Modelling pulverized coal combustion using air and O2+ recirculated flue gas as oxidant

This work uses a numerical model to analyse the flame structure and the radiations heat transfers of pulverized coal firing with Air and in oxyfuel conditions. The numerical model considers an axisymmetric approximation for the flow and coal simulation based on a Lagrangian method. The combustion in the gas phase is handled by the eddy dissipation model combined with global kinetics. The coal conversion is based on the CPD volatilisation model and the char conversion by a first order kinetic model. Radiation properties are calculated based on a spectral line-based weighted-sum-of-grey-gases (SLW) model that was found appropriate for this situation. The radiation properties of particles are considered through the use of approximate functions for the absorption and scattering efficiencies. Calculations are presented for tests carried out in the RWEn power's 0.5MWth combustion test facility (CTF) with a Russian coal fired in a burner with 3% O2 in the flue gases, for air firing and simulated recirculated flue gases (RFG) with oxygen injection. The predicted incident radiation heat fluxes to the furnace walls are compared with experimental data. The calculations indicate that the flow structure is modified by the operating conditions leading to similar results when using the higher recirculation ratio and air firing. The computed wall incident heat fluxes present greater dependency of the wall temperatures than the CO2 level or the recirculation ratio.