In a hollow cylindrical housing which stores a coolant, a feeding device having a rotating shaft and spiral screw vanes fixedly installed on the periphery of the rotating shaft is provided. At least one first diffusion nozzle is provided in each pitch of the screw vanes on the inner wall of the housing. A pair of second diffusion nozzles are provided for every pitch of the screw vanes on the outer periphery of the rotating shaft respectively at different positions in the axial direction of the rotating shaft and at mutually opposite positions in the circumferential direction of the rotating shaft. The first diffusion nozzles are supplied with wash water through a high-temperature water piping provided on the upper outside of the housing, while the second diffusion nozzles are supplied with wash water through a channel formed in the interior of the rotating shaft.
