CHEMICAL ENGINEERING TRANSACTIONS VOL. 80, 2020 A publication of The Italian Association of Chemical Engineering Online at www.cetjournal.it Guest Editors: Eliseo Maria Ranzi, Rubens Maciel Filho Copyright © 2020, AIDIC Servizi S.r.l. I SBN 978-88-95608-78-5; I SSN 2283-9216 Combined Influence of Inorganics and Transport Limitations on the Pyrolytic Behaviour of Woody Biomass Hernán Almuina-Villar a, *, Peter Sommersacher b , Stefan Retschitzegger b , Andrés Anca-Couce c , Alba Dieguez-Alonso a a Technische Universität Berlin, Institute of Energy Engineering, Seestr. 13 13353 Berlin, Germany b BEST – Bioenergy and Sustainable Technologies GmbH, Inffeldgasse 21b, A-8010 Graz, Austria c Technische Universität Graz, Institute of Thermal Engineering, Inffeldgasse 25B 8010 Graz, Austria h.almuinavillar@tu-berlin.de A deeper understanding and quantification on the influence of inorganic species on the pyrolysis process, combined with the presence of heterogeneous secondary reactions, is pursued in this study. Both chemical controlled and transport limited regimes are considered. The former is achieved in a thermogravimetric ana- lyser (TGA) with fine milled biomass in the mg range, while the latter is investigated in a particle level reactor with spherical particles of different sizes. To account for the influence of inorganics, wood particles were washed and doped with KCl aqueous solutions, resulting in K concentrations in the final wood of around 0.5% and 5% on dry basis. Gas species and condensable volatiles were measured online with Fourier transform infrared (FTIR) spectroscopy and a non-dispersive infrared (NDIR) gas analyzer. The removal of inorganic species delayed the pyrolysis reaction to higher temperatures and lowered char yields. The addition of inor- ganics (K) shifted the devolatilization process to lower temperatures, increased char and water yields, and re- duced CO production among others. Higher heating rates and temperatures resulted in lower char, water, and light condensable yields, but significantly higher CH4 and other light hydrocarbons, as well as CO. The in- crease in these yields can be attributed, at least in part, to the gas phase cracking reactions of the produced volatiles. Larger particle size increased the formation of char, CH 4 and other light hydrocarbons, and light con- densables for low and high pyrolysis temperatures, while reduced the release of CO 2 and H 2 O. This novel da- ta set allows to quantify the influence of each parameter and can be used as basis for the development of de- tailed pyrolysis models which can include both the influence of inorganics and transport limitations when cou- pled into particle models. 1. Introduction and Objectives The different reaction pathways during the pyrolysis process (pyrolysis mechanism) have a significant influ- ence on products yields and composition, as well as on products properties relevant for their further applica- tion (Anca-Couce, 2016). Many studies have been performed to understand the relation between initial feed- stock properties, pyrolysis conditions and products distribution and composition. Nevertheless, an accurate description of the pyrolysis mechanisms that can be globally applied is still missing due to the high degree of complexity of the reaction pathways involved and the numerous factors affecting their evolution (Anca-Couce, 2016; Anca-Couce et al., 2017). Alkali metals, with potassium being one of the most relevant, have been re- ported to play an important role on both devolatilization kinetics and products composition. Their catalytic ef- fect in biomass results in a preference of the ring fragmentation reactions at the expense of sugar formation reactions (depolymerization, transglycoxylation) for both cellulose and hemicellulose. The former would lead to the formation of low molecular weight compounds and furan-ring derivatives, while the latter would lead mainly to levoglucosan and similar compounds (Patwardhan et al., 2010; Patwardhan et al., 2011; Trendewicz et al, 2015; LeBrech et al., 2016). The presence of alkali species may as well catalyse dehydration reactions at low temperature enhancing char formation (LeBrech et al., 2016; Trendewicz et al, 2015). For lignin pyrolysis, al- kali species (Na) were shown to catalyse functional groups scission, favouring methanol release (demethoxy- lation) and dehydration reactions, as well as radicals recombination (Jakab et al., 1997). It was also shown DOI: 10.3303/CET2080013 Paper Received: 2 December 2019; Revised: 14 March 2020; Accepted: 7 April 2020 Please cite this article as: Almuina-Villar H., Sommersacher P., Retschitzegger S., Anca-Couce A., Dieguez-Alonso A., 2020, Combined Influence of Inorganics and Transport Limitations on the Pyrolytic Behaviour of Woody Biomass, Chemical Engineering Transactions, 80, 73- 78 DOI:10.3303/CET2080013 73