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Патент USA US3028342

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April 3, 1962
3,028,332
H. FORBES ETAL
LIQUID RECOVERY FROM AN ORIGINALLY VAPOROUS MIXTURE
Filed June 15, 1959
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1
INVENTORS:
GODFRIED J.VAN DEN BERG
HENRY FORBES
HUBRECHT VAN DER MAREL
THEIR ATTORNEY
3,028,332
S?ltes Patent
Patented Apr. 3, 1962
1
2
3,028,332
tially separated or a fraction from that liquid obtained
VAPOROUS MIXTURE
Henry Forbes, Huhrecht van der Marc], and Godfried
The conjoint liberation of the relatively light compo
nents from the pressurized gaseous and liquid portions
may, for instance, be brought about by treating the two
portions together (premix or otherwise) in a distillation
column with the light components being removed over,
head. In this instance the gaseous portion may, if de
LIQUID RECOVERY FROM AN ORIGINALLY
J. van den Berg, The Hague, Netherlands, assignors to
Shell 0i] Company, New York, N.Y., a corporation of
Delaware
7
Filed June 15, 1959, §er. No. 820,517
Claims priority, application Netherlands Oct. 7, 1958
9 Claims. (Cl. 208-340)
This invention provides an improvement in the process
say in a later distillation.
sired, be introduced into the distillation column on a tray
10 which is higher than the one on which the liquid portion
is introduced. It is, however, often advisable to mix the
two pressurized portions and then to liberate the light
involving pressurization of an originally vaporous hydro
components therefrom by subsequent cooling of the re
carbon mixture, containing normally gaseous components,
sultant mixture to promote condensation, after which
to recover further liquid therefrom, which improvement
permits a signi?cant reduction in the total compression 15 the mixture is passed to a separator wherein it is sepa
rated into gas and liquid. The separated liquid is prefer
work required for the operation.
It is conventional practice in the processing of a va
ably further treated in a distillation to remove additional
porous hydrocarbon stream, containing normally gaseous
light components therefrom, yielding a heavy liquid frac
components, to pressurize the stream to increase liquid
tion which may be combined with the original vaporous
recovery therefrom.
The stream may be ?rst cooled to 20 mixture, or it may be deemed more feasible to pass the
bring about a condensation, following which the stream
is separated into a gaseous portion and a liquid portion.
The individual portions are then separately pressurized
heavy liquid fraction to another fractionation to obtain
to substantially the same elevated pressure and then re
vaporous hydrocarbon stream undergoing treatment at a
a still more heavier material for the recycling.
Preferably, the recycled liquid portion is added to the
combined for further processing. There is an economic 25 point preceding the cooling of that stream, although it
may be combined with the cooled stream before its sep
advantage in separately pressurizing the two portions.
aration into its vaporous and liquid portion and prior to
Processing schemes of this general nature are used in
their separate pressurizations.
re?nery gas recovery and for gasoline stabilization in
The vaporous stream undergoing treatment may be the
some instances. A process of this general type is described
in Petroleum Re?ner, page 232, September 1949.
It is an object of the invention to provide an improve
ment in the process of pressurizing an original vaporous
top product of a primary distillation operated at approxi~
mately atmospheric pressure. The feed to the primary
distillation column may, for instance, be a hydrocarbon
mixture relatively rich in light components (such as hydro
hydrocarbon mixture and more particularly to provide an
gen and methane) which is therefore di?icult to con
improved process reducing the amount of work required
in pressurization. This and other objects will become 35 dense; such hydrocarbon mixtures include the effluent
from a reforming unit or from a hydrodesulfurization
more apparent in the following description of the process,
treatment.
taken in conjunction with the drawing which is a sche
In a preferred embodiment of the process the top prod
matic representation of a preferred embodiment of the
uct will be a gasoline range material containing lighter
improved process.
It has now been discovered that in the processing of a 40 components from an atmospheric primary distillation.
This top product prior to cooling is combined with a re
vaporous hydrocarbon stream, containing normally gas
cycle heavy gasoline (naphtha), then cooled and passed
eous components, to increase the liquid recovery there
to a separator maintained say at 1.1 atmospheres and
from, that it is advantageous to recycle a portion of the
around 45° C. There the liquid and gas phases separate
recovered liquid to the vaporous hydrocarbon stream un
and are separately removed, pressurized and subsequently
dergoing treatment. In the improved process the stream
recombined, passed to a second cooler to obtain further
is cooled to bring about a condensation, following which
condensation, and then to a second separator maintained
it is separated into a gaseous portion and a liquid portion
at say, 5 atmospheres and 40° C. A gaseous stream con
and the individual portions are then separately pressurized
taining principally non-condensibles is removed from this
to substantially the same elevated pressure. Following
latter separator. The liquid recovered in this second
50
pressurization, light components are conjointly liberated
separator is moved to a secondary distillation (a dc
from the two pressurized portions to obtain a liquid frac
butanizer) where the butane and remaining lighter com
tion. A portion of this liquid fraction is returned to the
ponents are distilled overhead. This column may operate
vaporous hydrocarbon stream at a point preceding its
at around 12 atmospheres. The liquid gasoline product
separation into the gaseous and liquid portions. The re
from
the base of the debutanizer goes to a fractionation
55
cycling of the portion of the recovered liquid in this man
column where it is separated into a top product boiling
ner will signi?cantly reduce the total compression work
below say 93° C. and a bottom product having the boil
required for the pressurization of the two separate por
ing range of approximately 93° C. to 165° C. A por
tion of this bottom product is now recycled according to
tions.
The term pressurizing and the like is employed to mean 60 the invention to combine with the top product from the
raising the pressure to which the vaporous mixture is
primary distillation column at a point preferably preced
under in the initial stage of the process which original
ing its initial partial condensation. As a result of the
pressure may be atmospheric, superatmospheric, or sub
recycle the compression work to be exerted on the liquid
atmospheric. The recycled or returned portion of the
portion is admittedly slightly increased, but that on the
recovered liquid may be a portion of the ?rst liquid ini 65 gaseous portion is greatly reduced. Since from an eco
8,028,332
3
nornic point of view it is much more attractive to pres
surize a liquid instead of a gas, the practice of the process
of the invention results in a considerable reduction of the
4
system. The liquid separating out in the accumulator 24
is removed via line 27 and is forced under the pressure
of a pump 28 to a central section of a secondary distilla
tion column 29 where it is separated into a butane-free
gasoline and an overhead fraction containing butane and
the two portions.
lower boiling components. The secondary distillation
When it is desired to change the cutting point in the
column operates under a pressure of approximately 12
primary column (for instance, when a change is necessary
atmospheres. The heat needed for the column is sup
to the preparation of a product answering di?erent speci
plied by a reboiler 30. The butane-free gasoline bottom
?cations), the quantity of the recycled liquid fraction
which is combined with the primary top product should 10 product is removed from the column in a line 31 to a
fractionation column 32 where it is separated into a light
be accordingly varied to hold the gas-compression work
gasoline discharge overhead through a line 33 and into a
substantially constant, thus permitting the gas compressor
total compression work required in the pressurization of
heavy gasoline (naphtha) which is withdrawn through a
to operate (with changes in the primary distillation cutting
line 34. A reboiler 35 supplies the heat required for the
points) at a capacity approaching the optimum. For
instance, if the cutting point in the primary column is 15 operation of this column.
The top product of the second distillation column 29
varied to take overhead a larger proportion of heavier
is withdrawn through a line 37, cooled in a cooler 38 and
material, the amount of recycle required will be less. It
is recommended that the amount of recycle material em—
collected in an accumulator 39.
The accumulator is
operated under a pressure of 12 atmospheres absolute
ployed be such that the total quantity of debutanized
gasoline removed from the secondary distillation column 20 and at a temperature of approximately 45 ° C. A portion
of the liquid collecting in the accumulator is returned via
remains substantially constant with variations in the cut
a line 40 as re?ux to the top of the second distillation
ting point of the primary column. In the instance where
column. The rest of the liquid is removed from the
the debutanized gasoline is passed to a subsequent frac
accumulator in a line 41 and forced under the pressure
tionation where it is separated into a light gasoline and
a heavy gasoline product, and a portion of the heavy 25 of a pump 42 to the central section of a distillation col
umn 43. In the latter column the material is separated
gasoline is used as the recycle material, the quantity of
into C; hydrocarbons on the one hand and lower boiling
the recycle and the quantity of heavy gasoline actually
components on the other. The C4 fractions are dis
withdrawn as product should give a total that remains
charged from the column through a bottom line 45 and
substantially constant at di?erent primary cutting points.
This practice will result, it will be seen, in the amount of 30 the top product is removed via an overhead line 46, to
a cooler 47 and an accumulator 48. In the accumulator
debutanized gasoline being maintained at substantially
a liquid substantially consisting of propane separates
constant volume.
which is withdrawn through a line 49 and partially re
The invention will now‘be further explained with refer
turned through a line 50 as re?ux to the distillation
ence to the accompanying drawing, which relates to the
use of the process of the invention in working up a hydro 35 column 43. The pressure in the distillation column 43
and the accumulator 48 is approximately 24 atmospheres
carbon oil having a relatively high content of normally
absolute. The temperature in the accumulator is about
gaseous components. The term gases as used herein
45° C.
includes vapors. The hydrocarbon stream is introduced
The uncondensed gases gathering in the accumulators
through a line 10 to an atmospheric primary distillation
column '12 which is operated with a cutting point at 40 39 and 48 are discharged through the lines 52 and 53,
respectively, which are provided with the necessary re
165° C. to separate overhead a light fraction containing
ducing valves.
.gasoline and lighter components and a heavier bottom
According to the present invention, a portion of the
fraction composed of kerosene and gas oil. The heavy
fraction is removed from the distillation column through
a line 14. In the present instance circulating re?ux is
‘supplied to the column via a line 60 opening into the top
naphtha fraction withdrawn through the line 34 is recycled
via a line 55 to the top product line 13 at a point preced
ing the cooler 15. The recycled naphtha may be mixed
with the top ‘product beyond the cooler 15 at a point pre
ceding the gas compressor and pump, although it is pref
erably combined with the top product stream before the
‘the column through a line 13 to a partial condenser 15
and then to an accumulator 16. The accumulator is 60 ‘cooler.
EXAMPLE
operated under a pressure of 1.1 atmospheres absolute
with a temperature of approximately 45° C. In the
A crude oil is separated by distillation into a fraction
cooler 15 there occurs only a partial condensation, with
boiling below 350° C. and a fraction boiling above 350°
the result that a partly gaseous and partly liquid product
C. The former fraction is subjected to a hydrodesulfuri
is collected in the accumulator. A liquid product is 55 zation treatment in which a cobalt oxide-molybdenum
removed from the bottom of the accumulator through a
oxide-alumina catalyst is used. After cooling the reac
line 17, while the gaseous product is led through a line 18
tion product is subjected to an expansion in stages to
‘to a gas compressor 19. The liquid ?owing in line 17 is
separate the bulk of the dissolved gases and vapors.
compressed by a pump 21 to substantially the same pres
The liquid ?nally obtained (486 tons per 1000 tons of
‘sure as the pressurized gas leaving the compressor 19 in
crude oil), in which small quantities of light components
line 20. The two pressurized streams combine in a line
such as hydrogen, hydrogen sul?de and normally gaseous
22 which opens into a cooler 23. From the cooler the
hydrocarbons are still dissolved, is then separated by dis
of the column. Conventional re?uxing may be-employed.
The light overhead fraction is removed from the top of
‘combined stream passes to an accumulator 2.4 which op
tillation into a number of fractions with the use of the
erates at a pressure of approximately 5 atmospheres and
Ya temperature of say 40° C. In ‘the accumulator a partly
plant shown in the above-described accompanying
drawing.
In the primary column 12 (for which circulating re
?ux is exclusively used again) a bottom product boil
ing above 165° C. is obtained at about atmospheric
distillation column 12 is impossible even at this relatively
pressure (1.1 atm. abs); the feed components boiling be
‘high pressure of 5 atmospheres and relatively low tem
70 low this temperature pass overhead as primary top prod
perature, because of the relatively high content of low
uct (184.15 tons per 1000 tons of crude oil) and are led
boiling components in the feed to the primary distilla
through the line 13 and the cooler 15, where they are
tion column 12. The uncondensed gases gathering in the
cooled to 45° C., into the accumulator 16 where the
head space of the accumulator 24 are discharged through
a line 25 and a pressure, reducing valve 26 from, the 75 pressure is 1.1 atm. abs.
gaseous and a partly liquid product is again collected.
Complete condensation of the top product of the primary
3,028,332
5
6
The liquid and the vapor are pumped, as shown in the
drawing, to the accumulator 23 where the pressure is 5
atm. abs. The temperature in this vessel is 40° C. The
point of 165° C., the quantity of gas to be compressed
is not more than about 34.7 tons per 1000 tons of crude
oil, i.e., a quantity only slightly greater than the quan
tity to be compressed at a cutting point of 185° C.; the
di?erence in compressor load at the two ?nal boiling
points is now not more than 2.5%. Recycling thus makes
it possible to use the same (relatively small) compressor
even though the cutting point in the primary column is
liquid collecting in the accumulator is removed and then
separated in the secondary distillation column 29 at an
elevated pressure into butane-free gasoline on the one
hand and butane+lighter components on the other. The
top product is obtained with the use of a conventional
re?ux system, as indicated in the drawing. The pressure
altered, thereby improving the operational economy and
and temperature, in the re?ux accumulator 39 are 12 atm. 10 also the ?exibility of the plant.
In this case the recycled quantity~ of the bottom prod
uct of the fractionation column 32 is equal to the differ
separated in the column 43 into a bottom product con
ence between the quantity of the bottom product (of col
umn 32) at a primary distillation cutting point of 185'
sisting of butanes, and into a more volatile top product.
The top product is again obtained with the use of a con 15 C. (145.4 tons per 1000 tons of crude oil) and the
quantity of bottom product at a primary cutting point
ventional re?ux system, the pressure and the temperature
in the re?ux accumulator 48 being 24 atm. abs. and 45°
of 165° C. (118.2 tons per 1000 tons of crude oil),
there being no recycling in the latter case. In other
C. respectively. The condensed top product consists sub
stantially of propane and is withdrawn through the line
words, care is taken to ensure that the total quantity
49.
20 of bottom product (viz. the quantity to be recycled plus
the quantity immediately withdrawn) is substantially con
Gases not condensed in the re?ux accumulators 24,
stant at the different primary cutting points.
39 and 48 are discharged through the lines 25, 52 and
We claim as our invention:
53. The bottom product of the column 29 is separated
1. In the processing of a vaporous hydrocarbon stream
in the column 32 into a top product boiling below 93°
C. and a bottom product boiling between 93° C. and 25 containing normally gaseous components to increase the
165° C. which is withdrawn through the line 34. Part
liquid recovery therefrom, wherein the stream is cooled
of this bottom product (27.2 tons per 1000 tons of crude
to effect a condensation, following which the stream is
separated into a gaseous portion and a liquid portion and
oil) is now recycled according to the invention through
the individual portions are separately pressurized to sub
the line 55, as a result of which the work to be done by
the gas compressor 19 is considerably decreased. This is 30 stantially the same elevated pressure, the improvement
comprising conjointly liberating light components from the
shown in the table.
abs. and 45° C. respectively.
The partly lique?ed top product of the column 29 is
two pressurized portions to obtain therefrom as one new
Table
Top Product Top Product Quantities of Gases and
Primary
Primary Vapors to be Compressed
Distillation Distillation .
by Compressor 19
Column 12 Column 12
Cutting Point In
Distillation In
185° C.
165° C.
185° C. 165° C. 165° C.
Column 12
Recycling 1 ________________________________ __
Quantitieszl
H2 ____________ ..
None
None
27.2
portion a liquid fraction recovered by fractional distilla
tion and returning a portion of said liquid fraction to the
35 hydrocarbon stream at a point preceding its separation
into the gaseous and liquid portions, thereby signi?cantly
reducing the total compression work required for the pres
surizations of the two separated portions.
2. A process in accordance with claim 1 wherein said
40 returned portion comprises a vfurther heavy ‘fraction ob
tained from said liquid fraction.
3. A process in accordance with claim 1 wherein the
returned portion of the liquid fraction is combined with
0.005
.
0. 005
0.33
0.005
0. 326
0.005
0.326
0.005
0.326
1. 79
2. 25
6.93
17. 18
155. 67
1.673
2.007
5. 532
9. 958
14. 158
1. 69B
2.11
5. 776
10. 891
16.257
1. 670
2. 075
5. 515
9. 909
15. 160
184. 155
33. 729
37. 062
34. 660
1 In tons per 1000 tons of crude oil.
the vaporous hydrocarbon stream at a point preceding
45 the cooling of said stream.
4. A process in accordance with claim 1 wherein a ?rst
liberation of light components is effected by ( 1) mixing
the two pressurized portions, (2) cooling the resulting
mixture, and (3) thereafter separating said light compo
50 nents from the cooled mixture.
5. A process in accordance with claim 4 wherein the
liquid separated ‘from the light components in step (3)
of that claim is subsequently distilled at a still more ele
The second data column of the table shows the quan
tity of top product supplied by the primary distillation
column 12 at the said ?nal boiling point of 165° C. The
last two data columns of the table show the quantities
of gas from this top product which are to be compressed
vated pressure to separate vfurther light components there
55 from to provide a heavy liquid fraction, a portion of
which is returned to the process at a point preceding the
initial separation of the hydrocarbon stream.
6. A process in accordance with claim 5 wherein the
heavy liquid fraction of that claim is subjected to a still
the line 55 of a quantity of the bottom product from the 60 further distillation to separate another heavy liquid frac
column 32 (27.2 tons per 1000 tons of crude oil). For
tion which is recycled in part to the process at a point
the purpose of comparison the ?rst data column of the
preceding the initial separation of the hydrocarbon stream.
table shows the quantity of the top product from the pri
7. A process in accordance with claim 4 ‘wherein the
mary distillation column 12 formed when the cutting
vaporous stream undergoing treatment is a reformed
point in this distillation column is 185 ° C.; the third col
naphtha and the light component separated in step (3)
umn shows the quantities of gas which are to be com
of claim 4 are principally normally non-condensibles in
by the compressor 19, without and with recycling through
l
l
1
pressed in this case by' the compressor 19.
When the bottom product of column 32 is not recycled
cluding hydrogen and the liquid fraction of step (3) is a
gasoline fraction containing butane and wherein the liquid
at a cutting point of 165° C. nor at a cutting point of
vfraction is passed to a ?rst distillation to separate the
185° C., the quantity of gas to be compressed by the 70 butane and light components therefrom and the resulting .
debutanized gasoline fraction is subjected to a further
compressor 19 is approximately 37.1 tons per 1000 tons
distillation to separate a light gasoline product overhead
of crude oil in the ?rst instance and approximately 33.7
from a heavy gasoline product which is returned in part
tons in the second. In the ?rst case the load on the com
to the vaporous stream of reformed naphtha prior to its
pressor 19 is 9.9% greater than in the second. ‘When
the recycling is, however, effected at a primary cutting 75 cooling and initial separation.
3,028,832
7
claim 1 is derived from a second distillation and a por
8
References Cited in the ?le of this patent
8. A process in accordance with claim 1 wherein the
vaporous hydrocarbon ‘stream is the top product of
a primary distillation operating at approximately at
mospheric pressure and wherein said liquid fraction of
UNITED STATES PATENTS
5
1,552,980
Blaise ________________ __ Sept. 8, 1925
2,175,180
Dieserud _____________ __ Oct. 10, 1939
2,895,909
Strickland ____________ __ July 21, 1959
226,724
Great Britain __________ __ I an. 1, 1925
tion of that liquid fraction is the material returned to
FOREIGN PATENTS
the top product of the primary distillation. '
9. A process in accordance with claim 8 wherein, when
the distillation cutting point in the primary distillation is
changed, the quantity, of the ‘liquid fraction combined
v10
OTHER REFERENCES
Fetroleurn Re?ner, vol. 28, No. 9, 1949, pages 213,
with the ‘top product is so regulated in amount that the
216, 217, 220, 22,1, 224, 225, 229, 232,233, 236, 237
total quantity of heavy components Withdrawn from the
secondary distillation remains substantially constant.
and 240.
-
Petroleum Re?ner, April 1950, pages 97 to 100.
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