Note: Descriptions are shown in the official language in which they were submitted.
1
DEWATERING THICK FINE TAILINGS USING DILUTION AND NEAR INFRARED
MONITORING TECHNIQUES
TECHNICAL FIELD
[0001] The technical field generally relates to dewatering thick fine
tailings, and more
particularly to dewatering operations that include dilution and/or near
infrared (NIR)
based monitoring techniques.
BACKGROUND
[0002] Tailings are left over material derived from a mining extraction
process.
Tailings derived from mining operations, for example, oil sands mining, are
often placed
in dedicated disposal ponds for settling. The settling or separation of fine
solids from the
water is a relatively slow process. Due to the behaviour of fine solids in the
aqueous
phase, a material that can be referred to as "thick fine tailings" (TFT) is
formed. TFT
material mainly includes water and fine mineral solids. The fines are small
solid
particulates having various sizes up to about 44 microns. TFT material has a
solids
content with a fines portion sufficiently high such that the fines tend to
remain in
suspension in the water and the material has slow consolidation rates.
[0003] In some scenarios, the TFT can form in a tailings pond. When whole
tailings
(which include coarse solid material, fine solids, and water) or thin fine
tailings (which
include a relatively low content of fine solids and a high water content) are
supplied to a
tailings pond, the tailings separate by gravity into different layers over
time. The bottom
layer is predominantly coarse material, such as sand, and the top layer is
predominantly
water. The middle layer is relatively sand depleted, but still has a fair
amount of fine
solids suspended in the aqueous phase. This middle layer is an example of TFT,
and is
often referred to as "mature fine tailings" (MET).
[0004] MFT can be formed from various different types of mine tailings
that are
derived from the processing of different types of mined ore. While the
formation of MET
typically takes a fair amount of time (e.g., between 1 and 3 years under
gravity settling
conditions in the pond) when derived from certain whole tailings supplied form
an
extraction operation, it should be noted that MET and MET-like materials may
be formed
CA 3053555 2019-08-29
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more rapidly depending on the composition and post-extraction processing of
the
tailings, which may include thickening or other separation steps that may
remove a
certain amount of coarse solids and/or water prior to supplying the processed
tailings to
the tailings pond.
[0005] Certain techniques have been developed for dewatering TFT.
Dewatering of
TFT can include contacting the thick fine tailings with a flocculent and then
depositing
the flocculated material on a sub-aerial deposition surface where the
deposited material
can release water and eventually dry.
[0006] In the context of dewatering TFT, there are a number of challenges
related to
the monitoring, handling, and management of the materials involved.
SUMMARY
[0007] In some implementations, there is a process for dewatering mature
fine
tailings (MFT) derived from oil sands extraction, the process comprising:
providing an in-
line MFT flow; obtaining near infrared (NIR) spectral measurements of the MFT
flow
using NIR spectroscopy, to determine an NIR derived clay content of the MFT
flow;
diluting the in-line MFT flow with an aqueous stream based on the NIR derived
clay
content to produce a diluted MFT flow having a clay-to-water ratio (CWR)
between about
0.25 and about 0.33; subjecting the diluted MFT flow to in-line homogenization
in a
series of in-line mixers to produce a pre-treated MFT flow; injecting an
aqueous
flocculant solution into the pre-treated MFT flow at a flocculent dosage based
on the NIR
derived clay content, to produce a flocculation material; and dewatering the
flocculation
material to produce an aqueous phase and a solids-enriched material.
[0008] In some implementations, the NIR spectral measurements are
obtained on-
line or at-line. In some implementations, the NIR spectral measurements are
obtained
using reflectance-type NIR spectroscopy.
[0009] In some implementations, the process includes determining the NIR
derived
clay content from the NIR spectral measurements in accordance with a pre-
determined
chennonnetric model correlating NIR spectral measurements and actual clay
content of
MFT samples.
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[0010] In some implementations, diluting of the in-line MFT flow based on
the NIR
derived clay content is controlled according to feedforward control.
[0011] In some implementations, the CWR of the diluted MFT flow is a pre-
determined CWR value. In some implementations, diluting of the in-line MFT
flow
comprises injecting an aqueous stream co-directionally into the MFT flow. In
some
implementations, diluting of the in-line MFT flow comprises injecting the
aqueous stream
within a central region of the MFT flow. In some implementations, diluting of
the in-line
MFT flow is controlled by adjusting of a flowrate of the aqueous stream.
[0012] In some implementations, diluting of the in-line MFT flow is
performed via
multiple dilution inlets provided along a flowpath of the MFT flow, wherein
the dilution
inlets are controlled for injection via only one of the dilution inlets at a
time.
[0013] In some implementations, there is provided a dilution unit for
injecting a
dilution fluid into thick fine tailings (TFT), the dilution unit comprising: a
main pipe for
transporting an in-line TFT flow; and at least one injector quill comprising:
a feed pipe
section extending into the main pipe and receiving a flow of the dilution
fluid; and an
outlet at a distal end of the feed pipe section, the outlet being configured
and positioned
within the main pipe to expel the dilution fluid co-directionally and within a
central region
of the TEl flow to produce a diluted TFT flow.
[0014] In some implementations, the outlet is positioned at a cross-
sectional center-
point of the main pipe.
[0015] In some implementations, the at least one injector quill comprises
a first
injector quill and a second injector quill. In some implementations, the first
and second
injector quills are located in spaced-apart relation to each other along a
length of the
main pipe. In some implementations, the first injector quill is sized and
configured to
provide lower flowrate of the dilution fluid compared to the second injector
quill. In some
implementations, the feed pipe section of the first injector quill has a
smaller diameter
than that of the feed pipe section of the second injector quill. In some
implementations,
the first injector quill is located upstream from the second injector quill.
In some
implementations, the first and second injector quills are configured for
injection of the
dilution fluid via only one of the injector quills at a time. In some
implementations, the
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first and second injector quills further comprise a control assembly
configured to control
the flowrate of the dilution fluid injected into the TFT. In some
implementations, the
control assembly comprises valves and a controller configured to adjust the
valves.
[0016] In some implementations, the unit also includes a common dilution
fluid
header in fluid communication with the first and second injector quills for
supplying
dilution fluid thereto.
[0017] In some implementations, the feed pipe section is oriented at an
oblique
angle relative to the main pipe. In some implementations, the oblique angle is
between
about 600 and about 30 facing upstream of a flow direction. In some
implementations,
the oblique angle is about 45 .
[0018] In some implementations, the outlet is formed by an oblique cut
through an
end of the feed pipe section. In some implementations, the oblique cut is
provided to
form an annular surface of the outlet that is substantially normal to a length
of the main
pipe.
[0019] In some implementations, the outlet comprises a nozzle. In some
implementations, the nozzle comprises an elbow-type nozzle that is oriented
and
positioned to point along a central longitudinal axis of the main pipe.
[0020] In some implementations, the unit also includes a bypass line
configured to
bypass at least a portion of the TFT past the at least one injector quill. In
some
implementations, the bypass line comprises: an inlet portion in fluid
communication with
the main pipe upstream of the at least one injector quill; an outlet portion
in fluid
communication with the main pipe downstream of the at least one injector
quill; and a
flow control assembly comprising valves or gates in order to provide or cease
fluid
communication with the main pipe.
[0021] In some implementations, the at least one injector quill is
configured to
provide sufficient dilution fluid to produce the diluted TEl flow having a
clay-to-water
ratio (CWR) within a CWR range between about 0.25 and about 0.33.
[0022] In some implementations, the at least one injector quill is
configured to
produce the diluted TFT flow having a target CWR value within the CWR range.
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[0023] In some implementations, the TFT is derived from an oil sands
extraction
operation.
[0024] In some implementations, the at least one injector quill is
configured for
injection of a liquid dilution stream comprising fresh water, process water,
and/or recycle
water streams from an extraction operation.
[0025] In some implementations, there is provided a pre-treatment system
for pre-
treating thick fine tailings (TFT) prior to flocculation and dewatering, the
pre-treatment
system comprising: a dilution unit for injecting a dilution fluid into a TFT
flow to produce a
diluted TFT flow; and a homogenization unit comprising: an upstream pipe
section
receiving the diluted TFT flow; a plurality of in-line mixers for subjecting
the diluted TFT
flow to mixing to produce a homogenized diluted TFT flow; and a downstream
pipe
section for supplying the homogenized diluted TFT flow to a flocculation unit.
In some
implementations, the dilution unit is as defined above or herein. The dilution
unit can be
configured to inject the dilution fluid into a central region of the TFT flow.
[0026] In some implementations, the dilution unit comprises one or more
branch
lines in fluid communication with the TFT flow to form one or more
corresponding Tee
junctions. In some implementations, the branch line is configured and operated
such that
a dilution fluid jet entering the TFT flow generally aligns with the central
region of the
TFT flow. In some implementations, the dilution unit comprises multiple
sequential
branch lines having different pipe diameters for providing different flowrates
of the
dilution fluid into the TFT flow. In some implementations, the dilution unit
comprises
multiple sequential side streams entering the TFT flow, and each side stream
comprises
multiple branch lines provided around the TFT flow for injection therein at
different
injection angles.
[0027] In some implementations, the in-line mixers are arranged in series.
In some
implementations, the in-line mixers comprise static mixers. In some
implementations, at
least eight of the static mixers are provided in series.
[0028] In some implementations, the upstream pipe section has a smaller
diameter
than a supply line supplying the diluted TFT thereto.
[0029] In some implementations, the dilution unit, the homogenization
unit, and a
connection conduit therebetween are configured such that the dilution fluid
within the
Date Recue/Date Received 2021-10-14
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TFT remains generally spaced away from side walls of the connection conduit
until the
diluted TFT arrives at the homogenization unit.
[0030] In some implementations, there is provided a process for dewatering
thick
fine tailings (TFT), comprising: supplying a TFT flow to a dilution unit as
defined above or
herein; supplying a diluted TFT flow to an in-line homogenization unit to
produce a pre-
treated TFT flow; subjecting the pre-treated TFT flow to flocculation to
produce a
flocculation material; and dewatering the flocculation material to produce an
aqueous
stream and a dewatered solids-enriched material.
[0031] In some implementations, there is provided a process for dewatering
thick
fine tailings (TFT), comprising: supplying a TFT flow to a dilution unit to
produce a diluted
TFT having a target clay content within a pre-determined clay-to-water (CWR)
range;
supplying the diluted TFT flow to an in-line homogenization unit to produce a
pre-treated
TFT flow; subjecting the pre-treated TFT flow to flocculation with a
flocculant dosage
based on the target clay content, to produce a flocculation material; and
dewatering the
flocculation material to produce an aqueous stream and a dewatered solids-
enriched
material. The dilution fluid can be injected into a central region of the TFT
flow.
[0032] In some implementations, the dilution unit is as defined above
and/or herein.
[0033] In some implementations, the process also includes retrieving the
TFT from a
tailings source to produce the TFT flow which has variable clay content;
monitoring clay
content of the TFT flow on-line or at-line; and controlling the dilution unit
in response to
the variable clay content of the TFT flow via feedforward control, in order to
maintain the
target clay content.
[0034] In some implementations, the process also includes monitoring clay
content
of the diluted TFT and/or the pre-treated TFT; controlling the dilution unit
in response to
the clay content of the diluted TFT via feedback control, in order to maintain
the target
clay content.
[0035] In some implementations, there is provided a process for treating
thick fine
tailings (TFT), comprising: determining clay content of an in-line flow of the
TFT using
near infrared (NIR) spectrometry; injecting a flocculant into the TFT at a
flocculant
dosage based on the clay content of the TFT to produce a flocculation
material; and
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dewatering the flocculation material to produce an aqueous stream and a
dewatered
flocculated material.
[0036] In some implementations, the process includes diluting the TFT
prior to
injecting the flocculant. In some implementations, the diluting is performed
upstream of
the NIR spectrometry. In some implementations, the diluting is performed
downstream of
the NIR spectrometry. In some implementations, the diluting is controlled
based on the
clay content using NIR spectrometry, in order to obtain a diluted TFT flow
having a target
clay-to-water ratio (CWR) which is subjected to flocculation. In some
implementations,
the target CWR is within a CWR range between about 0.25 and about 0.33.
[0037] In some implementations, there process includes controlling
dilution in
response to the clay content via feedforward control, in order to maintain the
target
CWR. In some implementations, the process includes controlling dilution in
response to
the clay content via feedback control, in order to maintain a target clay
content.
[0038] In some implementations, there is provided a process for treating
thick fine
tailings (TFT), comprising: determining clay content of an in-line flow of the
TFT using
near infrared (NIR) spectrometry; diluting the TFT based on the clay content
determined
by the NIR spectrometry to obtain a diluted TFT having a target clay content;
injecting a
flocculant into the TFT based on the target clay content of the diluted TFT,
to produce a
flocculation material; and dewatering the flocculation material to produce an
aqueous
stream and a dewatered solids-enriched material.
[0039] In some implementations, there is provided a process for treating
thick fine
tailings (TFT), comprising: diluting a TFT flow to obtain a diluted TFT;
determining clay
content of the diluted TEl using near infrared (NIR) spectrometry; controlling
the diluting
of the TFT flow based on the clay content determined by the NIR spectrometry,
to
maintain a target clay content of the diluted TFT; injecting a flocculant into
the diluted
TFT, to produce a flocculation material; and dewatering the flocculation
material to
produce an aqueous stream and a dewatered solids-enriched material.
[0040] In some implementations, there is provided a process for treating
thick fine
tailings (TFT), comprising: determining flocculant concentration of an in-line
flow of a
flocculant solution using near infrared (NIR) spectrometry; determining clay
content of an
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in-line flow of the TFT; injecting the flocculent solution into the TFT at a
flocculent
dosage based on the clay content of the TFT and the flocculent concentration,
to
produce a flocculation material; dewatering the flocculation material to
produce an
aqueous stream and a solids-enriched material.
[0041] In some implementations, the process includes controlling the
flocculent
concentration in the flocculent solution using feedback control.
[0042] In some implementations, the process includes controlling the
flocculent
dosage in response to a change in the clay content, comprising:
in response to an increase in the clay content:
increasing the flocculent concentration in the flocculent solution,
increasing a flowrate of the flocculent solution injected into the TFT,
increasing a relative flowrate of the flocculent solution with respect to the
TFT, and/or
performing or increasing dilution of the TEl with an aqueous stream to
reduce the clay content thereof; and
in response to a decrease in the clay content:
decreasing the flocculent concentration in the flocculent solution,
decreasing a flowrate of the flocculent solution injected into the TFT,
decreasing a relative flowrate of the flocculent solution with respect to the
TFT, and/or
decreasing or ceasing dilution of the TFT with an aqueous stream to
reduce the clay content thereof.
[0043] In some implementations, determining the clay content of the in-
line flow of
the TFT is performed using NIR spectrometry. In some implementations, the NIR
spectrometry comprises obtaining NIR spectral measurements on-line or at-line.
In some
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implementations, the NIR spectral measurements are obtained using reflectance-
type
NIR spectroscopy.
[0044] In some implementations, the process includes determining an NIR
derived
flocculant concentration from the NIR spectral measurements in accordance with
a pre-
determined chemometric model correlating NIR spectral measurements and actual
flocculant concentration in flocculant solution samples; and controlling
injection of the
flocculant solution based on the NIR derived flocculant concentration. In some
implementations, the flocculent concentration and the clay content of the TFT
flow are
continuously determined; and the flocculant dosage is continuously adjusted
based on
the flocculant concentration and the clay content.
[0045] In some implementations, there is provided a process for treating
thick fine
tailings (TFT), comprising: injecting a flocculant into a TFT flow to produce
a flocculation
material; obtaining near infrared (NIR) spectral measurements of the
flocculation
material using NIR spectroscopy, to provide an NIR derived dewatering
parameter;
dewatering the flocculation material to produce an aqueous stream and a
dewatered
solids-enriched material; and controlling a process operating condition based
on the NIR
derived dewatering parameter using feedback control.
[0046] In some implementations, the controlling comprises adjusting
injection of the
flocculent into the TFT flow as the process operating condition, in response
to a change
in the dewatering parameter. In some implementations, the controlling
comprises
adjusting dilution of the TFT flow prior to injection of the flocculant as the
process
operating condition, in response to a change in the dewatering parameter. In
some
implementations, the controlling comprises adjusting clay content of the TFT
flow prior to
injection of the flocculant as the process operating condition, in response to
a change in
the dewatering parameter.
[0047] In some implementations, the dewatering parameter comprises Net
Water
Release (NWR) determined after a NWR drainage time, wherein:
NWR = (quantity of water separated and recovered from the flocculation
material
¨ quantity of water added to TFT prior to flocculation including water from
dilution
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and/or flocculant addition ) / (quantity of initial water in TFT prior to
dilution and
flocculant addition).
[0048] When the dilution fluid is water and the flocculant is added in
the form or an
aqueous solution, this added water is subtracted from the water release from
the
flocculated material. The NWR can thus take into account the total amount of
water that
may be added to the TFT prior to the dewatering step.
[0049] In some implementations, the NWR drainage time is between 20
minutes and
48 hours, between one hour and 36 hours or between 12 hours and 24 hours. In
some
implementations, the controlling comprises adjusting the process operating
condition
when the NWR falls below an NWR threshold. In some implementations, the NWR
threshold is between 0.4 to 0.6 when the NWR drainage time is between 12 hours
and
36 hours.
[0050] In addition, it should be noted that other dewatering parameters
can be used.
For example, instead of determining NWR after a given time period (e.g., 24
hours), the
clay-to-water ratio (CWR) of the material can be measured after a given time
period. The
CWR can be determined as follows for the example time period of 24 hours after
initiating dewatering:
CWR = (wt% solids in 24 hrs x % Clay)/(wt% water in 24hrs).
[0051] When CWR parameter is used, a minimum target can be set. For
example,
the minimum target for a 24 hours CWR can be 0.6, 0.65, or 0.7. It is also
noted that the
two terms NWR and CWR are related (NWR= 1-(Feed CWR/24hr CWR)).
[0052] In some implementations, the TFT is derived from an oil sands
extraction
operation.
[0053] In some implementations, the dewatering comprises subjecting the
flocculation material to thickening in a thickener vessel and/or filtering by
a filter device.
[0054] In some implementations, the dewatering comprises sub-aerial
deposition. In
some implementations, the sub-aerial deposition is performed onto a sloped
deposition
surface.
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[0055] In some implementations, method for controlling polymer flocculant
dosing
into thick fine tailings (TFT), comprising: continuously obtaining near
infrared (NIR)
spectral measurements of the TFT using NIR spectroscopy, to provide an NIR
derived
clay content of the TFT; continuously obtaining NIR spectral measurements of a
flocculant solution comprising the polymer flocculation using NIR
spectroscopy, to
provide an NIR derived flocculation concentration in the flocculant solution;
and injecting
the flocculant solution into the TFT to produce a flocculation material; and
dosing the
flocculant on a clay basis in accordance with the NIR derived flocculation
concentration
and the NIR derived clay content of the TFT.
[0056] In some implementations, the method includes diluting the TFT
prior to
injecting the flocculant solution to produce a diluted TFT. In some
implementations, the
NIR derived clay content in the TEl is obtained upstream of the diluting. In
some
implementations, the NIR derived clay content in the TFT is obtained for the
diluted TFT
downstream of the diluting. In some implementations, the diluting is
controlled so that the
diluted TFT has a clay-to-water ratio (CWR) between about 0.25 and about 0.33.
[0057] In some implementations, the TFT is derived from an oil sands
extraction
operation.
[0058] In some implementations, the method further includes dewatering
the
flocculation material. In some implementations, the dewatering comprises
subjecting the
flocculation material to thickening in a thickener vessel and/or filtering by
a filter device.
In some implementations, the dewatering comprises sub-aerial deposition onto a
sloped
deposition surface. In some implementations, each of the NIR spectral
measurements is
obtained using a reflectance-type NIR probe.
[0059] In some scenarios, the dewatering may include discharging the
flocculated
material into a location (e.g., a pit of a mine) to form a permanent aquatic
storage
structure.
[0060] Dilution of the TFT combined with NIR measurements to obtain clay
content
properties can enable advantages related to facilitating efficient flocculant
dosage on a
clay basis to achieve consistent dewatering performance. In addition,
providing co-
directional and centerline injection of the dilution fluid prior to flocculant
injection can
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facilitate one or more of the following advantages: inhibiting plugging of the
dilution
injector outlets, enhancing mixing of the dilution fluid with the tailings by
reducing
segregation issues, and improving efficiency of downstream mixers. NIR
measurements
for obtaining NIR derived clay content in various TFT streams and/or
flocculant
concentration in the flocculent solution can also provide advantages, such as
effective
flocculant dosage on a clay basis, efficient flocculant usage, and enhanced
performance
of the dewatering process via feedback and/or feedforward control.
BRIEF DESCRIPTION OF DRAWINGS
[0061] Fig 1 is a flow diagram of an example thick fine tailings
dewatering operation.
[0062] Fig 2 is a plan partial-transparent view schematic of an example
dilution
device fluidly connected to a pipeline.
[0063] Fig 3 is a plan partial-transparent view schematic of components
of a dilution
device.
[0064] Fig 4 is a cross-sectional view schematic of components of a
dilution device.
[0065] Fig 5 is a plan view schematic of components of a dilution device.
[0066] Fig 6 is a plan view schematic of example components of a dilution
device.
[0067] Fig 7 is a schematic of a pipeline configuration including a
dilution device and
downstream mixers.
[0068] Fig 8 is a flow diagram of an example thick fine tailings
dewatering operation
[0069] Fig 9 is a graph of absorbance units versus wavelength number
showing
example NIR spectra of MET.
[0070] Figs 10 to 17 are graphs of predicted values versus true values
for various
different component concentrations and variables (clay, fines, water, bitumen,
MBI, etc.)
in tailings.
[0071] Fig 18 is a graph of absorbance units versus wavelength number
showing
example NIR spectra of a mixture of MET and polymer flocculant solution.
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[0072] Fig 19 is a graph of predicted values versus true values for a
dewatering
parameter.
[0073] Fig 20 is a close up of a graph of predicted values versus true
values
illustrating correlation lines over different ranges of data points.
DETAILED DESCRIPTION
[0074] The techniques described herein relate to the pre-treatment,
monitoring, and
handling of fluid materials in the context of dewatering thick fine tailings
(TFT). In
particular, enhancements described herein relate to the dilution of TFT prior
to the
addition of a flocculant solution, as well as the use of near infrared (NIR)
techniques for
determining properties of the TFT, the diluted TFT, the flocculant solution,
and the
flocculated material, which can be used for enhanced process control.
Overview of thick fine tailings dewatering operation
[0075] Referring to Fig 8, a thick fine tailings dewatering system 10 can
include a
thick fine tailings (TFT) source 12, such as a tailings pond, from which TFT
is retrieved
as an in-line TFT flow 14. The TFT flow 14 can then be supplied to one or more
pre-
treatment units 16 to produce a pretreated TFT stream 18. The pre-treatment
units 16
can include various different units for screening, diluting, pre-shearing
and/or chemically
pre-treating the TFT. The pretreated TFT stream 18 is then supplied to a
flocculant
injection unit 20 for injecting a flocculant stream 22 into the tailings.
Alternatively, there
may be no pre-treatment units in some scenarios, and the thick fine tailings
are supplied
directly from the source to the flocculant injection step. The resulting
flocculation material
24 can then be subjected to conditioning 26, which may include pipeline shear
conditioning, to form a conditioned material 28. The conditioned material 28
is then sent
to a dewatering unit 30, which may for example be a sub-aerial deposition
area. Release
water 32 separates from solid flocculated material and can be used a recycled
water
34a, 34b for addition to certain pre-treatment units 16 (e.g., dilution unit)
and/or to form
part of the flocculant stream 22.
[0076] It should also be noted that the TFT source can be generated in
various
ways. In some scenarios, extraction tailings¨that include course solids (e.g.,
sand), fine
solids (e.g., clay), water and residual compounds¨are supplied directly from
an
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extraction facility to a tailings pond where the extraction tailings separate
over time to
form different layers in the pond, the fine unsettled layer being composed of
thick fine
tailings. In some other scenarios, extraction tailings can first be subjected
to a separation
step where coarse solids are removed and a thin fine tailings material is
produced. The
thin fine tailings, which has a relatively low solids concentration, is then
supplied to a
settling area or pond to allow settling and consolidation to form thick fine
tailings
material. The step of removing coarse mineral solids from the extraction
tailings can also
include removal of some of the fine solids as well. Examples of producing
thick fine
tailings and treating extraction tailings are described in Canadian patent No.
2,796,025.
This patent describes, for example, a method that includes depositing
extraction tailings
to form a "sand dump" which facilitates removal of coarse solids and
entrapment of some
fine solids; collecting thin fine tailings next to the sand dump in a
collection basin; and
supplying a stream thin fine tailings from the collection basin to a
maturation pond in
order to generate thick fine tailings. Any of the techniques described in
patent No.
2,796,025 can be used to generate thick fine tailings that are then processed
using
techniques described herein.
[0077] Fig 8 also illustrates that various process streams can be
monitored using
measurement devices M. Such measurement devices M can measure process
parameters, such as composition, flow rates, rheological properties,
temperature, and so
on. The data from the measurement devices M can then be used to control
process unit
operations. For example, flocculant dosage is a relevant parameter for
enabling
consistent and efficient performance of the flocculation and dewatering of the
TFT.
Process parameters, such as flocculant concentration in the flocculant stream
22 and the
composition of the pretreated TFT stream 18, are relevant to flocculant dosage
and thus
can be measured and used to inform the flocculent dosage.
[0078] It should be noted that other types of dewatering chemicals can be
used
instead of or in addition to the flocculant. In addition, while the units
illustrated in Fig 1
may be provided as part of an in-line pipe-based system in which the materials
are
transported and treated in a continuous manner along a pipeline prior to being
deposited, in some implementations it is possible to use units that are not in-
line pipe-
based but are rather tank-based, for example, to perform certain process
steps. In some
implementations, the flocculant comprises an anionic polymer flocculent, which
may be a
CA 3053555 2019-08-29
15
sodium salt of an anionic polymer, such as a 30% anionic sodium polyacrylamide-
polyacrylate co-polymer. The polymer flocculant may also have a desired high
molecular
weight, for instance over 10,000,000, for certain flocculation reactivity and
dewatering
potential. The polymer flocculant may be generally linear or not according to
the desired
shear and process response and reactivity with the given TFT.
[0079] It should further be noted that various features, step and
implementations
described above may be combined with other features, step and implementations
described above or herein. For example, one or more pre-treatment methods may
be
selected in accordance with given TFT properties. For instance, in the case
where the
TFT to be treated has higher bitumen content (e.g., higher than 5 wt.%) a
bitumen
removal step may be included, whereas in the case that the thick fine tailings
to be
treated has a bitumen content lower than 5 wt.% one may opt not to implement a
bitumen removal step. Likewise, in the case where the TFT to be treated has an
initial
low yield strength (e.g., lower than 5 to 15 Pa) and/or low clay content, a
pre-shearing
step or dilution may not be performed. In some scenarios, the TFT to be
treated may
have one or more features where certain selected pre-treatment(s) would be
beneficial,
and thus may be selected based upon an initial analysis of the thick fine
tailings.
[0080] Dewatering techniques can be influenced by various properties of
the TFT
being treated. Some of the properties that can influence the process are yield
stress,
viscosity, clay-to-water ratio (CWR), sand-to-fines ratio (SFR), clay content,
bitumen
content, salt content, and various other chemical and rheological properties.
Various
additional methods and steps may be combined to improve the dewatering
operation in
accordance with certain properties of the TFT.
[0081] It is also noted that the flocculent injection unit can have
various designs,
such as an in-line co-annular injector or other types of injectors that
rapidly disperse the
flocculent solution into the TFT. In addition, the downstream handling of the
flocculation
material can include pipelining and expelling into a deposition area for
dewatering. The
pipelining can be managed according to various techniques that have been
previously
described, e.g., where the flocculation material is subject to sufficient in-
line shear to be
within a water-release zone upon deposition. The water-release zone can be
where the
flocculated material has passed a peak yield stress but is not over-sheared,
such that
CA 3053555 2019-08-29
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the water-release characteristics of the material are in a maximum region. The
design
and operation of the pipeline can be conducted according to the Camp Number,
for
example. It is noted that other downstream handling equipment can be used to
handle
the flocculation material in between flocculation and dewatering.
[0082] It is also noted that the dewatering step can be performed using
various
techniques. In some implementations, the dewatering includes depositing the
flocculated
material onto a sub-aerial deposition area in relatively thin "lifts" (e.g.,
approximately 20
to 30 centimeters) where each lift is allowed to dewater and dry by drainage
and
evaporation before a subsequent lift is deposited on the dewatered lift. In
some
implementations, the flocculated material can be discharged into a holding
structure
(e.g., a mine pit) where it fills the volume and eventually forms a permanent
aquatic
storage structure with solids at the bottom and water on top. Other dewatering
techniques can include supplying the flocculated material to a dewatering
device (e.g.,
gravity thickener, centrifugal separation device) which produces a solids-
depleted water
fraction and a solids-enriched water-depleted fraction that can be deposited
sub-aerially.
Dilution pre-treatment implementations
[0083] Referring to Fig 1, a dilution unit 36 can be used to pre-treat
the TFT by
adding an aqueous dilution stream 38. The dilution can be controlled in order
to obtain a
diluted TFT stream 40 having a clay-to-water ratio (CWR) within a CWR range
facilitating
the flocculation and dewatering of the TFT, for example by enhanced control of
flocculant dosage on a clay basis. In some implementations, the CWR of the
diluted TFT
stream 40 may be in between 0.25 and 0.33.
[0084] Still referring to Fig 1, the diluted TFT stream 40 can be
subjected to
homogenization 42 which may be accomplished by passing through mixing devices
in
order to thoroughly mix the added dilution fluid into the TFT. The resulting
pretreated
TFT stream 18 can then be supplied to the flocculant injection unit 20.
[0085] Referring to Fig 2, in some implementations the dilution unit 36
includes
various features that can be used in particular for in-line systems. The
dilution unit 36
can include a main pipe conduit 39 that receives the TFT flow 14, and a
diluting injector
quill 41 extending into the main pipe conduit 39 and having an dilution outlet
43 that is
CA 3053555 2019-08-29
17
sized and positioned within the main pipe conduit 39 such that the dilution
fluid is
injected co-directionally within the TFT flow 14 to form a dilution component
flow that is
surrounded by TFT material. In other words, the dilution fluid is injected co-
directionally
into a middle region of the TEl flow away from internal walls of the main pipe
conduit 39.
In some implementations, the dilution outlet 43 is positioned at a cross-
sectional center-
point 44 of the main pipe conduit 39. The dilution outlet 43 can also be
positioned at a
determined distance away from the surrounding side walls of the main pipe
conduit 39,
in order to prevent the dilution stream from contacting the side walls prior
to
homogenization 42. The dilution outlet 43 can also be designed to have a shape
that
limits the formation of an outward cone-like spray of the dilution liquid that
would impinge
on the side walls.
[0086] It should be understood that "co-directional" means that the
dilution fluid is
injected in the same general direction as the flow of TEl so that the injected
dilution fluid
remains within the bulk flow of the tailings rather than forming a segregated
flow against
the side pipe walls. Thus, co-directional injection does not require that the
outlet of the
dilution unit be oriented to expel the dilution fluid precisely parallel to
the longitudinal axis
of the pipe, but rather that the dilution fluid have a velocity component in
the downstream
direction sufficient to be carried with and mix into the bulk of the TFT flow.
In other
words, the dilution fluid can be injected at various angles relative to the
longitudinal axis
of the pipe, but should have sufficient forward momentum to avoid substantial
segregation that would lead to stratified flow along the pipe walls. As per
the description
of various implementations of the dilution unit, the dilution fluid can be
injected at certain
angles relative to the longitudinal axis of the pipe or parallel therewith.
[0087] As illustrated in Fig 2, the dilution unit 36 can include
additional features,
such as a bypass line 46 coupled to the pipeline so as to bypass a portion or
all of the
incoming TFT flow 14 past the diluting injector quill 41, which may be useful
when the
TFT material already has the desired properties. Appropriate valves or gates
48 (e.g.,
knife gates) can be provided on the bypass line 46 and the other pipeline
components
around the main pipe conduit 39 in order to operate the bypass.
CA 3053555 2019-08-29
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[0088] The piping and equipment of the dilution unit 36 can include
various elbows
50, Y-laterals 52, flanges 54, pipe sections 56, drains, reducers, and so on.
The dilution
unit 36 can be adapted to fluidly connect to an existing pipeline 60a, 60b.
[0089] Still referring to Fig 2, there can be more that one dilution
injector quill 41 for
providing the dilution fluid. In some implementations, there are at least a
first injector quill
and a second injector quill that are located in spaced-apart relation along a
length of the
main pipe conduit 39. In some implementations, the injector quills are
configured to
receive and inject at different flow rates in order to provide different
levels of dilution. For
example, one dilution quill may have a smaller feed pipe section 62 and
smaller dilution
outlet 43 for diluting at lower rates compared to a larger dilution quill.
Such high-rate and
low-rate dilution quills can be operated alternatively, i.e., only one is
operated at a time
depending on the dilution targets for a given incoming TFT. In other
scenarios, dilution
quills can be operated simultaneously, if desired. The multiple dilution
quills can be
supplied with dilution fluid via a single dilution fluid header 64.
[0090] Referring now to Figs 2 and 3, the injector quills 41 can each be
configured
such that the feed pipe section 62 is at an oblique angle 13 relative to the
main pipe
conduit 39, and the dilution outlet 43 is formed by providing an oblique cut
through the
pipe (also referred to as a biased-cut nozzle). The oblique angle may be, for
example,
between 60 and 30 (e.g. 45 ). Such constructions are easy and low-cost,
while
promoting the co-directional and center-line injection of the dilution liquid.
It should
nevertheless be noted that other injector quill configurations can be used,
which may
include a nozzle 66 as illustrated in Fig 6.
[0091] Referring to Fig 3, the dilution unit 36 includes equipment for
cooperation of
the injector quills 41 and the main pipe conduit 39, such as openings in the
main pipe
conduit 39 by which the feed pipe sections 62 enter, as well as associated
attachment
elements such as pads 68 that may each have a weeping hole 70 and upstream and
downstream sides 72, 74 abutting on the feed pipe sections 62.
[0092] Referring briefly to Fig 6, it should be noted that the injector
quills 41 can
have various constructions and configurations, which can be provided to
achieve the co-
directional and center-line injection of the dilution fluid. In some
implementations, the
injector quill 41 may have an elbow-type nozzle 66 that is oriented and
positioned to
Date Recue/Date Received 2021-03-30
19
point along the central longitudinal axis of the main pipe conduit 39. The
outlet 42 of the
injector quill 41 can be the same or similar diameter as the upstream pipe
section 62, or
the outlet can be tapered as illustrated in the elbow-type nozzle 66
embodiment of Fig 6.
[0093] In some implementations, the dilution unit 36 has a "Tee"
configuration,
examples of which are generally illustrated in Figs 4 and 5. Due to lower
maintenance
and ease of operation, a Tee joint can be used. The mixing performance of a
Tee joint
has been found effective particularly with certain conditions. First, the
approaching flow
to the Tee joint should be fully turbulent to promote effective mixing.
Second, it has been
found that the pipe diameters are a strong function of the ratio of the flow
rates for both
the streams (Equation 1):
q / Q = (d/ D) 1.5 (Equation 1)
where q and Q are flow rates of the side and main streams respectively.
Similarly, d and
D represent the side and main stream pipe diameters.
[0094] The mixing mechanism of a Tee joint can be divided into two parts.
The first
part where most of the mixing occurs is known as the initial mixing zone. The
length of
the initial mixing zone is relatively small and depends upon the ratio of
momenta of the
two streams. To maximize mixing in this zone, the jet of dilution fluid should
get the
maximum exposure to the approaching thick fine tailings flow. In other words,
the jet
should not prematurely bend to the side wall adjacent to the Tee inlet. In
situations
where the side stream is injected with very high momentum, the jet may strike
the
opposite wall, and unfortunately the understanding of mixing performance in
such
situations is not well established in the literature. Hence for optimum
mixing, the jet
should generally align to the centerline of the main pipe section 39, and be
designed as
per the correlation presented above.
[0095] Since the ratio of TFT and dilution water flow rates will depend
upon the
CWR of the TFT feed, the ideal ratio of the pipe diameters will also change
for each
CWR. To promote good mixing performance within practical measures, multiple
sequential Tee joints can be provided. In some implementations, referring to
Fig 5, three
sequential Tee junctions are provided, each with different branch diameters
(d3, d2, di)
suitable for low, mid and high CWR (0.35, 0.43, and 0.48) feeds respectively.
Date Recue/Date Received 2021-03-30
20
Furthermore, it has been found that the addition of the side stream through
multiple side
branches provides improved mixing over the single side inlet. In some
implementations,
each side stream can be split in to multiple side streams of equal diameters
(e.g., four
streams of equal diameters oriented at 90 to each other, as illustrated in
Fig 4). The
multiple inlets also encourage the dilution fluid jets to align on the
centerline of the main
pipe, thus promoting effective mixing.
[0096] Referring now to Fig 7, the homogenization unit 42 downstream from
the
dilution unit 36 can include multiple mixers 76 arranged in series. Fig 7 also
illustrates
that the dilution unit 36 can be incorporated within a pipeline system that
includes an
upstream supply pipeline 78 (with a diameter Di) and an upstream feed pipe 80
(with
diameter D2), where D2 may be smaller than Di to facilitate providing desired
turbulence
or flow rate conditions. In addition, there may be a downstream pipe section
82 in fluid
communication with the dilution unit 36 to provide the diluted TFT 40 to the
first mixer 76.
The mixers 76 may be static mixers that are provided in-line. The mixers 76
may be
followed by a second downstream pipe section 84, followed by a downstream
supply
pipeline 87 that supplies the pretreated TFT to the flocculant injection unit
20. The piping
and equipment downstream of the dilution unit 36 may be configured to fully
mix the
dilution fluid with the TFT. The pipe lengths L1, L2 and L3 as well as the
number and
design of the mixers 76 can be adjusted accordingly. In some implementations,
there
can be at least eight static mixers 76, at least ten static mixers, or between
eight and
sixteen static mixers arranged in series.
[0097] In some implementations, the homogenization is performed without
the use of
downstream static mixers. For example, the homogenization can be performed by
shear
imparted from the pipeline flow in combination with one or more pumps that are
located
in between the dilution and the flocculation. Shear provided by pipe walls and
pump can
be sufficient for attaining certain target mixing levels (e.g., 0.05 CoV or
below) prior to
flocculation. In addition, centerline injection of the dilution fluid can
facilitate such
homogenization techniques by inhibiting segregation of the dilution fluid from
the tailings.
When the dilution fluid is water with a specific gravity of 1 and the TFT have
a clay or
solids content that increases the density to about 1.2 or 1.3, for example,
the tendency
of the fluids being segregated can be significant. Thus, by providing the co-
directional
and centerline injection the dilution fluid can avoid contacting the side pipe
walls as a
Date Recue/Date Received 2021-03-30
21
segregated flow and can be pre-mixed with the tailings prior to a downstream
pump or
static mixer which can complete the homogenization prior to flocculation. For
thicker TFT
materials, the tendency for stratified flow can be greater, and thus the
benefit of
centerline injection can also increase.
[0098] Co-directional and centerline water injection followed by
homogenization
facilitates providing a well-mixed, non-stratified diluted TEl flow that can
be effectively
flocculated and subsequently dewatered. Simple addition of water to a TEl flow
without
mixing can result in a stratified flow which, in turn, can reduce the
efficiency of the
flocculation stage. Dilution can not only aid in providing a consistent CWR of
the TFT
flow to facilitate accurate flocculant dosing, but can also enhance flocculant
usage due
to improved in-line mixing of the flocculant with a well-mixed diluted TFT
flow.
[0099] Providing co-directional and centerline injection of the dilution
fluid can
facilitate various advantages, such as inhibiting plugging of the injector
outlets, reducing
segregation issues, and enhancing efficient operation of downstream mixers
when
present. For instance, providing the dilution fluid near the centerline of the
TFT flow so
that the dilution fluid is still surrounded by TFT material as the stream
engages the
downstream mixers, enables more efficient mixing. For example, if the dilution
fluid
contacts the pipe wall, then there can be increased risk of segregation
resulting in lower
mixing efficiency, performance, reliability, and/or adaptability to changes in
flow rates. In
some implementations, the centreline water injection for the injectors
promotes mixing
between the TFT flow 18 and the dilution water 38 prior to the downstream
static mixers
76 where the bulk of the mixing occurs.
[00100] In addition, multiple water inlets, as illustrated in Figs 2, 3
and 5, can provide
advantages, including facilitating the control of dilution water flowrates at
higher and
lower dilution water requirements. For example, when the incoming TFT flow has
a lower
CWR and thus lower dilution is indicated, the dilution unit can be operated by
injecting
water via only one of the water inlets which may be selected to be the smaller
feed pipe
section designed for providing lower flowrates. When the incoming TFT flow has
a higher
CWR and thus higher dilution is indicated, the dilution unit 36 can be
operated by
injecting water via the larger feed pipe section designed for providing higher
flowrates.
The different water inlets or feed pipe sections can be designed with a
flowrate capacity
CA 3053555 2019-08-29
22
sufficiently large that sufficient water can be supplied for a maximum CWR
that may be
encountered to enable a certain target diluted CWR level. The multiple feed
pipe
sections can also be equipped with valves or other devices so that one or more
can be
controlled to vary the water flowrate. The CWR of the TFT and its flowrate can
change
significantly depending on a number of factors (e.g., retrieval site of the
TFT, depth of
TFT in pond, composition of the TFT, pre-treatment of TFT, upstream operations
in the
dewatering process, etc.). The dilution unit can have multiple water inlets to
facilitate
control of the dilution water flowrate at both high and low range flows,
optionally with
only one water inlet operating at a time.
[00101] In some implementations, the dilution unit can be controlled in
order to obtain
a target CWR value within the CWR range (e.g., about 0.25 to about 0.33). The
CWR
range can be determined based on a number of factors, such as the composition
of the
TFTs to treat, the polymer flocculant to be used, additional chemicals or pre-
treatments
to be implemented, the design and operation of the flocculant injector and the
dilution
unit, and the mixing characteristics in the system. The CWR range can be
determined
using empirical testing and/or modelling. For instance, TFT samples having
different
CWRs can be tested by subjecting the samples to flocculation and dewatering
conditions
to determine a preferred CWR range in which maximum dewatering occurs, e.g., a
preferred Net-Water-Release (NWR) from the flocculated material. Studies have
determined that NWR and CWR can be correlated, and thus the CWR range can be
determined or defined in to obtain a desired NWR for the process design
criteria.
Empirical testing can include multiple runs using different polymer
flocculants and other
variables that may influence the NWR (or another dewatering parameter) in
order to
determine a CWR range. Once the CWR range is determined, the dilution can be
designed and operated to achieve target CWR values for the TFT flow prior to
flocculation.
[00102] In addition, the dilution control can be coordinated with
measurements, such
as NIR based readings, providing data that is correlated with compositional
properties
related to clay content (e.g., clay wt% per total weight of fluid, CWR, etc.).
In some
implementations, dilution control includes regulating or varying the flowrate
of the dilution
fluid, which may be done by manipulating a valve or orifice incorporated into
the feed
pipe section(s) of the dilution unit, by varying a pump that supplies the
dilution fluid, by
CA 3053555 2019-08-29
23
controlling the number of dilution inlets that are open, by varying the
relative flowrates
between the TFT flow and the dilution fluid, and/or by various other methods.
[00103] The dilution fluid can be an aqueous stream substantially composed
of water,
which may include or consist of fresh water, process effluent water (e.g.,
from an
extraction process from which the TFT was derived), and/or other water
sources. The
dilution fluid may include little or no clay or other suspended solid
materials. For
example, dilution water may be taken from oil sands or other mining
operations, and/or
may be recycled from the dewatering operation itself as part of the release
water. In
some implementations, the dilution may be carried out by combining a higher
water
content tailings stream into to a TFT stream. In the event that the dilution
fluid includes
clay, an additional measurement probe (e.g., NIR probe) may be incorporated
for
measuring the clay content of the dilution fluid, and that reading can be
incorporated into
the overall determination of the diluted TFT clay content for flocculent
dosing and
process control purposes. It should be noted that while NIR based methods are
described herein in detail, various other measurement and control techniques
could be
used in connection with the dilution methods (e.g., a density meter could be
used).
[00104] In some implementations, the TFT exhibits non-Newtonian rheology,
and the
dilution followed by homogenization enable the pre-treated TFT to be closer to
Newtonian behaviour.
[00105] In some implementations, the homogenization of the diluted thick
fine tailings
is performed to achieve a least a certain level of mixing, which may be
defined in a
number of ways, e.g., by coefficient of variation (CoV). For example, the
homogenization
can be done to produce a mixture having at least a target mixing level, such
as a CoV of
at most 0.05, at most 0.04, at most 0.03 or at most 0.02. The target CoV range
can be
0.05 to 0.01, which have been studied using modelling techniques and it has
been found
that this range provides desirable performance. Higher CoV values can also be
possible,
and can be verified by modelling, small scale testing, or other techniques.
Other mixing
parameters can also be used for process design and/or process control. The
homogenization level can be influence or controlled by a number of variables,
such as
flow rate, mixer type and number, pipe diameter and length, flow regime (e.g.,
turbulence, Reynolds Number), or other pipeline features that impart shear
and/or
CA 3053555 2019-08-29
24
enable turbulence. The mixers may be in-line static mixers, tank mixers, or a
combination thereof. The mixers may be monitored and controlled to impart a
controlled
and pre-determined amount of mixing energy to the diluted tailings, or the
mixers can
simply be provided without any active or ongoing control.
[00106] Referring to Fig 1, in some implementations, one or more control
units 86 can
be provided to receive data and to control a process variable, such as the
dilution flow
38. Fig 1 illustrates that there may be various measurement devices, e.g., NIR
sensors
(A) to (D), that are arranged at different points in the system, and there may
be
associated control units 86 (A) to (D) that are configured for receiving the
measured data
from the measurement devices and controlling one or more process variables
based on
the data. For example, measurements of CWR or clay content from the TFT flow
14 can
be used control dilution fluid 38 via control unit (A), and measurements of
CWR or clay
content from the diluted and well-mixed TFT flow 18 can be used control
flocculant 22
input via control unit (B). Other control units can be located at different
points in the
system to control process variables, such as flowrates, which can impact the
dewatering
process.
[00107] Control unit (A) can be configured to control the dilution unit
(e.g., the
different injector quills) to provide sufficient dilution fluid to obtain a
target CWR value for
the diluted TFT flow 40 depending on the clay content of the incoming TFT flow
14.
Control unit (A) can thus enable feedforward control for the dilution,
although it can also
be configured for feedback control of upstream operations such as dredging or
other
TFT retrieval activities.
[00108] Control unit (B) can be configured to control the flocculant
solution flowrate to
provide a target flocculant dosage based on the clay content of the incoming
diluted TFT
flow 18, as clay-based dosage can facilitate enhanced flocculant dosing and
usage.
Control unit (B) can thus enable feedforward control for the dilution,
although it may also
be configured for feedback control of the dilution.
[00109] Control unit (C) can be configured to control flocculant solution
preparation,
including the operation of a polymer make-down unit (PMU), the flocculant
content of the
flocculant solution (e.g., wt% of the polymer flocculant in the solution), and
the chemistry
of the flocculant solution (e.g., due to the water used for the flocculant
solution, which
CA 3053555 2019-08-29
25
may include process water, make-up water, fresh water, and/or distilled or
purified
water). Control unit (C) can operate based on measured properties of the
flocculent
solution 22 (e.g., measured flocculent content) that is supplied to the
flocculation
injection step 20. Control unit (C) can thus enable feedback control for
flocculation
solution preparation.
[00110] Control unit (D) can be configured to control various parts of the
process
based on measured data regarding the flocculated material (e.g., yield stress,
water
release characteristics, rheological properties, etc.). Control unit (D) can,
for example, be
coupled to other control units (A), (B) and/or (C) so that upstream process
variables can
be controlled or adjusted based on downstream flocculated material properties.
Control
unit (D) can thus enable feedback control for various aspects of the process.
[00111] The measurement devices M can be configured and operated to obtain
one
or more relevant data type regarding a process stream or unit operation of
interest. In
some implementations, the measurement devices include NIR based sensors. More
regarding NIR based measurements and clay content determination is discussed
further
below.
[00112] In some implementations, the NIR probe(s) can be angled and
positioned
within the pipeline(s) in certain ways according to the various streams to be
measured.
For instance, in homogeneous process streams the NIR probes may be positioned
at
various angles and locations within the pipe. In non-homogeneous streams, such
as
NIRD, it may be advantageous to locate the probe closer to the center of the
pipe and
identify one or more angle of immersion to obtain the best representative scan
of the
stream for compositional analyses. In addition, for segregated streams that
have distinct
layers of different fluid compositions, it may be desired to locate multiple
NIR probes at a
same location along a pipe length but at different positions within the pipe
(e.g., upper
and lower regions) for obtaining measurements regarding the two distinct fluid
layers.
[00113] While NIR probes can be advantageously used to determine various
characteristics of process streams, it should also be noted that alternative
methods can
be used. For example, when determining clay content of the TFT stream prior to
or after
dilution, it is possible to use other techniques, such as methylene blue index
(MBI)
methods. Various MBI methodologies can be implemented.
CA 3053555 2019-08-29
26
MR spectrometry and process control implementations
[00114] Referring to Fig 1, various NIR based measurement and monitoring
techniques can be implemented in connection with the flocculation and
dewatering
operation. For example, a first NIR probe (NIRA) can be provided to determine
clay
content of the TFT flow 14, which can be used to control or vary operation of
the dilution
36 (e.g., control the flowrate of dilution added to the TFT, and the operation
of the
dilution unit). A second NIR probe (NIRB) can be provided to determine clay
content of
the diluted TFT flow 18 after the homogenization 42, which can be used to
control or
vary operation of the flocculation step 36 (e.g., control the flowrate of the
flocculant
solution 22 added to the diluted TFT 18). A third NIR probe (NIRc) can be
provided to
determine polymer flocculant concentration of the flocculant solution 22 prior
to addition
into the diluted TFT 18. A fourth NIR probe (NIRD) can be provided to
determine
characteristics of the flocculated material. For example, an NIR probe located
at NIRD
can identify whether segregation of the flocculated material into a water
fraction and a
solids-enriched fraction is occurring.
[00115] It should be noted that the various NIR probes can be used to
obtain NIR
spectral data that can be used to determine a number of compositional
properties of the
process streams. Thus, for example, the NIR probe at NIRA can obtain data that
is used
to determine not only clay content for dilution control, but also bitumen
content to
determine whether a bitumen pre-treatment step should be implemented or
whether the
downstream process should be otherwise adapted to higher bitumen content. In
addition, other NIR probes and associated controllers not shown in Fig 1 can
also be
provided to monitor and control the process. The NIR probes and associated
controllers
can be automated to provide continuous data acquisition and control, or can be
manual
or semi-manual to provide more periodic data acquisition and control.
[00116] In some implementations, the overall dewatering process includes
multiple
NIR sensor locations generally corresponding to NIRA, NIR, NIRc and NIRD. The
MR
based measurements facilitate optimizing polymer flocculant addition based on
the TFT
feed composition to maximize water separation and production of treated,
dewatered
material. On-line or at-line NIR measurements can facilitate rapid data
acquisition of
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process variables that are relevant to flocculant dosage, and thus avoid
delays related to
laboratory-based sampling and measurement techniques.
[00117] In some implementations, NIR probes are used to obtain clay
content and
flocculant content data. The NIR probes can be installed on-line. Transmission-
type NIR
probes and/or reflectance-type NIR probes can be used. It was found that
reflectance-
type NIR probes (e.g., AlbedoTM probe) facilitate reduced fouling of the
probes. The NIR
probes can be used on-line, where the probes are physically integrated into
the tailings
treatment pipeline. The NIR probes can also be used at-line, where the probes
are
portable but are used at certain locations of the pipeline to take
measurements rather
than taking a sample and performing the measurement at another location (e.g.,
laboratory). The NIR probes can be used in conjunction with slipstreams taken
off of
certain process streams, either on-line or at-line, if desired.
[00118] In existing methods using NIR spectrometry for oil sands
materials, the
component of interest has typically been bitumen. However, according to
implementations described herein, NIR spectrometry is used to determine clay
related
properties of a TFT stream. Existing methods for measuring or estimating clay
content,
such as methylene blue index (MBI), have the challenge of being off-line
techniques. In
addition, clay content on a solids basis can vary widely in slurry streams,
for example
from 10 wt% to 100 wt% (or above 100% when MBI are used), and the variability
of clay
content can cause challenges in terms of fluid rheology, mixing, and
flocculant dosing.
Thus, accurate and real-time clay content measurements, which are facilitated
by NIR
spectrometry, can have a number of advantages in the context of flocculation
and
dewatering of slurry streams, such as TFT. Accurate clay content measurements
are
also relatively complex and time consuming, and thus an NIR-based correlation
enables
real-time NIR measurements that have been correlated to accurate information
to
leverage the painstaking baseline measurements.
[00119] In some implementations, the NIR probe is provided on-line or at-
line at a
location along the pipeline in which the pipe is full of tailings slurry.
Locating and
operating the NIR probes may therefore be done in conjunction with where the
slurry
completely fills the pipe. For example, at certain operating conditions of
lower flowrates,
a given pipe section having a larger diameter may not be completely full while
other pipe
CA 3053555 2019-08-29
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sections having smaller diameters will remain full. The NIR probes can be used
at such
slurry-filled locations of the pipeline for improved data collection. In
addition, certain flow
control devices may be installed and operated in order to ensure that a given
NIR
measurement location of a pipeline is full during NIR measurement collection.
[00120] In some operations that retrieve tailings (e.g., MFT) from
existing ponds, a
density-meter has been used to determine in-pond density in order to then
estimate clay
content based on density-clay correlations. However, this methodology may have
challenges with respect to new ponds or ponds that display different settling
and mixing
characteristics. Instead of using density as a correlated proxy for clay
content, NIR
based techniques described herein can enable rapid determination of clay
content for
flocculent dosage.
[00121] Existing flocculant injectors that have a particular design and
construction can
be used in an optimal fashion within a pre-determined range of CWR, which
influences
the rheology and mixing as well as the clay-basis flocculant dose. The NIR and
dilution
techniques described herein facilitate achieving accurate CWR levels within
the optimal
CWR range. The target CWR can be achieved by diluting the TFT with water,
where the
target CWR can be pre-determined based on a number of factors, such as the
flocculent
injector design, the composition of the TFT, and the nature of the polymer
flocculant to
be used. The target CWR may be determined based in part on existing
infrastructure
and equipment of a TFT dewatering system, to enhance operation of the system.
In
some scenarios, the NIR probes for determining clay content of the TFT can be
used to
determine the CWR after the TFT screens that remove coarse solids debris and
before
the dilution unit. Thus, the NIR based measurement techniques for determining
clay
content combined with dilution of the TFT prior to flocculation can facilitate
enhanced
flocculant injection and dosing on a clay basis.
[00122] In some implementations, statistical process control (SPC) can be
used. For
example, online NIR scans (e.g., at 1-minute frequency or faster) can provide
several
thousand data points at each scan. SPC can be used for the detection of
process
abnormalities based on changes to the statistical properties of the NIR scan
data.
Multiple scan data can be taken from "normal operation" (which can be called
"training
data"), and statistical limits can then be defined for the data. Subsequently,
the statistical
CA 3053555 2019-08-29
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properties of each NIR scan can be compared with these pre-determined
statistical
limits. If there are sustained deviations or excursions, the process may be
identified as
"abnormal" compared with the training data. In the context of flocculation and
dewatering
of thick fine tailings, "abnormal" operation can mean that the quality of
additives has
changed, that there are unknown components in the stream, or that the process
itself
has changed due to damage to the internal components that the operators are
not aware
of. When the SPC chart shows abnormality, the corrective action may be
automated or
non-automated. For example, further investigation may be needed to bring the
process
back to normal; or the so-called "abnormality" may be accepted and it may be
added to
the "training data" in order to recalculate the statistical limits. SPC can
help in detecting
the subtle changes in the process or a given process stream in real time.
Thick fine tailings and other tailings streams
[00123] As noted above, TFT material mainly includes water and fine
mineral solids,
where the solids content and the fines portion are sufficiently high such that
the fines
tend to remain in suspension in the water and the material has slow
consolidation rates.
More particularly, the TFT may have a ratio of coarse particles to the fines
that is less
than or equal to one. The TFT can have a fines content sufficiently high such
that
flocculation of the fines and conditioning of the flocculated material can
achieve a two
phase material where release water can flow through and away from the flocs.
For
example, TFT may have a solids content between 10 wt.% and 45 wt.% (or between
15
wt% and 40 wt%, or between 20 wt% and 35 wt%), and a fines content of at least
50
wt.% on a total solids basis (or at least 55 wt.%, 60 wt%, 65 wt%, 70 wt%, 75
wt%, 80
wt%, 85 wt%, 90 wt%, 95 wt% or 99 wt% on a total solids basis), giving the
material a
relatively low sand or coarse solids content. The TFT may be retrieved from a
tailings
pond or another source. While TFT is typically formed by gravity settling in a
pond or
other structure, it should also be noted that TFT material can also be formed
using other
separation devices.
[00124] As also mentioned above, TFT dewatering techniques may include
various
steps for pre-treating the thick fine tailings, chemically modifying the thick
fine tailings by
addition of a dewatering chemical such as a polymer flocculant, as well as
monitoring or
managing physical and chemical properties of the thick fine tailings.
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[00125] In the context of oil sands, for example, tailings may include
fine and coarse
mineral particles, water and residual bitumen. Tailings may be stored in large
reservoirs
called tailings ponds. The TFT supply arrangement and methodology may be
provided in
accordance with the properties of the TFT to be treated by the dewatering
operation. For
example, dredges, barges, submersible pumps, pipe layouts and pre-treatment
units
may be provided and operated based on thick fine tailings properties. The
dredges or
submersible pumps that may be used in the case of treating tailings withdrawn
from a
tailings pond may be operated to retrieve the TEl from a certain depth or
location to
obtain thick fine tailings within desired property ranges, such as clay-to-
water ratio
(CWR), sand-to-fines ratio (SFR), and/or bitumen content ranges.
[00126] It should also be noted that certain aspects of the dewatering
techniques
described herein may be adapted for different types of TFT. For example, the
structure,
properties and dosage range of the dewatering chemical, such as a polymer
flocculent,
may be modified and provided depending affinities with the particular type of
thick fine
tailings. In addition, certain pre-treatment steps may be performed for thick
fine tailings
having certain properties and compositions. For example, thick fine tailings
containing
quantities of hydrocarbons, e.g., heavy hydrocarbons such as bitumen, which
would
interfere with flocculation, may be subjected to an initial hydrocarbon
removal step below
a threshold concentration. In another example, thick fine tailings having a
relatively high
static yield stress, for example due to having a composition with a relatively
high fines
content and density, may be subjected to a pre-shear thinning or dilution
treatment prior
to addition of the dewatering chemical.
[00127] In general, TFT will have properties depending on its processing
history and
the nature of the mined ore from which it was derived. While water and fine
solids are
the main components of TFT, there may be various other compounds and materials
present in the TFT depending on its origin and upstream processing history. It
is also
noted that the TFT material that is supplied to the flocculation and
dewatering operation
may be variable in terms of one or more properties (flow rate, chemistry,
composition,
etc.) such that monitoring and process control can be adapted to the variable
TFT feed
stream.
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31
[00128] In addition, other tailings streams can be subjected to certain
treatments and
analyses that are disclosed herein. For example, the dilution device and
associated
methodologies can be implemented for tailings streams other than TFT in order
to obtain
desired dilution effects for such tailings streams, which may be desirable
prior to a
subsequent treatment (e.g., a chemical treatment, such as flocculation, or a
physical
treatment). In particular, tailings streams that can benefit from NIR
analyses, CWR
measurements and/or dilution can be used in connection with techniques
described
herein. Such NIR analyses, CWR measurements and/or dilution of various
tailings
streams can be done in the context of enhancing chemical treatment the
tailings stream,
for example by using clay based dosage of a chemical. For instance, depending
on the
composition of the tailings stream and the nature of the downstream treatment
of the
tailings stream, the NIR based methods can be adapted to monitor certain
relevant
properties. It should also be noted that the downstream treatment (e.g.,
flocculation) can
be adapted depending on the composition of the tailings stream.
[00129] The following are examples of tailings streams that may be
diluted, monitored
and/or otherwise treated using various techniques described herein: whole
tailings, froth
treatment tailings, thin fine tailings, secondary/tertiary tailings, or
blended/combined
tailings. Whole tailings are produced from an extraction plant and include
coarse mineral
solids (e.g., sand) and fine mineral solids (e.g., clay) with a typical solids
content of
about 45 to 55 wt% although other compositions are possible. Froth treatment
tailings
are tailings from a froth treatment operation, typically derived from an
underflow stream
of a thickener or a tailings solvent recovery unit (TSRU). Thin fine tailings
are relatively
low solids content tailings (e.g., about 5 to 9 wt%) with a high fines content
on a solids
basis due to the coarser solids having been removed typically by settling.
Thin fine
tailings are often considered a precursor to TFT or MFT, since when left to
settle thin fine
tailings slowly increase in fines concentration to form TFT over a few years.
Secondary
and tertiary tailings are tailings that are derived from certain parts of an
extraction
operation.
[00130] Various blended or combined tailings materials can also be used in
certain
methods described herein. A blended tailings material includes tailings from
multiple
different sources, each source having a different composition. A blended
tailings stream
can be diluted using a substantially water based stream as the dilution fluid,
or a first
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tailings stream can be diluted by adding a higher water content second
tailings stream to
thereby form a diluted blended tailings stream. For instance, a low clay
content tailings
(e.g., thin fine tailings) can be used as the dilution fluid that is injected
into a higher clay
content tailings (e.g., TFT), where NIR techniques can be used to analyse one
or both of
the tailings streams and/or the dilution device can be used for the injection.
Such
blending of multiple tailings streams can be controlled to achieve a desired
composition
of the diluted blended tailings stream to enhance downstream processing (e.g.,
flocculation or other chemical treatments). For example, NIR probes can be
deployed for
the input tailings streams and/or the diluted tailings stream and can be
coupled to a
controller in order to control the dilution to achieve the desired composition
of the diluted
tailings stream (e.g., the desired clay content).
[00131] It is also noted that tailings materials that are subjected to
treatments and
analyses as disclosed herein, can be retrieved from tailings disposal areas or
can be
supplied as tailings streams directly from a unit operation of an extraction
plant (e.g., an
underflow stream from a thickener, settling vessel, clarifier, centrifuge,
etc.).
Additional implementations of NIR based monitoring and process control
[00132] In some scenarios, NIR based monitoring techniques can be used in
the
context of various clay-containing oil sands slurry streams, such as
hydrotransport slurry,
primary extraction streams, secondary extraction streams, including various
overflow,
middlings and underflow streams. The clay-containing oil sands slurry stream
can have
an on-line or at-line NIR probe which obtains NIR spectral measurements, which
are
correlated to clay content properties to generate NIR derived clay content
data for the
given stream. The NIR derived clay content can then be used to control at
least one
upstream or downstream process operating condition. For example, extraction or
mixing
operations, which can be influenced by clay content, can be adjusted based on
the NIR
derived clay content. Thus, techniques described herein in relation to the
dilution and
flocculation of TFT streams can be adapted for use in other clay-containing
oil sands
slurry streams.
EXPERIMENTATION, MODELLING & RESULTS
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[00133] NIR spectrometry has been studied in the context of thick fine
tailings (TFT)
flocculation and dewatering operations. Experimentation, chennometric
modelling
information, and other results are described below.
Reflectance and transmission NIR probes
[00134] Both reflectance and transmission NIR probes were tested in the
context of
obtaining NIR data. At location NIRc (see Fig 1), the transmission-type NIR
probe
experienced fouling which reduced the efficiency in this case. The reflectance-
type NIR
probe (AlbedoTM) was then used at NIRc for improved on-line NIR data
collection for
polymer flocculant concentration determination. The reflectance-type NIR probe
was
also used at NIRB for successful NIR data collection for clay content
determination.
[00135] At locations NIRB and NIRc, the streams being analyzed are
substantially
homogeneous. On the other hand, at location NIRD the flocculated material may
have
undergone significant flocculation and in-line water release, making this
stream relatively
heterogeneous across a given cross-section of the pipeline. It is noted that
the NIR
spectrometry method and probe can be adapted depending on the data of
interest, the
composition of the stream, and the heterogeneity of the stream at the
measurement
point. For example, short or long NIR wavelengths can be selected depending on
the
desired application and the particular setup of the probe(s) at the given
measurement
location. Longer wavelengths can facilitate sampling of bulk material that may
be
heterogeneous, while shorter wavelengths can facilitate lower extinction
coefficients and
can permit longer path lengths to be used.
[00136] In some implementations, the NIR probe collects data and the
region of
interest of the spectra is from approximately 700 nanometers to 2,500
nanometers. The
region of interest may not be a specific peak that is monitored within this
range, but
rather a combination of peaks that enable determination of characteristics or
species of
interest.
[00137] The NIR probe can use diffuse reflection (bundle) type of
measurement and
can be an immersion-type probe. In terms of optics characteristics, the NIR
probe can
include a 2m fiber bundle, with multiple (e.g., 14) fibers, NIR 400nm bis
2200nm, with
600 micron core. The illuminated spot diameter can be 5 mm.
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Components or indicators for detection by NIR spectrometry and chemometric
modelling
[00138] For NIRc, the main component of interest in the flocculent
solution is the
polymer flocculent for determination of concentration. Other components of the
flocculent
solution could also be measured, particularly when the aqueous component used
to
make the solution is process-affected water derived from extraction operations
(e.g.,
tailings pond water, recycle water streams) and thus may contain dissolved or
suspended compounds.
[00139] For TFT streams, there are a number of components that can be
measured
using NIR spectrometry, including bitumen or hydrocarbons, mineral solids,
water, clay,
fines, sands, methylene blue index (MBI), and so on. Fig 9 is a graph of
absorbance
units versus wavelength number showing a typical NIR spectra of MET. MBI is
one
method for determining clay content of a sample, and depending on the
particular MBI
methodology that is used the MBI clay content can be above 100%. MBI is often
used in
the context of oil sands processing, and there may be significant amount of
existing data
based on MBI measurements. MBI of clays can thus be viewed as an indicator of
clay
content and can itself be determined by NIR in the context of the techniques
described
herein.
[00140] Chemonnetric modelling was undertaken to develop correlations
between the
NIR spectral data and actual compositions of the TEl under study. Figs 10 to
17 are
graphs illustrating predicted values versus true values for various different
component
concentrations, showing NIR chemometric model validations. Various other
chemometric
models have been developed for other variables, such as SFR and weight percent
of
certain components on a total solids basis.
[00141] Flocculated material was also subjected to NIR based testing. Fig
18 is a
graph of absorbance units versus wavelength number showing an NIR spectra of
MET
with polymer flocculent solution. Fig 19 illustrates a correlation with
respect to the NWR
from the flocculated material.
[00142] It was also found that there was a correlation between NIR spectra
from
flocculated MFT prior to dewatering and the NWR after 24 hours of dewatering,
which
CA 3053555 2019-08-29
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indicates that NIR spectrometry can be used to measure the flocculated
material prior to
dewatering to predict dewatering performance as well as provide feedback to
modify
upstream operating conditions to enhance the process. Thus, referring to Fig
1, for
example, the process can include obtaining NIR data at location NIRD; based on
the NIR
data, determining an NIR-predicted dewatering parameter (e.g., NWR after a
certain
time period, such as 24 hours); and then adjusting the upstream process, as
needed, to
increase the dewatering parameter for the process. Thus, rather than waiting
the full
NWR drainage time period (e.g., 24 hours) in order to determine the dewatering
performance, a real-time NIR measurement and correlation can be made to
quickly
predict general dewatering performance and make upstream adjustments to
enhance
the process.
[00143] It has also been found that chennometric modelling should be
performed in a
thorough and diligent manner in order to ensure that outlier data points are
excluded and
that the model is accurate over the relevant operating window. Fig 20 is an
example
pulled from modelling work for water content (wt% water), and illustrates that
data points
taken over too narrow a range gives an inaccurate correlation.
[00144] Tests have been also conducted on samples of oil sands MFT to
assess
flocculant dosage requirements. It has been found that dosing on a clay basis
provides
enhanced flocculation, dewatering and flocculate usage compared to dosing on a
total
mineral or total solids basis. It has also been found that clay based
flocculant dosage
can be performed over a CWR range of 0.23 to 0.44 to achieve the target
dewatering
performance for certain MFT samples and existing process equipment. Additional
work
has been conducted to develop a two-phase protocol to determine optimal
flocculant
dosages.
[00145] Additional studies sampling a TFT feed at intervals over several
hours
revealed that when feeding TFT from certain sources (e.g., ponds) most TFT
properties
can display little variance with the exception of the fines or clay content
which have
displayed some fluctuations for a single source. Blended TFT samples from
different
sources can display relatively consistent mineral content but significantly
varying fines
and clay content over the sampling periods. Therefore, when blending TFT
streams from
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different sources, the clay content can monitored rather than approximating
with mineral
content for determining optimal flocculant dosage.
[00146] In the course of further testing, it has been determined that the
clay content in
TFT can be used for determining the optimal target set-point for polymer
flocculant
addition to the TFT, which reduces over- or under-dosage of the polymer
flocculant that
can result in reduced on-spec production of flocculated material. The clay
content in TFT
can also be used for accurate and real-time measurement of polymer flocculant
concentration in the flocculation solution, which can help in maintaining the
required
concentration steady and consistent through closed-loop control. The clay
content in
TFT can also be used to maintain the specification of the TFT consistently in
real-time
for maximizing production of treated, solids-enriched, dewatered tailings
material.
[00147] It should be noted that various implementations and aspects
described herein
can be combined with others that are described herein. For example, various
pre-
treatments steps can be combined with each other and with the steps of
flocculent
addition and dewatering. As another example, multiple NIR measurement points
and
process control strategies can be used in combination with each other for
various parts
of the overall process. It should also be noted that various apparatuses,
systems and
structures can be used to implement the methods described herein. In addition,
methods
described herein do not necessarily require that all of the steps be performed
in the
order illustrated or shown herein. Implementations and aspects of the
techniques
described herein are meant to be examples, and it should be understood that
various
alternatives and variants could also be used.
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