Effect of the heating rate on the devolatilization of biomass residues

The devolatilization is the basic step of thermochemical processes and requires a fundamental characterization. Three biomass residues (rice husks, olive cake, cacao shells) are studied here in a thermogravimetric (TG) balance. The effect of the heating rate (HR) is evaluated in the range 5-100 K/min providing significant parameters for the fingerprinting of the fuels. Kinetics are obtained by applying traditional isoconversional methods. The activation energy as function of the conversion reveals the multi-step nature of the biomass devolatilization. Although average values allow the reactivity of different fuels to be compared, a first order reaction model can hardly predict the biomass devolatilization. A VEB (Variable activation Energy model for Biomass devolatilization) model is; developed, basing on the results of the kinetic analysis. A good agreement is obtained for the biomass residues in all HR runs in the entire range of temperatures. Similarities in the optimized E-VEB curves for the three fuels of this work suggest to pursue a generalization in the approach, enlarging the number and variety of fuels studied. (C) 2008 Elsevier B.V. All rights reserved.