Challenge

Intimate contact of process hydrocarbon with the cooling water through two atmospheric condensers resulted in severe fouling of this cooling system. Microbiological control, accomplished through use of chlorine tablets and liberal dosages of nonoxidizing biocides, was clearly inadequate. Fouling was so severe that throughput was limited. Mechanical exchanger cleaning was required every 3 – 4 months.

Solution

Chlorine dioxide was fed to the cooling tower basin pump suction. Demand in the water was so high (and chlorine dioxide reacted so rapidly) that it was 5 days before a residual could be measured in cooling tower recirculating pump discharge. 

Results

One critical exchanger was inspected before and after the cleanup and is shown below. This exchanger was the one, which would be cleaned next and was opened specifically to determine efficacy of treatment. Biofilm was approximately 3 inches thick on the bottom of the exchanger before treatment. After treatment, although almost all of the biofilm was removed, a small amount of biofilm was left in a low flow area.