Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a method and apoaratus for
se?aration or he~erogeneous phases, and more particularly to a
modified hot water process and apparatus for e~Ytracting bitumen
fro~ oil sands.
Oil sands, also known as tar sands or bituminous sands,
are sand deposits which are impregnated with bi~uminous oil.
The largest known deposit in ~he wor~d is in the Athabasca
region in Alberta, Canada. Athabasca oil sands are a mixture of
bitumen, solids and water. Bitumen content is variable, ranging
from 0 to 20% with an average of 12~. Water content is normally
bet~een 3 and 5%. A substantial portion of the oil sands is
situated near ~he surface, where it may readily be mined and
processed to synthetic crude oil.
Several extraction methods to separate bitumen from the
sand have been known for many years, but only those based on hot
water treatment are commercially used at presentO In their
different conigurationsj the processes based on hot water
treatment consist of several steps~
In the first step, known as the conditioning or
digestion step, oil sanas are mixed with alkaline hot water anc
(ootimally) steam ~o form a pulp or a slurry.
I~ the second step, known as the separation step, the
conditionea mixture of bitumen, water and solids separates into
its components. The bulk of the sand-sized solids separates
into a coarse solids or tailings phase and is withdrawn. Most
of the bitumen floats to the surface of the mixture to form a
bitumen froth phase and is recovered. A third phase, known as
the middlings phase, containing part of the bitumen and part of
the fine solids, is also withdrawn for further treatment. This
treatment may include a scavenging or a flocculation/
clarification stage.
~.3~5~
In the third s.ep, known as the froth clean-up step,
most o~ the water an~ solids in t~le froth are separated from the
bitumen be~ore the bitumen itself is sent to an upgrader.
~ or optimu~ separation the objectives to be achieve~
are to withdraw the tailinss phase with as little entrapoed
bitu~en as pos~ible; to recover ~he bituminous froth phase with
as little entralned water and solids as possible; and to
withdraw ~he middlings phase with as lit~le bitumen carryover as
possible.
In the prior art, the separation step of the process is
generally carried out in a single vessel in which~ in practice,
it is difIicult to achieve the above objectives. A single
vessel can be used to provide satisfactory separatian when good
grade oil sands are processed. Good grade oil sands contain at
least 13% bitumen and less than 10% fines. ~owever, oil sands
wlth higher amounts of clay and lower amounts of bitumen cannot
be separated satisfactorily using ~ si~gle vessel. This is
because the clay in the oil sands ~ends to act as an emulsion
s.abilizer. With incre~sing a~.ou~ts of clay in the oil sands,
the bitumen droplet size decreases and the viscosity of the
middlingc phase inc:e_ses, inhibiting the separation of bitumen
from the tailings ar.c m~aclings phases.
~ o decrease bitl,..en losses to the middlings and
tailings, additional s.e~s have been added to existing
processes. In one suc:~ process disclosed in U.S. patent no.
4,545,892 ~Cymbalisty), ~n addition ~o a sc~venging treatment of
the middlings stream, the solid tailin~s are recovered from the
bottom of the firs. se?ar~tion vessel and fed to a second
separation vessel in series with ~he first one. Part o the
bitumen ent~apped in the tailings is recovered in ~he second
separation vessel.
Another process (Cymbalis~Y ~. S. patent no. 3,g35,076)
has been proposed in which the conditioned oil sands are first
fed to a separation vessel in which coarse sand is backwashed
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with water and is separated fxom a liquid stream comprising both
aqueous and hydrocarbon phases. The coarse solids are dis~osed
and the licuid s~ream is passed to a second vessel where
liquid/liquid separation betweQn middlings and bituminous Eroth
takes place. In this process, the recovery of bi~u~en entrained
by the sand is accomplished only by the upward velocity or the
liquid phase through the coarse solids.
In U.5. patent number 3,951,799 (Anderson), a bitumen
extraction process is shown wherein ~he middlings from ~he
separation vessel are recycled to the bottorn or the separation
vessel. This method has the advantage of diluting the settled
sand, but requires uni~or~ distribution or the rec~cle through a
static distri~utor.
U.S. patent number 4,172,025 ~Porteous et al) shows
separate vessels for phase separation and air flotation.
In U.5. patent number 3,963,599 (Davitt), all process
streams are saturated with air, includi~y the solid slurry,
middlings and sludge accumulated at the bottom of the tailings
pond. In this process, sophisticated equipmen~ is required to
pump and maintain the s~re~s unce~ pressure. ~oreover, the
streams are saturated a~ h~gh t^...Deratures, whic:~ is less
efficient than saturating stre_~s at low temD@ra~ures.
A dif~erent approacb is shown in Canadian pate~t number
1,165,712 (Dente et al). Two se~arate streams~ a li~uid-rich
stream and a solids-rich s~ream, are recovered during the
conditioning s~ep. Each strea~ is fed into a separate vessel.
The liquid-rich stream is fe~ into an oil/wate! separator, and
the solids-rich stream is ~ed to a desander. The bitumen
ent-apped in the solids~rich s~ream is released and is recovered
at the top of the desander. This arrangement presents the
advantage of splitting the bituminous froth load between two
vessels instead of one. However, it is disadvantageOUS in that
the solid-rich stream tends to be diluted with
bitumen-contaminated middlings.
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In all of the prior art processes, the coarse solids
are discharged from the process at process temperature so that
substantiai amounts of the heat content of the stream are lost
from the process.
It is an object of this invention to provide an
improved method and appara~us for the recovery of bitumen from
oil sands.
Accordingly, the invention provides a process for
ex~racting bitumen fro~ oil sands. The oil sand~ are first
conditioned by adding alkaline hot water and op~imally steam
thereto. The conditioned sands are then introduced into a
separation zone. In this zone, the oil sands are allowed to
separate into a bitumen froth phase, a middlings phase and a
tailings phase. Water is continuously passed upwardly through
the separation zones~ This water is under pressure and has
dissolved air therein. The wa~er is also at a low temperature
relative to the conditioned oil s~nds. Subsequently, at least
two of the phases are withdrawn separately from the separation
zone.
The passing of water unde~ ~ressure into the separation
zone causes air dissolved in the wate- to be released as small
bubbles due ~o the decrease in pressure and increase in
temperature. These bubbles collide with the bitumen droplets
entrapped in the settled solids in the tailings phase and carry
the bitumen droplets to the bitumen froth phase. The injection
of water also establishes a net upwards liquid flow extending
throu~h the entire separator which helps to carry upwards
bitumen droplets not contacted by the air bubbles. The
injection of water thereby increases the a~ount of bitumen in
the froth. As ~he water is at a lower temperature than the
solids-rich and liquid-rich stream5 and as it is also preferably
injected directly below the interface between the middlings
phase and the tailings phase where the solids settle, it also
~3~
xchanges heat with the settling solids, thereby increasing the
thermal efficiency of the process.
Preferably, the middlings are treated to remove
impurities therefrom and obtain clarifie~ water. Optionally,
air may be ~issolved in the c~arified water and may then be
recycled upstream through the separation zone. This clarified
recycled water helps to carry air into the separation ~one and
give a net upstream liquid flow.
Preferably, the separation zone comprises a first
separation ~one and a second separation zone. The oil sands
separate into a solids-rich stream and a li~uid-rich strea~
after conditioning, and the solids-rich stream is introduced
into the first separation zone and said liquids-rich stream is
introduced into the second separation zone.
Preferably, the first separation zone which receives
the solids-rich stream is a desander and the second separation
zone which receives the li~uid-rich stream is a froth/middlings
separator.
The use of a separate desander and qeparator provides
tne advantage of de~reasing the specific load of froth,
middlings and tailings in each apparatus, thereby improving the
separation of the three phases.
The water is preferably at a temperature ranging
between 4 and 40C and has a pH in the range of 7 to 9.5. Most
preferably the pH is between ~.5 and 9Ø The water is
preferably saturated with air at a pressure of at least 250kPa,
preferably in the range ~50 to 700kPa, before entering the
desander and the separator. The desander and separator vessels
are preferably at atmospheric pressure. The location of
injection of water is preferably chosen to be approximately just
underneath the middlings/solids interface.
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In another of its aspects, the invention provides a phase separation device
to separate a feed into a tailings phase and at least one other phase. The device
comprises a vessel wherein the feed separates into a tailings phase and at least one other
phase. The vessel has a feed inlet to allow feed to enter the vessel, and outlets for each
of the separated phases. A rake is rotatably mounted near the base of the vessel to rake
the base of the vessel. A water injector is supporte(l on the rake and rotatable therewith.
This injector in~ects water with air dissolved therein under pressure at a location below
the interface of the tailings phase and one of the other phases.
A preferred embodiment of the invention will naw be described, by way of
illustration only, with reference to the following drawings in which:
Figure 1 is a schematic representation of a hot water process for extracting
bitumen from oil sands according to the invention;
Figure 2 is schematic representation of a hot water process for extracting
bitumen from oil sands according to the invention, which is an alternative embodiment to
that shown in Figure l;
Figure 3 is a schematic representation of a single vessel hot water process
for extracting bitumen according to the invention, which is an alternative embodim~nt to
that shown in Figure l;
Figure 4 is a schematic cross-section oi a separation apparatus according to
the invention;
Figure S is a top view of the separation apparatus of Figure 4;
Figures 6A and 6~ are side and front views respectively of another rake for
use in the apparatus of Figure 4; and
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Figures 7A and 7B are siae and front views respectively
of another rake for use in the apparatus in Figure 4.
As can be seen in Flgure 1, oil sands are fed into an
app2ratus for carrying out a process of e~t:rac~ing bitumen from
oil sanas through a line 10. These oil sands are contacted with
clarified recycle water through line 12 which is heated by steam
from pipe 11. The recycle water is obtained from water treater
13 through line 15, as will be discussed later. The mixture of
oil sanàs and ho~ water passes through pipe 14 to diqester 16.
In the digester, the mixture separates into a liquid-rich stream
ana a solids-rich stream. The solids rich stream passes through
a pipe 18 and is diluted with water passing through pipe 20.
The solids-rich stream then passes through a screen 21, wherein
larger particles are separated, passed through line 22 and
discarded. The solids-rih stream is ~hen fed into a desander
24. The liquid-rich stream is passed directly through line 26
to roth/middlings separator 2~. Cold make-up water, preferably
at about 4C, at a pH of 7.0 and saturated with air at 700kPa
~rom a make-up water source is injected under modera~e pressure,
to keep ~he air in solution, through line 30 into the lower part
o 'che desarlder 24 a~a in~o the separ~or 28 through pi3es 32
a 34 res~ec~ve'y~ Also, clarifie~ recJcle water at 6~C, at
a -~. of 9.0 and saturated with air at 700k~ is injec_ed under
moderate pressure into ~he lower parts o tne aesande 24 and
the separator 28 through pipes 36 and 38 res?ectively.
Separa~ion of ~he solids-rich and liquid-rich s~.reams
occurs in both the desander 24 and the separator 28. Each of
the s~reams separates into a bitum~n froth phase which floats on
the top, a tailings phase which settles in the bottom and a
middlings phase intermediate be~ween ~he froth and tailinss
phas es .
In the base of both ~he desander 24 and the separator
28, a tailings stream i5 collected through pipes 40 and 42
5~
respectively. The tailings stream from the desander 24 contains
most of the coarse solids originally present in the oil sands,
and some fine minerals and some hydrocarbons still entrapped in
the coarse solid matrix. The tailings stream collected at the
base of the separator 28 contains some coarse solids carried
from the digester and some settled fine minerals.
Froth streams containing most of the bitumen originally
present in the oil sands together with water and solids are
collected at the top o~ both ~he desander 24 and ~he separator
26 through pipes 44 and 46 respectively. These lines are
connected to combine the froth streams and the combined froth
strea~ is fed to a conventional froth treatn~ent apparatus 49
through pipe 480 In this apparatus, the bituminous froth is
diluted with a light hydrocarbon ad~ed through line 50 and is
treated for the removal of water and minerals which contaminate
the bitumen. ~iluted product exits from the froth treatment
apparatus through pipe 52 and is sent to downstream operations.
The water and minerals separated from the hydrocarbon phase exit
the froth treat~,ent apparatus through line 54 and are sent to
disposal.
~ iddlings st_ea~,s are withdrawn from both the desander
24 and the separator 2~ a~ a location intermediate between the
base and the top o. eac:~ or the ap~aratuses through pipes 56 and
5d respectively. The mi~dlings streams contain, in suspension,
so~e hydrocarbon and part of the fine materials originally
present in the oil sands and disaggregated in the digester. The
pipes 56 and 58 are connected to combine the middlings streamsJ
and the combined middlings stream is fed to a conventional water
treatment apparatus 13 through pipe 60. This conventional water
treat~ent apparatus 13 includes apparatus suitable for
flocculation, clarification, centrifuging and settling. The
recultant clarified water is saturated with air at a pressure of
700kPa and recycled back into the apparatus ~hrouqh pipe 15 to
lines 12, 36 and 38 as previously discussed. The sludge removed
in the water treatment apparatus is withdrawn through pipe 62,
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combined with the tailings strea~l passing through pipe 42 and
discarded.
Figure 2 shows a ~,odi~ied arrangement of the process.
Apparatus similar to the ap~aratus shown in Figure 1 is
indicated by the same reference rumerals, followed by the suffix
a
One difference between this modified arrangement and
the arrangement of ~igure 1 is that a single stream is removed
from the top of the desander 24a through pipe 64. This pipe is
connected to pipe 26a carrying the liquid-rich stream from the
digester 16a to form a single combined stream. ~he combined
stream is fed into the separator 28a. Another difference is
that make-up water from pipe 30a is only fed into the base of
the desander 24a and not into the separator 28a.
The apparatus of Figure 1 can be changed into the
configuration of Figure 2 simply by rearranging some of the
piping.
The configuration of Figure 2 is suitable for use when
good grade oil sands are processed havinc a bi~umen content of
at least 13%, an~ z f_nes content of less than 10%. When good
grade oil sand is used, there is less bitumen lost to the
tailings stream and to the middlings stream, and therefore it is
not necessary to inje~ make-up water into the separator 28a.
As less water is necessary when processing good grade oil sands,
the specific loads of the desander 24a and the separator 28a can
be reduced. The vessels can therefore be run in series rather
than in parallel. As less bitumen is entrapped in the
solids-rich stream with good grade oils, it is only necessary to
remove a single liquid stream from the desander ~6a.
Figure 3 shows an alternative embodiment of the
invention. Apparatus simi}ar to the apparatus shown in Fi~ure 1
is indicated by the same reference numerals, followed by the
suffix "b~. In this embodiment, all of the effluent from
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i~estoL 16b is sen~ to a desander 24b. Cold mak~-up water ana
clarifiea water are introduced countercurrently into the
desanaer 24~. A froth phase, a tailings phase and a middlings
phase are formed in the desander. T~ese phases are separately
remo~ea and treatea as describeà above with respect to Figure
1. In this embodiment, a sepa~ator is not required. This
embodiment is suitabLe for use with gooà grade oil sands.
.
Figures 4 and 5 show a separation apparatus 66
particularly suitable for use with the process of the present
invention. This apparatus 66 can ei~her function as a desander
24 or as a separator 28. This apparatus 66 consists of a
closed vessel 68 having a cylindrical walL 70, an inclinea
frustroconical base 72 and a frustroconical tailings outlet 74
at the centre of the base 72. A ~eed inlet pipe 76 extends
through the wall 70, to a feed well 80 near the centre of the
vessel. At least two middlings outlets a2 (only ~ne shown) are
located around the periphe~ of the vessel imtermediate the base
72 and top 86 of the vessel. A froth outlet 88 is located near
the top 86 of the vessel.
A rake ~ is disposed inside the vessel near the base
72 and includes a rotatabLe shaft 92 which e~tends from the base
72 through an opening 94 in ~he top 86 of the vessel 68. As can
best been seen in ~igure 5, the shaf~ 92 has three raaially
extending arms 96 attached to the base thereof, each with six
curved plate blades 9~ mounte~ thereon at an angle of more than
45 to the arm 96. The arms 96 are made up of two facing,
~arallel, spaced channels.
The apparatus operates as follows. Feed enters the
separator and settLes into tailings 91, middlings 93 and froth
phases 95. The rake 90 is adjustable in height so that the arms
96 are in the middlings phase 93 and the blades 98 are in the
tailings 91 phase. The shaft 92 is rotated by suitable means,
thereby rotating the ar~s 96 and blades 98. The blades 98 are
mounted at a suitable angle to the arms g6 so as to push the
tailings towards the tailings outlet 74~
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The moveme~t of the bLades 98 in the tailings phase
causes a zone of greater solids compaction in front of each
blade 98 and a zone oI low~r 501ids compaction behind each blade
98. This action o~ th~ blades 98 allows some bitumen droplets
trapped in the tailings to be freed.
The rake arms also serve as supports for the injection
of water containing dissolved air. Figures 6A, 6B, 7A and 7B
show water injectors sui~able ~or use with the apparatus of
Figures 4 and 5. As can be-seen in Figure 6, a water pipe 102
coaxial wi~h the rake shaf~ 92 and rotatable therewith e~tends
downwardly into the vessel 68 and terminates adjacent to the
arms 96. A number of headers 104, corresponding to the number
of arms 96 extend radially from the water pipe 102 between the
channels 100 ~f the arms 96. ~ plurality of liquid distributors
are mounted on the headers 104 in such a manner that they are in
fluid communic~tion with the headers 104. Each of these
distributors are positioned ~n the outermost side lOS of each of
the blades 98 of the rake~ As can be seen in Figures 6A, 6B, 7A
and 7Br these distributors 106 consist of a length of pipe 108
with nozzles 110 therein.
In oneration, as the rake shaf~ ~otatest the wate~ pipe
102 rotates s~ that the headers 104 and arms 96 rotate
together. ~ater is then injecte~ through the nozzle5 liO.
; Figures 6A and 6~ show an embodiment wherein
distributors 106 are all at the same elevation. In this
e~bodiment t~e blades 98 are of different heigh~s to correspond
to the shape of the base of the vessel.
In the e~bodiment of Figures 7A and 7B, the
distributors 106 ar~ ~Tn-shaped with the ~ail 112 of each ~T"
being connected to the header 1~. The length of the tails 112
varies with each distributor 106 SQ tha~ the outermost
distributors 106 are at a higher elevation ~han the innermost
distributors 106.
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It is to be appreciated ~hat modifications can be made
to the prererreà embodiment within the scope of the invention as
describea and claimed~ The distributors 106 may have holes
punched therein or simple nipDles instead of nozzles llO. The~e
can be any number o arms g6, blaaes 9~ and distributors 106.
The arms and dis~ributors can be either straight or curvea. The
distributo~s 106 could be located anywhere, although the~f are
each preferably loc~ted on the outermost siue of a respective
blade 98.
The invention will be further describea with reference
to the following e~ample.
EXAMPLE
A process similar to that shown in Figure 1 was
operated with a feed of l,000 kg per hour. The process
conditions in the desander and froth/middlings separation vessel
are summarized in Tables 1 and 2 respectively . As can be seen
from these tables, ~he bi~umen content of the tailings phase is
decreased when cold make-up w~er with air dissolved therein is
passed ^ountercurrently through the desanàer ana froth/middlings
separation vessel.
T~BLE 1
DESANDE_
~AS~3 ON 1,000 KG/E~ OIL SA~DS
~N 1 2
Desand e r
1,716.0 1,71~
% bitumen 2.38 2.40
% solids - 43O00 42.80
Nil 2g4.3
T C _ 4
P kPa - 700
Desanae~_Tails (Ra/H? . 1,135.3 1,130.00
96 bitumen 0 81 0.39
% soll~s 63 74 62.85
56.3 60.~
% bitumen 47 25 46.98
96 sa lids 5 75 6 .15
5 3 S . 4 8 2 ~ . a
% bitumen 0~g4 1.03
% solids 2.06 Z-50
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TABLE 2
E~OT~/MIO~LINGs S~ RATOR
. _
BAS~D ON l, 00C KG/H OIL SAN~S
RtlN 1 2
Feed (Ka/H) 1,540.1 1,Sl2.5
% bitumen 5 33 5 43
~6 so l id s 7 5
Clarifled Wa~er Re~-~cle (Ka/H) Nil 325.û
T C - 65
P k~a . - 600
SeDaratOr Tails (Ra/~) 124.3 130.5
% bitumen o.ao 0.38
% solias 58.22 55.6'
~ 13 g . 5 1 4 0 . 7
% bitumen 49.25 48.6;
% solids D,.66 4.80
Se~arator Mid~linas (~;a/E}) 1.275.a 1,5O6.3
% bitumen 0-~7 0~84
% s~lids 2.85 .Z.37
