Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND SYSTEM FOR REMOVING MATURE FINE TAILINGS OF A DESIRED
DENSITY FROM A TAILINGS POND
Field Of The Invention
The invention enables continuous, year-round removal of Mature Fine Tailings
(MFT)
out of oilsands tailings ponds including removal of MFT which density is
greater than
1.35 tones per cubic meter (t/m3).
It addresses the limitations of the current MFT removal technologies as
described in the
Description Of Current Art section.
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BRIEF SUMMARY
In accordance with an illustrative embodiment of the disclosure, there is
provided a
method comprising: selecting a desired density of mature fine tailings to be
removed
from an oil sands tailings pond; positioning a hollow conduit within the oil
sands tailings
pond such that a bottom end of the hollow conduit is open to the mature fine
tailings and
positioned to receive the mature fine tailings of a desired density and such
that a top
end of the hollow conduit is open above a free water surface of the pond, and
removing
the mature fine tailings of the desired density from within the hollow
conduit. The
mature fine tailings of the desired density fill the hollow conduit to a
hydrostatically
equilibrating level for balancing hydrostatic pressures inside the conduit
with hydrostatic
pressures outside the conduit;
The method may include adjusting a length of the hollow conduit.
The method may include coupling deflector plates to an outer surface of the
hollow
conduit.
The method may include coupling a buoyancy element to the hollow conduit.
The method may include selecting a desired density greater than 1.35 t/m3.
The hollow conduit may be a hollow cylindrical conduit.
The method may include pumping the mature fine tailings of the desired density
from
within the hollow conduit.
The method may include siphoning the mature fine tailings of the desired
density from
within the hollow conduit.
In accordance with another illustrative embodiment of the disclosure, there is
provided a
system for removing mature fine tailings of a desired density from a tailings
pond. The
system comprises a hollow conduit and means for removing the mature fine
tailings
from within the hollow conduit. The hollow conduit is configured to be
positioned within
the pond such that a bottom end of the hollow conduit is open to the mature
fine tailings
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and positioned to receive mature fine tailings of a desired density, such that
a top end of
the hollow conduit is open above a free water surface of the pond, and such
that the
mature fine tailings of the desired density fill the hollow conduit to a
hydrostatically
equilibrating level for balancing hydrostatic pressures inside the hollow
conduit with
hydrostatic pressures outside the hollow conduit. The hollow conduit has a
width or a
diameter selected to allow an inflow of the mature fine tailings of the
desired density
into the hollow conduit to sustain a selected mature fine tailings removal
capacity.
The means for removing the mature fine tailings may be any one of a pump, a
siphon,
an auger, a clam shell, or a shovel.
The system may further comprise at least one deflector element surrounding an
outside
surface of the hollow conduit, and/or a buoyancy element connected to the
hollow
conduit, and/or at least one support element extending from the hollow conduit
to a
bottom of the pond.
The hollow conduit may be a cylindrical hollow conduit, and may further
comprise a wall
extending between the top end and the bottom and having an adjustable section
that is
adjustable to change the location of the bottom end in the pond.
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BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, which illustrate non-limiting embodiments of the
invention,
Figure 1 illustrates an example of an oil sands tailings pond;
Figure 2 illustrates the oil sands tailings pond of figure 1 with one
embodiment of an
MFT transfer system situated therein;
Figure 3 illustrates an example of a vertical section through an oil sands
tailings pond;
Figure 4 illustrates an example of MFT density with depth in an oil sands
tailings pond;
Figure 5 illustrates pumping MFT out of an oil sands tailings pond;
Figure 6 illustrates an embodiment of an MFT transfer system situated within
an oil
sands tailings pond;
Figure 7 illustrates side and top views of an embodiment of an MFT transfer
system with
adjustable side walls;
Figure 8 illustrates an embodiment of an MFT transfer system including a pump;
and
Figure 9 illustrates an embodiment of an MFT transfer system including a
siphon.
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Mature Fine Tailings (MFT) is a byproduct of the bitumen extraction process of
oilsands
mining operations. The main components of MFT are water and oilsands fines.
Numerous
other ingredients are also found in MFT in smaller quantities, these are
either originally
found in the oilsands deposits, or are introduced into MFT through the bitumen
extraction
process.
The "fines" mentioned herein are solid particles smaller than approximately 44
microns
which do not settle to the bottom of the pond but stay in suspension for
prolonged period of
time thus creating MFT.
The oilsands tailings, which are produced through the bitumen extraction
process, are
delivered to the tailings ponds via hydro transport installations.
Typical configuration of an oilsands tailing pond is shown in Figure 1.
Coarse fractions of the tailings such as sand settle at the bottom of the
tailings pond or
form a beach.
A part of water contained within the tailings creates a layer of recyclable
water at the
surface level of the tailings pond. This layer of recyclable water is referred
to as the "water
cap" (1). The rest of the water combined with fines forms MFT (2) which is
located between
the water cap on the top and sand deposit (3) at the bottom of the pond.
MFT behaves as Non-Newtonian, Bingham fluid. Its main physical properties are
characterized by its specific gravity, shear strength and viscosity. The least
dense MFT is
found closer to the water cap. The MFT specific gravity, shear strength and
viscosity
increase with depth.
A vertical section through a typical oilsands tailing pond is shown in Figure
3. An illustration
of change of corresponding MFT density with depth is shown in Figure 4. The
MFT shear
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strength and viscosity increase as a function of its density.
MFT needs to be removed from the tailings ponds for either one of the
following reasons:
):. Meeting environmental regulations aimed at reducing the production rate of
MFT
and volume of MFT accumulated through the bitumen extraction process
> Tailings ponds reclaim operations
> MFT transfer operations as required to support bitumen production
):. Commercial processing of MFT for recovery of valuable ingredients
Description Of Current Art
Currently the MFT removal operations are mostly based on utilizing:
a. Stationary submersible pumping technology, or
b. Dredging technology
Both technologies noted above utilize pumping device(s) placed at a
predetermined depth
inside the MFT deposit. The MFT is than removed by pumping and transported by
hydro-
transport installations.
The limitations of the Current Art are as follows:
a. Limitations utilizing stationary Submersible pumping technology
Submersible pumps have been successfully used for removal of MFT of density up
to
approximately 1.35 t/m3. Higher density MFT is not practically pump-able
utilizing unaided
stationary submersible pumps because the physical properties of MFT at the
pumping
depth location, namely shear strength and viscosity, prevent fluid from
entering the pump
at a sufficient rate to avoid pump overheating and cavitation.
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In addition to this, the performance of submersible pumps is greatly
compromised by pump
suction plugging due to collection of various debris around the pump suction.
This debris is
commonly found in MFT deposits.
b. Limitations utilizing Dredging technology
Dredging technology can be utilized for removal of MFT with density higher
than 1.35 t/m3,
however it is not practical for use in year-round operations because of the
following
reasons:
= As shown in Figure 5, when pumping MFT of higher density, a more
pronounced
"cone" formation of lighter fluid fractions is formed around the pump suction
point (4)
due to physical properties of MFT. This cone formation allows penetration of
smaller
density MFT and water from the layers above to enter the pump therefore the
required density of MFT is lost.
= In order to maintain the required density of MFT, the dredge needs to be
frequently
relocated to a new location, so MFT is gathered from a large area of the lake.
This
dredge relocation requirement makes it impractical to maintain MFT removal
operation year-round because the majority of pond surface is covered with ice
during winter months.
This "cone" formation is present at pumping of MFT of any density and pumping
capacity
but its influence on maintaining required pumping density, when pumping MFT of
density
up to 1.35 t/m3, can be mitigated by adequate engineering of the pumping
system. At lower
densities this "cone" becomes shallower and eventually flattens out at water
level.
Description Of The Invention
As shown in Figure 6 and Figure 7, the invention involves utilization of a
hollow structure
("the structure") (5) which is fully enclosed around its perimeter and which
has continuous
solid walls up to the immersion depth "h". The structure is ideally but not
necessarily of the
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cylindrical form. The structure is placed at the surface of the tailing pond
and is kept on the
surface by utilizing either buoyancy devices (6), or rigid supports founded at
the pond
bottom.
The structure has continuous essentially vertical walls penetrating the MFT
layer to a
predetermined immersion depth "h", and has cross section width "D". The
dimensions "h"
and "D" as shown in Figure 6 and Figure 7 are determined as the function of
the MFT
physical properties, the density range which is intended for collecting
("required density")
and the required MFT collecting capacity ("required capacity").
The dimensions "h" and "D" are determined utilizing hydrostatic and
hydrodynamic
calculations and computational fluid dynamics (CFD) methods for a specific MFT
removal
project.
The dimensions "h" and "D" are determined so to prevent MFT of lower-than-
required
density and water to enter the confines of the structure while allowing
sufficient inflow of
required-density MFT to sustain the needed removal capacity.
Once the structure is installed, water and MFT of lower-than-required density
originally
located within the structure is moved out of the structure. Once the water and
MFT of
lower-than-required density are removed from within the confines of the
structure,
hydrostatic pressure acting on MFT surrounding structure forces MFT of
required density
to enter the confines of the structure and fill the structure up to the level
"h1" so that
hydrostatic balance is established between fluid outside and fluid inside the
structure.
This hydrostatic balance at point "A" of the structure as shown in Figure 6 is
defined as:
t.,
kl A
(4 a7- = S'o(z) Gt7-
Formula 1
0
0
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where:
4 ; - density of fluid inside the structure
4?c, - density of fluid outside the structure
In summary, the step-by-step process of implementing this invention is as
follows:
a. The structure (5) per Figure 6 of predetermined dimensions "D" and "h" is
placed at
the selected location in the tailing pond as per Figure 2.
b. Water and MFT of lower-then-required density is moved out of the structure,
while
MFT of the required density surrounding the structure simultaneously fills the
structure under the action of hydrostatic pressure. The fill level "h1" as per
the
Figure 6 is determined so that the hydrostatic equilibrium per Formula 1 is
maintained.
c. Once the operation of MFT removal from within the structure has started,
the
removed fluid is constantly being replaced by MFT of required density which is
pushed into the structure by hydrostatic pressure so that the hydrostatic
equilibrium
per Formula us maintained. This enables continuous removal operations of MFT.
As shown in Figure 7, the design of the structure walls can be done so the
immersed depth
"h" can be adjusted (9) to allow for change in MFT physical properties.
MFT is removed from inside the structure and transported away utilizing either
a pump (7)
(such as cutter-head dredge pump) as shown in Figure 8, a siphon (8) as shown
in Figure
9; or other suitable mechanical device.
This system also enables removal of organic debris contained within the MFT,
as now the
debris is located at or near the fluid surface.
Placing deflector elements (10) as shown in Figure 7 can further prevent
lighter fluid
surrounding the structure from entering it.
