Ozone use in cooling towers

Cooling Towers and Ozone

A range of packaged systems is available, from small, manually operated, to larger, 'Spec' built fully automatic systems with remote control and data logging.

Since ozone is an unstable oxygen molecule that cannot be stored or shipped, it must be generated on-site at the point of use. Problems associated with the ordering, shipping, handling, storing, record logging, and effluent disposal of standard water treatment chemicals are thus eliminated. The discharge water from an ozonated cooling tower will comply with current U.S. EPA and South African regulations.

Bacteria present in cooling tower water intensify scaling by forming a bio-slime layer that acts as a bonding agent for scale deposits and can harbour and proliferate Legionnaire's disease and other pathogens. Because ozone is a very strong biocide it destroys the bacteria, leaving the scale deposits free to be removed by the velocity of the water through the pipeline.

Years ago, the chromate/zinc inhibitor was one of the best inhibitors on the market to protect metal surfaces from corrosion in a cooling tower. Today, ozone is attaining the same recognition by providing the same or better corrosion protection than the old chromate/zinc inhibitor. Ozone provides a protective oxide coating on the metal surfaces within the condenser loop.

Ozone reduces operating costs by :

Reducing makeup water to the cooling towers by permitting more cycles between blowdowns.
Eliminating the cost and problems in ordering, shipping, handling, storage, and disposal of regular chemicals.
Reducing power consumption by keeping the chiller heat transfer efficiency high through cleaner condenser tubes.

Ozone systems must be sized individually. Our application specialists will review and utilize your existing equipment (such as aeration towers, pumps, filters and buildings) to be fitted for the new purpose. Manual and fully automatic systems are available. The reason for selecting either one can be purely economical.

A. MANUAL SYSTEMS
The manual systems require almost the same level of attention as the systems with chemical feed. In manual systems OZONE simply replaces biocides, with the following advantages:

Eliminates the use of chemicals except for pH balancing.
Ends discharge liabilities and chemical storage record keeping.
Destroys all types of micro-organisms like Legionnaire's disease etc.
Minimizes condenser fouling.
Decomposes organic waste by oxidation.
Prevents calcium carbonate scaling.
Removes existing calcium carbonate scale by destroying the biomass glue bonding agent.
Reduces the corrosion rate of metals, including copper heat exchangers.
Prevents delignification of wood frame towers.
Reduces water consumption by maintaining higher cycles of concentration in the cooling tower.
Saves on energy costs by increasing the heat transfer efficiency of the chiller.

The operation is easy:

Start with full ozone production to achieve the fastest initial cleanup.
When the water and all surfaces are clean, and all fallen scale has been removed, read the corrosion coupons. If the corrosion rate is high, use a PDP or ORP test to measure ozone residual. Record the corrosion, ozone residual, ambient temperature and pH, into your logbook. Reduce the ozone production by 20%.
Repeat once a week, until you obtain a pattern that is characteristic for your specific climatic conditions, cooling tower design, and makeup water characteristics.

Often the cooling towers already have automatic blow down installed — the new ozone treatment will not interfere. Elevated ambient temperatures require more ozone. If the tower was off-duty for a long time, or neglected, about one litre of hydrogen peroxide will dramatically speed up the initial cleanup without adding any chemicals to the discharge.

Manual systems are available for smaller towers where the additional cost for an automation system may not be justified. Ozone will still provide the great advantages listed above.

B. AUTOMATIC SYSTEMS
In automatic systems the corrosion, dissolved ozone, pH, conductivity, and AC current are measured in 0.5 second periods, and the ozone dosage is adjusted automatically. Data logging is also automatic, and easy to access from any telephone line via proprietary software. By precisely following the optimal pattern, the corrosion rate is very low in the first year and almost below detectable level in the years following. The heat exchangers are usually 10 times more expensive than an automatic ozone system of matching size.
The automatic system will extend the life span of the heat exchanger, and of other metal surfaces, by at least a factor of 10. Usually the initial investment for an ozonation system will return in just six months! A phone line access can also provide data for preventive maintenance, and security purposes.
The automatic system also allows for a more accurate blow down. The discharge water is very clean, and safe for accidental drinking.

C. MAKEUP WATER SYSTEMS
The makeup water should always meet the drinking water quality standards. In other words, a cooling tower is not a dumpsite for sewer or otherwise bad water.

Ozonation systems are available to treat makeup water to drinking water quality standards. Ozone is also very suitable to treat surface water sources. Surface waters are mostly very soft, thus ideal for use in cooling towers. We will calculate the proper makeup system based on your raw water test results.