Steam Boilers, Engines, Nozzles and Turbines
Gradually increasing temperature of flue gases at inlet to chimney for given steam outputs is an indication of

Fouling of heat transfer surfaces
High calorific value coal being burnt
Raising of steam temperature
Higher effectiveness of boiler

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

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

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