The largest cost driver of factory assembled cooling towers is the primary material that forms the casing of the cooling tower. This material not only contains the water being recirculated through the cooling tower but also must structurally support a mechanical fan system, internal components and water weight, including a sump full of water. Generally, there has been a trade-off between the long-term durability achieved through the choice of materials of construction and overall cooling tower cost.
Though least expensive, galvanized metal cooling towers are the
most susceptible to corrosion and, therefore can have a shorter life than stainless
steel towers. Galvanizing of steel will delay the corrosion of the underlying steel
because it corrodes preferentially to the steel. However, once a section or sliver
of the zinc galvanizing has become compromised, the steel sheet metal underneath
can corrode quickly.
One alternative is a hybrid cooling tower, which consists of a
stainless steel sump or basin and galvanized metal on the upper walls. This typically
provides better durability than all-galvanized construction and is typically
less expensive than an all stainless steel cooling tower.
Fiber-reinforced polyester (FRP) has been used as a cooling tower
casing material for some time. Pultruded FRP, when made heavy enough, can handle
cooling tower loads and provide good corrosion protection. Good quality FRP towers,
however, can be nearly as expensive as stainless steel towers.
Alternately, a line of unitarily molded corrosion-proof engineered
plastic (HDPE) cooling towers has been introduced. It seeks to eliminate the
need to trade off between durability (as measured by corrosion resistance) and cost.
Good corrosion protection is achieved at costs comparable with lesser corrosion-protected
cooling towers. The line is molded in an engineered plastic that forms a casing
without joints or seams.
Why Cooling Tower Materials of Construction Matter
October 1, 2011