A new deinking method for paper recycling using a fluid-jet cavitation technique has been developed. The in-house, laboratory-scale device could reveal that cavitation-jet (CV-jet) treatment without deinking chemicals decreased ink and dirt contents in deinked pulp. As the next step, the first pilot-scale deinking device, ten times larger than lab device, was designed. The specifications of the pilot device were determined by the experiments using lab device. The newly developed pilot device was settled in a deinked pulp mill. The effects of multi-jet nozzles within a reacting vessel depending on consistencies of the deinked pulp were investigated. The operation stability of the device was examined as well. It was found that the shape and size of effective CV zone for ink detachment were changed by the diameter of nozzle and upstream pressure of the jet. The results from batch CV treatment of deinked pulp revealed that the device could treat the pulp with the consistency up to 3.8 % by weight and decrease attached ink, dirt speckles and macrostickies without addition of deinking chemicals. Hydrophobic colloidal materials including microstickies after CV treatment became more difficult to attach to hydrophobic surfaces. Continuous CV treatment gave similar results those from batch treatment. Two types of multiple nozzle arrangements, parallel and cross nozzle modes, decreased dirt speckles to the same level of mill disperser. On the other hand, the reductions of macrostickies by those modes were higher than the disperser. Since the treatment consistency increased more than 3 %, the efficiency of the treatment and the performance of the device were significantly improved. This could be a big step to practical use of CV treatment. Consequently, it is considered that CV treatment is a new, practical technology for paper recycling.
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