Double-disc refiner

A double disc pulp refiner comprising:

• a first refining disc at a feed end of the refiner;
• and
• a second refining disc coaxial to and opposing the first refining disc;
• wherein:
• the first refining disc comprises:
• one or more inlet openings configured to receive lignocellulosic material,
• a first distal surface facing an opposing surface of the second refining disc,
• at least one refining segment configured to refine the lignocellulosic material and having a second distal surface facing the opposing surface of the second refining disc, the second distal surface having a first height relative to a plane of the first distal surface in a direction toward the opposing surface of the second refining disc,
• a center plate having a third distal surface, the third distal surface having a second height from the plane of the first distal surface toward the opposing surface of the second refining disc, the second height being greater than or equal to the first height,
• elongated protrusions extending from the center plate in a radial direction, at least a portion of each elongated protrusion having a fourth distal surface that is continuous with the third distal surface and having a third height from the plane of the first distal surface toward the opposing surface of the second refining disc, the third height being equal to the second height;
• and
• the third distal surface of the center plate is separated from the opposing surface of the second refining disc by 5-15 mm.