Development of a Variable Energy model for Biomass devolatilization

Devolatilization is a crucial step in all thermochemical processes (pyrolysis, gasification and co-combustion) for conversion of biomass into energy, fuels and/or chemicals. A thermogravimetric (TG) balance is used in this work to characterise different types of biomass, including residues (rice husks, olive cake, cacao shells), woods (poplar, beech, pellets), and grasses (mischantus) to achieve a fundamental insight into devolatilization kinetics. The effect of the heating rate is evaluated in the range 10-80 K/min providing significant parameters for the fingerprinting of the fuels. Kinetic parameters are obtained by applying traditional isoconversional methods. The activation energy as a function of the conversion reveals the multi-step nature of the biomass devolatilization. Although average values allow the comparison of the reactivity of different fuels, a first order reaction model can hardly predict the biomass devolatilization over the whole range of conversion, suggesting the need for more refined tools of kinetic analysis. A VEB (Variable activation Energy model for Biomass devolatilization) model is developed, based on the results of the kinetic analysis. A good agreement is obtained for all biomasses in all runs in the entire range of temperatures.