Steam Boilers, Engines, Nozzles and Turbines
Tertiary air is the air used to

Transport and dry the coal
Convert CO (formed in lower zone of furnace) into CO₂ at higher zone
Cool the scanners
Provide air around burners for obtaining optimum combustion

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Steam Boilers, Engines, Nozzles and Turbines
In forced recirculation type boiler,

Heating takes place at bottom and the water supplied at bottom gets converted into the mixture of steam bubbles and hot water which rise to drum
Water is converted into steam in one pass without any recirculation
Water is supplied in drum and through down comers located in atmospheric condition it passes to the water wall and rises to drum in the form of mixture of water and steam
Feed pump is employed to supplement natural circulation in water wall type furnace

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