3. Results and discussion
The methanol mole fraction contour maps are illustrated in Figure 1 for
the integrated combustion-reforming reactor in which combustion chambers
are in direct thermal contact to reaction chambers for an endothermic
steam reforming reaction. Channels refers to the generally accepted
meaning and includes conduits and other means for directing the flow of
a fluid. Channels include at least one opening, typically with an inlet
and outlet, and may include other openings. Fluid communication between
two areas means that a fluid can flow from one area to the other.
Thermal communication between two areas means that heat can flow from
one area to the other. Heat exchanger is a device or component designed
such that heat can be transferred from one fluid to another. The heat
source for the endothermic reaction is delivered directly to the wall in
contact with the endothermic catalyst. This follows from the fact that
metal conduction is a more efficient mode of heat transfer than either
convective or radiative heat transfer. In contrast to premixed
combustion, where the heat release will occur primarily in the
homogeneous phase, combustion jets can direct a concentrated stream of
air into a separate fuel channel stream. The two streams subsequently
mix and undergo an oxidation reaction. In order to suppress homogeneous
combustion and promote heterogeneous catalytic combustion on the channel
wall, unique jet design features can be implemented. Important features
include geometry, size, and relative location and spacing. The jets
should not only impinge on the wall but also spread out the combustion
oxidant as uniformly as possible along the entire width of the channel.
Furthermore, heterogeneous combustion is preferably concentrated at the
combustion wall in closest proximity to the endothermic reaction
catalyst. Combustion on other walls represents a heat loss and
furthermore has a disadvantageous impact on thermal stresses in the
device. In order to raise the temperature of an endothermic steam
reforming reaction and reduce the likelihood of coke formation at the
beginning of the reactor zone or in the heat exchanger zone reactant or
product channels, more air should be delivered for combustion against
the wall at the beginning of the reactor zone. Concentration of jets in
this region as well as application of non-circular jet orifices can
successfully meet this objective. All the goals above are desired to be
accomplished with a minimal pressure drop for both economic reasons as
well as for the purposes of preserving back pressure in the integrated
combustion-reforming reactor device to ensure good flow distribution. To
this end, a hybrid of circular and rectangular slot orifices can be
implemented in the jet design. Alternatively, other non-rectangular
non-circular jets could be used such as diamonds, triangles,
semi-circles, quarter-moons, and the like. Computational fluid dynamics
predictions indicate that a combination of these two jet geometries
provide a more ideal heterogeneous fuel-oxidant mixture distribution on
the combustion channel wall opposite the jet shim. It is recognized that
other non-circular jet orifices could also be used at the entrance of
the combustion zone or anywhere down the length of the reactor. It is
also recognized that the combustion orifices could start before the
reaction zone in the recuperative heat exchanger section to further
preheat the reactants or further tailor the thermal profile of the
device.