Usage Of Primary Air Fan In Thermal Power Plant

By Author: Neel Rao
Total Articles: 131
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Primary air fans are generally present in steam boilers with an external surface. These boilers also have secondary air inlets. Together, they aid the combustion process of fuel. In general, primary air refers to the basic volume of air that is necessary for the combustion process to get completed. It depends on the quality and composition of the fuel needed by the boiler. The amount of primary air would be different for each type of fuel.

Normally, primary air is provided through the airbox at the bottom. This fuel has to be fed into the furnace through the screw feeder or manually. Primary fans also assist the fuel particles in getting segregated. This ensures that each of these particles would directly come in contact with the available air. The fuel particles would, therefore, be combusted efficiently.

How Do PA Fans Work?
In PA fans, the suction takes place from the atmosphere. The discharge of these fans is segregated into two parts. One of these parts passes through the air heater. This works like a heat exchanger. During this process, it acquires heat from the hot flue gases that come in from the ...
... other end. This heated air is termed 'hot air'. Now, in the other part, the temperature is lesser than the hot air, and it is called 'cold air'. Now the cold and hot air are mixed in the necessary ratio so that the overall temperature comes around 75 degrees centigrade. This air is subsequently fed to a coal mill, which helps in lifting and drying the pulverized coal.

PA Fan System: Main Functions
• Supplying air for burning the fuel and helping in the combustion process.

• The pulverized coal is carried to the furnace from the coal mill by the fan system.

• It partially provides the pulverized coal with heat energy before it reaches the boiler.

• During the transportation of coal, the air from such fans helps the coal to be preheated. This evaporates the moisture present in the coal, removing the stickiness.

• PA fans supply cold and hot air in the mills.

• These fans help in maintaining positive pressure and works on clean air after the coal is carried to the furnace from the mill.

Usage In Thermal Power Plant
Primary fans have high pressure, which makes them suitable for boiler power plants. These are necessary for supplying air to transport the coal directly to the furnace from the pulverizer. In this process, steam is created a high pressure and high temperature. This steam is used to generate electricity with help of turbine and generator. In a thermal power plant, this is the primary process. The PA fans are capable of providing positive pressure upstream to the pulverizer, handling the coal and air combination into the furnace. These fans have a crucial role in power plants, as they supply the necessary air for the combustion of fuels and maintaining the desired temperature in the furnace.

PA air gains temperature when it passes through the air preheater. Next, a damper is necessary to mix it with the cold PA air. The damper successfully controls the airflow. Then it is supplied to the bottom of the coal mill. The PA fan then lifts the coal powder to all the corners of the furnace for combustion. Therefore, PA fans create a positive pressure in the furnace. It also lifts the coal powder. In case the PA fans fail, it results in a high vacuum in the furnace, which might potentially damage it.

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