Design of Boiler Forced Draft Fan [PDF]

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)



Forced draft fan: Given: Weight of air, Wa @ 40% excess air – 398,840 lb/hr Density of air, δa @ 30°C (86°F)



i) Volume of air @ MCR



= =



ii) Required capacity



Wa



- 0.0727 lb/cu.ft



/ 60 ( δ )



398,840 / 60 (0.0727)



=



91,435 cu.ft/min



=



91,435 cu.ft/min x 1.2



=



109,722 cu.ft/min



=



51.8 cu.m/sec



iii)Air pressure required: Furnace



-



+ (37 mm)



Air duct loss



-



+ (25 mm)



Changes in direction-



+ (25 mm)



Across air heater



+ (50 mm)



-



Total air pressure required =



137 mm



Add 40% on air pressure required = 191.8 iv) Required power of the fan, kWfd kWfd



=



Vf x Ps / 102 (ή); ή = motor eff.



=



51.8 x 191.8 / 102 (0.85)



=



114 kw, say 130 kW



v) The actual fan design is single inlet single width



backward curve blades centrifugal fan 160 kW 860 RPM