Competitive or additive behavior for H2O and CO2 gasification of coal char? Exploration via simplistic atomistic simulation

Here, a large-scale char atomistic structure (41,438 carbon atoms) and simple simulation approaches explored char gasification behavior for H O-2 and CO2 - comparing their mixture with one gas being passive (non-reactive) and the dual reactive mixture. Reactivity was captured through simplistic atomistic simulations via an automated sequence of gas diffusion, close-contact determination for gas (es) to reactive edge sites, then "reaction" via atom deletion. The higher reactivity of H2O was captured by a reaction probability function. For the reactive mixture (where both gases are reactive), the char consumption rate was 14% higher than with H2O alone, but lower (-80%) than the sum of the individual gases (where only one gas is reactive), demonstrating competitive behavior. The H2O out competed the CO2 molecules and contributed -83% to the char consumption - with the reaction rate being similar to that of H2O independently. The pore size development for individual gases also differed with H2O favoring development in the smaller pore sizes in comparison to CO 2 . With fewer gas molecules (using 10% to capture a lower pressure), the competitive behavior was muted and became much closer to additive behavior. These simple simulations are consistent with the emerging rationalization of contributing factors to char gasification. (C) 2018 Elsevier Ltd. All rights reserved.