The operation of galvanized metal cooling towers can be troubled by problems such as pH, corrosion and leakage, possibly leading to unscheduled downtime or even replacement. An alternative to consider is the engineered plastic cooling tower. A relative newcomer compared to their galvanized metal counterparts, plastic cooling towers are available in large sizes and are being used increasingly in industries where the coolant temperature ranges are critical to processes.
One company employing engineered plastic cooling towers is Bard Manufacturing, a maker of air conditioners, heat pumps and furnaces. Bard uses three engineered plastic cooling towers: one 30-ton tower is used for manufacturing operations and two 75-ton models are used by the engineering laboratory. The tower that services the manufacturing area cools water for spot welders and copper tube fabrication machinery.
“That tower is the ‘old timer’ at our Bryan, Ohio, plant, and has been operating since 1978,” says Courtney Perkins, engineering laboratory manager with Bard.
The two 75-ton towers cool process water for the environmental test chambers in Bard’s engineering lab. Comprising both indoor and outdoor sections, the test chambers simulate the same climatic situations that would exist in a home, business or other application.
“The chambers contain sophisticated heating, refrigeration and humidification systems,” Perkins explains. “In order to hold the chambers’ environmental temperature within one- to two-tenths of a degree [Fahrenheit], we must have very stable condenser control. You can’t get that kind of control with air-to-air condensers, so we use water condensers to transfer the heat out of the refrigeration system. Once heated, that process water is sent to the cooling towers on the roof and then returned. The cooling towers are vital to our continuing R&D.”
Without the cooling towers operating properly, accurate engineering testing could not be accomplished, says Perkins. “If the cooling towers fail or require extensive service, we might be looking at weeks or longer with no testing ability.”
Because the engineered plastic cooling towers are not affected by environmental elements and water treating chemicals, Bard has not experienced premature cooling tower failure.
Causes of Failure for Metal TowerThe nemesis of metal-clad cooling towers is pH, either high or low. A high pH leads to excessive calcium and other ceramic-like deposits. When the pH of a liquid coolant becomes acidic (low), either because of external (atmospheric) elements or infiltration of process elements (material fines), the veneer of zinc galvanizing used on most metal towers begins to deteriorate.
A pH lower than 4 will destroy the protective lining in a matter of months. At that point, the zinc galvanizing must be replaced using expensive coatings and any cavities and other damage that may have occurred must be repaired. If the repair process is extensive, costly process interruptions may be required.
Many manufacturers with metal cooling towers use solvents to prevent scale from occurring in the process fluids. Such chemicals sometimes leak into the cooling system and corrode the cooling towers. Solvents also may attack the metal at the cladding seams or simply wear down the galvanizing. Either way, once the zinc plating of a metal tower is undermined, the problem escalates, resulting in repairs or even replacement.
“Our towers get shut down and cleaned every couple of years,” says Perkins. “Over time, we’ve replaced the mist eliminators and one or two blower motors, and put new media inside the towers. But in all the years of operation, we have not experienced any structural failures.”
Using advanced resins and molding techniques, engineered plastic cooling towers are available in large sizes and modular configurations for high capacity applications (1,000 to 4,000 cooling tons). They are constructed as one piece so there are no problems with seams, welds and patches. They are rust and corrosion-proof. Some manufacturers offer rotary-cast versions with a double-wall UV-protective, polyethylene shell that is impervious to weather and harsh environmental elements. Water pH can vary widely without affecting the resin material, and stress from frequent turning on and shutting off cooling towers is not a factor.