Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including solid – extended surface – fluid contact reaction...
Reexamination Certificate
1999-05-27
2004-09-28
Johnson, Jerry D. (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including solid, extended surface, fluid contact reaction...
C422S177000, C422S180000, C422S198000, C422S211000, C165SDIG003, C165SDIG003, C165SDIG003
Reexamination Certificate
active
06797244
ABSTRACT:
TECHNICAL FIELD
This invention relates to a fuel gas steam reformer assembly. More particularly, this invention relates to an autothermal fuel gas steam reformer assembly which employs an open cell foam catalyst bed that reduces the size and weight of the reformer, assembly.
BACKGROUND ART
Fuel cell power plants include fuel gas steam reformers which are operable to catalytically convert a fuel gas, such as natural gas or heavier hydrocarbons, into the primary constituents of hydrogen and carbon dioxide. The conversion involves passing a mixture of the fuel gas and steam through a catalytic bed which is heated to a reforming temperature which varies depending upon the fuel being reformed. Catalysts typically used are nickel catalysts which are deposited on alumina pellets. There are three types of reformers most commonly used for providing a hydrogen-rich gas stream to fuel cell power plants. These are a catalytic steam reformer, an autothermal reformer, and a catalyzed wall reformer. In addition, hydrocarbon fuels a may be converted a hydrogen-rich gas stream by use of a partial oxidation reaction apparatus. A typical catalytic steam reformer will consist of a plurality of reaction tubes which are contained in a housing that is insulated for heat retention. The reaction tubes are heated by burning excess fuel gas in the housing and passing the burner gas over the reaction tubes. The reforming temperature is in the range of about 700° F. to about 1,600° F. The individual reaction tubes will typically include a central exhaust passage surrounded by an annular entry passage. The entry passage is filled with the catalyzed alumina pellets, and a fuel gas-steam manifold is operable to deliver the fuel gas-steam mixture to the bottom of each of the entry passages whereupon the fuel gas-steam mixture flows through the catalyst beds. The resultant heated mixture of mostly hydrogen and carbon dioxide gas then flows through the central exhaust passages in each tube so as to assist in heating the inner portions of each of the annular catalyst beds; and thence from the reformer for further processing and utilization. Such catalytic steam reformers are described in U.S. Pat. No. 4,098,587.
A typical autothermal reformer may-be a single bed or a multiple bed tubular assembly. Autothermal reformers are often used when higher operation temperatures are required for the reforming process because the fuel to be processed is more difficult to reform. In an autothermal reformer, the reaction gasses are heated by burning excess fuel within the reaction bed by adding air to the fuel and steam mixture so that the remaining fuel-steam mixture is increased to the temperature necessary for the fuel processing reaction. Typically, wall temperatures in an autothermal reformer are in the range of about 1,400° F. to about 1,800° F. Such reformers are described in U.S. Pat. No. 4,473,543.
A third type of prior art reformers have utilized catalyzed wall passages such as described in U.S. Pat. No. 5,733,347. Such reformers are formed from a sandwich of essentially flat plates with intervening corrugated plates which form reformer gas passages and adjacent regenerator-heat exchanger passages. Each of the reformer passage plate units is disposed directly adjacent to a burner passage plate unit so that the adjacent reformer and burner passages share a common wall.
Besides the reformer devices described above, a partial oxidation reaction apparatus may also be used to produce a hydrogen-rich fuel stream. This device is typically a chamber that is led a hydrocarbon fuel, steam and oxidant source, usually air, so that the mixture spontaneously partially oxidizes to form a hydrogen-rich mixture. Such devices, for example, are disclosed in PCT application WO 98/08771.
U.S. Pat. No. 4,451,578, granted May 29,1984 contains a discussion of autothermal reforming assemblages, and is incorporated herein in its entirety. The autothermal reformer assembly described in the '578 patent utilizes catalyzed alumina pellets. Although autothermal reformers allow a degree of system compaction, it would be desirable to further decrease the size and weight of an autothermal reformer, and also of any tubular reformer, particularly in systems which are utilized in vehicular applications. Attempts have been made to decrease the size and weight of autothermal and other tubular, reformers through the use of specially configured catalyst pellets. Such specialized pellet configurations include rings, flat pellets with holes, wagon wheel-shaped pellets, and lobed pellets, for example.
It would be desirable to provide an autothermal reformer assembly which does not require the use of specially configured catalyzed alumina pellets, and which is more compact and light weight than the prior art autothermal reformer assemblies which do utilize catalyzed alumina pellets. Such reformer assemblies would find particular utility in vehicular applications.
DISCLOSURE OF THE INVENTION
This invention relates to a fuel cell system autothermal reformer assembly which provides an enhanced catalyst and heat transfer surface area; is compact and light weight; and provides an enhanced gas mixing and distribution flow path. The catalyst bed structure of this invention is formed from a monolithic open cell foam core which is provided with a porous high surface area wash coat layer onto which the catalyst layer is deposited. Cells in the open cell foam onto which a catalyst is deposited are occasionally referred to herein as “catalyzed cells”. The wash coat may be alumina, lanthanum-stabilized alumina, silica-alumina, silica, ceria, silicon carbide, or another high surface ceramic material. The choice of wash coat will depend on the operating parameters of the specific catalyst bed.
The monolithic gas flow component is a foam with interconnected open cells, the surfaces of which are catalyzed with a catalyst. The foam monolith has an entry end portion which is coated with a catalyst consisting of lanthanum-promoted alumina, calcium oxide, and an iron oxide catalyst which can also be treated with a small amount of platinum, palladium or rhodium for improved low temperature fuel gas ignition. As an alternative configuration, the entry end may include a catalyst of platinum, palladium or rhodium without the iron oxide catalyst. The remainder of the foam monolith is provided with a nickel, copper or zinc catalyst, or with such noble metal catalysts such as platinum, palladium, rhodium, or the like. The open cell foam, once wash coated, provides the high surface area base required in order to achieve the deposition of the high surface area catalysts needed to properly process the fuel gas. The open cell foam also provides an enhanced mixing and distribution gas flow pattern for gases passing through the monolith since the gases will flow both laterally and longitudinally through the structure. The open cell foam also provides high surface area heat transfer paths that contribute to a more turbulent gas flow that enhances heat transfer rates in systems utilizing the catalyst bed. Additionally, the high heat transfer provided by the foam can be continued into and through adjacent walls of the reactor so as to create a highly efficient heat transfer device that results in improved process temperature control and reduces the size and weight of the reformer for a given output level. The intervening walls may be flat plates or they may be cylindrical walls with heat transfer capabilities. The monolithic open cell foam catalyst bed may be bonded to the reformer catalyst bed walls by brazing, or any other appropriate mechanism which is suitable for the system in question. When a ceramic foam catalyst bed is employed, the catalyst bed will not likely be bonded to the reformer bed walls.
All surfaces to be catalyzed will be primed by means of a conventional wash coating process such as that provided by United Catalyst, W. R. Grace and Co., or Englehard Corp. The wash coating process produces a porous layer on all surfaces of the foam, which layer forms a base for the catal
DTC Fuel Cells LLC
Johnson Jerry D.
Jongs William W.
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