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Depolymerization Model for Coal Devolatilization: Bridges and Side Chains as the Reaction Centers

Pan, Su, Hui, Shien, Liang, Ling
Energy & Fuels 2015 v.29 no.4 pp. 2162-2176
depolymerization, gases, lignite, models, temperature, uncertainty
A phenomenological extension is developed for coal devolatilization, based on FLASHCHAIN’s mechanism for tar and lumped noncondensables. It segregates the reaction center population further into bridges and side chains with dissimilar reactivities that vary with rank. At low and medium temperatures, most bridges dissociate to produce tar precursors and noncondensables, whereas only a minor portion of side chains decomposes into gases; a fraction of both types of reaction centers may also be shuttled away as an element in tar molecules. When devolatilization continues to sufficiently high temperatures, bridges are depleted and side chain decomposition takes over to dominate gas formation. In the evaluations against atmospheric reaction dynamics of 16 coals from lignite to anthracite, the extension predicts with accuracy the disparate time scales for the evolution of tar and noncondensables, as well as the rank-dependent devolatilization rates. Also, except for the earlier evolution history at low heating rates, the extension demonstrates extrapolations within experimental uncertainty over a broad domain of operating conditions (heating rates from 1 to 10⁴ K/s and pressures from vacuum to 9 MPa) for coals across the entire rank spectrum.