Numerical analysis of particle dispersion and combustion characteristics on a piloted coaxial pulverized coal jet flame

Abstract

A numerical simulation was performed and validated on a piloted coaxial pulverized coal jet flame by means of large eddy simulation (LES) in which the dynamic Smagorinsky SGS model and the Lagrangian particle tracking model were employed. In the devolatilization process, a postulate substance, CaHbOc, was considered as the devolatilized gas. For gaseous phase reactions, a simple two-step global kinetic mechanism was implemented. For a solid phase reaction, a two-step char oxidation reaction was installed. Results were compared to an experimental result in terms of particle distribution, gaseous temperature, gas composition, and particle velocity. The particle distribution result shows that particle dispersion for the combustion case is narrower than that for the non-combustion case. This phenomena is discussed by observing an axial interphase momentum transfer. The axial momentum of fluids can be maintained as high or similar to the particles by combustion, so momentum transfer is limited in the combustion case. It is also confirmed in the particle and gas velocity results. Time-averaged temperature and mole fractions of gases capture the featured characteristics of the experiment well. From these results, an effect of devolatilized gas combustion on particle dispersion and stream flow are discussed. And it is revealed from instantaneous results that particles tends to form groups following the edge of the devolatilized gas combustion.