Thermal chemical reaction characteristics of autothermal fixed bed reactors with structured catalysts and different surface features
Authors: Chen Junjie 
Published: February 2023

Conventional methods of producing a synthesis gas are expensive and
complex installations. In order to overcome the complexity and expense
of such installations, it is proposed to generate the synthesis gas
within autothermal fixed bed reactors that utilize structured catalysts
and different surface features to generate the heat necessary to support
endothermic heating requirements of the steam reforming reactions. The
present study is focused primarily upon the thermal chemical reaction
characteristics of autothermal fixed-bed reactors with structured
catalysts and different surface features. The heat capacity, thermal
conductivity, and viscosity of the mixture are calculated as a
mass-weighted average of the values for each constituent. In addition,
the material properties of each individual species are functions of the
local temperature. When solving the species mass transport equations,
binary mass diffusion coefficients are used directly. Only isotropic
catalyst structures are considered and the permeability and inertial
resistance factor are held constant. The effective thermal conductivity
of the catalyst structure system including the porous structure and
intervening gas is calculated based upon the porosity of the porous
medium, the fluid phase thermal conductivity, and the porous medium
effective thermal conductivity as measured in air at ambient conditions.
The present study aims to explore how to effectively generate the
synthesis gas within autothermal fixed bed reactors that utilize
structured catalysts and different surface features. Particular emphasis
is placed upon the heat and mass transport phenomena involved in
autothermal fixed bed steam reforming reactors. The results indicate
that for catalytic thermal chemical reactions, both kinetic impediments
are substantially reduced permitting realization of theoretical or near
theoretical reaction kinetics. The heat transfer chamber is in thermal
contact with the reaction chamber volume, the heat transfer chamber
transferring heat at the enhanced heat transfer rate across the wall
between the heat transfer chamber and the reaction chamber, thereby
obtaining the enhanced production rate per reaction chamber volume for
the thermal chemical reaction. Structured catalyst configurations result
in high rates of heat transport from the oxidation side to the reforming
side. Typically, combustion takes place at low or near-atmospheric
pressure, although high pressure combustion is widely practiced. The
heat that is generated on the combustion side is quickly transferred on
the reforming side. The heat integrated reforming reactor offers several
advantages over conventional flame-based reforming reactors. The
incorporation of a simultaneous endothermic reaction to provide an
improved heat sink may enable a typical heat flux of roughly an order of
magnitude above the convective cooling heat flux. The wall can be
constructed from any material, but materials that offer low resistance
to heat transfer such as metals and metallic alloys are preferred. In
this configuration, heat is generated by combustion in the catalytic
chamber and is transported very easily and efficiently though the wall
to the reforming chamber where the heat demanding reforming reactions
take place. The presence of a catalyst and lower temperatures permit
significantly higher space velocities to be used compared to flame-based
reformers.

Keywords: Hydrocarbons; Reactors; Structures; Properties;
Reforming; Combustion