Components of A Cooling Tower
Structural Components
1. Cold water basin
2. Tower framework
3. Water distribution system
4. Fan deck
5. Fan cylinder
6. Mechanical equipment supports
7. Fill (heat transfer surface)
8. Drift eliminator
9. Casing
10.Louvers
Mechanical Components
1. Fans
2. Speed reducers
3. Drive shafts
4. Valves
Electrical Components
1. Motors
2. Motor controls
3. Wiring system
Tower materials
1. Frame and casing
2. Fill
3. Nozzles
4. Fans
Structural Components
Most cooling systems are very vulnerable to corrosion.
They contain a wide variety of metals and circulate warm water at relatively high linear velocities. Both of these factors accelerate the corrosion process.
Deposits in the system caused by silt, dirt, debris, scale and bacteria, along with various gases, solids and other matter dissolved in the water all serve to compound the problem.
Even a slight change in the cooling water pH level can cause a rapid increase in corrosion.
Open recirculating systems are particularly corrosive because of their oxygen-enriched environment.
The structural components of cooling tower such as: cold water basin, framework, water distribution system, fan deck, fan cylinders, mechanical equipment supports, fill, drift eliminators, casing, and louvers.
1. Cold water basin
The cold water basin has two fundamentally important functions: collecting the cold water following its transit of the tower, and acting as the tower’s primary foundation.
2. Tower framework
The most commonly used materials for the framework of field-erected towers are fiberglass, wood, and concrete, with steel utilized infrequently to conform to a local building code, or to satisfy a specific reference.
3. Water distribution system
Lines might be buried to minimize problem of thrust loading, thermal expansion and freezing; or elevated to minimize cost of installation and repair. In either case, the risers to the tower inlet must be externally supported, independent of the tower structure and piping.
4. Fan deck
The fan deck is considered a part of the tower structure, acting as a diaphragm for transmitting dead and live loads to the tower framing. It also provides a platform for the support of the fan cylinders, as well as an accessway to the mechanical equipment and water distribution system. Fan deck materials are customarily compatible with the tower framework.
5. Fan cylinder
Fan cylinder directly affects the proper flow of air through the tower. Its efficiencies can be severely reduced by a poorly designed fan cylinder, or significantly enhanced by a well-designed one.
6. Mechanical equipment supports
Customary material for the unitized supports is carbon steel, hot-dip galvanized after fabrication, with stainless steel construction available at significant additional cost.
7. Fill (heat transfer surface)
Fill (heat transfer surface) is able to promote both the maximum contact surface and the maximum contact time between air and water determines the efficiency of the tower.
The two basic fill classifications are splash type and film type. Splash type fill breaks up the water, and interrupts its vertical progress, by causing it to cascade through successive offset levels of parallel splash bars.
It is characterized by reduced air pressure losses, and is not conducive to logging. However, it is very sensitive to inadequate support.
Film type fill causes the water to spread into a thin film, flowing over large vertical areas, to promote maximum exposure to the air flow.
It has capability to provide more effective cooling capacity within the same amount of space, but is extremely sensitive to poor water distribution.
8. Drift eliminator
Drift eliminators remove entrained water from the discharge air by causing it to make sudden changes in direction.
The resulting centrifugal force separates the drops of water from air, depositing them on the eliminator surface, from which they flow back into the tower.
Eliminator are normally classified by the number of directional changes or “passes”, with an increase in the number of passes usually accompanied by an increase in pressure drop.
9. Casing
A cooling tower casing acts to contain water within the tower, provide an air plenum for the fan, and transmit wind loads to the tower framework.
It must have diaphragm strength, be watertight and corrosion resistant, have fire retardant qualities, and also resist weathering.
10.Louvers
Every well-designed cross flow tower is equipped with inlet louvers, whereas counter flow towers are only occasionally required to have louvers.
Their purpose is to retain circulating water within the confines of the tower, as well as to equalize air flow into the fill.
Mechanical Components
1. Fans
Cooling tower fans must move large volumes of air efficiently, and with minimum vibration.
The materials of manufacture must not only be compatible with their design, but must also be capable of withstanding the corrosive effects of the environment in which the fans are required to operate.
A. Propeller fans:
They have ability to move vast quantities of air at the relatively low static pressure encountered.
They are comparatively inexpensive, may be used on any size tower, and can develop high overall efficiencies; but their application naturally tends to be limited by the number of projects of sufficient size to warrant their consideration.
B. Automatic variable-pitch fans:
They are able to vary airflow through the tower in response to a changing load or ambient condition.
C. Centrifugal fans:
They are usually used on cooling towers designed for indoor installations; their capability to operate against relatively high static pressures makes them particularly suitable for that type of application.
However, their inability to handle large volumes of air, and their characteristically high input horsepower requirement limits their use to relatively small applications.
All propeller type fans operate in accordance with common laws:
- The capacity varies directly as the speed ratio, and directly as the pitch angle of the blades relative to the plane of rotation.
- The static pressure varies as the square of the capacity ratio.
- The fan horsepower varies as the cube of the capacity ratio.
- At constant capacity, the fan horsepower and static pressure vary directly with air density.
2. Speed reducers
The optimum speed of a cooling tower fan seldom coincides with the most efficient speed of the driver (motor); thus a speed reduction or power transmission unit is needed between the motor and the fan.
3. Drive shafts
The driveshafts transmit power from the output shaft of the motor to the input shaft of gear reduction units.
4. Valves
Valves are used to control and regulate flow through the water lines serving the tower. Valves utilized for cooling tower application include:
A. Stop valves:
They are used on both counter flow and cross flow towers to regulate flow in multiple-riser towers, and to stop flow in a particular riser for cell maintenance.
B. Flow-control valves:
They are considered to discharge to the atmosphere, and essentially as the end-of-line valves.
C. Make-up valves:
These are valves utilized to automatically replenish the normal water losses from the system.
Electrical Components
1. Motors
Electric motors are used almost exclusively to drive the fans on mechanical draft cooling towers, and they must be capable of reliable operation under extremely adverse conditions.
2. Motor controls
Motor controls serve to start and stop the fan motor and to protect it from overload or power supply failure, thereby helping assure continuous reliable cooling tower operation. They are not routinely supplied as a part of the cooling tower contract but, because of their importance to the system, the need for adequate consideration in the selection and wiring of these components cannot be over stressed.
3. Wiring system
The wiring system design must consider pertinent data on the available voltage (its actual value, as well as its stability), length of lines from the power supply to the motor, and the motor horsepower requirements.
Tower materials
Originally, cooling towers were constructed primarily with wood, including the frame, casing, louvers, fill and cold-water basin.
Sometimes the cold-water basin was made of concrete. Today, manufacturers use a variety of materials to construct cooling towers.
Materials are chosen to enhance corrosion resistance, reduce maintenance, and promote reliability and long service life. Galvanized steel, various grades of stainless steel, glass fiber, and concrete are widely used in tower construction, as well as aluminum and plastics for some components.
1. Frame and casing
Wooden towers are still available, but many components are made of different materials, such as the casing around the wooden framework of glass fiber, the inlet air louvers of glass fiber, the fill of plastic and the cold-water basin of steel.
Many towers (casings and basins) are constructed of galvanized steel or, where a corrosive atmosphere is a problem, the tower and/or the basis are made of stainless steel.
Larger towers sometimes are made of concrete. Glass fiber is also widely used for cooling tower casings and basins, because they extend the life of the cooling tower and provide protection against harmful chemicals.
2. Fill
Plastics are widely used for fill, including PVC, polypropylene, and other polymers. When water conditions require the use of splash fill, treated wood splash fill is still used in wooden towers, but plastic splash fill is also widely used. Because of greater heat transfer efficiency, film fill is chosen for applications where the circulating water is generally free of debris that could block the fill passageways.
3. Nozzles
Plastics are also widely used for nozzles. Many nozzles are made of PVC, ABS, polypropylene, and glass-filled nylon.
4. Fans
Aluminum, glass fiber and hot-dipped galvanized steel are commonly used as fan materials.
Centrifugal fans are often fabricated from galvanized steel.
Propeller fans are made from galvanized steel, aluminum, or molded glass fiber reinforced plastic.