Types of cooling towers
Understanding the Different Types of Cooling Towers. A cooling tower is a heat exchanging system to cool down water by rejecting its heat in the atmosphere through exposure of water directly into the air and along surface area is used where water drips down and a fast heat exchange follows.
The heat from water turns into vapor and evaporates ultimately cooling down a large amount of water so that cooled water can be recycled into the industrial process to lower down equipment temperature and elongate their life.
Cooling towers are crucial to maintaining heavy industrial work where the process generates enough heat that needs to be controlled by water flow. These towers work wonders for refineries, thermal power stations, chemical factories, etc.
There are various cooling tower designs available today to cover different requirements and meet all weather conditions.
Let us know about their types:
Cooling towers are made to perform in different applications, so their types fall under three major categories:
- Air to water flow suction.
- Air through tower suction.
- Heat transfer method.
1.) AIR TO WATER FLOW SUCTION:
- Crossflow: Air passes perpendicular to the water flow in the cooling tower by entering vertical vents and enters the fill inside the tower. The hot water enters the basin over the tower and is spread by nozzles across the fill vents. A blower blows out excess heat and the exposure of water through the fill with air cools it down. The hot air is extracted out for the forced draft system. This system has lower operating cost and less maintenance with low energy consumption. But it attracts dirt in the tower fill. This method is used in chemical industries and aluminum die casting.
- Counterflow: In this cooling tower type, air is sucked up from the tower's bottom passing near the fills into an open space in the tower. Simultaneous, the water droplets flowing down the fills opposite to the air direction triggers faster heat transfer by clashing with the rapidly flowing air making water cooler by counterflow affect. Water droplets ease quick heat transfer but create noise by spraying and falling of water. It is also a difficult to clean system however, used commonly in refineries and natural gas plants.
2.) AIR THROUGH TOWER SUCTION:
- Natural draft: In this Cooling tower type, pumps are installed on the tower top that pull up hot water from hot water inlet and it is ejected out using nozzles that spray water over film fills. When water is trickling down from the fills, it contacts air from the tower bottom coming upwards. This exposure of water with air cools it down by natural convection causing heat escape in vapors going up the atmosphere. Finally, cooled water collects into the basin to cool down equipment. Natural draft towers have low maintenance, operations and energy saving yet use large space to install and depend upon climatic conditions to a degree. They are highly used in power stations and plant cooling.
- Mechanical draft type: These towers use mechanical devices such as cooling tower fan or blower to circulate air through the tower. It is of two kinds namely:
a). Forced Draft cooling tower
b). Induced draft towers.
- Forced Draft mechanical tower: In this tower type, counter flow of air and heat cause heat transfer. The fan at tower base blows up air that comes in contact with water dropping down the fills. This air and water meet causes atmospheric cooling with wet technology. This system is low on cost as the fan and motors can be easily maintained but a powerful fan needs more power to operate and might need recirculation due to the cooling tower design. Anyways, the petrochemical industry makes good use of this technology.
- Induced Draft mechanical tower: This tower method is similar to the forced draft mechanism but the cooling tower fan is located on top of the tower which pulls air from the bottom and exposes it to water at a high level through the fills. In this draft system, water to air exposure is greater which fastens heat transfer. It requires less recirculation and a small space to install yet fan and motor need protection from open moist air stream and corrosion is easy. It is applicable for A/C plants and sugar industries.
3.) HEAT TRANSFER METHOD:
a.) Dry cooling tower: This system uses minimum water but a high air transfer in its cooling tower design. It operates by transferring fluid from the air and its heat is then sucked out to the atmosphere by convection without evaporation taking place. It is used to cool processing liquid and is a great water conserver yet the high amount of mechanical noise is produced. It is used aptly in power generation units.
b.) Wet cooling tower: Also called open circuit cooling tower, the technique uses evaporative cooling. Hot water is pumped up the plant and scattered over the fills. Fills provide excellent contact time and exposure of water to air. This forms water vapor which lowers the temperature of water and also the air. This system is an apt example of thermal energy utilization and saves a lot of power. It is used in thermal power plants, petrochemical units.
c.) Fluid cooler: Similar to water cooling towers, closed circuit cooling tower evaporate heat load but by transferring heat from the process liquid to the air through a heat exchange coil. The water in the coil rotates in a closed loop system isolated from the atmosphere keeping it clean and contamination free. Here two fluid circuits are present inside the cooler. The internal circuit maintains fluid circulation while the external circuit is sprayed by water to create wet bulb effect. Outside air exposure evaporates the water. It is low on pumping cost and is compact but heavier. This process is used in air conditioning and refrigeration industries.
Cooling towers happen to be successful when you have the right specifications ready. For the purpose, you need to know what your plant requires. Certain criteria like space available, type of operations conducted, availability of water resources and the budget, all have to be considered to study the cooling tower working or meet an expert who can prepare a feasibility report for opting to the best cooling tower system you like. You can consult a Cooling Tower Manufacturer who will guide you to the best system possible.
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