Date of Award
Doctor of Philosophy
Chemical and Biological Engineering
The kinetics of the reaction between SO(,2) and calcium oxide were studied using thermogravimetric analysis (TGA). A thin layer of reagent grade Ca(OH)(,2) was deposited on quartz plates, calcined to form CaO, and then sulfated to obtain kinetic data under chemical reaction control. Reaction rate constants were determined directly from the initial rate data. Pellets pressed from Ca(OH)(,2) powder were calcined and sulfated to study the effects of diffusonal resistance on the overall reaction;Results from the TGA confirmed that sulfation of CaO produces different products at different reaction conditions. In the presence of oxygen, above 740(DEGREES)C, the product is all CaSO(,4) and the reaction is first order in SO(,2) concentration. At 836(DEGREES)C, the reaction rate constant was calculated to be 0.076 cm/sec with an activation energy of 19.1 kcal/mole. Below 450(DEGREES)C, the major product is CaSO(,3) and the reaction is zero order. The zero order reaction rate constant at 450(DEGREES)C was calculated to be 4.2 x 10('-8) cm/sec with an activation energy of 15.4 kcal/mole;The grains of CaO obtained by calcining Ca(OH)(,2) were found to contain micropores, with a large number of them around 22 (ANGSTROM) in radius. The effect of sintering and sulfation on the micropores was studied using mercury porosimetry. The solid-state diffusivity was measured by using two simple diffusion models and rate data from the reaction of highly sintered CaO. At 932(DEGREES)C, the solid-state diffusivity was found to be 40 x 10('-8) cm('2)/sec with an activation energy of 35.6 kcal/mole;Reaction measurements made on CaO pellets, sintered and unsintered, showed that the temperature for maximum conversion increased with either increasing initial porosity or increasing initial grain size. A one-dimensional expanding grain model was developed and applied to the lime pellet sulfation data. The model fit the data from highly sintered pellets quite well, but it generally did less well as pellet presintering time decreased. The inclusion of a grain size distribution in the model was found to be less important than improving the estimates of the average grain size and the diffusion coefficients. In addition, the effect of temperature changes during reaction was measured experimentally and explained by the model.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Daniel Walter Marsh
Marsh, Daniel Walter, "Experimental gas-solid reaction kinetics of lime sulfation " (1983). Retrospective Theses and Dissertations. 7681.