coal pyrolysis model, percolation


The chemical percolation devolatilization (CPD) model describes the devolatilization behavior of rapidly heated coal based on the chemical structure of the parent coal. Percolation lattice statistics are employed to describe the generation of tar precursors of finite size based on the number of cleaved labile bonds in the infinite lattice. The chemical percolation devolatilization model described here includes treatment of vapor-liquid equilibrium and a cross-linking mechanism. The cross-linking mechanism permits reattachment of metaplast to the infinite char matrix. A generalized vapor pressure correlation for high molecular weight hydrocarbons, such as coal tar, is proposed based on data from coal liquids. Coal-independent kinetic parameters are employed. Coal-dependent chemical structure coefficients for the CPD model are taken directly from 13C NMR measurements, with the exception of one empirical parameter representing the population of char bridges in the parent coal. This is in contrast of the previous and common practice of adjusting input coefficients to precisely match measured tar and total volatiles yields. The CPD mode successfully predicts the effects of pressure on tar and total volatiles yields observed in heated grid experiments for both bituminous coal and for lignite. Predictions of the amount and characteristics of gas and tar from many different coals compare well with available data, which is unique because the majority of model input coefficients are taken directly from NR data and are not used as empirical fitting coefficients. Predicted tar molecular weights are consistent with size-exclusion chromatography (SEC) data and field ionization mass spectrometry (FIMS) data. Predictions of average molecular weights of aromatic clusters as a function of coal type agree with corresponding data from NMR analyses of parent coals. The direct use of chemical structure data as a function of coal type helps justify the model on a mechanistic basis rather than an empirical basis.

Original Publication Citation

Fletcher, T. H., A. R. Kerstein, R. J. Pugmire, M. S. Solum, and D. M. Grant, "A Chemical Model of Coal Devolatilization: 3. Direct Use of 13C NMR Data to Predict Effects of Coal Type," Energy and Fuels, 6(4), 414-431 (1992). DOI: 10.1021/ef00034a011

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Peer-Reviewed Article

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Ira A. Fulton College of Engineering and Technology


Chemical Engineering

University Standing at Time of Publication

Full Professor