“Cooling Towers have their own unique microbiological idiosyncrasies. Being open systems, they are easily accessed by vermin, small animals and bird life, which then die within the tower, leading to spikes in microbiological loading ”
Cooling Towers and Process Water
About Cooling Towers
Cooling towers are evaporative coolers used for cooling water or other working medium to near the ambient wet-bulb air temperature. Cooling towers use evaporation of water to reject heat from processes such as cooling the circulating water used in oil refineries, chemical plants, power plants and building cooling, for example.
The towers vary in size from small roof-top units to very large hyperboloid structures
The counterflow design
In a counterflow design the air flow is directly opposite of the water flow (see diagram). Air flow first enters an open area beneath the fill media and is then drawn up vertically. The water is sprayed through pressurized nozzles and flows downward through the fill, opposite to the air flow.
Micro-organisms - Legionella
It is crucially important to use biocides in cooling towers in order to prevent the growth of micro-organisms such as Legionella. Legionella bacteria are the cause of Legionnaires' disease in humans. This disease is contracted via exposure to aerosols (the inhalation of mist droplets containing the bacteria).
Sources of Legionella
Common sources of Legionella include cooling towers used in open recirculating evaporative cooling water systems, domestic hot water systems, fountains. Natural sources include freshwater ponds and creeks. French researchers found that Legionella spread through the air up to 6 kilometres from a large contaminated cooling tower at a petrochemical plant in Pas-de-Calais, France. The outbreak killed 21 of the 86 people that had a laboratory-confirmed infection.
Outbreak in Australia
Australia's biggest outbreak of Legionella in Melbourne's Aquarium in 2002 left three people dead, seven hospitalised in critical condition and a total of 93 people, including Australian Finance Minister John Fahey, were confirmed as having contracted the disease.
Residual Disinfection
The necessity for a residual disinfection method such as copper/silver ionisation is also identified by the Department of Human Services in Victoria as well as chief engineers of major public service installations across the country. Otherwise it is not a question of 'if' but rather 'when' a major infection will occur.
Air borne droplets
As the water in the tower is cooled through evaporation, significant amounts of water are lost from the system. In addition, the fans at the top of the tower also extract water in the form of droplets. These droplets or aerosols, if originating from untreated water, will contain a biological cocktail of micro-organisms, including Legionella.
Other contaminants
Cooling Towers have their own unique microbiological idiosyncrasies. Being open systems, they are easily accessed by vermin, small animals and bird life, which then die within the tower, leading to spikes in microbiological loading.
Replacing water in the system
To replace the water in the system, a make up line is required. As this is a similar concept to potable and tepid water systems, the AccuIon™ technology is placed in the make up line. As new water enters the tower, it passes through the AccuIon™ device where it is accurately dosed with ions providing residual disinfection for the whole system. Even though cooling towers are by definition a recirculation system, for the purposes of ionisation they are regarded as a flow-through application due to the high water losses from the cooling system.
pH control, corrosion reduction and water savings
pH plays a pivotal role when it come to effects like corrosion or scaling in cooling towers.
If the pH deviates from neutral, i.e. pH=7, the effects of corrosion and/or scaling begin or increase. Therefore, BioN Water Synergetics Pty Ltd uses pH Control equipment to prevent any drift in pH. Another advantage of the pH control is the increased biocidal efficiency of copper/silver ionisation equipment.
Water Savings
Copper/Silver ionisation does not introduce harsh chemicals into the tower and therefore the Total Dissolved Solids (TDS) is not rising as quickly as in a chemical based system. The water can stay longer in the system and blow down periods can be prolonged, resulting in significant water savings.