Authors: J.F. Stubington, D. Sasongko∗
A numerical model for devolatilisation of a single coal particle was used to estimate the heating rates of coal particle sizes fed to atmospheric-pressure industrial fluidised bed combustors. This model incorporates an appropriate level of detail for each of the processes occurring during the devolatilisation: external heat transfer, internal heat transfer, devolatilisation, and transfer of volatiles. The volatiles flux out of the coal particle decreases the heating rates significantly for the fluidised bed combustion of coal particle sizes of medium- to high-volatile coals. The model was shown to predict accurately both the detailed centre temperature-time profile and the overall devolatilisation times as a function of particle size. The heating rates for coal particles fed to industrial fluidised bed combustors, calculated from this model, are of the order of 2–150 K s−1 for 2 to 20 mm diameter particles, and should not be confused with the much higher heating rates of pulverised fuel size particles. Since the heating rates are similar, it is not surprising that the volatile yields in a fluidised bed combustor are approximately the same as (or marginally greater than) the Proximate Volatile Matter determination. Further research is necessary to measure these volatile yields more accurately in a fluidised bed environment.