Cooling towers play a crucial role at many plants. Metals towers are often chosen because of their low initial cost and when large capacity is necessary. However, plastic towers can offer economic and operational advantages, and now come in modular designs suitable for bigger loads.
Metal towers frequently demand extensive maintenance. A single cut through the galvanizing or other protective coating to expose bare steel can severely compromise protection and lead to significant corrosion. Mineral deposits and scale (Figure 1) can build up.
Figure 1. Scale can deposit on metal surfaces (left), but not on engineered plastics, where removal only requires a washdown.
So, over time, such towers become increasingly thin-skinned and inefficient, and can prompt unscheduled process disruptions. Chronic “leakers” can cause secondary damage, while outdated tower fans and motors often consume more energy than necessary. All of this can add up to a “money pit.”
“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, Ill., manufacturer of hydraulic pumps and related tools. “My issues were really simple,” notes Glenn Burroughs, a test engineer with a major oilfield services firm. “I’m very busy running tests and don’t have the time or personnel for cooling tower maintenance, so I went looking for a cooling tower that I was not going to have to do any maintenance on.”
Replacing towers is time-consuming and expensive, as is the installation of additional towers to increase cooling capacity. “Given our choices, we were most likely going to install a new tower similar to the old one,” Richer says. “But first I wanted to look into a new plastic type of cooling tower that was said to be more reliable and require less maintenance than the old-fashioned metal-lined models.”
What Richer was looking for has become a new prescription for replacing ailing cooling towers or adding capacity: engineered molded-plastic cooling towers. Just as advanced plastics have supplanted metal in many high-tech and industrial applications, plastics also offer a remarkably comprehensive solution to the chronic deficiencies of metal-skinned cooling towers.
The latest engineered-plastic cooling towers also ease installation, especially on rooftops (Figure 2), because a lightweight plastic shell may weigh up to 40% less than a steel tower while being five-to-10 times thicker. Some models incorporate innovative I-beam “pockets” to reinforce the tower bottom so that they can be easily mounted on standard I-beams or imperfect pads.
Figure 2. The light weight of a plastic tower may make such an installation possible and allow better access to the wind.
Additionally, some engineered-plastic towers feature an induced-draft counter-flow design that provides improved cooling efficiency and thus a smaller footprint, which can be important where there are locating constraints.
Greater cooling capacities and improved structures aren’t the only innovations. Some manufacturers are pioneering direct-drive fan systems that require minimal maintenance because of fewer moving parts: no gear reducers, belts, couplings, additional shafts or extra bearings.
With Brock Equipment, it quickly became clear that the company was “throwing good money after bad” by continually spending time and cash on its old, deteriorating galvanized-metal-lined tower installed in 1950. “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.”
Richer appreciated the potential of plastic. “We thought this might be a better technology than galvanized steel,” he notes. “The installation of our new tower took a total of four days… In fact, the installation of the tower was a one-day deal, but some pipes coming into the building had to be reconfigured so that took extra time,” he says. “If you are familiar with plastics, you know that engineered plastic used to form Delta towers is very tough and this has proved to be the case. The new cooling tower has been trouble-free for over three years. We still have normal maintenance. We clean in the spring and make sure the filters are clean. But there has been no repair work on the tower, no leaks at all.”
Olin Brass in East Alton, Ill., is another company pleased with its switch to plastic. “The decision was to replace our galvanized-steel cooling towers with the newer molded-plastic cooling tower design,” explains Matt Niemeyer, staff engineer. “They were 10- or 12- years-old and had already rusted completely through in several areas. All of that was in terrible shape and had to be repaired several times.”
“The cooling tower was a straight splash bar design,” continues Niemeyer, “and because the tower would fill with all the heavy junk that collected as the dirty water was cooled, the grid and fill within the tower eventually collapsed.” Last year Olin changed its contact cooling method to a closed-loop clean water configuration.