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 N2 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: H2 + O2 → HO2 + H, H2 → H + 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 O2 delays ignition. However, for enriched CO2 mixtures, this substrate exerts a catalytic effect in the reactions H2 → 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 O2 + H → OH + O and H + O2 (+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.