FUEL FEEDER

For feeding fuel, usually two methods are followed: under bed pneumatic feeding and
over-bed feeding.
Under Bed Feeding:-
The fuel is (crushed coal/paddy Husk etc.), it is transported via one force draft fan from feed
hopper to rotary feeder to the combustor through a feed pipe piercing the distributor (by using
venture and fuel nozzle). Based on the capacity of the boiler, the number of feed points is
increased and its accessories, as it are necessary to distribute the fuel into the bed uniformly.
The boiler under bed feeding system almost 6-8% burning efficiency
increase, in upper bed feeding system decreases this burning efficiency.
For coal cussing  time minimum 10% coal cussing below 02 mm particles
 size , therefore when feeding upper bed system that under size (  below
02 mm )  coal particles carry out from  upper side of furnace to boiler
smoke tube & heat chamber, un-brunt condition. But feeding in under bed
system that's particular  under size coal particles not carry out from
furnace to boiler smoke tube & heat chamber, also burnt in boiler furnace.

Over-Bed Feeding:-
The (crushed coal, 6-10 mm/ Husk) is conveyed from coal bunker to a spreader by a screw
conveyor. The spreader distributes the coal over the surface of the bed uniformly. This type of
fuel feeding system accepts over size fuel also and eliminates transport lines, when compared to
under-bed feeding system.
Fluidized bed combustion has emerged as a viable alternative and has significant
advantages over conventional firing system and offers multiple benefits – compact boiler
design, fuel flexibility, higher combustion efficiency and reduced emission of noxious
pollutants such as SOx and NOx..