Cooling towers are especially susceptible to ice formation. Understanding temperature gradients is the first line of defense. A properly designed cooling tower promotes the maximum possible contact between air and water - and does so for the maximum possible time period. This effort on the part of the designer results in an efficiency that, although greatly appreciated in the summertime, has the capability to produce performance-degrading ice formations during winter operation. Therefore, means by which the cooling tower's efficiency either can be controlled or can be made to work toward the management of ice formations must be incorporated into its design, and they must be properly utilized by the operator.
While there are several methods of ice control, this article will closely examine temperature gradients and how they impact ice formation.
As on any outside structure, ice can form on a cooling tower in the wintertime purely by natural effect. In addition, being a device that moves air through water - cooling mainly by evaporation - a cooling tower can promote the formation of ice by its very operation.
Whether caused by nature or by the tower itself, the owner’s concern for an ice formation on a cooling tower should be a reflection of both its location and extent of icing. Ice on exposed working platforms can be a personnel hazard and should be corrected manually. Light random ice on the louvers, structure and the leading edges of fill is usually of minor concern. Ice allowed to form on fans and other mechanical equipment - not to mention the shrouds and control devices associated with that mechanical equipment - can lead to catastrophe.
Generally speaking, an acceptable level of ice formation is characterized by ice with a relatively thin cross-section and that forms on the louvers or air-intake structure of an induced draft tower. Figure 1 shows what might be considered an acceptable amount of ice formed inside the air-intake structure of a counterflow cooling tower, and it also shows a relatively light curtain of ice on the louvers of a crossflow tower. Because this amount of ice normally would be anticipated in a cooling tower’s design loading, it is customarily of little structural concern and. In some cases, its retardation of airflow through the tower achieves a result similar to the airside control procedures. (For more on airside control procedures, see the web exclusive “Airside Control,” posted on www.process-cooling.com.) However, although this ice may still be considered acceptable, it has proceeded to a point where measures that limit or remove it should be undertaken.
Check out the September 15, 2020 edition of Process Cooling: Improving cooling system reliability with filtration, cooling water corrosion control, choosing a water filtration system, new products and much more!