WO1997027923A1

WO1997027923A1 - High density thickener underflow withdrawal device

Info

Publication number: WO1997027923A1
Application number: PCT/US1997/001320
Authority: WO
Inventors: Granville P. Heeley; Roger S. Turley
Original assignee: Baker Hughes Incorporated
Priority date: 1996-01-31
Filing date: 1997-01-30
Publication date: 1997-08-07
Also published as: PE46798A1; ZA97846B; AU1843697A

Abstract

An underflow withdrawal device is described for use in connection with a thickener tank or other separation tank. The underflow withdrawal device includes an inducer which is positioned between the underflow outlet of a thickener tank and a centrifugal pump, and is positioned for contacting the underflow as it leaves the tank. The inducer shear thins the underflow to modify its flow characteristics, thereby increasing the flowability of the dense, thickened material through the centrifugal pump. The inducer is rotated by virtue of an extension of the drive shaft which operates the impeller of the pump. Therefore, the costs of manufacturing and operating the underflow withdrawal device are reduced.

Description

HIGH DENSITY THICKENER UNDERFLOW WITHDRAWAL DEVICE

BACKGROUND Technical Field: This invention relates to thickener tanks and similar separation tank which produce a thickened underflow for removal from the tank. Specifically, this invention relates to a structural means for removing highly viscous and thickened material from the tank through the underflow outlet.

Background Art: Thickener tanks are used in many industries, such as wastewater treatment and minerals/metallurgical processing, to process slurries and fluids containing solid particulate matter. Thickener tanks are generally used to separate the solids or particulate matter from the fluid component to reclaim and recycle the clarified liquid and/or to reclaim the solids component of the fluid/solids mixture. Thickener tanks typically comprise a large tank into which an influent fluid or slurry is piped via an influent feed pipe. An overflow trough is usually positioned near the top of the tank to receive clarified fluid which overflows a weir. The tank may include a rake arm or other means for facilitating settlement of solids and removal of particulate matter from the tank. The bottom of the tank is angled or sloped downwardly to encourage movement of the solid material, also referred to as the "underflow" or "sludge," out of the bottom of the tank through an underflow outlet or "sludge outlet."

Thickener tanks operate by providing an environment where the solids can settle out of the fluid, toward the bottom of the tank. The solid material, or sludge, moves by gravity flow along the bottom of the tank toward the sludge outlet. Movement of sludge to the sludge outlet can be facilitated by a rotating rake arm which directs the sludge downwardly toward the sludge outlet. A pump is often associated with the sludge outlet to enhance withdrawal or removal of the sludge from the outlet, and to move the sludge along to a point of disposal or recycling. For example, some sludge is dewatered and reclaimed after it is pumped away from the thickener tank through the sludge outlet. In some fluid processing applications, the solid material which settles out in the tank forms a particularly thick and viscous sludge. The thickness and viscosity of the sludge is due in part to the type and amount of solids being separated from the fluid, and may be increased by the use of flocculants which are added to facilitate settlement of the solids. Sludge removal through the outlet and pump can cause degradation of the pump, and can clog the pump and outlet as well, even in the most conventional fluid processing. However, when processing extremely thick and viscous sludge, friction in the suction line leading to the pump can reduce the suction head available to the pump such that the flow, at best, is erratic, or the sludge, at worst, cannot be withdrawn through the system. If the pump is rendered inoperative, the thickener unit must be taken off-line to clean and/or replace the pump. The phenomenon thus described is becoming more commonplace as industry requires higher solids proportions in the thickener underflow to improve water/liquor recovery and to improve sludge disposal methods.

It would be advantageous in industry to provide an underflow withdrawal device for use with a thickener tank which would overcome or modify the thickness and viscosity of the sludge so that the underflow could be easily and consistently withdrawn from the sludge outlet and through the pump without clogging the outlet or pump.

DISCLOSURE OF INVENTION In accordance with the present invention, an underflow withdrawal device for use with a thickener tank, or the like, is structured to modify the thickness and viscosity of the underflow, or sludge, exiting from the underflow outlet of a thickener tank to improve the flow characteristics of the underflow.

By modification of its flow characteristics, the underflow can move easily through the underflow outlet and pump, thereby avoiding degradation of the pump and clogging of the outlet and pump. The present invention has the particular advantage of being configured to employ the drive shaft of the pump to provide structure for modification of the underflow characteristics, thereby simplifying construction and reducing operating costs. The underflow withdrawal device of the present invention includes a motorized centrifugal pump and an inducer positioned between the underflow outlet of the thickener tank and the pump inlet. The inducer is positioned to contact the underflow, or sludge, as it exits the underflow outlet of the thickener tank. The inducer spins, thereby shearing the sludge as it enters the underflow withdrawal device. The shearing action of the spinning inducer thins the sludge and reduces its viscosity so that the sludge can be induced into the pump more easily. "Shear thinning" the underflow, brought about by the action of the inducer, not only improves movement of the underflow through the underflow withdrawal device, but avoids degradation of the pump.

The present invention has the added advantage of reducing the length of the underflow outlet in comparison to the length of outlet which is usually required to move the sludge out of the thickener tank and into the pump. The underflow withdrawal device may also include an isolation valve positioned between the underflow outlet and the inducer to facilitate maintenance of the inducer and pump. Additionally, the configuration of the present invention has the advantage over prior underflow system designs in its use of a single drive shaft and hence a single seal which reduces maintenance and use of seal water.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, which illustrate what is presently considered to be the best mode for carrying out the invention:

FIG. 1 is an elevational view, in partial cross section, of the underflow withdrawal device of the present invention, shown positioned vertically below the sloped bottom of a thickener tank;

FIG. 2 is a view in lateral cross of the inducer shown in FIG. 1 , taken at line 2-2;

FIG. 3 is an elevational view of an alternative embodiment of the inducer; and

FIG. 4 is a view in lateral cross section of the inducer shown in FIG. 3, taken at line 3-3. BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 , which is a side view in elevation of the present invention, illustrates the underflow withdrawal device 10 connected to the underflow outlet 12 of a thickener tank 14. It can be seen from FIG.1 that the bottom 16 of the thickener tank 14 is sloped or angled to aid in gravity flow of the underflow or sludge out of the thickener tank 14 and into the underflow outlet 12, as depicted by arrows 18. The underflow withdrawal device 10 includes an isolation valve 20 which is secured to the underflow outlet 12. The isolation valve 20 may be, for example, a gate valve which can be replaced as may become necessary over an extended period of operation.

The underflow withdrawal device 10 also includes an intermediate pipe section 22 which is positioned between, and secured to, the isolation valve 20 and the pump 24. The intermediate pipe section 22 is provided with a wear- resistant inner surface or liner 25 to counteract the adverse effects of abrasion caused by the underflow or sludge moving through the intermediate pipe section 22 and being impacted by the inducer 50, as described further below. The intermediate pipe section 22 may be provided with a view port flange 26 which allows inspection of the condition within the intermediate pipe section 22. The pump 24 is preferably a centrifugal slurry pump of the type conventionally used with thickener tanks, and facilitates withdrawal of sludge through the underflow withdrawal device 10 by creating suction in the area of the intermediate pipe section 22 and isolation valve 20. The pump 24 includes a pump outlet 28 through which the sludge exits the underflow withdrawal device 10 for disposal or further processing, such as dewatering. The pump 24 may also include a single seal in connection with a single water injection port 29 to inject water into the pump 24 as may be required to flush the pump 24. The configuration of the present underflow withdrawal device 10 with a single seal pump 24 provides a significant advantage over other configurations which require two or more seals. A single seal results in less maintenance and reduced operating costs. The pump 24 may be connected directly to a motor assembly 30, or to a housing 32 which encloses the mechanical components of the motor assembly 30. The motor assembly 30 generally comprises an electric motor 36, a drive shaft 38, a belt drive 40 and a bearing housing 42 through which the drive shaft 38 extends. An impeller 44 positioned within the pump housing 25 is connected to the drive shaft 38 and rotates by operation of the drive shaft 38 which is driven by the motor 36.

An extended shaft section 46 extends from the drive shaft 38 beyond the impeller 44 of the pump 24. The extended shaft section 46 may be an additional length of shaft section connected to the drive shaft 38 at the hub 48 of the impeller 44. Alternatively, the extended shaft section 46 may actually be a continuous extension of the drive shaft 38 as it projects beyond the impeller 44. An inducer 50 is secured to the end of the extended shaft section 46 and is oriented within the intermediate pipe section 22 which defines an inducer housing. As configured, the inducer 50 is caused to rotate in the same direction as the impeller 44 of the pump 24 by rotation of the drive shaft 38. Connection of the extended shaft section 46 and inducer 50 to the drive shaft 38 simplifies the construction of the underflow withdrawal device 10 and reduces the cost of manufacture. The inducer 50 has a dimension transverse a longitudinal axis 52 positioned through the extended drive shaft 46 which defines a circumference 54, as shown more fully in FIG. 2 which illustrates a lateral cross section of the inducer 50. The inducer 50 also has a length dimension 56 (shown in FIG. 1 ). The inducer 50 has an outer surface 58 which comes in contact with underflow or sludge as the underflow moves into the intermediate pipe section 22 of the underflow withdrawal device 10. The outer surface 58 is preferably configured with a structured or three-dimensional surface which provides a plurality of surfaces with which to contact the underflow. One example of a structured surface of the inducer 50 is shown in FIG. 2 where the outer surface 58 of the inducer 50 is formed as vanes 60 which radiate outwardly from a central hub 62 and extend in length co-extensively with the length 56 of the inducer 50. The vanes 60 provide additional inducer surface area to contact the underflow and result in a shearing action being imposed on the underflow.

FIG. 2 illustrates merely one type of inducer 50 design, and many other design configurations may be adopted in the inducer 50 to provide a structured surface which causes a shearing of the underflow, and which promotes induction of underflow into the pump. For example, as shown in FIGS. 3 and 4, the inducer 50 may be structured with angled vanes 64 which spiral about the outer surface 65 of the inducer 50. Each angled vane 64 provides a face 66 which contacts the incoming underflow to cause a "shear thinning" of the underflow. The angled face 66 of each angled vane 64 also promotes induction of underflow into the inducer housing and, thus, into the pump housing 25.

In operation, the underflow, or sludge, exits the thickener tank 14 through the underflow outlet 12, travels through the isolation valve 20 and enters into the intermediate pipe section 22. There, the sludge encounters the inducer 50 which imposes a shearing force on the sludge as the inducer 50 rotates under drive force from the motor 36. The shearing force imposed on the sludge results in a phenomenon known as "shear thinning" where the flow characteristics, thickness and viscosity of the sludge are modified from a highly viscous material to a less viscous and more flowable material. The inducer 50 not only "shear thins," or modifies, the sludge, but it enhances induction of the sludge into the pump 24. The induction action of the inducer 50 assists in moving sludge into the underflow withdrawal device 10 from the underflow outlet 12 and thereby enhances withdrawal of sludge from the thickener tank 14. As a result, the length of the underflow outlet 12 can be shortened considerably over conventional configurations of thickener tanks and underflow systems.

It should be noted that although the underflow withdrawal device 10 of the present invention is illustrated in FIG. 1 as being oriented vertically directly below the thickener tank 14, the underflow withdrawal device 10 may be oriented horizontally or at an angle to the thickener tank 1 . The underflow withdrawal device described herein is suitable for use with thickener tanks and in any other separation tank design where a particularly thick and/or viscous solids component is collected from the tank and withdrawn for disposal or further processing. The particular design of the underflow withdrawal device will vary commensurate with the tank design and may be varied to accommodate different thicknesses and viscosities of solids material being processed. Thus, reference herein to specific details of the illustrated embodiments is by way of example and not by way of limitation. It will be apparent to those skilled in the art that many modifications of the basic illustrated embodiment may be made without departing from the spirit and scope of the invention as recited by the claims.

Claims

CLAIMS What is claimed is:

1. An underflow withdrawal device for removing a sludge of thickened solids from a tank comprising: a pump having an inlet, an impeller and an outlet, said impeller being connected to a drive shaft; an inducer housing for communication with an underflow outlet of a tank for receiving said sludge, said inducer housing being in communication with said pump inlet; and an inducer positioned within said inducer housing upstream of said pump inlet to contact sludge received from said underflow outlet to induce said sludge into said pump, said inducer being rotatable with said drive shaft and being structured to impose a shearing force on said sludge to modify the flow characteristics of said sludge.

2. The underflow withdrawal device of claim 1 wherein said inducer is attached to an additional drive shaft connected to said drive shaft of said pump in axial alignment therewith.

3. The underflow withdrawal device of claim 1 wherein said inducer is attached to an extended drive shaft which is integrally formed with said drive shaft of said pump.

4. The underflow withdrawal device of claim 1 wherein said pump further comprises a single water injection port having a single seal.

5. The underflow withdrawal device of claim 1 further comprising an isolation valve positioned adjacent said inducer housing upstream from said pump.

6. A thickener unit for separating the liquid and solid phases of a slurry to form a sludge of relatively high solids concentration comprising: a tank having an interior space, an influent feed pipe positioned to deliver slurry to said interior space and an underflow outlet positioned to provide egress of sludge from said interior space; a pump positioned exterior to said tank in fluid communication with said underflow outlet, said pump having a drive shaft; an inducer housing positioned between said underflow outlet and said pump to receive said sludge from said underflow outlet; and a rotatable inducer positioned within said housing for imposing a shearing force on said sludge to modify the flow characteristics of said sludge and to induce said sludge into said pump, said rotatable inducer being driven by said drive shaft.

7. The thickener unit of claim 6 wherein said rotatable inducer is in axial alignment with said drive shaft of said pump and is attached to an extended drive shaft connected to said drive shaft of said pump.

8. The thickener unit of claim 6 wherein said rotatable inducer is in axial alignment with said drive shaft of said pump and is rotatably attached to an extension of said drive shaft extending into said inducer housing.

9. The thickener unit of claim 6 further compπsing an isolation valve positioned between said underflow outlet and said inducer housing.

10. The thickener unit of claim 9 wherein said isolation valve, said inducer housing and said pump are oriented substantially vertically below said underflow outlet of said tank.

11. The thickener unit of claim 9 wherein said inducer housing and said pump extend outwardly from said underflow outlet at an angle to said underflow outlet.

12. The thickener unit of claim 9 wherein said inducer housing and said pump extend outwardly from said underflow outlet and are oriented horizontally to said tank.

13. The thickener unit of claim 6 wherein said pump includes a single water injection port having a single seal.

14. A method for removing a thickened or viscous solids component from a thickener tank comprising: providing an underflow withdrawal device positioned relative to the underflow outlet of a tank and positioned to receive high density thickened or viscous material from the tank, said underflow withdrawal device comprising a pump having a drive shaft, and an inducer connected to an extended portion of said drive shaft for contacting said underflow and modifying the flow characteristics of said underflow; directing said underflow from said tank into said underflow withdrawal device; contacting said underflow with the inducer of said underflow withdrawal device to modify the flow characteristics of the underflow to facilitate movement of the underflow into the pump; and directing the underflow from proximate said inducer to said pump.