The cooling towers are used all over the world for different industrial applications. These systems are used to produce cooling through the water. The required amount of water is taken from the lake or river, transferred it into a process heat exchanger, and the hot discharged water is returned to the lake or river. However, the hot water from the process exchanger flows into the cooling tower. The cooling tower partially evaporates the water and lowers the temperature of the water. The forced draft cooling tower is a most famous type of cooling tower. It is a most powerful, flexible, and economical cooling technology for most industrial systems.
What is a Forced Draft Cooling tower?
A cooling tower in which the fan is installed on the side of the tower to allow air to flow from the bottom to upward of the tower is called a forced draft cooling tower. This is one of the most economical and powerful cooling towers used in different industrial plants.
These cooling towers are used for higher process inlet temperatures applications. The fans of the forced draft cooling towers are also used to force ambient air into the combustion chamber to preheat the air and improve the efficiency of the boiler.
These cooling towers need less structural support than induced draft fans. They offer longer mechanical life because cleaner ambient air doesn’t affect the fans as much as the air normally drawn in by induction draft fans.
The forced draft cooling towers have many advantages. Therefore, many industries choose this model over the induced draft cooling tower. They have low cost and high efficiency.
They eliminate the small potential heat produced during the manufacturing process. The combination of hot water with a counterflow of air transfers heat into the cooling pad. The fan of the forced draft cooling tower consumes low energy when running cool air.
The main disadvantage of this design is that it has leakage, air distribution, and hot and humid air circulating back into the tower issues. Chemical and paper mills often prefer forced draft cooling towers.
Forced Draft Vs. Induced Draft Cooling Tower
For heat exchangers using cooling water, if there is an internal leak in one of the tubes or the tube sheet and the working pressure is higher than the cooling water pressure, the combustible product will enter the cooling water. This combustible product mixes with the cooling water and then enters the cooling tower, where it vaporizes and, in some cases, ignites.
Therefore, if you have a heat exchanger with cooling water, it must have less pressure on the process side than the waterside. In such a case, if leakage still occurs there, water will go into the process stream. This is generally less dangerous than the case of hydrocarbons getting into the cooling water.
To minimize these severe issues with hydrocarbons in the cooling water, follow the below-given safety tips:
- You must design your cooling tower electrically. Pump motor, fan motor, and other electrical equipment must fulfill the demands of Class I, Division 2.
- You should install your cooling tower away from the furnace and process equipment.
- Install the standoff column or chamber in the cooling tower return line to discharge gas before the water entry into the tower distribution system.
- The water pump and its switchgear must be a minimum of 4 m away from the bottom of the cooling tower.
- The packaging in the tower must be fireproof.
- You must install two manual fan shut-offs on the cooling tower. One is on the top deck, and the other is on the ground floor. You should also install an anti-vibration switch.
- Monitored hydrants should be spaced so that any area of the cooling tower is covered by water currents in at least two directions.
- The cooling tower must be at least 28 m away from the processing device.
- Whenever possible, the cooling tower must be sited downwind of pipe racks, substations, and process devices to prevent cooling tower fog from causing corrosion or obstructing visibility.