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PILOT-SCALE INVESTIGATION OF CLOSED-LOOP FLY ASH SLUICING. VOLUME 1. FINAL REPORT
Citation:
Litherland, S., P. Nassos, M. Owen, AND S. Winton. PILOT-SCALE INVESTIGATION OF CLOSED-LOOP FLY ASH SLUICING. VOLUME 1. FINAL REPORT. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/7-85/021A.
Description:
The report gives results of a pilot-scale demonstration of the technical feasibility of closed-loop operation of fly ash sluicing systems. Chemical species leached from the ash increase the dissolved solids concentration of recycled sluice water to a point where equipment scaling may occur. Tests were conducted at two power plants using a 50-gpm pilot unit to demonstrate the feasibility of closed-loop operation, both with and without sluice water treatment. An ash sluice computer process model was developed to predict chemistry and process conditions in full-scale systems. Fly ash sluicing systems handling highly reactive alkaline ashes cannot be operated closed-loop without treating the sluice water to control scale formation. Adding acid to adjust pH was effective in controlling calcium carbonate scale formation in the sluice water return line; however, it increased the potential for gypsum scale formation. Gypsum was ultimately the limiting species which prevented reliable closed-loop operation at the plants tested. Increased ash/water contact time in a reaction tank was not adequate to control the potential for gypsum scale formation at the residence time tested. The ash sluice computer process model proved to be accurate in predicting the chemical composition and potential for scale formation in the pilot unit.