AQC boiler why sub-superheater, evaporator, economizer

This is based on the need to set up the heat recovery, the economizer is used to heat the water, the evaporator so that the water evaporates into saturated steam, the superheater will be heated into steam superheated steam, if there is still excess heat can be recovered, you can then add a section of the heat exchanger, and ultimately are as much as possible for the recovery of heat. SP boiler because the exhaust gas temperature reduction is small, the temperature difference is only more than 100 degrees, so it is not a coal economizer.