Cooling tower efficiency can be easily maintained by installing the right filtration system. Keeping process-water clean is essential to maximising the efficiency and performance of an industrial cooling system. Dirty process water clogs cooling tower and other heat exchange equipment, reducing heat transfer efficiency, driving up energy costs and leads to unnecessary water wastage. In addition, unclean water can lead to the growth of microbes such as the deadly Legionella bacteria.
Evaporative cooling towers dissipate unwanted heat through water evaporation. When water evaporates from the tower, dissolved solids (such as calcium, magnesium, chloride and silica) are left behind. As more water evaporates, the concentration of dissolved solids increases. If the concentration reaches a level higher than the saturation point of the cooling tower, the solids cause scale to form within the system, which eventually corrodes the process equipment, leading to reduced system efficiency and the need to replace system parts more frequently. A high concentration of solids can also lead to the growth of microbes, including the Legionella bacteria, which causes Legionnaires’ disease.
To reduce the build-up of dissolved solids, the cooling tower’s process water is flushed out (blow-down) and replaced with fresh water, known as make-up water.
“Blow-down is quantified by cycles of concentration, which is the ratio of the concentration of dissolved solids in the blow-down water compared to the make-up water. It is also approximately equal to the ratio of volume of make-up to blow-down water.” Says Mr Roger Rusch, CEO of Industrial Water Cooling (IWC).
In addition to controlled blow-down, the water is also chemically treated to reduce biological growth as well as reduce corrosion and scale formation. Used alone, these methods can lead to high water wastage and pollution as the treatment chemicals are released into the environment through cooling tower drift loss (small water droplets discharged from the top of the cooling tower).
Full flow and side stream filters are two of the most common filtration systems used in cooling towers. In a full flow system, the filter must be sized in order to handle the system’s design recirculation rate and then installed during cooling tower installation, on the discharge side of the pump. A full flow filter continuously cleans all of the recirculating water. Side stream sand filters are a cheaper alternative to full flow and work by directing water through a bed of graded filter media, usually made up of compounds such as silica, anthracite or garnet. Side stream filters are often the preferred choice for many cooling systems due to the fact that they can be installed on an operational cooling tower and they can be cleaned while the cooling system remains online, avoiding the need for downtime.
Says Rusch, “A side stream filtration system composed of a rapid sand filter or high-efficiency cartridge filter is particularly useful for cooling systems that are subject to dusty atmospheric conditions. These systems draw water from the cooling tower’s sump tank, filter out sediments, and return the clean water to the tower. This enables the system to operate more efficiently using less water and treatment chemicals.”
“With the increasing problems of pollution and water shortages, cooling tower operators must maximise cycles of concentration, which means more water reuse and, therefore, less make-up water. Implementing appropriate filtration systems increases cooling tower operational efficiency, reduces downtime, and helps control biological activity. Furthermore, it considerably reduces labour costs incurred from frequently draining and cleaning sediment from the cooling tower.”
“We provide a variety of filtration and screening equipment including a range of dual and multimedia filters as well as the SATI filtration range, which covers the entire field of normal filtration requirements from 5000µ down to 1µ,” concludes Rusch.
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