Combustion performance and sulphur capture during fluid bed combustion of a western sub-bituminous coal and an eastern bituminous coal

Abstract

The carbon combustion efficiency and solid phase sulphur retention of low-sulphur Alberta sub-bituminous coal and a high sulphur New Brunswick bituminous coal were examined in an atmospheric fluidized-bed combustor. Input variables were energy release (35 KW to 130 KW), bed temperature (750 0 , 850° and 950°C), and flue gas oxygen concentrations (2.5, 5%). The resulting range of superficial fluidizing velocities was 1 to 4 m/s which produced vigorous bubbling bed conditions. The sub-bituminous coal proved more reactive with a once through combustion efficiency in the range of 96% to 99%. Comparable figures for the bituminous coal were in the range of 90% to 98%. Attempts to correlate burn-out with bed temperature, excess air and fluidizing velocity indicate that burn-out with the sub-bituminous coal is primarily dependent on bed temperature. For the bituminous coal burn-out is chiefly dependent on bed temperature and fluidizing velocity. For both coals, sulphur capture in 'coal ash constituents' appear to be best below 750°C. With the high-sulphur bituminous coal (sulphur content of 9%) limestone was also used to vary the Ca/S mole ratio in the range of 2 to 5 and was able to produce up to a 90% reduction in sulphur emission. The degree of sulphur retention, Ret, followed the relationship: Ret r. 100 1 - exp(-0.46 [Ca/S1)