Devolatilisation times of coal particles in a fluidised-bed

Times required for devolatilisation of large coal particles in a fluidised-bed operating at 750, 850 and 950°C and in gas environments simulating pyrolysis, combustion and gasification conditions were investigated. The effect of coal type and coal moisture content was also investigated at a bed temperature of 850°C under fluidised-bed combustion conditions. The devolatilisation time was defined as the time taken from immersion into the bed until the centre temperature of the coal particle equalled the bed temperature. Six coals of varying rank in the size range from 6 to 17 mm, were used in this present study. The devolatilisation time was found to be influenced by the bed temperature, gas environment, coal moisture content and coal type which is in agreement with data reported in the literature. The results were correlated with the classic empirical particle diameter power law relation (tv=Adpn) where it was observed that the devolatilisation time was directly proportional to the particle diameter. A new definition to distinguish between heat transfer and chemical-kinetically controlled regimes during devolatilisation validates present method and explains experimental observations relating to the influence of bed temperature and gas environment.