4. Conclusions
The present study aims to provide a fundamental understanding of the
exothermic and endothermic reaction characteristics and operation
methods of integrated combustion-reforming reactors. Particular emphasis
is placed upon the simultaneous implementation of the endothermic steam
reforming and the heat-supplying exothermic catalytic combustion such
that the thermal stability of the reaction system is increased. The
effect of catalyst layer thickness on the reaction characteristics is
investigated in order to understand how to design and operate such
reactors with high efficiency. The major conclusions are summarized as
follows:
- Unique jet design features can be implemented in order to suppress
homogeneous combustion and promote heterogeneous catalytic combustion
on the channel wall.
- Diffusion within these small pores in the catalyst layers is typically
Knudsen in nature for gas phase systems, whereby the molecules collide
with the walls of the pores more frequently than with other gas phase
molecules.
- The composition in the combustion chamber is reacted to produce
sufficient heat to sustain the micro-combustion process without energy
input.
- The combustion and reforming processes can be stably and efficiently
operated at lower temperatures, without the need for energy input to
sustain or even to start the combustion process.
- Since a palladium component is alloyed with the zinc, generation of
carbon monoxide due to the methanol decomposition reaction is
suppressed.
- Direct heating is of considerable advantage as it largely overcomes
the problems encountered with reaction rates being limited by the rate
of heat transfer through the tube wall especially near the reformer
entrance and thus, for a given conversion, the reactor may be smaller,
more efficient and less expensive.
- The conventional methods are suitable for large scale hydrogen gas
production, but they are not adequate for middle to small scale
hydrogen gas production.
- As the channel dimension nears the quench diameter or drops below, the
contribution of the unwanted gas phase homogeneous combustion reaction
is reduced.