steam reformer adapted to produce a reformate stream containing hydrogen gas and other gases from water and at least one carbon-containing feedstock.

FIG. 3 is a schematic view of a fuel cell, such as may form part of a fuel cell stack used with a hydrogen-generation assembly according to the present disclosure.

FIG. 4 is a schematic view of a pressure swing adsorption assembly including a temperature-based breakthrough detection system according to the present disclosure.

FIG. 5 is a schematic cross-sectional view of an adsorbent bed that may be used with PSA assemblies according to the present disclosure.

FIG. 6 is a schematic cross-sectional view of another adsorbent bed that may be used with PSA assemblies according to the present disclosure.

FIG. 7 is a schematic cross-sectional view of another adsorbent bed that may be used with PSA assemblies according to the present disclosure.

FIG. 8 is a schematic cross-sectional view of the adsorbent bed of FIG. 6 with a mass transfer zone being schematically indicated.

FIG. 9 is a schematic cross-sectional view of the adsorbent bed of FIG. 8 with the mass transfer zone moved along the adsorbent region of the bed toward a distal, or product, end of the adsorbent region.

FIG. 10 is a schematic cross-sectional view of a portion of a PSA assembly that includes at least one adsorbent bed and a temperature-based breakthrough detection system according to the present disclosure.

FIG. 11 is a schematic cross-sectional view of a portion of a PSA assembly that includes at least one adsorbent bed and a temperature-based breakthrough detection system according to the present disclosure.

FIG. 12 is a schematic cross-sectional view of a portion of a PSA assembly that includes at least one adsorbent bed and a temperature-based breakthrough detection system according to the present disclosure.

DETAILED DESCRIPTION AND BEST MODE OF THE DISCLOSURE

FIG. 1 illustrates schematically an example of an energy producing and consuming assembly 56. The energy producing and consuming assembly 56 includes an energy-producing system 22 and at least one energy-consuming device 52 adapted to exert an applied load on the energy-producing system 22. In the illustrated example, the energy-producing system 22 includes a fuel cell stack 24 and a hydrogen-generation assembly 46. More than one of any of the illustrated components may be used without departing from the scope of the present disclosure. The energy-producing system may include additional components that are not specifically illustrated in the schematic figures, such as air delivery systems, heat exchangers, sensors, controllers, flow-regulating devices, fuel and/or feedstock delivery assemblies, heating assemblies, cooling assemblies, and the like. System 22 may also be referred to as a fuel cell system.

As discussed in more detail herein, hydrogen-generation assemblies and/or fuel cell systems according to the present disclosure include a separation assembly that includes at least one pressure swing adsorption (PSA) assembly that is adapted to increase the purity of the hydrogen gas that is produced in the hydrogen-generation assembly and/or consumed in the fuel cell stack. In a PSA process, gaseous impurities are removed from a stream containing hydrogen gas. PSA is based on the principle that certain gases, under the proper conditions of temperature and pressure, will be adsorbed onto an adsorbent material more strongly than other gases. These impurities may thereafter be desorbed and removed, such as in the form of a byproduct stream. The success of using PSA for hydrogen purification is due to the relatively strong adsorption of common impurity gases (such as, but not limited to, CO, CO.sub.2, hydrocarbons including CH.sub.4, and N.sub.2) on the adsorbent material. Hydrogen adsorbs only very weakly and so hydrogen passes through the adsorbent bed while the impurities are retained on the adsorbent material.

As discussed in more detail herein, a PSA process typically involves repeated, or cyclical, application of at least pressurization, separation (adsorption), depressurization (desorption), and purge steps, or processes, to selectively remove impurities from the hydrogen gas and then desorb the impurities. Accordingly, the PSA process may be described as being adapted to repeatedly enable a PSA cycle of steps, or stages, such as the above-described steps. The degree of separation is affected by the pressure difference between the pressure of the mixed gas stream and the pressure of the byproduct stream. Accordingly, the desorption step will typically include reducing the pressure within the portion of the PSA assembly containing the adsorbed gases, and optionally may even include drawing a vacuum (i.e., reducing the pressure to less than atmospheric or ambient pressure) on that portion of the assembly. Similarly, increasing the feed pressure of the mixed gas stream to the adsorbent regions of the PSA assembly may beneficially affect the degree of separation during the adsorption step.

As illustrated schematically in FIG. 1, the hydrogen-generation assembly 46 includes at least a fuel processing system 64 and a feedstock delivery system 58, as well as the associated fluid conduits interconnecting various components of the system. As used herein, the term "hydrogen-generation assembly" may be used to refer to the fuel processing system 64 and associated components of the energy-producing system, such as feedstock delivery systems 58, heating assemblies, separation regions or devices, air delivery systems, fuel delivery systems, fluid conduits, heat exchangers, cooling assemblies, sensor assemblies, flow regulators, controllers, etc. All of these illustrative components are not required to be included in any hydrogen-generation assembly or used with any fuel processing system according to the present disclosure. Similarly, other components may be included or used as part of the hydrogen-generation assembly.

Regardless of its construction or components, the feedstock delivery system 58 is adapted to deliver to the fuel processing system 64 one or more feedstocks via one or more streams, which may be referred to generally as feedstock supply stream(s) 68. In the following discussion, reference may be made only to a single feedstock supply stream, but is within the scope of the present disclosure that two or more such streams, of the same or different composition, may be used. In some embodiments, air may be supplied to the fuel processing system 64 via a blower, fan, compressor or other suitable air delivery system, and/or a water stream may be delivered from a separate water source.

Fuel processing system 64 includes any suitable device(s) and/or structure(s) that are configured to produce hydrogen gas from the feedstock supply stream(s) 68. As schematically illustrated in FIG. 1, the fuel processing system 64 includes a hydrogen-producing region 70. Accordingly, fuel processing system 64 may be described as including a hydrogen-producing region 70 that produces a hydrogen-rich stream 74 that includes hydrogen gas as a majority component from the feedstock supply stream. While stream 74 contains hydrogen gas as its majority component, it also contains other gases, and as such may be referred to as a mixed gas stream that contains hydrogen gas and other gases. Illustrative, non-exclusive examples of these other gases, or impurities, include one or more of such illustrative impurities as carbon monoxide, carbon dioxide, water, methane, and unreacted feedstock.

Illustrative examples of suitable mechanisms for producing hydrogen gas from feedstock supply stream 68 include steam reforming and autothermal reforming, in which reforming catalysts are used to produce hydrogen gas from a feedstock supply stream 68 containing water and at least one carbon-containing feedstock. Other examples of suitable mechanisms for producing hydrogen gas include pyrolysis and catalytic partial oxidation of a carbon-containing feedstock, in which case the feedstock supply stream 68 does not contain water. Still another suitable mechanism for producing hydrogen gas is electrolysis, in which case the feedstock is water. Illustrative examples of suitable carbon-containing feedstocks include at least one hydrocarbon or alcohol. Illustrative examples of suitable hydrocarbons include methane, propane, natural gas, diesel, kerosene, gasoline and the like. Illustrative examples of suitable alcohols include methanol, ethanol, and polyols, such as ethylene glycol and propylene glycol.

The hydrogen-generation assembly 46 may utilize more than a single hydrogen-producing mechanism in the hydrogen-producing region 70 and may include more than one hydrogen-producing region. Each of these mechanisms is driven by, and results in, different thermodynamic balances in the hydrogen-generation assembly 46. Accordingly, the hydrogen-generation assembly 46 may further include a temperature modulating assembly 71, such as a heating assembly and/or a cooling assembly. The temperature modulating assembly 71 may be configured as part of the fuel processing system 64 or may be an external component that is in thermal and/or fluid communication with the hydrogen-producing region 70. The temperature modulating assembly 71 may consume a fuel stream, such as to generate heat. While not required in all embodiments of the present disclosure, the fuel stream may be delivered from the feedstock delivery system. For example, and as indicated in dashed lines in FIG. 1, this fuel, or feedstock, may be received from the feedstock delivery system 58 via a fuel supply stream 69. The fuel supply stream 69 may include combustible fuel or, alternatively, may include fluids to facilitate cooling. The temperature modulating assembly 71 may also receive some or all of its feedstock from other sources or supply systems, such as from additional storage tanks. It may also receive the air stream from any suitable source, including the environment within which the assembly is used. Blowers, fans and/or compressors may be used to provide the air stream, but this is not required to all embodiments.

The temperature modulating assembly 71 may include one or more heat exchangers, burners, combustion systems, and other such devices for supplying heat to regions of the fuel processing system and/or other portions of assembly 56. Depending on the configuration of the hydrogen-generation assembly 46, the temperature modulating assembly 71 may also, or alternatively, include heat exchangers, fans, blowers, cooling systems, and other such devices for cooling regions of the fuel processing system 64 or other portions of assembly 56. For example, when the fuel processing system 64 is configured with a hydrogen-producing region 70 based on steam reforming or another endothermic reaction, the temperature modulating assembly 71 may include systems for supplying heat to maintain the temperature of the hydrogen-producing region 70 and the other components in the proper range.

When the fuel processing system is configured with a hydrogen-producing region 70 based on catalytic partial oxidation or another exothermic reaction, the temperature modulating assembly 71 may include systems for removing heat, i.e., supplying cooling, to maintain the temperature of the fuel processing system in the proper range. As used herein, the term "heating assembly" is used to refer generally to temperature modulating assemblies that are configured to supply heat or otherwise increase the temperature of all or selected regions of the fuel processing system. As used herein, the term "cooling assembly" is used to refer generally to temperature moderating assemblies that are configured to cool, or reduce the temperature of, all or selected regions of the fuel processing system.

In FIG. 2, an illustrative example of a hydrogen-generation assembly 46 that includes fuel processing system 64 with a hydrogen-producing region 70 that is adapted to produce mixed gas stream 74 by steam reforming one or more feedstock supply streams 68 containing water 80 and at least one carbon-containing feedstock 82. As illustrated, region 70 includes at least one reforming catalyst bed 84 containing one or more suitable reforming catalysts 86. In the illustrative example, the hydrogen-producing region may be referred to as a reforming region, and the mixed gas stream may be referred to as a reformate stream.

As also shown in FIGS. 1 and 2, the mixed gas stream is adapted to be delivered to a separation region, or assembly, 72 that includes at least one PSA assembly 73. PSA assembly 73 separates the mixed gas (or reformate) stream into product hydrogen stream 42 and at least one byproduct stream 76 that contains at least a substantial portion of the impurities, or other gases, present in mixed gas stream 74. Byproduct stream 76 may contain no hydrogen gas, but it typically will contain some hydrogen gas. While not required, it is within the scope of the present disclosure that fuel processing system 64 may be adapted to produce one or more byproduct streams containing sufficient amounts of hydrogen (and/or other) gas(es) to be suitable for use as a fuel, or feedstock, stream for a heating assembly for the fuel processing system. In some embodiments, the byproduct stream may have sufficient fuel value (i.e., hydrogen and/or other combustible gas content) to enable the heating assembly, when present, to maintain the hydrogen-producing region at a desired operating temperature or within a selected range of temperatures.

As illustrated in FIG. 2, the hydrogen-generation assembly includes a temperature modulating assembly in the form of a heating assembly 71 that is adapted to produce a heated exhaust stream 88 that is adapted to heat at least the reforming region of the hydrogen-generation assembly. It is within the scope of the present disclosure that stream 88 may be used to heat other portions of the hydrogen-generation assembly and/or energy-producing system 22.

As indicated in dashed lines in FIGS. 1 and 2, it is within the scope of the present disclosure that the byproduct stream from the PSA assembly may form at least a portion of the fuel stream for the heating assembly. Also shown in FIG. 2 are air stream 90, which may be delivered from any suitable air source, and fuel stream 92, which contains any suitable combustible fuel suitable for being combusted with air in the heating assembly. Fuel stream 92 may be used as the sole fuel stream for the heating assembly, but as discussed, it is also within the scope of the disclosure that other combustible fuel streams may be used, such as the byproduct stream from the PSA assembly, the anode exhaust stream from a fuel cell stack, etc. When the byproduct or exhaust streams from other components of system 22 have sufficient fuel value, fuel stream 92 may not be used. When they do not have sufficient fuel value, are used for other purposes, or are not being generated, fuel stream 92 may be used instead or in combination.

Illustrative examples of suitable fuels include one or more of the above-described carbon-containing feedstocks, although others may be used. As an illustrative example of temperatures that may be achieved and/or maintained in hydrogen-producing region 70 through the use of heating assembly 71, steam reformers typically operate at temperatures in the range of 200.degree. C. and 900.degree. C. Temperatures outside of this range are within the scope of the disclosure. When the carbon-containing feedstock is methanol, the steam reforming reaction will typically operate in a temperature range of approximately 200-500.degree. C. Illustrative subsets of this range include 350-450.degree. C., 375-425.degree. C., and 375-400.degree. C. When the carbon-containing feedstock is a hydrocarbon, ethanol, or a similar alcohol, a temperature range of approximately 400-900.degree. C. will typically be used for the steam reforming reaction. Illustrative subsets of this range include 750-850.degree. C., 650-750.degree. C., 700-800.degree. C., 700-900.degree. C., 500-800.degree. C., 400-600.degree. C., and 600-800.degree. C.

It is within the scope of the present disclosure that the separation region may be implemented within system 22 anywhere downstream from the hydrogen-producing region and upstream from the fuel cell stack. In the illustrative example shown schematically in FIG. 1, the separation region is depicted as part of the hydrogen-generation assembly, but this construction is not required. It is also within the scope of the present disclosure that the hydrogen-generation assembly may utilize a chemical or physical separation process in addition to PSA assembly 73 to remove or reduce the concentration of one or more selected impurities from the mixed gas stream. When separation assembly 72 utilizes a separation process in addition to PSA, the one or more additional processes may be performed at any suitable location within system 22 and are not required to be implemented with the PSA assembly. An illustrative chemical separation process is the use of a methanation catalyst to selectively reduce the concentration of carbon monoxide present in stream 74. Other illustrative chemical separation processes include partial oxidation of carbon monoxide to form carbon dioxide and water-gas shift reactions to produce hydrogen gas and carbon dioxide from water and carbon monoxide. Illustrative physical separation processes include the use of a physical membrane or other barrier adapted to permit the hydrogen gas to flow therethrough but adapted to prevent at least selected impurities from passing therethrough. These membranes may be referred to as being hydrogen-selective membranes. Illustrative examples of su