Patent Application
20050188616
The present disclosure is directed generally to fuel processing systems, which contain a fuel processor configured to produce hydrogen gas, and more particularly to treatment systems for use in fuel processing systems.
Fuel processing systems include a fuel processor that produces hydrogen, or hydrogen-rich, gas from at least one feedstock, such as a carbon-containing feedstock and/or water. The feedstock may be vaporized prior to formation of the hydrogen, or hydrogen rich, gas in the fuel processor. That vaporization may lead to changes in the chemical and/or physical characteristics of the feedstock that may cause operational and/or safety problems in the fuel processor. For example, vaporization of water may produce solids, such as colloidal silica and any impurities that are reduced to solid form upon vaporization of the liquid water. As another example, vaporization of a carbon-containing feedstock may result in the formation of coke or other carbon-containing solids. The solids may accumulate within the conduits through which the feedstocks flow and/or coat the catalysts used to produce hydrogen gas from the feedstocks. This increase in solids may also cause an increase in the pressure drop in the fuel processor or conduits within the fuel processing system between the vaporization region and the hydrogen-producing region of the fuel processor.
The present disclosure is directed to fuel processing systems, which contain a fuel processor, and to feedstock treatment systems for use in the same. The fuel processor is configured to produce a hydrogen, or hydrogen-rich, stream from a feed stream, which may include, for example, at least one carbon-containing feedstock and/or water. At least a portion of the feed stream is a vaporized feed stream. The fuel processing system further includes a treatment region configured to remove solids from at least the vaporized component of the feed stream prior to production of hydrogen gas from the feed stream. In some embodiments, a common housing at least substantially encloses one or more regions of the fuel processing system, and in some embodiments one or more of those regions are accessible from external the common housing without disassembling that housing.
A fuel processing system 10 is schematically illustrated in
Before describing in more detail fuel processing systems according to the present disclosure, the feed streams 14 for these systems will be first described. The one or more feed streams 14 contain the reactants, or feedstocks, that are consumed to form hydrogen gas in hydrogen-producing region 28. For example, the one or more feed streams typically will include at least water and/or a carbon-containing feedstock. Examples of suitable carbon-containing feedstocks include one or more alcohols and/or hydrocarbons. Nonexclusive examples of suitable alcohols include methanol, ethanol, and polyols, such as ethylene glycol and propylene glycol. Nonexclusive examples of suitable hydrocarbons include methane, propane, natural gas, diesel, kerosene, gasoline and the like.
When a feed stream contains more than one feedstock, the feedstocks may be delivered to the fuel processor and/or a hydrogen-producing region thereof as separate feed streams or as a single feed stream. Similarly, when the feedstocks are mixed together prior to delivery to the fuel processor or a hydrogen-producing region thereof, the mixture of feedstocks may be delivered in one or more feed streams, even though the composition of these streams may be the same, or at least very similar. As used herein, the term “feed stream” is used generally to refer to one or more fluid streams that contain at least one feedstock for the fuel processor's hydrogen-producing region. For example, fuel processing system 10 may contain a feed stream 14 containing one or more feedstocks and which is physically delivered to the fuel processor in any suitable number of fluid conduits.
Regardless of the composition and number of feedstocks in the one or more feed streams and the number of discrete streams delivered to a hydrogen-producing region, at least one feed stream 14 according to the present disclosure will include at least one feedstock or component that is received in liquid form and subsequently vaporized prior to being consumed as a reactant to form hydrogen-gas in a hydrogen-producing region of the fuel processor. For example, a component of a feed stream may be delivered to the fuel processing system, to the fuel processing assembly, and/or to the fuel processor in liquid form and then vaporized prior to being consumed to form hydrogen gas. As a more specific example, water may be delivered in liquid form and then vaporized to form steam, or even superheated steam, prior to being used to form hydrogen gas in hydrogen-producing region 28. As another example, a carbon-containing feedstock may be normally stored as a liquid, but vaporized prior to being used to form hydrogen gas in hydrogen-producing region 28.
It is not required that the entire feed stream, or all of the feedstocks, be delivered in liquid form and thereafter vaporized prior to being used to form hydrogen gas. For example, at least a portion of the feed stream may be gaseous, or in gas form, when delivered to the fuel processing system and/or when consumed to form hydrogen gas. As used herein, feed stream 14 may be described as containing a liquid component 20, with this liquid component being vaporized to form a vaporized component 22 prior to being used to form hydrogen gas in hydrogen-producing region 28. As used herein, the liquid and vaporized components of feed stream 14 also may be described as liquid feed stream components and vaporized feed stream components.
Feed stream 14 is typically delivered to the fuel processing assembly by a suitable feed stream delivery system, such as schematically illustrated at 17 in
Fuel processing system 10 and/or fuel processing assembly 11 may include a vaporization region 18 that is configured to receive at least liquid component 20 of feed stream 14 and to produce vaporized component 22 therefrom. Additionally or alternatively, the fuel processing assembly may be adapted to receive at least one vaporized component 22 of the feed stream, such as a component that was vaporized prior to delivery to fuel processing assembly 11. Vaporization region 18 may utilize any suitable vaporization structure to vaporize at least liquid component 20 of feed stream 14 to form vaporized component 22. Although only liquid component 20 and vaporized component 22 of feed stream 14 have been schematically illustrated in
Additionally, one or more components of feed stream 14 may bypass vaporization region 18 and combine with vaporized component 22 downstream from that region as schematically illustrated in
Any suitable mechanism and/or structure may be used to vaporize the liquid component of feed stream 14 to form vaporized component 22. For example, the vaporization region may include a burner or other heating assembly that is adapted to produce the heat required to vaporize the liquid feed stream component. As another example, the vaporization region may vaporize the liquid feed stream component by heat exchange with a heated fluid stream and/or conduction/convection of heat from a hotter component of the fuel processing system. For example, a liquid component of a carbon-containing feedstock may be vaporized by heat exchange and/or mixing with steam, or even superheated steam. It is within the scope of the disclosure that this steam also may form a water component of the feed stream 14. As another example, a heated exhaust stream from the fuel processing system may be used to vaporize the liquid feed stream component. As a further example, many hydrogen-producing regions are operated at elevated temperatures, such as may be obtained by a suitable burner or heating assembly, and the vaporization region may be in thermal communication with the hydrogen-producing or other heated region to receive the required heat to vaporize the liquid feed stream component. In such a configuration, it may be desirable for the vaporization region to take the form of one or more fluid conduits that extend through this heated region, around the exterior of this region, or along the exterior of this region. As yet another example, some hydrogen-producing regions are heated by exothermic reactions that are used to produce hydrogen gas, and the region may be cooled by being used to vaporize at least a liquid component of the feed stream, such as via suitable heat exchange conduits and/or mechanisms.
Fuel processing assembly 11 also includes at least one treatment region 24 that is configured to receive at least vaporized component 22 of feed stream 14 and to produce a treated component, or treated feed stream component, 26 therefrom. Treatment region 24 may be described as being adapted to remove solids from at least the vaporized feed stream component. It is within the scope of the present disclosure that both gaseous and vaporized feed stream components may be passed through the treatment region, and that the fuel processing system may include more than one treatment region. When the fuel processing system includes more than one treatment region, the regions may be arranged in series to treat the same stream, in parallel to treat portions of streams having the same or very similar compositions, and/or in parallel to separately treat different compositional portions of the feed stream.
In embodiments of fuel processing system 10 that include a vaporization region 18 that receives and vaporizes a liquid feed stream component, treatment region 24 is in fluid communication with vaporization region 18 and hydrogen-producing region 28. In embodiments of a fuel processing system that receives a vaporized feed stream component from external the fuel processing system, the treatment region is adapted to receive this component and is upstream and in fluid communication with the hydrogen-producing region. By “fluid communication,” it is meant that fluid (such as a liquid or gas, as appropriate) can flow between the respective elements that are in fluid communication with each other.
Treatment region 24 may utilize any suitable treatment structure 45 that is adapted to remove solids 40 from the portion of feed stream 14 that flows through the treatment region. Although solids 40 are schematically illustrated in
An illustrative, but not exclusive, example of a suitable treatment structure 45 is a filter assembly 46, such as schematically illustrated in
Treatment region 24 may be secured to other components and/or regions of fuel processor 12 by any suitable fastening mechanisms 42. Examples of suitable fastening mechanisms include permanent fastening mechanisms and releasable fastening mechanisms. “Permanent fastening mechanisms,” refers to mechanisms such as adhesives and welds that cannot be released without destruction of at least the fastening mechanism. On the other hand, “releasable fastening mechanisms,” refers to releasable couplings, bolts, clamps, and other mechanical fasteners that are designed to be repeatedly connected, disconnected, and reconnected without destruction of the fastening mechanism. Treatment region 24 may be, but is not required to be, partially or completely surrounded by an insulated shroud 44, such as a solid insulating material, blanket insulating material, and/or an air-filled, gas-filled, or vacuum cavity.
Filter 48 also may include a housing 55. Housing 55 may include one or more openings that are sufficiently large for an internal area 56 to be accessed by a user, such as for maintenance, adjustment, servicing, and/or repair, without requiring the user to disassemble filter 48. The opening may take any form, such as portals, ports, pathways, or other suitable forms. Openings in housing 55 typically will include covers associated therewith to maintain the integrity of filter 48 while in operation. An illustrative example of an opening and a cover are graphically depicted in
Hydrogen-producing region 28 may include any suitable structure, and accordingly utilize any suitable mechanism, to produce mixed gas stream 30 from feed stream 14. For example, electrolysis is a hydrogen-producing process in which hydrogen gas and oxygen gas are produced from water. Other types of suitable hydrogen-producing mechanisms, such as partial oxidation and pyrolysis, utilize a feed stream consisting of a carbon-containing feedstock, such as an alcohol or a hydrocarbon, to produce the mixed gas stream. In still other mechanisms, feed stream 14 includes water and a carbon-containing feedstock.
An example of a hydrogen-producing mechanism in which feed stream 14 comprises water and a carbon-containing feedstock is steam reforming. Another is autothermal reforming. In a steam reforming process, hydrogen-producing region 28 contains a reforming catalyst 62. In such an embodiment, fuel processor 12 may be referred to as a steam reformer 64, hydrogen-producing region 28 may be referred to as a reforming region 66, and mixed gas stream 30 may be referred to as a reformate stream 68. Illustrative examples of suitable steam reforming catalysts include copper-zinc formulations of low temperature shift catalysts and a chromium formulation sold under the trade name KMA by Süid-Chemie, although others may be used. The other gases that typically are present in the reformate stream include carbon monoxide, carbon dioxide, methane, steam and/or unreacted carbon-containing feedstock.
Preferably, steam reformer 64, or any other fuel processor 12 within the scope of the present disclosure, is configured to produce substantially pure hydrogen gas, and even more preferably, pure hydrogen gas. For the purposes of the present disclosure, substantially pure hydrogen gas is greater than 90% pure, preferably greater than 95% pure, more preferably greater than 99% pure, and even more preferably greater than 99.5% pure. Examples of suitable fuel processors, fuel processing systems, vaporization regions, steam reformers and the like are disclosed in U.S. Pat. Nos. 6,221,117 and 6,319,306, and in pending U.S. patent applications Ser. Nos. 09/802,361, 10/407,500, and 10/412,709, the complete disclosures of each of which is incorporated by reference in its entirety for all purposes.
Steam reformers typically operate at temperatures in the range of 200° C. and 700° C., and at pressures in the range of 50 psi and 300 psi, although temperatures and pressures outside of this range are within the scope of the disclosure. When the carbon-containing feedstock is an alcohol, the steam reforming reaction will typically operate in a temperature range of approximately 200-500° C., and when the carbon-containing feedstock is a hydrocarbon, a temperature range of approximately 400-700° C. typically will be used for the steam reforming reaction. When the carbon-containing feedstock is a hydrocarbon, the reformer may be adapted to initially break the longer chain hydrocarbons in a “pre-reforming” region, and thereafter produce the mixed gas stream in a primary reforming region, which is typically operated at higher temperature than the pre-reforming region.
Regardless of the mechanism by which the fuel processor produces hydrogen gas, fuel processing system 10 may, but is not required to, include at least one separation region 32. Separation region 32 may also be referred to as a purification region, as it is adapted to produce a stream that has, compared to the mixed gas stream, a greater purity of hydrogen gas and/or a reduced amount of one or more other components of the mixed gas stream. Separation region 32 may utilize any suitable process, including chemical and/or physical processes. In a physical process, physical barriers are used to provide the separation of purification. In a chemical process, one or more of the non-hydrogen components of the mixed gas stream are reacted to reduce their relative concentration.
For example, when the product hydrogen stream is going to be used as a fuel stream for certain fuel cell stacks, it may be desirable to remove, or at least reduce, the concentration of carbon monoxide and carbon dioxide in the mixed gas stream. In a separation region 32 in which a physical separation process is utilized, the mixed gas stream 30 produced in the hydrogen-producing region is separated into a hydrogen-rich stream 34, which contains at least substantially pure hydrogen gas, and a byproduct stream 36, which contains at least a substantial portion of other gases. Hydrogen-rich stream 34 may additionally, or alternatively, be described as containing a higher concentration of hydrogen gas than the mixed gas stream, and/or containing a lower concentration of one or more of the other gases than the mixed gas stream. At least a substantial portion of hydrogen-rich stream 34 is typically used to form product hydrogen stream 16. When the fuel processing system does not include a separation region, the mixed gas or other product stream from the fuel processor will form the product hydrogen stream. The byproduct stream may be used as a combustible fuel, exhausted, sent to a burner, used as a heated fluid stream, stored for later use, etc. It is within the scope of the present disclosure that the byproduct stream may actually not “flow” as a fluid stream from the separation region, with the region instead being adapted to at least temporarily trap or otherwise contain the portion of the mixed gas stream that is removed in the separation region.
Separation region 32 may utilize any suitable separation structure to separate mixed gas stream 30 into hydrogen-rich stream 34 and byproduct stream 36. An example of a suitable separation structure for separation region 32 is one or more hydrogen-permeable and/or hydrogen-selective membranes, such as schematically illustrated in
Hydrogen-selective membranes are typically formed from a thin foil that is approximately 0.001 inches thick. It is within the scope of the present disclosure, however, that the membranes may be formed from other hydrogen-permeable and/or hydrogen-selective materials, including metals and metal alloys other than those discussed above, as well as non-metallic materials and compositions, and that the membranes may have thicknesses that are greater or less than discussed above. For example, the membranes may be made thinner, with commensurate increase in hydrogen flux. Examples of suitable mechanisms for reducing the thickness of the membranes include rolling, sputtering, and etching. A suitable etching process is disclosed in U.S. Pat. No. 6,152,995, the complete disclosure of which is hereby incorporated by reference for all purposes. Examples of various membranes, membrane configurations, and methods for preparing the same are disclosed in U.S. Pat. Nos. 6,221,117, 6,319,306, 6,537,352, 6,569,227, and 6,596,057, the complete disclosures of which are hereby incorporated by reference for all purposes.
Another example of a suitable process for use in separation region 32 is pressure swing adsorption, as schematically illustrated at 72 in
Adsorption of impurity gases occurs at elevated pressure. When the pressure is reduced, the impurities are desorbed from the adsorbent material, thus regenerating the adsorbent material. Typically, PSA is a cyclic process and requires at least two beds for continuous (as opposed to batch) operation. Examples of suitable adsorbent materials that may be used in adsorbent beds are activated carbon and zeolites, especially 5 Å (5 angstrom) zeolites. The adsorbent material is commonly in the form of pellets and it is placed in a cylindrical pressure vessel utilizing a conventional packed-bed configuration. It is within the scope of the disclosure, however, that other suitable adsorbent material compositions, forms, and configurations may be used.
An example of a suitable chemical process for use in separation region 32 is methanation, in which a methanation catalyst is used to produce methane from carbon monoxide and carbon dioxide present in the mixed gas stream. It is within the scope of the disclosure that other chemical processes, such as partial oxidation, or water-gas shift reactions, may be used to increase the purity and/or reduce the concentration of selected impurities in the mixed gas or other product stream from the hydrogen-producing region. In
It is within the scope of the present disclosure that the fuel processor does not include a separation region, but is in fluid communication with at least one separation region, such as in the fuel processing assembly, or downstream from the fuel processor and/or the fuel processing assembly. Similarly, it is within the scope of the present disclosure that the fuel processing assembly may be described as including at least one separation region, and/or that the fuel processing assembly is in fluid communication with at least one separation region that is downstream from the fuel processing assembly. By “downstream,” it is meant that a component, such as a separation region, receives a stream from a component, such as a hydrogen-producing region. In other words, the upstream component receives or produces a stream that is subsequently received by the downstream component.
The scope of the disclosure includes any suitable arrangement or configuration of the above-described regions and components. For example, vaporization region 18 may at least substantially surround at least hydrogen-producing region 28.
In
Housing 74 may be composed of one or multiple layers and may be made of any suitable material. For example, housing 74 may be composed of any suitable metal. Additionally or alternatively, housing 74 may include or otherwise be at least partially formed from a ceramic material, such as a refractory ceramic material. Refractory ceramic materials are porous materials that are made from mechanically interlocked fibers formed from such materials as alumina, silica, zirconia and the like. A benefit of refractory ceramic materials is that they are comparatively light and inexpensive compared to multi-layer metal housings. Refractory ceramic materials also have low thermal conductivity and therefore are configured not to conduct heat from the reformer or its exhaust gases through the housing. Consider, for example, that a reformer heated to approximately 500° C. will typically require not only a multi-layer metal housing but also a coolant system (such as forced air or other fluid) to maintain the outer surface of the housing below a desired temperature, such as below 50° C. While effective, that metal housing tends to be heavy and expensive to produce, in addition to requiring a coolant system.
Unlike metal housings, however, refractory ceramic materials tend to be porous and therefore permeable to the exhaust gases from a reformer or other fuel processor. Accordingly, when the reformer or other fuel processor housed within the housing emits combustion or other exhaust gases, housing 74 may include a coating, as schematically illustrated at 76 in
Housing 74 may be formed through any suitable method for forming articles from refractory ceramic materials. A process that has proven effective is a vacuum forming process. In a vacuum forming process, a perforated mold is placed into a slurry of the ceramic material from which the housing is formed. A vacuum is placed on the inside of the mold and used to draw moisture from the slurry through the perforations in the mold. As this occurs, the ceramic fibers in the slurry accumulate on the outer surface of the mold. After a desired thickness of fibers has accumulated on the mold, the mold is removed from the slurry, and then the produced article is removed from the mold and dried or otherwise cured. After formation, the ceramic article can be milled, drilled, cut, or otherwise machined, if necessary, to a desired final shape. Although a vacuum forming process may be used to make standardized shapes, such as boards and cylinders, it also offers the benefit of being useful to produce more complex shapes, such as may be defined by a more complex mold and/or the final machining of the process.
Housing 74 may include one or more openings, such as to include an opening that is too small for fuel processing assembly regions or components to be removed from the compartment therethrough, but which is sufficiently large for those regions to be accessed by a user, such as for maintenance, adjustment, servicing, and/or repair. Such an opening allows the user to access one or more fuel processor regions from external housing 74 without requiring the user to disassemble housing 74. The opening may take any form, such as portals, ports, pathways, or other suitable forms. Such an opening is graphically depicted in
As a further variation, housing 74 may include one or more openings that define inlets or outlets from the compartment. The inlets may be used to deliver fluids into the compartment, such as for cooling within the compartment and/or for delivery to the fuel processing assembly, as well as for communication linkages to the fuel processing assembly or compartment. For example, the communication linkages may establish communication from external housing 74 with various sensors and/or flow control devices within the compartment (including within the fuel processor). The outlets may be used to exhaust fluids from the fuel processor and/or from the compartment. An illustrative example of such an opening is graphically depicted at 80 in
Openings in the housing will typically include a cover or conduit associated therewith so that heat within the compartment may not freely exit housing 74 to the environment. For example, an opening that is designed as an exhaust port for gases within the compartment may be coupled to an exhaust conduit that receives these hot exhaust gases. As another example, an opening that is designed to provide selective access to the compartment, such as for removal or servicing of the fuel processing assembly, may include a cover that is designed to be selectively and repeatedly removed and replaced relative to the opening. The cover may be formed from any suitable material, including a refractory or other ceramic material, insulating and/or metallic materials. As yet a further example, an opening that is used to establish communication linkages and/or receive a fluid-flow conduit may include sealing material to prevent gases within the compartment from exiting the compartment through the opening around the communication linkage or flow conduit. A cover is graphically depicted at 82 in
Housing 74 may, but does not necessarily, include insulated jacket 84, such as a solid insulating material, blanket insulating material, and/or an air-filled, gas-filled, or vacuum cavity. It is within the scope of the disclosure, however, that the fuel processing assembly may be partially or fully contained, or may not be contained in a housing or shell. When fuel processing assembly 11 includes an insulated jacket 84, the insulating material may be external the housing as schematically illustrated in
The scope of the disclosure also includes one or more of the components of fuel processing assembly 11 that may either extend beyond housing 74 or be located external at least housing 74. For example, treatment region 24 may be external housing 74 but internal insulated jacket 84, as schematically illustrated in
As discussed, fuel processing system 10 has been schematically illustrated in
As schematically illustrated in
Fuel cell stack 86 contains at least one, and typically multiple, fuel cells 92 that are configured to produce an electric current 88 from the portion of the product hydrogen stream 16 delivered thereto. A fuel cell stack typically includes multiple fuel cells 92 joined together between common end plates 94, which contain fluid delivery/removal conduits (not shown). Examples of suitable fuel cells include proton exchange membrane (PEM) fuel cells and alkaline fuel cells. Fuel cell stack 86 may receive all of product hydrogen stream 16. Some or all of product hydrogen stream 16 may additionally, or alternatively, be delivered, via a suitable conduit, for use in another hydrogen-consuming process, burned for fuel or heat, or stored for later use. In dashed lines in
The electric current produced by the stack may be used to satisfy the energy demands, or applied load, of at least one associated energy-consuming device 98. Illustrative examples of devices 98 include, but should not be limited to, motor vehicles, recreational or industrial vehicles, boats or other seacraft, tools, lights or lighting assemblies, appliances (such as a household or other appliance), households or other dwellings, offices, stores or business establishments, computers, industrial equipment, signaling or communication equipment, etc. Device 98 is schematically illustrated in
In dashed lines in
Steam reformers and other fuel processing systems according to the present disclosure are applicable to the fuel processing, fuel cell and other industries in which hydrogen gas is produced, and in the case of fuel cell systems, consumed by a fuel cell stack to produce an electric current.
It is believed that the disclosure set forth above encompasses multiple distinct inventions with independent utility. While each of these inventions has been disclosed in its preferred form, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. The subject matter of the inventions includes all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. Similarly, where the claims recite “a” or “a first” element or the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.
It is believed that the following claims particularly point out certain combinations and subcombinations that are directed to one of the disclosed inventions and are novel and non-obvious. Inventions embodied in other combinations and subcombinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such amended or new claims, whether they are directed to a different invention or directed to the same invention, whether different, broader, narrower, or equal in scope to the original claims, are also regarded as included within the subject matter of the inventions of the present disclosure.
