Application of Ozone to Spraying Water in Cooling Tower of Transformer

—Sterilization of Legionella—

Abstract

A biofilm of micro-organisms such as bacteria including Legionella, fungi and algae can sometimes grow very rapidly in the spraying water of cooling tower, and can reduce the heat transfer rate of the cooling tower. Bacterial growth can be reduced or prevented by ozone sterilization method effectively. In application of ozone to cooling system of transformer, it is necessary to control ozone concentration for both sterilizing bacteria and suppressing corrosion during 30 years operation. For this purpose, we used heat exchanger model in which sub ppm ozone containing water was flowed through surface part of Cu tube and Cu fin for three month. We verified that Cu corrosion resistance allows thirty years operation and appropriate ozone concentration was effective to sterilization of micro-organisms including genus Legionella. We also used cooling system model including tower spraying in which sub ppm ozone containing water was flowed and circulated. We clarified ozone dissolution and consumption characteristic of transformer cooling system. We proposed optimum operation mode of ozone supplying as intermittent or continuous ozone supply with high sterilizasion effect according to the seasonal temperature change.