申論題

An economizer is a simple heat exchanger that consists of a bank of tubes. These tubes are connected with an inlet and outlet header located in a relatively cool gas temperature zone beyond the main generating bank of boiler. The additional heat is supplied to the feedwater from the economizer by cooling the flue gas. If oxygen is contained in the feedwater to the economizer, the oxygen is released when the external heat is applied. This may result in the tube and header corrosion. The air heaters cool the hot flue gases by the incoming combustion air instead of the feedwater in economizer.