Date of Award
Degree of Engineer in Chemical Engineering
Chemical Engineering and Chemistry
John E. McCormick
Edward Charles Roche, Jr.
Double alkali (D/A) processes for the desulfurization of flue gases occupy an increasingly important role in applied technology.
D/A processes involve two steps, namely, scrubbing and regeneration. In the scrubbing step, the alkali (Na2SO3) reacts with SO2. In the regeneration step the acid formed, NaHSO3, reacts with an alkali to regenerate Na2SO3.
This study was focused on the regeneration step. Regenerants investigated were slurries of lime and limestone. The major factors studied were reactor configuration and mixing patterns.
These systems were investigated in a batch, backmix, and plug-flow reactors. Reactants were mixed to effect a large range of degrees of mixing.
It was observed that if the lime and Na2SO3 were effectively mixed initially, the regeneration of Na2SO3 occurs instantaneously.
In the limestone system, efficient mixing obviated the need for further mixing of reactants to effect regeneration. It is conjuctured that further mixing may even be detrimental. These results indicate that optimum design of regeneration must take into account the possible formation of agglomerations of "blinded" reactants. This "blinding" results from the deposition of solid insoluble products around clusters of solid reactants. This model explains why processes occur more efficiently with high initial mixing.
These are systems in which products are less soluble than the reactants. It is this difference which makes "blinding" occur to a significant degree.
These studies cannot be used to predict the optimum degrees of mixing necessary in a plant operation. The scale of these studies was too low. However, these studies uniquely point out the need for efficient initial mixing and also, a model to explain this need.
Rao, Krishna K., "SO2-scrubber technology : double alkali mode" (1977). Theses. 2098.