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

Abstract

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-e 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. The simulation results are first validated under cold conditions for the dynamics of the coal particles with the data reported by Biswas (1993) [8]. The second set of validation deals with hot model simulation reported by Guo et al. (2005) [9], where coal combustion and heat transfer simulation are included. After the validation study, the simulation has been extended to investigate the influence of operating parameters such as particle size distribution and wall temperature on the distribution of injected particles along the axial length of the kiln and thermal load provided by them.