Pyrolysis, annealing and char combustion/oxy-combustion for cfd codes

The goal of this paper was to set up a single particle model of coal pyrolysis and combustion simple enough to be implemented in CFD codes for the simulation of pulverized coal combustors, though not neglecting the evolution of coal and char structure and the progressive loss of reactivity that is induced by heat treatment [2] in parallel with combustion/gasification. The model was set up by coupling two previously developed detailed models of coal devolatilization [1] and of char combustion, the latter including also the effects of thermal annealing on the rate of heterogeneous reactions. In order to limit the complexity of the code some simplifications have been introduced in the kinetic scheme by using lumped kinetic expressions for the rate of char combustion, gasification and annealing. The performance of the model was interrogated in comparison to experimental data of carbon conversion obtained in a drop tube [3] in O2/N2 as well as in O2/CO2 environments typical of oxy-firing. Results confirm the need for an accurate prediction of the particle temperature history and of thermal annealing but show also that more detailed kinetic schemes for the heterogeneous char reactions would be appropriate.