Double disc refiners are currently the most widely used refiners. However, conventional conical refiners are also used, as well as high-angle refiners, Conflo type refiners with cone angle of 40 °, double-flow conical refiners with a double-sided conical rotor and two conical stators (Pilao), and the newest cylindrical refiners of Andritz. As far as technological and energy effectiveness of the refiners is concerned, hydrodynamic and rheological aspects are very important. Rheological state of the pulp, depending on hydrodynamic conditions in a particular point of refiner, determines, among other things, the size and consistency of floes. This contributes not only to the intensity of fibre processing, but also to the probability of introducing floes or fibres into the area of impact of refining pressure. In this area, the friction between fibres inside floes and direct mechanical action of bars (mainly during the phase of bar's edge of the rotor moving against bar's edge and surface of the stator) determine technological effect of refining (cutting of fibres, fines production, external fibrillation, internal delamination of wall structures). The probability of floes or fibres reaching this stage of fibre processing, determines the homogeneity of refining, which along proper refining intensity, determines optimal refining.
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