Separation of Mill Scale from Flume Wastewater Using a Dynamic Separator Toward Zero Wastes in the Steel Hot-Rolling Process

Abstract

Along with the production of hot-rolled steel, a large amount of mixture of mill scale, water, and oil is constantly generated. It is of great importance to thoroughly separate these components from one another to make them recyclable. In the current research work, an industrial trial was carried out at an ArcelorMittal hot-rolling mill for producing clean mill scale with negligible oil by separating the mill scale from flume wastewater using a dynamic separator. A slip stream of wastewater was continuously pumped from a roughing mill flume into a tangentially motivated dynamic separator. The mill scale particles settled to the bottom of the separator and continuously moved with the water into a classifier, where the mill scale was removed and dewatered. Results of the trial show that compared to the conventional practice of sedimentation and reclamation of the mill scale in the pits, using the new method, the mill scale is more than five times cleaner with negligible oil, and the effluent water is more than three times cleaner with much less total suspended solids. As a result, after separation with the new method, the mill scale and the wastewater are more recyclable. In addition, the new technology can also lead to recovery of more waste oil and significant reduction of oily mill scale sludge.