Side Stream Filters

---

Cooling towers, by design, are the world’s finest air scrubbers. As part of the cooling method, they flush airborne contaminates into the system, where they deposit on heat exchange and condenser surfaces. Suspended matter in the cooling water also supplies living microorganisms with a constant food source for sustaining life and multiplying.

A permanent medium filtration system can remove these contaminants before they increase the cost of operating the water-cooled equipment or shut the system down. And, combined with chemicals, constant side-stream filtration will result in a much cleaner system, with the chemicals providing a constant suppression of microorganism growth.

Cooling water system treatment programs must include the following four specific parameters of control for successful equipment protection: Scale, Corrosion, Biological fouling, and Airborne contaminants. Airborne dirt affects scale control, corrosion and biofouling, and is the only one that cannot be measured. No one knows which way the wind will blow and what it will pick up in its travels and deposit into the system.

With side-stream filtration, a portion of the water filters continuously. The whole system is filtered every 24 hour. Side-stream filtration works on the principle that continuous particles removal will keep the system clean. The filtration goal is to remove the fine dirt, dust, smoke and organic particles that collect in water.

The most effective filter system for cooling towers and process water is a permanent medium unit, one that requires very little attention or maintenance. The medium must be finer than 50 microns to trap the average airborne contaminant. Things to look for in filter systems are: self cleaning, simplicity, compactness and ease of operation. Also important are screens with pore sized down to 15 microns, providing consistent filtration and a short manual/automatic backflush cycle.

Typically, a side-stream representing about 3-20% of the total recirculated flow is adequate for sizing purposes. For example, a 6000 m3/hr circulation rate require 180 m3/hr side stream filter. Sizing the filter to handle flows is sufficient for cleaning the entire capacity of the tower once in every 24 hour.

In summary, when you add up all the benefits, permanent side stream filtration with chemicals pays for itself in less than two years. No water-cooled system, especially cooling towers, should operate without a filter/Chemicals combination.