Kinetics and Mechanisms of NO(x) - Char Reduction. Page: 4 of 70
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empirical description of this picture in order to describe the initial pore structure and its
evolution with gasification.
Perhaps the currently most widely used approach for describing reactions of porous
solids is again based upon the random pore model, in a version proposed independently by
Gavalas19 and Bhatia and Perlmutter20. In this implementation, experimentally determined
parameters of initial pore size distribution and reaction rate are used in these models to
characterize the porosity development.
Drawing somewhat upon the earlier qualitative descriptions, other recent models
have considered char to be comprised of two regions, a macropore "region" and a
micropore "region". In this case there should be different models to describe the porosity in
different regions. Sandmann and Zygourakis21 developed a discrete model which allows
modeling the pore development in char with a multimodal pore size distribution, in the
presence and absence of pore diffusion limitations and in the presence of particle
fragmentation. Bhatia22 proposed a model for coal to be comprised of microporous grains,
with the random pore model holding for the micropores in the grains. Ballal and
Zygourakis23 developed novel random pore models for predicting changes in porosity of
both unimodal and bimodal pore size chars, in which the model parameters are directly
related to the structural properties of "raw" char. Another model that separately described
macroporosity and microporosity was recently proposed by Kantorovich and Bar-
Ziv24,25. In this work a new picture for pore structure evolution were proposed. Whereas
usually uniform pore diameter increase with reaction is assumed (i.e. the surface
concentration of active sites is constant during reaction), in this study the changes in
concentration of active sites were modeled as involving coalescence of the microcrystals.
Using this model, in which changes in dimensions and coalescence of graphitic
"microrods" took place, the authors were able to explain the shrinkage phenomenon and the
evolution of internal surface area of highly porous carbons in the intrinsic reaction regime.
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Suurerg, E.M.; Lilly, W.D. & Aarna, I. Kinetics and Mechanisms of NO(x) - Char Reduction., report, December 31, 1997; United States. (digital.library.unt.edu/ark:/67531/metadc690356/m1/4/: accessed January 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.