Predicting Coal Quality Effects on P. F. Firing from a Coal's Ultimate Analysis

It is well-established that the rapid heating conditions in -pulverized coal flames enhance volatiles yields well above the Proximate Volatile Matter for some, but not all, coals. Such variations have made it impossible to assess the impact of coal quality on combustion efficiencies and emissions with simple engineering correlations based on the standard analytical data for coal. New coal samples must be characterized in drop tube furnaces or wire grid reactors at lab-scale or in pilot-scale combustors. Although these tests provide the necessary information, they are expensive and time-consuming, and usually do not describe heat release rates or product distributions in detail. SRI International's FLASHCHAIN computer model accurately simulates the devolatilization behavior of any coal at p.f. firing conditions. The model predicts the release rates and yields of volatiles, including the contributions from hydrocarbon gases, tars, oxygenated gases, and nitrogen species, and the residual nitrogen content and amount of char. The ultimate analysis is the only sample-specific information required, yet the model predictions match the observed sample-to-sample variability among even very similar coal types. The model has already been evaluated against the observed behavior of some 125 coals across the rank spectrum, representing heating rates from 0.5 to lOS K/s, pressures from vacuum to 70 atm, and temperatures to 1700 C. This paper will demonstrate the accuracy of the predictions and illustrate how the model can be used to supersede lab testing or to expedite and support pilot- and full-scale testing.