Kinetic and thermodynamic investigations of CO 2 gasification of coal chars prepared via conventional and microwave pyro
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Kinetic and thermodynamic investigations of CO2 gasification of coal chars prepared via conventional and microwave pyrolysis Peng Jiang1 • Yang Meng1 • Ziyao Lu1 • Lan Xu1 • Gang Yang2 • Xiang Luo2 Kaiqi Shi2 • Tao Wu1,2
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Received: 5 March 2020 / Revised: 8 May 2020 / Accepted: 3 August 2020 The Author(s) 2020
Abstract This study examined an isothermal CO2 gasification of four chars prepared via two different methods, i.e., conventional and microwave-assisted pyrolysis, by the approach of thermogravimetric analysis. Physical, chemical, and structural behaviours of chars were examined using ultimate analysis, X-ray diffraction, and scanning electronic microscopy. Kinetic parameters were calculated by applying the shrinking unreacted core (SCM) and random pore (RPM) models. Moreover, char-CO2 gasification was further simulated by using Aspen Plus to investigate thermodynamic performances in terms of syngas composition and cold gas efficiency (CGE). The microwave-induced char has the largest C/H mass ratio and most ordered carbon structure, but the smallest gasification reactivity. Kinetic analysis indicates that the RPM is better for describing both gasification conversion and reaction rates of the studied chars, and the activation energies and pre-exponential factors varied in the range of 78.45–194.72 kJ/mol and 3.15–102,231.99 s-1, respectively. In addition, a compensation effect was noted during gasification. Finally, the microwave-derived char exhibits better thermodynamic performances than the conventional chars, with the highest CGE and CO molar concentration of 1.30% and 86.18%, respectively. Increasing the pyrolysis temperature, gasification temperature, and CO2-to-carbon molar ratio improved the CGE. Keywords Coal char CO2 gasification Microwave pyrolysis Char properties Kinetics Thermodynamic
1 Introduction Coal is a particularly important energy resource and is currently responsible for approximately 70% of total energy consumption in China (Lan et al. 2018; Zhu et al. 2020). Urgent development of clean coal utilization technology is required because of increasing environmental pollution from coal-fired power plants. Coal gasification, & Tao Wu [email protected] 1
Department of Chemical and Environmental Engineering, The University of Nottingham Ningbo China, Ningbo 315100, China
2
Key Laboratory for Carbonaceous Wastes Processing and Process Intensification Research of Zhejiang Province, The University of Nottingham Ningbo China, Ningbo 315100, China
which converts solid coal into syngas at high temperatures, is considered to be the cleanest utilization approach because it offers near-zero sulphur and particulate emissions, high energy efficiency, and flexible chemicals (Attwood et al. 2003; Li et al. 2018). Char reaction with gasification agents is the rate-controlling step of the coal gasification process because it occurs more slowly than water evaporation, pyrolysis, or combustion (Dupont et al. 2011). As a greenhouse gas, CO2 is the largest contributor to global warming (
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