Factory-assembled cooling towers formed of engineered, molded plastics continue to gain favor over galvanized sheet metal models. Just as plastics have overtaken metal for applications ranging from plumbing to aerospace, they are now being widely used in cooling towers for a range of industrial applications. Utilizing advanced resins and molding techniques, engineered plastic cooling towers are now available in larger sizes and modular configurations that make them well suited for high-capacity applications (1,500 to 5,000 cooling tons) that traditionally depended on field-constructed installations.
Here are four reasons why you might want to considered an engineered plastic cooling tower to reduce costs and better meet your process requirements:
Life ExpectancyStandard metal cooling towers have casings with thin sheets of galvanized steel. These sheets usually have welded seams that can deteriorate over time and will require re-welding, patching or coating to prevent leakage.
Additionally, because the pH of cooling tower water constantly changes -- requiring chemical conditioning to accurately balance the pH -- the treated water tends to attack the galvanized metal, essentially wearing it out, sometimes in remarkably short time. Environmental conditions such as sunlight, salt air and harsh process chemicals also contribute to galvanized steel's life expectancy. Even ambient air pollution can affect galvanized steel, leading to premature failure.
Some processes require that cooling towers are turned on and off with great frequency. Because metal expands and contracts depending on temperature, repeated cycling causes stress that also can accelerate corrosion, rust and leakage.
Engineered molded plastic cooling towers are one-piece construction, so there are no seams or welds to wear. Engineered plastic cooling towers are also rust- and corrosion-proof. They can be supplied with a single- or double-wall, UV-protected polyethylene shell that is much less affected by weather conditions and harsh environmental elements. Water pH can vary without affecting the resin material. Stress from frequent turning on and shutting off cooling towers poses no risk factor for engineered plastic.
Flexible, Modular DesignIn the past, plastic cooling towers were too small for many industrial processes. For that reason, galvanized metal cooling towers were traditionally a “given” for most applications above 250 tons. Processors requiring high-capacity cooling were forced to build custom-designed towers on site, often at a high cost in labor and materials.
Today, factory-assembled plastic towers are offered that can be combined to provide up to 5,000 cooling tons in a single, modular unit. Modular cooling towers also facilitate the use of an extra margin of cooling capacity that can be helpful in adjusting to operational heat load or outflow changes, or in upgrading to meet future cooling requirements.
The modular design of plastic cooling towers helps conserve valuable plant real estate and may create a potential for substantial energy savings. By molding towers in a rectangular shape, some manufacturers enable users to cluster cooling towers in a group that occupies a much smaller footprint than ungrouped multiple towers. This configuration enables greater cooling capacity and the ability to dedicate towers to specific processes. Also, the towers may be turned on or off independently in accordance with intermittent process operations.
Continuous Operation, Operating Cost SavingsEngineered plastic also can reduce the expected and untoward consequences of operating a cooling tower, which include electric power usage, water-treatment chemicals, labor and materials for maintenance, and unscheduled process downtime for cooling system repairs.
Maintenance and repairs usually mean process interruptions, the costliest of all problems related to cooling towers. Corrosion-, rust- and leak-proof plastic cooling towers are can provide continuous and reliable operation with few disruptions.
For instance, the “white rust” that forms on galvanized towers operating at pH higher than 8.0 can quickly lead to failure and require replacement. The use of engineered plastic allows the use of better scale inhibitors that operate at higher pH.
Also, engineered plastic cooling towers can operate at higher cycles of concentration, leading to operational savings. Higher cycles of concentration are achieved by lowering the amount of blowdown or bleed-off of recirculating water. For example, assume a system operating with the cost of water at $1.50 per 1,000 gal and sewer fees at $2 per 1,000 gal. A cooling tower evaporating 50 gal/min at three cycles of concentration would bleed off 25 gal/min, for a total makeup water requirement of 75 gal/min. Increasing to five cycles of concentration would reduce blowdown to 12.5 gal/min and total makeup to 62.5 gal/min, resulting in a yearly savings of $22,955. Reducing bleed-off by 50 percent would also allow a 50 percent reduction of chemicals for scale and corrosion control for process equipment downstream from the cooling tower.
Utility savings also can be realized. While the cost of electric power to drive cooling tower fans may seem incidental to process costs, they can add up. Engineered plastic towers with direct-drive motors to power the cooling fans eliminate pulleys, bearings and belts that consume electrical power. Such direct-drive motors are more efficient and can reduce energy costs. When modular towers are incorporated into a cluster configuration, individual direct-drive tower motors can be shut off independent of others when supported processes are not operating, further conserving energy.
Typically, polyethylene plastic cooling water towers also save costs by reducing or eliminating the possibility of process material contamination. In particular, treatment chemicals can cause the leaching of zinc from galvanized metal. In some cases, this could result in the zinc migrating into the process, a potential environmental discharge problem.
Finally, while metal towers require maintenance for the routine application of coatings, removal of rust, and re-gasketing, such tasks typically are not required engineered plastic water towers. The avoidance of maintenance further preserves process up-time.
Ease of InstallationBecause a lightweight plastic shell weighs as much as 40 percent less than a steel tower it is easier to install, especially on rooftops. When modular cooling towers are combined in a cluster, installation is often faster and easier.
Given these considerations, and faced with a choice between metal or plastic, many engineers and plant managers are opting for the latter: lightweight, high-capacity, reduced-maintenance engineered plastic cooling towers. PH