Preventing Scale on Evaporative Condenser Tubes in a Cooling Tower
Evaporative condenser (or fluid cooler) type cooling towers create a unique water treatment problem as water is constantly flowing over the hot tubes, thus cooling the fluid that is inside. With just 1/32 of an inch of scale on the tubes, there is a significant loss of heat transfer efficiency (up to 9%). In fact, it has been shown that just ¼” of scale can reduce efficiency by up to forty percent!
Thus, it is very important to understand what type of scale can form under certain water conditions. In makeup water, dissolved solid concentrations need to be considered. As the water is cycling up (or increasing in concentration of dissolved solids), it is important to analyze what potential scales can form, especially in the presence of heat.
The most common form of scale to form is calcium carbonate. This can be prevented with the appropriate inhibitor blend combined with correct concentrations. Alternatively, silica scale (most commonly in the form of magnesium silicate) can form when dissolved silica concentrations exceed 120-150ppm in the cooling tower. Unlike most scales, silica scales are very hard to remove and could require a mechanical cleaning or cleaning with a dangerous acid. In short, it is important to understand all of the dissolved solids in your makeup water and choose an inhibitor that will prevent scale formation as the tower begins to cycle up.