Your cooling tower and heat exchanger are to your cooling system what the lungs and heart are to the human body. If your heart and lungs are not working properly, they affect other parts of the body and your health suffers. Similarly, when your cooling tower and heat exchanger are not clean, the heat exchange process does not work efficiently, and the health of your production and process cooling system suffers.
Process cooling systems that rely on cooling towers to dissipate heat from process cooling water accomplish this by drawing massive volumes of air into the cooling tower as the water travels through the fill material on its way back to the basin. Through the natural evaporative process, heat is dissipated from the water before it reaches the water basin, where it is recirculated through the chiller and heat exchanger and back again.
It is important to realize that cooling towers are gigantic air scrubbers that capture all airborne debris floating nearby. If your cooling tower does not have effective filtration, the debris can clog the tower fill and get circulated and trapped in the heat exchanger. Once in the system, debris can build up and restrict water flow, causing your process equipment to malfunction due to overheating.
The experience of a major automotive assembly facility illustrates this point. The facility had faced periodic downtime due to its robotic welding systems not holding tolerances and causing quality problems. After the robotic technicians spent several days trying to solve the problem, one of the maintenance workers opened the heat exchanger and discovered it was impacted with cottonwood seed, insects and other debris. Due to the debris in the heat exchanger, water flow had been reduced and the robotic equipment was running hot. Filtration equipment had not been installed when the facility was built because ambient conditions did not require it; however, as the area became more developed and cottonwood tree populations grew, the need for filtration eventually surfaced.
Interestingly, even though cleaning the heat exchanger brought the robotic welding system back online and running at peak performance, it did not solve the problem. In this case (as in many heat exchanger fouling situations), the root cause of the problem was the cooling tower. The solution is to prevent debris from getting into the cooling tower, thus protecting the entire process cooling system, including fill, cooling water, chiller and heat exchanger.
Selecting the Right Filtration System
Optimizing the ecology and operational efficiency of your evaporative cooling system is best accomplished by combining a chemical treatment regimen with some type of filtration. These two approaches work together: The chemical treatment specifically targets suspended solids and particulates of 40 micron and less while the filtration system stops larger debris, especially the kind that causes system clogging and fouling.
For cooling tower filtration, there are two general technologies: water-based and air intake filtration systems. With water-based systems, the choices include basic water strainers that remove debris by passing water through a mesh strainer; sand filtration systems that remove debris by passing the water through sand; and centrifugal separators that spin the water and remove debris through centrifugal action. Air intake filter systems remove debris by filtering the air as it is being drawn into the cooling tower. When considering your filtration options, the following questions should be asked:
- What is the cost associated with downtime due to heat exchanger or cooling tower fouling or clogging? Knowing this will help you justify your filtration system cost.
- What type of debris is most problematic? Can you see it or is it microscopic?
- Specifically, what parts of the system does the filter protect?
- How much surface area does the filter provide? This can directly impact frequency of cleaning -- the smaller the filter, the more frequently it may need cleaning.
- Can the system be installed without shutting down the cooling tower? If the cooling tower must be shut down for installation, you need to factor lost productivity in to the cost of your filtration system.
- What is the cost associated with the filter and installation?
- How easy is the system to install and maintain?
Answering the above questions will help you to fully understand your options and to make the best choice for your operation.
The automotive manufacturer mentioned earlier selected an air intake filter system. The company needed a system that would protect its entire process cooling system, including fill material, cooling water, chiller and heat exchanger. When evaluating water-based systems, the company discovered that the options provided varying degrees of protection for the chiller and heat exchanger but did not protect the cooling tower -- where the root of its problem was. If the company had selected a water-based system, its cooling tower still would have drawn airborne debris into both the fill and water where the water filter would have captured the debris before it circulated throughout the system. From a maintenance standpoint, that would have solved the heat exchanger problem but it would have done little to reduce maintenance on the cooling tower.
If you currently are not using a filtration system as part of your process cooling system, then any filtration technology will give you more protection. However, selecting a solution best suited to your operation requires that you know what kind of debris is the problem and where it is getting into the system. As a rule of thumb, do not select a small debris solution to solve a large debris problem. Conversely, do not select a large debris solution to solve a small debris problem. There is a place for both type of filtration, so be sure you are selecting the right filtration for your specific need.
If you are looking to protect only your chiller and heat exchanger from airborne debris, then one of the water-based filtration technologies in combination with a good water treatment program can help you manage the debris that gets into the cooling water. If you are looking for full process cooling system protection, then you should look at air intake filtration.