Q & A > Question Details
Why do we need Forced Draft and what is its function?
18/01/2017 A: Apoorv Gupta, IOCL Haldia, apoorv.work19@gmail.com
Forced Draft in furnace/boiler is used on the following cases:
1.Revamp of existing natural draft furnace for higher duty which requires high combustion air flow. Same may be achieved through natural draft furnace but of higher stack height which seems not a feasible solution.
2.Implementation of Heat recovery (APH installation) through fuel gas.
3. Improvement in burner performance.

14/01/2017 A: RAMAKRISHNA DADI, HMEL, dadi2rama@gmail.com
In Furnace heater for heading the feed by heater coils 1) natural 2) forced draft 3) balanced draft.
Mainly FD fan (forced draft ) is used in high quantity of fuel gas burning and required to maintain the temperature same tame ID (induced draft) fan is used to use as a preheat the natural air before entering the heater and this FD fan to through out the air to highest chimney.
Natural draft the chimney highest is low and local pollution created so FD fan (forced draft ) is used to to taller chimney to avoid the ground level pollution.
01/01/2017 A: Ravi shankar, HPCL, prskreddy@hpcl.co.in
Generally Drafts are 1) Natural Draft 2) Induced Draft 3) Balanced Draft.
Forced Draft is required
1) When the air and Heat Duty requirement is High compared to the Furnace surface/volume so that natural draft alone cannot achieve the Combustion air rate.
2) Depending upon the Burner design (Pressure drop/NOX Reduction )& Fuel quality (Viscosity etc).
3) Geometry of Furnace for symmetrical air/flue gas distribution.
4) for safety reasons (eg for purging furnace volume with air before lighting up)
31/12/2016 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Some air preheaters have pressure drop high enough to require either a forced draft fan or an induced draft fan or both to provide enough draft for the system as designed.
30/12/2016 A: Sridhar Balakrishnan, Bharat Oman Refineries Limited , laksrid@yahoo.com
Forced draft(FD) :- A fan is used to force air into the boiler to provide more air for combustion. This is called FD fan. Forced draft fan, is used basically for providing the required quantity of hot air to the furnace for smooth and uniform combustion of fuel. FD fan will produce the positive pressure inside the system i.e. furnace.FD fans are typically used to regulate the proper amount of air-to-fuel ratios in an effort to maximize fuel efficiency and to minimize EPA-regulated emissions, such as NOx (Nitrogen Oxides).
30/12/2016 A: Prakash Pimparkar, Environmental Consulting Services , prakash.pimparkar@yahoo.in
For efficient burning of fuel in furnace we need to provide combustion air.There are two ways of providing combustion air either you can force air through the furnace ( forced draft ) or you can pull air through the furnace ( induced draft ) for forced draft one has to put fan before the furnace and for induced draft fan is placed after the furnace.Both systems are followed depending upon design but induced draft is normal practice.
When forced draft, the furnace has few mm of positive pressure and this eliminates air incursion, induced draft furnace could have air incursion due to negative pressure.and air incursion affects the furnace performance adversely.
So depending upon requirement one can design the system