Seminar on Boiler Draught
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Draught means the force needed to draw. with regard to the boiler the requirement is to provide an adequate supply of the furnace grate to maintain the proper combustion of fuel, to draw the resulting gases from system and to discharge these flue gases from the chimney to the surrounding. it requires a static pressure difference to be maintained at the grate which causes the flow of air and gases to take place this static pressure difference maintained is called boiler draught means the force needed to draw. With regard to the boiler the requirement is to provide draught or in short draught.
…a force required to
Maintain air flow through a fire bed to aid complete combustion
Draw the resulting hot gases through the system
Remove the products of combustion and discharge to atmosphere
Classification of draught
We can classify the draught into:
NATURAL DRAUGHT: this is produced with the help of chimney; hence, it is called as chimney draught.
h= 353H [ 1/t1-(m+1/m t2)
ARTIFICIAL DRAUGHT: artifical draught produced by the fan steam jet.
What is “CHIMNEY”…
A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the stack, or chimney, effect. The space inside a chimney is called a flue. Chimneys may be found in buildings, steam locomotives and ships. In the United States, the term smokestack (colloquially, stack) is also used when referring to locomotive chimneys or ship chimneys, and the term funnel can also be used….
NATURAL DRAUGHT: this is the produced with the help of chimney. hence, it is also called as chimney draught. The difference in static pressure by the chimney is produced due to the difference in weight of column of the hot gases inside the chimney and the weight of equal column of cold air outside the chimney.
ARTIFICIAL DRAUGHT: modern power plants require a draught of the order of 25-300 mm. of water column whereas it is convenient to produce a draught more then 40mm. Of water column with the help of chimney because it is neither economical nor convenient to build a chimney of considerable height for larger amount of draught.