The main byproducts associated with forming and finishing are scales (typically iron oxides), an oily sludge that results from lubricating the rolls (water treatment plant sludges), and air pollution control dusts associated with treating effluents and cleaning exhaust gases. Coarse scale is separated from the sludge and collected in scale pits. The sludge, which is produced from the treatment of mill scale pit overflows, consists of oils, greases, and fine-grained solids that are collected in settling basins or other separation equipment. This sludge cannot typically be added to the sinter plant because of opacity problems. A number of sludge treating processes are used to de-oil fine sludges to as low as 0.1% at a reasonable cost. However, most oily sludge (containing more than 3% oil) is landfilled rather than recycled. The quantities of scale generated vary, but tend to range between 10 and 80 lb/t for nonoily scale and 4 to 60 lb/t for oily scale. Scale is usually sold or recycled and reused within the plant (usually for sintering), although recycling the oily scale without first deoiling it may cause problems with the opacity of the gaseous stream emitted from the plant or other operational problems. Another byproduct associated with cold rolling is fog exhaust sludge generated from the mist or fog produced during cold rolling. Fog exhaust systems are utilized to allow continuous observation of the strip during processing. Airborne particulates combine with steam and oil mist generated during cold rolling and are discharged to a settling chamber. The settled material is a sludge that is generally landfilled.1
Was this article helpful?