Abstract
Since January, 1989, ozone has been used as the sole method of water treatment in a 13,000 gpm (49,205 lpm) cooling tower at a gas production facility in the San Francisco Bay area. The system has operated efficiently at very high cycles of concentration for extended periods while eliminating the controlled blowdown of about 12 million gallons (45,420,000 liters) of water per year. Make-up water sources (ranging from 250 to 650 umhos/cm) have been used; and the tower has operated for extended periods at zero blowdown without significant adverse effects.
Once the organic demand in the cooling tower water was overcome by the ozone, the corrosion rates dropped to 2 - 4 mpy for mild steel and 0.2 - 0.4 mpy for copper. These corrosion rates are well within acceptable limits and are substantially lower than the rates measured during conventional chemical treatment. The concentration levels of copper and zinc in the cooling water circuit were also significantly reduced after ozone treatment.
All heat exchangers were inspected periodically, and those with normal cooling water velocities and skin temperatures less than 150 F° (65.6 C°) were found to be free from fouling and scaling. The approach temperatures in the gas aftercooler tube-in-shell heat exchangers were reduced by 8 - 10 F° (4.4 - 5.6 C°) as a result of the ozone treatment. In addition, the wetted cooling tower surfaces are free from scale and biological deposits.
This paper describes the application at the facility, the studies conducted, and discusses the functional performance of the system.
