4. Conclusions
The steady-state continuity, momentum, energy, and species conservation
equations are solved in the fluid phase and the heat equation is solved
in the solid phase using a finite volume approach. An adaptive meshing
scheme is used for the discretization of the differential equations.
Computational fluid dynamics simulations are carried out over a wide
range of material conductivities. Continuity in temperature and heat
flux is applied at the fluid-solid interfaces. Neither heat-transfer nor
mass-transfer correlations are employed. Parallel processing employing a
message passing interface is used to speed up the most demanding
calculations. The major conclusions are summarized as follows:
- The arrangement leads to improved heat transfer and therefore chemical
conversion.
- The honeycomb structure imparts strength to the overall system
permitting the walls to be very thin and thereby being responsible for
the low weight and rapid thermal response of the combined parallel
plate heat exchanger-reactor configuration.
- The heat transfer from the process catalyst to the dividing wall is
highly efficient, however, the uptake of the energy by the heat
transfer fluid will suffer from all of the limitations of traditional
heat transfer operations.
- The process provides more efficient utilization and uniform usage of
the heat generated by the exothermic oxidation reaction, thus allowing
the endothermic steam reforming reaction to be carried out at a
somewhat higher temperature.
- The temperature control possible with this system is extremely
efficient because all the catalytic material in the reactor channels
is on the surface of the walls that can transmit heat through the
walls directly to the thermal control channels.
- Adiabatic conditions prevail in the autothermal reactor due to the
fact that the oxidation reaction is exothermic in nature and the heat
generated in the course of such a reaction is usually sufficient to
initiate and sustain the steam reforming reaction which is endothermic
in nature.
- The thickness of the catalyst coating depends upon the process
proceeding within the catalyst matrix, and the process products are
highly dependent upon the catalyst thickness.
- The thin walls and small internal diameters of the channels result in
an extremely difficult system for carrying out reactions and
transferring heat by giving rise to a high ratio of wall surface area.