Devolatilization Rate Processes and Products

Pyrolysis (devolatilization in an inert atmosphere) and hydropyrolysis (devolatilization in a hydrogen atmosphere) of coal are particularly dependent on the organic properties and structural characteristics of the coal. Many approaches are taken to characterize coal conversion and reaction processes. The most advanced of these approaches relate the observed coal conversion processes to coal structure and composition. Much evidence supports the hypothesis that the devolatilization of coal is a chemical reaction (e. g., Gavalas, 1982). With an increased availability of coal structure and characteristics by advanced methods as documented in Chapter 4, a monumental task lies in understanding the devolatilization mechanisms, relating coal structure to its devolatilization behavior, and developing accurate predictive capabilities. New devolatilization models are being developed which are based, at least in part, on the chemical structure of coals. Devolatilization, as the first step in thermally driven coal conversion and utilization processes, has a profound effect on course of combustion processes (Howard, 1981; Brewster et al., 1988; Nelson et al., 1988). Previous studies have demonstrated the key role of devolatilization processes in coal conversion and utilization through the use of comprehensive combustion codes (J. D. Smith et al., 1987, 1991; Brewster et al., 1988; Smith and Smith, 1990). In parametric sensitivity studies of a two-dimensional combustion model, J. D. Smith et al. (1987, 1991; Smith and Smith, 1990) showed that one of the most critical issues or critical subprocesses in the combustion code for both coal combustion and gasification is the devolatilization process.