U.S. patent application number 14/063340 was filed with the patent office on 2014-05-01 for mixing systems for mixing oil sands tailings and polymer.
This patent application is currently assigned to SYNCRUDE CANADA LTD. in trust for the owners of the Syncrude Project. The applicant listed for this patent is SYNCRUDE CANADA LTD. in trust for the owners of the Syncrude Project. Invention is credited to BARRY BARA, RANDY MIKULA.
Application Number | 20140116925 14/063340 |
Document ID | / |
Family ID | 50546014 |
Filed Date | 2014-05-01 |
United States Patent
Application |
20140116925 |
Kind Code |
A1 |
BARA; BARRY ; et
al. |
May 1, 2014 |
MIXING SYSTEMS FOR MIXING OIL SANDS TAILINGS AND POLYMER
Abstract
A process for flocculating and dewatering oil sands fine
tailings in a pipeline is provided, comprising: pumping a tailings
feed having a solids content in the range of about 10 wt % to about
45 wt % through a pipeline; injecting an effective amount of a
polymeric flocculant into the tailings feed to provide an initial
quick dispersion of the polymeric flocculant into the tailings
feed; and providing a subsequent conditioning environment to form
flocs and release water without overshearing.
Inventors: |
BARA; BARRY; (Edmonton,
CA) ; MIKULA; RANDY; (Edmonton, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SYNCRUDE CANADA LTD. in trust for the owners of the Syncrude
Project |
Fort McMurray |
|
CA |
|
|
Assignee: |
SYNCRUDE CANADA LTD. in trust for
the owners of the Syncrude Project
Fort McMurray
CA
|
Family ID: |
50546014 |
Appl. No.: |
14/063340 |
Filed: |
October 25, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61719399 |
Oct 27, 2012 |
|
|
|
Current U.S.
Class: |
208/390 |
Current CPC
Class: |
C10G 1/045 20130101 |
Class at
Publication: |
208/390 |
International
Class: |
C10G 33/04 20060101
C10G033/04 |
Claims
1. A process for flocculating and dewatering oil sands fine
tailings in a pipeline, comprising: (a) pumping a tailings feed
having a solids content in the range of about 10 wt % to about 45
wt % through a pipeline; (b) injecting an effective amount of a
polymeric flocculant into the tailings feed to provide an initial
quick dispersion of the polymeric flocculant into the tailings
feed; and (c) providing a subsequent conditioning environment to
form flocs and release water without overshearing.
2. The process as claimed in claim 1, further comprising: (d)
optimizing the mixing potential of the tailings slurry by
introducing the tailings feed through a static mixer prior to step
(c).
3. The process as claimed in claim 1, further comprising: (d)
pre-shearing the tailings feed prior to step (b).
4. The process as claimed in claim 1, whereby step (b) and step (c)
occur at the end of the pipeline.
5. The process as claimed in claim 1, whereby a coagulant is also
added to the tailings feed.
6. The process as claimed in claim 1, whereby the tailings feed is
fluid fine tailings having a solids content in the range of about
30 wt % to about 45 wt %.
7. The process as claimed in claim 1, whereby the polymeric
flocculant is a water soluble polymer having a moderate to high
molecular weight and an intrinsic viscosity of at least 3 dl/g
(measured in 1N NaCl at 25.degree. C.).
8. The process as claimed in claim 1, whereby the flocculated
tailings are added to at least one centrifuge to dewater the oil
sands fine tailings and form a high solids cake and a low solids
centrate.
9. The process as claimed in claim 1, whereby the flocculated
tailings are added to a thickener to dewater the oil sands fine
tailings and produce thickened oil sands fine tailings and
clarified water.
10. The process as claimed in claim 1, whereby the removed
flocculated tailings are transported to at least one deposition
cell for dewatering.
10. (canceled)
11. The process of claim 1, wherein the polymeric flocculant is an
anionic, nonionic, cationic or amphoteric polymer.
12. The process of claim 11, wherein the dosage of polymeric
flocculant ranges from about 400 grams to about 2000 grams per
tonne of solids in the feed.
13. The process of claim 12, wherein the polymeric flocculant is
the form of a 0.2 to 2% by weight aqueous solution.
14. The process of claim 12, wherein the flocculant is in the form
of a 0.2 to 0.4% by weight aqueous solution.
15. The process of claim 11, wherein the flocculant comprises a
polyacrylamide anionic flocculant.
16. The process as claimed in claim 1, wherein the flocculant is
injected into the pipeline by means of a plurality of side ports in
a section of the pipeline.
17. The process as claimed in claim 1, wherein the flocculant is
injected into the pipeline by means of a venturi inserted into the
pipeline, said venturi having a plurality of polymer inlets.
18. The process as claimed in claim 3, wherein the tailings feed is
pre-sheared in an in-line mixer.
19. The process as claimed in claim 18, wherein the in-line mixer
is a static mixer.
20. The process as claimed in claim 1, wherein the conditioning
environment is a lower energy environment than the dispersion
environment in step (b).
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process for dewatering
oil sands tailings. In particular, tailings are treated with a
polymeric flocculant such as a water soluble polymer having a
moderate to high molecular weight and an intrinsic viscosity of at
least 3 dl/g (measured in 1N NaCl at 25.degree. C.) to form larger
structures (flocs) that can be efficiently separated from the water
when ultimately deposited in a deposition area.
BACKGROUND OF THE INVENTION
[0002] Oil sand generally comprises water-wet sand grains held
together by a matrix of viscous heavy oil or bitumen. Bitumen is a
complex and viscous mixture of large or heavy hydrocarbon molecules
which contain a significant amount of sulfur, nitrogen and oxygen.
The extraction of bitumen from oil sand using hot water processes
yields fine tailings composed of fine silts, clays, residual
bitumen and water. Mineral fractions with a particle diameter less
than 44 microns are referred to as "fines." These fines are
typically clay mineral suspensions, predominantly kaolinite and
illite.
[0003] The fine tailings suspension is typically 85% water and 15%
fine particles by mass. Dewatering of fine tailings occurs very
slowly. When first discharged in ponds, the very low density
material is referred to as thin fine tailings. After a few years
when the fine tailings have reached a solids content of about
30-35%, they are referred to as mature fine tailings (MFT), which
behave as a fluid-like colloidal material. MFT, which has a low
solids to fines ratio (<0.3), is often referred to as a type of
fluid fine tailings (FFT). FFT is generally defined a liquid
suspension of oil sands fines in water with a solids content
greater than 1% and having less than an undrained shear strength of
5 kPa, The fact that fluid fine tailings behave as a fluid and have
very slow consolidation rates significantly limits options to
reclaim tailings ponds. A challenge facing the industry remains the
removal of water from the fluid fine tailings to strengthen the
deposits so that they can be reclaimed and no longer require
containment.
[0004] Accordingly, there is a need for an improved method to treat
fine tailings to reduce their water content to create dry stackable
tailings and reclaim the land on which fine tailings are
disposed.
SUMMARY OF THE INVENTION
[0005] It has been discovered that proper mixing of a flocculant
such as a high molecular weight nonionic, anionic, or cationic
polymer with oil sands fine tailings such as FFT is critical to
creating the right floc structure that will dewater the tailings
rapidly. It is contemplated that the present invention can be used
in conjunction with centrifugation of the flocculated fine tailings
in, for example, decanter centrifuges; thickening of the
flocculated fine tailings in thickeners known in the art;
accelerated dewatering, or rim ditching, in specially constructed
dewatering cells; and "thin lift" operations, where the flocculated
fine tailings are spread over an area in a thin layer for rapid
dewatering, followed by additional layering and dewatering of
flocculated fine tailings. All of these technologies rely on proper
mixing of the fluid fine tails with polymer to create a material
that can readily dewater.
[0006] The two main methods of mixing polymer with oil sand
tailings with polymer are static/in-line mixing and dynamic mixing.
Dynamic mixing utilizes a motor driven mixing device such as an
impeller to cause fluid mixing while static/in-line mixing uses the
energy contained within the flowing fluid stream to mix the polymer
and oil sand tailings with polymer. Given that mixing energy is
directly coupled with flow rate for a static mixing system,
improper design can lead to an unstable mixing system.
[0007] The present invention applies in particular to thixotropic
suspensions where the viscosity and yield strength of the slurry
can be manipulated and optimized to improve mixing of polymeric
flocculants and other process aids. The current application is
directed to a process for dewatering oil sands tailings by treating
the tailings with flocculant by providing in-line mixing of polymer
and raw oil sand tailings such as FFT or MFT to produce a properly
flocculated mixture. The introduction of mixing energy to the
tailings slurry prior to addition of the flocculant allows one to
control the yield point and viscosity of the slurry in order to
create a fluid system into which the polymeric flocculant can more
easily be mixed.
[0008] In one aspect, an end of pipe mixing process for mixing oil
sand tailings with polymer is provided which includes in-line
mixing at the end of a pipe. There are two key steps when
flocculating oil sand tailings and polymer with an end of pipe
device. The first step is to very quickly disperse the polymer into
the oil sand tailings and then allow a flow conditioning period for
floc growth. Quick dispersion of polymer into oil sand tailings can
be enhanced if a conventional static mixer is placed directly
upstream of the end of pipe flocculating device to pre-shear the
raw oil sand tailings. Pre-shear is used to reduce the raw oil sand
tailings viscosity plus induce small scale eddies to aid in the
dispersion of the polymer in the oil sand tailings.
[0009] It is also important that the piping be sized as to ensure
turbulent flow of the raw oil sand tailings. The end of pipe
polymer injection device may consist of polymer jets that shoot
into the raw oil sand tailings stream to quickly disperse the
polymer throughout the oil sand tailings. After the polymer is
completely dispersed in the oil sand tailings, a large stilling
chamber or flow conditioning section is required to promote floc
growth. The flow conditioning section then overflows the
flocculated oil sand tailings into a thin lift or other accelerated
dewatering deposits. In one embodiment, the flocculated oil sand
tailings are treated by centrifugation.
[0010] In one embodiment, the stilling chamber has to be of
adequate size as to not cause excessive floc breakup and thereby
reducing the ability of the flocculated mixture to release water
prior to dewatering by, e.g., centrifugation.
[0011] In another aspect, a mixing system is provided that that
will allow for in-line mixing of raw oil sand tailings with polymer
within the pipeline itself. There are two important steps when
flocculating oil sand tailings with polymer in an in-line mixing
system. The first step is to very quickly disperse the polymer into
the oil sand tailings and then allow a flow conditioning period for
floc growth through the pipeline. Quick dispersion of polymer into
oil sand tailings can be enhanced if a conventional static mixer is
placed upstream of the polymer injection to pre-shear the raw oil
sand tailings. Pre-shear is used to reduce the raw oil sand
tailings viscosity plus induce small scale eddies to aid in the
dispersion of the polymer in the oil sand tailings.
[0012] It is also important that the piping be sized as to ensure
turbulent flow of the raw oil sand tailings. The polymer
injection/dispersion section may consist of an injection device
that will quickly disperse the polymer throughout the oil sand
tailings. After the polymer is completely dispersed in the oil sand
tailings, a flow condition section is required to promote floc
growth. The conditioning section should not be excessively long
otherwise it will result in excessive floc breakup, thereby
reducing the ability of the flocculated mixture to release
water.
[0013] The present invention is particularly useful with, but not
limited to, fluid fine tailings (FFT) such as MFT. Thus, a process
is provided for flocculating and dewatering oil sands fine tailings
in a pipeline, comprising: [0014] pumping a tailings feed having a
solids content in the range of about 10 wt % to about 45 wt %
through a pipeline; [0015] injecting an effective amount of a
polymeric flocculant into the tailings feed to provide an initial
quick dispersion of the polymeric flocculant into the tailings
feed; and [0016] providing a subsequent conditioning environment to
form flocs and release water without overshearing.
[0017] In one embodiment, the conditioning environment is a lower
energy environment that the dispersion environment. In another
embodiment, a coagulant such as gypsum is also added to the
tailings feed. In another embodiment, polymer is injected using an
injector design selected from (1) a plurality of side ports in a
spool section of the pipeline, (2) a single side port in a spool
section of the pipeline, and (3) a plurality of spargers, each with
a plurality of holes, in a spool section of the pipeline. In
another embodiment, an in-line mixer or static mixer is used in
conjunction with a polymer injector.
[0018] In one embodiment, the oil sands tailings is fluid fine
tailings, such as MFT, which fluid may be optionally diluted with
water to provide the tailings feed having a solids content in the
range of about 10 wt % to about 45 wt %. In another embodiment, the
tailings feed has a solids content in the range of about 30 wt % to
about 45 wt %.
[0019] In one embodiment, the polymeric flocculant is a water
soluble polymer having a moderate to high molecular weight and an
intrinsic viscosity of at least 3 dl/g (measured in 1N NaCl at
25.degree. C.). In one embodiment, the polymer dosage is about 1000
g/Tonne of tailings and the polymer jet shear rate is about 200
s.sup.-1.
[0020] In one embodiment, the removed flocculated oil sands fine
tailings are added to at least one centrifuge to dewater the oil
sands fine tailings and form a high solids cake and a low solids
centrate.
[0021] In another embodiment, the removed flocculated oil sands
fine tailings are added to a thickener to dewater the oil sands
fine tailings and produce thickened oil sands fine tailings and
clarified water.
[0022] In another embodiment, the removed flocculated oil sands
fine tailings are transported to at least one deposition cell for
dewatering.
[0023] In another embodiment, the removed flocculated oil sands
fine tailings are spread as a thin layer onto a deposition
site.
[0024] In one embodiment, the process further comprises
pre-shearing the oil sands fine tailings using at least one in-line
or static mixer prior to polymer injection. Without being bound to
theory, it is believed that, in certain cases, pre-shearing may
increase the maximum dewaterable solids loading.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Referring to the drawings wherein like reference numerals
indicate similar parts throughout the several views, several
aspects of the present invention are illustrated by way of example,
and not by way of limitation, in detail in the figures,
wherein:
[0026] FIG. 1 is a schematic of one embodiment of the present
invention for mixing oil sands fine tailings with polymer.
[0027] FIG. 2 is a schematic of another embodiment of the present
invention for mixing oil sands fine tailings with polymer.
[0028] FIGS. 3A to 3F show schematics of a variety of in-line
polymer injectors/mixers useful in the present invention.
[0029] FIG. 4 is a bar graph showing the hydraulic mixing times for
a variety of in-line polymer injectors/mixers.
[0030] FIGS. 5A to 5C shows three examples of polymer injectors
useful in the present invention.
[0031] FIG. 6 shows an example of an embodiment of the present
invention where a pre-mixer is used to first shear the MFT.
[0032] FIG. 7 is a CoV plot showing a comparison of Computational
Fluid Dynamics (CFD) simulations with and without pre-shearing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] The detailed description set forth below in connection with
the appended drawings is intended as a description of various
embodiments of the present invention and is not intended to
represent the only embodiments contemplated by the inventor. The
detailed description includes specific details for the purpose of
providing a comprehensive understanding of the present invention,
However, it will be apparent to those skilled in the art that the
present invention may be practiced without these specific
details.
[0034] The present invention relates generally to a process for
treating tailings derived from oil sands extraction operations and
containing a fines fraction, and dewatering the tailings to enable
reclamation of tailings disposal areas and to recover water for
recycling. As used herein, the term "tailings" means tailings
derived from oil sands extraction operations and containing a fines
fraction. The term is meant to include fluid fine tailings (FFT)
such as mature fine tailings (MFT) from tailings ponds and fine
tailings from ongoing extraction operations (for example, thickener
underflow or froth treatment tailings) which may bypass a tailings
pond. The tailings are treated with a flocculant to aggregate the
solids prior to dewatering by thin lift, accelerated dewatering
such as rim ditching, centrifugation, etc.
[0035] As used herein, the term "flocculant" refers to a reagent
which bridges the neutralized or coagulated particles into larger
agglomerates, resulting in more efficient settling. Flocculants
useful in the present invention are generally anionic, nonionic,
cationic or amphoteric polymers, which may be naturally occurring
or synthetic, having relatively high molecular weights. Preferably,
the polymeric flocculants are characterized by molecular weights
ranging between about 1,000 kD to about 50,000 kD. Suitable natural
polymeric flocculants may be polysaccharides such as dextran,
starch or guar gum. Suitable synthetic polymeric flocculants
include, but are not limited to, charged or uncharged
polyacrylamides, for example, a high molecular weight
polyacrylamide-sodium polyacrylate co-polymer.
[0036] Other useful polymeric flocculants can be made by the
polymerization of (meth)acryamide, N-vinyl pyrrolidone, N-vinyl
formamide, N,N dimethylacrylamide, N-vinyl acetamide,
N-vinylpyridine, N-vinylimidazole, isopropyl acrylamide and
polyethylene glycol methacrylate, and one or more anionic
monomer(s) such as acrylic acid, methacrylic acid,
2-acrylamido-2-methylpropane sulphonic acid (ATBS) and salts
thereof, or one or more cationic monomer(s) such as
dimethylaminoethyl acrylate (ADAME), dimethylaminoethyl
methacrylate (MADAME), dimethydiallylammonium chloride (DADMAC),
acrylamido propyltrimethyl ammonium chloride (APTAC) and/or
methacrylamido propyltrimethyl ammonium chloride (MAPTAC).
[0037] In one embodiment, the flocculant comprises an aqueous
solution of an anionic polyacrylamide. The anionic polyacrylamide
preferably has a relatively high molecular weight (about 10,000 kD
or higher) and medium charge density (about 20-35% anionicity), for
example, a high molecular weight polyacrylamide-sodium polyacrylate
co-polymer. The preferred flocculant may be selected according to
the oil sand tailings composition and process conditions.
[0038] The flocculant is generally supplied from a flocculant make
up system for preparing, hydrating and dosing of the flocculant.
Flocculant make-up systems are well known in the art, and typically
include a polymer preparation skid, one or more storage tanks, and
a dosing pump. The dosage of flocculant may be controlled by a
metering pump. In one embodiment, the dosage of flocculant ranges
from about 400 grams to about 1,500 grams per tonne of solids in
the FFT. In one embodiment, the flocculant is in the form of a 0.4%
solution.
[0039] As used herein, "fluid fine tailings" or "FFT" is a liquid
suspension of oil sand fines in water with a solids content greater
than 2%. "Fines" are mineral solids with a particle size equal to
or less than 44.mu.. "Mature fine tailings" or "MFT" are FFT with a
low solids to fines ratio (SFR), i.e., less than about 0.3, and a
solids content greater than about 30%.
[0040] As used herein, the term "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.
[0041] FIG. 1 is a flow diagram of one embodiment of the process of
the present invention. In this embodiment, oil sands fine tailings
are mature fine tailings (MFT) obtained from a settling basin 110.
However, it should be understood that the fine tailings treated
according the process of the present invention are not necessarily
obtained from a settling pond and may also be obtained from ongoing
oil sands extraction operations.
[0042] The tailings stream from bitumen extraction is typically
transferred to a settling basin 10 where the tailings stream
separates into an upper water layer, a middle MFT layer, and a
bottom layer of settled solids. The MFT layer is removed from
between the water layer and solids layer via a dredge or floating
barge having a submersible pump. In one embodiment, the MFT has a
solids content ranging from about 10 wt % to about 45 wt %. In
another embodiment, the
[0043] MFT has a solids content ranging from about 30 wt % to about
45 wt %. In one embodiment, the MFT has a solids content ranging
from about 37 wt % to about 40 wt %. The MFT is preferably
undiluted.
[0044] The MFT is then pumped through pipeline 112 (in-line flow).
In this embodiment, the MFT first passes through an in-line static
mixer 114 for pre-shearing the MFT. Suitable static mixers for use
in the present invention for pre-shearing oil sands fine tailings
are known in the art. A static mixer is a motionless mixer which is
inserted into a housing or pipeline with the objective of
manipulating fluid streams, in this instance, to significantly
accelerate the in-line reaction of flocculation. Typical designs of
static mixers comprise plates, baffles, helical elements or
geometric grids positioned at precise angles to direct flow and
increase turbulence.
[0045] In the embodiment of FIG. 1, the pre-sheared MFT is then
introduced into an end of pipe chamber 116 comprising a mixing
chamber 118 where polymer 122 is injected as a jet using a jet
mixer as shown in FIG. 3B. Other in-line polymer injection and
mixing concepts can also be used. End of pipe chamber 116 further
comprises a stilling chamber 120 where complete flocculation of the
FFT can occur without overshearing of the flocs taking place. The
flocculated FFT can then be further treated by centrifugation or
directly deposited in thin sloping layers (thin-lift), subjected to
accelerated dewatering (rim ditching) or deposited into other
tailings deposition cells.
[0046] FIG. 2 is a flow diagram of another embodiment of the
process of the present invention. In this embodiment, fluid fine
tailings (FFT) are primarily mature fine tailings (MFT) obtained
from a settling basin 210. However, it should be understood that
the fine tailings treated according the process of the present
invention are not necessarily obtained from a settling pond and may
also be obtained from ongoing oil sands extraction operations.
[0047] The MFT is pumped through pipeline 212 into an in-line first
static mixer 214 for pre-shearing the MFT. Suitable static mixers
for use in pre-shearing the MFT are known in the art. The
pre-sheared MFT is then introduced into a polymer
injection/dispersion zone 230 where polymer 232 is injected using a
polymer injector, for example, a 3'' Tee 80 on an 8'' pipe 312, as
shown in FIG. 5A, or a 1.5'' Tee 84 on an 8'' pipe 312, as shown in
FIG, 5B. Tee injectors were investigated due to the simplicity of
their design. In one embodiment, polymer injection/dispersion zone
230 comprises a venturi, as shown in FIG, 5C. With reference to
FIG. 5C, venturi 86 can be inserted between two pieces of pipe 312'
forming pipeline 312. Polymer is injected into the venturi 86 via a
plurality of polymer lines (not shown) connected to a plurality of
polymer inlets 88.
[0048] It is understood, however, that other polymer
injectors/mixers can be used in the polymer injection/dispersion
zone 230. FIG. 3 shows a number of different polymer
injectors/mixers that could be used in the present invention. FIG.
3A illustrates sparger-like injectors with spatial distribution;
FIG. 3B shows various nozzle-type injectors; FIG. 3C shows a number
of venturi-type injectors/mixers; FIG. 3D shows polymer injection
coupled with static mixers, FIG. 3E show wake mixers/injectors and
FIG. 3F shows vortex generators.
[0049] The MFT/polymer mixture continues through the pipeline 212
so that flow conditioning can occur, i.e., complete flocculation of
the MFT without over-shearing of the flocs taking place. The
flocculated MFT can then be further treated by centrifugation,
directly deposited in thin sloping layers (thin-lift), subjected to
accelerated dewatering (rim ditching) or deposited into other
tailings deposition cells.
[0050] Thus, in both embodiments described above, it important to
have a first step comprising quick dispersion of the polymer into
the FFT followed by a second step of providing a subsequent lower
energy region to promote floc growth. A well-dispersed polymer/MFT
product flowing through the conditioning pipe or stilling chamber
develops increasingly large flocs, builds rheological strength, and
then begins to dewater, either within the pipe or stilling
chamber.
[0051] In one embodiment, a coagulant is also introduced into the
in-line flow of FFT. As used herein, the term "coagulant" refers to
a reagent which neutralizes repulsive electrical charges
surrounding particles to destabilize suspended solids and to cause
the solids to agglomerate. Suitable coagulants include, but are not
limited to, gypsum, lime, alum, polyacrylamide, or any combination
thereof. In one embodiment, the coagulant comprises gypsum or lime,
In one embodiment, the dosage of the coagulant ranges from about
300 grams to about 1,500 grams per tonne of solids in the FFT.
[0052] Exemplary embodiments of the present invention are described
in the following Examples, which are set forth to aid in the
understanding of the invention, and should not be construed to
limit in any way the scope of the invention as defined in the
claims which follow thereafter.
EXAMPLE 1
[0053] The measure of uniformity or "mixedness" that is most often
used is the radical variation coefficient (CoV). A low CoV number
indicates better uniformity of flocculant and tailings (good
mixedness). FIG. 4 is a bar graph which illustrates the hydraulic
mixing time necessary to achieve a CoV reduction using a variety of
polymer injection devices and 32% MFT. It was observed that, with
the simpler designs such as the quill, tee and sparger, it took
longer for CoV reduction to occur with MFT having a relatively high
solids content (32%). However, use of Computational Fluid Dynamics
(CFD) suggested that mixing of 32% MFT and polymer flocculant could
be improved by using a pre-mixer. FIG. 7 is a CoV plot versus
distance from the injector point (m) showing a comparison of
Computational Fluid Dynamics simulations of polymer injectors
comprising a sparger, a 2'' quill in a 12'' pipe and a 3'' Tee in
an 8'' pipe without and with pre-shearing. It can be seen from FIG.
7 that with pre-shearing (pre-mixing) a lower CoV number could be
obtained for all injectors, which indicates better uniformity of
flocculant and tailings (good mixedness) when using 32% MFT.
EXAMPLE 2
[0054] In one test, a plurality of Komax.TM. flanged carbon steel
static mixers were placed in an 8'' pipeline upstream from the
polymer injection site for pre-mixing MFT. Following the static
mixers, a venturi (4'' contraction) having eight (8) port openings
was used for injecting polymer. Following the venturi was a length
of 8'' pipe, as shown in FIG. 6. The flocculated MFT was deposited
in a ditch and observed for dewatering properties. It was observed
that the addition of the Komax mixers promoted flocculation and
allowed excellent dewatering results over a wide range of
conditions, including a different number of injectors, polymer
dosages and MFT solids wt %. A Tee injector was also tested and
provided good dewatering conditions at discharge. It was further
observed that aggressive post mixing after polymer injection was
actually detrimental to instant dewatering observed at the end of
pipe and at the discharge.
[0055] One of the more surprising results when using a pre-mixer
for pre-shearing the MFT was that much higher solids content MFT
could be used. For example, MFT having a wt % solids of 31% and the
MFT density (kg/m3) of 1.24 still showed good dewatering properties
with good water runoff in the ditch when using a MFT flow rate
(m.sup.3/hr) of 250 and a polymer dosage (kg/Tonne MFT) of
1050.
[0056] The scope of the claims should not be limited by the
preferred embodiments set forth in the examples, but should be
given the broadest interpretation consistent with the description
as a whole.
* * * * *