Apparatus and method for processing wood fibers

A pulp refiner comprising:

• a frame;
• at least a first pair of refining members comprising:
• a first refining member associated with the frame and comprising a first refining body including a first refining surface comprising:
• first refiner bars separated by first refiner grooves and extending from a first radially inward position on the refining surface to a first radially outward position on the refining surface;
• and
• second refiner bars separated by second refiner grooves and extending from a second radially inward position on the refining surface to a second radially outward position on the refining surface, the second radially outward position being nearer to an outermost part of the refining body than the first radially outward position,
• wherein the first refiner bars have a first height extending upward from a floor of an adjacent first groove and the second refiner bars have a second height extending upward from the adjacent second groove floor, the second height being a minimum height of the second refiner bars and being spaced apart from the second radially inward position, wherein the second height is at least about 0.35 mm less than the first height;
• a second refining member associated with the frame and comprising a second refining body including a second refining surface comprising second member refiner bars separated by second member refiner grooves, the first refining member being spaced from the second refining member to define a refining space therebetween, wherein at least a portion of the second member refiner bars are positioned so as to be across from the second refiner bars to define a gap between the portion of the second member refiner bars and the second refiner bars;
• and
• a rotor associated with the frame and coupled to one of the first refining member or the second refining member such that rotation of the rotor effects movement of the one of the first or the second refining member relative to the other,
• wherein when a slurry of wood pulp comprising wood fibers is supplied to the frame, the wood pulp slurry passes through the refining space such that a significant number of the wood fibers in the wood pulp slurry are refined and a plurality of wood fiber bundles in the wood pulp slurry are separated.

A method for processing wood fibers comprising:

• providing a refiner comprising at least a first pair of refining members comprising:
• a first refining member comprising a first refining body including a first refining surface comprising:
• first refiner bars separated by first refiner grooves and having a first height extending upward from a floor of an adjacent first refiner groove, and second refiner bars separated by second refiner grooves and having a second height extending upward from a floor of an adjacent second refiner groove;
• and
• a second refining member comprising a second refining body including a second refining surface comprising second member refiner bars separated by second member refiner grooves, wherein the first refining member is spaced from the second refining member to define a refining space therebetween and at least a portion of the second member refiner bars are positioned so as to be across from the second refiner bars to define a gap between the portion of the second member refiner bars and the second refiner bars;
• rotating at least one of the first refining member or the second refining member such that the first and second refining members move relative to one another;
• supplying a slurry of wood pulp comprising wood fibers to the refiner such that the slurry passes through the refining space;
• and
• applying axial pressure to at least one of the first refining member or the second refining member as the slurry is supplied, wherein the gap increases along at least a section of the second refiner bars in a direction extending from a first radially inward position toward a first radially outward position on the first refining surface,
• wherein at least a portion of wood fiber bundles passing through the gap are separated.