FD Fans – PA and SA Fans & Applications

Draft fans are kinds of industrial fans, also called blowers, and are used in several plants and factories. Draft fans are further subdivided into two types – FD (Forced Draft) fans and ID (Induced Draft) fans.

The scope of this article is going to be focused on FD fans and the way they work as both primary air (PA) fans and secondary air (SA) fans. Firstly, it will help to have a basic understanding of forced draft fans.

What are forced draft fans?
FD fans are equipment used in plants involved in the generation of thermal power. These fans, which are installed at the boiler system’s inlet, take in fresh air from the outside atmosphere and push it inside the combustion chamber with increased pressure. In the chamber, the fuel gets mixed with this air and this leads to the creation of positive pressure.

As a direct result of that, the process of combustion goes on in an unhindered way. Here, it must be highlighted that the amount of power consumed by FD fans is on the lower side. This helps the business in saving costs specific to energy consumption. The FD fans are suitable to be used as primary as well as secondary air(SA) fans.

FD fans – PA and SA fans
These are some salient points related to how the FD fans play the dual role of both PA and SA fans.

• A boiler system has two inlets to enable the flow of air into the chamber where combustion takes place. The FD fan that serves as the primary air fan is installed near the first inlet. And, the second inlet is the site where the blower acting as the secondary air fan is deployed.
• Normally, the air provided by the primary air fan is sufficient to make sure that the process of combustion goes on appropriately. This blower separates particles of fuel so that each of those is touched by the air coming in at high pressure. This FD fan is helpful in constantly maintaining the temperature inside the furnace at the needed level, too.
• But at times, there are situations where the air supplied by the primary fan is inadequate for the completion of the process. The system then immediately requires an additional quantity of air. It is here that the FD blower operating as the secondary fan comes to the rescue. These fans lose no time in sending the added air within the boiler ensuring that the combustion process is not interrupted.
• In the above circumstances, the presence of secondary air fans is imperative to make certain that there is no fuel wastage. And, that is a key aspect that no business can ignore.
• Sometimes, it happens that out of the entire air brought in by the primary fan, a little part remains unused. Here, the air provided by the secondary fan also helps in the full utilization of that unused quantity.
• Thermal plants that are based on coal hold the number one position, in terms of the leading producers of electricity. Coal mining is an activity that carries huge costs, and thus; a plant cannot afford to leave even a small amount of coal unburnt in the chamber. In this respect, when secondary air fans are also there for the boiler system, the entire coal gets rightly combusted. Unwanted costs can be avoided.