Removal of fine- and micro-sticky particles from suspensions of waste paper fibers, combines fine fractionation screening with froth flotation

摘要

Following suspension and dispersion (1) of waste paper fibers (S) in water (W), and any pre-cleaning (2), the suspension is passed through the screen separator (11) in a fine fractionation (3) process. The fine fraction (6) contains impurities; the coarse fraction contains predominantly paper fibers. The fine fraction is subjected to a froth flotation process (4, 4') collecting the fine impurities into foam, for removal. Preferred features: Fine fractionation (3) and flotation (4) are controlled such that acceptable material (8) from flotation contains components, especially fine paper fibers, suitable for paper manufacture. This material is added to the coarse fraction. The fine fraction is removed in a flotation process, producing a clarified water (10). Fine fraction takes place in a pressure sorter containing a screen with openings. Coarse fraction overflows, the fine fraction passes through. Fine fractionation employs screen slots 0.15 mm wide. Round openings can be used, up to a diameter of 2 mm. The sieve is cleared to prevent blockage, using foil-like scrapers. A drum rotor carries scraper blades extending over 200 mm at the circumference. Fractionation is controlled such that fine impurities in the fine fraction have a particle size spectrum generally not exceeding 150 mu m. Control is such that this spectrum is returned by the Sommerville test method, using a slot width of 150 mu m. No adhesive particles, so-called micro-stickies, are removed as fine impurities. Fine fractionation takes place with a supply suspension density of 0.5-2.5%, or 0.5-1.5%. Fine fractionation is carried out at 40[deg]-80[deg]C.