If you are a utilities manager at a major chemical plant, the notion that cooling towers corrode should come as no surprise—it's a fact of life. How you choose to overcome the problem is another matter, as there are many products to choose from. Countless corporations, however, are turning to towers engineered with rugged plastics such as high-density polyethylene (HDPE) that remain impervious to harsh chemicals, bitter environments and pH deviations.
That was the decision Albemarle Corporation made for its fire retardant plant in Magnolia, AR, where a galvanized metal tower had been badly compromised by the chemical environment. The plant specializes in products that help plastic molders, compounders and foamers meet or exceed stringent legal and regulatory requirements to protect property. Each flame retardant also helps save lives. Now the company wanted to save a new cooling tower from the same fate as the one that was being replaced.
William Wright, a unit leader for Albemarle's utilities department, explains that company officials took a sensible approach to the decision, starting with looking for reasons the tower in question failed. "Among other things," he notes, "the tower was sitting right next to components that had the potential to give off corrosive vapors. We needed something that could withstand that and a whole lot more."
Wright calls HDPE the "ideal material" for replacing Albemarle's traditional metal-clad cooling tower. Just as plastics have overtaken metal for applications ranging from plumbing to aerospace, they now are eliminating the need for metal in cooling towers for a broad range of applications. In fact, the fire retardant plant already was using piping made from plastics when officials decided to buy a unit developed by Delta Cooling Towers.
According to Wright, the new tower has functioned without a hitch—and has helped his company save money. Since the interior surface of the tower is dark and protected from the sun, water temperatures remain cool with less biological growth. As a result, treatment chemical usage is down. "I'd like to replace about 10 more," Wright says.
Over the next five years, Wright may get the chance to do just that, as Albemarle fulfills its plan to upgrade the Magnolia plant's other 26 towers and equipment of various kinds. The overhaul comes at a time when the global corporation headquartered in Baton Rouge, LA, is expanding. It now develops, manufactures and markets specialty chemicals for consumer electronics, petroleum and petrochemical processing, transportation and industrial products, pharmaceuticals, agricultural products and construction and packaging materials.
As Wright puts it: "You try to get all the value you can out of something you've paid for. That's where we are now. We've got a five year plan. We'll take a look when the time comes. We keep a good eye on maintenance."
Low maintenance, easy installation
Using advanced resins and molding techniques, engineered plastic cooling towers are available today in sizes and modular configurations that make them ideal for even those types of high-capacity applications (1500-2000 cooling tons) that traditionally depended on expensive field-constructed installations. Plastic towers are easier to install because they weigh 40% less than their metal counterparts, yet they are five to 10 times thicker.
Engineered plastic equipment often means less maintenance—and, therefore, lower ownership costs. Over time, traditional metal towers require process downtime for patching and welding areas that have corroded. Traditional designs also will have more complicated fan systems incorporating gearboxes or belts and pulleys that wear. Delta uses direct-drive fan systems that eliminate these maintenance items. Less moving parts translate into less maintenance, less downtime and less aggravation.
Answering the skeptics
Despite advances in plastics technology, suggesting a plastic cooling tower can still draw some skepticism. Some people hear the word "plastic" and assume "new" and "unproven". These technologies, though, actually have been at work for decades—and HDPE products have an excellent track record. Individuals accustomed to a seven- to 12-year life cycle for galvanized metal may be very surprised to learn that an installed plastic tower may outlast their facility.
Wright, like other successful managers, is eager to embrace new technologies that help reduce the daily trouble-shooting so common around a large plant. "Most of our towers are quite old," he points out. "They're getting close to the end of their useful life. But a chemicals plant is a very corrosive environment. What do you expect?" Even so, it appears as though the new plastic tower has lived up to Albemarle's expectations, in terms of heat transfer, etc. "It now runs at 70% loaded," Wright continues, "and we're comfortable running it up to 100 percent soon."
The need for more capacity
Although age and failing efficiency are the main reasons for upgrading equipment, Wright reminds us that some old cooling towers were built with materials that included asbestos. "We're replacing those. Age makes them more difficult to maintain, and we're to a point where we need more capacity."
Corrosion problems at facilities in coastal locations also can be caused by pH levels. High or low (alkaline or acidic), a pH imbalance can trigger a destructive trend that causes metalclad cooling towers to fail early or require extensive service. For example, a pH level lower than four can destroy the metal protective lining of a tower within months. pH levels are affected by various harsh environmental conditions, such as sunlight and pollution—and even routine chemical treatments. HDPE towers are engineered to withstand these problematic pH deviations.
When replacing other towers, Albemarle will consider many issues, including flow rate and heat transfer capacity, and will carefully analyze the conditions of the plant that the new tower will service. The company may even consider ceramic and stainless steel towers—although the cost of those types generally exceed HDPE products.
While many questions will need to be answered, Wright already has made up his mind on one issue: "We won't buy galvanized metal. The Delta tower is working just fine. I'm anticipating it'll last a lot longer than what it replaced." MT