| The objective of this research was to investigate the effect of process variables and additives on the reaction rate of Ca(OH)(,2) with SO(,2) at conditions similar to those encountered in the bag filters used to collect solids following flue gas desulfurization by spray drying. The study was carried out in a bench scale fixed bed reactor, the bed consisting of powder reagent Ca(OH)(,2) dispersed in silica sand. The gas phase consisted of a mixture of N(,2), SO(,2), and water vapor. The effect of Ca(OH)(,2) loading, temperature, relative humidity, and inlet SO(,2) concentration were investigated. Of these variables, relative humidity showed the greatest impact on the reaction rate. The effect of small amounts of additives added to the Ca(OH)(,2) by a slurrying and drying process were also investigated. Of the additives tried (buffers acids, organic deliquescents, and inorganic deliquescents) deliquescent salts were the only additives that improved Ca(OH)(,2) reactivity towards SO(,2). The effectiveness of the deliquescent salts is a function of the type and amount of salt and of the relative humidity.;The reaction solids were characterized by scanning electron microscopy, powder x-ray diffraction, coulter counter size distribution, BET (N(,2)) surface area, energy dispersive spectrometry, and differential scanning calorimetry.;A shrinking core model with zero order kinetics in SO(,2) was used to model experimental data. An empirical correlation was included in the model to account for shape and surface roughness of the Ca(OH)(,2) particles. The diffusion coefficient of the SO(,2) through the product layer was found to increase linearly with relative humidity, and the kinetic rate constant increases exponentially with relative humidity. With a few exceptions the model was able to predict the experimental data within the margin of experimental error ((+OR-)10%). At high relative humidity and/or high SO(,2) concentration, reaction kinetics control the overall reaction rate, while at low relative humidity and/or low SO(,2) concentration, SO(,2) diffusion through the CaSO(,3) (.) 1/2H(,2)O product layer controls the rate. Deliquescent salt additives increase the SO(,2) diffusion coefficient and the kinetic rate constant in a manner similar to relative humidity. |
