Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including heat exchanger for reaction chamber or reactants...
Reexamination Certificate
2001-10-15
2004-12-28
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including heat exchanger for reaction chamber or reactants...
C422S211000, C422S198000, C422S204000, C422S206000, C048S061000, C048S06200R
Reexamination Certificate
active
06835360
ABSTRACT:
This invention relates to the use of endothermic catalytic reaction apparatus operable to produce hydrogen-containing gases from hydrocarbon feedstock.
Endothermic catalytic reaction apparatus, for converting hydrocarbon feedstock to hydrogen-rich gases, is well known in the art. Commercial production of hydrogen is commonly achieved by a process known as steam reforming, that involves the endothermic reaction between a mixture of hydrocarbon feedstock and steam passed through a catalyst filled reactor tubing that is heated.
In commercial steam reformers for large-scale production of hydrogen from hydrocarbon feeds, endothermic heat is commonly supplied by the combustion of carbonaceous fuel and oxidant in a diffusion or turbulent flame burner that radiates to the refractory walls of a combustion chamber, thereby heating them to incandescence, and providing a radiant source for heat transfer to a tubular reaction chamber. Uniform radiation to the surfaces of the tubular reaction chamber is essential since excessive local overheating of the tube surface can result in mechanical failure. In large-scale commercial steam reformers, mal-distribution of heat within the furnace chamber is minimized by providing large spacing between the individual reactor tubes, the furnace walls, and the burner flames. However, for small-scale catalytic reaction apparatus that is uniquely compact, such as for the production of hydrogen for small fuel cell applications, special design features are needed to prevent tube overheating.
U.S. Pat. No. 4,692,306 to Minet and Warren describes a compact reformer comprising an annular reaction chamber concentrically disposed around an internal burner chamber containing a vertically disposed cylindrical radiant burner that uniformly radiates in the radial direction. A uniform radiation pattern to a concentrically disposed annular reaction chamber that surrounds the radiant burner, is provided, thereby avoiding the problems with flame impingement and local overheating of tube surfaces that are associated with the use of diffusion or turbulent flame burners in compact reformer apparatus.
However, there are practical limitations regarding the use of an annular reaction chamber for small-scale reformers having hydrogen production rates of less than about 1500 SCFH. It is well known that the heat transfer coefficient of gaseous reactants contained within an annular reaction chamber is directly related to the velocity of the gaseous reactants within the annular space. In order to limit the reaction chamber wall temperature, the velocity of gaseous reactants within the annular space must be sufficiently high to absorb the radiant heat flux that impinges on the reaction chamber tube walls. However, for very small-scale reformers, this requires that the width of the annular reaction chamber space be small. It is common practice in the art to limit the maximum diameter of the catalyst particles packed within an annular space to less than 20 percent of the width of the annular space in order to ensure that the catalyst is evenly distributed within the reaction chamber and to prevent gas channeling along the walls of the reaction chamber. However, for an annulus having a small width dimension, this requires use of catalyst particles of particularly small diameters thereby resulting in an undesirably high pressure drop through the catalyst bed.
The benefits of a flameless radiant burner for use in compact catalytic reaction apparatus of annular reaction chamber geometry are known. For small-scale reformer applications, a tubular reaction chamber geometry is preferred over annular reaction chamber geometry in order to simultaneously achieve high heat transfer coefficients and low pressure drops within the reaction chamber.
There is need for a compact endothermic catalytic reaction apparatus as embodied in the present invention to achieve the objects of compact design, while avoiding the problems of flame impingement, excessive reaction chamber wall temperatures, and excessive reaction chamber pressure drop by application of a tubular reaction chamber that is heated by the radiant burner. The tubular endothermic reaction chamber as disclosed herein employs a combination of catalyst particle sizes and reactant mass velocities to control the reactor pressure drop and the maximum reaction chamber tube wall temperature within certain needed limits; and the radiant burner is operated at specific ranges of combustion intensity and excess air to control surface temperature of the radiant burner within certain needed limits. The present invention extends the practical range of tubular endothermic reaction chamber geometry that can be used in combination with radiant burners for converting hydrocarbon feedstock to useful industrial gases.
SUMMARY OF THE INVENTION
It is the general object of this invention to provide a novel endothermic catalytic reaction apparatus for the production of industrial gases from a hydrocarbon or methanol feedstock that is simultaneously compact, thermally efficient, has improved life expectancy and low pressure drop, and is particularly well suited for the small scale generation of useful gases for fuel cell applications in the range of 1 k W to 50 k W.
In the present invention, a compact burner chamber employing a radiant burner assembly is configured to distribute radiant energy along the axial length of a tubular reaction chamber. In one embodiment, the radiant burner assembly comprises a woven metal fiber attached to a support structure that permits the efflux of fuel and oxidant from the burner core to the outer surface of the metal fiber. The properties of the metal fiber stabilize the combustion in a shallow zone proximal to the outer surface of the metal fiber. The combustion reaction heats the metal fiber to incandescence and provides a source of radiant energy that is transferred to the reaction chamber. In another embodiment, the radiant burner assembly comprises a porous ceramic fiber burner that accomplishes the same object by serving as a radiant source of energy.
The metal fiber of the burner typically consists essentially of an alloy containing principally iron, chromium, and aluminum and smaller quantities of yttrium, silicon, and manganese having extended life at operating temperatures up to 2000° F.
In one embodiment, the tubular reaction chamber has U-shape, and is sometimes referred to as a hairpin tube, which is substantially filled with catalyst, the tube extending into and out of the combustion chamber for gaseous flow through. The radiant burner axis is preferably vertically disposed within the combustion chamber and oriented parallel to the axis or axes of the U-tube reaction chamber. The active radiant surface of the cylindrical radiant burner assembly is defined by a geometric arc that bisects the cylindrical assembly so as to maximize the flux of radiant energy that is directed to the surface of the U-tube reaction chamber. In this embodiment, the center to center spacing between the radiant burner and the U-tube reaction chamber, and the radiation angle of the radiant burner are simultaneously controlled, or configured for high efficiency of heat transfer.
In a third embodiment, the tubular reaction chamber comprises a helical coil that is substantially filled with catalyst and has inlet and outlet portions that pass into and out of the combustion chamber. The helical coil is wrapped to form turns at specific lead angles, so that the coil free area is in the range of 50% to 75%, wherein the free area is defined by the ratio of the free area between helical tube conduits or turns and the cylindrical surface that bisects the helical coil circle or cylinder. The radiant burner axis is typically vertically disposed within the combustion chamber and the cylindrical radiant burner is located at the center of the helical coil. In this embodiment, the active radiant surface of the cylindrical radiant burner assembly is defined by a 360-degree arc.
In each embodiment, the radiant burner is operated at a combustion intensity and an ex
Haefliger William W.
Harvest Energy Technology Inc.
Leung Jennifer A.
Tran Hien
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