Steam generator with gas recirculation to the ash hopper region of the furnace

In a steam generating unit having a furance and heat exchange means for generating steam therein, an ash hopper located beneath the furnace, said furnace having opening means connecting the ash hopper to the furnace, water-filled trough means surrounding the ash hopper, wall means extending down from the furnace into the trough means, which terminates below the water level so as to form a liquid seal for preventing hot combustion gases from escaping therefrom, duct means, said duct means having an inlet end connected to the steam generating unit downstream of the heat exchange means, and an outlet end positioned inside the liquid seal but below the furnace opening means, a fan located in the duct means which when actuated will cause combustion gases to flow from the inlet end to the outlet end, and damper means in the duct means located downstream of the fan which can be closed to protect the fan from hot furnace combustion gases when it is not operating.