The Situation

A major refinery complex in the Middle East had a history of chronic leaks on the seawater heat exchangers of their once-through seawater cooling system. The leaks had been identified as being caused by under-deposit corrosion related to bio-fouling. Due to biological growth at the seawater inlet settling basin and the seawater outfall, performance was impaired as the bio-fouling cooling water flow rates were reduced in some of the critical heat exchangers.

The Solution

Nalco Water assessed the situation from a Mechanical, Operational and Chemical (MOC) perspective and proposed the PURATE^TM biocide programme designed to prevent bio-fouling and improve the refinery’s reliability and efficiency. This patented technology produces chlorine dioxide on site from chlorate, making it the most cost effective programme for these large once-through seawater systems.

The Results

The Nalco Water Purate technology delivered significant improvement to the seawater circuit. In three months, the careful clean-up of the fouled system showed constant improvements without disrupting operations. The colony forming units (CFU) dropped and more importantly, a log 2 reduction in sulphate reducing bacteria (SRB), responsible for the localized pitting corrosion beneath bio-films, was found. After the Purate treatment, heat transfer efficiency increased by a factor of four, significantly improving the desalination throughput. 

The result of better bio-fouling control is improved heat transfer performance resulting in annual savings of $4 million. By maintaining a cleaner seawater system, maintenance cost could be reduced by $0.5 million annually.