Method and apparatus for contacting bubbles and particles in a flotation separation system
A flotation separation apparatus for separating particles in suspensions, feeds slurry containing the particles through an inlet into a contactor where gas is fed through an inlet to mix with the slurry, for example in a downwardly plunging jet, to form a gas-liquid bubbly two-phase mixture under pressure from an outlet restriction in a throttling duct. The mixture is passed through a flow manipulator configured to induce a high energy dissipation rate, for example by way of a Shockwave formed in a diverging section of the throttling duct reducing the size of the bubbles and brining those bubbles into intimate contact with particles in the mixture which is released into a separation cell where a flow manipulating draft tube is provided to reduce turbulence in the mixture. Alternative apparatus and methods for inducing the high energy dissipation rate and for reducing turbulence in the mixture are also described and claimed.
1. Apparatus for contacting bubbles and particles in a flotation separation system, said apparatus comprising:
a contactor arranged to receive under pressure a supply of feed slurry incorporating particles suspended in a liquid and a supply of gas, the contactor being arranged to mix the slurry with the gas forming a gas-liquid bubbly two-phase mixture;
an outlet from the contactor configured to provide a restriction to the flow of mixture therethrough and maintain the mixture within the contactor under pressure, the outlet further being configured to induce a supersonic shockwave within the mixture passing therethrough, and configured such that when slurry and gas are fed into the contactor at feed rates and pressures determined to form said gas-liquid bubbly two-phase mixture and force the mixture through the outlet at a rate that induces said supersonic shockwave within the mixture reducing the size of the bubbles within the mixture and bringing those bubbles into intimate contact with particles in the mixture; and
a separation cell including a mixture-directing device, the mixture-directing device arranged to receive mixture from the outlet and to control the release of that mixture into the separation cell,
wherein the mixture impinges against adjacent surfaces of the mixture directing device to create a high shear environment for the mixture before allowing bubbles with attached particles to rise to the surface of liquid within the cell.
2. Apparatus as claimed in claim 1 wherein the contactor comprises a substantially vertical column arranged to receive the feed slurry under pressure into the top of the column.
3. Apparatus as claimed in claim 2 wherein the contactor incorporates mixing means comprising a nozzle arranged to form a downwardly plunging jet of feed slurry within the column, and a gas inlet in the vicinity of the jet so formed such that in use gas is entrained into the jet forming said gas-liquid bubbly two-phase mixture.
4. Apparatus as claimed in claim 2 wherein the outlet from the contactor is configured to form at least one throttling duct providing said restriction to the flow of mixture therethrough.
5. Apparatus as claimed in claim 4 wherein the throttling duct has a converging section leading to a throat sized to provide said restriction.
6. Apparatus for contacting bubbles and particles in a flotation separation system as claimed in claim 1 , wherein the mixture from the outlet issues downwardly and the adjacent surfaces are formed by an impingement plate located substantially horizontally below the outlet.
7. Apparatus for contacting bubbles and particles in a flotation separation system as claimed in claim 6 , wherein the impingement plate forms the lower end of a shroud encompassing at least the lower part of the contactor.
8. Apparatus for contacting bubbles and particles in a flotation separation system as claimed in claim 1 , wherein the mixture from the outlet issues into a shroud located within the separation cell, and the adjacent surfaces comprised some of the internal surfaces of the shroud.