(57) Thermomechanical, chemimechanical, and chemithermomechanical pulps are produced in
a manner such that they have enhanced drainage and strength, and/or can be bleached
to enhanced brightness levels and in a simple manner. Chips are impregnated with chemical
or thermal treating fluid, such as by passing heated sulfite liquor countercurrent
to the flow of the chips (at 12). After impregnation, and where applicable cooking,
the chips are washed by a countercurrent flow of wash liquid (at 13,27) including
chelating and surface active agents. Immediately after washing the chips are mechanically
refined to produce a mechanical pulp by passing the chips through a first pressurized
refiner (14, 38), screening (at 15, 39) the pulp discharge from the first refiner
to provide first (16,40) and second (17, 41) streams, passing the first stream to
a second pressurized refiner (18, 43) having a discharge (19,44), and passing the
second stream directly to the discharge of the second refiner. Further treatment of
the pulp, including bleaching (at 21, 57) utilizing hydrosulfite and/or peroxide,
is effected in order to achieve a mechanical pulp having the desired properties.
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