Ash handling system

Ash is the remaining product of solid fuel after burning.

coal-fired:operated by burning coal

Total Ash Produced in coal-fired boilers can be divided into bottom ash and fly ash.

Bottom ash:Bottom ash is agglomerated ash particles, formed in pulverized coal furnaces, that are too large to be carried in the flue gases and impinge on the furnace walls or fall through open grates to an ash hopper at the

bottom of the furnace.

Fly ash:fine particles of ash of a solid fuel carried out of the flue of a furnace with the waste gases produced

during combustion.

Bottom ash handling system

Bottom ash is collected from furnace.Bottom ash removal is very difficult in a boiler.

Reasons:1.High temperature of ash.

2.abrasive and corrosive nature of ash

Ash Handling Systems

Ash handling systems are designed for the removal of ash from boilers

burning coal or other solid fuels.

These systems handle bottom ash andfly ash from stoker-fired, pulverized coal–fired, and

fluidized bed boilers.

A mechanical ash handling system is shown in Fig. 5.52. This system

handles both the bottom ash as well as the fly ash that is collected

in boiler, economizer, and air heater hoppers, designated as 1, 2, and 3

in Fig. 5.52.

The mechanical drag conveyor removes the bottom ash from below the boiler. The ash falls into a water

trough which has a continuouslymoving chain with flight bars which moves the bottom ash at a slow rate up an inclined dewatering section.

The flight bars are thenlooped back by the drive mechanism through the dry

bottom section of the drag conveyor to the submerged portion of the conveyor. In this

illustration, the bottom ash, with added fly ash from hoppers 1, 2 and 3, is discharged into a clinker

grinder (refer to Fig. 5.50), where it isproperly sized. The ash is then moved by a belt

conveyor to a storagebin for periodic unloading.

Fly ash separation system

In a solid fuel-fired boiler ,flue gas contains dust particles which are generated during combustion.

these dust particles are mainly ash.Fly ash is to be separated before flue gas is vented to

atmosphere.