Note: Descriptions are shown in the official language in which they were submitted.
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-BACKGROUND OF THE'INVENTION
The invention relates to the hot water extraction
process for extractlng bitumen from tar sand. More particularly
alternative processing a;ds are set forth herein that may be used in
the tar sand conditioning step of said hot water process to replace
some or all of the inorganic alkaline substance heretofore employed as
a processing aid.
As readily-available supplies of conventional crude
oil get used up, the oil industry has turned to tar sand deposits as
a source of hydrocarbons. The main tar sand deposit on the North
American continent is in the Fort McMurray region of the Pro~ince
of Alberta in Canada, in an area traversed by the Athabasca River,
and this deposit is being'actively developed at the commercial level
to contribute to Canada's hydrocarbon supplies.
Tar sand is essentially a mixture of sand grains, water,
salts, fine mineral solids of the particle size of clay minerals, and
a heavy o11 usually referred to as bitumen. It is the bitumen that
is of commercial Interest. Tar sand also goes by the names of oil sand
and bituminous sand. Although the composition varies throughout the0 deposit, speaking generally, the main constituents analyse at,
oil 11.59% by weight
water 4.41% by weight
solids 84.00% by weight
In theory,-there are advantages in extracting the
bitumen in situ since such processes obviate the need for mining and
associated materials handling of huge tonnages of tar sand and tailings,
the equipment for which requires large amounts of capital. In practice,
however, mining of tar sand followed by isolating the bitumen therefrom
by the hot water extractlon process is the preferred commercial method
because in spite of the problems o~ mining and materials handling,
bitumen recovery is very high, normally around 93%.
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According to the hot water extraction process as commonly
practiced, mined tar sand is added to a conditioning drum horizontally
mounted and capable of rotation about its longitudinal axis. Such
conditioning drum is hereinafter referred to as the tumbler. As well
as the tar sand, hot water (referred to as slurry water), steam and, for
most tar sand feeds, relatively minor amounts of NaOH are also added to
the tumbler. Steam is normally added as two streams, first in relatively
large amounts at the front end of the tumbler, and subsequently in the
form of trim steam via sparging valves set in small-bore pipes passing
along the length of the inside of the tumbler, to provide more delicate
temperature adjustment. The NaOH commonly added assists in the con-
ditioning action, and is used for all tar sand types except the very
rich material, that is, for all tar sands of bitumen content less than
about 12% bitumen. Commonly, for every 3250 tons of tar sand one adds
610.30 tons of water and such steam as to give a final conditioning
temperature in the range of 150 to 180F, although the process may be
operated outside this temperature range.
It is usual for the rate of feed to be set such that it
takes less than 10 mins. for tar sand to pass through the tumbler from
the inlet to the outlet end. During this time the bitumen is dislodged
from the sand particles so that what enters as tar sand, with bitumen
and sand tightly bound together (with interstitial water connate to
the deposit probably also involved in such bonding), leaves as a mixture,
with bitumen, sand, and water merely in loose association, and in such
a state that, should suitable conditions be provided, the sand and the
bitumen will separate severally from the mixture. This operation in the
tumbler is commonly called 'conditioning'. On emerging from the tumbler,
the tumbler is screened to remove oversized debris such as rocks and
lumps of undigested tar sand, and diluted with further hot water (called
flood water). The diluted slurry then is subjected to the first tar sand
components separation step, termed primary separation. This operation is
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conducted in a ~rimary separation vessel.
The primary separation vessel ;s a vessel wherein screened
d;luted slurry is maintained in a quiescent condition. The screened,
diluted slurry is discharged into the central region of the contained body
of slurry with the following effects:
Most of the sand, especially the coarse sand, sinks to the
bottom and may be pumped out as an aqueous tailings stream;
The bitumen in the form of globules, becomes aerated by
attachment of air bubbles present in the primary separation
vessel and being rendered buoyant thereby rises to the
surface of the vessel where it is collected as a froth
(primary froth)i
Bitumen that fails to get aerated, along with much of the
fine mineral matter, collectively having a density close
to that of the aqueous contents of the vessel, has little
tendency to either sink or rise and so remains in the central
region of the vessel.
The mixture of unaerated bitumen, water and fine solids
(collectively kno~n as "middlings") contains valuable amounts of bitumen
that it is advantageous to recover~ Hence a portion of the middlings
is continuously withdrawn to obtain a further yield of bitumen therefrom.
The middlings portion thus withdrawn is advanced to subaerated flotation
cells where it is vigorously agitated with air to produce a second froth
(secondary froth) and a further tailings stream (secondary tailings).
It is advantageous to operate the circuit in such a way as
to cause as much of the bitumen as possible to report to the primary
froth because the purity of said primary froth is high. Typically, primary
froth contains 66.40% by weight of bitumen while secondary froth has only
23.78% bitumen and also contains such large quantities of entrained water
and fine minerals that it should be cleaned in a froth settler. After
the cleaning step, the secondary froth is combined with the primary froth
and the bitumen is recovered out of the combined froth.
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The conditioning of the tar sand that occurs in the tumbler
has a marked influence in determining the tendency of the bitumen to
join the primary froth. Traditionally, process aids such as sodium
hydroxide and sodium silicate, that is, alkaline compounds of monovalent
metals, have been added to the tumbler to improve recovery. The present
invention is directed toward providing other compounds effective as pro-
cess aids that are compatible with the traditionally-used substances and
may be employed in place of part or all of such traditional conditioning
aids, and which result in considerable savings in costs. Since a com-
mercial tar sand processing plant, for producing 125,000 barrels of
synthetic crude oil per day, uses about 35,566 tons per year of sodiumhydroxide solution at a specific gravity of 1.22 at an annual cost of
between $4 million and $5 million (1977 Canadian dollars), a significant
reduction of NaOH consumption is desirable.
SUMMARY OF THE INVENTION
I have discovered that the addition of sodium hydroxide
solution in its raw state to the tumbler is an inefficient use of this
chemical for most tar sand types. By contrast, sodium hydroxide that
has been contacted with bitumen or an analogous organic material, on
being added to the tumbler, has enhanced power to contri`bute to the
recovery of bitumen from tar sand, said enhanced power being reflected in
similar levels of bitumen recovery from tar sand at reduced caustic usage.
In consequence, considerably less sodium hydroxide need be used after such
contact.
For example, raw sodium hydroxide is commonly used at the rate
of about 0.03% by weight expressed as a proportion of tar sand feed. When
bitumen is vigorously mixed or emulsified with sodium hydroxide solution
however, a rate of sodium hydroxide addition of 0.01% gives approximately the
same level of bitumen recovery. Since most of the bitumen added as the
organic phase of the emulsion is subsequently recovered along with the
bitumen from the tar sand, this bitumen is merely recycled in the process and
no significant loss in that respect occurs.
It is my theory that the mechanism by which sodium hydroxide
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aids conditioning in the tumbler is one whereby surfactants are produced
by interaction of the sodium hydroxide with organic substances. These
surfactants produced in situ in the tumbler assist in dislodging the
bitumen out of the tar sand, allowing the bitumen ultimately to report to
the primary froth of the primary separation vessel. If such speculation
is correct, it may further be said that the tumbler residence time of less
than 10 minutes, which is the commonly practiced period for conditioning
tar sand, is too short a time for the theoretical minimum quantity of
sodium hydroxide to produce a desired level of surfactants in the tumbler;
thus excess sodium hydroxide must be used. When however, according to the
invention, sodium hydroxide is held in contact with bitumen or analogous
organic material for a relatively prolonged period of time or intimately
mixed there with, higher concentrations of surfactants appear to be formed.
If thereafter this sodium hydroxide/organic material mixture is used as a
process aid in the tar sand tumbler, it is considerably more effective
than sodium hydroxide alone.
The preferred embodiment of this invention involves using
bitumen emulsified with aqueous sodium hydroxide solution as a process aid.
The emulsion may be used, when necessary, in conjunction with extra
sodium hydroxide solution. The emulsion may be prepared by mixing bitumen,
sodium hydroxide, and hot water in a simple mixing tank, in-line mixer or
similar device.
Another possible embodiment involves contacting sodium
hydroxide solution, preferably with vigorous mixing, with tar sand. The
resulting solution or emulsion may then be used as a process aid.
Another possible embodiment involves using refinery spent
caustic to form the processing aid. Said spent caustic contains dissolved
phenols and analogous organic acidic compounds in the form of sodium salts.
Their presence in the tumbler allows a large portion or all of the raw
sodium hydroxide of the prior art to be dispensed with.
: ' ' ` :.. .
~ 3 ~
What all these embodiments have in common is intimate
contact between sodium hydroxide and bitumen or other organic matter for
a sufficient period of time to permi:t the sodium hydroxide to react with
components of the organic matter to produce a desirable leYel of surfactants,
said surfactants being benefici:al to the conditioning of tar sand in the
hot water process. Other alkali metal substances, for instance
potassium hydroxide, may be used in place of sodium hydroxide, but there
would be no economic advantage i:n doing so. Other organic matter than
bitumen may be used to provide components for the organic moi.ety i.n the
surfactants, the limitat;on being that the surfactants should not add
obnoxious substances to the process tailings, that mi.ght adversely affect
the environment, or to the synthetic crude oil that is the eventual
product of the bitumen isolated from the tar sand.
Broadly stated the invention is an improvement in the hot
water process for extracting bitumen from tar sand wherein tar sand is
mixed with hot water to form a slurry and retained in a rotating tumbler
for a period of time to condition said slurry. The improvement comprises
adding as a process aid a surfactant prepared outside the tumbler by
mixing an alkali metal hydroxide with organic materi.al~
DESCRIPTION OF THE PREFERRED EMBODIMENT
The invention is exemplified by the following extracti.on
experiments, in which a series of additives were added to water and tar
sand in a vessel and s.tirred, to approximate the process in a tumbler7
and then held quiescent to approximate the process in a primary separation
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vessel. More particularly, the experiments were performed in a hatch
extraction apparatus. To a 1.5 L stainless steel vessel were added hot
water (0.14 L) to act as slurry water and then tar sand (500 9), followed
by such additives as are listed in the Table below. The vessel was
provided with a heated jacket, to maintain the contents at the desired
temperature (180F), and with a variable speed agitator. The slurry
was agitated at 600 r.p.m. for 10 minutes, 1 L of hot water was added (flood
water), and the mixture was stirred for an additi`onal 10 minutes. Then the
agitator was stopped and the resulting bituminous froth was skimmed from
the surface. (The single vessel laboratory procedure and the froth
produced by it have been shown to be reasonably analogous to the tumbler-
primary separation vessel procedure, as practiced in a pilot plant, and
to the froth produced by said pilot plant.)
Preparation of Emulsions
To 145 9 water held at 80 to 90C in a stainless steel
vossel fitted with an impeller-type agitator was added 1 ml of 1 N NaOH
solution and then the quantity of bitumen or bitumen froth called for in
the example. The mixture was stirred vigorously to react the components
This mixture was used as slurry water in the runs to extract bitumen
from tar sand.
Preparation of Tailings Concentrate
Secondary tailings collected from the process to extract
bitumen from tar sand were evaporated in a laboratory-scale rotary
evaporation apparatus under mild vacuum until reduced to one tenth their
original volume. The resultan~ concentrate was used as slurry water in
extraction tests.
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TABLE I
Comments Process Aid Amount of Process Bitumen Recovery
Ai:d (using 500 g via Primary Froth
tar s.and) (wt% of total
bitumen in tar
- sand feed)
_
Typical ex- sodium
ample using hydroxide 0 34
NaOH under
10 normal con- 3 ml of 1 N
ditions (0.024 wt% NaOH 76
on tar sand)
5 ml of 1 N
(0.04 wt% NaOH 89
on tar sand~
Shows how the
amount of NaOH sodium 1 ml of lN 79
required to hydroxide (0 008 wt% NaOH
achieve a on tar s.and)
20 given re-
covery is re- 3 ml of 1 N 88
duced by (0.024 wt% NaOH
prior mixing on tar sand)
of NaOH with
25 bitumen and bitumen/NaOH 1 ml of 1 N NaOH 84
bitumen froth mixed with 5 g
bitumen
bitumen froth/ 1 ml of 1 N NaOH 83
NaOH mixed with 5 g
bitumen froth from
average tar sand
(1 wt% 6i:tumen
expressed on tar
sand feed)
bitumen froth/ 1 ml of 1 N NaOH 86
NaOH mi.xed with 5 g
bi.tumen froth from
rich tar sand
bitumen froth/ 1 ml of 1 N NaOH 91
NaOH mixed wi:th 5 g
hi:tumen froth from
hign fines tar
sand
Shows in- No additive 0 60
45 creased re-
coveries unconcentrated 145 ml 59
when NaOH secondary (added as slurry water
is re- tailings and flood water)
placed by
concentra- concentrated 145 ml 87
ting tailings secondary tailings (added as slurry water)
water (reduced to 1/10
initial volume)
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T_ E I (continued)_
Comments Process Aid Amount of Process Bitumen Recovery
Aid (using 500 g via Primary Froth
tar sand) (wt% of total
bi:tumen in tar
sand feed)
Shows how NaOH Refinery 0 34
can be re- spent caustic
placed by re- 1 ml neat 55
finery spent
caust;c (largely 3 ml neat 83
organic
sulfonates~ 5 ml neat 90
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