PURPOSE: To improve the discharging of drain and enable to supply dry preheating air by a method wherein a rotor filled with up-and-down breathing matrix and having a drain discharging port at the lower surface thereof is supported by bearings rotatably horizontally so as to expose a half of it to a heat collecting chamber and the other half thereof to a heat depriving chamber.

CONSTITUTION: The rotor 3 is filled with the matrix having ventilating holes in parallel with the rotary shaft 2 thereof and the drain discharging hole 17 is provided at the bottom surface thereof. High-temperature gas from a heating device 10 becomes to low-temperature exhaust gas after the heat thereof is absorbed by the matrix of the rotor 3 through the heat depriving chamber 8 and is introduced into a chimney 31 via a duct 30. The drain, condensed in the matrix, is pushed out of the drain discharging port 17 by compressed air. Accordingly, the humidity of the matrix, shifted from the heat collecting chamber 8 to a preheating chamber 7 under being rotated, is lowered, therefore, the humidity of atmospheric air, heated by the preheating chamber 7, may be lowered. Thus, the discharging of the drain and the dryness of the preheating air may be improved.