Theory of Idealized Coal Devolatilization
The aerothermochemical interaction between a devolatilizing coal particle and its ambient is studied by means of an idealized model consisting of two solid-phase species, which thermally decompose to yield a single gas-phase species. Devolatilization is described by a classical linear theory involving both equilibrium and kinetic characteristics of each solid-phase species. The temperature history of the particle is treated in two different ways reflecting different experimental and applied situations. One simulates the direct heating of a particle, e.g., on a wire grid, so that the temperature history is prescribed. The second relates to injection of a cold particle into a hot ambient either under experimental conditions or in an entrained flow reactor. In the second situation both a frozen gas phase corresponding to devolatilization in inert ambients and equilibrium chemistry in the gas phase as described by a flame-sheet model are discussed. It is concluded that, despite the high degree of idealization involved in the analysis, a large number of thermochemical parameters, some with uncertain values, enter the description of particle behavior. It is difficult to determine kinetic data from direct heating experiments. The thermal response of a cold particle injected into a hot ambient is sensitive to the kinetics of devolatilization and to the heats of pyrolysis.
KeywordsParticle Temperature Temperature History Coal Particle Particle Behavior Coal Char
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- 5.E. M. Suuberg, W. A. Peters, and J. B. Howard, Product compositions and formation kinetics in rapid pyrolysis of pulverized coal — implications for combustion, in: Seventeenth Symp. (Int.) on Combust., pp. 117–143, The Combustion Institute, Pittsburgh, PA (1979).Google Scholar
- 6.H. Kobayashi, J. B. Howard, and A. E. Sarofim, Coal devolatilization at high temperatures, in: Sixteenth Symp. (Int.) on Combust., pp. 411–425, The Combustion Institute, Pittsburgh, PA (1977).Google Scholar
- 7.W. J. McLean, D. R. Hardesty, and J. H. Pohl, Direct observations of pulverized coal particles in a combustion environment, Eighteenth Symp. (Int.) on Combust., pp. 1239–1248, The Combustion Institute, Pittsburgh, PA (1980).Google Scholar
- 8.S. K. Ubhayakar, D. B. Stickler, C. W. von Rosenberg, Jr., and E. E. Gannon, Rapid devolatilization of pulverized coal in hot combustion gases, Seventeenth Symp. (Int.) on Combust., The Combustion Institute, Pittsburgh, PA (1977).Google Scholar