A free flow evaporator of the falling film type has the heating elements disposed in a circular configuration so that each extends radially a distance less than the interior radius of the evaporator cylindrical vessel. Heating vapor is introduced concentrically into the top of the vessel and passes into the tops of the heating elements, and condensate is withdrawn from the bottoms of the heating elements in the vessel. Excess vapor passes through a vapor vent in the bottom of the vessel. The boiling liquid, such as black liquor from paper pulp processing, is introduced through a header above an annular channel with a perforated plate bottom, the perforated plate being disposed on top of the heating elements. The evaporated liquid vapor passes radially outwardly in the vessel, and then upwardly, and is discharged from the top of the vessel and passes to the top of another vessel (providing another effect), to provide heating vapor to the other vessel.