The Terneuzen site on the southern shore of the Westerschelde estuary is Dow’s second-largest production facility, with 23 plastics and chemicals plants plus the largest Dow R&D operation in Europe. Because used cooling water returns to the estuary, Dow must use only the minimum necessary concentration of chlorine, says Eric Engelen of the site’s analytical department.
“Previously we used an analyzer based on diethyl-p-phenylenediamine (DPD) to monitor chlorine, but this had become outdated and was quite expensive to run,” Engelen explains. “The DPD analyzer wasn’t suited to seawater. It’s a colorimetric method, which works well when you are measuring chlorine in a swimming pool, but water from the Westerschelde is completely different. The water is salty and contains algae, mussels, seaweed and sand. This reduces the accuracy and reliability of the measurement, and means that the sensor has to be cleaned almost daily.”