Optimizing Cooling Systems: Strategies for Reliable Performance

A higher-efficiency axial flow fan can boost production output and reduce electrical equipment energy costs by lowering the amp draws of components, such as electric motors. This advantage applies to both cooling towers and ACHEs. During the construction of these plants, whether a week or two decades ago, most original equipment manufacturers (OEMs) typically try to install the cheapest fan option they can get their hands on to maximize profit margins. Upgrading to a more suitable fan, such as one with fiberglass-reinforced polymer (FRP) blades (Figure 1), can increase flow rates by 15% to 30% compared to the old aluminum blades. 

While FRPs are more expensive than metal blades, the upgrade can enable a facility to increase production output and reduce motor amp draws, which lowers electricity costs.

Weathering the Extremes: Basic Maintenance

Cooling towers can be two or three stories high, and ACHEs are sometimes positioned at the very top of these plants. This lack of visibility can lead to neglect and improper maintenance, especially when high flow rates are needed—such as in the summer months. Consequently, catastrophic failure could ensue, and production rates could drop, causing emergency maintenance.

The “summer” experience can vary greatly depending on a facility’s location. For example, along the Texas and Louisiana Gulf Coast, we have summer, and we have August—a typically miserable month with extreme heat. While humidity does not significantly affect cooling capacity, achieving 100% flow rates in the summer is critical. Temperatures can exceed 100°, thwarting the maximum production rate. This underscores the importance of proper year-round maintenance, as there is no time for preventive maintenance (PM) in the summer, when the plant must operate continuously to manufacture its chemical or polymer products. 

In northern latitudes, the cold winter months provide a window of opportunity for maintenance, as the cooling tower fan is not running 100% of the time. Maintenance teams in these regions should take advantage of scheduled downtime and plan accordingly.

Unexpected events can cause big problems. About four years ago, Texas experienced the hardest freeze ever, which extended into parts of western Louisiana. Such extreme weather events are a huge challenge because the infrastructure in this region is not equipped to withstand freezing conditions. Consequently, the plants had to do a hard shutdown, leading to severe operational issues.

Preparation is vital for those unexpected extreme temperatures. If severe weather is anticipated, properly bring down your equipment so it will be easier to start back up. Winterize your equipment when cold weather is forecasted—use insulation to protect against freezing temperatures.

In certain situations, 100% flow isn’t necessary, so adjustments on the electrical side can be beneficial. A variable frequency drive (VFD) on these components can lower the amp draw  on the motor and consume less electricity, thus reducing costs.

The impact on cooling capacity occurs as soon as you hit the “on” button, starting the power draw. Proper maintenance of cooling tower gearboxes is crucial, as they are located in the center of shrouds and inaccessible without shutting down the system. One unique aspect of these gearboxes is that the output shaft sticks up because the fan sits there. Gearboxes are typically heavy duty and must be appropriately lubricated to ensure smooth operation and mitigate unexpected failures.

Fiberglass-reinforced polymer blades typically have a 15- to 20-year lifespan, but it is easy to overlook their maintenance. If the blades start to fray or deteriorate (Figure 2), it can lead to loss of flow and reduce system performance. FRP blades need to be inspected annually. When you see fraying start, it is time to replace that blade.

Another essential task is properly maintaining the clearance tip on the blade’s leading edge to the shroud (Figure 3). Try to minimize that gap, as shrouds can become slightly oblong over time rather than remaining perfectly round. Those larger gaps can cause the heat you’re trying to dissipate to be reintroduced back into the fan assembly, which defeats the entire purpose of a cooling tower or ACHE.

Smaller in diameter, ACHEs are somewhat easier to maintain than larger cooling systems, but proper tip clearance on the shroud remains important. Small but effective adjustments, such as installing an inlet bell at the air inflow point, can increase efficiency by 2% to 3%.

Preventive maintenance schedules are typically established by each plant to ensure optimal equipment efficiency. Inspection frequencies can vary, with some plants conducting them monthly and others annually. It is critical to follow the schedules—stick to what is written in your PM plans.

Clear the Clogs, Clean the Systems

The simple yet essential task of cleaning the ACHEs, especially the bundles where the product passes through, is crucial over time—especially on the Gulf Coast. These components are prone to clogging and rust. Without proper cleaning, the bundles will eventually become so blocked that replacement is necessary.

Cleaning can be done chemically, but ensure the workers wear protective slicker suits. The process involves containing the chemicals, which is fairly inefficient. Alternatively, a dry blast is now recommended. This soda blast is basically a baking powder used to clean the bundles while the equipment is running, offering a less intrusive yet effective way to maintain cleanliness. 

The petrochemical industry competes globally, regardless of a company’s world headquarters location. Over the past decade, this industry has experienced a growth explosion of new plants and expansions. These plants can optimize that growth by properly maintaining their cooling towers and ACHEs with informed fan choices and thoughtful, scheduled PMs. Gather your team or engage a qualified third party to develop a smart strategy for successful operation. You will be glad you did. ⊕