Good things come to those who wait: Cooling water disinfection
Strict statutory limit values apply to water infeeds. An aluminium plant in Voerde has met these requirements for its cooling water for the first time ever with ProMinent technology – other methods trialled in the past weren't up to the job.
Ready, steady – chlorine dioxide!
Trimet Aluminium SE in Voerde (Germany) manufactures raw aluminium that is processed into particularly high-grade rolling and extrusion billets by means of gravity die casting. The billets get their superior material properties from the rapid dissipation of heat during processing which requires 1,600 m³ an hour of cooling water to be circulated in three cooling circuits. In 2005, German law on limit values for water infeeds was tightened up, meaning that Trimet had to change its cooling water disinfection process. Yet neither chlorine tablets nor a combination of sodium hypochlorite and hydroxidobromine proved successful. The limit values for adsorbable organically bound halogen (AOX) were still being exceeded. Finally, they tried chlorine dioxide (ClO2) and tested a chlorine dioxide system from ProMinent, initially in one of the cooling circuits.
Key data
- Disinfection of 1,600 m³/h of cooling water for aluminium production
- Stricter legal limit values demanded new disinfection processes
- Superior test results with chlorine dioxide prompted installation of chlorine dioxide system Bello Zon® CDKc
- Production and feed-in of 1,500 g of ClO2/h
- Excellent lab values and chemical costs halved
Worthwhile in every respect
The results were outstanding. The limit values were reliably observed and the costs for water disinfection fell significantly. As an added benefit, ClO2 has no impact on their high aluminium quality standards. So the decision to use chlorine dioxide was made and Trimet had the chlorine dioxide system Bello Zon® CDKc installed. The system produces 1,500 g of ClO2 every hour and is housed in a separate container from where the ClO2 is fed to seven metering points in the cooling circuits. An independent lab tests the water monthly for AOX, legionella and organic components and confirms the perfect water quality. But what does it cost? While the annual material costs for sodium hypochlorite and hydroxidobromine were approx. €90,000, chlorine dioxide comes in at around half that. The ProMinent system is worthwhile on all fronts.
Comply with limit values and reduce costs
- Reliable compliance with statutory limit values for AOX, legionella and organic components
- Assurance of high quality standards for aluminium
- Halving of cost of chemicals
- Safe preparation of disinfectant thanks to intelligent system design
- Documentation of operating parameters in the chlorine dioxide system