Method and device for cleaning fiber suspensions by means of flotation

A method for cleaning contaminated solid-liquid mixtures, comprising the steps of:

• supplying a liquid to a Venturi mixing element (5),
• conveying a gas to the Venturi mixing element (5),
• enriching in the Venturi mixing element (5) the liquid with gas bubbles of different size and size distribution,
• conveying the liquid enriched with gas bubbles of different size and size distribution to a contaminated solid-liquid mixture, wherein the liquid enriched with gas bubbles has a higher flow velocity than the solid-liquid mixture,
• intermixing the liquid enriched with gas bubbles and solid-liquid mixture whereby impurities and contaminants are detached from the solids of the solid-liquid mixture by the kinetic energy of the gas bubbles and accumulate at the gas bubbles, wherein the gas bubbles subsequently remove the impurities and contaminants from the solid-liquid mixture as foam, and
• separating the solid-liquid mixture and the foam in a subsequent flotation process;
• wherein the Venturi mixing element (5) has two oppositely directed cones (7, 11), with each of the cones opening with its respective small through-opening (12, 13) into a chamber (9) forming a cavity, wherein a region of the opening into the chamber (9) forming the cavity is designed so that each small through-opening (12, 13) of the cones (7, 11) is continued in a non-conical conduit section (8, 10) commensurate with a cross-sectional area of the small through-openings (12, 13), with these non-conical conduit sections (8, 10) opening into the chamber (9) disposed between the cones (7, 11), a large through-opening of the first cone (7) is connected via a third conduit (4) with a first conduit (2) and the large through-opening of second cone (11) is connected via the third conduit (4) with the second conduit (2), the small through-opening (12) of first cone (7) is formed to be smaller than the small through-opening (13) of the second cone (11), and the two oppositely directed cones (7, 11) and the non-conical conduit sections are arranged in longitudinal axial alignment,
• at least one fourth conduit (6) for conveying a gas, wherein the fourth conduit (6) opens into the chamber (9) of the Venturi mixing element (5) forming the cavity, and
• at least one fractionator arranged downstream of the second conduit (3) for removing a foam produced by flotation;
• wherein the chamber (9) forming the cavity enlarges a cross-sectional area in a lateral direction both above and below the non-conical conduit sections;
• and the enlarged cross-sectional area in the lateral direction of the chamber (9) forming the cavity exceeds that of a diameter of the large through-opening of the first cone (7);
• and the enlarged cross-sectional area in the lateral direction of the chamber (9) forming the cavity exceeds each of a diameter of the large through-opening of the first cone (7) and a diameter of the large through-opening of the second cone (11).