Fig. 1. Traditional metal-clad cooling tower showing corrosion and location of internal fan failure breaking through side wall of tower.
Yet advancements in the manufacture and design of today's engineered-plastic towers have initiated a change in the status of the cooling tower from that of a valuable support tool to one of a productivity booster that can save costs.
Because plastic cooling towers are noncorroding, offer increased cooling capacity, are lightweight, require no coatings, offer direct-drive fan systems, are immune to ambient weather conditions and are essentially leakproof, they are quickly currying favor with plant engineers who had previously been limited to metal cooling towers.
Fig. 2. Fluctuating pH in cooling systems caused corrosion resulting in development of the engineered-plastic cooling tower.
Increased Reliability and Reduced Maintenance Results in Increased Uptime
Cooling towers that are overworked, out of service, or require periodic rebuilding or replacement can exact a severe toll in terms of lost production, labor and materials. Hence, the focus of any metal-manufacturing plant engineer is to ensure that when time comes to retrofit or expand, reliability and lack of downtime ranks first in the selection of cooling-tower structures. Other factors include reduced maintenance, easy installation and lowered costs.Toward addressing these concerns, cooling towers have evolved significantly from the simple heat exchangers of the 1890s. Yet, only in recent years has the design of industrial cooling towers been fast-forwarded to prevent the need for expen-sive upkeep, repair and replacement.
The most significant advancement has come with the availability of the corrosion-proof polyethylene-plastic cooling tower that will not rust, chip, flake or peel – unlike metal. Nor does engineered plastic require the application and periodic reapplica-tion of paint or other protective coatings. High-density polyethylene also stands up better to harsh chemicals that eventually prove fatal to galvanized towers.
New-generation plastic towers are not only leakproof and impervious to weather and chemicals, but they are now more applicable to the majority of industrial applications because of recently expanded cooling capacities that reach and exceed 2,000 tons. These gargantuan capacities are made possible by a new modular-construction design where a group of smaller towers can be combined into one massive cooling unit.
The inherent and design advantages of the latest engineered-plastic cooling towers also provide easier installation (especially on rooftops) because a lightweight plastic shell weighs as much as 40% less than a steel tower. Additionally, the induced-draft, counter-flow design seen in some engineered-plastic towers provides improved cooling efficiency for the size, allowing a smaller footprint to fit where there are locating constraints. 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.
In conjunction with vastly enlarged capacities and improved structures, some plastic-tower manufacturers have broken new ground by offering simpler cooling systems in the form of direct-drive fan systems that require minimal maintenance because of less moving parts – no gear reducers, couplings, additional shafts or extra bearings – furthering the goal of maintaining “up-time” within the plant.
Fig. 3. Another plastic cooling tower configuration
Increased Productivity for Aluminum Extrusion
In the capital-intensive and fiercely competitive aluminum-extrusion industry, the reliability of cooling towers is critical to maintaining sufficiently cool oil for the hydraulic presses to continue operating safely and accurately. Hot ambient temperatures, such as the 85°F average weather found in Puerto Rico, can exacerbate this challenge.“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 mean lost production, but it would push orders back and delay shipments. It’s a domino effect.”
To meet these challenges, Aluminio del Caribe consulted with various industry representatives. Based on a compelling maintenance-free design – warranted 15 years – they installed a 200-ton plastic cooling tower from Delta Cooling Towers in January 2001. A second plastic tower was installed when a subsequent press became operational in April 2002.
“We only 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 the cool water to the oil filter at each press location, but that was also relatively easy.”
The reliability of the engineered-plastic cooling towers at Aluminio del Caribe has translated directly into ensured productivity.
“The basic improvements you get with a cooling tower like that are that you get cold water so that I can keep going all day long,” explains Bas. “That means I can keep my production rate up. I can schedule orders without worrying about whether the press is going to overheat. The temperature never goes over 120-125°F.”
Saving on Energy Usage in Metal Extrusion Operations
In some cases an engineered-plastic cooling tower allows industrial users to completely revamp the technologies supporting their cooling systems, achieving greater productivity and savings in the process.“The molded-plastic cooling tower is the only way for us to go, as I was able to eliminate double cooling – which was the case when we had metal cooling towers cooling down chillers for the process water,” says Doug Henderson, project engineer for Cerro Wire & Cable in Hartselle, Ala. “We switched over to plastic cooling towers and they give us enough cold water that we can do the job without any problems and don’t waste the energy.”
Today Cerro Wire & Cable uses four 200-ton Delta cooling towers for four different process areas. Three go through heat exchangers to cool process water, while the fourth cools an open loop that runs through water troughs to cool wire as it is encased with plastic. IH
For more information:Delta Cooling Towers, Inc., 41 Pine Street, Rockaway, NJ 07866; Phone (800) 289.3358; Fax 973.586.2243; E-mail: sales@deltacooling.com; or visit the web site: www.deltacooling.com
Additional related information may be found by searching for these (and other) key words/terms via BNP Media SEARCH at www.industrialheating.com: shim stock, carburize, oxygen probe, IR spe cooling tower, aluminum extrusion, corrosion, heat exchanger
SIDEBAR: A Cleaner, More Efficient Quenching System for Brass Manufacturing
“The decision was to replace our galvanized-steel cooling towers with the newer molded-plastic cooling tower design,” explains Matt Niemeyer, staff engineer for the brass division of Olin in East Alton, Ill. “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.
“We converted to a Delta cooling tower to overcome the inefficient, open-loop system that had collapsed the fill under the weight of dirt and scale in the water,” said Niemeyer. “The closed-loop, clean-water system made it possible to go with the different cooling tower design. Instead of having a splash-bar fill, which is about the best you can do for dirty water, we were able to go with a PVC-film fill. That also allowed us to change from a crossflow tower to a counterflow tower, which gives us greater cooling capacity for its size. We had a limited footprint for the tower, so that has worked out great.”
“The new plastic tower is corrosion proof, and so we don’t have to worry about rust,” Niemeyer adds. “It was also the most economical price, and we were very pleased about that.”