Standing Tall: Plastic Cooling Towers Capture Metal’s Old Territory
Maintenance and DowntimeFactory-assembled cooling towers made with engineered molded plastic are widely considered to be essential to longevity and savings on maintenance and downtime. "Problems with the old metal towers are now worsened by an EPA ruling that lowers the amount of zinc solids that can be used in the galvanizing of sheet metal," says Jim Raymus, maintenance supervisor at injection molder Tulip Corp.'s Milwaukee plant. "As a result, it is unlikely that you will find a galvanized cooling tower with a warranty of more than five years."
Today's engineered plastic cooling towers are available in larger sizes and modular configurations that make them suitable for high-capacity applications.
Like an aging fighter, an old metal-clad cooling tower becomes high-maintenance, and performance drops off. It becomes thin-skinned and inefficient, and it causes process disruptions. Chronic "leakers" also inflict secondary damage on other structures. In many cases, tower fans and motors are outdated, consuming more energy than necessary.
While the cost of electric power to drive cooling tower fans may seem incidental to process costs, Raymus says they can add up. Some manufacturers use direct-drive motors to power their cooling fans. With no pulleys, bearings, and belts, direct-drive motors are more efficient and provide substantial savings in energy costs while delivering more horsepower. When modular towers are incorporated into a cluster configuration, direct-drive tower motors can be shut off, independent of others, when supported processes are not operating.
Consistency and Corrosion"If a cooling tower goes down, we lose production, and it can adversely affect our delivery schedules," says Jim Palmer, Allied Universal president and CEO. "We have a very corrosive and tough environment to have any type of equipment. And even though the cooling towers are not in direct contact with our products, they are exposed to a corrosive environment." Allied Universal is the leading U.S. manufacturer of sodium hypochlorite (bleach), liquid sodium bisulfite, and swimming pool acid. With seven plants in Florida, Georgia, Mississippi, Arkansas, and soon Arizona, the firm has been using engineered plastic cooling towers for approximately 15 years with highly reliable results. For the most part, these have been the Paragon Series of factory-assembled cooling towers made by Delta Cooling Towers, a leader in packaged cooling systems. The Paragon Series features a modular, induced draft design that includes a corrosion-proof HDPE shell and many other design elements that enable the cooling towers to survive well in demanding manufacturing environments.
"We couldn't make our products if we didn't have consistent cooling towers," Palmer explains. "Because these chemicals are exothermic, they give off lots of heat. So, we run the product through one side of the heat exchanger and flow cool water through the other side. The heat is taken out of the cooling water by the cooling tower and given back to the environment before it recirculates. So, a continuous flow of cool water is essential."
Leaks and Bends"We were spending between $5,000 and $10,000 a year on cooling tower repairs patching metal, putting in rubber seals and gasketing. In other words, 'band-aid' fixes just to keep the tower from leaking," says Marvin Richer, president of Brock Equipment Co., a Crystal Lake, IL, manufacturer of hydraulic pumps and related tools. "As the tower got older, not only did we have ongoing leak problems, we started to have a structural problem," Richer explains. "Water is pretty heavy, and the tanks that hold the water on the bottom were getting heavier and heavier as we added more and more materials to fix the leaks. All that weight was beginning to bend the structural members that held the cooling tank together."
Metal cooling towers, such as Brock Equipment's towers, are usually subjected to constant changes in pH, requiring chemical treatments that attack the galvanized metal lining and essentially wearing it out in a year or so. Environmental conditions such as sunlight, pollution, salt air, and harsh process chemicals can also contribute to galvanized steel's early demise. With this inherent vulnerability, metal-lined cooling towers generally carry only a one-year warranty. On the other hand, engineered molded plastic cooling towers are one-piece designs, which means there are no problems with seams, welds, and patches that wear prematurely. They are also rust- and corrosion-proof and can carry a 15-year warranty.
Shock and Vibration
New plastic cooling towers use advanced resins and molding techniques.
Burroughs chose plastic.
"I needed a cooling tower with water-distribution power that is far from normal operating conditions. Secondly, I hate doing maintenance."
The environmental testing that Burroughs carries out encompasses shock and vibration on equipment that is used in oil exploration and drilling operations. The test equipment includes hydraulic and electrodynamic shakers that check if the equipment in question is tough enough. "These shakers emit a great deal of heat, and they're cooled by a closed distilled water system because distilled water doesn't conduct electricity," explains Burroughs. "Once heated, the distilled water flows through heat exchangers that are cooled by a chill water loop. Delta plastic towers are on the other end of that. They are both 100-ton units." One tower is 3 years old, and the other is more than 13 years old.
Timing and Schedules"When you spend $3 million on a piece of equipment, you have to be sure you can keep it working," says Hector Bas, maintenance director for Aluminio del Caribe in Humacaro, Puerto Rico. "We have two hydraulic extrusion presses a 1,850-ton and a 1,670-ton model which are cooled by copper loops in the presses that function as heat exchangers. We must keep the hydraulic oil temperature below 130°F at all times. If the oil gets too hot, we have to shut down the press. That would mean losing four hours or possibly an entire shift. Not only would that be lost production, but it would also make us push orders back, which would also mean delayed shipments. It's a domino effect."
To meet these challenges, Aluminio del Caribe consulted with various industry representatives. The company decided to install in January 2001a Delta 200-ton plastic cooling tower because of its maintenance-free design. A second unit was installed when the second press became operational in April 2002.
"We just had to install a concrete pad, then place the cooling tower, which is relatively lightweight, on top of it with the anchor chains and hook it up," says Bas. "It was easy. We had to install the motors and piping to get that cool water to the oil filter at each press location, but that was also relatively easy."
Size and ShapeIn the past, plastic cooling towers were considered too small for many industrial processes. For that reason, galvanized metal cooling towers were deemed the only choice for applications above 250 tons. Unfortunately, processors requiring such high-capacity cooling were forced to build these custom-designed towers on site at a high cost in labor and materials. However, factory-assembled plastic towers can now be combined to provide up to 2,000 cooling tons in a single, modularized unit. Modular cooling towers also facilitate an extra margin of cooling capacity that can be advantageous in adjusting to operational heat load or outflow changes. They can also be advantageous in upgrading to meet future cooling requirements.
The modular design of plastic cooling towers has also introduced new flexibility in conserving valuable real estate. By molding towers in a rectangular shape, some manufacturers enable users to cluster cooling towers in a group that occupies a much smaller footprint.
Technical information for this article was provided by Delta Cooling Towers Inc. in Rockaway, NJ, which developed the plastic cooling tower in the early '70s. More information is available by calling 800-289-3358 or visiting www.deltacooling.com.