FLASHCHAIN THEORY FOR RAPID COAL DEVOLATILIZATION KINETICS .1. FORMULATION

This theory invokes a new model of coal's chemical constitution, a four-step reaction mechanism, chain statistics, and the flash distillation analogy to explain the devolatilization of various coal types. It is called FLASHCHAIN. The constitution submodel segregates the elements into only four pseudocomponents using the ultimate analysis, the carbon aromaticity and aromatic cluster size from C-13 NMR analysis, the proton aromaticity, and the extract yield in pyridine. No functional groups appear. The theory's central premise is that the partitioning of the elements among aliphatic, heteroatomic, and aromatic constituents largely determines the devolatilization behavior of any coal type. Labile bridges comprise all aliphatic and oxygen functionalities in the coal and are the key reaction centers. The abundance of labile bridges in lignites promotes their extensive conversion to noncondensible gases, but their oxygen promotes the charring of bridges into refractory links, which inhibits fragmentation of the macromolecules into tar. Conversely, the paucity of labile bridges in low-volatility coals suppresses gas yields; these coals also have too few labile bridges for extensive fragmentation, so their tar yields are also relatively low. Charring establishes the gas flow which sweeps away tar vapor but also suppresses the subsequent fragmentation of coal macromolecules into additional tar precursors. This scheme delivers reliable yields of gas and tar and molecular weight distributions of tar for any coal at any condition, yet it requires only a few minutes per simulation on a personal microcomputer. The theory is introduced in three parts. Part 1 describes its phenomenological basis, the formulation of rate equations, and assignments of model parameters, while parts 2 and 3 are devoted to performance evaluations. In part 2, the theory's representation of broad ranges of temperature, time, heating rate, pressure, and particle size is evaluated against the extensive data base for high-volatile bituminous coals. In part 3, model predictions demonstrate that this theory depicts all of the continuous trends in the yield structure from coals across the rank spectrum.