U.S. patent application number 12/067322 was filed with the patent office on 2009-07-02 for method for producing a hydrogen-enriched gas stream from hydrogenated gas streams comprising hydrocarbons.
This patent application is currently assigned to L'Air Liquide Societe Anonyme Pour L'Etude Et L'Exloitation Des Procedes Georges Claude. Invention is credited to Bruno Alban, Sylvain Gerard, Francois-Xavier Haulle, Vincent Pudys.
Application Number | 20090166258 12/067322 |
Document ID | / |
Family ID | 36593675 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090166258 |
Kind Code |
A1 |
Haulle; Francois-Xavier ; et
al. |
July 2, 2009 |
Method for Producing a Hydrogen-Enriched Gas Stream from
Hydrogenated Gas Streams Comprising Hydrocarbons
Abstract
The invention concerns a method for producing a
hydrogen-enriched gas stream from at least one gas stream
comprising for the major part hydrogen and a gas stream comprising
hydrogen and hydrocarbons, using a pressure-modulated gas
adsorption unit, the temperature of the gas stream comprising
hydrogen and hydrocarbons being first lowered so as to condense the
hydrocarbons.
Inventors: |
Haulle; Francois-Xavier;
(Chatou, FR) ; Gerard; Sylvain; (Suresnes, FR)
; Alban; Bruno; (Massy, FR) ; Pudys; Vincent;
(Paris, FR) |
Correspondence
Address: |
AIR LIQUIDE;Intellectual Property
2700 POST OAK BOULEVARD, SUITE 1800
HOUSTON
TX
77056
US
|
Assignee: |
L'Air Liquide Societe Anonyme Pour
L'Etude Et L'Exloitation Des Procedes Georges Claude
Paris ,Cedex 7
FR
|
Family ID: |
36593675 |
Appl. No.: |
12/067322 |
Filed: |
September 21, 2006 |
PCT Filed: |
September 21, 2006 |
PCT NO: |
PCT/FR2006/050921 |
371 Date: |
August 7, 2008 |
Current U.S.
Class: |
208/100 |
Current CPC
Class: |
C01B 2203/146 20130101;
B01D 2256/16 20130101; B01D 2253/308 20130101; C01B 3/506 20130101;
B01D 2259/4145 20130101; B01D 2259/40081 20130101; C10L 3/12
20130101; B01D 53/047 20130101; B01D 2253/306 20130101; C01B
2203/048 20130101; B01D 2257/702 20130101; C01B 2203/043 20130101;
B01D 2259/4143 20130101; B01D 2259/416 20130101; C01B 3/56
20130101; B01D 53/002 20130101 |
Class at
Publication: |
208/100 |
International
Class: |
C10G 49/22 20060101
C10G049/22 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2005 |
FR |
0552972 |
Claims
1-7. (canceled)
8. A process for producing a hydrogen-enriched gas stream and a
liquefied petroleum gas from at least one gas stream mainly
comprising hydrogen at pressure P and a gas stream comprising
hydrogen and hydrocarbons, in which the following steps are carried
out: during step a), the gas stream comprising hydrogen and
hydrocarbons is adjusted to the pressure P; during step b), the gas
stream comprising hydrogen and hydrocarbons and adjusted to the
pressure P is treated in a pressure swing gas adsorption unit fed
will the gas stream mainly comprising hydrogen and having a
pressure P so as to supply: at a first outlet, the
hydrogen-enriched gas stream having a hydrogen concentration
greater than that of the gas stream mainly comprising hydrogen; and
at a second outlet, a waste stream characterized in that between
step a) and step b), the temperature of the gas stream comprising
hydrogen and hydrocarbons and adjusted to the pressure P is lowered
so as to condense the hydrocarbons and form the liquid petroleum
gas.
9. The process of claim 8, wherein the gas stream mainly comprising
hydrogen has a hydrogen concentration between 50 and 99 vol %.
10. The process of claim 8, wherein the gas stream comprising
hydrogen and hydrocarbons has a hydrogen concentration at least 10%
lower relative to the value of the hydrogen concentration of the
gas stream mainly comprising hydrogen.
11. The process of claim 8, wherein the gas stream comprising
hydrogen and hydrocarbons has a hydrocarbon concentration between
10 and 50 vol %.
12. The process of claim 8, wherein the gas separation unit is a
pressure swing adsorption (PSA) unit combined with an integrated
compressor, in which, for each adsorber of the unit, a pressure
swing cycle is carried out comprising a succession of phases which
define the phases of adsorption, decompression, purge and pressure
rise, such that: during the adsorption phase: during a first step,
the gas stream mainly comprising hydrogen and having a pressure P
is brought into contact with the bed of the adsorber; and during a
second step, introduced into contact with the bed of the adsorber
is the mixture of pressure P whose temperature has been lowered so
as to condense the hydrocarbons and that is composed of: on the one
hand, the gas stream comprising hydrogen and hydrocarbons; and on
the other hand, the PSA recycle gas, so as to adsorb the compounds
other than hydrogen and to produce, at the top of the adsorber bed,
the enriched stream having a hydrogen concentration greater than
that of the gas stream mainly comprising hydrogen; during the
decompression phase, the PSA waste stream is produced; during the
purge phase, a purge gas is produced; and where the PSA recycle gas
is either the waste stream compressed to the pressure P, or the
purge gas compressed to the pressure P.
13. The process of claim 8, wherein between step a) and step b),
the temperature of the gas stream comprising hydrogen and
hydrocarbons is lowered to at least 0.degree. C.
14. The of claim 8, wherein between step a) and step b), the
temperature of the gas stream comprising hydrogen and hydrocarbons
is lowered by means of a cryogenic device.
15. The process of claim 9, wherein the gas stream comprising
hydrogen and hydrocarbons has a hydrogen concentration at least 10%
lower relative to the value of the hydrogen concentration of the
gas stream mainly comprising hydrogen.
16. The process of claim 15, wherein the gas stream comprising
hydrogen and hydrocarbons has a hydrocarbon concentration between
10 and 50 vol %.
17. The process of claim 16, wherein the gas separation unit is a
pressure swing adsorption (PSA) unit combined with an integrated
compressor, in which, for each adsorber of the unit, a pressure
swing cycle is carried out comprising a succession of phases which
define the phases of adsorption, decompression, purge and pressure
rise, such that: during the adsorption phase: during a first step,
the gas stream mainly comprising hydrogen and having a pressure P
is brought into contact with the bed of the adsorber; and during a
second step, introduced into contact with the bed of the adsorber
is the mixture of pressure P whose temperature has been lowered so
as to condense the hydrocarbons and that is composed of: on the one
hand, the gas stream comprising hydrogen and hydrocarbons; and on
the other hand, the PSA recycle gas, so as to adsorb the compounds
other than hydrogen and to produce, at the top of the adsorber bed,
the enriched stream having a hydrogen concentration greater than
that of the gas stream mainly comprising hydrogen; during the
decompression phase, the PSA waste stream is produced; during the
purge phase, a purge gas is produced; and where the PSA recycle gas
is either the waste stream compressed to the pressure P, or the
purge gas compressed to the pressure P.
18. The process of claim 17, wherein between step a) and step b),
the temperature of the gas stream comprising hydrogen and
hydrocarbons is lowered to at least 0.degree. C.
19. The of claim 18, wherein between step a) and step b), the
temperature of the gas stream comprising hydrogen and hydrocarbons
is lowered by means of a cryogenic device.
Description
[0001] The present invention relates to a process for enhancing
various streams based on hydrogen and on hydrocarbons so as to
produce a high-purity hydrogen stream.
[0002] Refineries or petrochemical plants use large amounts of
hydrogenated streams, preferably of high purity. In many industrial
cases, the performances of the units, and especially the grades of
the products produced, are limited by the purity of the supplied
hydrogen. Furthermore, in these units, it is sometimes necessary to
eliminate gases that are still rich in hydrogen under the effect of
the recycle gas purges. This results in a cost premium for the
operation of the unit. In order to avoid these problems, processes
for recovering the hydrogen from streams of relatively low purity
in order to produce high-purity hydrogenated streams have been
proposed, especially in Application WO 2005/042640 which proposes
using a pressure swing adsorption unit to treat these various
hydrogenated streams and to obtain a high-purity stream. This type
of pressure swing adsorption unit may represent a significant
investment in terms of adsorbent cost and compressor cost.
[0003] The objective of the present invention is to propose a
process for enhancing various streams based on hydrogen and
hydrocarbons so as to produce a high-purity hydrogen stream, a
liquefied petroleum gas and a waste gas, the investment cost of
which is reduced by increasing the high-purity hydrogen production
yield.
[0004] Another objective of the present invention is to propose a
process for enhancing various streams based on hydrogen and
hydrocarbons so as to produce a high-purity hydrogen stream, a
liquefied petroleum gas and a waste gas, of which the energy
consumption is optimized.
[0005] For this purpose, the invention relates to a process for
producing a hydrogen-enriched gas stream and a liquefied petroleum
gas from at least one gas stream mainly comprising hydrogen at
pressure P and a gas stream comprising hydrogen and hydrocarbons,
in which the following steps are carried out: [0006] during step
a), the gas stream comprising hydrogen and hydrocarbons is adjusted
to the pressure P; [0007] during step b), the gas stream comprising
hydrogen and hydrocarbons and adjusted to the pressure P is treated
in a pressure swing gas adsorption unit (U) fed will the gas stream
mainly comprising hydrogen and having a pressure P so as to supply:
[0008] at a first outlet, the hydrogen-enriched gas stream having a
hydrogen concentration greater than that of the gas stream mainly
comprising hydrogen; and [0009] at a second outlet, a waste stream,
characterized in that between step a) and step b), the temperature
of the gas stream comprising hydrogen and hydrocarbons and adjusted
to the pressure P is lowered so as to condense the hydrocarbons and
form the liquid petroleum gas.
[0010] The process according to the invention allows the treatment
of two gas streams comprising hydrogen at various concentrations so
as to produce a hydrogen-enriched gas stream, a liquefied petroleum
gas (or LPG) and a waste gas. The first gas stream treated is a gas
stream that mainly comprises hydrogen, that is to say having a
hydrogen concentration between 50 and 99 vol %. This stream also
comprises hydrocarbons having from 1 to 8 carbon atoms and
compounds such as CO, CO.sub.2, H.sub.2S, etc. The second stream
treated is a gas stream comprising hydrogen and hydrocarbons having
a hydrogen concentration at least 10% lower, preferably at least
15% lower and more preferably still 15 to 50% lower, relative to
the value of the hydrogen concentration of the gas stream mainly
comprising hydrogen. This second stream also comprises hydrocarbons
having 1 to 8 carbon atoms, and also compounds such as H.sub.2O,
H.sub.2S, etc. Generally, this second gas stream has a hydrocarbon
concentration between 10 and 50 vol %. According to the invention,
the pressure of this second gas stream comprising hydrogen and
hydrocarbons is adjusted so that it is close to 2, either by
compression, or by pressure drop depending on the origin of this
stream. It is also possible that this stream already has a pressure
P, in this case it is used as is without a pressure adjustment.
These various streams may be derived from the purge of the gas loop
of a hydrotreatment unit such as a hydrodesulfurization or
hydrocracking unit of a refinery, or else such as a
hydrodealkylation or isomerization unit of a petrochemical site.
The first and second gas streams treated in the present invention
may be derived from mixtures of various purges of such units. These
mixtures may make it possible to attain the pressure P desired by
combining the streams having a pressure below P with streams having
a pressure above P.
[0011] By treatment of these various streams, the invention makes
it possible to enrich the gas stream mainly comprising hydrogen.
This enrichment is obtained by hydrogen depletion of the second gas
stream comprising hydrogen and hydrocarbons. The unit thus produces
the hydrogen-enriched gas stream generally having a hydrogen purity
greater than 99 vol %, and the unit also produces a waste stream of
low hydrogen purity and of low pressure which may be conveyed to
the fuel gas network. The pressure and hydrogen concentration of
the waste stream are respectively below the pressure and hydrogen
concentration values of all the effluents going into the unit (U).
This waste stream also comprises hydrocarbons (C.sub.1 to C.sub.8)
and compounds such as H.sub.2O, H.sub.2S, CO, CO.sub.2, etc.
[0012] Preferably, the gas separation unit (U) is a pressure swing
adsorption (PSA) unit combined with an integrated compressor, in
which, for each adsorber of the unit, a pressure swing cycle is
carried out comprising a succession of phases which define the
phases of adsorption, decompression, purge and pressure rise, such
that: [0013] during the adsorption phase: [0014] during a first
step, the gas stream mainly comprising hydrogen and having a
pressure P is brought into contact with the bed of the adsorber;
and [0015] during a second step, introduced into contact with the
bed of the adsorber is the mixture of pressure P whose temperature
has been lowered so as to condense the hydrocarbons and that is
composed of: [0016] on the one hand, the gas stream comprising
hydrogen and hydrocarbons; and [0017] on the other hand, the PSA
recycle gas, so as to adsorb the compounds other than hydrogen and
to produce, at the top of the adsorber bed, the enriched stream
having a hydrogen concentration greater than that of the gas stream
mainly comprising hydrogen; [0018] during the decompression phase,
the PSA waste stream is produced; [0019] during the purge phase, a
purge gas is produced; and [0020] where the PSA recycle gas is
either the waste stream compressed to the pressure P, or the purge
gas compressed to the pressure P. According to this PSA process, in
a first adsorption phase, the gas stream mainly comprising hydrogen
is brought into contact with a first PSA adsorbent bed and in a
second phase, it is the mixture of streams comprising hydrogen and
hydrocarbons and of the PSA recycle gas which are brought into
contact with this first adsorbent assembly. The recycle gas may be
composed of two gases, alone or as a mixture: the waste gas
resulting from the PSA which has been compressed, and the purge gas
resulting from the PSA which has been compressed. Preferably, it is
the purge gas and not the waste gas. The waste gas is derived from
the final step of the PSA decompression phase and is partly
compressed by the compressor integrated into the PSA unit of the
gas separation unit (U) whereas the purge gas is derived from the
purge phase of the PSA and is partly compressed by this same
compressor integrated into the PSA before being used as a recycle
gas. These two gases both comprise hydrogen and mainly impurities.
Once compressed, they are mixed with a stream comprising hydrogen
and hydrocarbons. This mixing may be carried out in various ways
depending on the pressure value of the stream comprising hydrogen
and hydrocarbons. This stream comprising hydrogen and hydrocarbons
may be mixed with the waste gas or with the purge gas, then this
mixture may be compressed by the compressor integrated into the PSA
unit to the pressure P. When the stream comprising hydrogen and
hydrocarbons has a pressure above P, its compression may be
avoided; in this case, only the waste gas or the purge gas is
compressed to form the recycle gas. Before its introduction into
the PSA unit, the mixture at pressure P of the stream comprising
hydrogen and hydrocarbons and the recycle gas is treated so as to
lower its temperature and condense the hydrocarbons. It may be
envisioned to then reheat the stream comprising hydrogen and
hydrocarbons by heat exchange with at least one other gas stream of
the process in order to avoid conveying a cold gas to the PSA unit.
Next, the introduction of these mixed gases at pressure P into the
adsorbent bed allows them to be retreated. During the adsorption
phase, the gas streams are introduced into the bottom part of the
bed in the direction known as the co-current direction. During this
contacting step, the most adsorbable compounds other than H.sub.2,
are adsorbed on the adsorbent and a gas mainly comprising hydrogen
is produced at the pressure P reduced by around 1 bar of pressure
drop. During this step, the hydrogen produced generally has a
purity greater than at least 99 mol %, preferably greater than at
least 99.5 mol %.
[0021] So as to obtain an effective purification, the adsorbent of
the PSA beds should, in particular, allow the adsorption and
desorption of impurities. The adsorbent bed is generally composed
of a mixture of several adsorbents, said mixture comprising, for
example, at least two adsorbents chosen from: activated carbons,
silica gels, aluminas or molecular sieves. Preferably, the silica
gels should have a pore volume between 0.4 and 0.8 cm.sup.3/g and a
specific surface area greater than 600 m.sup.2/g. Preferably, the
aluminas have a pore volume greater than 0.2 cm.sup.3/g and a
specific surface area greater than 220 m.sup.2/g. The zeolites
preferably have a pore size below 4.2 .ANG., an Si/Al molar ratio
below 5 and contain Na and K. The activated carbons preferably have
a specific surface area greater than 800 m.sup.2/g and a micropore
size between 8 and 20 .ANG.. According to one preferred embodiment,
each PSA adsorbent bed is composed of at least three layers of
adsorbents of different natures. Each PSA adsorbent bed may
comprise: in the bottom part, a protective layer composed of
alumina and/or silica gel surmounted by a layer of activated carbon
and/or of carbon-based molecular sieve and optionally in the upper
part a molecular sieve layer. The proportions vary as a function of
the nature of the gas mixture to be treated (especially as a
function of its percentages of CH.sub.4 and of C.sub.3+
hydrocarbons). For example, a water-free gas mixture comprising 75
mol % of H.sub.2, 5% of C.sub.3+ and 20% of light (C.sub.1-C.sub.2)
hydrocarbons, CO and N.sub.2 may be treated by an adsorption unit
whose beds comprise at least 10 vol % of alumina and 15 vol % of
silica gel in the bottom bed, the remainder being obtained from
activated carbon.
[0022] During the decompression phase of the PSA, the waste gas is
produced. This production of the waste gas may be obtained by
countercurrent decompression initiated at a pressure below P. This
waste gas comprises impurities and has a hydrogen content lower
than all the streams introduced into the PSA unit. This waste gas
may be discharged from the process and burnt or reused as a recycle
gas in the PSA unit as indicated previously.
[0023] The low pressure of the cycle being attained, a purge phase
is carried out to finalize the regeneration of the adsorber. During
the purge phase, a gas is introduced countercurrently into the
adsorber and a purge gas is produced. The gas introduced
countercurrently into the adsorber during the purge phase is a gas
stream derived from one of the steps of the decompression phase.
The purge gas is generally used as a recycle gas after
recompression.
[0024] During the pressure rise phase, the pressure of the adsorber
is increased by countercurrent introduction of a gas stream
comprising hydrogen such as the gas produced during the various
steps of the decompression phase.
[0025] According to the main feature of the invention, between step
a) of adjusting the pressure of the gas stream comprising hydrogen
and hydrocarbons and step b) of treating this stream via the gas
separation unit (U), the temperature of the gas stream comprising
hydrogen and hydrocarbons is lowered so as to condense the
hydrocarbons, preferably to less than 0.degree. C., more preferably
still to less than -20.degree. C. Preferably, this temperature drop
is carried out by means of a cryogenic device, such as cryogenic
(compression/expansion) loops using liquid ammonia or propane.
[0026] FIG. 1 illustrates the process according to the invention.
The stream 2 comprising hydrogen and hydrocarbons is compressed by
the compressor 3 to have a pressure P equal to that of the stream 1
that mainly comprises hydrogen. The stream 21 comprising hydrogen
and hydrocarbons and that is compressed is then treated by a device
4 that makes it possible to lower its temperature and to condense
the hydrocarbons. The device 4 produces: [0027] on the one hand, a
liquid stream 10 of hydrocarbons (LPG); and [0028] on the other
hand, a gas stream 22 comprising hydrogen and still some
hydrocarbons having a pressure P and a lowered temperature.
[0029] This stream 22 and the stream 1 are treated by the gas
separation unit 5 so as to produce: a hydrogen-enriched stream 6, a
waste gas 7 and a purge gas 8 which is mixed with the stream 2
comprising hydrogen and hydrocarbons before compression of the
latter. The process also makes it possible to treat another stream
9 comprising hydrogen and hydrocarbons that is equivalent to the
stream 2 but originates from another purge. This stream 9 already
has a pressure P or a pressure that is slightly greater than P; it
is therefore directly treated by the device 4 with the mixture 21
resulting from the compressor.
[0030] By implementation of the process as described above, it is
possible to reduce the size of the pressure swing adsorption unit
and to reduce the compression costs of the unit (U) while
increasing the hydrogen yield. The process additionally makes it
possible to produce, at the outlet of the temperature-lowering
device, a liquefied petroleum gas, which may be a stream of high
added value, that can be recovered as a fuel.
[0031] The process of the invention also has the advantage of
allowing a natural energy integration between the cryogenic device
enabling the temperature to be reduced and the compressor of the
pressure swing adsorption unit.
EXAMPLE
[0032] Two gas streams comprising hydrogen were treated by means of
a pressure swing adsorption unit. These two streams had the
following concentrations:
TABLE-US-00001 TABLE 1 Gas stream mainly Gas stream comprising
comprising hydrogen hydrogen and hydrocarbons Flow rate Sm.sup.3/h
10 000 5 200 Composition (vol %) H.sub.2 81.4 57 C.sub.1 9.3 23.7
C.sub.2 5 2.2 C.sub.3 2.6 5.35 C.sub.4 1.1 8.2 C.sub.5 0.6 2.9
N.sub.2 0 0.6
[0033] These streams were treated by a pressure swing adsorption
unit according to the invention as illustrated in FIG. 1 and by a
CPSA pressure swing adsorption unit according to the prior art
corresponding to the CPSA according to the invention but not
comprising means for lowering the temperature of the gas stream
comprising hydrogen and hydrocarbons so as to condense the
hydrocarbons. The features of the process according to the prior
art and of the process according to the invention are described in
table 2.
TABLE-US-00002 TABLE 2 Process according Process according to the
prior art to the invention Flow rate of the gas 3.06 3.06 stream
(1) mainly comprising hydrogen (t/h) Flow rate of the gas 3.48 3.48
stream (2) comprising hydrogen and hydrocarbons (t/h) Hydrogen
yield 82.3% 82.6% Volume of adsorbent 100 89.5 (relative)
Hydrocarbon recovery (t/h) 2.02 mol % C3 21.2 mol % C4 51.4 mol %
C5 27.4 Energy used by the 564 541 compressor (3) (kW) Energy used
by the 431 cryogenic device (4) for lowering the temperature
-25.degree. C. (kW)
[0034] It is observed that by the implementation of the invention,
it is possible: [0035] to reduce the volume of the adsorbents of
the PSA unit by 10 vol %; [0036] to decrease the power of the
compressor by 5%; and [0037] to increase the hydrogen yield by 0.3
points.
[0038] Furthermore, the stream of liquefied hydrocarbons may be
recovered as a commercial product within the plant.
[0039] The liquefied petroleum gas resulting from the cryogenic
device is a product of high added value which compensates for the
additional energy used by the cryogenic device of the process
according to the invention relative to the process of the prior
art.
* * * * *