Caustic-Free Repulping for Newsprint Production - Part II, Pilot Plant Trials

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Caustic-free repulping of ONP/OMG furnishes has the potential for significant cost savings when compared to the conventional alkaline repulping process. Part I of this work detailed laboratory studies which showed that a high quality pulp could be produced under caustic-free conditions by pulping for the shortest possible time at the lowest reasonable consistency and temperature, along with addition of an optimized dosage of deinking surfactant. Caustic-free repulping eliminates the need for the conventional alkaline chemistry usually added to the pulper, and in turn can significantly reduce cost. To confirm these results a series of pilot plant trials were performed on ONP/OMG furnishes from North America and Europe. Pulps produced using caustic-free repulping on these furnishes were equal or higher in quality compared to those produced using conventional alkaline repulping. Bleaching studies showed that the caustic-free pulps could be post bleached to a 60+ brightness. Micro and macro sticky measurements showed that the pulps produced under caustic-free conditions contained significantly less stickies than did those produced using alkaline conditions. In addition, the process water from the North American caustic-free trial was easier to clarify than the process water from the alkaline pulping run.