Isoconversional kinetic analysis of olive pomace decomposition under torrefaction operating conditions Paola Brachi a, ⁎, Francesco Miccio b , Michele Miccio a , Giovanna Ruoppolo c a Department of Industrial Engineering, University of Salerno, via Giovanni Paolo II 132, 84084 Fisciano, SA, Italy b Institute of Science and Technology for Ceramics (ISTEC-CNR), via Granarolo 64, 48018 Faenza, RA, Italy c Institute for Research on Combustion, National Research Council, P.le Tecchio 80, 80125 Napoli, Italy abstract article info Article history: Received 25 July 2014 Received in revised form 13 September 2014 Accepted 29 September 2014 Available online xxxx Keywords: Kinetic analysis Bio-waste Torrefaction Thermogravimetric analysis Isoconversional method Kinetic analysis of the olive pomace thermal degradation in the temperature range of interest for torrefaction was performed by using non-isothermal thermogravimetric measurements at different heating rates, ranging from 2 to 40 °C/min. A comparison is presented between two selected integral isoconversional methods, i.e., the nonlinear Vyazovkin incremental approach, which is more accurate but time-consuming, and the linear Ozawa–Flynn–Wall (OFW) method, which is less accurate but computationally simpler. Results show that the values of the activation energy by the OFW method are consistent with the ones provided by the Vyazovkin ap- proach. This implies that the OFW method, more user-friendly compared to the Vyazovkin procedure, is suitable for studying the torrefaction kinetics of residual biomass, such as olive pomace. The reliability of the OFW method was further confirmed by the successful application of the derived kinetic data to reproduce (i.e., predict) exper- imental TG curves not included in the kinetic computations. © 2014 Elsevier B.V. All rights reserved. 1. Introduction In the view of shortage of fossil fuels and with the increasing concerns regarding human impacts on the environmental, renewable energy sources and waste materials play an important role as a viable alternative to fossil fuels for both energy generation and production of chemicals [1]. Now on the brink of commercialization, torrefaction – a relatively new thermochemical treatment of biomass carried out at quite low tem- peratures (200–300 °C), atmospheric pressure and in an inert environ- ment – is currently considered as a key process in facilitating raw biomass (i.e., grass, woody, crop or processing industry residues) market growing for energy applications, due to its potential to convert any organic material into a high-energy-density solid fuel with superior properties in view of transport, handling, storage and in many major thermochemical end-use applications (e.g., co-firing in coal-fired power stations and gasification-based production of gaseous biofuels or bio-chemicals) [2]. Olive pomace is the solid and wet by-product generated by olive-oil extraction industries. Among other possibilities of utilization (e.g. ani- mal feed, production of fertilizer, composting, etc.), the thermal treat- ment is appealing because it is an intensive and effective method for converting the olive pomace into energy [3], avoiding release of pollut- ants and odors as well as uncontrolled fermentation [4]. Several studies [3,4] have been conducted on energy generation from the olive pomace; however, no one includes torrefaction as pretreatment, which is able to produce an intermediate and stable material and does not suffer high moisture content, low energy density, hygroscopic behavior and limited storage life. With this background, the primary aim of the present study was to propose a set of kinetic parameters to be used as an input to future computer-based simulations of the olive pomace torrefaction, which can be used to guide laboratory experiments as well as to generate and evaluate alternative designs [5–7] for renewable energy projects. Non-isothermal thermogravimetric analysis (TGA) was selected as the experimental technique to obtain kinetic data due to its ability to overcome one of the major problems associated with standard isother- mal experiments, i.e. the warm-up time. Actually, during the initial non- isothermal time of an isothermal TGA test the sample typically un- dergoes some transformations that are likely to affect the results of the subsequent kinetic analysis [8]. In addition, when a too slow heating rate is applied, the weight loss taking places during the warm-up phase is not negligible, which complicates the interpretation and deduction of kinetic data [9]. Even though traditional model fitting approaches, including single or multi-step reaction mechanisms and/or single or multiple pseudo- component models [9–13], have found to date the almost exclusive ap- plication in biomass thermochemical conversion kinetic analysis [14],a “model-free” approach based on integral isoconversional methods was adopted in this paper. This choice was motivated by the fact that the model fitting procedures, when applied to non-isothermal data, pro- duce Arrhenius parameters strongly depending on the adopted reaction Fuel Processing Technology 130 (2015) 147–154 ⁎ Corresponding author. Tel.: +39 089 964067. E-mail addresses: pbrachi@unisa.it (P. Brachi), miccio@irc.cnr.it (F. Miccio), mmiccio@unisa.it (M. Miccio), ruoppolo@irc.cnr.it (G. Ruoppolo). http://dx.doi.org/10.1016/j.fuproc.2014.09.043 0378-3820/© 2014 Elsevier B.V. All rights reserved. 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