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A 0.25 m 3 laboratory repulper was built for the purpose of determining which variables (pulp type, rotor tip speed, pulp suspension temperature, rotor design, rotor to extraction plate clearance, power to vat volume ratio, and pulp suspension consistency) affect the specific energy (kW-h/ton) required for repulping. Scale replicas of 3 commercial repulper rotors were constructed to test the effect of rotor geometry on repulping specific energy. The pulp types used included kraft aspen, C-flute corrugated cardboard, office printing paper, and unbleached paper towel. The energy required for repulping was found to vary with pulp type, temperature, consistency, and rotor design. It was found that a given material at a given temperature and consistency requires a unique quantity of energy to be repulped independent of the rate of energy addition. It was also found that repulper rotors show Reynolds independence at rotor tip speeds greater than 12 m/s. It was found that the specific energy consumption in a 0.25 m 3 laboratory repulper was identical to that for a 15 m 3 repulper given the comparison was made with identical pulp types, temperatures, consistencies, and rotor designs.

A Thune SP23 screw press dewatering parameters were studied. The dewatering efficiency was affected more by the rotational speed and the pulp properties. The counterpressure affects dewatering near the discharge end, and it was observed to influence the outlet consistency and filtrate flow rate of Kraft, which has much longer fibres and fewer fines compared to TMP and BCTMP.The feed stock freeness and consistency are very important variables to consider in the screw press performance. The freeness reflects the degree of drainage, which is an important parameter to consider when optimising the screw press, while the feed consistency is a parameter of the fibre-fibre contact degree. The pulp properties, especially the fines content and fibre flexibility are also two very important parameters that affect the screw press performance.This study was to provide an insight of the screw press performance and to show the complex effect of the operational parameters on the dewatering characteristics. Using three different pulps, Kraft and TMP softwood fibres and a BCTMP hardwood fibres, we have shown that the fines content and fibre properties are two dominant properties that should be highly considered when operating a screw press.

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