Wednesday, February 9, 2011

Ash Handling System in a Thermal Power Plant

Coal is burnt in the furnace to heat the boiler to produce steam. Burnt coal is called ash. Some part of the ash falls to the ground and is called bottom ash and the ligher ash particles fly in the air and are called fly ash.
There are different systems for dealing with bottom ash and fly ash.

Bottom Ash: The bottom ash falls through the furnace grating and is collected in a hopper. Its then grinded and crushed to produce find powder ash. The powder ash is then mixed with water to produce ash slurry.
The ash slurry is then pumped to an open pond called the ash dyke.

Fly Ash: The flue gas exits the furnace and is finally disposed off through the chimney. Before the chimney a device called the Electrostatic Precipator is present which is electrically charged. The fly ash sticks to the screens of the electrostatic precipitator while the rest of the flue gas escapes through the chimney.
The stuck ash is then scrapped off the screen using a automated scrapper mechanism and collected in a hopper where it's conveyed to a silo either using air or mechanical conveyor system. The fly ash is stored because it can be used in the manufacture of cement or fly ash bricks. Hence its stored in silos and sold to cement plants and not disposed off like bottom ash