Three dimensional cfd simulation of pneumatic coal injection in a direct reduction rotary kiln

The pneumatic coal injection and combustion process in a commercial rotary kiln is modeled in this work using a two phase flow theory approach. The physical and chemical phenomena of the turbulent reacting flow is simulated using a multiphase Eulerian-Lagrangian CFD approach where the gas phase is treated as a continuous phase and the pulverized coal particles are tracked in the flow field in a Lagrangian way. Three-dimensional, steady-state Reynolds averaged Navier-Stokes equations closed by the k-ε turbulence model are solved for the turbulent gas flow, including mass, momentum, turbulence kinetic energy, turbulent dissipation rate, enthalpy, and a number of gaseous species mass fractions. All the relevant phenomena like coal devolatilization, homogeneous volatile combustion, heterogeneous char reaction, particle dispersion and radiation are included in the mathematical model proposed in this work and the commercial CFD code ANSYS-CFX 11.0 is used to obtain the numerical results. Effect of various operating parameters such as initial air and particle velocity, and particle size on the distribution of injected particles along the axial length of the kiln and thermal load provided by them has been analyzed.