Cooling Tower Chemicals

A cooling tower cools by evaporating water, and evaporation removes only the water. Everything dissolved in it stays behind and concentrates, until hardness reaches the point where calcium carbonate deposits on the hottest surfaces in the system. Under a millimetre of that scale measurably cuts heat transfer, which shows up as rising approach temperature, longer chiller run times and a higher energy bill long before anything visibly fails.

Descaling uses an acid circulated through the system, and the inhibitor is what makes it usable: raw acid would dissolve the scale and then attack the tube walls, and copper and brass are particularly vulnerable. Progress is tracked by monitoring pH — when the acid stops being consumed, the scale is gone. The job is not finished at that point: the system must be neutralised, flushed until the effluent runs clear and neutral, then returned to treated service, because a freshly descaled surface is bare and corrodes quickly.

The second half of the problem is biological. A tower is close to an ideal incubator — warm water, sunlight, dissolved nutrients and continuous aeration — and biofilm forms within days on untreated systems. It insulates worse than mineral scale at the same thickness, shelters corrosion beneath it, and carries a genuine public-health obligation around Legionella. Oxidising and non-oxidising biocides are normally alternated so organisms cannot adapt to either.

Long-term control is cheaper than repeated shutdown descales. A scale-inhibitor programme with blowdown held at three to six cycles of concentration, monitored by conductivity, keeps a tower running for years without a shutdown clean.