High-Temperature Sulfation of High-Surface-Area Calcium Carbonate
Date Issued
2011
Date
2011
Author(s)
Hsu, Shu-Fan
Abstract
High surface area CaCO3 particles were produced by absorption of CO2 in aqueous suspensions of Ca(OH)2 in a bubble column. In the absence of any additive, CaCO3 with a surface area of 15.6 m2/g was obtained at 2.4 wt% Ca(OH)2 and 2.5 L/min CO2. CaCO3 with a surface area of 35.3 m2/g was obtained by adding 0.1 wt% Dispex A40 at pH 6.5 – 6.2, and with a surface area of 70.7 m2/g by adding 0.2 wt% PAAS at pH 11.4 –11.1. The primary CaCO3 particles agglomerated to form large particles, the average particle diameters of which were 10.4, 17.5, and 4.6 µm for the three CaCO3 samples prepared, respectively.
The initial rate and 1 min conversion for the sulfation of CaCO3 increased with increasing specific surface area, temperature, and SO2 concentration, but decreased with increasing CO2 concentration, and were independent of H2O concentration. A conversion of 0.88 was achieved when CaCO3 with a surface area of 70.7 m2/g was sulfated at 950ºC and 4400 ppm SO2 in a simulated flue gas for 1 min. The kinetics of the sulfation of CaCO3 particles can be described by the changing grain size model. Under the conditions that CaCO3 can decompose, the sulfation rate was controlled by grain product layer diffusion and particle pore diffusion. Under the conditions that CaCO3 cannot decompose, the sulfation rate was controlled by grain chemical reaction, grain product layer diffusion, and particle pore diffusion.
The initial rate and 1 min conversion for the sulfation of CaCO3 increased with increasing specific surface area, temperature, and SO2 concentration, but decreased with increasing CO2 concentration, and were independent of H2O concentration. A conversion of 0.88 was achieved when CaCO3 with a surface area of 70.7 m2/g was sulfated at 950ºC and 4400 ppm SO2 in a simulated flue gas for 1 min. The kinetics of the sulfation of CaCO3 particles can be described by the changing grain size model. Under the conditions that CaCO3 can decompose, the sulfation rate was controlled by grain product layer diffusion and particle pore diffusion. Under the conditions that CaCO3 cannot decompose, the sulfation rate was controlled by grain chemical reaction, grain product layer diffusion, and particle pore diffusion.
Subjects
calcium carbonate
calcium hydroxide
carbon dioxide
carbonation
sulfation
sulfur dioxide
Type
thesis
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