EVALUATION OF OZONE TREATMENT
IN COOLING TOWERS
Douglas T. MerriU, Principal Engineer
Denny S. Parker, Vice President
Brown and Caldwell
Walnut Creek, California 94596
Joseph A. Drago, Sanitary Engineer
Kennedy Engineers
San Franscisco, California 94105
INTRODUCTION
Currently accepted practice for controlling scale, corrosion, and fouUng in cooling tower
systems is through the use of chemical addition and the control of cycles of concentration.
Chlorine is usually used for control of biological growths. Recent concerns over chlorine
residuals and trihalomethanes in wastewater discharges, including cooling tower blowdowns,
have led to the evaluation of alternatives to chlorine. Ozone is one of these alternatives.
Although the reasons why are not immediately apparent, experience with ozone systems
has indicated that ozone may also be effective in controUing chemical scaling.
One manufacturer, Source Gas Analyzers, Inc. (SGA), of Garden Grove, CaUfornia, states
that its water treatment system, which uses ozone, can be employed as the sole source of
treatment for control of biofouling and chemical scaling in low temperature heat exchange
systems and furthermore, that cooling tower systems using this treatment can operate with
no blowdown. Thus, SGA claims, low temperature systems using ozone can be operated with
greatly reduced water and power consumption and reduced chemical and labor costs. SGA
has identified several sites in Southern California where ozone is successfully used in coohng
towers servicing air-conditioning systems [ 1 ]. Maximum water temperatures in such systems
are typically about 32 C, with temperature rises across the condenser in the 2 to 5 C range.
To our knowledge ozone has not been used with large-scale industrial cooling systems.
However, were ozone treatment to be as effective in general industrial cooUng as SGA
claims it is with air-conditioning systems, then similar benefits would occur, and on a very
large scale. There is justifiable reluctance to proceed directly with ozone testing in large-scale
systems, even if the claims made by SGA can be verified. For example, water temperatures
may be different than water temperatures in air-conditioning systems and scale-up problems
may also be encountered. Thus, results obtained in air-conditioning systems may not be
directly translatable to general industrial cooling. A more cautious step-by-step approach
to the issue was adopted instead.
The Electric Power Research Institute (EPRI) contracted with the firm of Brown and
Caldwell to conduct a preliminary investigation into the current use of ozone in air-
conditioning systems. The objectives of the investigation were to survey several operations
where ozone treatment is now used, to determine whether claims made by SGA are
confirmed in practice, and to provide a technical basis for a subsequent large-scale
comparison of ozone and proprietary chemical treatment at an electric power generating
station, if such testing seemed warranted. This paper summarizes the preliminary investigation as well as the scope of continuing activities. FuU detaUs of the preliminary investigation are presented elsewhere [2].
RESULTS
As previously mentioned   there are several sites in Southern California where ozone is
used  to  treat  air  conditioning  system  circulating  waters. Visits were arranged at four
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