X-ray diffraction parameters and reaction rate modeling for gasification and combustion of chars derived from inertinite-rich coals Raymond C. Everson ⇑ , Gregory N. Okolo, Hein W.J.P. Neomagus, Jaen-Mari dos Santos Coal Research Group, Unit for Energy Systems, School of Chemical and Minerals Engineering, North-West University, Potchefstroom Campus, Private Bag X6001, Potchefstroom, 2520, South Africa highlights " The standard and XRD properties occurring during devolitalization was determined. " Significant graphitization occurs at 900 °C with aromaticity equal to 0.95. " The random pore model showed that the intrinsic reactivity correlates with the aromaticity. " The activation energy increased with increasing aromaticity. article info Article history: Received 10 October 2012 Received in revised form 10 December 2012 Accepted 11 December 2012 Available online 2 January 2013 Keywords: Inertinite-rich coals Devolitalization Gasification and combustion reactivity X-ray diffraction properties Intrinsic reaction rates abstract An investigation was undertaken to determine the effect of carbon structural properties on the reactivity of chars derived from inertinite-rich coal. The structures of chars were characterized by X-ray diffraction and the reactivity evaluation with respect to gasification and combustion involving experimentation and reaction rate modeling was carried out. The effect of the aromaticity on the intrinsic reaction rates and associated activation energy for gasification and combustion of chars were determined based on chemical reaction rate controlled kinetics. Two sets of results were examined consisting of gasification with four char samples derived from different inertinite-rich coals prepared with a devolitalization temperature of 900 °C (Set 1) and three chars from the same parent coal also rich in inertinites prepared at different devolitalization temperatures, namely 550, 700 and 850 °C (Set 2). It was found that the aromaticity and fraction of crystalline carbon of the four chars prepared at the same temperature (Set 1) varied in the ranges 0.85–0.95 and 0.52–0.72 respectively and the chars prepared at different temperatures (Set 2) in the ranges 0.82–0.92 and 0.44–0.74 respectively. The structural properties of the chars within each set of results were also very different which required reaction rate modeling for the determination of intrinsic reactivities. The random pore model with chemical reaction controlling described the reaction kinetics accurately and it was found that the intrinsic reactivity of the char decreased with increasing aro- maticity while the activation energies decreased (aromaticity < 0.92) which indicated the effect of the variation of the distribution of aromatic/aliphatic structures on the intrinsic reaction rate. It is proposed that the aromaticity of chars be used as a predictive index for char reactivity under chemical reaction controlled conditions. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction The properties of coals used and chars formed in coal conversion processes which include chemical composition and structure, phys- ical structure, petrographic properties and mineralogy has an effect on the intrinsic chemical reaction and diffusion rates within the coal/char particles especially at the operating temperature used in fluidized bed combustion and gasification (750–900 °C). Also since the overall process consists of a fast devolitalization period followed by a slower gasification or combustion period with differ- ent reaction/diffusion mechanisms it is advisable to examine each of these periods separately [1]. Such a study would require an examination of the effect of the coal properties on the devolitaliza- tion mechanisms and on properties of the chars formed, followed by the influence of these char properties on the gasification or com- bustion reactions. Many investigators have proposed indices affect- ing overall reactivity based on standard properties such as fuel ratio, rank, reflectance and maceral index and alkali index of the parent coals [1–3]. These indices were deduced without consider- ation of the possible reaction regimes present and the distinct devolitalization and gasification/combustion periods. With the 0016-2361/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fuel.2012.12.043 ⇑ Corresponding author. Tel.: +27 18 299 1986. E-mail address: ray.everson@nwu.ac.za (R.C. Everson). Fuel 109 (2013) 148–156 Contents lists available at SciVerse ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel