Hydrocarbon fuel gas reformer assembly for a fuel cell power...

Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including heat exchanger for reaction chamber or reactants...

Reexamination Certificate

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C422S198000, C422S198000, C048S061000, C048S076000

Reexamination Certificate

active

06296814

ABSTRACT:

TECHNICAL FIELD
This invention relates to a catalytic reaction system. More particularly, this invention relates to a system having an array of catalyst tubes, each of which has an annular catalyst bed.
BACKGROUND OF THE INVENTION
Catalytic reaction apparatus have been commonly used in industry to produce industrial gases such as a hydrogen enriched fuel gas and are therefore well known in the art. The most common approach for producing hydrogen is the steam reforming process in which a raw fuel gas is mixed with steam and passed through catalyst beds disposed in a tubular reformer. Heat for this endothermic reaction is provided from a furnace in which the tubes are locoted in a widely spaced apart configuration.
As a result of the large size and limited operating flexibility characteristics of these industrial units, steam reforming technology was not successfully integrated for use with power plants that incorporated hydrogen consuming fuel cells until the successful application as disclosed in U.S. Pat. Nos. 4,098,587; 4,098,588 and 4,098,589. The new design represented by these patents consisted of a compact reaction apparatus with a number of important features that made it suitable for use within a fuel cell power plant.
Namely, it is a compact reaction apparatus for steam reforming a raw fuel that is mainly characterized by having: a plurality of vertical tubular reformers closely packed (by the then standard of the art) within a furnace and shielded so as to produce an evenly heated tube at any location within the array of tubes; having a burner cavity area and an enhanced heat transfer area; and having annular reformers incorporating regenerative heat transfer capability between the reaction products and the process stream.
This design resulted in a steam reformer apparatus that met the size and operating characteristic requirements of a fuel cell power plant while maintaining a high thermal efficiency that is necessary to ensure a competitive overall power plant operating efficiency.
While the design disclosed in the aforesaid patents was a milestone achievement for the application of hydrogen generation technology to fuel cell power plants, these early designs were in need of improvements to make it truly more compact, lighter in weight, more uniform in its heat distribution and catalyst bed stability. Chief among these problems is the need to develop an efficient supporting structure that keeps the tube bundle aligned and properly distributes the loading forces resulting from tubes and catalyst and ancillary equipment without undue weight penalty or complex and costly structural fixtures.
DISCLOSURE OF THE INVENTION
This invention relates to a compact and efficient reformer which is operable to produce a hydrogen-enriched process fuel from a raw fuel such as natural gas, or the like. The reformer of this invention includes a compact array of catalyst tubes which are contained in a heat-insulated housing. The catalyst tube array preferably includes a multitude of tubes that are arranged in a hexagonal array. The housing is preferably circular for manufacturing and structural efficiency, and the interior of the circular housing is fitted with a geometrically matching insulation. For example, when the hexagonal array of reformer tubes is employed, the insulation will provide a hexagonal perimeter which faces the reformer tube array. The outermost tubes in the array are thus equally efficiently insulated against heat loss. The diameter of the tubes is also sized so that spacing between adjacent tubes in the array can be minimized for efficient heat transfer. The stiff tube support structure maintains the critical spacing between tubes under dead weight loading at reformer operating temperatures.
The interior of each of the catalyst tubes includes a hollow dead-ended central tube over which processed fuel is passed after leaving the catalyst reaction bed. The dead-ended tube serves as a fines trap for collecting catalyst fines which become entrained in the fuel stream as the latter passes through the catalyst bed. The catalyst tubes are also provided with an uppermost conical cap which serves to extend the catalyst bed so that an excess of catalyst can be loaded into the bed when the tubes are constructed and assembled. The assembled and closed catalyst tubes thus will contain an excess of catalyst so as to maintain a desired height to the catalyst beds even when catalyst slumping and settling occurs. Catalyst settling is also controlled by the respective size of the catalyst pellets and the radial thickness of the catalyst bed. In addition, the conical cap shape prevents the fluidization of the catalyst bed in the upper portion of the catalyst reaction zone by lowering the gas flow velocity as the flow area increases. This is important because fluidization leads to excessive settling and crushing of the catalyst in this region with each thermal cycle. This exacerbates the catalyst layer height loss that is desirable to minimize.
This design is also characterized by the use of a side-fired startup burner instead of a central-fired startup burner as has been previously used. The side-fired burner allows for an improved diffusion burner orifice array at the top of the reformer. Thus, a burner orifice array which is not interfered with by the centrally located startup burner is achieved so as to make the heat distribution from the diffusion burners more easily and efficiently achieved. It will be appreciated that the presence of a centrally located startup burner will disrupt the diffusion burner pattern and will create a void in the central portion of the upper,end of the furnace when the startup burner is shut down. This undesirable result does not occur when the side-fired startup burner of this invention is used.
The design is also characterized by the use of reformer tube caps having a thickness that is greater than conventionally used so as to provide an added temperature operating range because the operating range is limited mainly by corrosion and strength requirements. Increasing the thickness of the cap, which is disposed in the hottest part of the reformer tube, improves the capability of the reformer to deal with design and structural variations, and increases the safety margin of the design.
The catalyst tubes are supported by side walls of the assembly housing in a manner that stabilizes the tubes in the assembly, and allows the assembly to take advantage of assembly components which provide unique structural features affording improved strength and stiffness, and also the resistance to thermal stresses without increasing weight or volume. In the aforesaid U.S. Pat. No. 4,098,587, the weight of the catalyst tubes is supported by the bottom wall of the apparatus, which is also a pressure boundary for the vessel. In the assemblage of this invention, the internal transverse manifold plates are tied together by portions of the tube assemblies so as to form a composite beam that supports the weight of the catalyst tube array. The manifold plates and the tying tube assembly portions interact with each other in a manner which creates the structure and effect of a composite beam that transfers the load from the tubes out to the cylindrical side wall of the assembly. The resultant structure provides Increased load bearing strength in a manner similar to a honeycomb panel.
The two internal transverse manifold plates serve as face sheets of the honeycomb-like structure, in which the tube sections between the manifold plates serve as a core for the honeycomb-like structure. By freeing the bottom area of the assembly from the need to provide tube weight and load support, the bottom area can be utilized for other functions such as the additional capture of fines, or integrated heat exchange options. This is a desirable feature which enables the achievement of maximum packaging density in a weight and volume sensitive power plant design.
It is therefore an object of this invention to provide a more efficient and compact apparatus for reforming a fuel supply so as to adapt

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