While evaporative towers are simple and very efficient machines, on the other hand they require some particular cares and maintenance attentions. This is especially related to the water treatment and the chemical additions to the water employed by the tower, which otherwise can easily lead to dirt deposition and the formation of biological scaling. In case of open circuit tower, the water is indeed in direct contact with the sunlight and the ambient air, fostering contamination and the growth of mold, algae and mucilage.
In order to avoid the problem it’s sufficient to implement a properly sized dosing system of chemicals. These products include anti-scaling, dispersion products (ensuring carbonates and salts to remain suspended within water) and algicides. Biocides and algicides prevent the formation of algae and mucilage in presence of light exposition and heat.
In addition, due to the natural water consumption that an evaporative tower involves, the water losses must be refilled. But this is not enough, because the loss of water lead to a higher concentration of salts and carbonates within the remaining water, thus requiring the presence of a purge system. The increase of salts and carbonates causes indeed scaling and fouling that reduce the flowing section of pipes for the water, lowering the thermal transfer coefficient.
Furthermore, not only the tower, but also condensers of the chillers and heat exchangers at the bottom of the process and served by the tower are impacted. The deposition of carbonates also causes an important decrease of their performances. Two purge options are then available: a continuous purge solution of an automated purge system equipped with a conductivity probe, aimed to measure the salts concentration within the water in the tower. The amount of the purged water must be comprised between 0,3% and 4% of the overall circulating water, based on the water hardness.
A correct maintenance of an evaporative tower then requires a periodical hygienization and washing of the tower, and also a legionella bacteria checking, with a water lab-analysis, and the control-application of a dosing and automatic purge system.
In short, an ideal water treatment system in a cooling tower should include:
In case of high hardness levels of the water, the integration of a water softener is also recommended.
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