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 H₂O 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 CO₂. 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.