Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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MF~THO]~ FOR ~XTRACTING OTT. FROM OTT--CONTAl~qTNAT~D SOTT.
Thir, invention relates to a method for extracting oil
from oil-contaminated soil using a solvent and sonic energy
in the low frequency range of 0.5 to 2.0 kHz.
Oil-contaminated soil, drill cuttings and other
S material, are wide spread in North America. The
contamin~tion level is high enough, 2 to 5 wt.~ oil, ~hat
the solids must be put aside, or in storage, awaiting some
remedial action. Many methods have been devised to remove
the oily contamination, but most are expensive and usually
still leave the solids residue partially oil contaminated.
This condition results in removal to designated landfills
where transportation and storage costs are high.
AppLicant's copending application, Mobil Docket No.
7758, entitled "Method for Extracting Bitumen From Tar
Sands" and commonly assigned, discloses a method similar to
-the present invention for extracting bitumen from tar sands
using a ,olvent and sonic energy in the low frequency range
of 0.5 to 2.0 kHz.
U.S. Patent No. 2,973,312 discloses a method of
removing oil from sand, clay and the like, including
employing ultrasonic vibration.
U.S. Patent Nos. 4,054,505 and 4,054,506 disclose a
method of removing bitumen from tar sand using ultrasonic
energy.
U.S. Patent No. 4,151,067 discloses a method for
removing oil from shale by applying ultrasonic energy to a
slurry of shale and water.
U.S. Patent No. 4,304,656 discloses a method for
extracting oil from shale by employing ultrasonic energy.
U.S. Patent No. 4,376,034 discloses a method for
recovering oil from shale employing ultrasonic energy at
frequencies between 300 mHz and 3,000 mHz.
U.S. Patent No. 4,443,322 discloses a method for
separating hydrocarbons from earth particles and sand
employing ultrasonic energy in the frequency range of 18 to
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27 kHz.
U.S. Patent Nos. 4,765,885 and 5,017,281 disclose
methods for recovering oil from tar sands employing
ultrasonic energy in the frequency range of 5 to 100 kHz
S and 25 to 40 kHz respectively.
U.S. Patent No. 4,891,131 discloses a method for
recovering oil from tar sands employing ultrasonic energy
in the frequency range of 5 to 100 kHz.
In contrast to the prior art, in the present invention
oil-contaminated soil is mixed with a solvent to form a
slurry, the slurry is fed into the top of a vertically
disposed acoustic chamber and fresh solvent is injected
into the bottom of the acoustic chamber and flows upwardly
at a controlled rate whereby the particles of oil-
lS contaminated soil fall by gravity through the solvent and
are subjected to sonic energy in the low frequency range of
0.5 to 2 . O kHz, whereby the oil is removed from the soil
and dissolved by the upwardly flowing solvent without
cavitation of the solvent.
Sllmmary of the Invent;on
A method for extracting oil from oil-contaminated soil
with a solvent which is miscible with the oil in the soil
comprising the steps of:
(a) mixing the oil-contaminated soil with a solvent
to form a slurry of oil-contaminated soil
suspended in the solvent;
(b) injecting the oil-contaminated soil slurry into
the upper end of a vertically disposed,
substantially rectangular shaped hollow chamber
of uniform cross-section and simultaneously
injecting a solvent into the lower end of the
hollow chamber that flows upwardly through the
hollow chamber at a rate low enough whereby the
oil-contaminated soil particles fall by gravity
through the upwardly flowing solvent;
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(c) subjecting the oil-contaminated soil particles
and solvent in the hollow chamber to sonic energy
in the frequency range of about 0.5 to 2.0 kHz by
means of an acoustic transducer attached to the
outer surface of one side of the hollow chamber
whereby the oil on the soil particles is
displaced therefrom and dissolved by the upwardly
flowing solvent without cavitation of the
solvent; and
(d) recovering the substantially oil-free soil
particles.
An object of this invention is to more effectively
remove oil from oil-contaminated soil by forming a slurry
of oil-contaminated soil particles in a solvent, injecting
the slurry into the top of an acoustic chamber, injecting
fresh solvent into the bottom of the acoustic chamber that
flows upw,ardly at a controlled rate whereby the particles
of oil-contaminated soil fall by gravity through the
solvent, ,and subjecting the particles of oil-contaminated
soil and solvent to sonic energy in the frequency range of
0.5 to 2.0 kHz whereby the oil is removed from the soil and
dissolved by the upwardly flowing solvent without
cavitation of the solvent. It is an advantage of the
present invention that the use of sonic energy in the low
frequency range of 0.5 to 2.0 kHz and the shape of thç
acoustic r-hamber prevents cavitation of the solvent and
enables tihe oil to be more effectively removed from the
soil.
Descri~t;on of the Drawings
Fig. 1 is a flow sheet schematically illustrating a
preferred procedure for extracting oil from oil-
contaminated soil in accordance with the invention.
Fig. 2 is a schematic diagram illustrating the
laboratory apparatus used according to the present
invention.
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nescr;ption of the Preferred Fmhodiment
According to the present invention, oil is removed
from oil-contaminated soil containing 2 to 5 wt.% oil by a
solvent extraction operation enhanced by sonic acoustic
energy in the audible frequency range of 0.5 to 2.0 kHz. D
Referring to Fig. 1, oil-contaminated soil containing 2 to
5 wt.% oil is first mixed with a solvent in tank 10 and the
mixture fed into a slurry mixer 12 through line 14. The
ratio of oil-contaminated soil to solvent is dependent upon
the soil properties. Usually, the operating range of the
ratio of oil-contaminated soil to solvent is about 0.3 to
15% by volume and preferably, about 8 to 10% by volume. In
the slurry mixer 12, the contaminated soil is thoroughly
mixed with the solvent to form a slurry of oil-
contaminated soil suspended in the solvent. During the
mixing of oil-contaminated soil and solvent a portion of
_the oil in the soil is dissolved in the solvent and a
portion of the solvent is dissolved in the oil remaining in
the soil. The oil-contaminated soil slurry is delivered by
gravity to a shaker screen 14. Coarse or large soil
particles having a particle size greater than 1/4 inch are
retained on the shaker screen 14 which are delivered from
the shaker screen 14 to a crusher (not shown herein) and
the crushed soil particles are recycled to tank 10 for
mixing with solvent. The oil-contaminated soil slurry
containing smaller soil particles equal to or less than 1/4
inch is then fed into the top of a vertically disposed,
rectangular shaped, hollow acoustic chamber 16 of uniform
cross-section. Fresh solvent is fed into the bottom of the-
acoustic chamber 16 through line 18 and flows upwardly
through the acoustic chamber. The fresh solvent is
injected into the bottom of the acoustic chamber 16 at a
controlled rate low enough whereby the oil-contaminated
soil particles in the slurry to fall by gravity through the
upwardly flowing solvent. The oil-contaminated soil
particles and solvent in the acoustic chamber 16 are
subjected to sonic energy in the low frequency range of
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_
about o.5 to 2.0 kHz, preferably 1.25 kHz, that removes the
remaining portion of oil from the soil particles thereby
permitting the oil to go into solution in the upwardly
flowing solvent. The upwardly flowing solvent-plus-oil is
q 5 removed from the top of the acoustic chamber 16 through
line 20. The substantially oil-free soil particles
containing 0.2 to 0.4 wt.% oil fall by gravity to the
bottom of the acoustic chamber 16 into a tank 22 containing
water delivered through line 24. The substantially oil-
free soil particles settle in the water to form a slurry ofoil-free soil particles suspended in water that is removed
through line 26. The slurry of substantially oil-free soil
particles in water containing only 0.2 to 0.4 wt.~ oil is
disposed of by spreading it over land for land farming
since the residual oil levels are legally low enough. The
use of sonic energy in the low frequency range, the shape
of the ac~ustic chamber, and the counter-current flow of
oil-contaminated soil particles and solvent significantly
enhances solvent extraction of the oil from the oil-
contaminated soil.
The acoustic chamber 16 consists of a verticallydisposed, rectangular shaped, hollow chamber of uniform
cross sectional area. Preferably, the acoustic chamber 16
is a vertically disposed, rectangular shaped, hollow
chamber of uniform cross-section having a first pair of
flat parallel sides and a second pair of flat parallel
sides wherein the first pair of flat parallel sides is
substantially greater in width than the second pair of flat
parallel sides. As shown in Fig. 1, the acoustic energy is
generated by attaching the transducers 28 to the mid-
section of one of the widest side of the acoustic chamber
16. The shape of the acoustic chamber and location of the
transducers enable the low frequency sonic energy to be
transmitted at the maximum amplitude, or power, without
cavitatio;n of the solvent that would possibly interfere
with the settling of the oil-contaminated soil particles by
gravity through the upwardly flowing solvent. In addition,
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the use of sonic energy in the low frequency range of 0.5
to 2.0 kHz without cavitation of the solvent more
effectively penetrates the oil/soil bond and results in the
detachment of the oil from the soil particles which is then
dissolved by the upwardly flowing solvent. The acoustic
chamber 16 has a volume proportionate to the size and power
output of the acoustic transducers.
The sonic energy generated by transducers 28 are of
the electrical-acoustic type adapted to convert electrical
energy into mechanical vibrations that are introduced into
the acoustic chamber 16. The flat surface of the acoustic
chamber 16 functions as a plate that contains the acoustic
energy. The transducers 28 are magnetostrictive
transducers. A suitable transducer is manufactured under
the trade designation "T"-Motor~ by Sonic Research
Corporation, Moline, Illinois, that generates sonic
vibrations having a frequency within the range of about 0.5
to 10.0 kHz. The transducers 28 consist of a
magnetostrictive material in the form of rods compressed
together and wrapped with a wire coil. The rods comprise
90% iron, 5% terbium and 5% dysprosium sold under the trade
designation "Terfenol-D" by Edge Technologies, Inc., Ames,
Iowa. The Terfenol-D rod is the only material known that
can produce variable frequency, and withstand high
temperature and pressure. The rods vibrate length wise
when a DC current flows through the coil. The induced
magnetic field causes the rods to expand and contract, i.e.
magnetostrictive motion. This motion, or vibration,
generates an acoustic wave or sonic energy having a
frequency in the range of 0.5 to 10.0 kHz which extends
forward from the transducer for some distance. The
transducer is powered by a standard frequency generator and
a power amplifier. A suitable transducer for use in the
present invention is disclosed in U.S. Patent No. 4,907,209
which issued to Sewall et al. on March 6, 1990. This
patent is incorporated herein by reference. The
transducers are powered by a standard frequency generator
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and a power amplifier. Depending on the resonant frequency
of the sonic transducers, the required frequency may range
~ from 0.5 to 2.0 kHz. Operating at the resonant frequency
of the sonic source is desirable, because maximum~ 5 amplitude, or power, is maintained at this frequency.
Typically~, this frequency is from 0.5 to 2.0 kHz for the
desired equipment, preferably 1.25 kHz.
The solvent may be any liquid hydrocarbon that is
miscible with the oil in the soil. Suitable solvents
include light crude oil or condensate which may be obtained
from a nearby oil or gas field or reservoir, raw gasoline,
kerosene and toluene or mixtures thereof. The preferred
solvent is condensate or light crude oil.
Fig. 2 illustrates the laboratory solvent extraction
testing apparatus. Re~erring to Fig. 2, a slurry of oil-
contaminated soil containing 2.5 to 3.8 wt.% oil suspended
_in a sol~ent (toluene) was introduced into the top of
acoustic chamber 30. Fresh solvent (toluene) is introduced
into the bottom of the acoustic chamber 30 through line 32
and flows upwardly through the acoustic chamber at a
controlle!d rate low enough whereby the oil-contaminated
soil particles in the slurry fall by gravity through the
upwardly flowing solvent. The oil-contaminated soil
particles and solvent in the acoustic chamber 30 are
subjectedL to sonic energy at a frequency of 1.25 kHz and a
power level of 6.5. The sonic energy is generated by
transducers 36 and 38 attached to the outer surface of the
acoustic chamber 30. The low frequency sonic energy
removes the oil from the soil particles which is dissolved
by the upwardly flowing solvent (toluene) without
cavitation of the solvent. The solvent-plus-oil exits from
the top of the acoustic chamber 30 through line 34. The
substantially oil-free soil particles settle by gravity
into flask 40 containing water to form a slurry of
substantially oil-free soil particles suspended in water.
The water-soil slurry was removed from flask 40 via line 42
and filtered to remove the water. The residual oil from
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--8--
the soil was collected in a Soxhlet extractor using
toluene. Alternatively, the soil sample was air-dried
overnight at about ambient temperature before Soxhlet
extraction to remove any residual solvent.
The operating conditions and results of solvent
extractions in conjunction with low frequency sonic energy
using the apparatus shown in Fig. 2 are shown in Table 1,
below.
TABr~F! 1
Counter-Current Solvent Extraction of Oily Soil
Oil Content of Soil = 2.5 - 3.8 wt% (Soxhlet)
E:~ e- i---."lt Flow R~te
# ~ soil~ ~ Tolucne. ml/min Residu~l Oil~ ~t. % Comrnents
1 285 18.3 1.96 dly soil
2 285 18.3 0 8 soil/toluene sluny
3 285 18.3 0.8 soil/toluene slu~y
4 285 500 1.7 dlv soil
285 500 0.2 soil/toluene slully
6 285 500 = 0.~8 soil/toluene slu~y
Analysis of the oil-contaminated soil shows that the
total amount of oil present in the oil-contaminated soil by
wt. percent is 2.5 - 3.8%. Samples of oily soil weighing
285 grams each were fed by gravity into the top of the
acoustic chamber, either alone (dry) or in a slurry of
toluene. Runs 1 and 4 indicate the amount of oil extracted
from dry soil samples at two different solvent (toluene)
flow rates. These results show that the higher solvent
(toluene) flow rate increased the amount of extracted oil
only slightly.
Runs 2 and 3 are duplicate runs identical to run 1
except that for runs 2 and 3, the sample of oil-
contaminated soil was slurried with toluene. These results
show that slurrying the soil with toluene significantly
increased the amount of oil removed. Run 5 was identical
to runs 2 and 3 except for a higher flow rate of toluene.
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The highe!r solvent (toluene) flow rate resulted in a
residual oil value of only 0.2 wt.% compared to 0.8 wt.%
for the lower toluene flow rates in Runs 2 and 3.
In accordance with another embodiment of the
invention, the present method may be used to remove oil
from oily sludge such as sludge from 2 or 3 separation
phases in heat treaters or oil-based drill cuttings. In
these embodiments, it would not be necessary to crush these
materials, or pass the oil-sludge slurry or oil-based drill
cuttings slurry through a shaker screen.
