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

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

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Steam Boilers, Engines, Nozzles and Turbines
In regenerative air preheaters, the heat is transferred

By direct mixing
Heat is transferred by bleeding some gas from furnace
From heating an intermediate material and then heating the air from this material
From a metal wall from one medium to another

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Steam Boilers, Engines, Nozzles and Turbines
The difference between Cornish boiler and Lancashire boiler is that

None of the listed here
Former contains one fire tube and latter contains two fire tubes
Former is water tube type and latter is fire tube type
Former is fire tube type and latter is water tube type boiler

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