U.S. patent number 3,617,472 [Application Number 04/889,449] was granted by the patent office on 1971-11-02 for production of shale oil.
This patent grant is currently assigned to Texaco Inc.. Invention is credited to Dale R. Jesse, Warren G. Schlinger, Joseph P. Tassoney.
United States Patent |
3,617,472 |
Schlinger , et al. |
November 2, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
PRODUCTION OF SHALE OIL
Abstract
Process for recovering shale oil from oil shale by retorting
with synthesis gas, i.e., a mixture of carbon monoxide and
hydrogen, generated by partial combustion of byproduct gas with
oxygen, wherein part of the heat required for retorting is provided
by the hot synthesis gas, and additional hydrogen is produced in
the oil shale retort by the water-gas shift reaction, the shale
acting as a catalyst; and the process being self-sufficient in
requiring no external source of water.
Inventors: |
Schlinger; Warren G. (Pasadena,
CA), Jesse; Dale R. (Hacienda, CA), Tassoney; Joseph
P. (Whittier, CA) |
Assignee: |
Texaco Inc. (New York,
NY)
|
Family
ID: |
25395110 |
Appl.
No.: |
04/889,449 |
Filed: |
December 31, 1969 |
Current U.S.
Class: |
208/414;
208/415 |
Current CPC
Class: |
C10G
1/06 (20130101); C01B 3/36 (20130101) |
Current International
Class: |
C10G
1/06 (20060101); C01B 3/36 (20060101); C01B
3/00 (20060101); C10G 1/00 (20060101); C10b
053/06 () |
Field of
Search: |
;208/11 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
3044948 |
July 1962 |
Eastman et al. |
3051644 |
August 1962 |
Friedman et al. |
3074877 |
January 1963 |
Friedman et al. |
3480082 |
November 1969 |
Gilliland et al. |
|
Primary Examiner: Davis; Curtis R.
Claims
We claim:
1. A process for hydrotorting raw oil shale to produce shale oil
which comprises: generating synthesis gas comprising CO and H.sub.2
by the partial oxidation of byproduct gas from the subject shale
hydrotorting process as defined hereinafter; contacting raw oil
shale with said synthesis gas in a shale retorting zone at a
temperature in the range of about 750.degree. to 1,500.degree. F.
and for a sufficient time to pyrolyze said oil shale thereby
producing a vaporous effluent stream comprising denitrogenated and
desulfurized shale oil vapor, H.sub.2 O, H.sub.2, CO, CO.sub.2, and
CH.sub.4; introducing said vaporous effluent stream into a
separating zone; separately withdrawing from said separating zone
hydrogenated shale oil and uncondensed fuel gases; and supplying at
least a portion of said uncondensed fuel gases to said synthesis
gas generator as feed.
2. The process of claim 1 with the added steps of introducing
H.sub.2 O into said shale retorting zone and withdrawing water from
said separating zone.
3. The process of claim 2 wherein said H.sub.2 O is introduced in
the amount of about 0.01 to 0.6 tons of H.sub.2 O per ton of raw
oil shale treated.
4. The process of claim 1 wherein sufficient synthesis gas is
introduced into said shale retorting zone to provide 1,000 to
20,000 s.c.f. of H.sub.2 +CO per ton of raw oil shale treated.
5. The process of claim 1 wherein said synthesis gas is generated
at a pressure substantially equivalent to the pressure in said
shale retorting zone and is introduced into said shale retorting
zone and is introduced into said shale retorting zone at a
temperature in the range of about 800.degree. to about
1,000.degree. F. and at a pressure in the range of about 300 to
1,000 p.s.i.g.
6. The process of claim 1 wherein said shale retorting zone
comprises a tubular retort, and said raw oil shale is pulverized
and slurried with shale oil.
7. The process of claim 1 with the added step of cooling said
synthesis gas in a quench zone with water obtained from said
separating zone.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for the recovery of oil from
oil shale. In one of its more specific aspects, it relates to an
improved process of hydrotorting oil shale with carbon monoxide and
hydrogen generated by partial oxidation of gaseous byproducts to
produce shale oil of improved quality and yield.
2. Description of the Prior Art
Oil shale consists of compacted sedimentary inorganic rock
particles, generally laminated and partly or entirely encased with
a high molecular weight organic solid material called kerogen,
which is present in the amount of about 6 to 22 wt. percent.
Crude shale oil may be obtained by pyrolysis of raw oil shale.
Thus, raw shale may be subjected to destructive distillation in a
retort at a temperature of about 850.degree. to 950.degree. F. The
chemical decomposition of the kerogen which takes place by the
action of heat along yields crude shale oil vapors, together with
water, gas, and spent shale containing a carbonaceous residue and
mineral matter.
The application of hydrogen to the retorting of oil shale, for
example by the processes of U.S. Pat. No. 3,117,072 and U.S. Pat.
No. 3,224,954 issued to DuBois Eastman and Warren C. Schlinger,
gives increased yields of shale oil of improved quality. Oil shales
usually occur in desert areas where the lack of process water has
traditionally been considered a drawback to development of the oil
shale deposits for recovery of shale oil.
SUMMARY
We have devised a continuous process for retorting raw oil shale,
thereby obtaining near maximum yields of shale oil of reduced
nitrogen and sulfur content, as compared with the Fischer Assay. In
our system, a synthesis gas generator produces a mixed stream
comprising hydrogen and carbon monoxide at a temperature in the
range of about 1,700.degree. -3,000.degree. F. by the partial
oxidation of recycled byproduct gases from the process. At a
temperature in the range of about 750.degree. to 1,500.degree. F.
and a pressure in the range of about 100 to 20,000 p.s.i.g. the raw
oil shale in a shale retort zone is then contacted by the effluent
gas stream from the reaction zone of the synthesis gas generator,
thereby supplying hydrogen and some of the heat for hydrotorting
the raw oil shale. Further, water-gas shift reaction occurs
simultaneously with the hydrotorting in the shale retorting zone.
In such instance, spent shale serves as a shift catalyst so that
some of the CO in the synthesis gas is converted into H.sub.2.
Thus, a gaseous mixture comprising hydrogenated shale oil vapors,
H.sub.2 O, and uncondensed H.sub.2 + carbon oxide gases is produced
by the process. All or a portion of the uncondensed gases may be
then introduced into a gas-purifying zone, where byproduct fuel gas
is removed and is recycled to the gas generator as feed, along with
the unpurified portion of said uncondensed gases and optionally
with a minor amount of makeup fuel gas from an external source.
Addition of H.sub.2 O to the gas generator or to the shale retort
zone or both is optional. However, no external source of water is
required as sufficient H.sub.2 O is produced by the process to
fulfill any process requirements.
THe principal object of this invention is to provide an improved
process for recovery of shale oil from oil shale.
Another object of this invention is to provide a process for
pyrolyzing and hydrogenating raw oil shale to produce an upgraded
shale oil, utilizing hot synthesis gas to provide heat and hydrogen
for the process.
Still another object is to provide a process which is
self-sustaining with respect to process water requirements, wherein
fuel gases produced in the system are reacted with oxygen in the
absence of H.sub.2 O in a synthesis gas generator to produce hot
process gas for recovery of shale oil from oil shale.
A still further object of this invention is to provide a process
for simultaneously retorting oil shale and hydrogenating the shale
oil vapor released to produce increased yields of a shale oil with
a substantially reduced nitrogen and sulfur content.
The accompanying FIGURE illustrates diagrammatically process steps
in the method of this invention.
DESCRIPTION OF THE INVENTION
The present invention pertains to an improved hydrotorting process
in which synthesis gas i.e., gaseous mixture comprising H.sub.2 and
CO is used to recover high quality shale oil from raw oil shale at
greater yields than the Fischer Assay.
The synthesis gas is produced by the partial oxidation of gaseous
byproducts from the subject process in a separate conventional
noncatalytic free-flow synthesis gas generator. A suitable gas
generator for use in the process is described in U.S. Pat. No.
2,582,938 issued to DuBois Eastman. The synthesis gas is produced
in the gas generator at a pressure in the range of about 100 to
3,500 p.s.i.g. and a temperature in the range of about
1,700.degree. to 3,000.degree. F.
Feed gas to the synthesis gas generator consists of a gaseous
mixture substantially comprising the combustible gaseous byproducts
from the subject process, optionally with a relatively minor
quantity of supplemental makeup fuel gas from an external source.
The feed gas mixture comprises mostly CO, H.sub.2, and CO.sub.2 and
relatively smaller amounts of CH.sub.4 and H.sub.2 S. Preferably,
the gaseous feed is introduced into the gas generator at a
temperature in the range of 300.degree. to 750.degree. F. It is
optional to provide water as part of the feed to the generator.
The oxidizing gas which is fed to the synthesis gas generator,
preferably at a temperature in the range of 250.degree. to
350.degree. F., may be selected from the group consisting of
substantially pure oxygen (greater than 95 mole percent 0.sub.2),
and oxygen-enriched air (greater than 21 mole percent of O.sub.2).
Suitably, sufficient free oxygen is introduced into the reaction
zone so that the ratio of atoms of oxygen to atoms of carbon
therein is in the range of about 0.08 to 1.5.
Raw oil shale in the shale retort zone is then contacted with the
aforesaid synthesis gas at a temperature in the range of about
750.degree. to 1500.degree. F., and preferably below 1,000.degree.
F. for example 800.degree. to 950.degree. F., at a pressure in the
range of about 100 to 20,000 p.s.i.g. Preferably, to save on gas
compression costs, the pressure in the synthesis gas generator and
the shale retort zone are substantially the same, less ordinary
pressure drop in the lines. Sufficient synthesis gas is supplied to
the shale retort zone to provide a H.sub.2 +CO consumption in the
range of about 1,000 to 20,000, and preferably about 1,300 s.c.f.
of H.sub.2 +CO per ton of oil shale treated.
The oil shale may be in a dry form when treated or slurried with a
liquid hydrocarbon fuel e.g., shale oil, crude oil. The shale
retort zone may constitute a fixed or fluidized bed of raw oil
shale particles, as described for example in U.S. Pat. No.
3,224,954 issued to Warren G. Schlinger and DuBois Eastman; a
tubular retort, as more fully described in the aforementioned U.S.
Pat. No. 3,117,072; or a fractured subterranean oil shale stratum
as described for example in U.S. Pat. No. 3,084,919 issued to
William L. Slater, thereby effecting pyrolysis and hydrogenation in
situ. A particular advantageous method for retorting the raw oil
shale is described in our coassigned copending application Ser. No.
786,951. Further, the oil shale retort zone may be externally
heated; or substantially all or part of the heat required for
retorting may be supplied by the synthesis gas.
Optionally, the raw oil shale is contacted with H.sub.2 O in the
shale retort zone at the same time that the shale is contacted with
hot synthesis gas. The H.sub.2 O, either in the form of
supplemental liquid water or steam, may be introduced into the
shale retort zone along with the synthesis gas, or the H.sub.2 O
may be separately introduced. Introducing supplemental H.sub.2 O
into the oil shale retort zone was found to have several new and
unobvious results, making it a preferred mode of operation. It was
unexpectedly found that when oil shale is contacted with H.sub.2 O
in the shale retort zone, the endothermic decomposition of
inorganic carbonates in the production of CO.sub.2 is repressed.
This saves hydrogen, as CO.sub.2 would ordinarily react with
H.sub.2 to form H.sub.2 O and CO. Thus by H.sub.2 O addition, there
is a savings of energy in the form of heat ordinarily consumed by
the decomposition of inorganic carbonates; and further, there is a
considerable reduction of hydrogen consumption. Also, the mass
velocity of the gas mixture through the shale retort zone, and the
heat transfer coefficient of the mixture are increased by the
addition of H.sub.2 O. In addition, vaporization and expansion of
water in the oil shale tends to disintegrate the shale particles
and facilitate the atomization of the shale oil. Also, coking of
the shale may be minimized or eliminated at a substantially reduced
hydrogen consumption.
Unobvious advantages for introducing H.sub.2 O underpressure into
the oil shale during hydrotorting of shale slurries in a tubular
retort include: (11 ) greater concentrations of shale may be
incorporated in pumpable oil-shale slurries, and (2 ) clogging of
the retort tubing is prevented. Thus, a portion of the water
produced by our process, at a suitable temperature in the range of
about 100.degree. to 500.degree. F. is preferably recycled to and
introduced into the shale retort zone in an amount of about 0.01 to
0.6 ton of H.sub.2 0 per ton of raw oil shale, and preferably about
0.1 to 0.4 ton of H.sub.2 O per ton of raw oil shale. Both the
synthesis gas and the supplemental H.sub.2 O may be supplied to the
oil shale retort zone, for example, at a pressure of about 25 to
200 p.s.i.g. greater than the system line pressure.
In one embodiment of our invention a portion of the H.sub.2 O
produced by the process may be used to cool the hot effluent gas
from the synthesis gas generator from a temperature of about
2,200.degree. F. to about 1,000.degree. F. by recycling byproduct
H.sub.2 O to a synthesis gas quench zone and quenching the effluent
synthesis gas from the gas generator in the manner shown in U.S.
Pat. No. 3,232,728 issued to Blake Reynolds. One advantage of this
embodiment of the invention is that all of the water required in
the shale retorting step may be picked up by the synthesis gas
vaporizing the quench water during cooling.
It was unexpectedly found that spent shale in the shale reaction
zone acts like a shift catalyst, and that simultaneously with the
hydrotorting in the oil shale reaction zone the CO supplied by the
synthesis gas undergoes an exothermic water-gas shift reaction to
produce additional hydrogen gas and CO.sub.2. Thus the following
additional savings are brought about by our improved process: (1 )
costly pure hydrogen may be replaced by relatively inexpensive
synthesis gas containing H.sub.2 to effect denitrogenation and
desulfurization of shale oil, (2 ) additional H.sub.2 is produced
by the water-gas shift reaction from CO supplied by low cost
synthesis gas, and (3 ) additional heat is released in the tubular
retort during the water-gas shift reaction.
The residence time in the oil shale retort zone must be long enough
to permit pyrolysis and disintegration of the raw oil shale and
hydrogenation of the shale oil vapors. However, excess time in the
shale retort zone may cause coking and result in degraded shale
oil. Thus at the previously mentioned conditions, the preferred
residence time is from about 20 minutes to 5 hours and generally
about 30 minutes in a batch retort or a fixed bed of shale at a
pressure in the range of about 1,000 to 2,500 p.s.i.g. Further, the
residence time is preferably maintained at about one-fourth to 5
minutes in a tubular reactor at a pressure in the range of about
100 to 20,000 p.s.i.g. and preferably in the range of 300 to 1,000
p.s.i.g.
The gaseous effluent stream leaving the reaction zone comprises
vapors of shale oil and water, unreacted hydrogen, NH.sub.3, CO,
CH.sub.4, H.sub.2 S, CO.sub.2, and may contain a small amount of
entrained spent shale particles (about 250 to 350 mesh). When
necessary, the entrained spent shale particles may be separated
from the remaining gaseous stream by means of a conventional
gas-solids separator, or for example a chamber with a downwardly
converging bottom equipped with baffling elements. The hot gaseous
effluent leaving overhead from the reaction zone or the gas-solids
separator is cooled below the dewpoints of the water and the shale
oil. In a gas-liquids separator the shale oil and water are
separated by gravity from each other and from the uncondensed
gases.
Depending on the composition of the synthesis gas to the oil shale
reaction zone, the uncondensed gases withdrawn from the top of the
gas-liquids separator having the following approximate composition
in mole percent dry basis: H.sub.2 45 to 85, H.sub.2 S 0 to 2.0,
CO.sub.2 1.0 to 15.0, NH.sub.3 0.05 to 0.50, CO 3.0 to 30.0, and
CH.sub.4 2.0 to 20.0. This gas may be compressed and recycled to
the synthesis gas generator either alone or in combination with
makeup fuel gas. However, to prevent the build-up of impurities all
or a portion of this gas stream may be first diverted into a gas
purifier. A suitable gas purifier of conventional type utilizing
refrigeration and chemical absorption to effect separation of the
gases, such as described in U.S. Pat. No. 3,001,373 issued to
DuBois Eastman and Warren G. Schlinger may be used. A purified
gaseous mixture, essentially comprising H.sub.2, and CO with a
minor amount of CH.sub.4, is withdrawn from the gas purifier and
recycled as feed to the synthesis gas generator.
In conclusion, by the process of our invention, oil shale is
treated with a hot hydrogen-rich gas, i.e., synthesis gas, and
preferably H.sub.2 O. As previously described, the following
occurs: (1 ) kerogen in oil shale is raised to a high enough
temperature to fracture, (2 ) pyrolysis of the kerogen and
hydrogenation of the shale oil produced, (3 ) the porous structure
of the shale is maintained during retorting to enable cracked
kerogen in the interior to quickly escape before being converted to
polymeric or gaseous products, and (4 ) rapid disintegration of raw
oil shale into minute particles free of carbonaceous matter. In our
process, shale oil, H.sub.2 O, and synthesis gas act as heat
transfer agents by conducting heat to the surface of the shale
particles. The H.sub.2 O also reduces the hydrogen consumption and
heat load for a given yield of shale oil. The hydrogen is able to
permeate into shale matrix so that it is available to properly
terminate the hydrocarbon fractures before coke is formed plugging
the pathway to the surface of the shale particle. By the process of
our invention, the higher boiling hydrocarbons are subjected to
viscosity breaking with substantially immediate hydrogenation of
the molecular fragments and without further breakdown, thereby
materially increasing the production of material boiling in the
400.degree. -700.degree. F. range without substantially increasing
the lower boiling gasoline range materials or forming normally
gaseous hydrocarbons and heavy tars and coke. Thus, the formation
of heavy polymers, unsaturated hydrocarbons and carbonaceous
residues, which characterize known processes, are suppressed.
Evidence of the success of this method can be seen by the unusually
high yield of high quality product shale oil, the production of
sufficient water to satisfy the needs of the process, and by the
finely ground kerogen-free quality of the spent shale. For example,
shale oil yields of about 34.0 gallons and more per ton of raw
shale may be produced by the subject process in comparison with
Fischer Assay shale oil of about 31.0 gallons per ton. This
represents a minimum increase in yield of about 10 percent and
marks an improvement over the yield from contemporary processes.
Also, examination of the hydrotorted shale oil produced shows it to
be of superior quality; that is, compared with Fischer Assay shale
oil from the same shale, the sulfur and nitrogen content are each
about 25 to 35 percent lower. Finally, the self-sustaining features
of the process makes it particularly attractive for use in arid
lands.
EXAMPLE OF THE PREFERRED EMBODIMENT
The following example is offered as a better understanding of the
present invention but the invention is not to be construed as
limited thereto.
In run 1, chunks of Colorado Oil Shale having a maximum
cross-sectional dimension of about 4 inches and having a Fischer
Assay of about 31.2 gallons of shale oil per ton of raw oil shale
and 2.9 gallons of H.sub.2 O per ton of raw oil shale are charged
into a fixed bed vertical oil shale retort 1 foot in diameter by 40
feet long. The retort is charged hourly with 2,000 pounds of oil
shale per batch. The system is purged of air and 10,170 s.c.f.h. of
synthesis gas, to be further described, at a temperature of about
950.degree. F., and 30 gallons per hour of supplemental H.sub.2 O
at a temperature of 900.degree. F. are passed through the oil shale
retort zone maintained at a pressure of about 500 p.s.i.g. The
gaseous effluent stream leaving from the top of the oil shale
retort comprises essentially vaporized hydrogenated kerogen
products, e.g., shale oil, and water, as well as such gases as
CO.sub.2, H.sub.2, CO, H.sub.2 S, NH.sub.3, and CH.sub.4. The
gaseous effluent stream is then cooled below the dewpoint of the
product shale oil and the water, which are thereby liquefied and
separated by gravity in a gas-liquids separator from each other and
from an uncondensed gaseous mixture. To prevent the build-up in the
system of gaseous impurities, the uncondensed gas mixture is
introduced into a conventional gas purifier.
A continuous stream of about 938 s.c.f.h. of noncombustible off-gas
from the gas purifier is discharged from the system, while the
remaining purified gas is introduced into the top of the synthesis
gas generator. This fuel gas mixture comprises in mole percent dry
Basis: H.sub.2 57.3, CO 38.2, CO.sub.2 0.0, CH.sub.4 3.5, H.sub.2 S
0.0, and N.sub.2 1.0. Further, about 550 s.c.f.h. of makeup gas
from an external source having the following composition is also
fed to the synthesis gas generator: CH.sub.4 95.1, C.sub.2 H.sub.6
2.0, and CO.sub.2 2.9.
About 71 lbs./hr. of 95+ mole percent of oxygen at a temperature of
about 300.degree. F. are fed to the reaction zone of the synthesis
gas generator. In this example, the synthesis gas generator
operates without the addition of supplemental H.sub.2 O. About
10,170 s.c.f.h. of synthesis gas is produced in the reaction zone
of the generator at a temperature of about 2,200.degree. F. and a
pressure of about 550 p.s.i.g. The synthesis gas has the following
composition (mole percent dry basis):
H.sub.2 58.5, co 38.2, co.sub.2 2.4, n.sub.2 0.8 and Ch.sub.4 0.1.
The synthesis gas is cooled in a waste heat boiler to a temperature
of about 950.degree. F. and is introduced into the shale retort
zone, as previously mentioned.
For comparative purposes, run 2 was made under the same conditions
as run 1 but with no supplemental H.sub.2 O being introduced into
the shale retort zone.
A summary of the operating conditions and the products recovered
for runs 1 and 2 are shown in table I along with, for comparison,
shale oil produced by the Fischer Assay. ##SPC1##
By a comparison of the results in table I, it may be shown that in
run 1 with supplemental H.sub.2 O being introduced into the shale
reaction zone the consumption of hydrogen (as supplied by the
synthesis gas) is less than in run 2 where no H.sub.2 O is added.
However, the water yield for run 1 is less than that for run 2.
This supports the theory that water injection into the shale retort
inhibits the undesirable decomposition of shale carbonate, which
reaction absorbs heat and liberates CO.sub.2 that reacts with
hydrogen to form water.
The results clearly show that compared with the Fischer Assay
(column 3 , superior yields of product shale oil are obtained from
runs 1 and 2 and the quality of the shale oil is improved. Further,
adding supplemental H.sub.2 O to the shale retort zone, as in run
1, is preferred.
The process of the invention has been described generally and by
examples with reference to oil shale and gas mixtures of particular
compositions for purposes of clarity and illustration only. It will
be apparent to those skilled in the art from the foregoing that
various modifications of the process and materials disclosed herein
can be made without departure from the spirit of the invention.
* * * * *