Processing Magazine

Plastic Cooling Tower Six-Packs Address Issue of Cooling Capacity

February 24, 2010
Plastic cooling towers – now available in 2, 4 and 6 “packs” - meet the high capacity cooling requirements of the manufacturing, petrochemical, pulp & paper, plastics and metalworking industries.

For many years, modular plastic cooling towers have suffered from a virtual Napoleon complex – overcompensating for its smaller cooling capacity by providing leak-free, rust-free, highly efficient operation with low maintenance requirements, minimal use of consumables, and unheard-of 15-year factory warranties on some models.

But molded plastic cooling towers are no longer the small kid on the block. Previously limited to smaller cooling applications in the 250 cooling ton range, these molded plastic cooling towers are now available as integrated, multi-cell 2, 4 and 6 “packs” that work as a single system and can provide cooling capacities from 500 to 2,000 cooling tons.

This is welcome news for many broad based manufacturing industries including petrochemical, pulp & paper, plastics, chemical, metalworking and many other industries that previously had to rely on less durable metal cooling tower construction as its only option.

“The evolution of the classic molded plastic cooling tower into the modular system offers a very attractive solution for many industries that need higher cooling capacities for larger, more demanding applications,” says John Flaherty, president of Delta Cooling Towers (Rockaway, NJ).

“These modular systems, available in arrays of 2, 4 and 6 cells, offer a scalable, cost-saving alternative to traditional welded, riveted or gasketed metal towers for manufacturing, petrochemical, pulp & paper, metalworking, and other industries, as well as many commercial and institutional facilities,” he explains.

The key to increased cooling capacity is its configuration. Manufactured and assembled at the factory, modular cells interlock as a single system. Each cell includes an independent seamless basin, but all cells are “equalized” by plumbing connections that keep the overall water level balanced.

Although they often work together to cool a specific application, the modular cells can be split so that they handle more than one function. For example, a 6-pack can be configured so that four cells handle process cooling while two units handle HVAC support. Because of this flexibility, they can also be shut off when not needed. For instance, those cells that are used for HVAC support can be shut off during colder winter months.

Best of all, they offer all the advantages of the seamless plastic cooling towers that were innovated by Delta Cooling Towers in the 1970s, including much longer life cycles, minimal maintenance, vastly reduced risk of costly downtime and substantial savings on water treatment chemicals.

Seamless vs. Panels
Paneled linings (fills) are the bane of many cooling towers applications. In the classic metal-clad designs, galvanized panels of sheet metal are welded together to form a water-tight vessel. However, the impending corrosion of welded seams due to water treatment chemicals and environmental factors can rapidly lead to leakage and other operational problems. Even stainless steel basin welds routinely fail, due to under deposit corrosion or water chemistry fluctuations.

Cooling tower leakage is particularly disruptive, requiring not only extensive tower repair maintenance and replacement, but also the rebuilding of damaged tower decking and supports as well as roofing and other plant structural members.

For an increasing number of applications, the ideal solution for avoiding all those maintenance, replacement and downtime costs is the seamless molded plastic cooling tower. This design features a seamless, molded shell composed of engineered plastic, rather than individual panels that have to be fitted and welded or sealed with gaskets.

Although other plastic cooling towers have been available for some time, most of those are also composed of many individual PVC or fiberglass panels. However, while impervious to the corrosion that plagues metal linings, leakage is still a problem because plastic panels are joined with gaskets or seals that are subject to the stresses of expansion and contraction that occur with temperature changes caused by weather or process water.

Unlike cooling towers fabricated of individual panels, seamless plastic models are factory assembled. This eliminates the need to hire and transport construction crews to construct towers in the field.

“This can make a major difference in installation costs as well as downtime,” explains John Flaherty. “Factory-assembled plastic cooling towers are virtually a drop-in installation, requiring only hours to install rather than days or even weeks. So, the savings on labor, transportation and process downtime can be very significant.”

More Economical Operation
Cooling towers of seamless engineered plastic can also reduce the expenses of operating costs, which include: electric power usage, water-treatment chemicals, labor and materials for maintenance, and unscheduled process downtime for cooling repairs.

Maintenance and repairs usually means process interruptions, the costliest issue associated with cooling towers. Given their short lifespan, metal-lined models inevitably invite such interruptions in operations, while corrosion-proof plastic cooling towers are more likely to provide continuous and reliable operation.

For instance, the “white rust” that forms on galvanized towers operating at pH higher than 8.0 can quickly lead to failure and replacement requirement. On the other hand, the use of engineered plastic allows the use of better scale inhibitors that operate at higher pH.

Virtually impervious to pH levels and mineral deposits, 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. Conceivably reducing bleed-off by 50% would also allow a 50% reduction of chemicals for scale and corrosion control for process equipment downstream from a conventional metal-clad cooling tower. In many applications this chemical savings can exceed $10,000 per year.

The use of more efficient direct-drive motors also improves both reliability and operating efficiencies of cooling tower fans and can result in substantial power savings throughout the year. Not to mention, the costly downtime and disruption that is caused due to belt replacement or failure in a belt driven fan cooling tower.

Ease of Installation
One of the difficulties associated with cooling tower installation or replacement is the need to support heavy loads. Delta Cooling Towers solved this problem with its TM Series, a modular, lightweight design that includes a self-supporting base with I-beam pockets, enabling users to install up to six cooling tower modules on a simple I-Beam support structure utilizing a relatively small footprint.

Featuring a more attractive, less “industrial” appearance, the smaller footprint of these modular cooling towers may be an ancillary benefit for commercial applications such as shopping centers, schools, hospitals and office buildings.

—By Ed Sullivan
Ed Sullivan is a technology writer based in Hermosa Beach, California