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 EVEB curves for the three fuels of this work suggest to pursue a generalization in the approach, enlarging the number and variety of fuels studied.