Boiler economizer is an energy-saving device installed at the tail of boiler flue. Its working principle is to heat boiler feed water into saturated water under drum pressure by absorbing waste heat in flue gas. As the economizer absorbs the heat of high temperature flue gas, it further reduces the exhaust temperature of flue gas, thus reducing the exhaust loss, improving the thermal efficiency of the boiler and effectively reducing the fuel consumption of the boiler. It is one of the important equipment of boiler system.