Compact floatation unit

1. A liquid purification system for a method for purifying a contaminated liquid flow (A), the method comprising the steps of (a) introducing a first type of gas bubbles ( 8 ) into the contaminated liquid flow (A), the first type of gas bubbles being obtained by at least partly saturating a liquid with a first gas (B′) at a first pressure, followed by lowering the first pressure to a second pressure; (b) introducing a second type of gas bubbles ( 9 ) into the contaminated liquid flow (A) downstream of the introduction of the first type of gas bubbles, the second type of gas bubbles being formed by sparging, entrainment or attrition of a second gas (B″) with the contaminated liquid flow; (c) extracting a reject stream (C) comprising aggregates formed by the interaction of contaminants from the contaminated liquid flow with both the first type and the second type of gas bubbles; and (d) obtaining a purified liquid flow (D) downstream of the introduction of the second type of gas bubbles, the liquid purification system comprising:

a gas saturation unit ( 10 );

a vessel ( 1 ) having a cylindrical wall ( 2 ), a first inlet ( 3 ) for the contaminated liquid flow (A), a second inlet ( 4 ) for the second gas (B″), a first outlet ( 6 ) for the reject stream (C), and a second outlet ( 5 ) for the purified liquid flow (D); and

a distribution unit ( 7 ) which is connected to the second inlet ( 4 ) and is located in a lower half of the vessel at a position at least as high as the second outlet;

wherein the first inlet ( 3 ) is arranged in an upper half of the vessel, the first outlet ( 6 ) is arranged in the upper half of the vessel above the first inlet ( 3 ), and the second outlet ( 5 ) is arranged in the lower half of the vessel; and

wherein the gas saturation unit ( 10 ) has an inlet for the first gas (B′) and is arranged upstream of the first inlet ( 3 ) such that at least a part of the contaminated liquid flow (A), and/or a recirculated part of the purified liquid flow (D), is at least partly saturated with the first gas (B′) at a first pressure prior to entering the upper half of the vessel.

2. The liquid purification system according to claim 1 , further comprising an eductor ( 12 ) which is fluidly connected to the second outlet ( 5 ), the second inlet ( 4 ) and a gas source for the second gas (B″), wherein a fraction of the purified liquid flow (D) may be mixed with a second gas (B″) from the gas source prior to being introduced to the vessel ( 1 ) via the second inlet ( 4 ) during use.

3. The liquid purification system according to claim 1 , further comprising a pressure lowering device which is arranged in or downstream of the gas saturation unit such that the pressure of the at least partly saturated part of the contaminated liquid flow (A), and/or the at least partly saturated recirculated part of the purified liquid flow (D), is lowered before or upon entering the vessel during use.

4. The liquid purification system according to claim 1 , wherein the second outlet ( 5 ) is fluidly connected to the gas saturation unit ( 10 ) by a conduit ( 29 ).

5. The liquid purification system according to any of claims 1 - 4 , wherein the vessel comprises a first vessel stage ( 20 ) and a second vessel stage ( 21 ), the first vessel stage being arranged above the second vessel stage and comprising the first inlet ( 3 ), and the second vessel stage comprising the second outlet ( 5 ) and the distributor unit ( 7 ), wherein each of the first and second vessel stage comprises a first outlet ( 6 ) for a reject stream, and wherein the first and second vessel stages are fluidly connected by a conduit ( 23 ) extending between a connecting outlet ( 22 ) arranged in a lower half of the first vessel stage and a connecting inlet ( 24 ) of the second vessel stage.

6. A vessel ( 1 ) for use in a method for purifying a contaminated liquid flow (A), the method comprising the steps of (a) introducing a first type of gas bubbles ( 8 ) into the contaminated liquid flow (A), the first type of gas bubbles being obtained by at least partly saturating a liquid with a first gas (B′) at a first pressure, followed by lowering the first pressure to a second pressure; (b) introducing a second type of gas bubbles ( 9 ) into the contaminated liquid flow (A) downstream of the introduction of the first type of pas bubbles, the second type of gas bubbles being formed by sparging, entrainment or attrition of a second gas (B″) with the contaminated liquid flow; (c) extracting a reject stream (C) comprising aggregates formed by the interaction of contaminants from the contaminated liquid flow with both the first type and the second type of gas bubbles; and (d) obtaining a purified liquid flow (D) downstream of the introduction of the second type of gas bubbles, the vessel comprising:

a cylindrical wall ( 2 );

a first inlet ( 3 ) for the contaminated liquid flow, the first inlet being arranged in an upper half of the vessel;

a second inlet ( 4 ) for the second gas, the second inlet being fluidly connected by a conduit to a distributor distribution unit ( 7 ) arranged in a lower half of the vessel;

a first outlet ( 6 ) for the reject stream, the first outlet being arranged in the upper half of the vessel above the first inlet; and

a second outlet ( 5 ) for the purified liquid flow, the second outlet being arranged in the lower half of the vessel;

wherein the vessel comprises an internal sleeve ( 11 ) having a frusto-conical shape with an upper end ( 14 ) and a lower end ( 15 ), the upper end having a diameter which is smaller than the diameter of the lower end, and the diameter of the lower end being smaller than the diameter of the circular wall ( 2 ) such that a flow area is provided between the circular wall and the lower end, the lower end ( 15 ) being arranged above the distribution unit ( 7 ).

7. The vessel according to claim 6 , wherein the first inlet ( 3 ) is arranged below the upper end ( 14 ) of the internal sleeve ( 11 ) and above the lower end ( 15 ) of the internal sleeve.

8. The vessel according to claim 6 , wherein the first inlet ( 3 ) is arranged such that the contaminated liquid flow will enter the vessel in a direction substantially tangential to the cylindrical wall ( 2 ).

9. The liquid purification system according to claim 1 , wherein the distribution unit ( 7 ) comprises a pipe having at least one radial perforation.

10. The vessel according to claim 6 , wherein the distribution unit ( 7 ) comprises a pipe having at least one radial perforation.