Cooling towers take advantage of the difference in air densities below and above them. This interaction results in evaporation of water and condensation of air.
The cooling tower is commonly found in power plants, oil refineries and steel manufacturing plans as well as commercial buildings with water cooled chillers. The cooling tower is usually shaped like a hyperboloid.
What Is a Cooling Tower?
Cooling towers are used in industrial settings to remove the heat absorbed from the circulating cooling water systems used in steel mills, petrochemical plants, natural gas processing plants and thermal power stations. They are also found in HVAC systems used in office buildings, airports and college campuses.
Cooling Towers use evaporative cooling to reduce the temperature of the water circulating in the system. As the hot water evaporates it takes the heat energy (in the form of vapor) with it, reducing the overall temperature of the cooling tower water.
The cooled water is then pumped back into the industrial process or returned to the water supply. Cooling towers are typically classified as wet, dry or forced draft and based on the way air enters the cooling system.
Wet cooling towers are the most common and are the most versatile and efficient. They reduce heat by evaporative cooling and have the ability to provide freshwater or chilled water to the industrial process. A wet cooling tower requires a constant supply of make-up water to compensate for the water lost due to evaporation and drift (the loss of water from a cooling tower that does not have constant blow down).
The make-up water is added at the tower inlet and distributed throughout the fill pack by motor-driven electric cooling tower fans. The fan’s output is controlled by a control to maintain a specific airflow pattern that will optimize water-to-air contact for maximum heat rejection.
A key factor to the operation of a wet cooling tower is the nozzles that spray the water. Good nozzle design ensures that the water is spread evenly across the entire surface of the fill pack to maximize water-to-air surface area for efficient vapor transfer and cooling. A poorly designed nozzle can create areas in the fill that do not receive any water at all and can choke the flow of air causing poor cooling.
The efficiency of a wet cooling tower is impacted by many factors including fan efficiency, water distribution, tower design, and most importantly the size of the fill pack. The higher the heat rejection per cubic foot of fill pack the better the cooling tower will perform. This is why larger towers tend to be more expensive than smaller ones.
How Does a Cooling Tower Work?
Cooling towers are designed to reject heat from the system by evaporative cooling. The water is pumped in through pipes and sprays through nozzles over banks of fill material, which increases the surface area for air-water contact. The interaction between the water and air causes a small amount of the water to evaporate, which cools the remaining water and rejects the rejected heat into the atmosphere. The cooled water then collects in a cold water basin where it is redirected to the process equipment.
There are three types of cooling towers: counterflow, crossflow, and forced draft. The type used will be determined by factors such as the size of the system/application, geographical location/climate, and water quality.
Each type of cooling tower utilizes the same basic principle of rejecting heat through evaporative cooling and uses a mix of latent and sensible heat transfer methods. Latent heat is lost through evaporation, while sensible heat is transferred by convection and conduction.
Regardless of the design type, all cooling towers are divided into structural and mechanical parts. Structural components include the basin, tower framework, and fan deck. Mechanical parts include the fans, driveshafts, and speed reducers. The most important part of any cooling tower is the nozzles, which are designed to distribute water in an evenly spread pattern over the fill pack. If there are areas in the pack that don’t receive any water, the heat rejection capacity is reduced significantly. There are a variety of different nozzle designs that can be used to achieve the proper pattern distribution.
A drift eliminator is also an important feature of cooling towers. Without one, drifting water drops lose their way into the atmosphere and fall back into the basin, reducing the overall thermal capacity of the tower. Some nozzles are designed to be variable flow to provide an even distribution over a range of process water flow rates, which further enhances the thermal capacity and efficiency of your cooling tower.
Fouling, corrosion, freezing, and other problems can interfere with the performance of your cooling tower. They may result in loss of water flow, which can cause major disasters such as hydrocarbon leaks and fires when your machinery doesn’t have enough cooled water to operate properly.
What Are the Benefits of Using a Cooling Tower?
Cooling towers help businesses reduce operating expenses by lowering energy costs, reducing water consumption, and increasing the life of industrial equipment. They can also help protect the environment and conserve fresh water resources.
The main benefit of a cooling tower is that it helps businesses maintain a continuous supply of cooled water. This is important because equipment that fails to receive adequate cooling can overheat and cause a shutdown. In some cases, this can lead to major problems like hydrocarbon leaks and fires. A cooling tower can prevent these problems by keeping the coolant circulating.
Cooling Towers also help businesses cut down on the amount of water that is drained from lakes and rivers, which can cause habitat destruction for wildlife. This is because the system recirculates the water it pulls in, which means that only a small percentage of it is lost to the surrounding ecosystem.
Some cooling towers are preassembled and then shipped to the site where they will be used. These are called packaged cooling towers and are typically used in food processing plants, hotels, and other facilities that don’t generate as much heat as a power plant or manufacturing facility.
Another benefit of a cooling tower is that it can help protect equipment from corrosion and reduce the risk of fouling or freezing. This is because the system recirculates a lot of water, which keeps it away from other parts of the building and the machinery that it’s cooling. Cooling towers can also be fitted with a drift eliminator, which helps to prevent the movement of water droplets into the surrounding area.
There are many different types of cooling towers, which can be classified by how they work and the type of heat transfer they use. For example, a cooling tower can be classified as a natural draft, forced draft, hybrid, or induced-draft cooling tower.
Natural draft cooling towers operate by spraying hot water through nozzles in the tower. This causes the air in the surrounding area to interact with the hot water and exchange heat. The water evaporates and becomes cooler, which then carries the evaporated steam back to the condenser or process equipment. The cooled water is then pumped back to the cooling tower to be re-evaporated, and the cycle continues.
How Do I Maintain a Cooling Tower?
A cooling tower that isn’t regularly cleaned and treated can be vulnerable to corrosion, resulting in costly repairs. By investing in routine inspections and cleaning, a facility manager can extend the lifespan of the equipment, as well as maximize energy savings.
Cooling towers are often located in open areas, where dirt and dust can easily get into them. These particles can clog pores and impede heat transfer, leading to diminished performance. Cleaning is a vital part of maintaining a cooling tower, and it is recommended that the equipment is professionally cleaned every six months.
The first step in any cooling tower maintenance service is conducting a visual inspection. Check the structure for physical damage, corrosion, or leaks, as well as the fan blades, access doors, and louvers. It’s also important to examine the distribution pans for sludge, scale, sediments, and biological growth.
In addition to reducing efficiency, improper tower maintenance can lead to health hazards for building occupants. Cooling towers that are not disinfected on a regular basis can harbor harmful bacteria like Legionella. When water with this bacterium blows off the cooling tower, it can infect people downwind with illnesses like Pontiac Fever or Legionnaire’s Disease.
During cleaning, a professional technician will open all distribution pans and drain the basins to inspect for the presence of biofilm. They will then clean off all surfaces and wash the basins, sanitizing the interior of the cooling tower. This process can be time-consuming, but it is essential for maintaining a cooling tower.
Cooling towers that are not properly maintained will work harder to produce the same results, requiring more electricity to generate an ideal output. Over time, this can lead to higher electricity bills for the facility owner. By ensuring that the cooling tower is clean and treated with chemicals, the system will function as efficiently as possible, generating more output while using less energy. This will result in significant savings on electricity costs and will help the environment as well. The best way to protect a cooling tower is to plan and execute cleanings twice a year, along with a routine water treatment program.
