Reactive molecular dynamic simulations of the CO2 gasification effect on the oxy-fuel combustion of Zhundong coal char

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In this paper, the effect of CO2 gasification on the oxy-fuel combustion of Zhundong coal char was studied by reactive molecular dynamic (ReaxFF-MD) method combined with experiments. The structural representation of Zhundong coal char was constructed based on experimental analysis. ReaxFF simulations of char combustion in O2/N2 and O2/CO2 environments at various conditions were carried out to investigate the effect of CO2 on the conversion of char. The flat-flame entrained flow experiments were also performed to compare with the ReaxFF MD simulations. The results showed that CO2 reduced the diffusion rate of O2 and thus inhibited the oxidation rate of char. However, the total carbon consumption of char was found to be increased by the CO2 gasification reaction, especially at low O2 concentration at high temperatures. The contributions of CO2 gasification to the total carbon consumption of char at 3500 K were 51.38%, 34.74% and 19.88% in 5%, 10% and 20% O2 concentrations, respectively. The activation energy of CO2 gasification was determined as 250 kJ/mol in the temperature range of 3000–3500 K. Finally, the detailed and dynamical description of CO2 gasification reaction pathways were revealed in atomic scale. CO2 molecule was initially adsorbed on the active carbon site, and then the CO bond broken resulting in the formation of CO.