Single-disc refiner

A single-disc refiner for refining lignocellulosic material of 25-75% consistency for paper and board manufacturing, comprising:

• a stationary refining element and an opposed rotatable refining element, the rotatable refining element having an axis about which it rotates which defines a center of the refiner, and a radial direction extending radially from the axis, an axial direction being defined by the axis;
• wherein the stationary refining element has at least one radially extending stationary blade element having stationary guide bars and grooves therebetween, which stationary guide bars and grooves extend from an innermost edge of the stationary refining element closest to the axis, which guide bars and grooves are followed in the radial direction after a transition point by a defibration zone which is followed by a refining zone extending to an outermost edge furthest from the axis;
• wherein the stationary refining element and the rotatable refining element define a feed zone radially inwardly of the transition point;
• wherein the rotatable refining element has at least one radially extending blade element having rotatable feed bars and grooves therebetween, which extend from an innermost edge closest to the axis, wherein the feed bars and grooves are followed in the radial direction after the transition point by a defibration zone followed by a refining zone extending to an outermost edge furthest from the axis;
• wherein the stationary refining element and the opposed rotatable refining element form a blade gap therebetween, wherein the rotatable refining element feed grooves have bottoms, and the stationary refining element guide grooves have bottoms, and the blade gap having a height defined as a distance, in the axial direction, between the rotatable refining element groove bottoms and the stationary refining element groove bottoms of the opposed refining elements at a selected radial distance in the radial direction;
• wherein the rotatable refining element feed bars extend toward the stationary refining element over an imaginary center line halving the blade gap in the height direction of the blade gap, wherein the rotatable refining element feed bars extend over the imaginary center line continuously from the innermost edge closest to the axis to substantially the transition point;
• wherein at the transition point, the stationary refining element guide bars form an abrupt rise in height toward the rotatable refining element and at the transition point there is an abrupt decrease in height of the rotatable refining element feed bars;
• wherein a first radial length is defined from the axis to the outermost edge in the radial direction of the stationary refining element and the opposed rotatable refining element;
• wherein a second radial length is defined in the radial direction from the innermost edge of the stationary refining element and the opposed rotatable refining element to the outermost edge of the stationary refining element and the opposed rotatable refining element in the radial direction;
• wherein the transition point is located on the stationary refining element and the opposed rotatable refining element at a radial distance of 75-80% of the first radial length and said transition point is also located at a radial distance of 60-70% of the second radial length.