Lattice Monte Carlo simulation of single coal char particle combustion under oxy–fuel conditions

•Model for single char particle combustion in air and oxy conditions was developed.•Model is based on lattice percolation, random walkers and Monte Carlo simulation.•Model points out char structure influence on randomness of the combustion process.•Model was verified by comparison with experimental data from single particle reactor.•Special care was given to the CO2 gasification reaction influence on char combustion.

A descriptive model for isolated char particle combustion under conventional and oxy–fuel conditions was developed. Suggested model is based on the percolation theory and Monte Carlo simulation technique. Char particle was modeled as a square lattice consisting of a large number of small sites. Sites correspond either to fixed carbon, ash, or pore, and they were distributed randomly inside char lattice using percolation concept, at the start of simulation. Random walk model was used to represent gaseous species diffusion through particle pores. Char combustion was modeled using power law Arrhenius model which assumes that reaction rate depends of particle temperature and oxygen partial pressure on particle surface. The main aim of the proposed model was to take into account influence of heterogeneous char particle structure to randomness of the char combustion process. The suggested model’s behavior was validated by qualitative comparison with experimental data obtained in single particle reactor. It was found that simulated combustion time, char burnout and particle temperature values are in good agreement with experimentally determined data. Special emphasis was given to the CO2 gasification reaction influence on char conversion and particle temperature values. Further development of the proposed model with appropriate simplifications would enable its inclusion in comprehensive CFD codes.