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.