For almost 30 years, ozone has been used to remove and prevent the growth of these organisms while reducing contaminant levels (e.g. AOX and COD) through direct oxidation. Contrary to conventional halogen-based biocides, ozone does not produce unwanted by-products such as halocarbons (AOX).
Cooling systems operations entails extensive treatment as it provides an idyllic growth environment for bacteria, Legionella, algae, fungi and molluscs which can adhere to the pipeline, heat exchanger and cooling tower surfaces. Three main areas of concern are identified:
Malpractices in these areas can lead to reduced heat efficiency and potential overall system failure. Important to note that these facets must be addressed together as fixing one aspect might lead to augmented failure in the other one, an example of higher corrosion level of metals by lowering water Ph levels to inhibit scaling.
Ozone acts as one solution to all these aspects without the need to keep experimenting with different chemicals.
Why using ozone in cooling towers?
Ozone is produced on-site from oxygen gas and is introduced directly into the cooling water via sidestream injection. Ozone may also be injected directly into the cooling tower reservoir. Once it is dissolved in water, ozone proceeds to oxidise organic contaminants and microorganisms. The ozone dosing is regulated automatically by the control system of the ozone generator and varies with the water demand. Ozone, combined with suitable corrosion and scale inhibitors, provides the optimum treatment solution for cooling water.
Some of the advantages with ozone:
The key reason why Ozcon ozone solution is exceptional for cooling water towers is its robustness and reliability. It should not be acceptable any longer for operators and users to have stops in operations because the cooling system is unsafe (Legionella) or inefficient (biofouling formation).
Cooling towers environment is famous to have strict safety rules and regulations, so leakage of flammable gas into power plant environments should be avoided at all cost, here is where Primozone’s patented way of distributing the gas into the enclosure, through the gas-tight anodized aluminium framework, is a guarantee against leakages in the ozone generator.
Cooling towers are usually installed in remote locations, unless there is full-time personnel on-site dedicated to the water treatment system (which is an extra expense), sending someone to the site for maintenance, repair and regulation is not optimal as it takes time and involves additional costs. The Primozone system has no preventive maintenance need, and it is fully automated, hence remote monitoring and regulation is possible.
Full automation makes things easier in environments where not all the personnel is experienced in the operation of water treatment equipment. Plus, the Primozone Human-Machine Interface is so user-friendly that operation and diagnostics are straightforward, even if done manually.
In the cooling towers case, the ozone system is usually to be installed in its building, so the compact footprint of Primozone technology comes in very handy. The system is so small that it might be containerised.
This building/container often has to be placed quite far from the injection point. In these conditions, the naturally high outlet pressure of the Primozone ozone gas is fundamental to be able to distribute the ozone on a long distance.
High pressure is useful also because recirculating water in cooling towers is pressurised. Unless you choose Primozone, it’s most likely not possible injecting the ozone directly into the water – you must use a Venturi injector. If the water pressure is above 3 bar(g) and a Venturi injector is needed in any case, with Primozone high concentration the injection system will be much smaller, much cheaper and much less energy-consuming than with traditional low concentration.
Last but not least, power plants pay a low cost for electricity. Oxygen instead won’t likely be available in the immediate surroundings of the plant and might be very expensive. That’s when powering up the generator and running at high concentration can lead to significant OPEX savings.
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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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WATERZONE ozone injection system is designed to quickly integrate into an existing water line. The Waterzone Ozone Injection systems offer turn-key ozone systems, with reliability and performance you can trust.
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