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When people think of water treatment, they think of adding chemicals to the water to change it. That is the internal water treatment option. There is another option in water treatment. Today the R. L. Deppmann Monday Morning Minutes looks at external water treatment for cooling tower systems.
What is External Water Treatment?
External water treatment is the science of reducing or removing contaminants from water from outside the system, often without adding chemicals to the water. There are ways to accomplish this, and we look at three of them today. The three options are filters, ultraviolet light, and electromagnetic fields.
External Treatment: Filters
We don’t want dirt, debris, and biologicals in the cooling tower water. Why not just get rid of them? Strainers, separators, and filters are one way to accomplish this. We introduced strainers and separators in our blogs, Tower/Condenser Water Systems: Side Stream Separator Systems and Hydronic System Dirt Control – Side Stream and Single Pass Methods. These devices eliminate particulate sizes above 60 microns in size. Just for approximate reference, table salt is around 90 microns and a baby’s fine hair is around 60 microns thick. We can still see these. What about things we cannot see?
Filters are used for those unseen contaminants. There are a variety of filter types available. Here are examples of the material and size of filtering.
Sand filters – 30-60 microns; Pleated fiber filters: 10 – 30 microns; DE filters: 1-10 microns; Sub-micron filters: 0.5 – 1 micron.
Legionella bacteria is about 2 microns in size. Once a filter gets to the sub-micron range it can remove bacteria and the food it eats.
External Treatment: Ultraviolet Light (UV)
Ultraviolet light has a single purpose in the cooling tower piping, UV is there to inactivate pathogenic bacteria. These external treatment products can be full flow devices in the main piping system. They may also be installed in a side stream application with other external devices. The two issues with full flow installations are cost and maintenance. The bulbs and sleeves will require cleaning and/or replacement. The tower system will be shut down to change bulbs that are full flow. If the owner is pulling a section of pipe with the bulbs, there may also be pipe alignment issues after the bulbs are replaced.
External Treatment: Electromagnetic Devices
As water temperature increases, the solubility of calcium and magnesium salts will decrease resulting in precipitation onto heat surfaces. Electronic water conditioning devices prevent tree branch-like minerals from adhering to the surface of pipes forming scale. These devices work by creating an electrical charge in the water which attracts mineral ions in the cooling tower water.
The mineral ions change shape and do not attach to the pipe walls where they create low velocity places for biofilm or scale to grow. As more minerals are released, the crystals become larger and continue to stay in suspension. Eventually they are large enough and purged by external filters and tower blowdown.
The electromagnetic external treatment is a type of water softening device. These devices may operate using a continuous charge or electric pulses. They do require a power source.
Save the Water for Future Generations
The chemicals added to cooling tower systems end up being purged to sewers and septic systems. They remain in the water and will affect the quality of the water around us. Using external water treatment will reduce the amount of chemicals used in systems. Good for the owner and good for the world. We will look at products using external water treatment two weeks from now.
Water Solutions Group offers innovative water quality solutions for cooling tower systems.
Water Solutions Group is a separate division of the R.L. Deppmann Company created to provide end users and engineers with a valuable resource in efforts to improve water quality. Proper water quality management protects the equipment, operations, occupants, and environment. Water quality should be considered at the time of design to ensure safe and efficient operating systems. Our intimate knowledge of water systems positions Water Solutions Group to be the ideal partner when evaluating operational issues that may arise because of poor water quality.
