absorb low temperature flue gas quantity of heat, reduce exhaust smoke temperature, reduce exhaust smoke loss and save fuel.

due to feed into the drum before in the economizer heating, thus reduce the water supply in the heating surface of heat absorption, can use the economizer instead of part of the cost of higher evaporation surface. 
feed temperature raised, into the drum will be reduced wall temperature, thermal stress corresponding decreases, and extend the service life of the drum.