COMBUSTION OF VOLATILES FROM LARGE COAL PARTICLES UNDER AGITATED CONDITIONS

Coking coals are not easy to burn in fixed-bed retorts, and they need a stirred bed to prevent formation of coke trees. In order to simulate the combustion behaviour in a moving bed, a laboratory-scale agitated combustor has been developed which allows data on emission of volatil es to be determined for large coal particles. The particle sizes are u p to 25 mm-typical of those used in rotating and fixed-bed retorts. A regression analysis is used to correlate volatiles-release times t(v) with particle size over a range of temperatures. This results in a pow er-law relationship between volatiles-release time t(v) and particle s ize d(p) given by t(v) = a.d(p)n, where 'a' varies with coal type and 'n' is approximately 2 for large particles. The effect of temperature T is correlated with t(v) = A.TB, and design data for A and B are repo rted. This investigation into the behaviour of volatile matter during the combustion of coking coals provides useful data for the design of fixed-bed combustors.