How often do you think about your cooling tower or the fill that provides the cooling engine for your process? Unfortunately, if you’re like many plant operators, your cooling tower is but one piece of equipment in your large facility, and its ranking on your priority list is probably lower than many other expensive and more intricate pieces of equipment in your plant.
One of the challenges this lack of priority can yield is a lack of in-depth knowledge for a critical piece of the puzzle: the cooling tower. Just how critical it is becomes evident in the summer months, during the hottest days of the year, when production must be unexpectedly scaled back because the return cooling water from the cooling tower is so high it’s negatively impacting plant efficiency.
Whether you have an existing cooling tower that needs some work done, or you’re looking to purchase a new cooling tower to meet a plant capacity expansion, one of the choices you’ll have is the fill around which the cooling tower is built. Choosing the right fill for your process and installation is an important decision since it can impact your plant’s operation for years to come.
How Fills Work
Before discussing fills it’s important to understand the basic function of a cooling tower. In general, cooling towers are fairly simple devices. The goal is to take water heated by your plant’s process and cool it down, removing the same quantity of heat that your process added to it so that you can re-use the water in a recirculating loop.
The cooling tower is essentially just a box built to contain the water to be cooled. Because the water is cooled via the evaporative heat and mass transfer of water, the box has components that enhance that mechanism, such as air-moving equipment and components that improve the interactions of air and water, namely “fill.”
There are many types of fills available to cooling tower repair/rebuild and manufacturing companies. Some basic examples are splash fills and film fills.
- Splash fills derive their name via the mode of cooling they provide: water splashes on fill surfaces, which increases the air/water contact.
- Film fills are so named because of the water film that forms on the surfaces of the fill. The generation of this very thin film of water on the fill’s surface provides a very high amount of surface area for air/water contact, and as a result, film fills can offer the most amount of cooling for a given volume amount. Since film fills came into existence in the 1960s, fill manufacturers have developed a wide variety of different fill types and designs to address different water quality challenges that plant operators face.
Water Quality a Key Factor in Fill Choices
Due to the potential large volume of material, fill can be a substantial purchase. However, choosing the wrong fill can have an even greater impact on your bottom line due to reduced efficiencies and lost production on a day-to-day basis, and a need to replace fill many years sooner than expected. The key to choosing the right fill for your plant lies in your water quality, matching that water quality with a fill design that is appropriate, and utilizing a companion water treatment program that complements both.
There are three main factors that are evaluated when looking at choice of fill: Total Suspended Solids (TSS), Biological Activity/Control (via Total Aerobic Bacteria [TAB] plate counts), and Oil/Grease content in the circulating water. These can also be supplemented by calcium, magnesium, and silica evaluations related to the scaling potential of the water; ammonia, sulfide, and nitrate evaluations related to the nutrients available to promote biogrowth; and information on the process being cooled, make-up water source, and circulating water cycles of concentration.
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