Industrial Process Fans – ID, FD, PA And SA Fans In Brief 

The induced draft (ID), forced draft (FD), primary air (PA) and the secondary air (SA) fans are the most important types of industrial blowers. Let us briefly elaborate on their features. 





The Induced Draft (ID) fans 

The draft fans are significant components of every manufacturing unit, especially the thermal power plants. These fans are further divided into two more sub-categories: The induced draft fans and the forced draft fans. 

  • The induced draft fans are usually curved in the backward direction. This particular design is necessary for fans that have to handle high levels of pressure. And, the ID fans exactly do that! 
  • There is an accumulation of hot flue gases in systems like furnaces and boilers. The ID fans operate in such a way that these gases get pushed out of the system, into the external atmosphere. 
  • These fans achieve that by generating negative pressure within the system. 
  • The boiler system’s outlet is the precise point where the ID fans are present. 
  • The induced draft fans are of immense value, from the perspective of energy efficiency. The fans consume less power and hence the plant does not have to be concerned about high electricity bills. 
  • As these fans continuously handle gases of extreme heat, they tend to develop problems related to erosion and corrosion frequently.






The Forced Draft (FD) Fans  

The salient aspects of the FD fans are:

  • The basic operation of a forced draft fan is opposite to that seen in an ID fan. The FD fan takes in the air present in the outside environment and directs it into furnaces/boilers. As a result, a positive pressure gets created and that contributes to the smooth completion of the combustion process. 
  • The FD fans are fixed close to the inlet of the furnace/boiler. 
  • The FD fans also make sure that the volume of air that is there in the system is consistently balanced. This balance is mandatory for proper combustion. 
  • Just like the induced draft fans, even the FD fans utilize less power. 
  • The maintenance cost of the forced draft fans is much lower when compared with the ID variants. Similarly, the FD blowers are cleaner, too. 







Primary Air (PA) Fans

The primary air fans are extensively used in thermal power plants. 

  • The major objective of the PA fan is to ensure that the coal that has been pulverized is properly transported into the furnace. In the furnace the process of combustion happens and coal gets burned generating much heat. 
  • The PA fans operate to generate extreme pressure, which is needed to thrust the coal particles and air towards the furnace. 
  • These fans assist in separating the particles of fuel from one another and thus making sure that combustion gets completed devoid of any hindrances. 







Secondary Air (SA) Fans 

The chief function of the SA fans is to support the primary air fans. 

  • Whenever the situation arises, the secondary air fans bring about a rise in the amount of airflow. This both prevents fuel wastage and also enhances the overall efficiency of the combustion process. 
  • There are instances where it so happens that some air is left unutilized by the PA fans. Here, the presence of a secondary fan makes certain that added air is promptly supplied to the system. With that, there won’t be any hassles in the combustion process.  






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