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Evan John Scheepers
The Complete Guide to Cooling Tower
What is Cooling Tower?
Cooling towers started to work in the 19th century for use in the steam engine. Condensers use the cool water, via different means, to condense the steam leaving the cylinders or turbines. This decreases the back pressure, which in turn lowers the steam usage, and thus the fuel consumption. However, the condensers need an ample supply of cooling water, without which they are useless. Although water usage in marine engines is not an issue, it creates an important limitation for many land-based systems.
Cooling towers range in size from small roof-top to very large hyperboloid units with a height up to 200 meters and diameter of 100 meters, or rectangular structures over 40 meters tall and 80 meters long. The hyperboloid cooling towers are usually applied in nuclear power plants. However, these cooling towers may also be used in some coal-fired plants and to some extent in some large chemical plants and other industries. Although these huge towers are very outstanding, the vast majority of cooling towers are very smaller, including many units placed on or near buildings for venting heat.
What is Cooling Tower Types?
Cooling towers are designed for special purposes. Not all cooling towers are applicable for all industrial processes. Different types of cooling towers are:
Cross-Flow Cooling Towers
In cross-flow cooling towers, the water flows vertically through the fill media, and the air flows horizontally across the falling water.
Counter-Flow Cooling Towers
In counter-flow cooling towers, the air flows vertically upwards, counter to the direction of water flow in the fill media. Because the air flows vertically, it is not practical to use the basin gravity-flow similar to the cross-flow towers.
Forced Draft and Induced Draft Cooling Towers
Cooling tower fans are applied on induced draft cooling towers to draw air up through the fill media. On forced draft cooling towers, the air is forced by blowers provided at the bottom of the air inlet louver.
Factory Assembled (FAP) and Field Erected (FEP) Cooling Towers
The factory-assembled cooling towers are somewhat disassembled and are shipped in several sections, ready for final assembly or field installation. However, small factory-assembled cooling towers can be wholly shipped. FAP cooling towers can be crossflow, counterflow, induced draft, or forced draft, depending on the application.
Field-erected cooling tower systems are constructed at the destination site. The large FEP is normally prefabricated, marked with a piece, and shipped to the installation site for assembly. The cooling tower manufacturer manages all the cooling tower construction processes, final destination assembly, and labor involved. This type of tower can be cross-flow or counter-flow, depending on the utilization. For heavy industrial applications or where more power is needed, field-erected cooling towers can be manufactured according to your exact specifications, performance, structure, plume abatement, and drift.
What is Cooling Tower Working Principles?
A cooling tower is a device that discards waste heat to the atmosphere by cooling a coolant stream, typically a water stream, to a lower temperature. They may either apply the evaporation of water to eliminate the process heat and cool the working liquid to a wet-bulb temperature close to that of the air or, in closed-circuit cooling towers or dry cooling towers, operate only on air to cool the working fluid to a dry-bulb temperature near the air using radiators.
Water heated through an industrial system or in an air-conditioning condenser is pumped to the cooling tower. The water is sprayed through nozzles on banks of material called âfill,â which slows the water flow through the cooling tower, exposing the highest feasible water surface area for maximum air-to-water contact. When the water passes through the cooling tower, it is exposed to air drawn into the tower by an electric motor-driven fan.
As the water and air face, a small quantity of water is evaporated, and thereby, the cooling operation takes place. Then, the cooled water is sent back to the condenser or process equipment, where the heat is absorbed. After that, It is pumped back to the cooling tower to repeat the cooling process.
What is Cooling Tower Used for?
Typical applications include cooling the circulating water in oil refineries, petrochemical and chemical plants, HVAC systems, thermal power stations, and nuclear power stations.
Based on the use, the cooling towers are generally classified into HVAC (Heating, ventilation and air conditioning) and industrial cooling towers.
HVAC Cooling Tower
An HVAC cooling tower is applied to repel unwanted heat from a chiller. Liquid-cooled chillers are usually more energy-efficient than air-cooled chillers because the liquid-cooled chillers reject the heat into tower water at or close to wet-bulb temperatures.
In hot climates, hospitals, large office buildings, and schools, typically one or more cooling towers are used as part of the air conditioning systems.
Another application of cooling towers is in HVAC systems with several water source heat pumps sharing a common piping water loop. In these systems, the water circulating inside the water loop eliminates heat from the condenser of the heat pumps when the heat pumps operate in the cooling mode. Then, the externally installed cooling tower is applied to remove heat from the water loop and dispose of it in the atmosphere.
Industrial Cooling Tower
Industrial cooling towers are used to remove heat from different sources such as machines and heated process material. The main application of large, industrial cooling towers is to eliminate the heat absorbed in the cooling water systems employed in power plants, natural gas processing plants, petroleum refineries, petrochemical plants, semiconductor plants, food processing plants, and other industrial applications, including the condensers of distillation columns, cooling liquid in crystallization, and so on.
What is Cooling Tower Life Expectancy?
The life expectancy of industrial cooling towers is between 15 and 25 years. While some believe that it is necessary to establish a completely new system, the old cooling tower systems can be refurbished or upgraded.
Which Type of Cooling Tower Is More Efficient?
As discussed above, liquid-cooled chillers have higher energy efficiency than air-cooled chillers. Air-cooled chillers have to reject heat at a higher dry-bulb air temperature than liquid-cooled chillers in which heat rejection occurs at or near wet-bulb temperatures. Thus, Air-cooled chillers have lower reverse-Carnot cycle effectiveness.
Between cross-flow and counter-flow cooling towers, the cross-flow tower works better for access to maintenance, variable flow, and operation in cold weather. Counter-flow towers may be better in tight spaces under 750 tons or in spaces that require less operating weight.
Are cooling towers dangerous?
Maintaining cooling towers may put you at risk for respiratory infections by Legionella bacteria. Legionella can live in lakes, rivers, ponds, groundwater, and human-made water systems. Diseases can be caused by inhaling mist from polluted water into the lungs. Legionella mainly causes two types of diseases: Legionnaires disease and Pontiac Fever.
There are also some environmental impacts of the cooling towers due to the huge vapor amount emitted into the atmosphere. The production of a great visible plume reduces the solar radiation below the plume.