What is the function of the economizer recirculation door?

　　The purpose of installing the economizer recirculation door is to protect the economizer when the boiler fires up and shuts down, and when the water supply is interrupted. Because the water in the economizer does not flow when the fire is raised and the furnace is shut down, the high-temperature flue gas may burn the economizer tube. Open the economizer recirculation door and use the difference in working fluid density between the steam drum and the economizer to generate natural circulation, which can cool the economizer tube.