Economizer working principle in boilers

Economizer : An economizer is a device used to heat feed water by utilizing the heat in the exhaust flue gases before leaving through the chimney.Economizer improves the economy of the steam boiler.The following are the advantages of using an economizer.

1.It increases the steam raising capacity of a boiler i.e., it shortens the time required to covert water into steam.
2.It prevents formation of scale in boiler water tubes.
3.There is about an average of 18% of coal saving.
4.since the feed water entering the boiler is hot,therefore strains due to unequal expansion are minimized.