A technique for determining devolatilization rates of large coal particles in a fluidized bed combustor

Abstract

A non-interference technique has been developed for measuring devolatilization rates of large coal particles in a cylindrical fluidized bed at 850 °C by on-line analysis of oxygen and carbon dioxide concentrations in the flue gas. The experiments were conducted over a range of inlet oxygen concentrations (3–10 vol%). Oxygen concentrations were analysed by a zirconia probe, and carbon dioxide concentrations were analysed by an on-line infrared gas analyser. Associated problems and suitability of the measuring technique are discussed. A bituminous coal ( d = 9–16.3 mm) was used and devolatilization periods >130 s were observed. The devolatilization times showed a dependence on the inlet oxygen concentration, particularly at the lower (3 vol%) inlet oxygen concentration. A simple calculation to demonstrate the need for considering devolatilization rates, ‘coal’ dispersion coefficients, excess air levels and combustor geometry in FBC modelling is also given.