CA2930616A1

CA2930616A1 - Removal of mature fine tailings from tailings ponds and screening debris

Info

Publication number: CA2930616A1
Application number: CA2930616A
Authority: CA
Inventors: Peter Vert
Original assignee: Weir Canada Inc
Current assignee: Weir Canada Inc
Priority date: 2016-05-19
Filing date: 2016-05-19
Publication date: 2017-11-19
Anticipated expiration: 2036-05-19
Also published as: CA2930616C

Abstract

A hollow conduit is positioned within a tailings pond. A bottom end of the hollow conduit is open to inflow of mature fine tailings (MFT) and a top end of the hollow conduit is above a surface of the tailings pond. A removal apparatus, such as a submersible pump, is positioned within the hollow conduit to remove MFT from within the hollow conduit. A debris screen is located at the bottom end of the hollow conduit. The debris screen is sized to allow inflow of MFT into the hollow conduit and to prevent inflow of debris having a size exceeding a maximum opening size of the debris screen.

Description

Removal of Mature Fine Tailings from Tailings Ponds and Screening Debris Field [0ool] This disclosure relates to removal of mature fine tailings (MFT) from tailings ponds, such as those in the oil sands industry.
Background

[0002] Oil sands tailings are a by-product of bitumen extraction from oil sands. Tailings ponds are intended to be temporary settlement basins for tailings. However, tailings ponds have become one of the main environmental challenges in the oil sands industry.

[0003] One component of tailings is mature fine tailings (MFT), which is a mixture of mainly water and fine clay. MFT may also include other components that may be hazardous or that may have detrimental effects on the environment. In a tailings pond, MFT is typically found between a top layer of water and the base of the pond, which may include settled sand.

[0004] Removal of MFT from tailings ponds is key to reclamation of land, to recovery of potentially valuable materials within MFT, and for other reasons. MFT can take a very long time to settle or solidify on its own.

[0005] Removal of MFT from tailings ponds is conventionally done using submersible pumps or dredging. When pumps are used, they are often lowered from barges to a depth at which MFT of desired density is located. However, one complication in MFT
removal is the presence of debris such as tree branches, vegetation, industrial debris, and the like in the tailings pond.

[0006] Another method for removing MFT from tailings ponds is described in Canadian patent 2,812,202. This method proposes positioning a hollow cylindrical structure in the tailings pond. The structure is open at top and bottom and serves to draw MFT of desired density into the bottom of the structure for removal by a pump or similar apparatus from within the , structure. This patent suggests that debris can be removed from within the structure, as the debris would be located at or near the fluid surface.

[0007] The above technologies are not without their drawbacks.
Particularly, the technique described in the above-mentioned patent brings debris in close proximity to the pump or other apparatus charged with removing MFT from the structure. This can cause the pump or other apparatus to become clogged or damaged by debris. In addition, a separate debris handling process to remove debris from the structure and process it would need to be implemented.
Summary

[0008] A hollow conduit is positioned within a tailings pond. A bottom end of the hollow conduit is open to inflow of mature fine tailings (MFT) and a top end of the hollow conduit is above a surface of the tailings pond. A removal apparatus, such as a submersible pump, is positioned within the hollow conduit to remove MFT from within the hollow conduit. A debris screen is located at the bottom end of the hollow conduit. The debris screen is sized to allow inflow of MFT into the hollow conduit and to prevent inflow of debris having a size exceeding a maximum opening size of the debris screen. The risk of damage or clogging of the removal apparatus is thus reduced or eliminated and the debris remains in place, thereby removing the need for a separate debris handling process.
Brief Description of the Drawings

[0009] The drawings illustrate, by way of example only, embodiments of the present disclosure.

[0010] FIG. 1 is a partial section side view of a system for removing mature fine tailings (MFT) from a tailings pond.

[0011] FIG. 2 is a schematic view of a tailings pond with the system deployed.

[0012] FIG. 3 is a perspective view of the system showing detail of a debris screen.

[0013] FIG. 4 is a plan view of the debris screen.

,

[0014] FIG. 5 is a plan view of another debris screen.

[0015] FIGs. 6A ¨ 6E are side views of other systems for removing MFT from a tailings pond.

[0016] FIG. 7 shows removal of a portion of the debris screen.
Detailed Description [003.7] FIG. 1 shows a system 10 according to the present invention. The system 10 is for removing mature fine tailings (MFT) from a tailings pond to solve or mitigate at least one of the problems discussed above.
[0018] The system 10 includes a hollow conduit 12, a removal apparatus 14, and a debris screen 16.
[0019] The hollow conduit 12 is configured to be positioned within a tailings pond. In this embodiment, the hollow conduit 12 is shaped as an open-ended cylinder. In other embodiments, the hollow conduit 12 takes other shapes (e.g., a rectangular tube). A bottom end 20 of the hollow conduit 12 is open to inflow 22 of MFT 24 and a top end 26 of the hollow conduit 12 is above a surface 28 of the tailings pond.
[0020] The removal apparatus 14 is positioned within the hollow conduit 12 and is configured to remove MFT from within the hollow conduit 12 for ultimate removal to a facility for further processing. In this embodiment, the removal apparatus 14 includes a submersible pump 30 suspended within the hollow conduit 12 at an adjustable depth by a line 32 from a support 34, which may be affixed to the hollow conduit 12 or to a nearby barge. The submersible pump 30 can be a submersible vertical turbine pump or similar. The line 32 is configured to support the submersible pump 30 and can include conductive wires for signal transmission, so as to convey control commands to the pump 30. A discharge conduit 36 is further provided to convey discharge of the pump 30 to outside the hollow conduit 12. In other embodiments, more than one submersible pump 30 is provided for increased pump-out rate and/or for redundancy.

, [0021] The debris screen 16 is fitted to the bottom end 20 of the hollow conduit 12. The debris screen 16 is sized to allow inflow 22 of MFT into the hollow conduit 12 and to prevent inflow of debris 40 having a size exceeding a maximum opening size of the debris screen 16. In this embodiment, the maximum opening size of the debris screen 16 is selected based on a clogging characteristic of the submersible pump 30. For example, the maximum opening size of the debris screen 16 can be selected to be approximately equal to or smaller than the throughlet size of the pump 30. The result is that debris that would present a clogging or damage risk to the pump is prevented from entering the MFT removal zone 42 within the hollow conduit 12, so that the pump 30 can be operated reliably and effectively. Small debris, which presents tolerable or no risk of clogging or damaging the pump 30, is permitted to enter the MFT removal zone 42. The maximum opening size of the debris screen 16 can be selected to maximize flow 22 of MFT into the MFT removal zone 42, while minimizing the risk of clogging or damaging the pump 30.
[0022] In this embodiment, the system 10 further includes a buoyancy device 50 connected to the hollow conduit 12 to allow the hollow conduit 12 to float in the tailings pond. The buoyancy device 50 can include one or more chambers filled with air or other material that is less dense than the contents of the tailings pond by an amount sufficient to float the weight of the system 10. The buoyancy device 50 and height of the hollow conduit 12 are selected such that the top end 26 of the hollow conduit 12 floats above the surface 28 of the tailings pond and the bottom end 20 is located within MFT of target density. The depths and densities of the contents of the tailings pond, such as the MFT 24 and any water cap 52, as well as the weight of the system 10 should be taken into account when designing the buoyancy device 50.
[0023] The scientific principles by which MFT is drawn into the hollow conduit 12 are well understood. Canadian patent 2,812,202 describes such in detail and they will not be unnecessarily repeated here. To summarize, when the hollow conduit 12 is lowered into the tailings pond, the strata of the tailings pond is enveloped by the hollow conduit 12. Water 52, intermediate material of lower-than-target density (e.g., less dense MFT), and MFT 24 of target density may be present in the hollow conduit 12 in roughly the same layers as outside the , , hollow conduit 12 in the undisturbed pond. Water 52 and intermediate material is then removed from the hollow conduit 12, using the pump 30 for example, causing the free surface 54 in the hollow conduit 12 to drop due to the density differential between material outside and material inside the hollow conduit 12. Eventually, hydrostatic equilibrium is reached between the material (mainly or entirely MFT) inside the hollow conduit 12 and water 52 and other material outside the hollow conduit 12. Thereafter, as the pump 30 is operated and MFT
is removed from inside the hollow conduit 12, a hydrostatic imbalance is created between material outside and material inside the hollow conduit 12. The hydrostatic imbalance tends to cause material outside the hollow conduit 12 near its bottom end 20 to flow into the hollow conduit 12. Hence, MFT 24 of target density outside the hollow conduit 12 is drawn into the hollow conduit 12 and to the removal zone 42 for removal from the tailings pond. A relatively continuous inflow 22 of MFT can be achieved, while at the same time debris 40 is advantageously excluded from the removal zone 42 by the debris screen 16.
[0024] In other words, the bottom end 20 of the hollow conduit 12 is open to MFT, but not to problematic debris, and the bottom end 20 is positioned to receive MFT of a desired density.
The MFT of the desired density fills the hollow conduit 12 to a hydrostatically equilibrating level for balancing hydrostatic pressures inside the conduit with hydrostatic pressures outside the conduit. As MFT is removed from inside the hollow conduit 12, MFT outside the hollow conduit 12 flows into the hollow conduit as the hydrostatic pressures seek to restore equilibrium.
[0025] FIG. 2 shows the system 10 in use in a tailings pond 60. A
removal conduit 62 connected to the pump discharge conduit 36 can be floated on the pond 60 to deliver MFT to a shore facility 64 for processing and/or removal from the site.
[0026] FIG. 3 shows the debris screen 16 affixed to the bottom end 20 of the hollow conduit 12.1n this embodiment, the debris screen 16 includes a structural framework 70 that is connected, at connection points 72, to the wall at the bottom end 20 of the hollow conduit 12.
[0027] As shown in FIG. 4, the structural framework 70 of the debris screen 16 can include radially arranged structural members 74 (e.g., C channels, angle iron, box tubing, etc.) and a , central member 76. The outer end of each structural member 74 is connected to the hollow conduit 12 at a connection point 72. The inner end of each structural member 74 is connected to the central member 76. Disposed between the structural members 74, the central member 76, and the hollow conduit 12 is one or more pieces of grating 78. The grating 78 defines the maximum opening size of the debris screen 16.
[0028] Each of the connections between the structural members 74, the central member 76, the hollow conduit 12, and the pieces of grating 78 may be permanent (e.g., welded) or removable (e.g., bolted, clipped in place, etc.).
[0029] FIG. 5 shows a debris screen 80 according to another embodiment. The debris screen 80 includes linearly arranged members 82, such as rods or similar, having ends affixed to the bottom end 20 of the hollow conduit 12 at connection points 84. Each member 82 may be permanently or removably connected to the bottom end 20. The spacing between the members 82 defines the maximum opening size of the debris screen 80.
[0030] FIGs. 6A ¨ E show other embodiments of systems for removing MFT from a tailings pond according to the present invention. Individual features of these systems can be used with the system 10 and vice versa. That is, any combination of features of the systems discussed herein that include a debris screen 16 can be used in other embodiments of the present invention.
[0031] As shown in FIG. 6A, a system 100 includes as its removal apparatus a siphon 102, and the maximum opening size of the debris screen 16 is selected based on a clogging characteristic of the siphon.
[0032] As shown in FIG. 6B, a system 110 includes a hollow conduit 112 configured with an adjustable wall height, so that the depth of the bottom end 20 of the hollow conduit can be adjusted to target different densities of MFT. In this embodiment, the adjustable wall height is achieved by forming the hollow conduit 112 from two concentric shells. An inner shell 114 is slidably positionable within an outer shell 116.

[0033] As shown in FIG. 6C, a system 120 includes one or more supports 122 connected to the hollow conduit 12 and extending downward to support the hollow conduit 12 from the bottom of the tailings pond. The buoyancy device can be omitted. When the inner and outer shells 114, 116 (FIG. 6B) are used, the one or more supports 122 can be affixed to the outer shell 106.
[0034] As shown in FIG. 6D, a system 130 includes a deflector 132 disposed at an outside surface of the hollow conduit 12 to deflect undesirable fluid 134 away from the bottom end 20 of the hollow conduit 12. Undesirable fluid, such as water or MFT of density lower than targeted, may, by operation of the system 130, be drawn down and into the inflow 22 of what is desired to be mainly or exclusively MFT of target density. In this embodiment, the deflector 132 includes a skirt positioned around the circumference of the hollow conduit 12, the skirt being angled downward and outward so as to deflect downward flowing undesirable fluid 134 outward and away from the bottom end 20 of the hollow conduit 12.
[0035] As shown in FIG. 6E, a system 140 includes as its removal apparatus a dredge 142, and the maximum opening size of the debris screen 16. The dredge 142 can be of any suitable type, such as a ladder dredge, clamshell dredge, bucket dredge, backhoe dredge, and similar.
The dredge 142 can be suspended from the support 34 (FIG. 1) or similar suitable support.
[0036] FIG. 7 shows removal of a screen portion 150 of the debris screen 16, while the system 10 is within a tailings pond. The support 34 (FIG. 1) or similar suitable support can be used to remove the screen portion 150. In this example, a lifting hook 152 is used to hook onto a lifting eye 154, lifting lug, or similar suitable structure provided to each removable screen portion 150 of the debris screen 16. The screen portion 150 can thus be completely removed from the hollow conduit 12. This allows for ongoing preventive maintenance, such as cleaning, or replacement of screen portions due to damage or the collection/growth of organic matter, which may plug the openings in the screen portion 150.
[0037] Advantages of the present invention should be apparent from the above. For instance, the debris screen keeps debris away from the pump or other removal apparatus, , which helps prevent clogging and damage to the pump or other removal apparatus. In addition, a separate debris handling process is not needed, as debris is kept outside the MFT removal process and remains in the tailings pond. Debris macerators are also not required. Further, the debris screen can be easily removed, while the system is deployed on site or within a tailings pond, for cleaning using equipment that is often already on site.
[0038] While the foregoing provides certain non-limiting example embodiments, it should be understood that combinations, subsets, and variations of the foregoing are contemplated.
The monopoly sought is defined by the claims.

Claims

What is claimed is:

1. A system for removing mature fine tailings from a tailings pond, the system comprising:
a hollow conduit configured to be positioned within the tailings pond with a bottom end of the hollow conduit being open to inflow of mature fine tailings and a top end of the hollow conduit being above a surface of the tailings pond;
a removal apparatus positioned within the hollow conduit and configured to remove mature fine tailings from within the hollow conduit; and a debris screen at the bottom end of the hollow conduit, the debris screen sized to allow inflow of mature fine tailings into the hollow conduit and to prevent inflow into the hollow conduit of debris having a size exceeding a maximum opening size of the debris screen.

2. The system of claim 1, wherein at least a portion of the debris screen is removable from the hollow conduit.

3. The system of claim 1 or 2, wherein the removal apparatus comprises a pump and the maximum opening size of the debris screen is selected based on a clogging characteristic of the pump.

4. The system of claim 1 or 2, wherein the removal apparatus comprises a siphon and the maximum opening size of the debris screen is selected based on a clogging characteristic of the siphon.

5. The system of claim 1 or 2, wherein the removal apparatus comprises a dredge.

6. The system of any one of claims 1 to 5, further comprising a buoyancy device connected to the hollow conduit to allow the hollow conduit to float in the tailings pond.

7. The system of any one of claims 1 to 6, further comprising a support connected to the hollow conduit and extending downward to support the hollow conduit in the tailings pond.

8. The system of any one of claims 1 to 7, wherein the hollow conduit is configured with an adjustable wall height.

9. The system of any one of claims 1 to 8, further comprising a deflector at an outside surface of the hollow conduit to deflect undesirable fluid away from the bottom end of the hollow conduit.

10. A method for removing mature fine tailings from a tailings pond, the method comprising:
attaching a debris screen to a bottom end of a hollow conduit, the debris screen sized to allow inflow of mature fine tailings into the hollow conduit and to prevent inflow into the hollow conduit of debris having a size exceeding a maximum opening size of the debris screen;
positioning the hollow conduit within the tailings pond, the bottom end of the hollow conduit with the debris screen being open to inflow of mature fine tailings, and a top end of the hollow conduit being above a surface of the tailings pond; and removing mature fine tailings from within the hollow conduit.

11. The method of claim 10, wherein at least a portion of the debris screen is removable from the hollow conduit.

12. The method of claim 10 or 11, wherein removing mature fine tailings from within the hollow conduit comprises using a pump, the maximum opening size of the debris screen being selected based on a clogging characteristic of the pump.

13. The method of claim 10 or 11, wherein removing mature fine tailings from within the hollow conduit comprises using a siphon, the maximum opening size of the debris screen being selected based on a clogging characteristic of the siphon.

14. The method of claim 10 or 11, wherein removing mature fine tailings from within the hollow conduit comprises using a dredge.

15. The method of any one of claims 10 to 14, further comprising floating the hollow conduit in the tailings pond using a buoyancy device.

16. The method of any one of claims 10 to 15, further comprising supporting the hollow conduit from a bottom of the tailings pond.

17. The method of any one of claims 10 to 16, wherein the hollow conduit is configured with an adjustable wall height.

18. The method of any one of claims 10 to 17, further comprising deflecting undesirable fluid away from the bottom end of the hollow conduit.