Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention relates to the treatment of hydro-
carbon oils and, more particularly, to the hydrocracking
; of heavy hydrocarbon oils to produce improved products of
lower boiling range.
Hydrocracking processes for the conversion of
heavy hydrocarbon oils to light and intermediate naphthas
of good quality for reforming feed stock~, fuel oil and
gas oil are well known. These heavy hydrocarbon oils can be such mat-
erials as petroleum crude oil, atmospheric tar bottoms
products, vaccuum tar bottoms products, heavy cycle oils,
shale oils, coal-derived liquids, crude oil residuum, top-
ped crude oils and heavy bituminous oils extracted from
tar sands. Of particular interest are the oils extracted
from tar sands and which contain wide boiling range mat-
erials from naphthas through kerosene, gas oil, pitch,
etc. and which contain a large portion of material
boiling above 524C. These heavy hydrocarbon oils contain
nitrogen and sulfur compounds in extremely large
quantities and often contain excessive quantities of
organo-metallic contaminants which tend to be detrimental
to various catalytic processes which may subsequently
be carried out, such as hydrofining. Of the metallic
contaminants those containing nickel and vanadium are
most common, although other metals are often present.
These metallic contaminants, as well as others, are
usually present within the bituminous material as organo-'
metallic compounds of relatively high molecular weight.
A considerable quantity of the organo-metallic complexes
are linked with asphaltenic material and contains sulphur.
As the reserves of conventional crude oils
decline, the heavy oils must be upgraded to meet the
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demands. In this upgrading, the heavier material is con-
verted to lighter fractions and most of the sulphur,
nitrogen and metals must be removed. This is usually
done by means of coking or hydrocracking processes. The
coking processes involve removal of carbon resulting in
20~ by weight or more material as coke. This material
referred to as "coke" is a carbonaceous material which
may contain insoluble organic material, mineral matter,
metals, sulphur, quinoline and benzene soluble organic
materials. The content of these other materials means
that the coke cannot be used as a fuel and this represents
an excessive waste of resources.
Various special procedures have been developed in
an effort to prevent the formation of coke within the
hydrocracking zone as well as the deposition of coke on
the surface of any catalyst used and on the interior walls
of the hydrocracking chamber itself. A second particularly
troublesome area in terms of coke deposits is the down-
stream liquid-gas hot separator. For instance, U.S. Patent
3,842,122, issued October 15, 1974, describes a procedure
in which the conditions in the liquid-gas hot separator
are very carefully controlled in terms of temperatures
and superficial liquid velocities to prevent coking within
the separator. They found these conditions to be critical
and also found that increase in pressure did not prevent
the formation of coke within the separator. Of course, it
becomes a major added expense if the hot separator must
be operated at conditions different from that of the
hydrocracking zone.
3~ U.S. Patent 3,841,981, iss~ed October 15, 1974,
describes another procedure aimed at preventing formation
of coke in the separator and avoiding phase separation of
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the liquid in the separator. In that case, the effluent
from the hydrocracking zone was quenched with a quench
oil so as to lower the temperature of the effluent before
it entered into the gas-liquid separator.
Yet another method of preventing fouling is des-
cribed in U.S. Patent 3,544,477, issued December 1, 1970,
which involves reducing the pressure of a high boiling
hydrocarbon liquid stream obtained from a hydrocracking
process and immediately contacting this liquid stream
with a cool liquid hydrocarbon stream , this pressure
reduction and quenching being aimed at substantially!re-
ducing the polymerization of polymerizable constituents.
It is the object of the present invention to pro-
vide a method of operating a liquid-gas separator down-
stream of a hydrocracking zone such that fouling will
be substantially eliminated while avoiding the need of
going to the complex additional equipment and procedures
as outlined in the prior systems.
SUMMARY OF THE INVENTION
This invention relates to a hydrocracking process
in which a heavy hydrocarbon oil feed is treated with
hydrogen in a reaction zone under conditions of high
pressure of about 500 to 3,500 psig. and high temperatures
of about 400 - 490C., resulting in a mixed effluent
containing a high boiling hydrocarbon liquid component
at the above pressures and temperatures and a gaseous
component. This mixed effluent is passed into a sep-
aration zone maintained substantially at the pressure of
the hydrocracking zone whereby the mixed effluent is
separated into a gaseous phase comprising hydrogen and
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vaporous hydrocarbons and a liquid phase comprising
heavy hydrocarbons. The gaseous phase is removed from
an outlet in an upper region of the separation zone and
the liquid phase is removed through an outlet in a lower
region of the separation zone. According to the novel
feature of this invention, a minimum liquid level is
maintained in the separation zone sufficient to maintain
a liquid seal in the liquid phase outlet and the mixed
effluent from the hydrocracking zone is introduced intc
the separation zone below the liquid level therein.
This has been found to provide an excellent mixing
action in the liquid phase in the bottom of the separation
zone including mixing of the hydrogen in the effluent
stream with the heavy hydrocarbon liquid and stripping
most of the light hydrocarbons from the heavy hydrocarbon
li~uid. This procedure has been found to be very effective
in reducing settling of mineral matter contained in the
effluent, preventing phase separation of the heavy
hydrocarbon liquid, reducing hydrogen starvation thereby
preventing polymerization and coking of the heavy hydro-
carbon liquid and substantially eliminating sludge form-
ation within the separator and plugging of the heavy
hydrocarbon liquid outlet.
The effluent stream from the hydrocracking zone
must, of course, be introduced into the liquid in the hot
separator so as to provide as uniform distribution as
possible through the liquid phase. Thus, the number and
spacing of effluent discharge out~ets depend on the size
of the separator vessel. Also, the necessary minimum
liquid level and the distance of the effluent discharge
outlets below the liquid level vary widely depending on
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the design of the separator vessel and the process
conditions. The optimum separator conditions for each
particular separator design and hydrocracking process
can be easily determined by routine procedure.
The process of this invention is particularly
well suited for the treatment of heavy oils having a
large proportion, preferably at least 50% by volume, which
boils above 524C. The hydrocracking can be operated at
quite moderate pressure in the range of 500-3,500 psig.,
preferably 500-2,500 psig., most preferably 1000-2000
psig, without coke formation in the hydrocracking zone.
The hydrocracking temperature can be in the range of
400 to 490C., with 430 to 470C. being particularly
preferred. The hot separator can be operated over a
wide temperature range of from 150 to 500C.
The process according to this invention can be
carried out with advantage in a variety of known reaction
systems. For instance, it is useful with either non-
catalytic or ~atalytic hydrocracking systems, using fixed
bed or slurry-type reactors. Moreover, it is advantageous
when used with once-through systems without recycle of
heavy hydrocarbon liquid as well with systems which include
heavy hydrocarbon liquid recycle. It is particularly well
suited to an up-flow tubular reactor, with the effluent
from the top of the reactor passing into the hot separator
maintained near the temperature of the hydrocracking zone.
~ or best results the heavy hydrocarbon from the
hot separator is recycled back into the frec;h fe-d to the
hydrocracking zone in a volume ratio of recycle to fresh
feed of at least 2:1. It is also preferred that the
combined recycle and fresh fee~ flow be at a rate such that the
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superficial liquid upflow velocity in the hydrocracking
zone is at least 0.25 cm./sec. The liquid houriy space
velocity is preferably in the range of 0.5 to 4Ø
It has also been found that the system does not
require a high hydrogen recirculation to avoid coking.
Thus, a hydrogen recirculation of about 2,000 to 10,000
scf per bbl of feed stock can be used.
The gaseous stream from the hot separator is
preferably passed to a cold seParator maintained at about
25C. The non-condensable gases from the cold separator
are passed through a water scrubber to remove ammonium
sulphide and then through an oil scrubber to
remove ~2S and light hydrocarbons. The effluent gas
from the oil scrubber, rich in hydrogen, together with
makeup hydrogen is recycled to the hydrocracking zone
where it is combined with the feedstock, including re-
cycled heavy hydrocarbons from the hot separator . The
liquid stream from the cold separator represents the
light hydrocarbon oil product of the present invention
and can be sent for secondary treatment.
For a better understanding of the invention,
reference is ~ade to the accompanying drawings which
illustrate diagrammatically preferred embodiments of
the present invention. In the drawings:
Figure 1 is a schematic flow sheet of a hydro-
cracking process;
Figure 2 is a schematic illustration of a liquid-
gas separator; and
Figure 3 is a further illustration of a liquid-
gas separator.
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Heavy hydrocarbon oil feed 10 is pumped via feed
pump 11 through inlet line ~2 and preheater 40 into
the bottom of an empty tower 15. Recycled gases and
makeup hydrogen from line 13 are simultaneously fed into
tower 15 through line 12 along with recycle heavy hydro-
carbon liquid through line 14. A liquid-gas mixture is
withdrawn from the top of tower 15 through line 16 and
introduced into the bottom of hot separator 17. In the
hot separator, the effluent from tower 15 is separated
into a gaseous stream 22 and a liquid stream 18. The
liquid stream 18 is in the form of a heavy hydrocarbon
oil containing pitch and a portion of this stream 18 is
recycled through pump 19 and line 14 into inlet line 12
upstream or downstream of preheater 44 The balance of
liquid stream 18 exits via line 20 and is withdrawn via
pump 21 for collection. The pump 21 may be replaced in a
commercial operation by let-down valves.
The ga~eous stream from hot separator 17 is
carried by line 22 into a cold separator 23. Within
this vessel the product is separated into a gaseous
stream rich in hydrogen which is drawn off through line
26 and an oil product which is drawn off through line 24
and collected in receiver 25. This represents the light
oil product of the invention.
The hydrogen rich stream 26 is passed through
a water scrubher 27 to remove dmmonium sulphide
and the stream 28 from the water scrubber is passed
through a packed tower 29 where it is scrubbed
by means of organic liquid 32 which is cycled
through the tower by means of pump 31 and recyc~e loop 30.
The scrubbed hydroyen rich stream emerges from the scrubber
via line 33 and is combined with fresh make up hydrogen
added through line 34 and recycled by 1ine 35, through
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gas pump 36, orifice 37 and line 13 back to tower 15.
The hot separator 17 is shown in greater detail
in Figures 2 and 3. It includes a main cylindrical
portion 40 with a truncated conical lower portion 41
merging into a liquid phase outlet pipe 18. A gaseous
phase outlet pipe 22 is provided at the top of the sep-
arator.
The liquid phase is maintained with a liquid
level 42 and this is kept at a minimum sufficient to
achieve a liquid seal into the pipe 18 while minimizing
the residence time of the liquid within the separator.
As shown in Figure 2, the effluent from the hydrocracking
zone is introduced into the separator by way of pipe 16
which is brought directly down through the cylindrical
portion 40 below the liquid level 42. This pipe 16
terminates in a distributor 43 which uniformly distri-
butes the effluent into the liquid.
An alternative embodiment is shown in Figure 3
in which the pipe 16 is introduced through the sidewall
at a point below the liquid level 42, again connecting
to a distributor 43 for uniformly distributing the
effluent within the liquid phase.
Certain preferred embodiments of the invention
will now be further illustrated by the following non-
limitative examples.
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Example 1
The charge stock employed was an ~thabasca
bitumen having the ~ollowing propertles:
Specific gravity, 60/60F1.010
Sulphur, wt. % 4.73
. Ash, wt. % 0.56
Viscosity, cst at 210F 175.8
Conradson Carbon Residue, wt.% 13.7
Pentane Insolubles, wt. %15.6
10 Benzene Insolubles, wt % 0 57
Nickel, ppm 68
Vanadium, ppm 211
The above feed stock was passed through the
reaction sequence shown in the attached drawing using
two different operating conditions as follows:
, .._ _
Run Number R-2-1-2 R-2-2-4
, .__ . .. _
Duration, h 477 283
Pressure MPa 13.89 13.89
Gas Flow, g mol/kg of feed51.56 51.56
H2 Purity, vol. % 85 85
LHSV, 1.0 1.0
Reactor Temp. C. 4'0 460
l~ot Separator Temp. C., 450 450
2l Actual Feed Flow, q/ll 4535 ~554
Recycle Oil Flow , g/h 9060 12700
Recycle/Actual Feed Ratio ~ 2.8
There were no operational problems encountered
during these runs. After completion of the runs, the
pilot plant was dismantled and inspected for coke de-
position or any type of contamination. No major foulinq
of the hot separator was observed.
The yields and properties of the heavy hydrocarbon
liquid withdrawn from the hot separator were as follows:
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TABLE 3
Reactor Temperature 450C 460 C
Run Number R-2-1-2 R-2-2-4
_
Yield on feed, wt. % 20.74 16.43
Yield on total liquid 22.95 18.33
product, wt. %
Specific gravity, 1.095 1.129
S. wt. ~ 3.6~ 3.59
N, ppm 8916 availahle
Ni, ppm 241 361
V, ppm 755 1041
Ash, wt. % 2.67 3.53
Conradson Carbon residue, wt.~ 30.14 36.52
Pentane-insoluble, wt. % 30.62 38.15
Benzene-insoluble, wt. % 10.82 14.95
Distillate, (-524C), wt. %55.6 54.2
Distillate, sp. gr. 0.990 1.004
Pit~h (+524C), wt.% 44.4 45.8
. . . .
Example 2
In order to demonstrate the effects of the liquid
velocities in the hot separator, parallel tests were run
with and without recycle of heavy hydrocarbon liquid from
the hot separator. The results are shown in the following
table.
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TABLE 4
Run Number A-450 B-450 A-460 B-460
. _ . .. . ._. .
Reactor temp. C. 450 450460 460
Average liquid flow, g/h 219211261 1955 14906
Recycle oil withdrawal_ 976 _ 748
rate, g/h
Superficial liquid velocity O. 053 0.274 0.048 0.360
in the reactor, cm/~ec.
Superficial average1.54 0.301.53 0.23
residence time for
the firs t pass, h .
10 Total residence time for _ 3.8 _ 5.4
the recycle oil, h.
Liquid velocity in0.059 0.244 0.037 0.330
the separator, cm/sec.
__ ..
No major fouling of the hotseparatorwas observed
during the above runs.
Example 3
(a) Hydrogenation reactions were carried out using the same
pilot plant as in Example 1, with the same feedstock and the
same reaction condition except a hot separator temperature
of only 350C. The reactions were carried out both with
and without a dip tube to introduce the mixed effluent
below the liquid level in the separator and the results
were compared.
After a running time of only 2 hours without dip
tube being used, the bottom core and outlet line of the
hot separator had become completely plugged. On the other
hand, after a running time of 16 days using the dip tube,
the system was still operational. Total deposits of about
6600 g. had formed in the total system, mostly within the
hydrocracking reactor. Only small amounts of deposit
had formed within the hot separator, mainly on the walls
of the separator and the separator bottom. E~owever, these
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separator deposits were not sufficient to interfere with
its operaticn.
(b) Because of the substantial deposits in the
hydrocracking reactor, further tests were carried out
under the same conditions as part (a) above using both a
dip tube in the hot separator and a coal getter in the
oil feed to the hydrocracking reactor. The coal getter
was utilized as described in copending Canadian application
Serial no. 269,020 filed December 31, 1976.
In one test with the coal getter and dip tube, only
132 g. of total deposits in the system had accumulated
after 21 days of operation. In another test a total
of 940 g. of deposits had accumulated after 3 days.
However, in both of these tests substantially all of the
deposits were in the reactor and the hot separator was
substantially free of any deposits.
Thus, it will be seen that the method of operating
the hot separator according to this invention is highly
effective in eliminating the problem of coke deposits in
the hot separator regardless of the conditions in the
hydrocracking reactor.
