Using the distributed activation energy model to interpret oxidative coal pyrolysis experiments performed by flat-flame burner, entrained-flow reactor and thermogravimetric analyzer

Coal pyrolysis experiments with a Flat Flame Burner an Entrained Flow Reactor and a Thermogravimetric Analyzer has been done on a Pittsburg 8 coal-type. The instruments offer extremely different conditions with respect to environment for- and heating rate of the particles examined. The results obtained from each of the instruments are combined to provide a better background for modelling the pyrolysis of the coals under varying conditions.

A procedure for using the Distributed Activation Energy (DAE) model to describe coal devolatilization in a flame is proposed. It is described how to calibrate and test the DAE model from experiments performed with a Flat-Flame Burner and an Entrained-Flow Reactor. The model enabled realistic predictions of devolatilization characteristics for a Pittsburg 8 coal dust for a range of heating/oxidizing environments.

The results indicate that for rapid heating (10"5K/s) release of primary volatiles occurred within 3-10 ms and before calculated particle peak temperatures of 1200-1500K were reached. The calibrated DAE-model approach combined with a model describing the heat balance for a coal particle in a hot environment, allows comparison of coal particle conversion rates due to kinetic reaction rates and mass- and heat transfer effects.

Reported kinetic parameters derived under inert slow heating rate conditions by thermogravimetry (TGA) were shown to be applicable under high heating rate conditions. However with the calibrated data applicable for the Flat Flame Burner experiments lower temperature yields obtained by an Entrained Flow Reactor were underestimated.

This showed that the simple DAE-model is not able to cover a large temperature regime when high heating rates are applied. A comparison between the TGA proximate volatiles of the coal and the chars processed in the Flat-Flame Burner is performed.