Figure 3. Ethane mole fraction profiles along the fluid centerline of the catalytic reactor with an integral heat exchange structure in an array of longitudinally disposed, adjacent reaction passageways or channels which are either catalyst-coated or catalyst-free.
The ethane mole fraction contour plots in the catalytic reactor are illustrated in Figure 4 with an integral heat exchange structure in an array of longitudinally disposed, adjacent reaction passageways or channels which are either catalyst-coated or catalyst-free. The design requires that the fluid exiting the exothermic catalytic reaction channel exit and the fluid exiting the conduit outlets must come into contact to permit some degree of mixing to form the ultimate combustion mixture. To accomplish this, the exothermic catalytic reaction channel exit and the conduit outlets must be proximately located. Proximately located means that the exits are spatially located to permit the fluids exiting the exit and the outlets to come in contact so some degree of mixing is possible prior to ultimate combustion. The design does not require symmetry in securing the upstream and downstream ends of the conduits and the different securing structures could be combined in a single structure. For instance, the conduits could be secured at the upstream end by a retaining structure and at the downstream end by an expanded conduit structure. In addition, the casing and the conduits may operate at different temperatures, resulting in different amounts of thermal expansion. Thus, clearance may be provided between the conduits and the upstream or downstream retainers, to allow for thermal growth of the conduits. The conduits may be secured to each other and to the casing only at one end, as for example at the inlet or upstream end, with the other end free to move longitudinally so that differential thermal growth of the conduits may be accommodated. If a clearance is allowed between the conduits and the retainers, or if differential thermal growth between adjacent conduits is expected, the conduits' expanded sections should be of sufficient axial length that lateral support and positioning of the conduits is provided even when adjacent tubes move in opposite axial directions to the maximum extent allowed by the clearance space or the expected difference in thermal growth. If the conduits penetrate or pass through the retainers, respectively, and if they are laterally positioned by the retainers, the expanded sections need not provide lateral support to the conduits. In this case, it may also be advantageous to allow the conduits to slide freely through at least one of the retainers, to allow for thermal expansion of the conduits. An oxidation catalyst is applied to the exterior of the conduits within the exothermic catalytic reaction channel. While the entire exterior of the conduits could be catalyst coated, as a practical matter catalyst coating should not be applied where the channels touch one another or the casing. This allows close fabrication and assembly tolerances, without concern for variable coating thickness, and allows for welding or brazing of metal-to-metal contact points, if desired. In the catalyst structures, a variety of structure modifications can be made to the channels coated with catalyst to increase their tortuosity relative to the non-catalytic channels. In particular, the tortuosity of the catalytic channels can be increased by periodically changing their direction, for instance, by using channels having a zig-zag or wavy configuration or by repeatedly changing their cross-sectional area through periodic inward and outward bending of channel walls along their longitudinal axis or through the insertion of flaps, baffles or other obstructions to partially obstruct or divert the direction of reaction mixture flow at a plurality of points along the longitudinal axis of the channel. In some applications, it may be desirable to use a combination of changes in direction and changes in cross-sectional area to achieve an optimum difference in tortuosity but in all cases the tortuosity of the non-catalytic channel will be less on average than the tortuosity of the catalytic channels. Preferably, the tortuosity of the catalytic channels is increased by changing their cross-sectional area at a multiplicity of points along their longitudinal axes. One preferred way of accomplishing this change in tortuosity for the catalytic channels involves the use of a stacked arrangement of non-nesting corrugated sheets of catalyst support material which are corrugated in a herringbone pattern with at least a portion of one side of a given corrugated sheet facing and stacked against another corrugated sheet being coated with catalyst such that the stacked sheets in question form a plurality of catalytic channels. By stacking the corrugated sheets together in a non-nesting fashion, the channels formed by the stacked sheets alternately expand and contract in cross-sectional area along their longitudinal axis due to the inwardly and outwardly bending peaks and valleys formed by the herringbone pattern of the corrugated sheets. Other preferred ways of changing the cross-sectional area of the catalyst-coated channels include the periodic placement of flaps or baffles on alternate sides of the channels along their longitudinal axis or the use of screens or other partial obstructions in the flow path formed by the catalytic channels.