Role Of Primary And Secondary Air Fans In Power Plants And Industrial Boilers

Neel Rao

When power plants and industrial boilers are considered, the efficient completion of the combustion process is essential. Only then will the required amount of energy be generated, and the noxious emissions can be reduced as well. Here, the PA (primary air) and SA (secondary air) fans are highly pivotal elements. These fans ensure that there is no disruption in the flow of fresh air into the combustion chamber.

These blowers keep the air-to-fuel ratio balanced and enhance the efficiency of combustion. Also, primary and secondary air fans bring a marked decline in the volume of toxic pollutants. The presence of these fans is indispensable to avoid an abnormal rise in operational costs, along with the quantity of fuel consumed.

  • PA fans provide air that has already been heated, to move pulverized coal between the mill and the furnace. These blowers supply air that is necessary in the initial stages of the process. They make sure that fuel is equally distributed throughout the combustion chamber.
  • SA blowers provide extra air to the furnace so that the combustion process progresses smoothly. If fuel particles are left unburnt even after the initial air supply, these fans provide sufficient oxygen to speed up the process.
  • The scope of primary air fans is centered on the starting stages of combustion. Completing the combustion process appropriately is the job of the secondary air blowers.

Primary and secondary air fans – significance in power plants
Power plants depend heavily on both these fan variants. In particular, they play a very key role in plants that make use of coal-fired boilers.

  • Primary air fans ensure that air and pulverized coal mix efficiently.
  • The PA and SA fans constantly keep the air supply to the combustion chamber balanced. This drastically minimizes both the wastage of fuel and the overall operational costs. They even prevent overheating of the system.
  • When the quantity of unburnt fuel is consistently on the lower side, there is a significant improvement in the longevity of the boiler.
  • Both the blowers enable a noteworthy decline in emissions of toxins like nitrogen oxides and carbon monoxide.
  • Secondary air fans make certain that pressure within the furnace is always at the specified level. SA fans avert backflow, too. This takes care of the safety of equipment and the plant premises.

PA and SA fans – Working principle
These are a few salient points related to the working principle.

  • The primary air fans take fresh air from the outside environment and direct it into preheaters. From there, the air is sent inside the pulverizer.
  • The preheated air gathers fuel particles and moves them via burner nozzles into the furnace.
  • Proper regulation of the PA fan velocity is imperative for properly blending air and fuel.
  • The secondary air fans collect fresh air in the atmosphere and send it into the furnace from a spot just over the burner.
  • SA fans make the air equally spread throughout the chamber.
  • Changing the flow rate of an SA fan impacts the efficiency of combustion, the shape of a
    flame, and the level of pollutants formed.
  • Many models of PA and SA blowers are now fitted with VFDs (variable frequency drives) to change airflow based on the actual requirements of the system. This is done in real-time.