Modelling coal combustion with air and wet recycled flue gas as comburent in a 2.5 MWth furnace

•CFD based simulation of a swirl air coal flame and an oxy-fuel coal flame.•The importance of the CO2 in the char reactions is discussed.•The computational results are compared with detailed experimental data.•The CO2 char gasification reaction is secondary, but also important.•The CO2 char gasification becomes significant at high temperature and low O2.

This work reports a CFD based numerical simulation of a swirl air coal flame and an oxy coal flame using wet recirculated flue gases from a large combustion test facility (2.5 MWth). Special attention is given to the importance of the CO2 in the gas phase and char reactions. The gasification kinetic rates published in the literature were reviewed and two sets of gasification/oxidation rates obtained in the same device were used in the simulations. The computational results are compared to detailed experimental data of the velocity, temperature and major gases species (O2, CO2 and CO).One of the simulations provides results in good agreement with the experimental data. These results were used to discuss the relevance of the gasification reaction on the char consumption under oxy-fuel conditions. The gasification reaction is secondary, but also important, representing 16.5% of the total char carbon consumption. The CO2 gasification reaction becomes more relevant in regions of high temperature and low O2. The numerical results also show that both flames present the same structures and have similar in-flame temperature distributions.