Thermogravimetric characterization and gasification of pecan nut shells Hugo Aldana, Francisco J. Lozano, Joaquín Acevedo, Alberto Mendoza ⇑ Tecnológico de Monterrey, Campus Monterrey, Av. Eugenio Garza Sada 2501, 64849 Monterrey, Mexico highlights  Waste-to-energy of bulk pecan nut shell residue through gasification is explored.  Pyrolytic decomposition rates were adjusted to an independent parallel reaction model.  A single rate equation describes the thermal lag phenomena and the final mass loss.  Performance of a bench-scale fixed-bed downdraft gasifier was obtained.  Particle size and air flow rate are critical to maintain stable operation conditions. article info Article history: Received 23 July 2015 Received in revised form 14 September 2015 Accepted 20 September 2015 Available online 28 September 2015 Keywords: Waste-to-energy Downdraft gasifier Independent parallel reaction Biomass gasification Waste valorization abstract This study focuses on the evaluation of pecan nut shells as an alternative source of energy through pyrol- ysis and gasification. The physicochemical characteristics of the selected biomass that can influence the process efficiency, consumption rates, and the product yield, as well as create operational problems, were determined. In addition, the thermal decomposition kinetics necessary for prediction of consumption rates and yields were determined. Finally, the performance of a downdraft gasifier fed with pecan nut shells was analyzed in terms of process efficiency and exit gas characteristics. It was found that the pyr- olytic decomposition of the nut shells can be modeled adequately using a single equation considering two independent parallel reactions. The performance of the gasification process can be influenced by the par- ticle size and air flow rate, requiring a proper combination of these parameters for reliable operation and production of a valuable syngas. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction The promotion of renewable energies entails several benefits, from the mitigation of greenhouse gas emissions to the diversifica- tion of the energy portfolio of a country for a secure fuel and energy supply (Ceylan and Topcu, 2014). Residual biomass (espe- cially agricultural residue) has the advantage of a large annual gen- eration rate and a low economic value when compared to other renewable energy sources. An example of this is the shells gener- ated from the production of pecan nuts (Carya illinoinensis). In Mexico, the second largest producer in the world of this fruit, pro- duction is estimated to be between 40 Gg y 1 and 48 Gg y 1 . Bioresidues can be processed through thermochemical routes (gasification, pyrolysis or volatilization) to produce heat, electric- ity, liquid fuels, or chemical products (Goyal et al., 2008). To adequately model, design and control thermochemical processes, it is necessary to know the physicochemical characteristics of the materials (moisture content, size and shape, solid and bulk density, chemical composition, and the heating value) and investigate their influence on the process. Of particular interest are the pyrolysis reaction kinetics and gasification performance (Ceylan and Topcu, 2014; Dogru et al., 2002; Kumar et al., 2008). Pyrolysis is an important step during gasification and combus- tion (Damartzis et al., 2011; Slopiecka et al., 2012). The pyrolysis decomposition kinetics of biomass are key for accurate prediction of biomass consumption rates and product yields as a function of the chemical (cellulose, hemicellulose, lignin, and volatile mater) and physical (particle size) properties (Ceylan and Topcu, 2014; Damartzis et al., 2011; Demirbas, 2001). Thermogravimetric anal- ysis (TGA) is a useful technique to determine the pyrolysis reaction kinetics, and it has been used extensively for the characterization of various feedstocks (Kumar et al., 2008). To process the data generated through this analysis, two approaches have been applied: considering the process as a series of independent parallel reactions (IPR), or considering the process as a single step http://dx.doi.org/10.1016/j.biortech.2015.09.069 0960-8524/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: School of Engineering and Sciences, Tecnológico de Monterrey, Av. Eugenio Garza Sada 2501, 64849 Monterrey, Mexico. Tel.: +52 81 83582000x5436. E-mail address: mendoza.alberto@itesm.mx (A. Mendoza). Bioresource Technology 198 (2015) 634–641 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech