NUCLEATION AND CRYSTAL-GROWTH OF CALCIUM SULFITE HEMIHYDRATE

In slurry scrubbing processes for flue gas desulfurization the precipitation rate of calcium sulfite affects scrubber solution compositon, SO2 absorption, sulfite oxidation, and limestone utilization. Sludge quality and disposal costs are also a function of precipitation kinetics. The nucleation and crystal growth rates of calcium sulfite hemihydrate were measured in a continuous flow crystallizer at conditions that produced agglomerate crystals. At 28 and 55-degrees-C, the nucleation rate, B-degrees, varied from 0.25 to 23 x 10(8) #/m3-sec and was given at pH 5.5 by the correlation: [GRAPHICS] The suspension density, M(T), was varied from 7 to 90 kg/m3. The linear growth rate, G (m/sec), varied from 0.5 to 9 x 10(-9) m/s as residence time was varied from 42 to 360 minutes. The nucleation rate constant had a maximum near pH 5.5 and was about 50% lower at pH 4.2 and pH 6.5. Gypsum saturation in solution caused both the nucleation and growth rates to decrease.