U.S. patent application number 16/752639 was filed with the patent office on 2020-05-21 for process for flocculating and dewatering oil sand mature fine tailings.
The applicant listed for this patent is Suncor Energy Inc.. Invention is credited to Trevor Bugg, Jamie Eastwood, Thomas Charles Hann, Hugues Robert O'Neill, Oladipo Omotoso, Adrian Peter Revington, Ana Cristina Sanchez, Marvin Harvey Weiss, Patrick Sean Wells, Stephen Joseph Young.
Application Number | 20200157432 16/752639 |
Document ID | / |
Family ID | 43757979 |
Filed Date | 2020-05-21 |
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United States Patent
Application |
20200157432 |
Kind Code |
A1 |
Revington; Adrian Peter ; et
al. |
May 21, 2020 |
PROCESS FOR FLOCCULATING AND DEWATERING OIL SAND MATURE FINE
TAILINGS
Abstract
A process for dewatering oil sand fine tailings is provided and
comprises a dispersion and floc build-up stage comprising in-line
addition of a flocculent solution comprising an effective amount of
flocculation reagent into a flow of the oil sand fine tailings; a
gel stage wherein flocculated oil sand fine tailings is transported
in-line and subjected to shear conditioning; a floc breakdown and
water release stage wherein the flocculated oil sand fine tailings
releases water and decreases in yield shear stress, while avoiding
an oversheared zone; depositing the flocculated oil sand fine
tailings onto a deposition area to form a deposit and to enable the
release water to flow away from the deposit, preferably done in a
pipeline reactor and managing shear according to yield stress and
CST information and achieves enhanced dewatering.
Inventors: |
Revington; Adrian Peter;
(Fort McMurray, CA) ; Omotoso; Oladipo; (Edmonton,
CA) ; Wells; Patrick Sean; (Fort McMurray, CA)
; Hann; Thomas Charles; (Onoway, CA) ; Weiss;
Marvin Harvey; (Calgary, CA) ; Bugg; Trevor;
(Fort McMurray, CA) ; Eastwood; Jamie; (Fort
McMurray, CA) ; Young; Stephen Joseph; (Fort
McMurray, CA) ; O'Neill; Hugues Robert; (Fort
McMurray, CA) ; Sanchez; Ana Cristina; (Fort
McMurray, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Suncor Energy Inc. |
Calgary |
|
CA |
|
|
Family ID: |
43757979 |
Appl. No.: |
16/752639 |
Filed: |
January 25, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15820707 |
Nov 22, 2017 |
10590347 |
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16752639 |
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13496176 |
Mar 14, 2012 |
9909070 |
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PCT/CA2010/000634 |
Apr 22, 2010 |
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15820707 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10G 1/047 20130101;
C02F 2103/10 20130101; B01F 5/0463 20130101; B01F 2005/0034
20130101; C02F 11/14 20130101; B01F 5/0466 20130101; C02F 1/56
20130101; C10G 33/04 20130101 |
International
Class: |
C10G 1/04 20060101
C10G001/04; C10G 33/04 20060101 C10G033/04; B01F 5/04 20060101
B01F005/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 15, 2009 |
CA |
2678818 |
Oct 30, 2009 |
CA |
2684232 |
Dec 2, 2009 |
CA |
2686831 |
Claims
1. A process for producing a hydrocarbon product derived from oil
sands ore, the process comprising: subjecting an aqueous slurry
comprising the oil sands ore to separation to produce the
hydrocarbon product and fine tailings comprising water and fine
solids; and treating the fine tailings to separate the fine solids
from the water, wherein the treating comprises: adding a flocculant
in-line into a flow of the fine tailings to cause dispersion of the
flocculant and build-up of flocs to form flocculated fine tailings;
transporting the flocculated fine tailings in-line and subjecting
the flocculated fine tailings to in-line shear conditioning to
increase a yield stress thereof to a peak yield stress and produce
tailings material; subjecting the tailings material to further
in-line shear conditioning to reduce the yield stress from the peak
yield stress and produce an in-line flow of a pipeline-conditioned
flocculated tailings material; discharging the pipeline-conditioned
flocculated tailings material from a pipeline discharge outlet; and
dewatering the discharged pipeline-conditioned flocculated tailings
material.
2. The process of claim 1, wherein the dewatering comprises
depositing the discharged pipeline-conditioned flocculated tailings
material onto a deposition area formed of a solid land surface to
form a non-flowing tailings material deposit and allow release
water to drain and flow away from the non-flowing tailings material
deposit.
3. The process of claim 2, wherein the deposition area comprises at
least one deposition beach having a sloped bottom surface.
4. The process of claim 1, wherein the dewatering comprises
providing the discharged pipeline-conditioned flocculated tailings
material to a dewatering device.
5. The process of claim 4, wherein the dewatering device comprises
a filter, a thickener, a centrifuge, or a cyclone, or a combination
thereof.
6. The process of claim 1, wherein the dewatering comprises
subjecting the discharged pipeline-conditioned flocculated tailings
material to thickening.
7. The process of claim 6, wherein the thickening is performed in a
thickener unit that produces a thickened underflow that is removed
from an overflow.
8. The process of claim 1, wherein the dewatering comprises
settling flocculated solids such that water separates upward away
from the flocculated solids.
9. The process of claim 1, wherein the dewatering comprises
draining water from the discharged pipeline-conditioned flocculated
tailings material.
10. The process of claim 1, wherein the dewatering comprises
subjecting the discharged pipeline-conditioned flocculated tailings
material to filtration.
11. The process of claim 1, wherein the adding of the flocculant
into the flow of the fine tailings and the in-line shear
conditioning to produce the pipeline-conditioned flocculated
tailings material up to the discharging thereof are performed in a
pipeline reactor.
12. The process of claim 11, wherein the pipeline reactor comprises
a co-annular injection device for in-line injection of the
flocculant solution into the fine tailings.
13. The process of claim 1, further comprising providing the
in-line shear conditioning such that the pipeline-conditioned
flocculated tailings material is discharged from the pipeline
discharge outlet when the yield shear stress of the
pipeline-conditioned flocculated tailings material is within a
decrease zone following a plateau zone.
14. The process of claim 1, wherein the in-line shear conditioning
is controlled by a pipeline length through which the flocculated
fine tailings travels prior to the discharging.
15. The process of claim 1, wherein, immediately after addition of
the flocculant, the flocculated fine tailings are transported
in-line directly to the dewatering step via a pipeline
assembly.
16. The process of claim 15, wherein the pipeline assembly
comprises a main pipeline section receiving the flocculated fine
tailing from a flocculant addition point, and a plurality of
spigots communicating with the main pipeline for expelling the
conditioned flocculated fine tailings to be dewatered.
17. The process of claim 16, wherein the spigots are arranged in
spaced-apart relation with each other and in series so as to
communicate with the main pipeline section.
18. The process of claim 16, wherein the spigots are arranged in
parallel, such that the main pipeline section is split to form
multiple pipeline sections that communicate with respective
spigots.
19. The process of claim 1, wherein the flocculant is provided in
the form of an aqueous flocculant solution that is added to the
in-line flow of the fine tailings.
20. A process for producing bitumen from oil sands fine tailings,
the process comprising: retrieving oil sands fine tailings
comprising bitumen, water and fine solids from a tailings pond;
subjecting the oil sands fine tailings to separation to produce
recovered bitumen and a bitumen-depleted fine tailings; treating
the bitumen-depleted fine tailings to separate the fine solids from
the water, wherein the treating comprises: adding a flocculant
in-line into a flow of the bitumen-depleted fine tailings to cause
dispersion of the flocculant and build-up of flocs to form
flocculated fine tailings; transporting the flocculated fine
tailings in-line and subjecting the flocculated fine tailings to
in-line shear conditioning to increase a yield stress thereof to a
peak yield stress and produce a tailings material; subjecting the
tailings material to further in-line shear conditioning to reduce
the yield stress from the peak yield stress and produce an in-line
flow of a pipeline-conditioned tailings material; discharging the
pipeline-conditioned tailings material from a pipeline discharge
outlet; and dewatering the discharged pipeline-conditioned tailings
material.
21. A process for producing a mined product from mined ore, the
process comprising: subjecting an aqueous slurry to separation to
produce the mined product and fine tailings comprising water and
fine solids; and treating the fine tailings to separate the fine
solids from the water, wherein the treating comprises: adding a
flocculant in-line into a flow of the fine tailings to cause
dispersion of the flocculant and build-up of flocs to form
flocculated fine tailings; transporting the flocculated fine
tailings in-line and subjecting the flocculated fine tailings to
in-line shear conditioning to increase a yield stress thereof to a
peak yield stress and produce a tailings material; subjecting the
tailings material to further in-line shear conditioning to reduce
the yield stress from the peak yield stress and produce an in-line
flow of a pipeline-conditioned flocculated tailings material;
discharging the pipeline-conditioned flocculated tailings material
from a pipeline discharge outlet; dewatering the discharged
pipeline-conditioned flocculated tailings material.
22. The process of claim 21, wherein the mined product is bitumen
and the mined ore is oil sands ore.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. patent
application Ser. No. 15/820,707, filed Nov. 22, 2017, which is a
Continuation of U.S. patent application Ser. No. 13/496,176, filed
Mar. 14, 2012, now U.S. Pat. No. 9,909,070, which is a National
Stage of International Patent Application No. PCT/CA2010/000634,
filed on Apr. 22, 2010, which claims priority to foreign patent
application CA 2,678,818, filed on Sep. 15, 2009, foreign patent
application CA 2,684,232, filed on Oct. 30, 2009, and foreign
patent application CA 2,686,831, filed on Dec. 2, 2009, the
disclosures of which are incorporated herein by reference in their
entirety.
FIELD OF THE INVENTION
[0002] The present invention generally relates to the field of
treating oil sand fine tailings.
BACKGROUND
[0003] Oil sand fine tailings have become a technical, operational,
environmental, economic and public policy issue.
[0004] Oil sand tailings are generated from hydrocarbon extraction
process operations that separate the valuable hydrocarbons from oil
sand ore. All commercial hydrocarbon extraction processes use
variations of the Clark Hot Water Process in which water is added
to the oil sands to enable the separation of the valuable
hydrocarbon fraction from the oil sand minerals.
[0005] The process water also acts as a carrier fluid for the
mineral fraction. Once the hydrocarbon fraction is recovered, the
residual water, unrecovered hydrocarbons and minerals are generally
referred to as "tailings".
[0006] The oil sand industry has adopted a convention with respect
to mineral particle sizing. Mineral fractions with a particle
diameter greater than 44 microns are referred to as "sand". Mineral
fractions with a particle diameter less than 44 microns are
referred to as "fines". Mineral fractions with a particle diameter
less than 2 microns are generally referred to as "clay", but in
some instances "clay" may refer to the actual particle mineralogy.
The relationship between sand and fines in tailings reflects the
variation in the oil sand ore make-up, the chemistry of the process
water and the extraction process.
[0007] Conventionally, tailings are transported to a deposition
site generally referred to as a "tailings pond" located close to
the oil sands mining and extraction facilities to facilitate
pipeline transportation, discharging and management of the
tailings. Due to the scale of operations, oil sand tailings ponds
cover vast tracts of land and must be constructed and managed in
accordance with regulations. The management of pond location,
filling, level control and reclamation is a complex undertaking
given the geographical, technical, regulatory and economic
constraints of oil sands operations.
[0008] Each tailings pond is contained within a dyke structure
generally constructed by placing the sand fraction of the tailings
within cells or on beaches. The process water, unrecovered
hydrocarbons, together with sand and fine minerals not trapped in
the dyke structure flow into the tailings pond. Tailings streams
initially discharged into the ponds may have fairly low densities
and solids contents, for instance around 0.5-10 wt %.
[0009] In the tailings pond, the process water, unrecovered
hydrocarbons and minerals settle naturally to form different
strata. The upper stratum is primarily water that may be recycled
as process water to the extraction process. The lower stratum
contains settled residual hydrocarbon and minerals which are
predominately fines. This lower stratum is often referred to as
"mature fine tailings" (MFT). Mature fine tailings have very slow
consolidation rates and represent a major challenge to tailings
management in the oil sands industry.
[0010] The composition of mature fine tailings is highly variable.
Near the top of the stratum the mineral content is about 10 wt %
and through time consolidates up to 50 wt % at the bottom of the
stratum. Overall, mature fine tailings have an average mineral
content of about 30 wt %. While fines are the dominant particle
size fraction in the mineral content, the sand content may be 15 wt
% of the solids and the clay content may be up to 75 wt % of the
solids, reflecting the oil sand ore and extraction process.
Additional variation may result from the residual hydrocarbon which
may be dispersed in the mineral or may segregate into mat layers of
hydrocarbon. The mature fine tailings in a pond not only has a wide
variation of compositions distributed from top to bottom of the
pond but there may also be pockets of different compositions at
random locations throughout the pond.
[0011] Mature fine tailings behave as a fluid-like colloidal
material. The fact that mature fine tailings behave as a fluid
significantly limits options to reclaim tailings ponds. In
addition, mature fine tailings do not behave as a Newtonian fluid,
which makes continuous commercial scale treatments for dewatering
the tailings all the more challenging. Without dewatering or
solidifying the mature fine tailings, tailings ponds have
increasing economic and environmental implications over time.
[0012] There are some methods that have been proposed for disposing
of or reclaiming oil sand tailings by attempting to solidify or
dewater mature fine tailings. If mature fine tailings can be
sufficiently dewatered so as to convert the waste product into a
reclaimed firm terrain, then many of the problems associated with
this material can be curtailed or completely avoided. As a general
guideline target, achieving a solids content of 75 wt % for mature
fine tailings is considered sufficiently "dried" for
reclamation.
[0013] One known method for dewatering MFT involves a freeze-thaw
approach. Several field trials were conducted at oil sands sites by
depositing MFT into small, shallow pits that were allowed to freeze
over the winter and undergo thawing and evaporative dewatering the
following summer. Scale up of such a method would require enormous
surface areas and would be highly dependent on weather and season.
Furthermore, other restrictions of this setup were the collection
of release water and precipitation on the surface of the MFT which
discounted the efficacy of the evaporative drying mechanism.
[0014] Some other known methods have attempted to treat MFT with
the addition of a chemical to create a thickened paste that will
solidify or eventually dewater.
[0015] One such method, referred to as "consolidated tailings"
(CT), involves combining mature fine tailings with sand and gypsum.
A typical consolidated tailings mixture is about 60 wt % mineral
(balance is process water) with a sand to fines ratio of about 4 to
1, and 600 to 1000 ppm of gypsum. This combination can result in a
non-segregating mixture when deposited into the tailings ponds for
consolidation. However, the CT method has a number of drawbacks. It
relies on continuous extraction operations for a supply of sand,
gypsum and process water.
[0016] The blend must be tightly controlled. Also, when
consolidated tailings mixtures are less than 60 wt % mineral, the
material segregates with a portion of the fines returned to the
pond for reprocessing when settled as mature fine tailings.
Furthermore, the geotechnical strength of the deposited
consolidated tailings requires containment dykes and, therefore,
the sand required in CT competes with sand used for dyke
construction until extraction operations cease. Without sand, the
CT method cannot treat mature fine tailings.
[0017] Another method conducted at lab-scale sought to dilute MFT
preferably to 10 wt % solids before adding Percol LT27A or 156.
Though the more diluted MFT showed faster settling rates and
resulted in a thickened paste, this dilution-dependent small batch
method could not achieve the required dewatering results for
reclamation of mature fine tailings.
[0018] Some other methods have attempted to use polymers or other
chemicals to help dewater MFT. However, these methods have
encountered various problems and have been unable to achieve
reliable results. When generally considering methods comprising
chemical addition followed by tailings deposition for dewatering,
there are a number of important factors that should not be
overlooked.
[0019] Of course, one factor is the nature, properties and effects
of the added chemicals. The chemicals that have shown promise up to
now have been dependent on oil sand extraction by-products,
effective only at lab-scale or within narrow process operating
windows, or unable to properly and reliably mix, react or be
transported with tailings. Some added chemicals have enabled
thickening of the tailings with no change in solids content by
entrapping water within the material, which limits the water
recovery options from the deposited material. Some chemical
additives such as gypsum and hydrated lime have generated water
runoff that can adversely impact the process water reused in the
extraction processes or dried tailings with a high salt content
that is unsuitable for reclamation.
[0020] Another factor is the chemical addition technique. Known
techniques of adding sand or chemicals often involve blending
materials in a tank or thickener apparatus. Such known techniques
have several disadvantages including requiring a controlled,
homogeneous mixing of the additive in a stream with varying
composition and flows which results in inefficiency and restricts
operational flexibility. Some chemical additives also have a
certain degree of fragility, changeability or reactivity that
requires special care in their application.
[0021] Another factor is that many chemical additives can be very
viscous and may exhibit non-Newtonian fluid behaviour. Several
known techniques rely on dilution so that the combined fluid can be
approximated as a Newtonian fluid with respect to mixing and
hydraulic processes. Mature fine tailings, however, particularly at
high mineral or clay concentrations, demonstrates non-Newtonian
fluid behaviour. Consequently, even though a chemical additive may
show promise as a dewatering agent in the lab or small scale batch
trials, it is difficult to repeat performance in an up-scaled or
commercial facility. This problem was demonstrated when attempting
to inject a viscous polymer additive into a pipe carrying MFT. The
main MFT pipeline was intersected by a smaller side branch pipe for
injecting the polymer additive. For Newtonian fluids, one would
expect this arrangement to allow high turbulence to aid mixing.
However, for the two non-Newtonian fluids, the field performance
with this mixing arrangement was inconsistent and inadequate. There
are various reasons why such mixing arrangements encounter
problems. When the additive is injected in such a way, it may have
a tendency to congregate at the top or bottom of the MFT stream
depending on its density relative to MFT and the injection
direction relative to the flow direction. For non-Newtonian fluids,
such as Bingham fluids, the fluid essentially flows as a plug down
the pipe with low internal turbulence in the region of the plug.
Also, when the chemical additive reacts quickly with the MFT, a
thin reacted region may form on the outside of the additive plug
thus separating unreacted chemical additive and unreacted MFT.
[0022] Inadequate mixing can greatly decrease the efficiency of the
chemical additive and even short-circuit the entire dewatering
process. Inadequate mixing also results in inefficient use of the
chemical additives, some of which remain unmixed and unreacted and
cannot be recovered. Known techniques have several disadvantages
including the inability to achieve a controlled, reliable or
adequate mixing of the chemical additive as well as poor efficiency
and flexibility of the process.
[0023] Still another factor is the technique of handling the oil
sand tailings after chemical addition. If oil sand tailings are not
handled properly, dewatering may be decreased or altogether
prevented. In some past trials, handling was not managed or
controlled and resulted in unreliable dewatering performance. Some
techniques such as in CIBA's Canadian patent application No.
2,512,324 (Schaffer et al.) have attempted to simply inject the
chemical into the pipeline without a methodology to reliably adapt
to changing oil sand tailings compositions, flow rates, hydraulic
properties or the nature of particular chemical additive. Relying
solely on this ignores the complex nature of mixing and treating
oil sand tailings and hampers the flexibility and reliability of
the system. When the chemical addition and subsequent handling have
been approached in such an uncontrolled, trial-and-error fashion,
the dewatering performance has been unachievable.
[0024] Given the significant inventory and ongoing production of
MFT at oil sands operations, there is a need for techniques and
advances that can enable MFT drying for conversion into reclaimable
landscapes.
SUMMARY OF THE INVENTION
[0025] The present invention responds to the above need by
providing processes for drying oil sand fine tailings.
[0026] Accordingly, embodiments of the present invention provide a
process for dewatering oil sand fine tailings. One embodiment of
the process comprises (i) a dispersion and floc build-up stage
comprising in-line addition of a flocculent solution comprising an
effective amount of flocculation reagent into a flow of the oil
sand fine tailings; (ii) a gel stage wherein flocculated oil sand
fine tailings is transported in-line and subjected to shear
conditioning; (iii) a floc breakdown and water release stage
wherein the flocculated oil sand fine tailings releases water and
decreases in yield shear stress, while avoiding an oversheared
zone; (iv) depositing the flocculated oil sand fine tailings onto a
deposition area to form a deposit and to enable the release water
to flow away from the deposit.
[0027] In an optional aspect of the process, the stages (i), (ii)
and (iii) are performed in a pipeline reactor. The pipeline reactor
may include a co-annular injection device for inline injection of
the flocculating fluid within the oil sand fine tailings.
[0028] In an optional aspect of the process, the flocculent
solution is in the form of an aqueous solution in which the
flocculation reagent is substantially entirely dissolved. The
flocculation reagent preferably comprises a polymer that is
shear-responsive in stage (i) thereby dispersing throughout the oil
sand fine tailings, and enables shear-resilience during stages (ii)
and (iii). The flocculation reagent may comprise a polymer
flocculent that is selected according to a screening method
including: providing a sample flocculation matrix comprising a
sample of the oil sand fine tailings and an optimally dosed amount
of a sample polymer flocculent; imparting a first shear
conditioning to the flocculation matrix for rapidly mixing of the
polymer flocculent with the sample of the oil sand fine tailings,
followed by imparting a second shear conditioning to the
flocculation matrix that is substantially lower than the first
shear conditioning; determining the water release response during
the first and second shear conditionings: wherein increased water
release response provides an indication that the polymer flocculent
is beneficial for the process. The water release response may be
determined by measuring the capillary suction time (CST) of the
flocculation matrix.
[0029] In an optional aspect of the process, the process also
includes a step of measuring the capillary suction time (CST) of
the flocculated oil sand fine tailings during stages (ii) and (iii)
to determine a low CST interval; and managing the shear
conditioning imparted to the flocculated oil sand fine tailings so
as to ensure deposition of the flocculated tailings before entering
the oversheared zone.
[0030] In an optional aspect of the process, the process also
includes a step of measuring the shear yield stress of the
flocculated oil sand fine tailings during stages (ii) and (iii);
determining a gradual decrease zone following a plateau zone; and
managing the shear conditioning in stages (ii), (iii) and (iv) to
ensure depositing of the flocculated oil sand fine tailings within
the gradual decrease zone before entering the oversheared zone.
[0031] In an optional aspect of the process, the shear conditioning
is managed by at least one of adjusting the length of pipeline
through which the flocculated oil sand fine tailings travels prior
to depositing; and configuring a depositing device at the
depositing step.
[0032] In an optional aspect of the process, step (iv) of
depositing the flocculated oil sand fine tailings is performed
within the gradual decrease zone of the yield shear stress and
within the low CST interval.
[0033] In an optional aspect of the process, the flocculated oil
sand fine tailings is deposited into a deposition cell having a
sloped bottom surface that is sloped between about 1% and about
7%.
[0034] In an optional aspect of the process, the process also
includes a step of working the deposit to spread the deposit over
the deposition cell and impart additional shear thereto while
avoiding the oversheared zone.
[0035] In an optional aspect of the process, the process also
includes a step of providing the deposit with furrows that act as
drainage paths. Preferably, substantially all of the furrows extend
lengthwise in the same general direction as the sloped bottom
surface.
[0036] In an optional aspect of the process, the deposition area
comprises a multi-cell configuration of deposition cells. The
deposition cells of the multi-cell configuration may be provided at
different distances from the in-line addition of the flocculating
fluid to enable varying the shear conditioning imparted to the
flocculated oil sand fine tailings by varying the pipeline length
prior to depositing. At least some of the deposition cells may be
arranged in toe-to-toe relationship to share a common water
drainage ditch.
[0037] In an optional aspect of the process, the process also
includes a step of imparting sufficient hydraulic pressure to the
oil sand fine tailings upstream of stage (i) so as to avoid
downstream pumping.
[0038] In an optional aspect of the process, the stage (i)
dispersion is further characterized in that the second moment M is
between about 1.0 and about 2.0 at a downstream location about 5
pipe diameters from adding the flocculent solution.
[0039] In an optional aspect of the process, the deposit dewaters
due to drainage or release of release water and evaporative drying,
the drainage or water release accounting for at least about 60 wt %
of water loss, and drainage occurring at a rate of at least about
1.4 wt % solids increase per day until the deposit reaches about 55
wt % to 60 wt % solids.
[0040] Also provided is a process for dewatering oil sand fine
tailings, comprising: introducing an effective dewatering amount of
a flocculent solution comprising a flocculation reagent into the
fine tailings, to cause dispersion of the flocculent solution and
commence flocculation of the fine tailings; subjecting the fine
tailings to shear conditioning to cause formation and rearrangement
of flocs and increasing the yield shear stress to form flocculated
fine tailings, the shear conditioning being controlled in order to
produce a flocculation matrix having aggregates and a porous
network allowing release of water; allowing release water to flow
away from the flocculated fine tailings prior to collapse of the
porous network from over-shearing.
[0041] In an optional aspect of this process, the flocculated fine
tailings may be deposited and may be done so to achieve a
dewatering rate of at least 1.4 wt % solids increase per day.
[0042] Various embodiments, features and aspects of oil sand fine
tailings drying process will be further described and understood in
view of the figures and description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1 is a general representative graph of shear yield
stress versus time showing the process stages for an embodiment of
the present invention.
[0044] FIG. 2 is a general representative graph of shear yield
stress versus time showing the process stages for another
embodiment of the present invention.
[0045] FIG. 3 is a graph showing the relationship between shear
stress and shear rate for an MFT sample, illustrating the
non-Newtonian nature of MFT at higher solids contents.
[0046] FIG. 4 is a side cross-sectional view of a pipeline reactor
for performing embodiments of the process of the present
invention.
[0047] FIG. 5 is a partial perspective transparent view of a
pipeline reactor for performing embodiments of the process of the
present invention.
[0048] FIG. 6 is a partial perspective transparent view of the
pipeline reactor of FIG. 5 with cross-sections representing the
relative concentration of flocculent solution and MFT at two
different distances from the injection location.
[0049] FIG. 7 is a close-up view of section VII of FIG. 6.
[0050] FIG. 8 is a close-up view of section VIII of FIG. 6.
[0051] FIG. 9 is a side cross-sectional view of a variant of a
pipeline reactor for performing embodiments of the process of the
present invention.
[0052] FIG. 10 is a side cross-sectional view of another variant of
a pipeline reactor for performing embodiments of the process of the
present invention.
[0053] FIG. 11 is a side cross-sectional view of another variant of
a pipeline reactor for performing embodiments of the process of the
present invention.
[0054] FIG. 12 is a partial perspective transparent view of yet
another variant of a pipeline reactor for performing embodiments of
the process of the present invention.
[0055] FIG. 13 is a graph of shear yield stress versus time
comparing different mixing speeds in a stirred tank for mature fine
tailings treated with flocculent solution.
[0056] FIG. 14 is a bar graph of water release percentage versus
mixing speeds for mature fine tailings treated with flocculent
solution.
[0057] FIG. 15 is a graph of yield shear stress versus time in a
pipe for different pipe flow rates for mature fine tailings treated
with flocculent solution.
[0058] FIG. 16 is a schematic representation of treating mature
fine tailings with a flocculent solution.
[0059] FIG. 17 is another schematic representation of treating
mature fine tailings with a flocculent solution.
[0060] FIG. 18 is another schematic representation of treating
mature fine tailings with a flocculent solution.
[0061] FIGS. 19 and 20 are graphs of percent solids as a function
of time for deposited MFT showing drying times according to trial
experimentation.
[0062] FIG. 21 is a graph of second moment M versus MFT flow rate
for different mixers.
[0063] FIG. 22 is a top view schematic of a multi-cell
configuration of deposition cells.
[0064] FIG. 23 is a bar graph of water release percentage versus
mixing speed regimes for mature fine tailings treated with
flocculent solution, particularly a comparison of mixer methods and
initial net water release, where net water release is water release
after all the water added by the polymer is released and all doses
are 1000 PPM.
[0065] FIG. 24 is a graph of shear yield stress versus time
comparing different mixing speed regimes in a stirred tank for
mature fine tailings treated with flocculent solution, particularly
yield stresses of 100 rpm, 230 rpm and fast-slow mixing.
[0066] FIG. 25 is a graph of shear strength progression of
flocculated MFT highlighting four distinct stages.
[0067] FIG. 26 is a graph of shear strength progression of
flocculated MFT highlighting four distinct stages.
[0068] FIG. 27 is a graph of maximum water release from
polymer-treated MFT during mixing.
[0069] FIG. 28 is a graph of variation of polymer dosage with yield
stress and water release.
[0070] FIG. 29 is scanning electron micrographs of 40 wt % MFT
showing the fabric at different shear regimes (a). Untreated MFT,
(b) high yield strength and (c) dewatering stage.
[0071] FIG. 30 is a graph of shear strength progression for
optimally dosed MFT samples diluted to varying solids
concentration.
[0072] FIG. 31 is a graph of yield stress progression of MFT
optimally dosed with a preferred polymer (Poly A) and a high
molecular weight linear anionic polyacrylamide aPAM (Poly B).
[0073] FIG. 32a is a graph of shear progression curves of the pilot
scale flocculated MFT (35 wt % solid).
[0074] FIG. 32b is a photograph of jar samples taken at each sample
point in FIG. 32a at ideal dosage and low shear.
[0075] FIG. 33 is a graph of water release rate of flocculated MFT
at various distances from the injection point.
[0076] FIG. 34 is a photograph of crack formation in an optimally
flocculated MFT after a few days.
[0077] FIG. 35 is a graph of yield stress variation in MFT with
variable sand-to-fines, clay-to-fines and clay-to-water ratios
expressed as a function of the solids content. The Bingham yield
stress measured with a Bohlin rheometer is reported for all the MFT
samples except Pond B and Pond A (dredge 2) which are Brookfield's
static yield stresses.
[0078] FIG. 36 is a graph of yield stress variation in MFT with
variable sand-to-fines, clay-to-fines and clay-to-water ratios
expressed as a function of the clay content in MFT.
[0079] FIG. 37 is a graph of yield stress variation in MFT with
variable sand-to-fines, clay-to-fines and clay-to-water ratios
expressed as a function of the CWR. R2 of the fitted curve to the
Ponds A and C (Bingham yield stresses) is 0.96. The Bingham yield
stress measured with a Bohlin rheometer is reported for all the MFT
samples except Pond B and Pond A (dredge 2) which are Brookfield's
static yield stresses.
[0080] FIG. 38 is a graph of yield stress variation in MFT with
variable sand-to-fines, clay-to-fines and clay-to-water ratios
expressed as a function of the clay-to water+bitumen ratio. R2 of
the fitted curve is 0.96.
[0081] FIG. 39 is a graph of yield stress variation in MFT with
variable sand-to-fines, clay-to-fines and clay-to-water ratios
expressed as a function of the CWR (clay by size).
[0082] FIG. 40 is a graph of yield stress variation in MFT with
variable sand-to-fines, clay-to-fines and clay-to-water ratios
expressed as a function of the Fines content.
[0083] FIG. 41 is a graph of Pond A low density MFT response to
shear at different polymer dosages. Optimum dosage is approximately
1200 g of polymer/tonne of solid.
[0084] FIG. 42 is a graph of Pond C MFT response to shear at
different polymer dosages. Optimum dosage is between 1600 and 1800
g of polymer/tonne of solid.
[0085] FIG. 43 is a graph of Pond A high density MFT response to
shear at different polymer dosages. Optimum dosage is 800 g of
polymer/tonne of solid.
[0086] FIG. 44 is a bar graph of amounts of MFT water released at
the optimum polymer concentration for Pond C (1600 g/tonne of
solid), low density (1200 g/tonne of solid) and high density (800
g/tonne of solid) MFT respectively.
[0087] FIG. 45 is a graph of viscosity measured a few hours after
solution preparation at various shear rates and temperatures for
six polymer mixtures.
[0088] FIG. 46 is a graph of viscosity coefficients plotted versus
concentration.
[0089] FIG. 47 is a graph of CST and water release versus
conditioning pipe length using a co-annular injector.
[0090] FIG. 48 is a two part distance-weighted-least-square graph
of polymer flocculent dosage versus conditioning pipe length
comparing the quill-type and co-annular-type injectors.
[0091] FIGS. 49a, 49b, and 49c are graphs of various deposition
data over time for three cells into which flocculated MFT was
deposited, showing dewatering and drying of the deposit.
[0092] FIGS. 50a and 50b are graphs of various deposition data over
time for two cells into which flocculated MFT was deposited,
showing effect of overshearing the flocculated MFT.
[0093] FIG. 51 is a diagram of an exemplary decision tree for
flocculation reagent indication, screening and identification.
[0094] FIG. 52 is a bar graph comparing the net water release of
two polymer flocculents in the first step of the screening
technique.
[0095] FIG. 53 is a graph of net water release versus dosage for
the two polymer flocculents.
[0096] FIG. 54 is a graph of yield stress versus camp number for
the two polymer flocculents.
[0097] FIG. 55 is a graph of yield stress and CST versus time in
mixer for gel state and water release treated MFTs with a polymer
flocculent.
[0098] FIG. 56 is a graph of sloped drying test showing the %
solids evolution over time for gel state and water release treated
MFTs with a polymer flocculent.
DETAILED DESCRIPTION OF THE INVENTION
[0099] Referring to FIGS. 1 and 2, the general stages of an
embodiment of the process will be described. The oil sand fine
tailings are treated with a flocculent solution by in-line
dispersion of the flocculent solution into the fine tailings, then
conditioning the fine tailings by inputting a sufficient energy to
cause the formation and rearrangement of flocculated fine tailing
solids to increase the yield shear strength while enabling water
release without over-shearing the flocculated solid structure that
can then form a generally non-flowing deposit. The flocculated fine
tailings are deposited to allow the water release and the formation
of a deposit which is allowed to dry.
[0100] The present specification should be read in light of the
following definitions:
[0101] "Oil sand fine tailings" means tailings derived from oil
sands extraction operations and containing a fines fraction. They
include mature fine tailings from tailings ponds and fine tailings
from ongoing extraction operations that may bypass a pond, and
combinations thereof. In the present description, the abbreviation
MFT will be generally used, but it should be understood that the
fine tailings treated according the process of the present
invention are not necessarily obtained from a tailings pond.
[0102] "In-line flow" means a flow contained within a continuous
fluid transportation line such as a pipe or another fluid transport
structure which preferably has an enclosed tubular
construction.
[0103] "Flocculent solution comprising a flocculation reagent"
means a fluid comprising a solvent and at least one flocculation
reagent. The flocculent solution may contain a combination of
different flocculation reagents, and may also include additional
chemicals. The solvent preferably comprises water but may include
other compounds as well, as desired. Flocculation reagents are
compounds that have structures which form a bridge between
particles, uniting the particles into random, three-dimensional
porous structures called "flocs". Thus, the flocculation reagents
do not include chemicals that merely act electrostatically by
reducing the repulsive potential of the electrical double layer
within the colloid. The flocculation reagents have structures for
forming floc arrangements upon dispersion within the MFT, the flocs
being capable of rearranging and releasing water when subjected to
a specific window of conditioning. The preferred flocculation
reagents may be selected according to given process conditions and
MFT composition.
[0104] "Molecular weight" means the average molecular weight
determined by measurement means known in the art.
[0105] "Dispersion", as relates to the flocculent solution being
introduced into the in-line flow of MFT, means that upon
introduction within the MFT the flocculent solution transitions
from droplets to a dispersed state sufficient to avoid
under-reacting or over-reacting in a localized part of the MFT
which would impede completion of the flocculation in the subsequent
conditioning stage to reliably enable dewatering and drying.
[0106] "Flocculation conditioning" is performed in-line and
involves the flocculation reagent reacting with the MFT solids to
form flocs and through rearrangement reactions increase the
strength of the flocculating MFT.
[0107] "Water release conditioning" means that energy is input into
the flocculated MFT so as to initiate rearrangement and breakdown
of the structure to release water from the flocculated matrix. The
energy input may be performed by in-line shearing or by other
means. "Release of water" in this context means that water
selectively separates out of the flocculated MFT matrix while
leaving the flocs sufficiently intact for deposition.
[0108] "Over-shearing", which is a stage that defines the limit of
the water release conditioning stage and is to be avoided, means
that additional energy has been input into the flocculated MFT
resulting in dispersing the structure and resuspending the fines
within the water. Over-sheared MFT releases and resuspends fines
and ultrafines entrapped by the flocs back into the water,
essentially returning to its original fluid properties but
containing non-functional reagent.
[0109] "Non-flowing fine tailings deposit" means a deposited
flocculated MFT that has not been over-sheared and has sufficient
strength to stand while drying. While the water release from the
flocs is triggered by conditioning, the MFT deposit may have parts
that continue to release water after it has been deposited. The
drying of the MFT deposit may then occur by gravity drainage,
evaporation and permeation. The removal of water from the
flocculated MFT may also occur before deposition, for instance when
a stream of release water separates from the flocculated MFT upon
expelling for deposition. Upon deposition, deposits may undergo
some amount of movement or flow, before coming to a standstill.
[0110] "Yield shear strength" means the shear stress or pressure
required to cause the MFT to flow. It should be noted that in the
present description, the terms "yield shear strength", "yield shear
stress", "yield strength", "yield stress", "strength", "stress" and
similar such terms are sometimes used interchangeably.
[0111] "Deposition area" means an area where the flocculated MFT is
deposited and can take the form of a beach leading back into a
tailings pond, a deposition cell that may have defined side walls,
or another type of natural, synthetic or constructed surface for
receiving the flocculated MFT.
[0112] In one embodiment of the process of the present invention,
the oil sand fine tailings are primarily MFT obtained from tailings
ponds given the significant quantities of such material to reclaim.
The raw MFT may be pre-treated depending on the downstream
processing conditions. For instance, oversized materials may be
removed from the raw MFT. In addition, specific components of the
raw MFT may be selectively removed depending on the flocculation
reagent to be used. For instance, when a cationic flocculation
reagent is used, the raw MFT may be treated to reduce the residual
bitumen content which could cause flocculent deactivation. The raw
MFT may also be pre-treated to provide certain solids content or
fines content of the MFT for treatment or hydraulic properties of
the MFT. More regarding possible pre-treatments of the raw MFT will
be understood in light of descriptions of the process steps herein
below. The fine tailings may also be obtained from ongoing oil sand
extraction operations. The MFT may be supplied from a pipeline or a
dedicated pumped supply.
[0113] In one embodiment, the process is conducted in a "pipeline
reactor" followed by deposition onto a deposition area. The
pipeline reactor may have various configurations, some of which
will be described in detail herein below.
[0114] The MFT to be treated is preferably provided as an in-line
flow in an upstream part of the pipeline reactor. The properties of
the MFT and its particular flow characteristics will significantly
depend on its composition. At low mineral concentrations the yield
stress to set the MFT fluid in motion is small and hydraulic
analysis can approximate the fluid behaviour of a Newtonian fluid.
However, as mineral concentration increases a yield stress must be
overcome to initiate flow. These types of fluids are a class of
non-Newtonian fluids that are generally fitted by models such as
Bingham fluid, Herschel-Bulkley yield-power law or Casson fluid.
The rheological relationship presented in FIG. 3, illustrating a
yield stress response to shear rate for various mineral
concentrations in a MFT sample, considers MFT as a Bingham fluid.
MFT may also be modelled in viscometric studies as a
Herschel-Bulkley fluid or a Casson Fluid.
[0115] Empirical data and modelling the rheology of in-line MFT
have confirmed that when a flocculent solution is added by
conventional side injection into a Bingham fluid MFT, solution
dispersion is very sensitive to flow rate and diameter ratios as
well as fluid properties.
[0116] In one aspect of the process, particularly when the
flocculent solution is formulated to behave as a non-Newtonian
fluid, the dispersion stage is performed to cause rapid mixing
between two non-Newtonian fluids. Rapid non-Newtonian mixing may be
achieved by providing a mixing zone which has turbulence eddies
which flow into a forward-flow region and introducing the
flocculent solution such that the turbulence eddies mix it into the
forward-flow region. Preferably, the flocculent solution is
introduced into the turbulence eddies and then mixes into the
forward-flow region.
[0117] FIGS. 4 and 5 illustrate a pipeline reactor design that
enables such rapid mixing of non-Newtonian fluids. The MFT is
supplied from an upstream pipeline 10 into a mixing zone 12.
[0118] The mixing zone 12 comprises an injection device 14 for
injecting the flocculent solution. The injection device may also be
referred to as a "mixer". The injection device 14 may comprise an
annular plate 16, injectors 18 distributed around the annular plate
16 and a central orifice 20 defined within the annular plate 16.
The MFT accelerates through the central orifice 20 and forms a
forward-flow region 24 and an annular eddy region 22 made up of
turbulence eddies. The injectors 18 introduce the flocculent
solution directly into the eddy region 22 for mixing with the
turbulent MFT. The recirculation of the MFT eddies back towards the
orifice 20 results in mixing of the flocculent solution into the
MFT forward-flow. The forward-flow region 24 expands as it
continues along the downstream pipe 26. For some mixer embodiments,
the forward-flow region may be a vena-contra region of a jet stream
created by an orifice or baffle. The main flow of the MFT thus
draws in and mixes with the flocculent solution, causing dispersion
of the flocculent solution, and flocculation thus commences in a
short distance of pipe. The injection device 14 illustrated in
FIGS. 4 and 5 may also be referred to as an "orifice mixer". For
the mixer of FIGS. 4 and 5, the preferred range of orifice diameter
"d" to downstream pipe diameter "D" is 0.25-0.75.
[0119] FIGS. 6-8 illustrate the performance of an orifice mixer
based on computational fluid dynamic (CFD) modeling and empirical
data obtained from a test installation on a MFT pipeline reactor.
The MFT flow rate in a 2 inch diameter pipe was 30 LPM and
flocculent solution was injected at about 3 LPM. The 2 inch long
orifice mixer had an orifice to downstream pipe diameter ratio
d/D=0.32 with six 0.052 inch diameter injectors located on a 1.032
inch diameter pitch circle. Due to the density difference between
the MFT and flocculent solution, a useful method of characterizing
the degree of mixing is to determine the second moment M of the
concentration C over the pipe cross section A in the following
equation where C is the mean concentration for the fully mixed case
(thus directionally M=0 is desired).
M = 1 A .intg. A ( C C _ - 1 ) 2 dA ##EQU00001##
[0120] In FIGS. 6-8, the dark areas represent MFT that has not
mixed with the flocculent solution (referred to hereafter as
"unmixed MFT"). Just downstream of the mixer, the unmixed MFT
region is limited to the central core of the pipe and is surrounded
by various flocculent solution-MFT mixtures indicative of local
turbulence in this zone. As the flocculent solution is miscible in
MFT, the jetting of the flocculent solution into the turbulent zone
downstream may cause the flocculent solution to first shear the
continuous phase into drops from which diffusion mixing disperses
the flocculent into the MFT.
[0121] The CFD model was based on a Power-law-fluid for the
flocculent solution and a Bingham-fluid for the MFT without
reactions. The Bingham-fluid approximation takes into account the
non-Newtonian nature of the MFT as requiring a yield stress to
initiate flow. Bingham-fluids are also time-independent, having a
shear stress independent of time or duration of shear. In some
optional embodiments, the CFD model may be used to determine and
improve initial mixing between the flocculent solution and the MFT
as well as other aspects of the process.
[0122] The injection device 14 may have a number of other
arrangements within the pipeline reactor and may include various
elements such as baffles (not shown). In one optional aspect of the
injection device shown in FIG. 9, at least some of the injectors
are oriented at an inward angle such that the flocculent solution
mixes via the turbulence eddies and also jet toward the core of the
MFT flow. In another aspect shown in FIG. 10, the orifice has a
reduced diameter and the injectors may be located closer to the
orifice than the pipe walls. The injectors of the mixer may also be
located at different radial distances from the centre of the
pipeline. In another aspect, instead of an annular plate with a
central orifice, the device may comprise baffles or plates having
one or multiple openings to allow the MFT to flow through the
mixing zone while creating turbulence eddies. In another aspect
shown in FIG. 11, the injectors face against the direction of MFT
flow for counter-current injection. FIG. 12 illustrates another
design of injection device that may be operated in connection with
the process of the present invention. It should also be noted that
the injection device may comprise more than one injector provided
in series along the flow direction of the pipeline. For instance,
there may be an upstream injector and a downstream injector having
an arrangement and spacing sufficient to cause the mixing. In a
preferred aspect of the mixing, the mixing system allows the
break-up of the plug flow behaviour of the Bingham fluid, by means
of an orifice or opposing "T" mixer with MFT and flocculent
solution entering each arm of the Tee and existing down the trunk.
Density differentials (MFT density depends on concentration
.about.30 wt % corresponds to a specific gravity of .about.1.22 and
the density of the flocculent solution may be about 1.00) together
with orientation of the injection nozzles play a role here and are
arranged to allow the turbulence eddies to mix in and disperse the
flocculent solution.
[0123] The following table compares the second moment values for
the orifice mixer (FIG. 4) and a quill mixer (FIG. 12) at various
locations downstream of the injection location for the same flows
of MFT and flocculent reagent solution.
TABLE-US-00001 Downstream Distance M L/D Orifice Mixer (FIG. 4)
Quill Mixer (FIG. 12) 1 11.75 5.75 2 3.17 3.65 3 1.75 2.89 5 1.10
2.24 10 0.65 1.39
[0124] Near to the injection point of the orifice mixer as shown on
FIG. 7, there is a larger region of unmixed polymer surrounding a
strong MFT jet with a "M" value of 11.75. However, the mixing with
the MFT jet occurs very rapidly so that by 5 diameters downstream
of the injection point shown as FIG. 8 with a second moment M value
of 1.10. In contrast, for the quill mixer as shown FIG. 12, the
initial mixing with a second moment M value of 5.75 only improves
to 2.24 by 5 diameters downstream of the injection point. Mixing by
the orifice mixer is preferred to the quill mixer.
[0125] Preferably, the mixing is sufficient to achieve an M<2 at
L/D=5, and still preferably the mixing is sufficient to achieve an
M<1.5 at L/D=5, for the pipeline reactor. Controlling the mixing
at such preferred levels allows improved dispersion, flocculation
and dewatering performance.
[0126] Initial mixing of the flocculent solution into the MFT is
important for the flocculation reactions. Upon its introduction,
the flocculent solution is initially rapidly mixed with the fine
tailings to enhance and ensure the flocculation reaction throughout
the downstream pipeline. When the flocculent solution contacts the
MFT, it starts to react to form flocs made up of many chain
structures and MFT minerals. If the flocculent solution is not
sufficiently mixed upon introduction into the pipe, the
flocculation reaction may only develop in a small region of the
in-line flow of tailings. Consequently, if the tailings are
subsequently mixed downstream of the polymer injection, mixing will
be more difficult since the rheology of the tailings will have
changed. In addition, the flocs that formed initially in the small
region can be irreversibly broken down if subsequent mixing imparts
too much shear to the flocs. Over-shearing the flocs results in
resuspending the fines in the water, reforming the colloidal
mixture, and thus prevents water release and drying. Thus, if
adequate mixing does not occur upon introduction of the flocculent
solution, subsequent mixing becomes problematic since one must
balance the requirement of higher mixing energy for flocculated
tailings with the requirement of avoiding floc breakdown from
over-shearing.
[0127] The initial mixing may be achieved and improved by a number
of optional aspects of the process. In one aspect, the injection
device is designed and operated to provide turbulence eddies that
mix and disperse the flocculent solution into the forward flow of
MFT. In another aspect, the flocculation reagent is chosen to allow
the flocculent solution to have decreased viscosity allowing for
easier dispersion. The flocculent solution may also be formulated
and dosed into the MFT to facilitate dispersion into the MFT.
Preferably, the flocculation reagent is chosen and dosed in
conjunction with the injection conditions of the mixer, such that
the flocculent solution contains sufficient quantity of reagent
needed to react with the MFT and has hydraulic properties to
facilitate the dispersion via the mixer design. For instance, when
a viscous flocculent solution displaying plastic or pseudo-plastic
non-Newtonian behaviour is used, the mixer may be operated at high
shear injection conditions to reduce the viscosity sufficiently to
allow dispersion into the MFT at the given hydraulic mixing
conditions. In yet another aspect, the flocculation reagent is
chosen to be shear-responsive upon mixing and to form flocs having
increased shear resistance. Increased shear resistance enables more
aggressive, harsh mixing and reduces the chance of premature
over-shearing of the resulting flocs. The increased shear
resistance may be achieved by providing the flocculent with certain
charge characteristics, chain lengths, functional groups, or inter-
or intra-linking structures. In another aspect, the flocculation
reagent is chosen to comprise functional groups facilitating shear
mixing, rearrangement and selective water release. In another
aspect, the flocculation reagent is chosen to form large flocs
facilitating rearrangement and partial breakdown of the large flocs
for water release. In another aspect, the flocculation reagent may
be an organic polymer flocculent. The polymer flocculent may have a
high molecular weight, such as above 10,000,000, or a low molecular
weight. The high molecular weight polymers may tend to form more
shear resistant flocs yet result in more viscous flocculent
solutions at the desired dosages. Thus, such flocculent solutions
may be subjected to higher shear injection to reduce the viscosity
and the turbulence eddies may be given size and spacing sufficient
to disperse the flocculent solution within the pipeline mixing
zone.
[0128] In some optional aspects, the flocculation reagent may be
chosen and dosed in response to the clay concentration in the MFT.
The flocculation reagent may be anionic, cationic, non-ionic, and
may have varied molecular weight and structure, depending on the
MFT composition and the hydraulic parameters.
[0129] It should be noted that, contrary to conventional teachings
in the field of MFT solidification and reclamation, the improvement
and predictability of the drying process rely more in the process
steps than in the specific flocculation reagent selected. Of
course, some flocculation reagents will be superior to others at
commercial scale, depending on many factors. However, the process
of the present invention enables a wide variety of flocculation
reagents to be used, by proper mixing and conditioning in
accordance with the process steps. By way of example, the
flocculent reagent may be an organic polymer flocculent. They may
be polyethylene oxides, polyacrylamides, anionic polymers,
polyelectrolytes, starch, co-polymers that may be
polyacrylamide-polyacrylate based, or another type of organic
polymer flocculents. The organic polymer flocculents may be
obtained from a flocculent provider and subjected to selection to
determine their suitability and indication toward the specific
commercial application.
[0130] Nevertheless, some polymer reagents may be preferred. In an
optional aspect, the polymer flocculent is shear-responsive during
stage (i) and shear-resilient during stages (ii) and (iii). Thus,
the polymer solution is able to rapidly mix with the MFT upon
injection in response to high shear conditions, and then provide a
certain amount of shear resilience to allow formation and
rearrangement of the flocs and avoid premature or rapid floc
breakdown within the downstream pipeline in response to wall shear
stress. The polymer flocculent may have some monomers that enable
the shear responsiveness in the mixing stage and other monomers or
structures that enable shear resilience during the subsequent
stages. The shear responsiveness may be enabled by a polymer
solution's low viscosity at high polymer dosage, thus low viscosity
polymer solutions may be preferred. At the same time, the shear
resilience may be enabled by structural features of the polymer for
resisting shear breakdown under shear conditions that are
experienced from pipelining.
[0131] In one optional aspect, the polymer flocculent may be
selected according to a screening and identification method. The
screening method includes providing a sample flocculation matrix
comprising a sample MFT and an optimally dosed amount of a sample
polymer flocculent. Preferably, the sample MFT is identical or
representative of the MFT to be treated, e.g. from the same pond
and same location. The method then includes imparting a first shear
conditioning to the flocculation matrix for rapidly mixing the
polymer flocculent with the sample of the oil sand fine tailings,
followed by imparting a second shear conditioning to the
flocculation matrix that is substantially lower than the first
shear conditioning. This may be performed by mixing the matrix with
an impeller at two RPMs, e.g. 230 rpm and then 100 rpm, which
respectively simulate rapid dispersion and pipeline conditioning.
One determines the water release response during the first and
second shear conditionings, preferably by measuring the CST. An
increased water release response provides an indication that the
polymer flocculent may be preferred for use in the process.
[0132] In some optional aspects of the process, the flocculation
reagent may be a polymer flocculent with a high molecular weight.
The polymer flocculent is preferably anionic in overall charge,
preferably approximately 30% anionicity, which may include certain
amounts of cationic monomer and may be amphoteric. The polymer
flocculent is preferably water-soluble to form a solution in which
the polymer is completely dissolved. It is also possible that the
polymer is mostly or partly dissolved in the solution. The polymer
flocculent may be composed of anionic monomers selected from
ethylenically unsaturated carboxylic acid and sulphonic acid
monomers, which may be selected from acrylic acid, methacrylic
acid, allyl sulphonic acid and 2-acrylamido-2-methyl propane
sulphonic acid (AMPS), etc., and the salts of such monomers,
non-ionic monomers selected from acrylamide, methacrylamide,
hydroxy alkyl esters of methacrylic acid. N-vinyl pyrrolidone,
acrylate esters, etc.; and cationic monomers selected from DMAEA,
DMAEA.MeCI, DADMAC, ATPAC and the like. The polymer flocculent may
also have monomers enabling interactions that results in higher
yield strength of the flocculated MFT. In this regard, it is known
that synthetic polymers used as thickeners in various industries,
such as mining, have hydrophobic groups to make associative
polymers such that in aqueous solution the hydrophobic groups join
together to limit water interactions and stick together to provide
a desired shear, yield stress or viscosity response in solution and
when reacted with the MFT. The polymer flocculent may also have a
desired high molecular weight, preferably over 10,000,000, for
preferred flocculation reactivity and dewatering potential. The
polymer flocculent may be generally linear or may be branched by
the presence of branching agent providing a number of branching or
cross-linking structures according to the desired shear and process
response and reactivity with the given MFT.
[0133] In a preferred aspect of the process, the polymer flocculent
may be a high molecular weight branched anionic polymer such as a
polyacrylamide-sodium polyacrylate co-polymer with about 20-35%
anionicity, still preferably about 30% anionicity.
[0134] Initial mixing was further assessed in a conventional
stirred mix tank by varying the initial speed of the mixer. FIG. 13
presents indicative lab test results comparing rapid mixing (230
RPM) and slow mixing (100 RPM). The test results with the mixer at
the higher initial speed developed flocculated MFT with a higher
shear yield strength significantly faster than tests with the mixer
at a lower speed. For the lower speed, the time delay was
attributable to dispersing the flocculent solution into the MFT.
Moreover, FIG. 14 indicates that the fast initial mixing also
resulted in higher initial water release rates, which results in
reduced drying times.
[0135] Referring briefly to FIGS. 23 and 24, it can be seen that
rapid initial mixing at high shear followed by a lower shear regime
results in higher net water release from the flocculated material
upon deposition compared to slow or fast mixing used alone.
[0136] While the lab scale stirred tank demonstrated benefits from
fast mixing, other results also demonstrated the effect of
over-mixing or over-shearing, which would break down the
flocculated MFT such that the MFT would not dewater. The lab scale
stirred tank is essentially a batch back-flow reactor in which the
mixer imparts shear firstly to mix the materials and secondly to
maintain the flocculating particles in suspension while the
reactions proceed to completion. As the operational parameters can
be easily adjusted, the stirred tank provides a valuable tool to
assess possible flocculation reagent performance. Lab scale stirred
tank data may be advantageously coupled with lab pipeline reactor
tests and CFD modelling for selecting particular operating
parameters and flocculation reagents for embodiments of the
continuous in-line process of the present invention.
[0137] The MFT supplied to the pipeline reactor may be instrumented
with a continuous flow meter, a continuous density meter and means
to control the MFT flow by any standard instrumentation method.
There may also be pressure sensors enabling monitoring the pressure
drop over pipe sections to help inform a control algorithm. An
algorithm from the density meter may compute the mineral
concentration in MFT and as an input to the flow meter determine
the mass flow of mineral into the pipeline reactor. Comparing this
operating data to performance data for the pipeline reactor
developed from specific flocculation reagent properties, specific
MFT properties and the specific pipeline reactor configurations,
enables the adjustment of the flowrate to improve processing
conditions for MFT drying. Operations with the mixer in a 12 inch
pipe line processing 2000 USgpm of MFT at 40% solids dewatered MFT
with a pipe length of 90 meters.
[0138] Referring back to FIGS. 4 and 5, after introduction of the
flocculation reagent in the mixing zone 12, the flocculating MFT
continues into a conditioning zone 28. In some aspects described
below, the conditioning stage of the process will be generally
described as comprising two main parts: flocculation conditioning
and water release conditioning.
[0139] At this juncture, it is also noted that for Newtonian fluid
systems, research into flocculated systems has developed some tools
and relationships to help predict and design processes. For
instance, one relationship that has been developed that applies to
some flocculated systems is a dimensionless number called the "Camp
number". The Camp number relates power input in terms of mass flow
and friction to the volume and fluid absolute viscosity. In
non-Newtonian systems such as MFT-polymer mixing both pipe friction
and the absolute viscosity terms used in the Camp number depend on
the specific flow regime. The initial assessment of the pipeline
conditioning data implies the energy input may be related to a Camp
number or a modified Camp number. The modified Camp number would
consider the flocculating agent, the rheology of the flocculated
MFT in addition to the flow and friction factors.
[0140] Flocculation conditioning preferably occurs in-line to cause
formation and rearrangement of flocs and increases the yield shear
stress of the MFT. Referring to FIGS. 4 and 5, once the MFT has
gone through the mixing zone 12, it passes directly to the
flocculation conditioning zone 28 of the pipeline reactor. The
flocculation conditioning zone 28 is generally a downstream pipe 26
with a specific internal diameter that provides wall shear to the
MFT. In one aspect of the process, the flocculation conditioning
increases the yield shear stress to an upper limit. The upper limit
may be a single maximum as shown in FIG. 1 or an undulating plateau
with multiple local maximums over time as shown in FIG. 2. The
shape of the curve may be considered a primary function of the
flocculent solution with secondary functions due to dispersion and
energy input to the pipeline, such as via baffles and the like.
[0141] Water release conditioning preferably occurs in-line after
the flocculation conditioning. Referring to FIGS. 1 and 2, after
reaching the yield stress upper limit, additional energy input
causes the yield stress to decrease which is accompanied by a
release of water from the flocculated MFT matrix. Preferably, the
water release conditioning occurs in-line in a continuous manner
following the flocculation conditioning and before deposition. In
this case, the water release may commence in-line resulting in a
stream of water being expelled from the outlet of the pipe along
with depositing flocculated MFT. The release water will quickly
flow away from the MFT deposit, especially on a sloped deposition
area, while the MFT deposit has sufficient strength to stand on the
deposition area. Here, it is preferred to have no high-shear units
such as pumps in the downstream pipe. The hydraulic pressure at the
MFT pipeline reactor inlet is preferably established so that no
additional pumping which may over-shear the flocs would be required
to overcome both static and differential line head losses prior to
deposition. It is also preferred not to disturb the deposited MFT
with further shearing, but rather to let the MFT deposit dry after
in place, upon deposition. Alternatively, instead of being
performed in-line, the water release conditioning may occur in a
controlled shearing apparatus (not shown) comprising baffles, an
agitator, a mixer, or a rotary separator, or a combination thereof.
The water release conditioning may also occur after the flocculated
MFT is deposited, for instance by a mechanical mechanism in an
ordered fashion. In such a case, the flocculated MFT could be
deposited as a gel-like mass at a shear yield strength allowing it
to stand but tending not to promote water release until additional
energy input is applied. By conditioning the flocculated MFT back
down from a yield stress upper threshold, the process avoids the
formation of a gel-like water-retaining deposit, reliably enabling
water release and accelerated drying of the MFT.
[0142] Care should also be taken not to expel the MFT from a height
that would accelerate it to over shear due to the impact on the
deposition area or the previously deposited MFT.
[0143] The flocculation conditioning and the water release
conditioning may be controlled in-line by varying the flow rate of
the MFT. Preferably, the flow rate may be as high as possible to
increase the yield stress evolution rate of the flocculating MFT,
while avoiding over-shear based on the hydraulic shear of the
pipeline to the deposition area. Tests were conducted in a pipeline
reactor to determine conditioning response. FIG. 15 identifies the
response to varying the pipeline flow rate. A 34 wt % solids MFT
was pumped through a 2 inch diameter pipe at a flow rate of about
26 LPM for the low flow test and about 100 LPM for the high flow
test. A 0.45% flocculent solution was injected at about 2.6 LPM for
the low flow test and at about 10 LPM for the high flow test. At
high flows, the maximum yield shear stress of the flocculated MFT
occurs earlier than at low flows. This observed response indicates
that the total energy input is an important parameter with input
energy being hydraulic losses due the fluid interacting with the
pipe wall in this case.
[0144] Referring to FIGS. 4 and 5, the conditioning zone 28 may
include baffles, orifice plates, inline static mixers or reduced
pipe diameter (not shown) particularly in situations where layout
may constrain the length of the pipeline reactor, subject to
limiting the energy input so the flocculated MFT is not over
sheared. If the flocculated MFT is over sheared, the flocs
additionally break down and the mineral solids revert back to the
original colloidal MFT fluid which will not dewater.
[0145] In one preferred embodiment of the process, when the yield
stress of the flocculated MFT at release is lower than 200 Pa, the
strength of the flocculated MFT is inadequate for dewatering or
reclamation of the deposited MFT. Thus, the yield shear stress of
the flocculated MFT should be kept above this threshold. It should
be understood, however, that other flocculation reagents may enable
a flocculated MFT to dewater and be reclaimed at a lower yield
stress. Thus, although FIGS. 1 and 2 show that a yield stress below
200 Pa is in the over-shearing zone, these representative figures
do not limit the process to this specific value. When an embodiment
of the process used 20%-30% charge anionic polyacrylamide high
molecular weight polymers, the lower threshold of the yield shear
stress window was about 200 Pa, and the flocculated MFT was
deposited preferably in the range of about 300 Pa and 500 Pa,
depending on the mixing and MFT solids content. It should also be
noted that the yield shear stress has been observed to reach upper
limits of about 400-800 Pa in the pipeline reactor. It should also
be noted the yield shear stress of the MFT after the initial water
is released when the MFT is deposited has been observed to exceed
1000 Pa.
[0146] In general, the process stage responses for a given
flocculation reagent and MFT are influenced by flocculent type,
flocculent solution hydraulic properties, MFT properties including
concentration, particle size distribution, mineralogy and rheology,
dosing levels and energy input.
[0147] The process provides the advantageous ability to predict and
optimize the performance of a given flocculent reagent and solution
for dewatering MFT. The mixing zone ensures the efficient use of
the flocculation reagent and the pipeline conditions of length,
flow rate and baffles if required provide the shear necessary to
maximize water release and avoid over-shearing when the MFT is
discharged from the pipeline reactor.
[0148] In one embodiment of the process, after the in-line water
release conditioning, the flocculated MFT is deposited to form a
non-flowing MFT deposit. The conditioned MFT is suitable for direct
deposition on a deposition area, where water is released from the
solids, drained by gravity and further removed by evaporation to
the air and optionally permeates into the deposition area. The
deposition area may comprise sand surfaces to facilitate draining
and permeation. The MFT deposit dries so as to reach a stable
concentration of the MFT solids for reclamation purposes. In other
alternative embodiments for dewatering flocculated MFT,
solid-liquid separation equipment may be used provided the shear
imposed does not over-shear the flocculated MFT. The MFT pipeline
reactor may be used to treat MFT or other tailings or colloidal
fluids having non-Newtonian fluid behaviour for deposition or for
other dewatering devices such as filters, thickeners, centrifuges
and cyclones.
[0149] In one aspect of the process, the MFT is continuously
provided from a pond and has a solids content over 20 wt %,
preferably within 30-40 wt %. The MFT is preferably undiluted.
After the flocculent solution is dispersed into the MFT, the
flocculated MFT releases water thus allows in-line separation of
the water from the flocculated MFT.
[0150] In one aspect of the process, the deposition area may
include a multi-cell configuration of deposition cells, as shown in
FIG. 22. Each deposition cell may have its own design and the cells
may be arranged to improve water release and land use. Each
deposition preferably has a head region at which the flocculated
MFT is deposited and a toe region spaced away from the head region
by a certain length. A sloped bottom surface extends from the head
region to the toe region such that the toe region is at a lower
elevation than the head region. The cells preferably have side
walls such that deposited MFT will at least partially fill the
cell's volume. Multi-cell configurations such as shown in FIG. 22
may be combined with various mixer, pipeline transport and
conditioning arrangements such as those schematically shown in
FIGS. 16, 17, and 18. The flocculent solution may be injected into
the pipeline at various points depending on the desired shear
conditioning to impart to the flocculated MFT prior to deposition
to achieve the desired dewatering effect. Valves may be used to
manage the transport of the flocculated MFT in accordance with the
availability of deposition cells, required shear conditioning and
observed drying rates, to provide flexible management of an MFT
dewatering operation.
[0151] Embodiments and aspects of the present invention will be
further understood and described in light of the following
examples.
EXAMPLES
Example 1
[0152] As mentioned in the above description, lab scale stirred
tank tests were conducted to assess mixing of a flocculent solution
into MFT. The lab mixer was run at initial speeds of 100 RPM or 230
RPM. The dosage of 30% charge anionic polyacrylamide-polyacrylate
shear resistant co-polymer was about 1000 g per dry ton. FIGS. 13
and 14 show that the fast initial mixing shortens the yield stress
evolution to enable dewatering and also increases the water release
from the MFT.
Example 2
[0153] As mentioned in the above description, lab scale stirred
tank tests were conducted to assess mixing of different dosages of
flocculent solution into MFT. The lab mixer was run at speeds of
100 RPM or 230 RPM for flocculent solutions containing different
doses of dissolved flocculation reagent. The dosages of flocculent
ranging from 800 to 1200 g per dry tonne of MFT indicated adequate
mixing and flocculation for dewatering. The flocculation reagent
here was a 30% charge anionic polyacrylamide-polyacrylate shear
resistant co-polymer with a molecular weight over 10,000,000. A
dosage range of 1000 g per dry tonne .+-.20% was appropriate for
various 30 charge polyacrylamides for MFT with clay content of 50
to 75%.
Example 3
[0154] As mentioned in the above description, continuous flow
pipeline reactor tests were conducted.
[0155] Results are shown in FIG. 15 comparing high and low flow
rates. A 34 wt % solids MFT was pumped through a 2 inch diameter
pipe at a flow rate of 26 LPM for the low flow test and 100 LPM for
the high flow test. A 0.45% organic polymer flocculent solution was
injected at 2.6 LPM for the low flow test and at 10 LPM for the
high flow test. The distance from injection to deposition was 753
inches or 376.5 pipe diameters. The 2 inch long orifice mixer had
an orifice to downstream pipe diameter ratio d/D=0.32 with six
0.052 inch diameter injectors located on a 1.032 inch diameter
pitch circle. For the high flow test the six injector diameters
were increased to 0.100 inch.
Example 4
[0156] As mentioned in the above description, computational fluid
dynamic (CFD) modelling was conducted. The CFD modeling considered
the flocculent solution as a Power-law-fluid and the MFT as a
Bingham-fluid in the mixing zone and confirmed both the adequate
mixing of the injection device of FIGS. 4 and 5 and the inadequate
mixing of the conventional side branch tube as discussed in the
Background section under the same conditions. The MFT flow rate in
a 2 inch diameter pipe was 30 LPM and polymer solution was injected
at 3 LPM. The 2 inch long orifice mixer had an orifice to
downstream pipe diameter ratio d/D=0.32 with six 0.052 inch
diameter injectors located on a 1.032 inch diameter pitch circle.
The MFT had a density of 1250 kg/m.sup.3 and a yield stress of 2 Pa
while the polymer solution had a density of 1000 kg/m.sup.3, with a
power-law index n=0.267 and a consistency index of 2750 kg
s.sup.n-2/m.
[0157] Furthermore, the visualization shown in FIGS. 6-8 is only
possible by CFD modelling due to the opaqueness of actual MFT. For
MFT, the CFD model incorporates non-Newtonian fluid behaviours into
the hydraulic analysis to develop a robust design for a variety of
possible combinations and permutations between various MFT
properties and flocculation reagent solutions.
Example 5
[0158] As described above, the present invention resides in the
process steps rather than in the specific flocculation reagent
selected. A person skilled in the art may select a variety of
flocculation reagents that enable in-line dispersion, flocculation,
water release and deposition. One selection guideline method
includes taking an MFT sample representative of the commercial
application and using a fast-slow mixer test to observe the water
release capability of the flocculent. In the fast-slow mixer test,
the flocculent is injected into the mixer running at a fast mixing
rate and after a delay of 7 seconds the mixer is switched to slow
mixing. Water release may then be assessed. For instance, tests
have been run at 230 RPM (corresponding to a shear rate of 131.5
s.sup.-1) for fast mixing and 100 RPM (corresponding to a shear
rate of 37 s.sup.-1) for slow mixing. A fast-slow mixer test was
conducted on 10%, 20%, 30% and 40% charge anionic polyacrylamide
flocculants and the 30% charge anionic polyacrylamides enabled
superior water release. The use of such 30% charge anionic
polyacrylamides in the pipeline reactor and CFD modeling validated
this approach. In addition, the fast-slow mixer test was conducted
on high and low molecular weight linear anionic polyacrylamide
flocculents and the high molecular weight polyacrylamides enabled
superior water release. The fast-slow mixer test may be combined
with the CFD model to test the mixing of the flocculent solution at
the density of the desired formulation. Such cross-validation of
flocculation reagents and solutions helps improve the process
operating conditions and validate preferred flocculation reagents
and solutions.
[0159] FIGS. 23 and 24 show results of the fast-slow test conducted
on a polyacrylamide polymer. It has been noted that this fast-slow
test may identify some acceptable polymers that would have
otherwise been screened out using standard one-speed mixing tests.
Rapid identification and screening of potential polymers is
relevant to process improvement, process flexibility and cost
reduction. Using the fast-slow methodology and obtaining capillary
suction time (CST) data of the treated MFT enables selection of
advantageous flocculents.
[0160] In another investigation of candidate flocculents, two 30%
anionic high molecular weight polymer flocculents were tested using
a multi-step screening process. In the first step, the chemical
activity is evaluated and in the second step a water release curve
is developed for a given solids or clay content of MFT around the
optimal dose identified in the first step. In the first step, the
two polymers were used with a made-up 10 wt % tailings mixture,
optimally dosed by gradually adding increments of 100 ppm of
polymer during stirring until settling is observed. Once settling
is observed, the reaction is stopped and the precipitate and
supernatant are placed upon a sieve. The supernatant is collected
and the volume recorded. A moisture analysis is then performed on
the supernatant. In the second step, a water release curve is
generated for e.g. 40 wt % MFT around the optimal dose identified
in the first step, using the fast-slow methodology. Preferably,
yield stress and CST data are obtained in this evaluation.
Example 6
[0161] Trials were performed and showed that a flocculation reagent
could be injected into MFT in-line followed by pipeline
conditioning, deposition and drying. FIGS. 16-18 schematically
illustrate different setups that may be used. For FIGS. 16 and 17,
the flocculated MFT was deposited onto beaches and for FIG. 18 into
a deposition cell.
[0162] The MFT was about 36 wt % solids and was pumped from a pond
at flow rates between 300 and 720 gal/min. The flocculent solution
was injected in-line at different locations. One of the flocculent
reagents used was a 30% charge anionic polyacrylamide-sodium
polyacrylate co-polymer with a molecular weight over 10,000,000.
The flocculated MFT was conditioned along a pipeline and then
expelled out of spigots arranged in series.
[0163] In order to monitor the progress of the drying, samples were
taken and analyzed for percent solids. The drying times to achieve
75 wt % solids ranged from 5 to 7.5 days depending on the sample
location. Deposition areas having a slope showed faster drying.
FIGS. 19 and 20 show some results at two different sample points of
the drying times of deposited MFT.
[0164] Dosages between 0.6 Kg to 1.1 Kg per dry tonne of MFT
provided preferred drainage results, and much cleaner effluent
water than those outside this range. Trials revealed that incorrect
dosage may reduce dewatering for a number of reasons. If the dosage
is too low, some of the MFT goes unflocculated and overall there is
a lack of dewatering performance. Overdosing flocculent
applications may also lead to reduced dewatering due to allowing
water to become bound up in semi-gelled masses with the solids
making it more difficult to provide conditioning sufficient to
allow water release with the given pipeline dimensions and
hydraulic conditions. Both of these situations were observed and
dosage adjustments were made to compensate. In addition, water
quality depends on dosage control. Overdosing or inadequate mixing
(resulting in localised overdosing) resulted in poor release water
quality with at times over 1 wt % solids. Increased dosing control,
the preferred dosage range and rapid initial mixing helped resolve
water quality issues and improve dewatering and drying of the
deposited MFT. Other observations noted that the deposited MFT
dewatered and dried despite significant precipitation, thus
resisting re-hydration from precipitation.
[0165] Reclamation of the MFT deposits was further observed as
vegetation from seeds tossed on the deposition area was later noted
to be growing well.
Example 7
[0166] One of the challenges to successful treating of MFT is the
process variations encountered in operations. It may be desired to
use a side injection nozzle to for mixing liquids into MFT.
[0167] Using the mixing algorithm developed for the MFT pipeline
reactor model, FIG. 21 compares a typical side injection nozzle to
the orifice nozzle of FIG. 4 on a 2 inch pipeline for a range of
MFT flows based on: [0168] The MFT is 30 wt % solids and modeled as
a Herschel-Bulkley fluid with a yield stress of 2 Pa and high shear
rate viscosity of 10 mPa s. Density was 1250 kg/m.sup.3. [0169] The
flocculent solution was modeled as Power Law fluid with n=0.267 and
consistency index (k) of 2750 kg s.sup.n-2/m. Density was 1000
kg/m.sup.3 and the flow rate was 1/10 the MFT volume flow rate
[0170] The orifice mixer had a 0.32 orifice ratio. [0171] The flow
area for injecting the polymer solution was the same for both
mixers.
[0172] FIG. 21 illustrates that the orifice mixer of FIG. 4
provides significantly preferred mixing than the conventional side
injection nozzle over the range of MFT flows.
Example 8
[0173] In preliminary investigations regarding the preferred
performance requirements for an additive chemical, the focus was
put on strength gain and resistance to shear. Another objective was
enhanced dewatering, as several previous attempts to flocculate MFT
required dilution of the material prior to mixing with the
flocculant, and then only achieved clay to water ratios similar to
or slightly less than that found in the source MFT. Commercial
application of polymeric flocculation in oil sands is restricted to
rapid dewatering of low solids content thin fine tails. In short,
flocculants had been unable to collapse the clay matrix any further
than that found in the ponds.
[0174] During the course of bench scale tests, a certain polymer
type (high molecular weight branched polyacrylamide-sodium
polyacrylate co-polymer with about 30% anionicity) showed promise
in both material strength gain as well as shear resistance. In
addition, the polymer appeared to promote initial dewatering of the
MFT shortly after mixing by generating a highly permeable floc
structure. This means that the process no longer relies on
evaporative drying alone, but rather a combination of initial
accelerated dewatering and drainage in the deposit slope as well as
evaporation. No dilution of the MFT was required beyond the polymer
make up water and the polymer could be injected in line without the
use of a thickener. The polymer was quite effective for MFT up to
40 percent by weight (roughly 0.4 clay-to-water ratio).
[0175] Initial field tests produced surprising results, allowing
for 20-30 cm lifts to reach 80% solids in less than 10 days. Given
the weather conditions at the time, the minimum amount of water
released as free water was 85% as the potential evaporation rates
were too low to account for the dewatering rate. This initial
success appeared to be robust and relatively insensitive to changes
in fluid density and injection locations.
[0176] Subsequent testing began to illustrate, however, that there
was a basic understanding of the behaviour of the flocculated
material that was not obtained during the initial laboratory or
field tests. Deposits were attempted with lower levels of control
on the density and flowrates of the source MFT, resulting in a
wider variety of deposit dewatering rates. Many of these deposits
did not behave as previously observed, and several attempts at
enhancing the dewatering performance through additional mixing,
changes in the deposition mechanisms, or mechanical manipulation of
the deposits met with limited success. It became apparent that more
testing was required.
[0177] In investigations of undiluted MFT flocculation, it was
attempted to manipulate the MFT floc structure such that initial
dewatering is maximized and the MFT gained just enough strength to
stack in a thin lift when deposited on a shallow slope. Dewatering
occurs as a function of mixing and applied shear during pipeline
transport as well as on the deposition slopes.
[0178] Bench and pilot scale experiments were conducted to
replicate the field observations and to investigate the dewatering
potential as a function of polymer dosage, injection type, mixing,
total applied shear and clay-to-water ratio of the MFT. The
experiments highlight several key factors. [0179] 1. Polymer dosage
is best determined by clay content, measured as clay activity using
methylene blue adsorption method. [0180] 2. Mixing of the
polymer-treated MFT using laboratory or in-line static mixers can
cause less than optimum dewatering potential and stacking in the
deposition slopes. [0181] 3. Shear energy applied to the
flocculated materials can greatly affect the dewatering and
strength performance. Insufficient shear often create a high
strength material with minimal dewatering and excess shear reduces
the strength to MFT-like strengths with reduced permeability and
dewatering.
[0182] Regarding polymer dosage, although it is recognized that the
rheology of flocculated systems is governed by the finest particles
in a slurry, polymer is often added on a gram per tonne of solids
basis. This is often adequate for a homogeneous slurry. However,
fine tailings are deposited in segregating ponds and the mineral
size distribution of MFT depends on the sampling depth. Therefore
dosing on a solid basis would often result in an underdosed or an
overdosed situation affecting maximum water release. This is
highlighted in the below Table for three MFT samples that show
large swings in the optimum polymer dosage on solids or fines
basis. The MFT samples were sourced from two different ponds at
different depths and with similar water chemistries.
TABLE-US-00002 TABLE Optimum polymer dosage for maximum initial
water release. Optimum polymer dosage Wt % Wt % (g/tonne of Sam- Wt
% clay* on fines on (g/tonne fines < 44 (g/tonne ple ID solids
solids solids of solids) .mu.m) of clay) MFT A 44.0 48.9 59.8 800
1424 1742 MFT B 32.6 78.9 89.3 1200 1428 1616 MFT C 22.3 99.6 98.8
1700 1707 1693 *Wt % clay is based on the surface area determined
from methylene blue adsorption and could be greater than 100% for
high surface area clays (Omotoso and Mikula 2004).
[0183] Regarding rheology of flocculated MFT, a static yield stress
progression over time was used to evaluate optimal yield stress for
deposition and water release in the laboratory, pilot and field
experiments. The shear yield stress was measured by a Brookfield
DV-III rheometer. The water release was measured by decanting the
initial water release and by capillary suction time (CST). The
capillary suction time measures the filterability of a slurry and
is essentially the time it takes water to percolate through the
material and a filter paper medium, and travel between two
electrodes placed 1 cm apart. The method is often used as a
relative measure of permeability.
[0184] FIG. 25 shows an optimally dosed MFT mixed in a laboratory
jar mixer with the rpm calibrated to the mean velocity gradient.
The figure shows the shear yield stress progression curve for a 40
wt % solids MFT. The polymer was injected within a few seconds
while stirring the MFT at 220 s.sup.-1. Mixing continued at the
same mean velocity gradient until the material completely broke
down. At each point on the curve, mixing was stopped and the yield
stress measured. Water release during mixing is often dramatic and
was clearly observed. The extent of water release is given by the
capillary suction time. A low suction time correlates to high
permeability and a high suction time correlates to low
permeability. MFT dosed at ideal rates released the most water and
about 20-25% of the initial MFT water was released at the lowest
CST.
[0185] In further studies, MFT was mixed with a shear-resistant
polymer flocculant in a laboratory jar mixer with the rpm
calibrated to total mixing energy input. The shear-resistant
polymer was a high molecular weight branched polyacrylamide-sodium
polyacrylate co-polymer with about 30% anionicity. FIG. 26 shows
the shear yield stress progression curve for a 40 wt % solids MFT
dosed at different polymer concentrations. The experiment was
conducted in two mixing stages. In the first stage, MFT was mixed
at 220 s.sup.-1 during polymer injection. This stage lasts for a
few seconds and defines the rate of floc buildup. In the second
stage, the material was mixed at 63 s.sup.-1 until the material
completely broke down. At each point on the curve, mixing was
stopped and the yield stress measured. Water release during mixing
is often dramatic and was clearly observed. MFT dosed at 1000
g/tonne of solid released the most water (FIG. 27). The material
released about 20% of the initial MFT water immediately whereas the
under-dosed and over-dosed MFT released very little water through
complete floc breakdown.
[0186] Four distinct stages were identified in the shear
progression curve: [0187] Polymer dispersion or floc build-up stage
displaying a rapid increase in yield stress as the polymer contacts
the minerals and poor water release. [0188] A gel state of high
shear yield stress which can be a plateau depending on the applied
shear rate and % solids of the MFT. The rates of floc build-up and
breakdown in this stage appear to be roughly the same. [0189] A
region of decreasing shear strength and floc breakdown where
significant amount of polymer-free water is released. [0190] An
oversheared region characterized by rapidly decreasing shear
strength where the material quickly reverts to an MFT state and
releases very little water.
[0191] These stages are used to quantify the behaviour of
polymer-dosed MFT and to compare behaviours under different shear
regimes and the third stage was the target design basis. An optimal
dose of polymer with a good initial dispersion into MFT achieves
preferred permeability to release water. Without an optimal dose
and good dispersion, the MFT has a tendency to remain in the gel
state and only dries by evaporation. This is highlighted in FIG. 28
where the same MFT in the underdosed or the overdosed state fail to
release significant amount of water despite developing significant
yield stresses. A key advantage of preferred polymers is having
prolonged resistance to shear which allows operational flexibility
when pipelining flocculated MFT to deposition cells.
[0192] Shown in FIG. 29 are the microstructures corresponding to
different shear regimes in the preferred flocculated MFT in FIG.
25. The MFT and flocculated slurries were flash dried to preserve
the microstructure to some extent. Samples were platinum coated and
examined in a scanning electron microscope. The starting MFT showed
a more massive microstructure on drying and a greater tendency for
the clays to stack along their basal planes in large booklets. This
results in a low concentration of interconnected pores and poor
dewatering. The middle micrographs in FIG. 29 show microstructures
exhibited by flocculated MFT in the second stage (383 Pa) at the
onset of floc breakdown and water release. The microstructure is
dominated by dense aggregates and randomly oriented clay platelets
with more interconnected pores. The third set of micrographs (86
Pa) show less massive aggregates and a more open structure most
likely responsible for the large water release observed in the
third stage. The starting MFT is highly impermeable, whereas the
flocculated MFT contains large macropores and significant amounts
of micropores not visible in the starting MFT. At higher mixing
time, the porosities start to collapse with an attendant reduction
in the dewatering rates.
[0193] Optimally dosed MFT with varying solids content were also
investigated (FIG. 30). As the solids content decreases polymer
dispersion becomes easier. The maximum yield strength of the
material also decreases with increasing water content. A
substantial amount of water is released at lower solids content
(for example, 10 wt % settles to 20 wt % immediately--the water
release at a lower solids content was much greater at 10 wt %
solids (51% of the water in the original MFT) than at 40 wt %
solids where 20% of the water in the original MFT was released);
however the floc structure is weaker and more difficult to stack in
a deposition slope without being washed off.
[0194] Further laboratory testing has shown that the strength gain
and dewatering effects are possible with many anionic polymers, and
are not limited to the particular formulation used in the first
successful tests. FIG. 31 compares a 40 wt % MFT optimally dosed
with a preferred polymer A (high molecular weight branched
polyacrylamide-sodium polyacrylate co-polymer with about 30%
anionicity) and polymer B (high molecular weight linear anionic
polyacrylamide (aPAM) typically used for flocculating oil sands
tailings). The optimum dosages for both polymers, in terms of
maximum water release, were the same (1000 g/tonne of solids) and
were compared at two different shear rates. Polymer dispersion and
shear stress response of the polymers differ significantly.
Increasing the dispersion rate by increasing the mixer speed
increases the yield stress instantaneously, but the traditional
aPAM required additional mixing before the onset of flocculation.
This decrease in the dispersion rate means that MFT treated with
traditional polymer is more likely to stay in a gel state and not
release as much water. The flocculation reagent used in the process
is preferably highly shear-resistant especially during the second
and third stages, and is also highly shear-responsive especially in
the first stage of dispersing and mixing.
[0195] It is generally expected for a linear aPAM that a higher
mixing energy rapidly builds up the yield stress but the floc
breakdown also occurs at a faster rate. The lower viscosity of the
preferred polymer A coupled with a high resistance to shear allow
the flocculated MFT to be transported over long distances to
deposition cells without significant floc breakdown. Nevertheless,
polymers displaying responses such as aPAM's could be more
appropriate in applications demanding very short pipe lengths to
achieve the desired dewatering.
[0196] Various polymers that have been developed with high shear
resistance may be used in the process to improve the dewatering.
Preferably, such shear-resistant polymers would also be in the
general class of branched high molecular weight 30% anionic
polyacrylamide-polyacrylate co-polymer flocculants.
[0197] In order to optimise the behaviour of the flocculated
material, it is preferable to limit the variance in the shear
energy applied to the various flocs which are created during
mixing. This is achieved with an in-line orifice injector system,
which has been described hereinabove and with reference to various
Figs. The concept here is to inject the polymer as a "mist" through
the orifice instead of as a stream. However, it should be
understood that the quill-shaped injector device may be modified by
adapting the size of the perforations to approach a mist-like
injection into the flow of MFT. When injected into a turbulent
back-flow regime as shown in FIG. 6, the polymer is evenly
distributed and flocculation is occurring throughout the pipeline
cross section within 4 pipe diameters of the injection point. This
rapid dispersion allows for precise control of the shear energies
from the injection point to the point of deposition, and increases
the percentage of the material that falls within the dewatering
zone at a design point in the system. This fundamental behavioral
understanding advances improved application of this technique, and
allows results obtained from bench scale testing to be used in CFD
modeling and scaled up to field operations.
[0198] In a pilot test for the determination of mixing parameters,
a 20-m long and 0.05-m diameter pipe loop fitted with the in-line
orifice injector was used to investigate the shear response and
dewatering behaviour of flocculated MFT. Sample ports are fitted to
two locations along the length of the pipe. FIG. 32a shows that the
yield strength progression in the pipe loop is similar to that
observed in the laboratory jar mixer although the mixing energies
are not directly comparable. MFT flow at 30 L/min corresponds to a
mean velocity gradient of 22 s.sup.-1 compared to 63 s.sup.-1 in
the bench scale test. Another test conducted at 100 L/min (176
s.sup.-1) showed a more rapid floc buildup and breakdown similar to
the 220 s.sup.-1 test in the jar mixer. FIG. 32b shows flocculated
MFT sampled at different locations during the test run for the
optimally dosed MFT at 30 L/min (1000 g/tonne of solids in this
case). Such data from the pilot and field tests may be used to
inform and further develop mixing models for process design and
monitoring of commercial scale MFT drying plants.
[0199] Regarding field observations, the rapid polymer dispersion
by the orifice mixer caused the yield strength of flocculated
material to increase very rapidly and resulted in the deposition of
a two-phase fluid. Flocculated MFT and a separate water stream were
observed at the discharge in one of the pilot tests.
[0200] A scaled up version of the orifice mixer was investigated in
the field with optimally dosed 35-40 wt % MFT flowing at
.about.7500 L/min (32 s.sup.-1) in 0.3 m pipe diameter, and
deposited in cells at various distances from the injection point.
FIG. 33 shows the extent of water release for each cell, both from
actual sampling after 24 h and a capillary suction test conducted
on the as-deposited flocculated MFT. The dewatering trend is
analogous to the shear progression profile for the laboratory and
pilot tests. Over 25% of the MFT water was released immediately
after injection up to 175 m. Beyond this length, the water release
rate decreased rapidly and the flocculated material properties
resemble MFT.
[0201] Further dewatering occurs in the deposition slopes through
drainage enhanced by the slope and by evaporation. The under-mixed
material deposited at roughly 7 m from the discharge was further
dewatered by mechanically working the material to reach the floc
breakdown stage where more water is released from the flocculated
material. Aggressive mechanical working however could break the
deposit structure resulting in lower permeability and a restricted
water release. Once the permeable structure is broken, dewatering
is only by evaporation.
[0202] Evaporation results in crack formation as shown in FIG. 34.
Deepening cracks through dewatering allow for side drainage of
release water into cracks and down the slope. Typical deposits up
to 20 cm thick was found to dry beyond 80 wt % solids in 6-10 days
after which a subsequent lift could be placed. Deep cracks as shown
in FIG. 34 may also ameliorate the water drainage or release of a
second flocculated MFT deposit laid on its surface by providing
naturally occurring channels.
Example 9
[0203] Studies were conducted for automated polymer dosage control
to compensate for variations in MFT feed properties in the
dewatering process. Although the materials property limiting the
polymer dosage of MFT is the clay mineral content in MFT, polymer
has often been added on a solids or fines basis because of the
difficulty in measuring the clay content in real time in a
continuous process. The solids content (or slurry density)
approximation is adequate when the polymer addition is optimized
for a particular MFT stream with little variation in density or
clay-to-water ratio (CWR). Variability in the feed properties,
which often occurs when a dredge is used for MFT transfer, lead to
an under- or over-dosed situation when polymer is added on a solids
basis. Empirical correlations were developed between the yield
stress and the CWR for MFT from three tailings ponds: Pond A, B and
C. The MFT samples have varying bitumen contents, sand-to-fines,
clay-to-fines and clay-to-water ratios. Coupled with the online
density and volumetric flow measurements, a real-time clay-based
polymer dosing strategy was developed. Unlike direct clay
measurements, the yield stress of the MFT feed is amenable to rapid
determination in a field environment either in a stand alone vane
rheometer or in an online rheometer.
[0204] Four MFT samples were characterized to develop the
relationship between yield stress and clay content. Three MFT
samples were sourced from Pond A (with different slurry densities),
Pond B and Pond C. Process effected water (PEW 2) was used as
dilution water.
[0205] To facilitate the development of relationships between the
yield stress and materials properties, detailed baseline
characterization of the MFT samples was conducted. This includes
solids content, Dean Stark extraction for bitumen, mineral and
water determination, particle size distribution, methylene blue
adsorption for clay activity (expressed as clay content) and
process and pore water chemistry. Rheological tests were conducted
in a Bohlin rheometer with the focus on yield stress measurement.
Flow curves were generated in a controlled-stress mode permitting
the application of Bingham plastic model for yield stress
determination. A range of solids content was produced by dilution
with PEW water or partial evaporation at a low temperature.
Laboratory tests were on Pond A and C MFT. For actual field
correlations, rheological measurements were conducted on another
set of Pond A and B MFT samples. The polymer was a high molecular
weight branched polyacrylamide-sodium polyacrylate co-polymer with
about 30% anionicity.
[0206] The optimum polymer dosage required to flocculate and
dewater three of the four characterized undiluted or dried MFT
samples was determined using established procedures.
[0207] Regarding the relationship between shear yield stress and
clay content, the below Tables show the baseline properties of the
four MFT samples used in this study. The properties of interest,
bitumen, minerals, fines, clay contents and water chemistry span
the range typically observed for various MFT ponds. Pond A and STP
have similar pore water chemistries and are similar to PEW 2 with
very high Na/Ca equivalent ratios. Pond B pore water has similar
total dissolved solids (ppm) as Ponds A and C but the chemistry is
very different. Pond B has a significantly higher divalent ion
concentrations (3-6 times less sodic than Ponds A and C). Both Ca
and Mg are better coagulants than the monovalent ions and
destabilize the clay suspension more effectively prior to
flocculation. It is therefore conceivable that the mechanism of
polymer interaction with Pond B MFT may have differences from Ponds
A and C. The measurable Fe and the very low sulphate concentration
in Pond B compared to Ponds A and C are due to presence of froth
treatment tailings and the action of sulphate reducing bacteria
feeding on a copius Fe source. Because of the different water
chemistries, any correlation between the yield stress and the CWR
may either include a correction factor for interaction forces
between particles or, as done in this study, an empirical
correlation for MFT with similar chemistries.
TABLE-US-00003 TABLE Baseline characterization of MFT samples used
for determining yield stress-clay content relationship. % Solids
Dean Stark Avg. of duplicate (oven Methylene Blue on MFT slurry
analysis drying) PSD (solid basis) Wt % clay Wt % Wt % Wt % Wt %
Wt. % fines < 44 Wt % clay < 2 (activity) - solids Sample ID
Bitumen Water Mineral Solid .mu.m (sieve) .mu.m (sedigraph) basis
CWR C(W + B)R LAB 1 STUDIES Pond A Bulk as-received 4.5 57.5 37.9
42.0 74.0 46.8 55.8 0.37 0.34 (Dredge 1 Jul. 2009) Pond A Low
Density 2.1 66.8 30.4 32.6 89.3 50.3 78.9 0.36 0.35 (Dredge 1 Jul.
2009) Pond A High Density 1.9 55.4 42.6 44.0 59.8 35.8 48.9 0.38
0.36 (Dredge 1 Jul. 2009) Pond C 0.6 76.4 22.0 22.3 98.8 65.5 99.6
0.29 0.29 LAB 2 STUDIES Pond A (dredge 2 Jan. 1.2 79.3 19.7 21.9
99.1 N.M 91.0 0.23 0.22 2010) - 9.5'' Pond A (dredge 2 Jan. 1.8
66.0 32.5 33.8 98.0 N.M 72.1 0.35 0.35 2010) - 13.5'' Pond A
(dredge 2 Jan. 1.7 56.9 41.6 42.4 91.7 N.M 54.5 0.40 0.39 2010) -
15.5'' Pond A (dredge 2 Jan. 2.1 54.5 43.0 46.3 78.8 N.M 51.3 0.39
0.38 2010) - 18'' Pond C (January 3.7 58.9 37.1 N.M 95.3 N.M 71.3
0.45 0.42 2010)- Average of 5 pails CWR--Clay-to-water ratio C(W +
B)--Clay-to water + bitumen ratio N.M--Not measured.
TABLE-US-00004 TABLE Chemistry of PEW 2 water used for dilution and
MFT pore water .SIGMA.(Na + K)/ Cation concentration (ppm) Anion
concentration (ppm) (Ca + Mg) Sample ID Ca K Mg Na Fe Cl SO.sub.4
HCO.sub.3 CO.sub.3 pH IB TDS mole ratio Pond A Bulk as- 9 21 4 707
0 323 179 1061 25 8.6 1.03 2329 80 received (Dredge 1 Jul. 2009)
Pond A Low 7 18 2 672 0 321 150 1010 22 8.7 1.02 2202 115 Density
(Dredge 1 Jul. 2009) Pond A High 8 18 2 645 0 280 144 1011 22 8.6
1.03 2130 101 Density (Dredge 1 Jul. 2009) Pond C 9 19 4 813 0 536
241 940 15 8.5 1.02 2577 92 Pond A (dredge 2 8 13 5 668 0 438 219
976 0 7.9 0.92 2327 73 January 2010) Pond B (January 29 18 14 614 1
250 4 1434 0 8.2 0.97 2364 21 2010)- Average of 5 pails PEW 2 10 12
5 617 0 409 194 651 9 8.4 1.06 1907 60 IB--ion balance; TDS--Total
dissolved solids
[0208] FIG. 35 gives the relationship between yield stress and
solids content for Ponds A and C MFT. The large variation observed
especially between Pond C and the Pond A MFT samples reflects the
clay activity variation in the MFT samples. Pond B MFT with a lower
clay activity than Pond C follow a similar trend due to the higher
divalent cations in Pond B. When the relationship is expressed as
total clay content in MFT (derived from MB adsorption) rather than
solids content, a better relationship is observed as shown in FIG.
36. However, given that flow behaviour is directly related to the
amount and arrangement of active surfaces in the aqueous phase, a
better correlation is between yield stress development and
clay-to-water ratio shown in FIG. 37. Ponds A and C MFT now follow
the same trend, but Pond B MFT does not. The empirical relationship
between the CWR and the Ponds A and C MFT (Bingham yield
measurements only) is expressed as a power function in Equation
1.
CWR(.+-.0.02)=0.048+0.203+*.sigma..sup.0.303 Eq. 1
.sigma..quadrature. is the shear yield stress in Pa.
[0209] Using an in-house Brookfield vane rheometer, the following
empirical correlations are obtained for Pond A (dredge 2) and Pond
B MFT.
CWR(PondA)=0.439-2.626*.sigma..sup.-1.789 Eq. 2
CWR(PondB)=0.970-0.734*.sigma..sup.-0.114 Eq. 3
[0210] The MFT samples did not develop significant yield stresses
until the material reaches a CWR greater than 0.3.
[0211] To determine the clay content from rheology measurements,
the water content was required. In the field, this can be provided
by a rapid moisture analyzer which counts the bitumen content as
part of the solids. If a rapid moisture analyzer is not available
the specific gravity (determined from a Marcy scale or nuclear
density gauge) can be used. This entails developing a calibration
between the clay-water+bitumen ratio and the yield stress (FIG.
38). The Marcy scale and nuclear density gauge measure the mineral
content given that the specific gravity of bitumen is approximately
1. Empirical relationships between the clay to (water+bitumen)
ratios are given below:
C(W+B)R(STP,PondA)=0.065+0.174*.sigma..sup.0.324 Eq. 4
[0212] The relationship in Equation 4 is for Ponds C and A
measurements using the Bingham yield stress. Equations 5 and 6 are
for static yield stresses measured with a Brookfield vane
rheometer.
C(W+B)(PondA)=0.421-2.692*.sigma..sup.-1.857 Eq. 5
C(W+B)R(PondB)=0.855-0.645*.sigma..sup.-0.124 Eq. 6
[0213] FIG. 39 and FIG. 40 describe the yield stress as a function
of particles sizes (clay size and fines respectively). Both clay
and fine sizes describe the flow behaviour better than solids
content but they are approximations of the clay activity and not a
true measure of the slurry rheology.
[0214] For use as a process control tool, the MFT static yield
stress is measured and converted to CWR and C(W+B)R using Equations
1 to 6. If a moisture analyzer is available, the clay content in
the MFT is simply:
Wt % clay in MFT=CWR*wt % Moisture in MFT Eq 7
[0215] If the specific gravity (SG) is available either from a
Marcy scale or a nuclear density gauge, Equation 8 should be
used.
Wt % clay in MFT = 100 * C ( W + B ) R * [ 1 - 2.62 1.62 * ( 1 - 1
SG ) ] Eq . 8 ##EQU00002##
[0216] Fines density may be approximately by about 2.62 g/cm3.
[0217] Regarding "optimum" polymer dosage, the response of Pond C
and Pond A (dredge 1) MFT samples to polymer dosage is given by the
strength curves in FIG. 41 to FIG. 43. The optimum polymer dosage
frequently gives the optimum yield stress and highest water release
rate. While the optimum was clearly established for the high
density MFT at 800 g/tonne of solid (FIG. 43), the low density MFT
has an optimum slightly higher than 1200 g/tonne of solid and Pond
C MFT has an optimum between 1600 and 1800 g/tonne of solid. The
amounts of water released are given in FIG. 44. The water release
is highest for the high density MFT with a well defined optimum.
The below table also gives the optimum polymer dosage of some of
the MFT samples.
TABLE-US-00005 TABLE Optimum polymer dosage at 220 s-1 initial
mixing and 63 s-1 until complete floc breakdown. Optimum Optimum Wt
% clay polymer dosage polymer dosage Sample ID Wt % solids (MB)
(g/tonne of solids) (g/tonne of clay) Pond A Bulk as- 42.0 55.8 Not
determined Not determined received (Dredge 1 Jul. 2009) Pond A Low
Density 32.6 78.9 1275.sup.1 1616 (Dredge 1 Jul. 2009) Pond A High
Density 44.0 48.9 851 1742 (Dredge 1 Jul. 2009) Pond C 22.3 99.6
1686.sup.2 1693 Pond A (dredge 2 Jan. 21.9 91.0 1693 1861 2010) -
9.5'' Pond A (dredge2 Jan. 33.8 72.1 1278 1773 2010) - 13.5'' Pond
A (dredge 2 Jan. 42.4 54.5 1002 1839 2010) - 15.5'' Pond A (dredge
2 Jan. 46.3 51.3 983 1914 2010) - 18'' Pond B (January 2010)- 40.8
71.3 Pending Pending Average of 5 pails (bit + min) .sup.1Slight
underdose .sup.2Approximate dose.
[0218] An equivalent dosage on a dry clay basis can be calculated
as:
g polymer / Te of clay = g polymer / Te of solid * wt % solid in
MFT wt % clay in MFT Eq . 9 " Te " means metric tonnes .
##EQU00003##
[0219] When expressed on a clay basis as in Equation 9, the polymer
dosage is essentially equivalent at approximately 1850 g of polymer
per tonne of dry clay (an average of the more accurately measured
Pond A MFT samples from dredge 2), irrespective of the solids
content or the types of minerals present in MFT. For this MFT type,
if the dosage changes because of a more efficient polymer mixing,
it will still be dependent on the available solids surface area,
which is essentially the clay content which can be measured by
methylene blue.
[0220] Embodiments of the present process can utilise flocculent
dosing on a continuous and automated basis based on MFT solids with
the solids (minerals) content determined using a nuclear density
gauge and a volumetric flow meter. A simple relationship could be
derived from Equations 1 to 8 to allow automatic polymer addition
based on clay content while still using the solids (or minerals)
content as input parameter.
g polymer / Te of mineral = 1850 * wt % clay in MFT ( Eq . 9 ) 2.62
1.62 ( 1 - 1 SG ) Eq . 10 ##EQU00004##
[0221] OR for Pond A and Pond C MFT using measuring the static
yield stress and S.G,
g polymer / Te of mineral = 1850 * 0.421 - 2.692 * .sigma. - 1.857
* [ 1 - 2.62 1.62 * ( 1 - 1 SG ) ] 2.62 1.62 ( 1 - 1 SG ) Eq . 11
##EQU00005##
[0222] Equations 10 and 11 provide a useful guideline and
relationship between the preferred polymer dosage and the measured
clay content or shear yield stress of MFT. It permits a much closer
control of dosage and dewatering characteristics of an MFT feed
during operation. This relationship has been found to be
particularly suitable to MFTs having lower divalent to monovalent
cation ratios. It should also be noted that while this relationship
has been pursued in detail with respect to specific Pond MFTs and
process water, similar work may be done using MFTs and process
waters with differing chemistries in order to derive a
corresponding detailed relationship. It should also be noted that
modifications to the type of flocculent used in the process may
require modifications to this detailed relationship. The rationale
behind using the yield stress as a measure of clay activity stems
form the ease and speed of measuring rheological properties in a
field operation environment. It has been found that the process
setup can deliver the preferred dosage within 30 minutes of start
up, from sampling to analysis and reporting, if appropriate field
test facilities are provided onsite. In addition, given a fairly
constant MFT density and flow rate, this setup can be successfully
used as a process control tool. Alternatively, online rheometers
may be incorporated into the setup to measure the rheology in real
time and could be coupled to the polymer flocculent solution
plant.
Example 10
[0223] In studying the rheology of a preferred polymer flocculent
(a high molecular weight branched polyacrylamide-sodium
polyacrylate co-polymer with about 30% anionicity), viscosity
measurements for different concentrations of the branched polymer
at several temperatures and shear rates were conducted using a
Brookfield DV-III viscometer in order to develop a general
rheological model for the polymer solutions used to flocculate
MFT.
[0224] Six solutions were prepared to investigate a wide range of
polymer concentrations and also to determine the effect of the
water type used to prepare the mixtures. Five of the solutions were
prepared with process water while one solution was prepared with
distilled water, as shown in the below Table.
TABLE-US-00006 TABLE Polymer Solutions. Solution Water
Concentration Type Water pH 0.1% Process 8.22 0.2% Process 8.22
0.3% Process 8.22 0.45% Process 8.22 0.6% Process 8.22 0.3%
Distilled 7.86
[0225] The viscosity was measured over a wide range of shear rates
and at three temperatures using the SSA (Small Sample Adapter)
Spindle 18. The first set of measurements were made a few hours
after mixing up the solutions (first Table below) and the
measurements were repeated 24 hours later (second Table below):
there was almost no difference in the measured viscosity for the
two data sets. The data in the first Table is plotted in FIG. 45,
from which it is evident that the polymer is a shear-thinning
power-law fluid for which the viscosity increases with
concentration and decreases with temperature. Comparing the two
curves for a solution concentration of 0.3%, it is clear from FIG.
45 that a mixture with distilled water has significantly higher
viscosity.
TABLE-US-00007 TABLE Viscosity measured a few hours after solution
preparation at various shear rates and temperatures for six polymer
mixtures. Temperature Concentration Viscosity (cP) at defined Shear
Rate (.degree. C.) (%) 3.96 s.sup.-1 7.92 s.sup.-1 14.5 s.sup.-1
37.0 s.sup.-1 73.9 s.sup.-1 100 s.sup.-1 132 s.sup.-1 25 0.1 10.7
10.7 11.6 10.3 8.57 8 7.36 25 0.2 64 48 40.7 27.4 20.6 18.5 16.3 25
0.3 160 112 84.4 52.6 37.7 32.4 28.8 25 0.45 373.3 250.7 180.4 104
69.7 58.9 50.9 25 0.6 693.3 458.7 311.3 171.4 110.3 91.8 78.4 25
0.3* 906.7 544 346.2 171.4 105.1 86.3 71.7 15 0.1 21.3 16 14.5 12.6
10.3 9.26 8.64 15 0.2 74.7 58.7 46.5 32 24 21.1 19.2 15 0.3 170.7
128 93.1 58.3 42.3 36.6 32.6 15 0.45 416 277.3 197.8 114.3 77.1
65.7 57.6 15 0.6 757.3 496 337.5 185.1 120 101.1 86.7 15 0.3* 949.3
570.7 360.7 180.6 112.6 90.9 76.5 4 0.1 21.3 21.3 20.4 16 12.6 11.8
10.9 4 0.2 85.3 69.3 55.3 38.9 29.1 25.7 23.4 4 0.3 202.7 149.3
107.6 68.6 49.1 43.4 39 4 0.45 469.3 314.7 221.1 128 87.4 75.8 66.2
4 0.6 842.7 544 369.5 203.4 135.4 114.1 97.9 4 0.3* 981.3 597.3
381.1 194.3 122.3 99.8 84.2 *Solution prepared with distilled water
instead of process water
TABLE-US-00008 TABLE Viscosity measured 24 hours after solution
preparation at various shear rates and temperatures for six polymer
mixtures. Temperature Concentration Viscosity (cP) at defined Shear
Rate (.degree. C.) (%) 3.96 s.sup.-1 7.92 s.sup.-1 14.5 s.sup.-1
37.0 s.sup.-1 73.9 s.sup.-1 100 s.sup.-1 132 s.sup.-1 25 0.1 10.7
10.7 11.6 10.3 8.57 8 7.36 25 0.2 64 48 40.7 28.6 21.1 18.5 16.6 25
0.3 149.3 112 81.5 52.6 37.7 32.4 28.5 25 0.45 362.7 250.7 177.5
102.9 69.1 58.5 50.6 25 0.6 682.7 453.3 308.4 169.1 109.1 90.9 77.8
25 0.3* 906.7 544 346.2 171.4 105.7 86.3 72 15 0.1 21.3 16 14.5
12.6 10.3 9.26 8.64 15 0.2 74.7 58.7 46.5 32 24 21.1 18.9 15 0.3
170.7 128 93.1 59.4 42.3 36.6 32.3 15 0.45 405.3 277.3 197.8 113.1
76 64.8 57 15 0.6 757.3 496 337.5 184 119.4 100.2 86.1 15 0.3*
949.3 570.7 360.7 180.6 112.6 91.8 76.5 4 0.1 21.3 21.3 20.4 16
12.6 11.8 10.9 4 0.2 85.3 74.7 55.3 37.7 28.6 25.3 23 4 0.3 202.7
149.3 110.5 68.6 49.1 43.4 39.4 4 0.45 458.7 314.7 221.1 128 87.4
75.4 65.9 4 0.6 842.7 544 369.5 203.4 133.7 113.3 97.9 4 0.3* 1003
602.7 381.1 195.4 122.9 100.2 83.2 *Solution prepared with
distilled water instead of process water
[0226] It should be noted that the data points at the lowest
concentration and the lowest shear rate have a certain degree of
uncertainty due to the very low torque value at those conditions.
The viscosity measurements at the lowest polymer concentration
could be repeated using the lower torque Brookfield DV-III Ultra-LV
viscometer to improve the accuracy of the results.
[0227] Regarding curve fits, a standard expression for
non-Newtonian power law fluid viscosity is given by:
.mu.==k{dot over (.gamma.)}.sup.n-1e.sup.T.sup.0.sup./T
where k is the consistency index, n is the power-law index and
T.sub.0 is the reference temperature. The data points in the first
Table were fit to this form of curve and are plotted as lines in
FIG. 45. It is obvious from FIG. 45 that a very good fit of the
data can be obtained using the expression in the above Equation,
with the exception of the 0.1% solution data at low shear.
[0228] The coefficients for each of the six solutions are given in
the below Table. In FIG. 46, the coefficients are plotted versus
concentration.
TABLE-US-00009 TABLE Curve-fit coefficients for six polymer
mixtures. Concentration (%) Coefficient 0.1 0.2 0.3 0.45 0.6 0.3* k
[cP s.sup.n-1] 0.0199 1.634 9.7939 42.250 141.01 798.14 n 0.8102
0.6242 0.5176 0.4278 0.3749 0.2701 T.sub.0 [K] 2034.6 1248.2 1024.1
1024.1 733.1 337.3 *Solution prepared with distilled water instead
of process water
[0229] Viscosity measurements for different concentrations of a
preferred branched anionic polymer at several temperatures and
shear rates resulted in the following indications: [0230] The
polymer mixtures were shear-thinning power-law fluids for which the
viscosity increases with concentration and decreases with
temperature. [0231] The viscosity is highly dependant on the type
of water used to prepare the polymer solution: use of distilled
water results in much higher viscosity than process water. [0232]
Viscosity of all samples remained essentially unchanged when
measured a few hours after the solution was prepared and again 24
hours later. [0233] Curve-fits of the viscosity data were obtained
using a power-law expression with a temperature correction term and
could be correlated with polymer concentration to provide a
complete model of the polymer viscosity, for that water and
polymer.
[0234] The polymer flocculent solution may be prepared depending on
the given polymer and water chemistry to obtain the desired
viscosity and reactivity.
Example 11
[0235] Trials on MFT from Pond A were conducted to assess various
aspects of the dewatering process. An important understanding
gained from this experimental program was that while polymer
treatment was necessary to initiate flocculation of fine clays and
dewatering of MFT, in some instance it was preferable to remove the
release water from the deposit to permit further drying. Hence,
details such as cell slope, length and drainage paths are
considerations in the design of drying cells to achieve improved
drying time.
[0236] The main findings from these tests are discussed in this
example section. The MFT dewatering process can be said to consist
of two operations, the polymer treatment and water removal in
drying cells; using both is preferred for the drying of treated MFT
solids. Note that the configuration of Pond A deposition cells is
shown in FIG. 22.
[0237] Regarding polymer treatment performance, successful
treatment of Pond A MFT with a high molecular weight branched
polyacrylamide-sodium polyacrylate co-polymer with about 30%
anionicity, was demonstrated with the use of two types of polymer
injectors over different mixing lengths. The purpose of this
treatment was to quickly disperse the polymer into the MFT stream
using quill-type and co-annular mixers to flocculate clays
particles. The flocculated aggregate of water, clays and polymer up
to this point gained enough shear strength to stack up, but if
deposited too soon was still a network and would not release free
water. Further pipeline transport provided more shearing of the
material; when the right amount of structural breakdown of flocs
had been applied, free water was then released while flocculated
material consolidated which may have been from their own weight.
The amount of structural breakdown was controlled by varying
pipeline transport distance between the injector and the deposition
cell (also referred to herein as a "drying cell"). The significance
of attaining the right breakdown has at least two important
aspects: 1) the initial water release was significant as about 30%
of original MFT water was shed within the 1st day, and 2) the
deposit also had the lowest water retention, which improved water
drainage from the deposit during the subsequent drying.
[0238] When too long a pipe length was used, flocs became
"oversheared" (too much breakdown occurred): the flocculated
material turned back to a continuous network and no water was
released. Drying in such case was accomplished mainly by
evaporation, a slower process than drainage.
[0239] It was possible to determine the degree of flocculation
(under/overshear condition) and the dewatering zone of treated MFT
by measuring its yield stress and CST. To maintain optimal
treatment, both parameters would preferably be monitored frequently
throughout the MFT dewatering operation. CST is an apt indication
of the deposit's readiness in releasing water initially (e.g. as
surface run-off) as well as the ease with which water migrates
through the deposit toward the toe of cells. It is reasoned that
the first property has a significant dependence on self-weight
consolidation of clay flocs (a function of the flocs' hydrodynamic
characteristic and type of polymer) and the second property is
related to the connectivity and size of network of pores within the
deposit.
[0240] It was found that the co-annular injector was superior to
the quill-type injector notably because of the former's rapid
dispersion of polymer solution into the MFT stream, hence
generating flocs that consolidate more readily. This injector
yielded better dewatering rate, higher solid content after 1st day
and greater % solids increase rate (also referred to herein as
"rate of rise"). On a practical field trial level, the co-annular
injector-mixer has a preferred range of 50 m-150 m of mixing length
for the pipeline reactor prior to deposition. This range
corresponds to the low CST interval, i.e. the lowest CST values,
and hence yields greater initial dewatering: both result in shorter
drying time (FIG. 47). When the analysis was extended to include
polymer dosage, it appeared there was an optimal region of polymer
dosage and shear level to yield the lowest CST. A contour plot of
CST versus polymer dosage and mixing length for the co-annular
injector suggested the best operating range to be about 950 to
about 1050 ppm for polymer dosage and about 90 m to about 200 m for
pipeline conditioning length (FIG. 48). It is nonetheless suggested
to use a conservative limit of 150 m and to perform post-deposition
shearing techniques on the deposit if necessary. For the quill
injector, tested for deposition cells 1-6, 11-13, the CST contour
plot suggested these cells were slightly underdosed. Optimum dosage
seemed to increase with mixing length, conceivably to offset the
extra polymers consumed in re-flocculating the broken flocs. The
quill injector also appeared to require higher polymer rate than
the co-annular injector.
[0241] Certain difficulties were encountered in treating low
density MFT (e.g. below 28% mineral) as there was a higher tendency
to overshear the material. To mitigate or avoid this occurrence,
one may preferably avoid low density MFT if possible or, when
treating low density MFT, use short mixing lengths or change
injection location to minimize the pipeline length.
[0242] Regarding drying performance, dewatering and drying took
place in drying cells where water was released from solids flocs
until the deposit reaches 75% solids content. Two mechanisms were
noted. First, as solids flocs started to stack on the surface of
drying cells there was an initial release of water whereby free
water was seen running off the surface of the deposit toward the
toe of cells. Solids content reached around 45% after the first
day. Water continued to release but most of the migration through
the deposit occurred below surface. Water migration was a far more
effective means in removing water than evaporation (two to three
times better). Evaporation was a secondary and slower drying
mechanism. It becomes apparent that the ability to drain water away
from the deposit is preferred to the performance of drying cells.
As was seen with some cells, insufficient slope and inadequate
drainage or runoff facility can hinder drying beyond 60% solids
content.
[0243] Pond A drying cells displayed two types of drying trends. In
the first category, solids content in the deposit rose steadily at
a "rate of rise" of 1.5%-2% per day. Drying was completed in 15 to
20 days. This mode of drying is similar to the drying of a
previously tested pond treated MFT. FIGS. 49a, 49b and 49c
illustrate these trends. The operating conditions of these cells
are tabled below.
TABLE-US-00010 MFT % Solids Mineral Drying "Rate of Cell % after
Drying loading factor Rise" - % No Min 1.sup.st day time (t/m2)
(t/ha/mo) per day 7 23.5 42 20 0.06 900 1.9% (Marcy) (thin lift) 11
33.8 41.2 18 0.17 2833 1.4% 12 40.6 41.7 15 0.38 5700 .sup. 2%
(Marcy)
[0244] Given a typical rate of rise from to evaporation at 0.5% per
day (25 cm lift), the rate of rise due to water release and
migration was 0.90%-1.5%/day, 64% to 75% of the total. At a rate of
rise of 1.4%-2% per day, cell will dry to 75% in 16-23 days,
assuming a solid content of 42.5% after the first day.
[0245] In the second type of drying trend, drying started well with
an adequate rate of rise around 2% per day until solids content
approached 55%-60%. From then on, the rate of rise slowed down to
about 0.5% as if driven by evaporation. In some cases with rain
falls, the rate of rise remained flat for several days, or even
negative (i.e. accumulating precipitation water). In other cases,
the rate of rise eventually picked up again after that. Drying was
slower than with the first type and cells were able to reach 75%
solids content only with plowing and disc harrowing techniques.
Post-deposition working and farming techniques were thus able to
treat such deposits to reach dewatering and drying targets.
[0246] Though a precise cause of degradation was not pinpointed, in
the cases above, the slow-down in drying rate appeared to follow a
period of rains. This suggests an issue with surface drainage which
prevented water from running off at the surface of the deposit.
Field observation confirmed that trapped water was found in part of
one of the cells. Surface drainage may be hindered by insufficient
slope or by surface irregularities such as depressions caused by
process variability (on spec/off spec quality) as well as circular
ridges from plowing in circular patterns.
[0247] FIGS. 50a and 50b show a case of a cell that did not dry
effectively because the significant amounts of the material were
oversheared due to an overly long pipeline conditioning length. As
water release was halted in oversheared condition, the deposit
essentially dried by evaporation.
[0248] Drying performance was also impeded in some cases when
release water from adjacent cells was allowed to travel over a
cell. The situation was exacerbated when processing low density
MFT. Deposition cells should be designed and deposition should be
managed in order to avoid release water spill over.
[0249] For multiple layers of deposited flocculated MFT, it may be
desired to obtain undamaged deep cracks in the deposit, e.g. as
shown in FIG. 34, to facilitate water release to flow away from the
second layer deposit. Accordingly, in an optional aspect of the
process, the deposit is left so that it remains substantially
untouched by post-deposition handling or mechanical working, to
retain the deep crack channel structure before a second lift is
made.
[0250] It should also be noted that solids content samples taken
from drying cells can vary. It is normal to expect the top of cell
to dry faster than the toe area. Difference in dryness can also be
found in other areas of the cell. Uneven drying increases drying
time and could be caused by one of the following reasons:
variability in the polymer treatment process, producing off-spec
products and by consequence uneven lift thickness, sampling
protocols, or material movement from plow/harrow activity.
[0251] Regarding the effect of plow/disc harrow activity, the
plow/disc harrow released trapped water and accelerated drying in
cells 1 and 3, which had little slope, and helped drying in cells 7
and 8. Multiple plows in both cells did not seem to bother its
performance. It was noted that producing circular ridges can trap
release and rain water and with multiple plows were probably not be
necessary: potential harm may exceed benefit. The preferred
strategy is to let drying cells take their own course for the first
few days while drying performance is being monitored and intervene
if desired to adjust drying performance. It is also preferred to
avoid circular plow or disc patterns: fish bone patterns are a good
alternative as they shorten water migration pathway and may improve
dewatering.
[0252] Regarding drying capability, it was attempted to obtain and
derive the following general drying factors compiled from in-situ
cells which had reached 75% solids content or higher.
[0253] The drying factor was based on total mineral in MFT and
provide a general indication.
TABLE-US-00011 Cell Tonnes of Drying Mineral loading Drying factor
No. minerals days (t/m2) (t/ha/month) 1 231 13 0.03 702 2 1636 21
0.22 3102 3 1759 18 0.20 3379 7 1919 20 0.19 2817 8 1731 17 0.17
2943 9 1558 22 0.25 3477 11 1489 18 0.17 2886 12 2890 15 0.38 7510
13 5597 18 0.11 1910
Example 12
[0254] Trials were conducted and protocols developed for the
identification of MFT dewatering process flocculation reagents.
[0255] The protocol developed has the following exemplary steps,
though variations of the protocol may be used depending on the
nature, class and number of flocculation reagents to be testes and
the MFT being used: [0256] Identification of chemical activity: 10%
Solids MFT is mixed with the flocculation reagent polymer and
beaker settling test followed by a drainage test is performed to
determine activity. The Target is 20% SBW precipitate after 20
minutes of drainage or a net water release of >50%, and <1%
solids in supernatant. [0257] 24 hour water release performance
using fast-slow methodology: Sieve test on 40% SBW standard low
calcium MFT to determine dose range. Target range is 10% net water
release from MFT and less than 1% solids in supernatant. [0258]
Yield Stress and CST data using fast slow methodology: Once water
release potential has been confirmed yield stress and CST data are
run. [0259] Slope drying test. 2L of material are dried in a sloped
lab cell: Target lift height 8-10 cm. Target drying time less than
10 Days.
[0260] FIG. 51 is an exemplary decision tree for the above protocol
screening and identification technique. It should be understood
that the thresholds pertaining to water release quantities, MFT and
release water solids content, dewatering and drying rates, etc.,
are meant as exemplary guidelines and different thresholds may be
used depending on the given MFT to be treated and the set of
polymers to be tested, as the case may be.
[0261] The following is a more detailed example of the flocculation
reagent identification protocol, where a 0.45% solution of the
chemical is made up by dissolving 2.25 g of chemical in 500 mL of
process water. [0262] Identification of chemical activity: 320 mL
of 10% Solids MFT was measured out into a 500 mL beaker. The
optimal dose of chemical must now be determined. Starting at a 300
PPM dose polymer and increasing in increments of 100 PPM polymer is
added to the 500 mL beaker that is stirred at 320 rpm using the
laboratory mixer until settling is observed. Once settling has been
observed the reaction is stopped and the precipitate and
supernatant is then placed upon a 500 mL kitchen sieve over a 1 L
beaker. The supernatant is collected over 20 minutes, the volume is
then recorded using a measuring cylinder. A moisture analysis is
then performed on .about.10 g of the supernatant using a halogen
lamp oven. [0263] 24 hour water release test using fast slow
methodology: For a 24 hour water release test a water release curve
must be generated for 40% SBW around the optimal dose identified in
the chemical activity test. 320 mL of 40% SBW MFT was measured out
into a 400 mL metal container. The amount of polymer for the
optimal dose and 100 PPM and 100 PPM higher than the optimal dose
is calculated. The laboratory mixer is increased to 320 rpm until
the polymer was completely dispersed in 10-20 s stop-go steps. The
mixer speed is then reduced to 100 rpm after dispersion is
completed. The mixer is stopped just after the point of maximum
strength which is visually identified. The flocculated matrix is
then placed upon a 500 mL kitchen sieve over a 1 L beaker. The
supernatant is collected over 24 hours, the volume is then recorded
using a measuring cylinder. [0264] Yield stress and CST using
fast-slow methodology: 320 mL of 40% SBW MFT was measured out into
a 400 mL metal container. The amount of polymer for the optimal
dose is calculated. The laboratory mixer is increased to 320 rpm
until the polymer was completely dispersed in 15 s stop-go steps.
The mixer speed is then reduced to 100 rpm after dispersion is
completed and 30 s stop-go steps are performed until the MFT yield
stress has reached a plateau. At each stop step the CST and yield
stress data is taken. [0265] Slope drying test: 320 mL of 40% SBW
is measured out into a 400 mL metal container.
[0266] The optimal dose is calculated. The fast slow methodology
and time for minimum CST identified in 3.3 is then used to
condition the flocculated MFT. This is repeated 7 times to generate
2 L of conditioned MFT. This is placed on a 45 cm.times.30 cm tray
containing a sand base. The lift height in cm is then measured.
After 24 hours a sample is taken and the moisture content is
monitored using a halogen lamp oven. This is repeated every 24
hours until the material has reached 75% SBW.
[0267] The following is an exemplary run for two candidates, one of
which is a step 2 failure chemical. [0268] Identification of
chemical activity: Two 30% charge anionic polyacryamides, Polymer A
(mentioned above) and Polymer C rheology modifier, underwent the
chemical activity test on 10% solids by weight MFT. The precipitate
reached >20% SBW (releasing >50% of the water present in the
original MFT) in both cases. The supernatant was also below 1%
solids, 0.54% for Polymer A and 0.74% for Polymer C. FIG. 52 shows
the net water release data for optimal dose Polymer A (1000 PPM)
and Polymer C (800 PPM). [0269] 24 hour water release test using
fast slow methodology: The floc structure generated by Polymer C
seemed similar to Polymer A, however there was no observable water
release. The 24 hour water release numbers indicate that the floc
matrix generated by Polymer C has gelled up retaining some of the
polymer water (FIG. 53, showing net water release curves data for
Polymer A and Polymer C). This data shows that Polymer C is not an
appropriate chemical for field trials. [0270] Yield stress and CST
using fast slow methodology and slope drying test: Although Polymer
C does not release any water after 24 hours the yield stress data
was performed during the water release test (FIG. 54, showing yield
stress data Polymer C (800 PPM) vs. Polymer A (1000 PPM)). There
are two very interesting pieces of information that indicate why
the Polymer C did not become an appropriate chemical. First of all,
although the dose of polymer and hence the physical amount of
polymer added to the MFT was much lower than Polymer A, the amount
of energy required to mix the polymer into the MFT was much
greater. Once mixed in, a very strong gelled matrix was formed with
a very high yield stress. This started to breakdown and over-shear
at a very fast rate. When compared to Polymer A, which not only
mixed in very quickly but also breaks down at a slow rate, it
becomes very easy to identify a preferred chemical from a chemical
that will gel the MFT. Generally, preferred flocculation reagents
have a wide dewatering stage in between the gel matrix stage and
the over-shearing zone.
[0271] Although testing for Polymer C was halted at this point,
data from Polymer A in a gel state (under-dose) can be used as a
reference point for the effect of a gel state MFT (FIG. 55 showing
CST data for an optimal dose water release (800 PPM) and an
under-dose that generated a gel state with no initial water release
(500 PPM)). In a gel state the CST data generally improves from raw
MFT but does not undergo a sudden dip upon water release which
lasts until the flocculated material has been over-sheared.
[0272] The effect observed visually and by the CST relates directly
to the effect on drying (FIG. 56, showing drying data for an
optimal dose that releases water (1000 PPM) vs. an under-dose (600
PPM) that enters a gel state with no initial water release, both
sets of data being 8 cm lifts 1 L of material on a sand base with
starting solids of 40% SBW). The gel state material dries at a
slightly quicker rate than evaporation whereas the water-releasing
material has reached 75% SBW in less than 5 days.
[0273] The process of the present invention, which is a significant
advance in the art of MFT management and reclamation, has been
described with regard to preferred embodiments and aspects and
examples. The description and the drawings are intended to help the
understanding of the invention rather than to limit its scope. It
will be apparent to one skilled in the art that various
modifications may be made to the invention without departing from
what has actually been invented.
* * * * *