OZONE IN COOLING TOWERS
Operators generally look at the cooling tower in terms of heat, checking whether this device has cooled the cooling water sufficiently. However, when operational problems begin, it turns out that it is not right to just look at the cooling tower in terms of heat. The main problem in cooling towers is the treatment of water. During the cooling tower water treatment process, three main factors should be controlled;
– Corrosion of pipes and heat exchanger units
– Solids formed in pipes and (mostly) heat exchangers
Microbial growth (bacteria, algae)
These three features cannot be treated at the same time. For example, lower pH values can prevent solidification in the water but increase metal corrosion. Thanks to the ozone treatment, all these features can be controlled collectively without adding chemicals.
Traditional purification techniques are the application of chemical biocides. Ozone is an alternative method for calcification, corrosion and treatment of microbial pollutants in cooling tower water.
The deposits formed as a result of calcium and magnesium ion deposits in the units of the cooling system cause the formation of a layer that forms an insulating layer in the heat exchangers. This adversely affects heat transfer. Due to evaporation and loss of water, salt concentrations in the water increase. At some point, these salts precipitate by reaching the saturation rate. This limits the number of recycling of coolant.
The thickening factor is a measure for an increase in salt and ion concentrations in cooling water. Indicates the number of times the water needs to be regenerated to prevent salt from settling.
Biofilm can also form in the coolant system. A biofilm normally receives ions that form microcrystals, which increases sedimentation. Over time, inorganic and organic matter will thicken this layer.
Ozone application limits sedimentation. Ozone is a disinfectant that breaks down the biofilm and prevents the ions from binding. This causes a decrease in deposit formation. Even water with high dissolved solids content can now be recycled, thereby reducing cooling water discharges.
For this system to work, ozone concentrations that will keep the microbial level that provides sediment to a certain extent must remain in the cooling water.
Each material has a limited life. The life span depends on the nature of the material and environmental conditions. The first anti-corrosion method is the most permanent material and a solid construction choice of the cooling system. Corrosion can be prevented by changing the water quality when the cooling water system is used. In practice, this is accomplished by adjusting the pH and changing the dissolved solids concentration. When these measures do not produce the desired result, corrosion inhibitors can be added to the coolant. But corrosion inhibitors are quite expensive.
Another method of preventing corrosion is the application of ozone. Corrosion is mainly caused by microorganisms that strengthen corrosion-forming conditions. Ozone limits microbial growth. Ozone also causes a certain electric current to form in the water. This current allows metals to form a passive, anti-rust film on the materials. Such a passivating oxidative film is found on stainless steel and aluminium. This film can be created only in certain water flow and certain types of materials.
Various experiments have shown that when ozone is applied, corrosion is usually reduced by more than 50%.
A small amount of ozone is required to create an anti-corrosion film on metals. High doses can corrode some metals. In practice, approximately 0.1 g / m3 ozone is supplied to the recirculating water. Ozone, which does not react with organic matter, decomposes into oxygen. No toxic residue remains.
We cannot prevent microbial growth in any water system. Because there is a certain amount of bacteria in the water and air we use. Bacteria can also enter the water during procedures, even if bacteria are not available.
Ozone is a much stronger disinfectant than other chemicals. Ozone treatment in a cooling tower is a very important application to treat the water. It’s also known, ozone is the most effective disinfectant in the inactivation of Legionella bacteria.
Ozone application in cooling water treatment is a good option for water quality control in the cooling water system. Ozone leads to the following savings:
– The use of chemicals such as anti-lime and anti-corrosion is minimized.
– Water consumption is reduced.
– Storage and transportation costs of chemical biocides are reduced.
– Pump capacity increases. (more efficient heat transfer; lower energy use; higher efficient heat exchanger)
Ozone application can only be made when certain factors are taken into account:
Water quality; Cooling towers with hard or high COD value are less suitable for ozone treatment.
The time that ozone remains in the system. The half-life of ozone is usually less than 10 minutes in a cooling tower. Primary ozone concentration should be sufficient to achieve a significant concentration of ozone.
Ozone solubility and half-life of ozone drop at higher coolant temperatures. This limits the coolant temperature for adequate ozone application. The limit is usually 45 ° C coolant temperature.
Material selection. The material formed by the cooling tower must be ozone resistant.
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