JANUARYCONSTRUCTIONBUSINESSREVIEW.COM 19Thousands of manufacturing and other industrial plants require cooling water for numerous process applications. These cooling systems, many of which utilize cooling towers for primary heat transfer, are critical for plant operation and productivity. However, corrosion and fouling issues require constant attention to prevent productivity losses and sometimes even plant shutdown. New technologies have emerged to greatly assist in the battle against cooling system corrosion.While comprehensive cooling water treatment programs typically include chemistry to control scale formation, they also must be designed to protect metal surfaces from corrosion. Cooling systems often incorporate multiple metallurgies, but by far the most common material for piping and other equipment such as heat exchanger shells is carbon steel. For many years in the last century, a common cooling tower treatment program utilized sulfuric acid combined with chromate treatment to protect the various metals within systems, and most notably carbon steel. The chemistry inhibits calcium carbonate scaling by reaction of sulfuric acid with bicarbonate ions (HCO3-) to convert the ions to CO2, which escape as gas. A typical pH control range was within or near 6.5 to 7.0. The second compound in the formulation, disodium chromate (Na2Cr2O7), provides chromate ions that react with carbon steel to establish a protective pseudo-stainless steel layer, which can be particularly effective in the oxygen-saturated cooling water generated by cooling towers.Almost universally, chromate treatment was abandoned in the 1980s due to dawning knowledge, including efforts led by Erin Brockovich, of the toxicity of hexavalent chromium (Cr6+). The most common (by far) replacement programs were based on a combination of inorganic and organic phosphate, aka phosphonate, chemistries, with supplemental chemical additives to control both scaling and corrosion. These treatment methods can be quite complex, and for corrosion protection rely on deposition of reaction products to protect metal surfaces. The deposition products are often subject to process variations or upsets that negatively influence program effectiveness. So, the search for better chemistry came along. Another driving factor in this search involved the increasing concern regarding the impact of phosphorus on the environment, and in particular the growing problem of toxic algae blooms in natural bodies of water. Toxic algae blooms have been well-documented in such warm weather locations as Florida and the Gulf of Mexico below New Orleans, but they have occurred in many other areas including Lake Erie.Modern polymer chemistry has emerged that are serving as an alternative to phosphate-based treatment methods for corrosion control. Original polymers developed for scale control contained carboxylate functional groups (COO-), where the negatively-charged oxygen atoms bind with hardness ions to modify crystal growth. More advanced compounds such as co- and ter-polymers have structures that may include carboxylate, amide (R-CO-NH2), sulfonic acid By Brad Buecker, Senior Technical Publicist, ChemTreatMINIMIZING COOLING SYSTEM CORROSIONBrad BueckerCXOINSIGHTS
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