Cooling Tower Side Stream Filtration Implementation

When considering a side stream filtration system, there are several key parameters that are important to weigh including the level of particle removal, filtration sizing, installation methods, and cost and water savings potential. Carefully examine the following features to properly specify the proper side stream filtration system for the appropriate application:

Particle removal analysis: Understanding the specific characteristics of suspended solids in the cooling water is crucial to selecting the most appropriate type of side stream filtration system. The total volume of space that particles occupy can cause significant clogging and fouling of cooling tower systems. Therefore, the total volume of the particle matter that needs to be eliminated must be determined when choosing a filtration system. Particle size distribution and total suspended solid (TSS) tests are inexpensive and clearly indicate the population size of the contaminants and each size group’s contribution to the TSS volume. Once the particle size and TSS volume are determined, the side stream filtration technologies’ efficiency at removing different sized particles and targeted total particle volume removal can be evaluated. A properly selected and sized side stream filtration system should be able to eliminate enough solids to reduce clogging and fouling.

Filtration sizing: Properly sizing a side stream filtration system is critical to achieving optimum filter performance. Flow rate and filtration efficiency are major factors in sizing a filter. The flow rate should be targeted to achieve a certain 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 has been shown to damage cooling systems, causing fouling throughout the cooling loop.

Installation methods: Two common methods are used to install side stream filters in cooling systems. One method is to install a filtration system on a tap off the water flow line. The installation on a tap off the water flow line takes a percentage of the flow downstream of the pumps and then delivers the filtered water back to the basin or back to the full flow stream with the aid of a booster pump. When a filter is tapped on the water supply line and filtered water is returned to the basin, additional pumps are not required. A major consideration with this installation is the downstream effect on the cooling capacity since it may affect the flow rate pressure of cooling water 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 suction from the tower sump and returns treated water back to the basin. This installation method requires a dedicated include downtime, labor, lost water, and additional chemicals. Therefore, these operational and maintenance savings including water, labor and water treatment savings should be estimated and accounted in the financial analysis.

 


Aldo Zaffalon
Aldo Zaffalon

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