The Distributed-Energy Chain Model for Rapid Coal Devolatilization Kinetics. Part I: Formulation

Abstract The distributed-energy chain model (DISCHAIN) interprets coal devolatilization in terms of independent influences from chemical reaction rates and from macromolecular configuration. Coal is represented by three components: (1) aromatic units that are attached pairwise by (2) labile bridges to form nominally infinite linear chains, with (3) peripheral groups branching from the aromatic units. These components are the building blocks for unreacted coal, free monomers (mobile aromatic units), gas, tar, and char. Four chemical reactions represent bridge dissociation, peripheral group elimination, and tar and char formation. Analytic probability expressions and competitive reactions describe the conversion of bound aromatic units into free monomers, and enter into the formation of all products except gas. There are no hypothetical ultimate yields. The model is introduced in two parts. Here in Part I, the coal model, chemical reactions, and chain statistics are derived and formulated into rate equations. Mechanisms leading to major products are identified, including a novel mechanism for yield enhancement by faster heating. Whenever bridge dissociation and char formation occur concurrently, as for slow heating, the subsequent generation of monomers is inhibited. Aromatic units are thereby excluded from the competition between tar and char formation. Conversely, bridge dissociation and char formation occur consecutively for rapid heating, and a greater proportion of the original bound aromatic units become monomers and, ultimately, tar.