A fully integrated North American steel mill runs a secondary non-contact cooling tower that provides cooling to the plant’s closed loop heat exchangers.
To mitigate deposit issues caused by calcium and phosphate, the steel mill was feeding acid to depress pH but still had to reduce cycles of concentration to only two. This mode of operation generated an excessive amount of blowdown water and sent a lot of treatment chemicals to the drain.
Veolia moved on-site and implemented its GenGard technology, an exclusive treatment program designed to allow systems to handle a high load of contaminants in alkaline conditions safely. GenGard combines a stress-tolerant polymer (STP), alkaline enhanced chemistry (AEC), and halogen resistant azole (HRA) with phosphate-based steel corrosion inhibitors.
The GenGard program allows cooling towers to operate safely and effectively with a much higher calcium and phosphate residual. The STP and AEC polymers keep the calcium and phosphate in solution, greatly reducing the risk of forming deposits. Veolia recommended that the tower operates at four concentration cycles without adding acid for pH depression.
Result
Increasing the system’s cycles from two to four significantly reduced the amount of water discharged by blowdown and saved an equal amount of freshwater. These water savings amounted to over 250MM liters per year, a reduction of 50%.
Without the dispersing properties of STP and AEC, the plant was previously spending $5,000 per year in acid to sufficiently depress the pH and was also using deposition and corrosion control chemicals in excess due to the high blowdown rates.
Graph 1 shows that while applying GenGard, cycles of concentration (yellow line) were increased from two to four, with calcium cycles (blue line) showing a similar trend. This indicates that calcium was not depositing, which would be seen with a downward trend. Veolia is now providing a best-in-class water treatment program that is acid-free without causing harmful deposition in the system. The increased cycles reduced the amount of water and chemicals being consumed.
Total savings equate to $28,000 per year and eliminate the environmental, health & safety (EHS) risk associated with the use of acid.
Graph 1: Cycles of calcium remain in line with tower cycles, showing no loss of calcium due to deposition within the system without pH depression