Patent ID: 7237733

Claim:
Method for producing thermomechanical fibers from wood chips comprising at least the steps of providing least two refining stages, each refining stage including a rotor and a stator, feeding at least wood chips and steam into the first refining stage, defibrating the wood chips to fibers in the first refining stage to obtain a flow of steam and once refined fibers, removing the flow of steam and once refined fibers from the first refining stage, feeding the flow of refined fibers and steam into the second refining stage, refining the once refined fibers in the second refining stage to produce a flow of twice refined fibers and steam, and removing the flow of twice refined fibers and steam from the second refining stage; said method being characterized by feeding the flow of once refined fibers and steam forward in the first refining stage by rotary energy of the rotor of the refining stage so that no essential back-flow of the steam occurs, transferring the total flow of the once refined fibers and steam exiting the first refining stage into the second refining stage without separating steam from the flow, and feeding the flow of once refined fibers and steam through a flow path having a cross section that is constant or decreasing between at least the exit of the first refining stage and infeed of the second refining stage.