Continuously refining raw fibrous material to produce mechanical refiner pulp

Claim 1

A continuous method of producing a mechanical refiner pulp from raw fibrous material comprising the steps of preheating said fibrous material in a preheater in the presence of steam under a pressure which exceeds atmospheric pressure to a temperature exceeding 110° C., so as to soften said fibrous material, continuously introducing said softened fibrous material through a conduit to a disc refiner to refine said softened fibrous material between refining surfaces of said disc refiner, without prior defibration, whereby steam is generated in said disc refiner during refining of said softened fibrous material, continuously conducting at least a portion of said steam generated in said disc refiner away from said disc refiner as subsequent fibrous material is continuously being introduced between the refining surfaces of said disc refiner in order to obtain a desired pressure between said refining surfaces of said disc refiner and to prevent the entire amount of said steam generated in said disc refiner from passing between the discs thereof said desired pressure being greater than atmospheric pressure, but less than the pressure in said preheater, and maintaining the gap between said refining surfaces such that the preheated fibrous material is refined to produce a mechanical refiner pulp of a sufficiently high quality that can be used for making cardboard or paper.