Cooling Water Treatment

Ozone in Cooling Water

Some of the problems facing cooling water treatment are the control of micro-organisms, scaling and corrosion. Cooling water is an ideal medium for breeding bacteria due to higher water temperature and the presence of sunlight helps the growth of algae. If not checked, the algae can choke the heal transfer tubes shutting down the plant. Biocides are required to control the growth of these micro-organisms. Due to the loss of water due to its evaporation in the cooling process, make-up water is added continuously in to pool water basin. While water evaporates, dissolved salt remains in the water. Addition of make-up water brings in more dissolved salt in to the system. This results in the increase of concentration of dissolved salts in water over a period of time. In order to reduce the concentration of solids in water, some portion of water is rejected. This is called blow down. The increased concentration of solids in water leads to increased scaling on the heat exchanger surfaces bringing down the efficiency of heat transfer.

Increased scaling also contributes to the higher rate of corrosion. The formation of scaling is also attributed to the formation of a slimy bacterial layer on the metal surfaces called Biofilm. In addition to the use of biocides, scale inhibitors and corrosion inhibitors are also used to control these factors. Ozone is an extremely powerful oxidising and disinfecting agent. It is advantageous to use ozone as a biocide to destroy the micro-organisms including algae in the cooling water. Ozone also destroys the biofilm formed in the heat exchanger surfaces. Since biofilm is also responsible for scaling, destroying it helps in the control of scaling, which, in turn helps reducing the corrosion rate. The use of ozone thus also reduces the requirement of scale and corrosion inhibitor chemicals improving the quality of the blow down water.

This decreases load on downstream waste water treatment plant. The result of using ozone in cooling water treatment is better control of bio-growth and scaling and corrosion of the metal parts. The capital cost of the ozone plant and cost of electricity used for running the ozone plant; when compared with the cost of all the cooling water chemicals, cost of inventory, storage space cost, cost of personnel involved in handling the chemicals and sometimes the cost of downstream water treatment, the ozone plant pays for itself in 2 to 4 years depending upon the cooling water capacity and the water circuit. The bonus is the environment friendly cooling water treatment.