Note: Descriptions are shown in the official language in which they were submitted.
o ~ 38~77
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Description
Process for Recoverlng a Solid Bitumen
Product from Tar Sands
_ _ _
Technical Field
The invention relates to the recovery of bi~umen
from tar sands, more particularly, it relates to a
refined process for the recovery of the bitumen in
solid form.
The recovered bitumen is more conveniently
handled and transported in the solid form than in the
liquid form in which it is ord.inarily recovered.
Background Art
The following U. S. patents are related to the
recovery of bitumen from tar sands: 2 ~ 965 ~ 557;
3~041~26~; 3~070~541; 3~161~581; 3~392~105; 3~475~318,
3~5531099î ~248r693; and 4~264~431. Patents
2~9651557; 3~041~267; 3~070~541; 3~161~581; and
` 3~553~099 all relate generally to obtaining more
effective contact between sand and solvent by causing
some special type of relative movement therebetween,
such as, upward movement of solvent throuyh sand layer
(3~5331099) ~ forming a lower layer of fluidized sand
and an upper laye.r of oil and silt in a separation
zone (2~9651557 an~ 3,070,541), separating bitumen-
loaded solvent and sand in a wash tank by causing
relative movement therebetween on an inclined surface
(3~041~267) r and separating by centriEuglng an oil
solvent slurry in a specially constructed contrifuge,
the preferxed embodiment having an inclined surfac~
(3,161,5811. The process of patent 3,392,105 dis
closes slurrying tar sands with a soluble oil (sur-
factants in non-polar solvents) and mixing the product
.
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with a solvent-diluen~ followed by separation in a
cyclone separator. Patent 3,475,318 dlscloses a
process for in situ deasphalteneizing of oil from
tar sand by use of a hydrocarbon solvent having
from 5-9 carbons per molecule prior to steam
stripping and recovery of solvent and product.
Patent 4,248,623 relates to the production from -tar
sand of a hydrocarbon product low in nitrogen and
sulfur by use of an alkali metal sulfide or an
alkanolic alkali metal hydrosulfide reagent. Patent
4,264,431 relates to a process for thermally cracking
the residue obtained by thermally distilling bitumen
obtalned from oil sand.
The bitumen product recovered from tar sands by
the disclosed processes of all of the above patents
is in liquid form, none of the patents disclosing a
bitumen product in solid form or a process for pro-
ducing a solid bitumen produc-t.
Disclosure of Invention
~ In accordance with the invention, tar sand is
processed so that the solid bitumen in the sand is
solubi}ized with a volatile organic solvent, separ-
ated from the sand, and recovered as a product which
is cooled to form a solid in the form of flakes for
shipmentO That is, the solid bitumen in the sand is
solubilized to separate it from the sand and later
converted back to solid form as solvent recovery is
accomplished by thermal distillation.
As shown in Fig. 1, the tar sand containing silt
is leached with volatile solvents in a leaching drum
preferably employing pebbles as a grinding media.
The resulting slurry is centrifuged to separate the
sand and pregnant solution. The pregnant solution
is steam distilled to recover the bitumen, which after
)1377
cooling is a solid flake product. The recovered
solvent is recycled to the leachi,ng system.
The centrifuged sand is subjected to success-
ive agitation leach and centrifuging steps with the
solvent from the final centrifuging step being
recycled to the first agitation leach, the biturnen
pregnant solvent from the second centrifuging step
being continuously recycled to the drum leach, and
the recovered solvent from the product recovery
; lO distillation step and the residue distillation step
being continuously recycled to the ~inal agitation
leach step.
The advantage of the critical multiple step
processing is that the bitumen pregnant solution
sent to the product recovery distillation s-tep is
substantially free of fines and other so]id parti-
cles, and'an almost complete removal of solvent from
the bitumen product is accomplished in the product
distillation step with the overall result that a
solid flaked bitumen product is produced with its
attendant advantages.
Brief ~Description of Drawings
The figure of the single drawing is a flow sheet
of the process of the invention.
Best Mode for Carrying Out the Invention
The background of the development of processes
for the recovery of bitumen from tar sands is set
forth in the prior art patents discussed above. As
set forth, for a process to be economically feasible
the bitumen ultimately produced must be competitive
with petroleum feed stock from other sources. Almost
complete solvent recovery must be accomplished to
make a process commercially feasible.
The present process was applied to Utah tar
V~7 ~ -
sands. The Utah tar sands are predominantly in the
Green River Formation and consist of weakly bonded
sandstones where the bonding material is primarily
~itumen. When contacted with a solvent, the mater-
ial rapidly disintegrates into individual sand
grains and silt together with dissolved or sus-
pended bitumen in solution in the solvent.
The present process is basically a countercur-
rent leach system employing centrifuges for liquid-
solid separation between stages. It uses relatively
low cost volatile solvents such as kerosene or
naphtha and produces a solid bitumen product.
To permit reasonable leach times, the ma-terial
is first crushed to at least minus one inch and then
fed to a drum type primary leaching vessel which pre-
ferably contains a pebble grinding media. In this
leach, the sandstone disintegrates to a point where
subsequent leaching steps are carried out in agi-tation
type leachiny vessels.
The pregnant leach solution obtained from the
first stage leach is subjected to vacuum distillation
for solvent recovery and the bitumen is produced as
a flaked solid product suitable for transport to a
refinery.
The solvent remaining with the final solids is
recovered by thermal distillation and recycled to
the system.
The presence of finely di~ided silt in -the Utah
sandstones nullifies the use of thickeners as liquid-
solid separation devices while the need to limit sol-
vent to tar ratios results in solutions with relative-
ly high viscosity thus limiting -the use of filters
or liquid-solid separation. For these reasons the
use of centrifuges was dictated as a preferred liquid-
solid separation -technique.
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Using centrifuges it is possible to obtain good
elimination of the nonbitumen solids from t~e loaded
organic solutions. In the test program, bitumen pro-
ducts containing less than one percent ash were pro-
duced.
The complete process is illustrated in the
accompanying flowsheet. Utah tar sand crushed to a
preferable size of about minus 3/8 inch is fed in
step 1 to a drum type leachiny vessel preferably
provided with a pebble grinding media. The solvent
is one having a relatively low distillation point,
preferably a kerosine type solvent. Other relatively
volatile solvents, such as, naphtha may be used.
epending upon economic considerations, leach time
may vary up to about four hours. A preferred feed
size is about minus 3.5 mesh to minus 1 inch and a
preferred leach time is about 1 to 4 hours.
Liquid-solid separation on the slurry from step 1
is effect~d by centrifuging in step 2. The liquid
from step 1 is sent to bitumen solvent separation and
the solids are further processed to recover addition-
al bitumen in agitation leach steps, the skeps each
being followed by centrifuging steps. Pregnant
solution from -the second centrifuging step following
the fixst agitation leach step is recycled to the
first or drum leach leaching step. Solvent from the
final cen-trifuging step is recycled to the first
ayitation leach step.
Recovered solvents Erom the solvent recovery
steps along with make up solvent are recycled to the
system, preferably to the second agitation leach step.
After-the sand from the first centrifuging step
has passed through the multiple agitation leach and
contrifuging steps it is almost completel~ free of
bitumen. This resul-ts in a high yield of bit~men.
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The process is not limited to the number of
agitation leach and centrifuging steps or the exac-t
route ofrecycle of liquids. The recovered solvent
may be recycled direc-tly to the first leach step.
It was found that the additional processing follow-
ing the first centrifuging step resulted in the
pregnant solution being sent to solvent--bitumen
separation being substantially free of fines and
other particles so that a more complete separation
of bitumen and solvent was effected with -the result
that a solid bitumen product was more easily recov-
ered.
The pregnan-t solution from the first centri-
fuging step is sent to thermal distillation where
it is disti]led at a tempeature below 400C to
effect a practically complete separation of solvent
and bitumen. Upon cooling, the bitumen solidifies
into a flaked solid product suitable for transpor-t
to a refinery for production of a final oil product.
Typical Utah sands to which the process was
applied had the following analysis
Specific
gal gal Gravity S
Sample No. tar/ton water/ton Bitumen
.. . .... _ ..
19342 15.4 1.0 0.908 0.47
19301 10.7 1.0 0.806 N.A.*
. .......... _. ._ . , .
*Not analyzed.
Tests were directed toward the objective of
de-termi.ning the relationship between feed particle
size and leaching time versus tar extration. This
study developed the following data:
Time Series, Single-Cycle
Feed size, minus 4-mesh; feed grade 15.4 gal
tar/ton.
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Leach time Bitumen in Residue -
min~al/ton
.
8.7
4.2
240 0.2
. _ . _ _ _ _ _ _ _ . _ _
Feed Size Series, Three-cycle
.. . _ . . .. _ , .
Leach t-ime-30 minutes; feed grade 15.4 gal
ton
Bi-tumen in Residue
Feed Size ~al/ton
-3/8 inch - 4.7
-4 mesh 1.8
-35 mesh 0.0
. _ _ _ . _ _ ._ _ _ _ _ _ _ _ _ ~
These data indicate that while bo-th longer
leach times and finer feed si~e are-capable o~
providing high extractions, it is probable that the
most e~fective commercial procedure would be shorter
leach.times, about minus 3/8 inch feed, and -the use
of pebble grinding media i.n the primary drum leach
step. With this configura-tion, extractions approach~
ing 99 percent are obtainable.
Application of the process illustrated in -the
flow sheet produced a pu.re solid bitumen product with
recovery of substantially all of the solvent :Eor
reuse in.the leach circui-t. It was demons-trated -that
a loaded organic solvent could be produced with a
ratio of two par-ts of solvent to one part of bitumen,
although the process is not restricted to this ratio.
Tests on this type of loaded solvent showed that when
the mixture was heated to a temperature of about
250c,.the solvent could be stripped with steam to
recover the solvent and leave a purified bitumen
product which, when cooled~ became a solid at room
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temperature.
This solid bitumen product t suitable for bulk
transport, has an analysis similar to crude oil as
shown in the following table.
Comparative Product Analysis
.... _ ~ .
C H S N O
.. . 2
Bi.tumen product 83.3 10.6 0.3 0.72 3.24
California crude oil 84.0 12.7 0.75 1.70 1.20
Lo Mexican crude oil 83.7 10.2 4.15
Texas crude oil 85.5 12.3 1.75 0.70 0.00
.... .
Discussions with officials of various refineries indi-
cate that this type of product can be fed directly to
many western refineries by b.Lendiny it with the crude
now being prod-uced.
The product bitumen used as oil ~eed stock prob-
ably reports to the gas oil fr.action which could be
used as cat-cracker feed. The multi-ring compounds
contained in the bitumen, aFter some degree of crack-
ing, are valuable components of gasoline due to theirvery high octane rating.
