Note: Descriptions are shown in the official language in which they were submitted.
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PROCESSES FOR TREATING OIL SANDS TAILINGS
Cross reference to related application
[0001] This specification includes materials in common with a patent
application US
61/149,285 filed on February 2, 2009 and a patent application US 61/242,035
filed on Sep 14,
2009 with the same title, inventor and assignee as this application. This
application also
includes two additional embodiments.
Field of the Invention
[0002] The invention relates to processes for oil sands tailing treatment with
application of
different chemicals for different purposes (thickening, settling and
consolidation), such as
flocculants, coagulants, and pH modifiers (flue gas (mainly for carbon
dioxide, CO2) or acetic
acid). For thickening, the chemicals can be any kind of high performance
flocculants and/or
coagulants, regardless of their potential adverse impacts on bitumen
extraction. The
chemical's adverse impacts on bitumen extraction is minimized and controlled
within tailing
treatment area. Flue gas or acetic acid is used as a pH modifier to improve
dewatering and
consolidation of tailing sediment. The invention also relates to a process for
tailing deposit
reclamation to a trafficable surface using hydroponic power of deep-rooted
plants, e.g. alfalfa.
Background
[0003] Oil sand is essentially a matrix of bitumen, mineral material and
water. Oil sand
deposits are mined for the purpose of extracting bitumen from them, which is
then upgraded
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to synthetic crude oil. First, the oil sand is mined in open-pit mine using
trucks and shovels.
The oil sand lumps are crushed and then mixed with recycle process water in
mixing boxes,
stirred tanks, cyclo-feeders (Syncrude Canada Ltd.) or rotary breakers (Suncor
Energy Inc. and
Albian Sands Energy Inc.). The conditioned oil sand slurry is introduced to
hydrotransport
pipelines or to tumblers, where the oil sand lumps are sheared and size
reduction takes place.
Within the tumblers or the hydrotransport pipelines bitumen is released, or
"liberated", from
the sand grains. Chemical additives, used as dispersants, can be added during
the slurry
preparation stage. Entrained or introduced air attaches to bitumen in the
tumblers and
hydrotransport pipelines. Second, the slurry is separated by allowing the sand
and rock to
settle out, and the bitumen, having air entrained within it floats to the top
of the slurry and is
withdrawn as bitumen froth. Third, the remainder of the slurry, which is
referred to as a
middling, is then treated further or scavenged by froth flotation techniques
to recover bitumen
that did not float to the top of the slurry during the separation step.
[0004] To assist in the recovery of bitumen during the separation step, sodium
hydroxide
(caustic) is typically added to the slurry during the conditioning step in
order to disperse the
sand grains and maintain the slurry slightly basic, having a pH in the range
of 8.0 to 8.5. This
has the effect of chemically dispersing the clay in the slurry during the
conditioning step,
which results in the middling stream a huge disposal problem, since it
constitutes a sludge that
tends to settle and consolidate very slowly. Current practice for the disposal
of the sludge
remaining after the scavenging step involves pumping it into huge tailing
ponds, where the
fines slowly settle and stratify. After several weeks, some of the water
forming the sludge will
be present at the top of the tailing pond containing only a small amount of
suspended fines.
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The remaining sludge continues to settle and gradually increases in density
over a period of
perhaps 10-20 years, the solids concentration of the sludge may increase to up
to 50%.
Complete settlement and consolidation of the sludge may take in the order of
hundreds of
years. It is thought that the reason for the slow consolidation of the sludge
is that the clays that
become physically and chemically dispersed during the water process partially
re-flocculate
into a fragile gel network.
[0005] In any event, because of the characteristics of the middling sludge,
the tailing ponds
can not be completely rehabilitated for many years, and only a portion of the
water that enters
the tailing ponds can be recovered and reused in the bitumen extraction
process, thus creating
a requirement that a large amount of make up water be available to make up for
the water that
is lost to the tailing ponds.
[0006] Some attempts have been made to improve the oil sand process in two
ways: 1)
modification of the bitumen extraction process to minimize dispersing the
clays in middling,
such as U.S. Pat. No. 4,414,117 and U.S. Pat. No. 5,723,042; and 2)
application of flocculants
in tailing treatment, such as U.S. Pat. No. 4.225,433 and U.S. Pat. No.
5,723,042.
[0007] U.S. Pat. No. 4,414,117 and U.S. Pat. No. 5,723,042 disclosed methods
to control
carbonate and bicarbonate ions in bitumen extraction process to minimize
dispersion of clays
in middling. U.S. Pat. No. 4,414,117 teaches that the removal of carbonate and
bicarbonate
ions can be accomplished in several ways, such as by the use of an ion
exchange resin, the
addition of an ion precipitant, or the use of a mineral acid such as
hydrochloric acid to convert
the carbonate and bicarbonate ions to CO2. It is stated that best results are
obtained when
essentially all of the carbonate and bicarbonate ions are removed from the
system with the
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result being that the settlement rate of the sludge is significantly
accelerated. U.S. Pat. No.
4,414,117 teaches that the concentration of bicarbonate ions in the warm water
should
preferably be maintained at less than about 6 Meq/liter. Since bicarbonate
ions tend to form in
solution when the pH of the solution is higher than about 7 and will leave the
solution when
the pH is lower than about 7, the bicarbonate ion concentration in the warm
water is
preferably controlled by adding an acid to the warm water to reduce its pH.
[0008] U.S. Pat. No. 4.225,433 and U.S. Pat. No. 5,723,042 disclosed methods
to promote
settlement of the dispersed fine material in suspension by adding a flocculant
to the
suspension, which relates to a process whereby the solid material and the
sludge that is
generated during the bitumen extraction process is combined together, mixed
with a
flocculating agent to separate water and solid material. The fines form
agglomerates with the
coarse particles and that the agglomerates settle at a rate comparable to that
of the solid
material alone.
[0009] Other efforts have focused on the characteristics of the solids
tailings and sludge
tailings as a whole in the feasibility of combining them together to create a
waste stream that
is easier to handle. Cymerman, G. J., Prediction of Viable Tailings Disposal
Methods.
Proceedings of a Symposium: Sedimentation Consolidation Models, ASCE/October
1984,
San Francisco, Calif.). This paper indicates that tailings typically produced
by Syncrude
Canada Ltd. at Fort McMurray, Alberta tend to be a segregating mix so that the
solid material
settles out from the tailings quickly, leaving the sludge. Segregation is
detrimental due to the
problems associated with the disposal of the sludge. To prevent fines
segregation, it is stated
that it is necessary to lower the water content of the tailings stream,
increase the fines content
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of the tailings, or do both. Based upon this analysis, the authors conclude
that promising
proposals include the mixing of mature sludge taken from the bottom of tailing
ponds with a
thickened sand tailing to produce a non-segregating mix, or the mixing of
sand, sludge and
overburden stripped from the mine site in order to produce a non-segregating
mix.
[0010] To accelerate tailings handling, Suncor and Syncrude are using
consolidated
(composite) tailings (CT) process. This process entails adding gypsum to
mature fine tails to
consolidate the fines together with the coarse sand into a non-segregating
mixture. CT is
disposed of in a geotechnical manner that enhances its further dewatering and
eventual
reclamation. At Albian Sands, the tailings from the extraction plant are
cycloned, with the
overflow (fine tailings) being pumped to thickeners and the cyclone underflow
(coarse
tailings) to the tailing pond. Fine tailings are treated with flocculants,
then thickened and
pumped to a tailing pond. The three oil sand operators are considering the use
of paste
technology (addition of flocculants /polyeletrolytes), consolidated or
composite tailings, CT,
or a combination of the two (i.e., CT and paste technology) for fast water
release and recycle
of the water in CT to the extraction plant for bitumen recovery from oil
sands.
[0011] As a general rule, the higher the fine material content in an oil sand
deposit, the more
difficult the oil sand is to process for the extraction of bitumen. The higher
the content of the
fine material in the oil sand, the more sludge that is generated by the
extraction process; and
the more difficult the disposal problem for the sludge.
[0012] It can therefore be seen that the challenge in extracting bitumen from
oil sand is to
maximize the recovery of bitumen while minimizing the amount of sludge that is
generated,
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and while controlling the physical characteristics of the sludge so that it
may be more easily
disposed of in an economical and environmentally acceptable.
Limitation of the existing technologies
[0013] It is imperative to achieve as high bitumen recovery as possible and
recycle as much
process water as possible so that the amount of makeup water required is
minimized. Practice
experiences showed that good chemicals (flocculants/coagulants) for tailing
treatment
normally have an adverse impact on bitumen extraction, and good chemicals for
bitumen
extraction have adverse impacts on tailing settlement. The adverse impacts do
not show up
immediately after chemical applications. Because it takes a long time for the
added chemicals
to reach a dynamical chemical equilibrium in huge tailing ponds and for the
adverse effects of
chemical addition take place in the use of recycle water. The potential
adverse impacts of
chemical application in tailing treatment on bitumen extraction must be
considered in any
attempt of tailing treatment due to their opposite (dispersion for bitumen
extraction and
sedimentation for tailing treatment) technical natures. It is highly demanded
that there is a
method available to control the potential adverse impacts within tailing
treatment area. The
adverse impacts will be enhanced after the Directive 074 is in effect that was
release in
February 2009, as more recycle water will be available and less fresh water
will be required,
meaning the residual chemicals in recycle water would be concentrated to
negatively influence
extraction processes if the adverse impact is not minimized or eliminated
within tailing
process. This adverse impact will limit the application of some high
performance chemicals
and lead engineers have to use moderate chemicals for tailing treatment that
have lower
adverse impacts on bitumen extraction. The use of moderate performance
chemicals for
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tailing treatment results in instability of forming non-segregating tailing
deposit, and
incapability of meeting the criteria of Directive 074.
[0014] In addition, current available composite tailing (CT) technology has
operational
instability in forming non-segregating tailings due to insufficient coarse
sands for CT, as some
sands are used for building tailing pond dykes. To form stable non-segregating
tailing deposit,
sand to fine ratio needs to be 4-5. The sand to fine ratio in raw oil sands is
typically 4.25,
meaning that almost all sands are required for capturing fines in CT process.
Using part of
coarse sands deposited on beach for tailing pond dykes will make remaining
coarse sands
impossible to capture all fines, and hence results in CT operation instable.
[0015] Further more, the CT deposit needs more than 10 years to drain its
water, and can not
reach strength of 10 kPa or the trafficable criteria of Directive 074 within 5
years.
[0016] Some attempts of planting deep-rooted perennials in overburden that
covers the CT
deposit as top soil to remove water from CT deposit have failed due to
inhomogeneity of the
overburdens. Overburdens have a variety of segregated compositions and may be
not suitable
for plants to grow, such as mainly sands or mainly clay overburden layers.
Sorting
overburdens into desirable loam soil textures is a challenging and costly
task.
Summary of The Invention
[0017] An adverse impact minimization process (AIMP) is provided, which can
minimize or
eliminate the potential adverse impacts of chemical addition in tailing
treatment on bitumen
recovery in bitumen extraction from oil sands. With AIMP, any high performance
chemicals
(flocculants/coagulants) can be used for tailing treatment to significantly
enhance in both
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dewatering and consolidation of the sludge layer in a small thickening pond or
a vessel
regardless of their potential adverse impacts on bitumen extraction. As a
result, more process
water can be available and recycled for bitumen extraction, and fresh water
import can be
reduced by 36.6%.
[0018] There are two types of AIMP applications: dynamic pond and static pond.
Dynamic
pond processes use a small moving thickening pond and a moving settling pond
and are
suitable to capture a portion of fines, e.g. 50%. The tailing deposits
accumulate at dykes and
expend inward to the thickening pond, requiring the thickening pond expansion
in the
opposite side; at the same time, the un-captured fines accumulate in the
settling pond as
inventory and requires its pond expansion in size. The static pond processes
use a small size-
fixed thickener and a size-fixed settling pond and are suitable to capture all
fines. The tailing
deposits are transported to and stacked in a dedicated disposal area. A
variety of application
cases with AIMP are disclosed. A pH modifier (flue gas or acetic acid) could
be optionally
used to accelerate water drainage from the tailing deposits. Make-up loam soil
that is formed
by using tailing materials (sands, clays and silts) is placed on top surface
of the tailing deposit
for deep-rooted plants, such as alfalfa, to grow and remove water
hydroponically and make the
surface trafficable within 3 years.
[0019] Four cases of the applications with AIMP are disclosed, two of them
belong to
dynamic pond; they are the base case without a pH modifier (embedment 1) and
the case with
a pH modifier (embedment 2) for accelerating water drainage from tailing
deposits. Another
two cases belong to static pond, one is raw tailing split process (RTSP,) and
another is fine
tailing split process (FTSP). The RTSP (embedment 3) applies AIMP principle to
raw tailings
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directly and split the raw tailing between a thickener and sand collector;
while the FTSP
(embedment 4) applies AIMP principle to fine tailings after coarse sands are
removed using a
sand collector, the fine tailing is then split between a thickener and a
settling pond.
[0020] Each of the four cases can be considered as an independent service
process with a
tailing receiving line and a recycle water delivering line. The tailing
receiving line can receive
sludge's from different streams individually as a localized tailing process or
any kind of
combined sludge of different streams as a whole process.
Brief Description Of The Drawings
[0021] Fig. 1 is a schematic flow diagram of the process (embedment 1) for
treating oil sands
tailings with a feature of minimizing or eliminating the adverse impacts of
chemical
(flocculants/coagulants) addition in tailing treatment on bitumen extraction.
[0022] Fig. 2 is a schematic flow diagram of the process (embedment 2) for
treating oil sands
tailings with a feature of tailing sediment dewatering, compaction and
consolidation.
[0023] Fig. 3 is an illustration of sediment placement for compaction
(sectional view and bird
view).
[0024] Fig. 4 is a schematic flow diagram of the process (variation of
embedment 2) for
treating oil sands tailings with a feature of tailing sediment compaction and
a self contained
flue gas generator.
[0025] Fig. 5 is a chart showing dependent carbonate equilibrium
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[0026] Fig. 6 is chart showing total CO2 concentration in water as a function
of pH at
different CO2 volume percentages.
[0027] Fig. 7 is a raw tailing split process (embedment 3).
[0028] Fig. 8 is a fine tailing split process (embedment 4).
[0029] Fig. 9 is an illustration of the performance for both the raw tailing
split process and the
fine tailing process.
[0030] Fig. 10 is a site plan option A of the present invention: tailing
settling pond in
overburden area adjacent to mining area.
[0031] Fig. 11 is a site plan option B of the present invention: tailing
settling pond in an
external area.
[0032] Fig. 12 is a schematic illustration of the mixed tailing deposit
disposal with a layer of
make-up loam soil spreading on top surface suitable for deep-rooted plants to
grow in a
dedicated disposal area.
Detailed Description of Preferred Embodiments
[0033] One of the embedment of the present invention is described below with
reference to
Fig. 1. Fig. 1 is a schematic illustration of one embedment (embedment 1) of
the present
invention, including an adverse impact minimization process (AIMP) that
minimizes or
eliminates the adverse impacts of chemical (flocculants/coagulants) addition
in tailing
treatment on bitumen extraction. The AIMP process for treating oil sands
tailings comprising:
a thickening pond to receive tailings from bitumen extraction units and
bitumen froth
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treatment unit via a tailing receiving line, a tailing settling pond to
receive and hold a mixture
of the fines-containing water, transferred via a water transfer line from the
thickening pond to
the settling pond, and the tailing received for further solids/water
separation, a recycle water
line with a chemical injection point for withdrawing recycle water from the
settling pond for
water reuse in bitumen extraction from oil sands, and a sludge transfer line
for transferring
sludge/suspension from the settling pond back to the tailing receiving line.
The chemical
injection point can accept any kind of high performance chemicals
(flocculants/coagulants),
regardless of their adverse impacts on bitumen extraction, as the residual
amount of added
chemicals in the water withdrawn from the thickening pond can be consumed by
mixing the
tailing received from tailing receiving line before discharging the water to
the settling pond.
[0034] Detailed descriptions of the embedment of the present invention are as
follows:
[0035] With reference to Fig. 1, showing a schematic flow diagram of the
process for treating
oil sands tailings, the oil sands are fed into the system through a line 1 and
passed to a
conditioning drum 10. Water is introduced into the drum through line 2. The
total water
introduced is a minor amount based on the weight of the oil sands processed.
The conditioned
pulp passes through a line 3 to a screen 20. The purpose of the screen 20 is
to remove oversize
materials 21, such as rocks or oversized lumps of clay from the pulp. The
oversize materials
are discarded at a suitable site. The conditioned pulp passes through a line
22 to a feed sump
30 which serves as a zone for diluting the pulp with additional water before
it enters a
separation zone 40.
[0036] The diluted pulp is continuously flushed from the feed sump 30 through
a line 31 into
the separation zone 40. The settling zone within the separator 40 is
relatively quiescent so that
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bituminous froth rises to the top and is withdrawn through a line 41 while the
bulk of the sand
component settles to the bottom as a tailing layer which is withdrawn through
line 42.
[0037] A relatively bitumen-rich middling stream is withdrawn through line 43
to maintain
the middling layer between the froth and the sand layer at a functional
viscosity. This
middling material is transferred to a flotation scavenger zone 50 where an air
flotation
operation is conducted to bring about the formation of additional bituminous
froth which
passes from the scavenger zone 50 through line 51, in conjunction with the
primary froth from
the separation zone 40 passing through line 41, to a froth settler zone 60. A
bitumen-lean
water stream is removed from the bottom of the scavenger zone 50 through line
52. In the
froth settler zone 60, some further bitumen-lean water is withdrawn from the
froth and
removed through line 61 to be mixed with the bitumen-lean water stream from
the flotation
scavenger zone 50 and the sand tailings stream from the separation zone 40.
The bitumen
from the settler 60 is removed through line 62 for further treatment.
[0038] Bitumen-lean water from the froth settler 60, the scavenger zone 50,
and the separation
zone 40, all of which make up a mixed discharge stream carried by line 44, are
split into two
tailing streams: branch line 44a and branch line 44b. The line 44 that carries
the mixed
discharge stream is also referred to as tailing receiving line to the tailing
treatment of present
invention. The tailing carried in line 44a is discharged into a tailing
thickening pond 70 which
has a clarified water layer 71 and a sediment layer 72. The sands included in
the tailing stream
quickly settle in the region 73, and the fines-containing water flows into the
body of the pond
70 where settling takes place. The sediment layer 72 of the thickening pond 70
is overlayed
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with a clarified water layer 71. A mineral-to-water ratio in the sediment
layer 72 increases
from top to bottom.
[0039] In a application of high performance chemicals
(flocculants/coagulants), the clarified
water in the thickening pond consists of some residual high performance
chemicals
(flocculants/coagulants) and is withdrawn through a water transfer line 75 and
mixed with the
tailing from the branch line 44b then transferred to the tailing settling pond
80 at an inclined
sand pile 81 situated adjacent a dyke 82. The volume ratio of the clarified
water to tailing is
controlled in a range so that the residual high performance chemicals
(flocculants/coagulants)
in the clarified water can be consumed to the level at which its adverse
impacts on bitumen
extraction can be minimized or even eliminated by the mixed excess amount of
tailing. To
improve the tailing settling in the settling pond, a moderate performance
chemical
(flocculants/coagulants), such as gypsum or a mixture of gypsum and lime, is
added to the
clarified water at the chemical injection point 76, denoted as chemical for
settling pond (C.S.).
The type of the C.S. must be proven no significant adverse impacts on bitumen
extraction; and
the amount of the C.S. must be well controlled.
[0040] The sands included in the mixture quickly settle at the inclined sand
pile 81 situated
adjacent the dyke 82, and the fines-containing water flows into the body of
the settling pond,
which comprises a clarified water layer 83 on the top and a sludge/ suspension
layer 84 at the
bottom. The sludge/suspension 84 is commonly referred to as mature fine
tailing (MFT). The
MFT 84 is withdrawn from the settling pond 80 via a sludge withdrawal mean 90
and is
transferred to a line 93 by a pump 92 which is supported by a flotation mean
91 on the surface
of the pond 80. The MFT transferred from the line 93 is combined with the
tailing material
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carried by the branch line 44a from the extraction process for recovering
bitumen from oil
sands.
[0041] The MFT 84 withdrawn from the bottom of the settling pond may be mixed
with the
clarified water 83 withdrawn from the top of the settling pond by a pump 94
via a water
transfer line 95 then a branch line 95a to archive a high water to solids
weight ratio for a better
solids/water separation in the thickening pond. Preferably, water to solids
weight ratio is in a
range of 0.5 to 5. The higher the water to solids ratio, the larger the size
of the flocs can be
formed, hence the quicker settling speed and the denser of the flocs.
[0042] Chemicals (flocculants/coagulants) are capable of enhancing in both
solids settling and
sediment thickening. High performance chemicals (flocculants/coagulants) can
be added at the
chemical injection point 100, denoted as chemical for thickening pond (C.T.),
to the MFT
being transferred by the line 93. To obtain a very high degree of thickening
and dewatering,
the high performance chemicals (flocculants/coagulants) can be relatively over
dosed;
regardless the potential negative impacts on bitumen extraction due to
recycling the clarified
water. However, the high performance chemical dosage should be optimized in an
ideal
fashion. If little chemicals are used, adequate thickening of the sludge may
take longer than
the desired time. If too much chemicals are used, large, loose flocs tend to
be generated,
which do not thicken in an ideal fashion. Different amounts of chemicals may
be required if
different types of chemicals (flocculants/coagulants) are used.
[0043] The clarified water layer 83 in the settling pond only consists of
marginal amount of
chemicals due to that significant excess amount of tailing from the tailing
branch line 44b can
consume most of or all of the residual high performance chemicals
(flocculants/coagulants) in
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the clarified water layer 71, minimizing the potential negative impacts of
recycling the
clarified water 83 back to bitumen extraction.
[0044] Recycle water withdrawn by the pump 94 from the clarified water layer
83 in the
settling pond is transferred via the line 95 back to bitumen extraction
process for water reuse.
The line 95 comprises three branch lines, one line 95a combines with the MFT
transfer line
93, another two branch lines 95b and 95c for oil sands conditioning and
diluting the
conditioned oil sands, respectively.
[0045] The embedment of the present invention enclosed in the dashed box as
shown in Fig. I
can be considered as an independent service process with one tailing receiving
line 44 and one
recycle water delivering line 95. The tailing receiving line 44 can receive
sludge from
different streams individually as a localized tailing treatment process or any
kind of combined
sludge of different streams as a whole tailing treatment process.
[0046] There is an internal circulation loop in the process of treating oil
sands tailings of the
present invention to minimize even eliminate the adverse impacts of high
performance
chemical addition in tailing treatment on bitumen recovery in bitumen
extraction from oil
sands. The internal circulation comprises the MFT transfer line 93 and the
water transfer line
75. The high performance chemicals (flocculants/coagulants) can be slightly
over dosed (if
required) into the MFT transfer line 93 to achieve better solids/water
separation, while excess
amount of tailing can be combined into the water transfer line 75 to consume
the over dosed
or residual chemicals.
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[0047] A significant difference between the C.T. and the C.S. is that C.T. can
be any kind of
high performance chemicals (flocculants/coagulants), while C.S. must be proven
type that has
no significant adverse impacts on bitumen extraction.
[0048] Referring now to Fig. 2, whereby another embedment (embedment 2) of the
current
invention is employed in combination with a pH modifier (such as flue gas
(CO2) or acetic
acid) injection and replacement of materials that were settled previously and
contain less
moisture to improve tailing sediment compaction and eventually consolidation
along the dyke
of the thickening pond. Flue gas or acetic acid is injected at an injection
point 112 to the
sediment carried by the sludge line 111 and is withdrawn from the sediment
layer 72 in the
thickening pond by a sludge pump mounting on a suspension unit 110. The
sediment after pH
modification is then discharged along the dyke 73 directly or combined with
the materials
taken from the outside of the dyke 73 in a mixing mean 114 before discharging
it to the inside
of the dyke 73. Carbon dioxide (CO2) present in the injected flue gas reacts
with water and
produces carbonic acid. This reaction changes the pH of the sediment and
allows fines clays,
silts and sands to settle and the water to release. The low moisture materials
taken from the
outside of the dyke 73 help the dewatering, compaction and eventually
consolidation of the
low pH sediment. The low moisture materials can be loaded using loaders or
transported using
a conveyer 113 to the mixing mean 114. After mixing with the low pH sediment,
the mixture
is discharged to the inside of the dyke 73 using an auger or a conveyer 115.
The mixing ratio
of low moisture material to the low pH sediment needs to be changed according
to the water
content in the sediment to achieve the best compaction.
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[0049] Fig. 3 is a more detailed illustration of the mixed material placement
for compaction
(sectional view and bird view) and consolidation according to embedment 2 of
the present
invention. The dyke is formed from two discharging operations; one is from the
line 44a
where there is no pH modifier involved; another is from the auger or conveyer
115 where a
pH modifier is involved. The dyke can be built in such a way that the
discharges with (120
and 122) and without (73, 121 and 123) a pH modifier can be placed
alternatively to achieve
the best compaction and eventually consolidation.
[0050] Another benefit of flue gas injection to tailing sediment is that the
CO2 can react with
the minerals in the tailings to form mineral carbonates. Flue gas can be
captured from utility
or upgrading facilities and piped to the injection point. This process will
reduce the footprint
of the tailing ponds and the amount of fresh water needed to process bitumen.
At the same
time, it can be expected that this process of sequestering CO2 into tailings
will eliminate some
of CO2 emission produced in oil sands operations.
[0051] Chloride acid should not be used as a pH modifier, because residual
chloride stays in
recycle water and can be taken into downstream and creates significant
corrosion problems in
upgrading.
[0052] Referring to Fig. 4, whereby a variation of embedment 2 of the present
invention is
employed in combination of a self contained flue gas generator to produce flue
gas (CO2) and
replacement of the low moisture material to improve tailing sediment
compaction and
eventually consolidation along the dyke of the thickening pond. The flue gas
is generated
using a co-combustion burner 123 that burns variety of inexpensive fuels 124,
such as used
oils, scrape tires, coal, petroleum coke and sludge's containing high level of
oil. The heat
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contained in the hot flue gas is recovery by using a heat exchanger 120 that
heats up the
recycle water before its delivery to bitumen extraction plant via line 121.
After heat recovery,
the flue gas is then injected to the sediment at the injection point 112 on
sludge line 111. This
self contained flue gas generator 123 combining with the heat exchanger 120
provides warm
recycle water for bitumen extraction, which can reduce the load to utility.
[0053] Fig. 5 is a chart showing dependent carbonate equilibrium. Bitumen
extraction is
operated at approximately pH 8.5. To further dewatering by using CO2 in flue
gas to produce
sufficient carbonic acid, it is necessary to bring pH of the water in sludge
from 8.5 to 4.5 as
shown in Fig. 5.
[0054] Fig. 6 is a chart showing total CO2 concentration in water as a
function of pH at
different CO2 volume percentages. Based on lab tests, to achieve significant
dewatering
performance, total CO2 concentration in sludge needs to be higher than 50 mg/L
at pH 4.5,
which requires that CO2 concentration in the flue gas injected should be
higher than 5% by
volume. This requirement can always be satisfied as any flue gas has more than
5% CO2, for
example, CO2 volume concentration is 9.5% in flue gas produced by burning
natural gas; and
14.4 % by burning bitumen.
[0055] Embedment 1 shown in Fig. 1 and embedment 2 shown in Fig. 2 as well as
the
variation of embedment 2 shown in Fig. 4 are deployed by using a dynamic
thickening pond
and a dynamic settling pond. Fines are captured partially, e.g. 50%, and the
sand deposits on
beach of the settling pond can be used for building dykes to expend the
settling pond.
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CA 02689684 2010-01-04
[0056] Referring to Fig. 7, whereby another embedment (embedment 3) of the
present
invention is employed by changing the dynamic thickening pond into a static
thickener 130
and the dynamic setting pond into a static sand collector 140 and a static
settling pond. Raw
tailing in line 44 is split into two streams of branch line 44a to the
thickener 130 and branch
line 44b to the sand collector 140 where coarse sands settle at the bottom and
the fines
overflow into the settling pond via line 142. The sand collector works as if
it collects sands
from beach in the case of dynamic thickening pond and allows only fines to run
off. All
settled sands in the sand collector are collected and exit as underflow 141
and mixed with
thickener underflow 131 using a blender 150 to make a stackable tailing
deposit for disposal
in a dedicated disposal area. Both the thickener underflow 131 and the sand
collect underflow
141 are exited by using a screw or a spiral mechanism as they are not
pumpable.
[0057] To capture all fines using coarse sands, sediment in the settling pond
is withdrawn via
line 93 and a high performance chemical is injected at the injection point 100
into the
sediment. After combining the sediment in line 93 into line 44a and mixed
using an inline
mixer, the mixture is discharged into the thickener for flocculation and
separation. To
minimize adverse impacts of the residual high performance chemical remaining
in thickener
overflow, the thickener overflow 132 is mixed with raw tailing in the branch
line 44b to
consume the residual amount of the high performance chemical. A moderate
performance
chemical is added to the thickener overflow 132 at injection point 76 before
mixing the
overflow 132 with the raw tailing 44b to facilitate remaining fines to settle
in the settling
pond.
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CA 02689684 2010-01-04
[0058] Referring to Fig. 8, whereby another embedment (embedment 4) of the
present
invention is employed in a similar way to embedment 3 by changing the dynamic
thickening
pond into a static thickener 130 and the dynamic setting pond into a static
sand collector 140
and a static settling pond. However, raw tailing in line 44 is directly
discharged to the sand
collector and coarse sands contained in the raw tailing are settled and exited
as underflow 141
from the sand collector to the blender 150; and only the fines in overflow 142
split into two
streams: one stream 142a to the thickener 130 and another stream 142b to the
settling pond.
The sand collector works as if it collects sands from beach in the case of
dynamic thickening
pond and allows only fines to run off. All settled sands in the sand collector
are collected and
mixed with thickener underflow 131 using the blender 150 to make a stackable
tailing deposit
for disposal in a dedicated disposal area. Both the thickener underflow 131
and the sand
collect underflow 141 are exited by using a screw or a spiral mechanism.
However, the
thickener underflow can also be exited by using a sludge pump as it is
pumpable.
[0059] To capture all fines using coarse sands, sediment in the settling pond
is withdrawn via
line 93 and a high performance chemical is injected at the injection point 100
into the
sediment. After combining the sediment in line 93 into line 142a and mixed
using an inline
mixer, the mixture is discharged into the thickener for flocculation and
separation. To
minimize adverse impacts of the residual high performance chemical remaining
in thickener
overflow, the thickener overflow 132 is mixed with fine tailing in the branch
line 142b to
consume the residual amount of the high performance chemical. A moderate
performance
chemical is added to the fine tailing in the branch 142b at injection point 76
before mixing the
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CA 02689684 2010-01-04
fine tailing 142b with the thickener overflow 132 to facilitate remaining
fines to settle in the
settling pond.
[0060] Composition of the mixed tailing deposit after blending in the blender
150 can be
adjusted by changing mixing volume ratio of the sand collector underflow 141
to the thickener
underflow 131 to form loam soil (20-52% sands, 10-30% clays and 30-50% silts)
for deep-
rooted plants, such as alfalfa, to grow and remove water from the tailing
deposit
hydroponically. The loam soil having 25-52% sands formulated using tailing
materials (sands,
clays and silts) is spread on top of the tailing deposit as a top soil in the
dedicated disposal
area and the deep-rooted plants reclaim the surface of the tailing deposit to
trafficable within
three years. There are two ways of producing the make-up loam soil; one is to
split the sand
collector underflow into two streams 141 and 143, adjusting the volume ratio
of the stream
141 and the stream 143 so that the mixture of streams 141 and 131 can produce
a loam soil
composition: 20-50% sands, 10-30% clays and 30-50% silts, leaving stream 143
and placing it
at the bottom of the stack of the tailing deposit. Another way of producing
the loam soil is to
introduce sufficient inventory tailing and combine it with the thickener
underflow and then
use the mixture to consume all sand collector underflow.
[0061] The raw tailing split (embedment 3) shown in Fig. 7 and the fine
tailing split
(embedment 4) shown in Fig. 8 are deployed by moving mixed stackable tailing
deposits to a
dedicated disposal area, keeping the thickener, sand collector and settling
pond unchanged.
All fines are captured and more recycle water is available for reuse, hence
reducing fresh
water import and land disturbance significantly.
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[0062] Fig. 9 illustrates the performance of the raw tailing split (A) and the
fine tailing split
(B) at volume ratio of 1:1, respectively. Figs. 10 and 11 illustrate two
different site plans of
the present invention; one having settling pond in overburden dump area,
another having the
settling pond in an external area. The tailing deposit is stacked within an in-
pit toe berm.
[0063] Fig. 12 is a schematic illustration of the mixed tailing deposit
disposal with a layer (0.5
to 1 meter in thickness) of make-up loam soil spreading on top surface
suitable for deep-
rooted plants to grow. Deep-rooted plants, e.g. alfalfa, are used to remove
water retained in
the stable non-segregating tailing deposit hydroponically and to reclaim the
tailing deposit to
trafficable criteria of ERCB Directive 074 within 3 years. Alfalfa can produce
2-3 tonnes of
dry matter per acre, and take approximately 500 tonnes of water for each tonne
of dry matter.
Upon germination, a strong taproot develops rapidly and penetrates almost
vertically
downward. It often reaches a depth of 5 to 6 feet in the first season, 10 to
12 feet by the end of
the second year, and may ultimately extend to depths of 20 feet or more.
Alfalfa can grow
when temperature is above 3 C; and grow its roots at below 20 C and its
stems and
leaves above 20 C. Alfalfa can develop its roots in April, May, June and
November; develop
its stems and leaves during June - October at northern Alberta. These features
make it perfect
to remove water from the formed stable tailing deposit hydroponically, and
turn the tailing
deposit trafficable within 3 year.
[0064] Proper amount of fertilizer and a thin layer of garden or landscape
soil (10-15 cm) are
spread on top of the make-up loam soil before plant seeding. Optionally,
shredded dry alfalfa
can be mixed with the make up loam soil to improve soil quality and reduce
fertilizer level.
Alfalfa needs to be cut twice every summer and shredded for recycle back to
the newly formed
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CA 02689684 2010-01-04
loam soil. Alfalfa can take some pollutants from the contaminated process
water and can not
be used as forage or hey to avoid pollutant coming into food chain.
[00651 Using tailing pond materials (sands, clay and silt) to formulate
desirable texture of
loam soils (25-52 % sands, 10-30 % clays, 30-50 % silts) that can be spread on
top surface of
the tailing deposit for alfalfa initial growth can eliminate cost of
transporting overburden as
top soil and avoid its inhomogeneity problem. With global warming, the climate
in northern
Alberta will be more suitable for alfalfa and other deep-rooted plants to grow
for a longer time
period, taking more water out of the tailing deposits.
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