Abstract :
FLASHCHAIN has been developed to predict yields and product characteristics from any coal for any operating conditions. This evaluation demonstrates the modelʹs utility for the usual situation where the ultimate analysis is the only sample-specific information available. It also identifies the key reaction centers in coal as its structural components called labile bridges. Their elemental compositions are grossly different than the analogous whole-coal properties, showing much stronger rank dependences and a much higher degree of sample-to-sample variability. In light of these findings, it is inconceiveable that bridge conversion rates are rank-independent. Parameters in the rate law for bridge conversion in FLASHCHAIN are now explicitly related to the elemental compositions of bridges. The (O/C)B ratios are the best regression variable for the rate constants because oxygen is the most effective promoter of pyrolytic decompositions. The (O/H)B rates are best for the selectivity coefficient between scission and condensation into char links because oxygen promotes crosslinking but hydrogen addition to broken bridge fragments stabilizes them. These extensions are evaluated in comparisons against a database of 27 coals that span all ranks from lignite to anthracite, for heating rates from 5 to 5000 K/s, ultimate temperatures to 1300 K, and pressures from vacuum to 70 MPa. In four out of five cases, predicted total and tar yields are within experimental uncertainties. The model is also used to rigorously define nominal devolatization rates for diverse coal types and broad ranges of operating conditions. Nominal rates have very low activation energies, proving that heat and mass transport resistances are not responsible for the low values because this theory is completely free of these considerations. Whereas nominal rates are rather insensitive to coal type variations and independent of pressure, they vary in proportion to changes in heating rate.
