Steam Boilers, Engines, Nozzles and Turbines
In designing air preheaters, the important design consideration is that

Handling and maintenance should be easier
Stack gases should not be cooled to the dew point
Approach temperature should be as low as possible
Heat transfer area should be optimum

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Steam Boilers, Engines, Nozzles and Turbines
Blow off cock in a boiler is used to

Empty the boiler when required and to discharge the mud, scale or sediments which are accumulated at the bottom of the boiler
Increase the temperature of saturated steam without raising its pressure
Put off fire in the furnace of the boiler when the level of water in the boiler falls to an unsafe limit
Control the flow of steam from the boiler to the main pipe and to shut off the steam completely when required

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