Thermochimica Acta 472 (2008) 55–63 Contents lists available at ScienceDirect Thermochimica Acta journal homepage: www.elsevier.com/locate/tca Effect of the heating rate on the devolatilization of biomass residues E. Biagini a,∗ , A. Fantei b , L. Tognotti b a Consorzio Pisa Ricerche, Divisione Energia e Ambiente – Lungarno Mediceo 40, 56127 Pisa, Italy b Dipartimento di Ingegneria Chimica – Universit` a di Pisa – via Diotisalvi 2, 56122 Pisa, Italy article info Article history: Received 7 December 2007 Received in revised form 14 March 2008 Accepted 24 March 2008 Available online 29 March 2008 Keywords: Pyrolysis Lignin–cellulose materials Solid fuels Thermal degradation Kinetic analysis Fundamental model abstract The devolatilization is the basic step of thermochemical processes and requires a fundamental characteri- zation. 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. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Agricultural and food residues represent a renewable energy source, may be abundant in specific local areas and cause dis- posal problems. Thermochemical processes constitute interesting options for biomass utilization [1–5]: co-combustion is a short time opportunity for benefitting the biomass advantages (CO 2 neutral fuels, low emissions of sulphur and heavy metals); gasification is a clean and efficient alternative for converting biomasses into upgraded fuels (syngas for direct energy generation or hydrogen production in a mid-term scenario); pyrolysis is a versatile process for recovering chemicals and fuels. Devolatilization is the first step of all these thermochemical pro- cesses. It consists in the release of volatile matter (condensable and light gases) during the continuous heating of the solid fuel. The thermal scission of chemical bonds in the natural polymers (cellu- lose and lignin) causes the formation of cracked compounds (the lighter products passing to the vapour phase), activated intermedi- ates for further decomposition and the re-organization of the solid matrix. Therefore, the process is a complex mechanism because consecutive and parallel paths act in a very narrow range of tem- peratures. The global behaviour can be studied in thermal analysis developing procedures commonly accepted for a useful character- ization of the fuel. The thermogravimetric (TG) technique is the ∗ Corresponding author. Tel.: +39 0502217850; fax: +39 0502217866. E-mail address: e.biagini@ing.unipi.it (E. Biagini). basis for a fundamental investigation and gives the fingerprint- ing of the fuel. It provides important characteristics (temperature of devolatilization, volatile matter released), reaction kinetics and significant parameters for preliminary modelling. The subsequent phase of the fuel characterization should evalu- ate the effect of the operating conditions to give a more detailed and complete information on the devolatilization. In fact, the thermal history of solid fuels influences strongly the devolatilization param- eters [6–9]. Although different specific experimental techniques should be compared to widening the range of conditions to those of large scale applications, a coherent fundamental study is required in the first phase of the characterization. Recent experimental ther- mogravimetric analyzers can reach very high temperatures and guarantee a negligible discrepancy between the programmed ther- mal history and the effective sample temperature in a relatively wide range of heating rate (HR). Nevertheless, a preliminary study should be carried out to minimize the heat transfer problems: - limitation of temperature gradients in the sample testing a low amount of sufficiently fine particles, - feed of relatively high gas flow rate to avoid secondary reactions, - evaluation of buoyancy effects. Therefore, the first aim of this work is to perform a fundamen- tal study on the devolatilization of biomass residues, determine the most suitable and representative parameters and evaluate the effect of the operating conditions. 0040-6031/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2008.03.015