High-density polyethylene cooling towers have eliminated corrosion at the Bronx Zoo. (Photo courtesy of Suzanne Bolduc ©WCS.)

In many ways, the Bronx Zoo stands in stark contrast to its home in the most famous metropolitan area in the world, New York City.

Began in 1895 with the establishment of the New York Zoological Society (today its known as the Wildlife Conservation Society) it has always had the task of “wowing” city dwellers with an up-close look at exotic animal life.

Now the zoo is taking steps to operate in the green with improvements that promise cleaner operation while saving maintenance costs. One major step was taken years ago with purchase of new cooling towers.

Today, after more than 14 years, the cooling towers, which chill the intercooler for the natural gas engines at the power generation station, are still running strong and saving substantial costs on maintenance and manpower 12 months a year.

Installed when the zoo switched over to natural gas engines to avoid the corrosive and acidic vapors that resulted from the sulfur content in its earlier diesel-powered generators, the high-density polyethylene (HDPE) cooling towers became part of the zoo’s first steps into a green program.

Piping and Towers and Bears, Oh My!

When the power station upgraded to natural gas engines, two advanced Delta cooling towers were also installed to draw heat off the intercooler water system. Four Superior natural gas engines ranging from 665 kW to 1,660 kW now provide energy to the 265-acre park - with much cleaner emissions.

One of the main elements of the latest environmental upgrading and restoration projects at the park is the integration of HDPE piping systems. Used for piping fresh and marine water to various sites, HDPE was specified because of its wide acceptance by the water industry for its maintenance-free operation.

Strong evidence of the leak-free and durability properties of HDPE can be seen in the long life of the power station’s cooling towers. Similar metal-clad designs often require frequent re-cladding and re-painting of galvanized shells as well as other labor-intensive maintenance such as cleaning and replenishment of water treatment chemicals.

“By eliminating the corrosion effects on our cooling towers we are virtually eliminating the need for repetitive routine service,” says Mike Henry, manager of technical services at the power generation station. “That means saving money on maintenance costs for relining and other repairs, plus labor. So, there is much less downtime involved, including repairs and cleaning. We don’t need to upkeep the painting and also have lower chemical costs.

Standing Up To Time

Virtually impervious to corrosion, the plastic cooling tower was developed by Delta Cooling Towers (Rockaway, NJ) in the early 1970s. They are becoming increasingly popular throughout industries where coolant temperature ranges are critical to processes.

The nemesis of conventional 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 (e.g., atmospheric) elements or infiltration of process elements (e.g., material fines), the veneer of zinc galvanizing used on most metal towers immediately begins to deteriorate. A pH lower than four will destroy this protective lining in a matter of months.

At that point, contractors are required to replace the zinc galvanizing with expensive coatings and repair any cavities and other damage that may have occurred. 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 their process fluids. Such chemicals sometimes leak into the cooling system and they corrode the cooling towers. Solvents may also 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 expensive repairs or even replacement.

Composed of material that is literally impervious to the harsh pH environments that devastate metal cooling towers, engineered plastic cooling towers are energy efficient, available in a wide array of capacities and airflows, and will operate with both process and energy efficiency for many years.

Because the engineered plastic cooling towers are impervious to the harsh environmental elements and cleaning agents that cause so many metal towers to fail early, they carry a much longer factory warranty, up to 15 years.

For the Bronx Zoo, this is just a beginning in what will be an even greener future. ES