MODELING THE DEVOLATILIZATION BEHAVIOR OF VARIOUS COALS

Abstract

This chapter describes the modeling the devolatilization behavior of various coals. The FLASHCHAIN theory rationalizes the influences of all of the important operating conditions on the devolatilization behavior of various coal types. The theory correctly depicts that weight loss is constant for coals of increasing rank to the HVA bituminous, and then falls sharply and becomes negligible for anthracites; that tar yields are fixed for lignites and then rise to a maximum value for HVA coals; and that while the tar yields fall for coals of higher rank, the tar fraction increases steadily for coals from HVA through low volatile bituminous. The chapter presents predictions for selected coal types for temperatures to 1200 K, heating rates from 1 to 103K/s, and pressures from vacuum to 6.9 MPa. Qualitatively, the predicted behavior agrees with observed trends and, quantitatively, the predictions are within the variations among data from different laboratories for very similar coal types. In lignites, most of the bridges are labile, but their dissociation leads to char links, because of the crosslinking propensity of oxygen functionalities. Tar evolution occurs early in the process but also ends rapidly as the char links accumulate.