By Ed Sullivan
Natural gas engines replaced diesel-powered generators years ago at the world-famous Bronx Zoo in New York City. High-density polyethylene (HDPE) cooling towers were installed at the time and have proven to be less expensive to maintain than metal-clad designs.—Nancy Spring
In many ways, the Bronx Zoo stands in stark contrast to its home in one of the most famous metropolitan areas in the world, New York City. The zoo has always had the task of “wowing” city dwellers with an up-close look at exotic animal life. Over the years, the zoo has also taken steps to operate in the “green” with improvements that promised cleaner operation while saving on maintenance costs.
 Factory-assembled plastic towers to suit almost any size requirements up to 2,000 cooling tons can be built in a single, modularized unit. |
One major step was taken years ago with the purchase of new cooling towers. When the power station upgraded to natural gas engines to avoid the corrosive and acidic vapors that resulted from the sulfur content in its diesel-powered generators, two advanced Delta high-density polyethylene (HDPE) cooling towers were installed to draw heat off the intercooler water system.
Four Superior natural gas engines ranging from 665 kW to 1,660 kW provide energy to the 265-acre park and today—after more than 14 years—the cooling towers that chill the intercooler for the natural gas engines are still running strong and saving substantial amounts on maintenance and manpower.
Plastic or Metal-Clad?
Virtually impervious to corrosion, the plastic cooling tower was developed by Rockaway, N.J.-based Delta Cooling Towers in the early 1970s. Evidence of the durability and leak-free properties of HDPE can be seen in the long life of the zoo’s power station’s cooling towers.
Metal-clad designs often require re-cladding and re-painting of the galvanized shells as well as other maintenance operations such as cleaning and replenishment of water treatment chemicals, which can be labor-intensive. 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, while a low pH of a liquid coolant can cause the veneer of zinc galvanizing used on most metal towers 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 with coatings. Cavities and other damage that may have occurred have to be repaired.
Many manufacturers with metal cooling towers use solvents to prevent scale from occurring in their process fluids. These chemicals sometimes leak into the cooling system and 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.
Composed of material that is impervious to harsh pH environments that affect metal cooling towers, engineered plastic cooling towers are energy efficient, available in a wide array of capacities and air flows and will operate with both process and energy efficiency for many years.
In the past, plastic cooling towers were too small for many industrial processes. Until recently, galvanized metal cooling towers were the best option for most applications above 250 tons and processors requiring high-capacity cooling built custom-designed towers on site. Today, that situation has changed. Delta, for example, has introduced factory-assembled plastic towers to suit almost any size requirements up to 2,000 cooling tons in a single, modularized unit.
One of the latest environmental upgrading and restoration projects at the Bronx Zoo also takes advantage of the benefits of HDPE. HDPE piping systems have been integrated into the system and are 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.
Author: Ed Sullivan is a technology writer based in Hermosa Beach, Calif.