Customized solutions for better water quality in the rolling process
Our customer, the operator of a hot rolling mill, had persistent problems with turbidity in the circulating water and a high particle density, which consisted mainly of sinter. The rolling process adds a lot of particles and contaminants to the water, an unavoidable process that causes many challenges and costs in maintenance. In combination with the lack of a disinfection program for legionella and regular test value exceedances (>1000 CFU/100ml), the cooling water treatment was not optimal during our first on-site appointments.
The previous neglect of water treatment at our current customer led to a vicious circle of turbidity and legionella risk. The inadequate dosing of biocides and the lack of adequate treatment of the circulating water contributed to the deterioration in water quality. However, with our tailor-made water treatment concept, we were not only able to effectively control and minimize the risk of legionella, but also drastically reduce the turbidity of the water and minimize the particle density enormously.
In the upstream furnace, a layer of scale forms on the surface of the slabs due to the high heat and oxygen in the air, which is sprayed off again in the rolling process using press water. In addition, water is sprayed during the rolling process to cool down the bar, whereby additional mill scale enters the circulating water. This spraying takes place in the immediate vicinity of employees, which naturally exposes them to a higher risk. Permanent monitoring of the legionella concentration is therefore essential in order to effectively prevent infections. Due to the process itself, the process water also has the optimum temperature for Legionella to colonize and multiply. This makes it all the more important to keep a constant eye on the legionella concentration and to dose biocide as required so that the legionella cannot spread further. Since the use of our chlorine dioxide-based biocide, the legionella concentration in the water has always remained below the prescribed test value 1 (< 100 CFU/100ml). The biocide is dosed as required, depending on the measured redox potential via the INWATROL expert. Due to the exact design of the dosage, microorganisms and especially legionella can be effectively avoided without resulting in overdosing. In addition, the demand-controlled dosing prevents biofilm formation in order to protect the system from undercoating corrosion. Biofilms can also promote corrosion problems, so it is important to always take a holistic approach to water treatment.
Another challenge was the extreme turbidity of the water due to sintered particles that enter the circulation from the steel in the rolling process. The heat exchangers were constantly blocked and cleaning was only possible to a limited extent, as cleaning would expose corroded areas. Due to the use of hydrochloric acid, the water also had an extremely high tendency to corrode, as the chlorides in the circulating water were highly concentrated. In combination with high thickening, this brings the spray nozzles and the heat exchanger to their knees. By using anionic polymers for sintered flocculation, however, the turbidity could be reduced to <5. These are significant advances that were hardly conceivable for our customer at the beginning.
Before INWATEC’s comprehensive water treatment concept, the spray nozzles had to be changed every month due to the high turbidity in the water. Now the spray nozzles have not been replaced for over a year as they no longer clog up so quickly. This saves a lot of time and money and reduces the downtime of the rolling mill.
A further step towards optimum water quality was the adjustment of the thickening process and the switch from hydrochloric acid to sulphuric acid. As a result, the corrosion tendency was reduced from 0.3 mm/a to 0.03 mm/a. A further trial is currently underway to reduce the corrosion tendency. You will find out more about this soon.
Do you also need a customized water treatment concept? Then contact us at any time. We will be happy to help you.
