Friday, September 22, 2006
2:00pm – 3:00pm
Professor Anthony M. Dean
Chemical Engineering Department
Colorado School of Mines
ÒEngineering
Applications of Detailed Chemical KineticsÓ
Abstract:
This talk will outline how the
combination of improved understanding of elementary chemical reactions and
subsequent incorporation into realistic flow models has markedly improved our
ability to describe Òreal-worldÓ systems. Such approaches require development
of accurate, detailed chemical mechanisms, which in turn require careful
analysis of different types of elementary reactions. This talk will describe
our approach to the characterization of elementary reactions, the construction
of detailed mechanisms, and the combination of these mechanisms with the
appropriate transport models to model the behavior of solid-oxide fuel cells.
In terms of elementary reactions, the C2H5 + O2
reaction system will be used to illustrate the complexities of chemical
activation. Here the initially formed adduct contains the energy of the newly
formed C–O bond. The subsequent reactions of this energized adduct
reflect the competition between its unimolecular reactions and its bimolecular
collisional stabilization. As a result, multiple reaction pathways are
available, and the rate coefficients for the various pathways depend on both
temperature and pressure.
We illustrate kinetics/transport coupling by considering solid-oxide
fuel cells. SOFCs are currently in development for use in a number of
applications, including distributed power generation. These systems offer the
potential for direct electrochemical oxidation of hydrocarbons without the
requirement for upstream fuel reforming. However, at nominal operating
temperatures of 600-1000¡C, fuel stability and carbonaceous deposits within the
fuel channels and porous anode structures present potential limitations to cell
performance. Several illustrations of the application of detailed kinetics to
SOFC operation will be considered.
One
such example is the description of experimental and modeling investigations of
methane reforming chemistry in a porous Ni-YSZ cermet anode. Using specially
designed experiments and computational models, our objective is to develop and
validate models that quantitatively describe chemical kinetics and gas
transport within the anode structure of a solid-oxide fuel cell (SOFC). Another
topic will be a description of the approach used to develop gas-phase molecular
weight growth kinetics to characterize deposit formation within SOFCs. The
ability of the model to quantitatively describe the differences in both
conversion and deposit formation between butane and ethanol fuels will be
described. We will then illustrate how these chemical mechanisms can be
combined into a larger model that includes both transport and electrochemistry
to predict SOFC behavior under a variety of operating conditions (e.g.,
upstream steam reforming of JP-8).