Flotation of Recycled Pulp in a Centrifugal Force Field, 1997 Recycling Symposium Proceedings

There are basically only two techniques which have gained industrial importance - wash deinking and flotation deinking. The latter gradually becomes the dominating strategy all over the world. Both techniques have been successively optimized for quite a number of years by machine suppliers, chemical suppliers as well as mill personnel. Today they have attained a very high technical standard, which makes further impro-vements in terms of selectivity, brightness gains and overall cleaning efficiency (not only with respect to ink particles) ex-tremely difficult. In the case of flotation deinking this is true as long as the underlying separation principle, which relies mainly on differences in surface chemistry, is not modified or combined with other effects.

At PTS this was the starting point for the development of a new deinking cell for a newly developed deinking technique based on the flotation process. This concept for the first time permits operation with air/suspension ratios - one of the decisive operating parameters in flotation deinking - far beyond those typically prevailing in conventional cells. After commissioning of the system and optimizing its design and operating parameters, trials were conducted with different recycled fibre inputs. For a close-to-reality mix of offset printed newspapers and gravure printed magazines, very good brightnesses at reduced fibre losses were achieved in the cen-trifugal flotation cell whilst dwelling times were considerably shortened in comparison to conventional standard flotation cells. Significantly, the results of the trials suggest that the centrifugal field copes with distinctly higher consistencies.