EXPERIMENTAL FACTORS AFFECTING COAL DEVOLATILIZATION TIME IN FLUIDIZED BED COMBUSTION

Abstract

Abstract Coal particle devolatilization times were determined by analysis of the flue gas from an air-fluidized bed at 850 °C, when single coal particles were injected. The CO2concentration versus time profile was corrected for gas flow and dispersion in the sampling line and analyser, and the devolatilization time was measured as the time from particle injection to the time corresponding to the minimum CO2concentration separating volatiles and char combustion. No differences in devolatilization time were observed for the three Australian bituminous coals studied, and similar times were measured for both spherical and irregularly-shaped particles, provided the equivalent-mass definition of diameter was used. Comparison with literature data showed that this method for measuring coal particle devolatilization time gave similar values to the visual flame extinction time and greater values than visual flame period. From a critical analysis of the literature, it was deduced that batch size (i.e. number of panicles in each batch) could affect the measured devolatilization time, but that no such effect was present for some of the data for small numbers of large diameter particles in larger diameter beds. A single correlation was fitted to the present data and acceptable literature data, for individual coal particles from 1 to 30 mm in diameter in fluidized bed combustors at 850 °C in air: tv = 1.84 dp 1.5particles in a fluidized bed, using FET and/or CO evolution measurements, and that sufficient particles be studied to identify the variability of the measurements, in order to assess whether any effect observed is significant compared to the particle-to-particle variability.