Atomistic simulations of syngas oxy-combustion in supercritical CO2

The growing energy demand worldwide is currently supplied by the direct use of fossil fuels, which are limited in nature and represent an environmental concern. Syngas/oxy-combustion technologies have become popular due to recent advances in carbon capture and storage and the possibility to avoid NOX formation by replacing N-2 with supercritical CO2. However, the successful implementation of these systems faces several drawbacks: variability in syngas composition and lack of understanding of the chemical kinetics at elevated temperature and pressures in the presence of CO2. In this work, we carried out a molecular dynamics study of syngas oxy-combustion using ReaxFF force field. Three main initiation reactions were identified: H-2 + O-2 -> HO2 + H, H2H -> + H, and CO2 -> CO + O, with the last being dominant at high temperatures and high concentrations of CO2. We also found that increasing the initial CO2 concentration and decreasing that of O-2 delays ignition. However, for enriched CO2 mixtures, this substrate exerts a catalytic effect in the reactions H-2 -> H + H and H2O -> OH + H by forming the intermediate HCO2. In the absence of initial CO2, formyl radical (HCO) chemistry is lacking due to the prominent consumption of H species by molecular oxygen via O-2 + H -> OH + O and H + O-2 (+M) -> HO2 (+M). However, we observed the association between HCO and OH radicals to form stable formic acid, a reaction not implemented in syngas mechanisms.