In this paper it is shown that the defibration and fibrillation work in thermo mechanical pulp refiners can differ significantly dependent on the process conditions. This has a direct impact on the distributed force in the refining zones obtained when the bars hit the fibers or fiber bundles. The distributed force, which is defined as a vector along the surface of the refining segments, is estimated using a model where the total work can be split into reversible and irreversible work. Besides traditional refiner variables such as motor load, dilution water added and inlet- and casing pressures, measurements of temperature profiles in the refining zone and plate gaps from a fullscale CD-refiner are available as inputs. Three data sets are analyzed and it is shown that the shape of the temperature profile and the force distribution vary significantly. This means that the fiber distribution in the refining zone varies as well which affects the final development of the pulp properties. The refining segment pattern and taper play an important role when estimating the force distribution and it is stated that the force distribution close to the contraction part of the flat zone as well as the outer part of the conical section are larger than in other positions. Therefore, specific energy which can be seen as the integral of the total energy distribution along the refining segments cannot be used when describing the variations in the distributed forces.
© 2018 by Walter de Gruyter Berlin/Boston