Abstract: A falling film evaporator having vertical outer tubes with closed upper ends connected to an upper tube plate disposed in the lower region of the evaporator. Other parallel tubes are disposed inside the outer tubes and are connected to a lower tube plate under the upper tube plate. The evaporator also has a mechanism for distributing the material to be evaporated onto the upper ends of the outer tubes in such a way that the material flows down along the tubes and forms a film on the external surface of the tubes. The space between the tube plates, in which the ends of the outer pipes are located, is divided by an intermediate wall into an inlet and an outlet compartments. Heating steam is fed to the inlet compartment. Clean condensate is recovered from the inlet compartment and contaminated condensate from the outlet compartment.