A Cold-rolled Steel Plant Acidic Waste Water Treatment System Design

In steel production, to cold roll the steel, eliminating the scale on the surface of the material is essential. The method of acid cleaning is generally adopted, which will create acid pickle and pickling rinse water. The key components of the acid pickle created in cold rolling process are: FeSO4-100g/l and free acid-20%, which will lead to serious river pollution and ecological destruction if directly released into rivers without any treatment. Thus, the treatment of acid waste water which enables the released water conforming to the "Integrated Wastewater Discharge Standard" is inevitable.The essay aims at eliminating the ferrous salts in the acid waste water created in cold rolling process, diminishing its total dissolved solids and improving the utilization of effluent. A controlling system for processing the acid waste water created by cold rolling has been developed, in which the neutralization process of chemical dosing and percolation are adopted, i.e. using lime as the neutralizer to oxidize and precipitate the ferrous salts to eliminate it. The system is controlled by fieldbus, in which field equipments are controlled automatically by Siemens PLC S7-300 (Programmable Logic Controller) and through remote distributed I/O ET 200M. With regard to software design, in host computer, Step 7 is adopted to develop the procedures for controlling technical process while the control system of the host computer is developed through WniCC configuration software, which is responsible for monitoring the whole technical process as well. This research realizes the intelligent integration of acid waste water processing for cold rolling of steel and guarantees the priority processing of acid waste water.