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FLY ASH RECYCLE IN DRY SCRUBBING
Jozewicz, W. AND G. Rochelle. FLY ASH RECYCLE IN DRY SCRUBBING. Environmental Progress & Sustainable Energy 5(4):219-224, (1986).
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The paper describes the effects of fly ash recycle in dry scrubbing. (Previous workers have shown that the recycle of product solids improves the utilization of slaked lime--Ca(OH)2--for sulfur dioxide (SO2) removal by spray dryers with bag filters.) In laboratory-scale experiments with a packed-bed reactor, utilization was increased several-fold when the Ca(OH)2 was first slurried with one of several different fly ashes. The enhancement increased with the higher loading of fly ash--g fly ash/g Ca(OH)2. Much higher Ca(OH)2 utilization was achieved when silic acid was used instead of fly ash. Scanning electron microscopy supports the explanation that Ca(OH)2 and silica dissolve and reprecipitate as a more reactive calcium silicate. Other major constituents of fly ash have less or no effect at all on Ca(OH)2 utilization. The amount of calcium in the fly ash did not affect the overall SO2 removal after Ca(OH)2 was added. Slurrying for longer than 2 hours at higher than 60 C can improve the utilization of Ca(OH)2 slurried with fly ash.