energies Article Entrained-Flow Coal Gasification Process Simulation with the Emphasis on Empirical Char Conversion Models Optimization Procedure Jakub Mularski * and Norbert Modli ´ nski   Citation: Mularski, J.; Modli ´ nski, N. Entrained-Flow Coal Gasification Process Simulation with the Emphasis on Empirical Char Conversion Models Optimization Procedure. Energies 2021, 14, 1729. https://doi.org/10.3390/en14061729 Academic Editor: Bjørn H. Hjertager Received: 19 February 2021 Accepted: 17 March 2021 Published: 20 March 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Department of Energy Conversion Engineering, Wroclaw University of Science and Technology, Wybrze˙ ze Wyspia ´ nskiego 27, 50-370 Wroclaw, Poland; norbert.modlinski@pwr.edu.pl * Correspondence: jakub.mularski@pwr.edu.pl; Tel.: +48-71-320-21-81 Abstract: Computational fluid dynamics (CFD) modeling of an entrained-flow reactor is demon- strated and compared with experimental data. The study is focused on char conversion modeling and its impact on gasification simulation results. An innovative procedure of optimizing input data to empirical char conversion kinetic-diffusion model is investigated, based on the complex carbon burnout kinetic model for oxidation (CBK/E) and gasification (CBK/G). The kinetics of the CBK/G model is determined using the data from char gasification experiments in a drop tube reactor. CFD simulations are performed for the laboratory-scale entrained-flow reactor at Brigham Young Univer- sity for the bituminous coal. A substantial impact of applied kinetic parameters on the in-reactor gas composition and char conversion factor was observed. The effect was most considerable for the reduction zone, where gasification reactions dominate, although a non-negligible impact could also be observed in the flame zone. Based on the quantitative assessment of the incorporated optimization procedure, its application allowed to obtain one of the lowest errors of CO, H 2 , CO 2 , and H 2 O axial distribution with respect to the experimental data. The maximum errors for these species were equal to 18.48, 7.95, 10.15, and 20.22%, respectively, whereas the average errors were equal to 4.82, 5.47, 4.72, and 9.58%, respectively. Keywords: CFD; coal gasification; char conversion; entrained-flow reactor 1. Introduction More than 80% of the world’s energy comes from fossil fuels [1]. Coal is one of the main sources of fossil fuel energy as it generates nearly 40% of the world’s electricity [2]. Coal-fired power plants were the single largest contributor to the growth in emissions observed in 2018 [3]. As a result, coal-fired electricity generation made up 30% of global CO 2 emissions [3]. Unfortunately, this ongoing trend tremendously impacts the natural en- vironment, climate, and human health. As a result, specific measures are taken to promote and develop efficient technologies which can mitigate the negative impact on our planet. Coal, despite its gradually decreasing consumption in many countries, will continue to be a meaningful energy source for many years to come. This results in continuous research into environmentally benign coal-based technologies. Gasification is one of the most promising technologies for solid fuels since it allows the conversion of solid materials to gas consisting of H 2 , CO, CO 2 , CH 4 , and smaller amounts of different hydrocarbons [4,5]. Production of such gas enables effective implementation of alternative ways of electricity generation (e.g., internal combustion engines, fuel cells, gas turbines) as well as a synthesis of different products (e.g., Fischer-Tropsch process, production of H 2 ). Therefore, gasification is a beneficial coal technology, offering high efficiency, low environmental impact, and new possibilities regarding the synthesis of chemicals [6]. However, gasification is still not fully understood on a fundamental level, and although CFD has been proven to be an efficient Energies 2021, 14, 1729. https://doi.org/10.3390/en14061729 https://www.mdpi.com/journal/energies