Flertrækskedel

The invention relates to a multipass boiler (2) for cooling, or cooling while simultaneously cleaning, a flue gas (1) of a refuse incinerator, said boiler comprising a first flue (3) having a lower opening (5) into which the flue gas (1) is introduced, and a second flue (4), a superheater (8), a heat exchanger (9), a base with a lower opening (12), and an ascending channel (11) through which the flue gas (1) leaves said second flue, there being a downward-moving feed material (6) consisting of spherical parts in the second flue (4) of the boiler, which is removed through the lower opening (12) of the base and fed into the second flue (4) through an upper opening. The solution according to the invention is advantageous in that, by decoupling the superheater from the flue gas, a higher superheating temperature can be achieved, the rate of corrosion of the superheater can be reduced, continuous cleaning of the heating surfaces is achieved, and deposited ash can be ground up and removed from the boiler.