Thickener

• US 5,147,556 A
• Filed: 12/19/1990
• Issued: 09/15/1992
• Est. Priority Date: 11/17/1988
• Status: Expired due to Term

• Current Assignee: Supaflo Technologies Pty Limited
• Original Assignee: Supaflo Pty., Limited
• Inventors: Taylor, David
• Primary Examiner(s): HRUSKOCI, PETER A
• Application Number:
  US07/629,339
• Time in Patent Office: 636 Days
• Field of Search: 209/5, 209/173, 210/702, 210/709, 210/712, 210/714, 210/723, 210/732, 210/738, 210/96.1, 210/800, 210/801, 210/127, 210/128, 210/129, 210/194, 210/205, 210/207, 210/208, 210/242.1 , 210/195.1, 210/519
• US Class Current: 210/712
• CPC Class Codes: B01D 21/0024 Inlets or outlets provided with regulating devices, e.g. valves, flaps B01D21/24 takes precedence
• CPC Class Codes: B01D 21/0042 Baffles or guide plates
• CPC Class Codes: B01D 21/02 Settling tanks with single outlets for the separated liquid
• CPC Class Codes: B01D 21/08 provided with flocculating compartments
• CPC Class Codes: B01D 21/2405 Feed mechanisms for settling tanks
• CPC Class Codes: B01D 21/2411 having a tangential inlet
• CPC Class Codes: B01D 21/2427 The feed or discharge opening located at a distant position from the side walls
• CPC Class Codes: B01D 21/34 Controlling the feed distribution; Controlling the liquid level ; Control of process parameters

Abstract

A thickener for liquids or pulps includes a tank in which flocculation takes place. A feedwell for feed liquid is disposed within the tank and has a restricted bottom opening in fluid communication with the tank. The bottom opening has an effective cross-sectional flow area substantially less than the mean cross-sectional area of the feedwell to restrict the flow of liquid between the tank and the feedwell through the bottom opening and thereby promote homogeneous mixing of the feed liquid within the feedwell. A conduit supplies feed liquid to the feedwell. An aperture is formed in the feedwell or the conduit above the bottom opening and below the upper marginal edge of the feedwell to permit the recirculation of dilute liquid directly from the tank through the aperture and into the feed liquid when the surface level in the tank is higher than the surface level in the feedwell to provide for autogenous dilution of the feed liquid.

Claims

1. A thickener for liquids or pulps comprising:

a tank in which flocculation takes place whereby precipitate of higher relative density tends to settle towards the bottom of the tank and dilute liquid of lower relative density is thereby displaced toward the top of the tank;

a feedwell for feed liquid disposed generally within the tank and having a restricted bottom opening in fluid communication with the tank, the bottom opening having an effective cross-sectional area substantially less than the mean cross-sectional area of the feedwell to restrict the flow of liquid between the tank and the feedwell through the bottom opening and thereby promote homogeneous mixing of the feed liquid within the feedwell;

a conduit for supplying the feed liquid to the feedwell; and

an aperture formed in the feedwell or the conduit above the bottom opening and below the upper marginal edge of the feedwell, the aperture and the bottom opening being sized and arranged to create a difference in height between the surface level of the surrounding dilute liquid in the tank and a more dense feed liquid contained within the feedwell, the aperture being positioned to permit the recirculation of dilute liquid directly from the tank through the aperture and into the feed liquid when the surface level of the tank is higher than the surface level in the feedwell to provide for autogenous dilution of the feed liquid.

2. A thickener according to claim 1 wherein the conduit is disposed generally tangentially with respect to the feedwell to supply the feed liquid tangentially into the feedwell and thereby promote homogeneous mixing of the feed liquid.

3. A thickener according to claim 1 wherein the effective cross-sectional flow area of the feedwell progressivley decreases toward the bottom opening.

4. A thickener according to claim 1 wherein the feedwell has a bottom section comprising a generally frustro-conical side wall converging progressively downwardly toward the bottom opening to define a progressively decreasing cross-sectional flow area.

5. A thickener according to claim 1 comprising a plurality of apertures in the feedwell to permit recirculation of dilute liquid directly from the tank into the feed liquid.

6. A thickener according to claim 1 wherein the aperture comprises an opening in a side of the feedwell.

7. A thickener according to claim 6 further comprising a weir plate connected with the side of the feedwell adjacent the aperture for vertical sliding movement between an open position permitting the dilute liquid to flow from the tank into the feedwell through the aperture and a closed position substantially restricting flow through the aperture.

8. A thickener according to claim 1 wherein the conduit comprises a channel extending through the thickener tank and into the feedwell and having an aperture formed therein for permitting flow of the dilute liquid directly from the tank into the channel to dilute the feed liquid.

9. A thickener according to claim 1 wherein the conduit comprises a venturi section including at least one aperture to induce flow of the dilute liquid directly from the tank through the aperture and into the conduit by means of a velocity induced pressure differential to dilute the feed liquid.

10. A thickener for liquids or pulps comprising a tank in which flocculation takes place and a diluting liquid is displaced toward the top of the tank, a feedwell having a bottom opening in fluid communication with the tank, a conduit for a feed liquid extending through the thickener tank and into the feedwell, a venturi in the conduit, and aperture means for introducing the diluting liquid directly from the tank into the conduit in response to a pressure differential caused by flow of a fluid through the venturi for autogenous dilution of the feed liquid.

11. A thickener according to claim 10 wherein the conduit has an end extending into the feedwell substantially tangentially with respect to the feedwell.

12. A thickener for liquid or pulps comprising:

a tank in which flocculation forms a precipitate settling towards the bottom of the tank and displacing a diluting liquid of lower density than the precipitate toward the top of the tank;

a feedwell for a feed liquid disposed within the tank and having an upper edge and a bottom;

an inflow aperture for the diluting liquid formed in the feedwell between the upper edge and the bottom of the feedwell;

a conduit having an end extending into the feedwell for supplying a feed liquid into the feedwell; and

a discharge opening having an area formed in the feedwell lower than the inflow aperture, the area of the discharge opening restricting the flow of the feed liquid from the feedwell into the tank, the inflow aperture and the discharge opening being sized and arranged to create a difference in height between the surface level of the surrounding diluting liquid in the tank and a more dense feed liquid contained within the feedwell.

13. A thickener according to claim 12 wherein the feedwell has a cross-sectional area that progressively decreases from the inflow aperture toward the discharge opening.

14. A thickener according to claim 12 wherein the feedwell has a frustro-conical bottom and the discharge opening is formed in the frustro-conical bottom.

15. A thickener according to claim 12 wherein the conduit includes a venturi and aperture means for introducing the diluting liquid directly from the tank into the conduit when liquid flow through the venturi generates a pressure differential for autogenous dilution of the feed liquid.

16. A method of thickening liquid or pulps in a tank comprising:

supplying a feed liquid via a conduit to a feedwell disposed generally within the tank and having a bottom opening in fluid communication with the tank;

flocculating the liquid in the tank whereby precipitate of higher relative density tends to settle toward the bottom of the tank and dilute liquid of lower relative density is thereby displaced toward the top of the tank;

mixing the contents of the feedwell at least partially by restricting the flow of liquid between the tank and the feedwell through the bottom opening such that the feed liquid is substantially homogeneous; and

directing a flow of the dilute liquid from the tank through an aperture in the conduit or the feedwell disposed above the bottom opening and below the upper marginal edge of the feedwell and into the feed liquid when the surface level in the tank is higher than the surface level in the feedwell to dilute the feed liquid, the aperture and the bottom opening being sized and arranged to create a difference in height between the surface level of the surrounding dilute liquid in the tank and a more dense feed liquid contained within the feedwell.

17. A method of thickening liquids or pulp in a tank in which flocculation takes place and dilute liquid is displaced toward the top of the tank comprising supplying a feed liquid via a conduit into a feedwell having a bottom opening in fluid communication with the tank and an aperture below an upper edge of the feedwell, and opening and closing the aperture in accordance with the level of liquid in the feedwell to introduce dilute liquid directly from the tank into the feedwell for autogenous dilution of the feed liquid.

18. A method of thickening liquids or pulps in a tank comprising:

supplying a feed liquid via a conduit to a feedwell disposed within a tank and having a bottom opening in fluid communication with the tank;

flocculating the liquid in the tank to produce a precipitate settling toward the bottom of the tank and displacing a diluting liquid of lower density than the precipitate toward the top of the tank;

restricting the flow of feed liquid between the tank and the feedwell through the bottom opening of the feedwell such that the relative density of the feed liquid contained within the feedwell is higher than the relative density of the diluting liquid in the tank; and

introducing the diluting liquid from the tank into the feedwell via an aperture in the feedwell, the aperture and the bottom opening being sized and arranged to create a difference in height between the surface level of the surrounding diluting liquid in the tank and a more dense feed liquid contained within the feedwell.

19. A method as claimed in claim 18 wherein the step of introducing the diluting liquid into the feedwell comprises creating a pressure differential between the inside of the conduit and the inside of the tank and drawing the diluting liquid into the conduit from the tank through an aperture in the conduit.

20. A thickener for liquids or pulps comprising:

a tank in which flocculation takes place whereby precipitate or higher relative density tends to settle towards the bottom of the tank and dilute liquid of lower relative density is displaced toward the top of the tank;

a feedwell disposed generally within the tank to contain feed liquid and having a restricted bottom opening in fluid communication with the tank, the bottom opening having an effective cross-sectional flow area substantially less than the mean cross-sectional flow area of the feedwell to restrict the flow of liquid between the tank and the feedwell through the bottom opening and thereby promote homogeneous mixing of the fed liquid within the feedwell;

a conduit for supplying the feed liquid to the feedwell; and

an aperture formed in the feedwell or the conduit and disposed above the bottom opening below an upper marginal edge of the feedwell to permit a flow of dilute liquid directly from the tank through the aperture and into the feed liquid, the aperture and the bottom opening being sized and arranged to create a difference in height between the surface level of the surrounding dilute liquid in the tank and a more dense feed liquid contained within the feedwell, the rate of the flow corresponding to the height differential between the surface level in the tank and the surface level in the feedwell, thereby providing automatically controlled recirculation of dilute liquid directly from the tank for autogenous dilution of the feed liquid.