Study of the pyrolysis kinetics of Datong coal using a sectioning method

Abstract

shortage of good-quality coking coal, the COREX process was designed as a new ironmaking technology, attracting wide attention (Fang et al., 2005). In this process, lump coal and a small quantity of coke are directly charged into the melter-gasifier, where a high-quality reducing gas is generated for the reduction of the iron ore (Kumar et al., 2009). In contrast to the conventional blast furnace (BF) process, non-coking lump coal is used as the reducing agent and as the energy source, and the iron charge consists of lump ore and/or pellets, which results in the elimination of the coke oven and sintering plant as well as a decrease in investment (Kumar et al., 2009; Liu et al., 2012). Although the COREX process has made great progress, in current production practice the energy consumption greatly exceeds that of the BF, and it requires a certain amount of coke to maintain permeability of the semi-coke bed (Wang et al., 2008). In addition, the process consumes a lot of good-quality lump ore and lump coal. The pyrolysis of coal is the first step in most coal conversion processes, such as carbonization, gasification, and combustion (Aboyade et al., 2013). The reaction behaviour of lump coals in the COREX melter-gasifier is crucial, as it determines energy utilization and gas composition, as well as the metallurgical properties and particle size of the semi-coke produced (Prachethan et al., 2011; Zhang et al., 2014). In order to optimize the process and improve its competitiveness, the pyrolysis kinetics of Datong coal used in Baosteel’s COREX C-3000 facility was studied. Generally, the Coasts-Redfern method (Xu et al., 2010), ‘model-free’ method (Xu et al., 2010), and DAEM method (Tang et al., 2005) are used to investigate the kinetics of coal pyrolysis. In the Coasts-Redfern method, commonly used mechanism functions are inserted into the non-isothermal kinetic equation to fit the experimental data one-byone. The mechanism function with the largest correlation coefficient is selected as the best (Zhang et al., 2013). In this process, the reaction order is often replaced by the apparent reaction order to obtain the best fit (Zhang et al., 2014). However, the physical and chemical meanings of the reaction model are ignored. In the ‘model-free’ method (or DAEM method), the activation energies under different conversion rates can be calculated. However, there is no way to calculate the kinetic mechanism functions and the related parameters (Xu et al., 2010; Tang et al., 2005). Therefore, based on the previous research, a sectioning method was proposed to study the kinetics of coal pyrolysis. The kinetic parameters at different heating rates were Study of the pyrolysis kinetics of Datong coal using a sectioning method by R. Du*†, K. Wu*†, X. Yuan*†, D. Xu*†, and C. Chao*†