Paralyzing and pricey problems like excessive downtime, destruction of downstream equipment and loss of product quality may result from cooling capability losses in industrial cooling towers.
Think of cooling towers like an automobile: When a car is continuously run “in the red,” it likely will experience a series of heat-related problems, including damaged gaskets and seals, premature cylinder wear, warped cylinder heads and even catastrophic engine damage. Similarly, when a cooling tower suffers from a lack of preventive maintenance, the owner can expect severe operational consequences such as overheated equipment, increased scrap material, refrigeration losses and heat exchanger inefficiencies.
It is important to prevent these losses from occurring because cooling towers play a critical role in most process industries, including pulp and paper production, petrochemical processing, plastics, metals and textiles manufacturing, as well as food, beverage and pharmaceutical processing.
Inadequate cooling tower preventive maintenance can cause system fatigue, which in turn can put a strain on system equipment and downstream processes, no matter what the application. Remember that water cooling towers provide cooling to downstream devices such as heat exchangers, production machinery or HVAC systems, and a fatigued or poorly performing tower will make the downstream equipment also less able to remove heat. For example, the “cold side” of a heat exchanger will receive water that is not as cool as it should be. As a result, the heat exchanger will be less able to remove heat from process fluids.
Regardless of the application, the cost of overlooking the maintenance of a cooling tower can be high. In the pulp and paper industry, for example, a process interruption for unscheduled service can run into hundreds of thousands of dollars. The same thing can occur in the chemical or other process industries. If equipment is not sufficiently cooled, maintenance technicians will be repairing and replacing hardware with such frequency that there will be a detectable loss of production and significant loss of capital equipment.
In addition, the impact of neglect will be amplified in applications where there are cooling towers with many downstream devices and operations relying upon them. For example, in the injection molding industry, there are always concerns about cooling tower-related downtime, plus the loss of machinery. If the cooling tower is not cooling enough, causing a series of injection-molding machines to overheat, the expensive molding equipment will, at the very least, produce scrap or, at the worst, lock up like a seized engine. It could takes weeks to replace the equipment, if necessary, and certainly days to clean it up if no catastrophic damage has occurred.
In the food industry, where a cooling tower supports critical food processing machinery, the HVAC system, and refrigerators and freezers, the loss of even part of the cooling power can cause extensive losses of frozen products, produce or other perishable products.
Both Routine and PreventiveJust as with automobiles, routine and preventive maintenance of cooling towers is necessary to avoid such costly scenarios. Some of the most the common preventive maintenance tasks include the following.
Preventing Fouled Fill Material. One of the most important services involves fill material and wet decking. These cooling tower components should be checked frequently and serviced or replaced as needed. Fouled fill material will not allow sufficient air volume, preventing efficient dissipation of heat, which will result in significantly higher energy costs because the fans and motors will have to work harder.
Cleaning Fouled Wet Decking. Another related problem results downstream when water runs through fouled cooling tower wet decking. When this occurs, the necessary dissipation of heat will not be achieved, and the water flowing down to the tower sump will not be cold enough for the processing equipment. For this reason, ventilation louvers should be washed down along with the wet decking, which facilitates the cooling evaporation process.
Preventing Unnecessary Water Loss. Drift eliminators also should be checked to prevent unnecessary water loss. Plus, any repairs such as patching, welding or cleaning of cooling tower sheeting should be done as required.
Scale Removal. Because cooling towers cool water through heat transfer and evaporation, scaling is a common and expensive issue. With a loss of one percent water for every 10°F of cooling required, the evaporation factor can be significant - 20 or 30 gallons per minute is not uncommon for small towers. When evaporation occurs, scale is left behind, which can interfere with cooling tower efficiency and require expensive maintenance or acid cleaning. If corrosion is a problem, replacement with a plastic cooling tower can be considered because plastic cooling towers are impervious to residual salts. The plastic towers cannot be damaged by the salts or caustics and the fill material can be cleaned with aggressive descalers. Metal towers can be irreparably harmed by descalers, potentially leading to premature tower rebuilds or replacement.
While there are other routine and preventive maintenance tasks that should be tackled on a regular basis, depending on the application, frequency of use and age of the cooling tower, finding time and capital to fit these common activities into all maintenance programs will go a long way toward preventing cooling tower fatigue and the resultant process, productivity and capital losses that will surely result if maintenance is neglected.