LAUSR

Abstract Due to the extensive use of coal particles as a fossil fuel, reliable studies on combustion of coal particles can optimize the efficiency, safety and cost of coal-fired systems. In this study, a mathematical analysis is performed to model the trajectory of fuel particles in a multi-zone counter-flow non-premixed combustion system using an asymptotic approach. For this purpose, drag, buoyancy and gravity forces are considered in momentum equation. To obtain the temperature and mass profiles of fuel and oxidizer, a system of mass and energy balance equations are solved considering appropriate boundary and jump conditions. The effects of convective and radiative heat losses are included in the energy equation. Preheating, drying, and pyrolysis processes, heterogeneous and homogeneous reactions are investigated. Eventually, trajectories of char, gas and ash, and coal particles are tracked using Lagrangian concept. Based on the results, trajectory of particles mainly depends on the Stokes number, S t k . The analysis reveals that the damped oscillations of ash occur and ash might cross the flame front several times before leaving the system. Maximum temperatures of the system under adiabatic and non-adiabatic (in presence of both radiative and convective heat losses) conditions are equal to 2500 K and 1935 K, respectively.