Patent ID: 7281631

Claim:
A process for de-inking paper pulp in a flotation cell, the process comprising: introducing the paper pulp into a top of the flotation cell; passing air bubbles into the flotation cell from a bottom of the flotation cell; moving the pulp from said top of the flotation cell toward said bottom of the flotation cell through a plurality of stages; crossing the moving pulp with the air bubbles in each of said plurality of stages so as to mix the air bubbles with the moving pulp, the air bubbles moving from said bottom of the flotation cell toward said top of the flotation cell through bubble passageways formed on each of the stages; separating the air bubbles from the mixture of air bubbles and the moving pulp in each of the stages so that the pulp is de-inked; forming a foam of the separated air bubbles in the flotation cell, said foam having hydrophobic particles therein; evacuating the foam from the flotation cell; evacuating the de-inked pulp from a lower portion of the flotation cell, said step of moving the pulp comprising: guiding the pulp along guide surfaces corresponding to each of said plurality of stages, each of the guide surfaces extending on both sides of a central axis of the flotation cell, the guide surfaces having said bubble passageways therethrough, the air bubbles following a face of the guide surfaces while passing upwardly; and accelerating a speed of the pulp moving directly from one of said plurality of stages to another of said plurality of stages within the flotation cell without the use of a pump by gradually reducing a cross-section between the guide surfaces immediately upstream of said bubble passageways.