Patent ID: 7300540
Filing Date: 2007-11-27
Classification: B02C,D21B,D21D

Abstract:
1. A system for producing thermomechanical pulp in a rotating disc refiner from wood chips that have been steamed, comprising: a pressurized macerating screw device having an inlet end for receiving the steamed chips, a working section for subjecting the chips to maceration and dewatering under high mechanical compression forces in an environment of saturated steam to destructure the chips, and a discharge end where the dewatered and destructured chips expand; means at the discharge end of the screw device, for introducing dilution water into the dewatered and destructured chips, whereby the dilution water penetrates the expanding chips and together with the chips forms a refiner feed material having a solids consistency in the range of about 30 to 55 percent; a primary refiner having relatively rotating discs each having a working plate thereon, the working plates being arranged in confronting coaxial relation thereby defining a refiner gap which extends substantially radially outward from the inner diameter of the discs to the outer diameter of the discs; each plate having a radially inner fiberizing ring and a radially outer fibrillating ring, each ring having an inner feeding region and an outer working region, wherein the working region of the inner ring is defined by a first pattern of alternating bars and grooves, and the feeding region of the outer ring is defined by a second pattern of alternating bars and grooves, said first pattern on the working region on the inner ring having relatively narrower grooves than the grooves of said second pattern on the feeding region on the outer ring; and a refiner feed device for receiving the feed material and delivering the feed material between the discs at substantially the inner diameter of the discs. wherein the working section of the pressurized macerating screw includes a dewatering portion, having a perforated tubular wall and a flighted coaxial shaft of uniform diameter rotatable therein, and a plug portion immediately following the dewatering portion, having a solid tubular wall and an unlighted shaft of greater diameter than in the dewatering portion, thereby defining a constricted flow cross section for macerating the chips under high compression; and wherein the discharge end of the pressurized macerating screw includes an expansion wall that outwardly flares from the solid tubular wall of the plug portion and a conical valve coaxial with the shaft and confronting the expansion wall in axially adjustable spaced relation, thereby defining an adjustable expansion volume.