from a metal wall from one medium to another

from heating an intermediate material and then heating the air from this material

by direct mixing ,

heat is transferred by bleeding some gases from furnace

water

dry steam

wet steam

super heated steam

100°C

above dew-point temperature of flue gases

below dew-point temperature of flue gases

less than wet bulb temperature of flue gases

from a metal wall from one medium to another

from heating an intermediate material and then heating the air from this material

by direct mixing

heat is transferred by bleeding some gas from furnace

approach temperature should be as low as possible

handling and maintenance should be easier

heat transfer area should be optimum

stack gases should not be cooled to the dew point