Spouted, fluidized and spout-fluid bed combustion of bituminous coals

Abstract

Spouted, fluidized and spout-fluid bed combustion of three bituminous coals or coal rejects of differing ash contents was carried out in a 0.3 m internal diameter combustor. Coal feed rates were between 6 and 22 kg h −1, excess air was usually 15–20%, the internal coil coolant was either air or water, and the average bed temperature ranged from 740 to 980 °C. Each of the three contacting modes was able to burn the coal to which it was subjected. Although differences in combustion performance between the three modes were generally small, the experimental results indicated that the spout-fluid bed tended to give somewhat higher combustion efficiencies at the lower temperatures, greater temperature uniformity and improved bed-to-immersed-surface heat transfer compared with the other two modes of operation. For all three modes, combustion efficiencies were over 90%, provided that bed temperatures were higher than 870 °C and that fines captured in the primary cyclone were recycled to the bed. The size and density of inert bed materials played a significant role. Denser and coarser inert particles tended to segregate, leaving burning char particles at or near the bed surface. Bed-to-cooling-coil heat transfer coefficients were of similar magnitude to those measured in earlier studies.