Dealing with Corrosion When Saving Water

Evaporative cooling towers are popular because they are cost effective but high water usage remains an ongoing problem.

The techniques used to reduce water requirements involve alkaline, which can destroy galvanized metal cooling towers.  So to engage in water conservation, facility engineers are faced with the prospect of replacing galvanized metal cooling towers at the accelerated rate of every five to eight years on average. This has opened the door for more applications for engineered plastic cooling towers. 

Engineered HDPE (high-density polyethylene) plastic is impervious to very high (and low) pH water as well as other chemicals introduced during the life of the tower. The water lost to both evaporation and drift must be replaced on an ongoing basis for the system to remain at full efficiency. But this water contains scale forming miners such as calcium and magnesium salts.

Left undiluted, these minerals cause scaling on equipment surfaces.  Even a small amount of scale in the system decreases the efficiency of heat transfer, resulting in decreased productivity in industrial processes. In severe cases, scale can completely plug heat exchangers and piping.

The goal is to keep water loss to a minimum and achieve zero blowdown. The primary method of reducing blowdown involves using chemical additives to impede scaling.  These chemicals extend the solubility of the minerals so higher concentrations can exist in the water without causing scale or corrosion.

More advanced techniques include using treated “soft” water (no calcium or magnesium salts) through the cooling tower.  Available from companies like ProChemTech, soft water chemistries such as its patented SofTek technology can reduce water use by up to 40 per cent, according to company president, ” Timothy Keister.  Another option is plastic cooling towers which are 40 per cent lighter than steel towers making them easy to install. “Delta Cooling Towers are considerably lighter then steel.  That means less money is required for support beams.  This can save a considerable amount of money,” Keister said.

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