Reasonable use of recovered paper - Removal of low-grade fiber material of recovered fiber suspensions

摘要

Recovered paper, worldwide the most important fiber source for the paper industry, consists of a wide spectrum of materials. Next to chemical pulp and mechanical pulp fibers also fiber fines, fillers, pigments and impurities like ink or stickies are part of the recovered paper mixture. These impurities are removed in various separation processes in the stock preparation of paper mills. The complete stock preparation is normally optimized to gain a maximum yield. But by this remaining impurities are concentrated over several product cycles in recovered paper and can disturb the paper production process in a later life cycle.Many impurities are small particles which are found in the fine particle classes of recovered paper suspensions. Fine particles can be removed from fiber suspensions whereby the inorganic content is reduced in the suspensions and the brightness of the suspension is improved. Also the VOC/SVOC content in the suspensions is reduced by a fines particle removal. The effect of strength properties is different. Therefore the fiber fines must have different quality in different recovered paper grades. It is considerable whether a recycling of removed fiber fines is sensible in some cases.The thermal utilization of fines particles is one possibility for use of removed fiber fines. Because the calorific value depends linear on the inorganic content, it is reasonable that removed fines particles are separated in an organic and an inorganic fraction and that only the organic fraction is used for energy production.