- Cooling Tower Definition: A cooling tower is defined as a device that reduces the temperature of hot water from the condenser for reuse in the boiler.
- Working Principle: Hot water is sprayed, slowed down, and cooled by evaporation with the help of fans.
- Cooling Tower Parts: Key parts include eliminators, spray nozzles, PVC filling, mesh, float valve, and bleed valve.
- Natural Draught Cooling Tower: This type uses chimney effects for air circulation, leading to high capital costs but low operating costs.
- Mechanical Draught Cooling Tower: This type uses fans for air circulation, suitable for high-load conditions with either forced or induced draught systems.
A cooling tower cools hot circulating water from a steam-turbine condenser so that water can return to the condenser. It does not cool boiler feedwater. Heat leaves mainly by evaporation as air and water meet in the fill.
How Cooling Tower Works?
Hot water enters the tower and is pumped to the header, which has nozzles and sprinklers to spray the water and raise its surface area. The water then passes through PVC fill, which slows the fall. On an induced-draught tower, fans at the top pull air from the bottom to the top.
The slower fall and larger contact area give air more time on the water surface. Evaporation then drops the remaining water temperature. The cooled water collects in the basin and is pumped back to the condenser that serves the boiler steam cycle.
Different Parts of Cooling Tower
- Eliminator: Drift eliminators sit near the air outlet and catch water droplets so they fall back into the tower instead of leaving with the exhaust air.
- Spray Nozzles and Header: The header feeds the nozzles that break the hot water into drops or films so more surface is open to air.
- PVC Filling: Film or splash fill, often a honeycomb PVC pack, slows the water and holds a large wet surface.
- Mesh: Inlet screens or louvers keep leaves and coarse dust out of the cooling tower when the fan draws in outside air.
- Float Valve: Makeup water replaces evaporative loss and blowdown so the basin level stays in range.
- Bleed Valve: Blowdown removes a fraction of circulating water so dissolved minerals and salts do not keep concentrating.
- Body: Small package towers often use an FRP (fibre-reinforced plastic) shell. Large natural-draught shells are usually reinforced concrete.
Types of Cooling Tower
Cooling towers are grouped by how air is moved
1) Natural Draught Cooling Tower: No fan is used. Warm, moist air in the shell is lighter than outside air, so a chimney effect draws fresh air in. A large hyperbolic concrete shell costs more to build than a fan tower, but it avoids fan power. Timber rectangular towers were an older natural draught cooling tower form. Large power-station shells are usually reinforced concrete hyperboloids.
2) Mechanical or Forced Draught Cooling Tower: Mechanical draught uses a fan. A power plant on high load still needs enough circulating water, but the fan does not set that water flow by itself. Fan motor speed is a design choice; about 1000 rpm appears in some notes and is not a universal figure. Evaporative cooling is the same idea as a natural draught cooling tower, except a fan moves the air. An induced-draught fan sits at the top air outlet and pulls air through the fill. A forced draught cooling tower has the fan on the air inlet, often at the base with a horizontal shaft.
