Cooling towers use large volumes of water, so having a tower that operates efficiently can mean big savings. The best way to improve efficiency is by keeping all heat transfer surfaces as clean as possible. Reducing suspended solids means less downtime due to maintenance, repairs and shut downs, resulting in improved water quality and energy efficiency. Side stream filtration helps by removing particles from cooling water to aid in this process. In addition, keeping a system clean also reduces the chance of biofilm, microbiological contamination and under deposit corrosion. Generally speaking, bugs don’t like to grow on clean surfaces.  

 

There are several types of side stream filtration systems on the market to fit a variety of applications and requirements. A few common types are sand, multi-media, centrifugal, cartridge/bag, fully automatic self-cleaning screen filters and fully automatic self-cleaning disk filters.  

 

 

Carefully examine the following items to specify the proper side stream filtration system for the system's application.

 

Understanding the specific characteristics of suspended solids in a cooling system is crucial to selecting the best side stream filtration system. The total volume of space that particles occupy can cause significant clogging and fouling of cooling tower systems. Therefore, it is important to determine the total volume of the particle matter that needs to be eliminated when choosing a filtration system. Particle size distribution and total suspended solid (TSS) tests are inexpensive and clearly display population size of the contaminants and each size group’s contribution to the TSS volume. Once the particle size and TSS volume are determined, then it is easier to evaluate which side stream filtration technology will be the most efficient. A properly selected and sized side stream filtration system should be able to eliminate enough solids to reduce clogging and fouling.     

 

 

Properly sizing a side stream filtration system is vital to achieving optimum filter performance. Two main components to think about when choosing the proper filter are flow rate and efficiency. The flow rate should be targeted to achieve a known percentage of the entire recirculation flow rate, depending on how efficiently the chosen technology removes the identified particles in the recirculation water. More efficient technologies require a smaller percentage of the recirculation flow since they capture more particles per gallon. The number of system volume turnovers per day is equally important to properly sizing the side stream filtration for a cooling system. A common guideline is to size the filter to handle a flow rate that turns the system volume over once an hour. A side stream filtration system’s flow rate generally ranges from 3 to 10% (but can be up to 20%) of the total recirculated cooling water flow rate. A side stream filtration percentage of 3% or less of the total circulation flow rate may damage cooling systems, causing fouling throughout the cooling loop because such a small percentage of the system's water volume is properly filtered.   

 

Two common methods are used to install side stream filters. The first method is to install a filtration system off the water flow piping. This method takes a percentage of the water from the pressurized side of the pumps and then delivers the filtered water back to the basin.  Returning the filtered water back into the piping system would require the use of a booster pump or if possible, the piping would be plumbed into the suction side of the pump piping. When a filter is installed off the water supply line and is returned directly back to the basin, additional pumps typically are not required. One thing to consider with this installation is the downstream effect on the cooling capacity since it may affect the flow rate and pressure of the cooling water being sent to the heat source.   

 

The second method is to install the system off the basin/sump of the cooling tower. With this type of installation, the system takes cooling water directly from the tower sump and returns filtered water back to the basin. This installation method requires a dedicated?pump and the associated maintenance requirements which may include downtime, labor, spare parts and additional headaches. Filters work best alongside sump sweeper piping which increases water circulation and agitation in the basin preventing the solids from settling in the sump or basin. Some key benefits of sump sweepers are improved filtration system performance, less equipment cleaning, and helps prevent under deposit corrosion.    

 

 

This blog is a general overview of things to consider when choosing side stream filtration. When considering the options for your system, many factors must be evaluated: particulate loading, space requirements, flow rates, capital cost, installation costs, operational cost, and maintenance. Please be sure to partner with someone with experience so they can help you review all of the pertinent criteria. The goal of side stream filtration is to remove headaches and improve system performance, certainly not to add new headaches and cost to your operations. Following these guidelines and taking the time to choose the proper system will help assure this outcome.  

 

If you want to improve your cooling system efficiency, Watertech can help. Reach out for a free site survey to help determine the best options for your system.    

 

 

Jake is part of Watertech's equipment and applications team. The equipment group focuses on sourcing best-fit equipment solutions to improve water management and efficiency. He has a BS degree from the University of Wisconsin-Milwaukee in Conservation and Environmental Science.

 

Dave Kerr has been part of the Watertech applications team for over 7 years, providing equipment design, build out, and support. He has over 20 years' experience in the water treatment industry.