(343d) Multi-Physics Modeling of Auto-Thermal Diesel Surrogate Reforming

Abundant
supply and existing infrastructure makes diesel a favorable candidate for
portable energy supply. Diesel generators are widely used in locations where
there is no reliable electric grid, but they are noisy, have emission issues,
and often have poor fuel efficiency in practical operations. Because of these
drawbacks, there is interest in developing Solid Oxide Fuel Cell (SOFC) systems
which use diesel fuel, but which deliver electricity quietly and with lower
emissions and higher efficiency.

The
current study is part of a larger effort aimed at developing 1-5 kW diesel fed solid
oxide fuel cells at SOFC-Canada and is mainly focused on understanding and
deconvoluting the mechanism of diesel surrogate auto-thermal reforming in an
experimental packed bed reactor. Gas phase kinetics play
an important role during auto-thermal reforming and this study employs a
detailed kinetic model developed using the automated Reaction Mechanism Generator
(RMG) software. The generated model has about 9500 reactions and 450 species incorporating
updated parameters from experiment and theory. The model has been validated
against ignition delay data at different equivalence ratios and was found to
perform reasonably well. The model has also been validated against the packed
bed reactor steady state concentration data at different operating conditions. Coupling the
fluid dynamics and heat transfer effects defined above with the large number of
reactions and species was found to be very difficult using currently available
commercial software such as Fluent and COMSOL. Hence an iterative approach was
used in which simplified packed bed plug flow reactor model with heat transfer
was solved using a finite element solver while the kinetics equations were
solved using the CHEMKIN plug flow solver. The generated model shows the
importance of entrance region effects for auto-thermal reformer design. Gas
phase oxidation/pyrolysis consumes a large part of the hydrocarbon leading to lower
molecular weight products that reach the catalyst surface and participate
primarily in steam reforming reactions dominant on the surface of the
catalyst.