Among all the refining processes, only vacuum degassing uses process water and generates effluent streams. Vacuum degassing involves direct contact between gases removed from the steel and condenser water. The principal pollutants contained in the effluent are low levels of total suspended solids (TSS) and metals (particularly lead and zinc, but also chromium, copper, and selenium) that volatilize from the steel. Applied water rates for vacuum degassing are typically around 1250 gal/t of steel; with discharge rates of 25 gal/t achieved through high-rate recycle.15
Water use in the continuous casting process may be categorized as primary, secondary, and auxiliary. The primary cooling process is a closed-loop, nonevaporative, noncontact cooling of the molten steel shell in the mold (or molds on a multistrand machine) employed to obtain high surface and strand quality. Secondary or spray cooling occurs as the strand moves out of the mold with contact water sprays covering its surface. Auxiliary cooling is noncontact cooling of the casting equipment. Direct contact water cooling system is also used for flume flushing to transport mill scale from the caster runout table.1
Applied water rates for the contact systems are typically about 3600 gal/t of cast product; discharge rates for the better controlled casters are less than 25 gal/t. The principal pollutants are total suspended solids, oil, and grease, and low levels of particulate metals.15
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