Cooling Towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or, in the case of closed circuit dry cooling towers, rely solely on air to cool the working fluid to near the dry-bulb air temperature. Common applications include cooling the circulating water used in oil refineries, petrochemical and other chemical plants, thermal power stations and HVAC systems for cooling buildings. Cooling towers vary in size from small roof-top units to very large hyperboloid structures that can be up to 200 metres tall and 100 metres in diameter, or rectangular structures that can be over 40 metres tall and 80 metres long. Although these large towers are very prominent, the vast majority of cooling towers are much smaller, including many units installed on or near buildings to discharge heat from air conditioning.
Cycles of Concentration
Cycles of concentration represents the accumulation of dissolved minerals in the recirculating cooling water. Draw- off (or blow down) is used principally to control the buildup of these minerals. As the cycles of concentration increase, the water may not be able to hold the minerals in solution. When the solubility of these minerals have been exceeded they can precipitate out as mineral solids and cause fouling
and heat exchange problems in the cooling tower or the heat exchangers. The temperatures of the recirculating water, piping and heat exchange surfaces determine if and where minerals will precipitate from the recirculating water. Concentration cycles in the majority of cooling towers usually range from 3 to 7.
Besides treating the circulating cooling water in large industrial cooling tower systems to minimize scaling and fouling, the water should be filtered and also be dosed with biocides and algaecides to prevent growths that could interfere with the continuous flow of the water.. Bio film can be reduced or prevented by using chlorine or other chemicals. Other technologies to control algae and bio film include:
Ultrasonic algae and bio film control: algae by emitting ultrasonic frequencies which can rupture different cell organelles such as the vacuole’s tonoplast, cell wall or membrane and the gas vesicles of blue-green algae. Specific ultrasonic vibrations around a submerged surface can inhibit bacteria from settling and thus forming a bio film.
Chlorine Dioxide Generation Systems: Chlorine dioxide is effective in the control of microbiological growths in industrial cooling waters under conditions unfavorable to chlorine. For closed loop evaporative towers, corrosion inhibitors may be used, but caution should be taken to meet local environmental regulations as some inhibitors use chromates. and creeks.