Forced draft fans
Forced draft fans
The fans are for supplying pressurized air that required to system or boilers, we called them as forced draft fans(FD) or multi-purpose centrifugal fans.
When it is in balanced ventilation, the forced draft fan must overcome all resistance from the entrance of air duct to the furnace. It includes the resistance of air preheater, air supply duct, grate and fuel layer. During positive pressure ventilation, forced draft fan (FD) overcome all the resistance of smoke and air duct from the entrance of the air dust. This includes all flue resistance of air preheater, air supply duct, grate, fuel layer and chimney exit.
Introduction to FD fans
Most of the time, use the forced draft fans in boilers. Install it in front of the boiler air preheater. It sucks the air from the atmosphere. And then sends the air to the air preheater and heated to the requested temperature. Use part of it as the secondary air of the boiler and directly send to the furnace of the boiler through the burner. But the other part enters the pulverized coal preparation system as a desiccant. Or as primary air, convey coal powder to the furnace through the burner (depleted air powder feeding system), or as tertiary air directly into the furnace through the burner (hot air powder feeding system)
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What is the difference between ID fan and FD fan?
Induced Draft:- A fan is used to extract the air from boiler post combustion to exhaust through the chimney. This is called ID fan. 1. It located in between the Boiler/ESP and the chimney/stack. Suction from ESP / Boiler and discharge to the stack. 2. Used to exhaust gases to atmosphere through chimney. 3. In balanced draft used to maintain slight negative pressure (-10 mm Hg typically) with respect to atmosphere to prevent pressurization of boiler(reduces the risk of explosion.). 4. Size is largest as it exhaust all air (secondary air and primary air) and is first to start as is necessary for safe boiler operation to prevent pressurization of boiler.
Forced draft:- A fan is used to force air into the boiler to provide more air for combustion. This is called FD fan, the location near mills and discharges directly to wind box of boiler for uniform air distribution. 1. Suction from atmosphere and discharge to the wind box of the boiler. 2. Used to provide secondary air that is the main air supply for fuel combustion. 3. It pressurizes boiler so is started only after the ID fan is started. Is much smaller than ID fan.
