Many commercial and industrial processes depend on cooling towers to maintain temperature in a designated range. The one most people are familiar with is building cooling (HVAC systems), but many important industrial processes also require cooling towers such as electrical power generation.
Cooling towers use the principle of evaporative cooling to reduce the temperature of water. The human body uses the same principle. As we heat up we sweat, as this water evaporates from the surface of our skin we cool down. In a building the air conditioning system uses cooling heat transfer fluid to carry heat from inside the building to the outside. This fluid in turn needs to be cooled so it can return to the building and pick up more heat. Water is used for this purpose. The cooling water is then taken to a cooling tower where it is allowed to evaporate cooling the water so it in turn can lower the temperature of the heat transfer fluid used inside the building.
Since the cooling water is constantly evaporated more water must be added to the tower (make-up water) to maintain the volume. In addition, because the minerals in the water concentrate with evaporation, some water has to be released to reduce the concentration of the minerals (blow down). Since the cooling tower water is warms, oxygenated and constantly exposed to the environment, it is a good medium for the growth of bacteria. Some of these bacteria can be harmful such as the Legionella bacteria that can cause illness in humans. Other bacteria can form surface films (biofilms) on the heat exchange equipment that reduce the efficiency of the cooling system and thus waste energy. Some of the organism can also cause the materials in the cooling system to corrode requiring replacement of expensive equipment. As a result the growth of micro organisms in the cooling water must be controlled.
Ozone generators have been used extensively for the treatment of cooling water. This is due to the fact that ozone is a powerful, but environmentally friendly biocide. Ozone's effectiveness has been studied by the various agencies of US government and shown to be effective. For example, NASA uses ozone to treat cooling water at the Kennedy Space Center where they conduct racket launches.
Ozone is a powerful biocide, which, when compared to conventional chlorine based biocides, not only combats microbial growth processes but also reduces organic impurities often found in the cooling water reducing potential discharge problems with the blow down. In addition, by reducing the concentration of these impurities the amount of water blown down or wasted can also be reduced.
Ozone is produced in an ozone generator and usually injected continuously into the cooling water system in a branch stream. The microorganisms in the systems are thus under permanent attack and micro organism counts are held at a very low level. This also applies to the bio films in the systems, so the tendency for coatings to form is kept to a minimum. This means that intervals between overhauls and maintenance sessions can be extended.
A residual ozone concentration of 0.1 to 0.2 ppm is typically effective in keeping the cooling tower and the cooling circuit clean.
Advantages of ozone generator use in cooling towers include:
- Lower Corrosion Rates
- No Toxic Chemicals in Blow Down (ozone breaks down to oxygen).
- Lower Overall Chemical Use
- Eliminates Storage of Biocides (ozone is produced on site from air)
- Effective in a Wide pH Range
- Improved Heat Transfer Efficiency
- Reduced Water use
Ozone use in cooling towers requires consideration of the following factors:
- Make-up Water Quality (Hardness, COD Levels)
- Dead Spots in the Circulation System
- Water Temperature
- Materials of Construction
When applied properly and in the proper circumstances ozone can improve the operation of cooling towers while saving money and protecting the environment.
Anthony Sacco is a director of Spartan Environmental Technologies, LLC. Spartan supplies ozone generators, ozone water treatment systems and other advanced oxidation processes. You can learn more about Spartan at http://www.spartanwatertreatment.com and ozone cooling water treatment at http://www.spartanwatertreatment.com/cooling-water-treatment.html
