CHARACTERIZATION OF CALCIUM-OXIDE FLY-ASH SORBENTS FOR SO2 REMOVAL

Sorbents for SO2 removal from humidified simulated flue gas have been prepared from CaO-fly ash slurries using a pressure hydration technique. The fly ash materials were obtained from the combustion of four bituminous, six sub-bituminous, and two lignite coals. The CaO/fly ash ratio, and the slurry reaction time and temperature were varied in the preparation step. The sorbents were characterized by measuring thermogravimetrically the SO2 uptake from flue gas, and by X-ray diffraction, surface area, particle size, and optical microscopy studies. The X-ray diffraction results indicated that calcium silicate hydrate, Ca2SiO4.H2O, and calcium aluminum silicate hydroxide, Ca3Al2(SiO4)(OH)8, were the principal Ca-containing species formed during the hydrothermal reaction between CaO and fly ash. There was a good correlation between the surface area of the sorbent and the SO2 uptake. Particle size measurements and optical microscopy studies indicated that the glass-like spheres in fly ash remained largely intact during the hydrothermal preparation step.