The effect of additives on lime dissolution rates. Final report, September 1, 1993--August 31, 1994

Abstract

This project was funded in part by the Ohio Coal Development Office, Department of Development, State of Ohio. D I S CLAi MERPortions o f this document may be illegible in electronic image products. Images are produced from t h e best avaiiable original document. EXECUTIVE SUMMARYIn spray dryer flue gas desulfurization, lime slurry is injected into a spray dryer where it contacts with the hot flue gas and desulfurization occurs. This process is complex owing to the heat and mass transfer which must take place. One of the most important fundamental steps in the scrubbing process is the rate at which lime dissolves from the solid particle in the slurry drop and becomes available for reaction with the absorbed sulfur &oxide. This dissolution rate to a large extent controls !he degree of reactivity and is the rate controlling step for this process. However, studies on this dissolution rate have been very few and its magnitude under a variety of operating conditions is not well known. This research has as its objective, the study and understanding of the lime dissolution rate. This understanding should lead to a better method of predicting and optimizing spray dryer performance for flue gas desulfurization.The lime dissolution rate has been successfully measured by means of a spinning disc experimental method. It was found that lime dissolution rate was dependant on the disk rotating speed when the rotzting speed was below 300rpm. Whsn the disk rotating speed was greater than 300rpm, lime dissolution rate become constant. Lowering the solution pH increased lime dissolution rate, and lowering the solution temperature reduced lime dissolution rate.Two groups of additives have been tested for their effects on lime dissolution rate.Among the organic chemicals, sugar and phenol were the most effective in enhancing lime dissolution rate. Glycerin slightly increased the lime dissolution rate, and ethyl-alcohol depressed the lime dssolution.The most prominent chemical tested was in the inorganic chemicals group. In its 20% by weight solution at 50" C, the NH4Cl solution increased lime dissolution rate more than a hundred times compared with dissolutior, in pure water. The other two inorganic chemicals, (NH,),SO, and CaCI,, just slightly increased lime dissolution rate.