Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates ~o a me~hod for separating and solidify-
ing fluid sludge or middlings, as produced in the process for recovering
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tar and oil from the tar sands in Northern Alberta. More particularly,
this invention relates to a method for treating the sludge layer which is
approximately one hundred and fifty feet down in a retention pond to recover
bitumen and water.
Tar sands, which are also known as oil sands and bituminous sands,
are silicious materials which are impregnated with a heavy petroleum. The
largest and most important deposits of the tar sands are the Athabasca
sands, found in Northern Alberta, Canada. These sands underlay more than
13,000 square miles at a depth of 0 to 2,000 fee~ or more. Total recoverable
reserves ater extraction and processing are estimat~d at more than 300
billion barrels- just equal to the world-wide reserves of conventlonal oil -
sixty percent of which is in the Middlc East. By way of contrast, the
America Institute estimated total United States oil reserves at the end of
1965 at 39.4 billion barrels.
Tar sands are 'primarily silica' having closely associated there-
with an oil film which varies from about 5 percent to 21 percent by weight,
with a typical content of 13 weight percent of the sand. The oil is quite
viscous - 6 to 8 A.P.I. gravity - and contains typically 4.5 percent
sulfur and 38 percent aromatics.
The sands contain, in addition to the oil and sand components,
clay and silt in quantities from 1 to 50 percent weight, more usually 10
to 30 percent. The sands also contain a small amount of water~ in
quantities o 1 to 10 percent by weight, in the form of a film around the
sand grains.
Several basic extraction methods have been known for years for
the separa~ion of oil from the tar sands. In the so called "Cold Water"
method, the separation is accomplished by mixing the sands with a solvent
capable of dissolving the bitumen cons~ituent. The mixture is then intro-
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duced in~o a large volume of wa~er, water with a surface agent added, or a ~ -
solution of a neutral salt in water, which salt is capable of acting as an
electrolyte. The combined mass is then subjected to a pressure or gravity
separation.
In the "Hot Water" method, as disclosed in the Canadian Patent `
841,581 issued May 13, 1970, the bituminous sands are jetted with steam and
mulled with a minor amount o ho~ water at temperatures of 170 to 190F.
The resulting pulp is ~hen dropped into a turbulent s~ream of circulat-
ing hot water and carried to a separation cell maintained at a temperature
of about 185~. In the separation cell, sand settles ~o the bottom as
tailings and oil rises to the top in ~he form of a roth. An aqueous
middlings layer comprising clay and silt and some oil is formed between
these layers. This basic process may be comblned with a scavcngcr stop Eor
further treatment of the middlings layer obtained from the primary separat-
ion step to recover additional amounts of oil therefrom.
The middlings layer, either as it is recovered from the primary
process or as it is recovered after the scavenger step, comprises of water,
clay, and oil. The oil content is, of course, higher in middlings which
have not undergone secondary scavenger steps. `
Effluent discharge is middling material of depleted oil content
whlch has undergone final treatment and which comprises clay dispersed in
water. The tailings layer also contains some clay and bitumen and other
discharged water-containing fractions such as the sand tailings of the
extraction cell which are not the primary products of the hot water pro-
cess but are recovered as waste products. The effluent discharge is
removed from the process plant as a slurry of about 35 to SS percent,
typically 45 percent, solids by weight. Included in the slurry is sand,
silts, clay, and small quantities of bitumen ranging from about 0.5 to 20
weight percent of total discharge. In this invention, sand refers to ~;
silicious material which will pass a 325 mesh screen, silt will pass 325
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mesh but is larger than 2 microns. Clay is material smaller ~han 2 microns ;
including some silicious ma~erial of that size.
Since the effluent contains oil emulsions, finely dispersed clay
with poor settling characteristics and other contaminants, water pollution
considerations prohibit discarding the effluent into rivers, lakes, or
other natural bodies of water. The disposal of the effluent discharge
has therefore presented a serious problem. ;
CurrentlyJ effluent discharge is stored in evaporation or retent- :
ion ponds which involve large space requirements and the construction of
expensive enclosure dikes which may be 120 feet high. A portion of the
water in the e~1uent discharge is recycled back into the hot water
extraction process as an economic measure to conserve both heat and water. ;;
~loweverJ experience has shown that the dispersed silt and clay content
of the recycled water can reduce pr~mary froth yield by lncr~asLng the
viscosity of the middlings layer and retarding the upward settling of oil
flecks. When this occurs, the smaller oil flecks and those that are more
heavily laden with mineral matter stay suspended in the water of the pond.
The effluent discharge from the hot water process contains a
substantial amount of mineral matter much of which is colloidally dispersed ;
and therefore does not settle very readily when stored in the retention
pond. The lower layer of the retention pond can contain up to 50 percent
dispersed mineral matterJ substan~ially of clay and silt as well as up to
5 percent bitumen. This part of the pond water is normally referred to as
sludge. Sludge is not suitable for recycling to the hot water extraction
process for the reason that i~s addition into the separation cell or the
scavenger cell at the normal inlet means it would raise the mineral
content of the middlings of the cell to the extent that recovery of bitumen
would be substantially reduced. GenerallyJ the settling which does take
place in the pond provides a body of water in which the concentration of
mineral matter increases substantially from the surface of the pond to the
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bottom thereof. For example, A pond of effluent discharge having a surface
area of a~out lO00 acres and an average depth of 40 feet can be character-
ized as follows:
From the surface of the pond to a depth of 15 feet the mineral
concentration, which is primarily clay, is found to be about 0.5 to 5.0 weight
percent. This pond water can normally be recycled to a hot water extraction
plant without interfering with the extraction of bitumen from the tar sands.
The layer of water in the pond between 15 and 25 feet from the surface
contains between 6 and 15 percent mineral matter. If this water were
recycled to the separation cell feed with fresh tar sands, the mineral content
of the middlings portion of the cell would increase to the point that little
bitumen would be recovered.
~inally, the scction o~ thc poncl between 25 ~ect aTld thc l~ottom
of the pond contains 16 to 50 pcrcont mineral m.atter and is nornlally re-
~erred to as sludge which, for purposes of the descriptlon of the present
invention, includes the composition of water, mineral matter, and bitumen.
Many solutions to the problem of bitumen recovery and water
recycling from the retention ponds have been proposed among wh;ch are
flocculation, filtration, use of hydrocyclones and centrifuges, distillation
and freeze-thaw methods
All of these approaches have either failed for technical reasons
or have been totally uneconomic.
Ideally, if these sludges could be converted to solid material in
the tailing pond, an ecological balance and recovery would result. ;
This invention attempts to provide an effective and economic pro-
cess for converting these fluid sludges to a solid form in the retention
pond, so that the oil and water may be recovered and the water utilized in
the primary extraction process back in the plant.
According to the present invention, there is provided a process
for recovering bitumen from an aqueous bitumen-containing sludge produced as
tailings during the recovery of bitumen from tar sands, which process
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comprises rapidly dispersing throughout the aqueous sludge at least one
additive compound selected from the group consisting of sodium aluminate and
methanamide under pressure in an amount sufficient to coagulate sludge solids
into an inert solid material, bitumen in the aqueous sludge separating out as
a froth on the surface of the aqueous sludge in a tailings pond and then
collecting said bitumen from said surface.
The sludge solidification process o the present invention provides
solidification at an extremely low cost as compared to any other treatment
process ~e.g. a cost of 0.1¢ or less per gallon of sludge based on 1977 costs).
Thus, the process of the invention provides a tar sands tailings
solidification process whereby the tailings are soLi.dified in the retention
pond and the oil and water are recyclecl to the plant.
Pre~erred additive compounds wh:icll are su:itablo ~or tlle proeos~ of
the invention include, Sod:ium Aluminate, NaA102, ancl Methanalni~le or formamide,
HCON~l2. These compounds are preferred additives because they are highly
effective even in very small amounts. ~urthermore, these compounds are
normally available at low cost at the site of most commercial oil sands treat-
ment plants.
The quantity of additive compound used depends on the particular
additive compound~ the desired rate of solidification, and economic factors.
The minimum amount of additive compound is that which will be èffective to
cause the break down of the sludge, and the separation of the oil and water
therefrom. In general, as little as 0.006% Sodium Aluminate by weight additive
compound is sufficient to initiate the action which results in the separation
of the oil and water from the sludge although quantities several times larger
than this may be employed if circumstances warrant it.
If the additive compound is dispersed throughout the entire mass
of sludge under treatment before initial reaction between the additive compound
and the sludge is complete, then the entlre mass of the sludge will be solicli-
fied as the reaction proceeds to completion.
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In a commercial scale operation where very large volumes of sludge
must be handled, it is not generally economical or feasable to inject the
chemical into the discharge or tailings pipes although this can be done if
desired in a particular instance.
Because of the very complex chemical and physical nature of the
oil sands tailings sludges, it is not possible to explain the precise
mechanism of the reactions which occur as a result of the rapid dispersal
of the additive compounds in the sludge in accordance with the invention.
However, it is believed that the present invention will be more readily
understood by an app~eciation of the following preferred embodiment, which
is given by way of example only, with reference to the accompanying drawings
in which:
~igure 1 is a diagranlmatic illustrati.on oE capparatus eor carry:ing
out the present invention.
~igure 2jis a diagrammatic illustration of a pumping system used
in the apparatus of ~igure 1.
A barge 1 with two tanks, one tank 2 containing 25,000 gallons
of NaA102 and the other tank 3 containing 25,000 gallons of HCONH2, is
pulled by a tug or is self-propelled on a tailings pond 4. A seismic rig 5
is placed on the barge 1 having a capacity depth of two hundred feet, option-
ally with a T-bar (not shown) revolving at the desired speed to agitate the
bottom of the pond. At least one of the chemical additives is pumped,
together with water taken from an upper zone A of the pond 4, through drill ';
stem 6 and into, primarily, the sludge zone C where the sludge is agitated `
and the chemical additive rapidly dispersed through the sludge. The depth
of the drill stem 6 can be varied and, since there is no clear boundary
between zone C and zone B twhich is approximately between 15 and 25 feet from
the pond surEace and contains less bitumen), the drill stem may be introduced
into zone B depending upon the demands for bitumen recovery. Bitumen Eroth
rises to the surface of the pond 4 while mineral and water sink and form a
lower layer in the pond 4. The
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froth product is ~hen recovered from the pond 4 by suction and recycled :~
to the plant for further processing. The layer of water below the bitumen
froth is also recycled back into the plant for reuse.
In the tar sands hot water extraction process, steam and water are ~
introduced into a hot water extraction zone. The present invention provides `
for recycled pond water from the surface of the pond to be transferred into
the hot water extraction zone. The efluent discharge from the hot water
extraction process is then, in turn, transferred into the tailings or retent-
ion pond. As mentioned above, the pond can be thought of as having three
zones A, B and C having separate concentrations of mineral matter and
bitumen dispersed in water. The upper zone A oE the pond normally contains
about 5 to 80 percent of the pond volume and extends to a dopth oE approx~-
mately 15 feet. This layer of the pond generally contains between 0.5 and
5.0 weight percent mineral matter generally in the form of fine clay less than
two microns in size. The intermediate zone B of the pond 4 contains somewhere "
in the range of 5 to 20 percent mineral matter including clay and silt
colloidally dispersed. The lower layer or slud~e zone C of the pond can com-
prise 10 to ~0 percent of the volume of the pond. This layer normally con-
tains the highest quantity of mineral matter which can be up to 50 percent
by weigh~ of mineral dispersed in the water. This layer of the pond is commonly
referred to as sludge and is normally not suitable for use in any part of
the primary hot water extraction process as diclosed above. However, this is
the layer of the pond which is particularly suited for treatment by the pro-
cess of the present invention for recovering additional bitumen.
Recycled tailings water in the pond which is pumped down into the
treating zone of the pond is admixed with the sludge. ~his water from the
pond is transferred together with the above-mentioned chemical additive down
into the treating zone. The sludge material is also agitated in the treating
zone by drill steam under approximately 1,500 psi and the trapped bitumen and
water is permitted to rise to the top of the retention pond.
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Referring now to Figure 2, tanks 2 and 3 hold the preferred chemical
additives, sodium aluminate and methanamide. Pumps 7 and 8 pump the chemical
additive from tanks 2 and 3 respectively through feed lines to the drill stem
6. Sight gauges 9 and 10, pressure gauges 11 and 12, quick opening valves 13
and 1~ and variable speed drives 15 and 16 from motor 17 control the flow
of chemical additive to the drill stem 6. An oriice arrangement 18 prevents
pressure back-up of the chemical additive from tank 3.
Water is drawn from zone A of the pond 4 by high pressure pumps 19
and 20 and mixed with the chemical additive in the feed line before entering
drill stem 6.
Thus by the method of the present invention, bitumen, and water pre-
viously not recovered Erom retention ponds and which is ~ound ln the bo~tom
zone of the retention pond is now rocoverable.
Thus, in summary, retention pond water is fed, together with a `
chemical additive down a drill stem or pipe under a pressure of between ,~
1,000-2,500 psi, and preferably about 1,500 psi, into the treating zone -
wherein material near the bottom of the retention pond is mixed with the
above mentioned chemical additive allowing the bitumen and water to rise as
a froth to the top of the retention pond so that it can be recycled back into
the primary extraction plant.
The present invention is preferably operable with feed material at ~^
any temperature in the range of approximately 50 below to 200F.
Although water used in the feed material is generally the effluent
stored in zone A of the retention pond, water from any source may be used.
As a practical matter, the bitumen content of the water stored in the retention
pond is higher in the sludge layer of the pond. Thus the sludge layer at the
bottom of the retention pond is most attractive for processing in accordance
with the method of the present invention. This sludge layer can contain
5 to 50 percent mineral and 0.5 to 25 percent by weight bitumen.
Furthermore, in some instances, this sludge layer can also contain ~`
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0.2 to 5.0 weight percent light hydrocarbons which result from a particular
method of hot water extraction. In the instance where the sludge layer
contains heavy hydrocarbons, a slightly longer agitation period or increased
pressure in the feed line provides a more efficient recovery of bitumen and
water from the sludge layer. In general, the water recovered from the top ~
of the retention pond and recycled down through the drill stem to the sludge ~ -
layer can be adjusted to get complete recovery of bitumen and water from the
sludge layer. Bitumen froth and water recovered from the top of the retention
pond is normally transferred into a froth recovery line wherein it is combined
with a froth recovered during the primary hot water extraction. The froth is
thereafter processed further to provide a synthetic oil suitable Eor use in a
general commercial trade.
By the method of this invcntion, additional bi-tuln~ll and water arc
recovered from the bottom of the retention pond, therefore providing an addi-
tional bitumen product as well as more efficient use of fresh water since
water from the pond is now made suitable for recycling to the primary hot
water extraction process.
As a typical example of the operation of the method of the present
invention and again referring to the drawing, the feed material from the pond
2~ which is transferred directly to the sludge zone C can be characterized as
having 74.2 percent water, 22.5 percent mineral matter, and 3.3 percent
bitumen. After treatment in the sludge zone the bitumen and water rise to the
top of the retention pond. The bitumen and water froth at the top of the
retention pond is characterized as containing 36.7 percent water, 1~.8 percent
mineral matter, and 52.5 percent bitumen.
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