Simulations on pressurized oxy-coal combustion and gasification by molecular dynamics method with ReaxFF

Pressurized oxy-fuel combustion (POFC) is recognized to have the potential to effectively capture CO₂ with low cost and high efficiency. To investigate the chemical mechanism of oxy-fuel combustion and the effects of different operating parameters on combustion characteristics, a gasification reaction model and the pressurized oxy-fuel combustion model were constructed. A series of reactive molecular dynamics (MD) simulations were conducted on the POFC model using ReaxFF force field under the pressure of 0.2, 0.3 and 0.5 MPa, and with the temperature at 1600, 1800 and 2000 K, respectively. The activation energy for atmospheric oxy-fuel combustion was firstly calculated, in agreement with reported experimental results, which verified the accuracy of ReaxFF MD method. The results of gasification and combustion showed that both temperature and pressure positively affect coal decomposition and the combustion reaction rate. The conversion mechanism of C in coal to CO₂ is a process with dehydrogenation, coal decomposition and oxidation reaction. Compared with atmospheric oxy-fuel combustion, the increase of pressure/density would accelerate the dehydrogenation reaction and the decomposition of coal structure, and improve the performance of coal combustion and promote the decomposition of coal molecule into smaller fragments, and further promote the releasing of CO₂ and small fragments.