Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
iL09~0~
This invention relates to an improvement in the opera-
tion of an oil sands hot water extraction plant.
In the extraction o~ oil from oil sands, oil bearing
material is mined, usually by a bucket wheel excavator or drag-
line, and is transported for hot water extraction processing in
which it is mixed with hot water such that the bitumen floats
as a froth and the solid matter sinks, making it possible to
skim off the froth for further separation and eventual refine-
ment to finished products, and dump the solid matter.
Presently 87% by weight of bitumen and diluent naphtha
are recovered from the oil sands by this hot water extraction
process with a loss of 13% by weigh~ being dumped with the solid
matter. The disposing of the solid matter involves passing the
solid matter together with accompanying hot water from the hot
water extraction process out to tailings ponds. The hot water
which is lost is at a temperature of approximately 185 - 195F.
The loss of this hot water considerably reduces the overall
plant thermodynamic efficiency as the heat loss must be made
up when reheating cold water for the hot water extraction
process.
In present commercial operations, the tailings contain-
in~ solid matter, hot water, and hydrocarbons not removed by the
ho~ wa~er extraction process, are sluiced, after the process,
into retaining areas which are often large ponds formed from
dams or dykes built from the tailings. When the first pond has
been filled, a second dam is built in the mined out area and
this process of building dams and filling the ponds formed bet-
ween the dams is continued until the reserve of mineable oil
sands has been depleted. At this future time most of the area
of the mined out acreage will be covered under almost a continu-
ous pond consisting of water, oil emulsions, and clay fines gel.
~(~9~6(~
With the present method of tailings disposal, environmental
authorities have determined that there has been and will continue
to be pollution impacts on underground water streams, surround-
ing lakes and other fresh water bodies adjacent to the mining
areas. Under the present tailings disposal little, if any, of
the mined out land can be reclaimed and put to useable form since
it will all be under the water, oil emulsion and unstable clay
fines gel.
- The basic method of recovery of oil from oil sands is
disclosed in the following Canadian patents, however none of
these patents are concerned with the efficiency of the system
b~t onl~ with general methods and apparatus for removing the oil.
Thc disposal of the tailings and the deleterious environmental
impact of the tailings on the land and surrounding water bodies
were not considered of importance nor even recogni2ed in these
patents.
Patent No. Date Patentee
448,231 May 4, 1948 Karl Adolf Clark
488,928 Dec. 16, 1952 Oil Sands Limited
493,081 May 26, 1953 Robert C. Fitzsimmons
Some of the major hitherto unresolved problems in the
~ontinuad development o~ the oil sands are (1) to increase the
xqcovery o~ bitumen from the sands and limit the loss of diluent
u~ in a hot water extraction process, (2) to increase the
th~rmodynamic efficiency of the overall process by recovery of
hot water which is presently lost in the tailings ponds, (3) to
reclaim the mined out areas, leaving them in a useable form,
and ~4) to eliminate the environmental impact of pollution of
surrounding bodies of water by seepage of contaminated sluice
3~ pond water into fresh water ~odies and underground streams, etc.
-- 2 --
1~160gt
~ It has been observed that large bitumen losses; considerably
larger than indicated on page ]; occur in commercial operation
periodically due to plant malfunctions or upsets due to many
causes. This invention acts as a safeguard back-up system to
recover approximately 99% by weight of such high commercial
bitumen losses whether continuous or discontinuous.
This invention overcomes these unresolved problems by
passing the various liquid tailings through a further separation
step in which the hot water is recovered together with hydro-
carbons, this recovered liquid being returned into the hot waterextraction process and the froth cleanup unit. The tailings
which remain are then almost dry and can be disposed of in the
mined out areas. It is preferable, although not essential, to
utilize a vacuum filtration process for extraction of the hot
water and hydroaarbons, this process utilizing filter clo-ths
and Eilter cakes made from the dried tailings.
By utilizing this invention, the following advantages
are achieved over all known processes:
1. Essentlally most of the hot water is recovered from the
tailings streams of the hot water extrac-tion plant and is re-
cycled within the process thus increasing the thermodynamic
eEficiency of the process. There is thus a considerable saving
in energy required to operate the process.
2. As the hot water and hot solvent extracting diluent
are recycled wi-thin the hot water extraction ancl the froth
cleanup units, additional bitumen and diluent are recovered
and the ~xtraction efficiency rises -to approximately 99~ by
w~ight from the present recovery of 87% by weight.
3. As wet tailings are not being disposed of, the need
for dams or dy]ces is not required and land reclamation problems
and operational problems involved with the present wet tailings
systems are eliminated thus making additional land available
~or mining.
~0~
4. As the wet tailings ponds are eliminated, -the environ-
mental pollution impact on all ]and and water bodies in the area
of the mining operation is minimized.
5. As dry tailings are being disposed of, they can be mixed
with overburden thus increasing the soil stability of the dis-
posal area and enabling the land to be reclaimed. Revegetation
and regrowth can begin as soon as the commercial development
starts, thus eliminating the necessity to wait for years or de-
cades until the present tailings ponds dry up and disappear.
6. By increasing the efficiency of the process, poorer
grades of oil sands can be worked, thus permitting greater flexi-
bility in the mining and mixing of varying grades and qualities
of oil sands.
7. The capacity of the boiler plant can be considerably
rqduced as the recovered hot water which is recycled in the hot
water extraction process saves approximately half of the boiler
plant requirements over the present systems if included in the
initial plant design. If converting an existing plant, addition-
al boiler capacity is achieved which can be used to increase
~0 the size of the facilities.
~ . Increased hydrocarbon yields and increased energy con-
servation lead to a reduction in capital and operating costs
per unit barrel of synthetic crude oil production.
~ he invention will now be described with reference -to
khe accompanylng drawing in which a block diagram of the process
is shown.
Referring to ~he drawing, the conventional process
including known improvements is indicated above the chain line
and consists generally of feeding oil sands from a mining area
~o~
- into a hot water extrac-tion llnit 1. The hot wa-ter and oil
sands are mixed and then trarlsported as a pulp -to a primary
separation unit 2 where the major separation of oil in the
form of froth, consisting of recoverable bitumen, water and
mineral matter, and solid tailings occurs. A middlings
stream is also formed with part beinc3 transported to a
secondary separa-tion unit 4 and part being recycled back to
unit 1. ,The froth is transported to a ~roth clean-up unit 3
'wherein the froth is mixed with a light hydrocarbon diluent
from stream 5 to assist in the clean-up process. A secondary
separation unit 4 is u-tilized to recover more bitumen from
the oil and water middlings stream from the primary separa-tion
unit 2. The bitumen recovered from the secondary separation
unik ~ is -transpor-ted, tocJether with the primary recovered
bitumen ~roth stream to the ~roth clean-up unit 3. Clean dry
bitumen and diluent are obtained ~rom the froth clean-up unit
3 and the solid matter is discharged as wet tailings. The
clean dry bitumen plus diluent are then transported to up-
grading facilities where the diluent is separated and returned
to stream 5 and the bitumen is upgraded to synthetic crude
oil.
The improvement in the conventional sys-tem is to now
collect the wet tailings from the primary separation uni-t2,
the secondary separa-tion unit ~, and the froth clean-up unit
3 and transpor-t them to a vacuum filter un.it 6.
A vacuum Eilter unit which is satisfactory ~or this
~uxpose. has a number of radiall~ disposed :~iltration segments
~hich provide Eor a continuous operation. Each sec3ment in
turn is passed under the wet tailings stream from the primary
separation unit 2, this being the stream which includes the
bulk of the solid material. The wet tailings in a segment is
vacuum filtered to recover bitumen and hot water and forms a
tailings cake. ~he driecl. cake is then pa~sed under the wet
-- 5 --
- lQ5~l6~9~
.
tailings streams from the seco~ldary unit 4 and the froth
clean-up unit 3 and againthe cake is dewatered by vacuum fil-
tration to recover the hot water, bitumen and diluent filtrate
which is recovered and returned to the ho-t water extraction
unit 1. For more efficient utilization of the filter, the
wet tailings streams from the secondary separation unit 4 and
froth clean-up unit 3 maybe added into the massive wet tailings
stream from the primary separation unit 2 which will act as a
wet tailings cake bed for the tailings from units 3 and 4.
The combined wet tailings are then vacuum filtered to recover
bitumen , diluent and hot water and form a tailings cake. To
aid the filtration rate, the feed to the filters mày be elutri-
ated with hot water and a portion of the relatively solid free
liquid layer maybe decanted and combined with the filtra-te
stream for recycle to the hot wa-ter extraction system unit 1.
The dried filter cake is then passed under a hot solvent extrac-
tion diluent to extract bitumen and the diluent filtrate re-
covered separately and forwarded to the froth clean-up unit 3
where the diluent portion can be utilized in the froth clean-up
unit. The dried cake is then passed under a hot wash water
stream to recover more bitumen and diluent and hot wash water
from the cake. The recovered bitumen, diluent and hot water
filtrate is recovered and forwarded to the hot water ex-traction
unit 1. Finally, the segment is rotated through 180 to dis-
charge the dry cake, the filter cloth is washed and dried, and
the cycle can again be~in.
The discharge dried Eilter cake can then be trans-
ported to a dry tailings disposal area whereas all the liquid
hydrocarbons and hot water recovered during the filtration will
be passed back into the hot water extraction plant 1 and -the
froth clean-up unit 3.
To aid filtration of the "fines" mineral matter con-
tained in the wet tailings streams Erom the secondary separa-tion
6 -
04
unit 4 2nd the froth clean-up ~nit 3, ~ Elocculant can be
added to these wet tailings before they are passed lnto the vac-
uum filter unit 6. Depending on -the type of oil sands feed-clay
mixture mined and delivered to the hot water extraction unit 1,
as well as the mode of operation of the vacuum filter unit 6,
the flocculant may be added to the recovered and recycled
hot water-bitumen stream prior to re-entry to the hot water
extraction unit 1. The floccula-ted precipitate portion o~ said
stream may be returned and removed in, but not limited to, the
froth clean-up unit 4 and vacuum filter unit 6, or be sent
directly to a tailings dump. Thus the fine clay particles
concentration in the hot water extraction system may be kept
at whatever concentration the individual plant operation may
re~uire or desire. The clay concentra-tion varies ~reatly with
the type of oil sands feed as well as wi-th the design of various
components of the hot water extraction 1, primary separation
unit 2, secondary separation unit 4, froth clean-up unit 3,
vacuum filter unit 6, and type of flocculant used as well as the
operational objectives and policies oE each organization involved
in oil sands operation.
Adclitional steam and hot water are introduced di-
rectly into the ho-t water extrac-tion unit -together wlth -the oil
sands .Eeed to provide make-up water requlrements and to rais~
-khe -temperature of the oil sands ~eed to the requ.ir~d operating
temperatuxe.
By usin~ the vacuum Eilter unit 6 to process all
o~ the we-t tailings, additional bitumen and diluent are recovered,
the hot water is recovered, and the mineral matter is dried so
that it can be transported by conveyor belt or other convention~l~
type of transportation to the mined out disposal area.. The dry
tailings can be mixed with overburden and stacked in the mined
out area by means oE stackers or other conventional mining
e~uioment to increa.se the stakility o:E the soil in the disposal
~91~
area and reduce the water content of the total overburden and
tailings solids. Reclamation of the disposal area can then
begin immediately.
It will thus be seen that a novel and extremely
useful improvement has been made to the conventional oil sands hot
water extraction process, this improvement clearly falling with-
in the guidelines which have been laid down by the Alberta
Energy Resources Conservation soard and the Alberta Oil Sands
Environmental Research Project. These guidelines apply to
present operators, future operators, approved applicants and all
future applicants to be approved for oil sands surface mining
projects and are as follows:
1. Improve -the recovery yield of bitumen and saleable
synthetic crude oil above the present level.
2. Improve the thermodynamic efficiency of project
operations by reducing heat and other forms oE energy losses.
3. Reclaim the mined out land area.
4. Reduce, or remove and eliminate, any causes of
environmental impact on the land, water and air,
Although the invention has been described utili~ing
a vacuum filter unit, it is understandable that any type of sepa-
ration unit which can remove liquids from solid ma~ter as
encountered in ail sands could be used bearin~ in mind that the
separation unit must be capable of handling vast quantities of
material in a continuous operation.
-- 8
