U.S. patent application number 15/744987 was filed with the patent office on 2018-07-26 for production of helium from a stream of natural gas.
The applicant listed for this patent is L'Air Liquide, Societe Anonyme pour I'Etude et I'Exploitation des Procedes Georges Claude. Invention is credited to Paul TERRIEN.
Application Number | 20180209725 15/744987 |
Document ID | / |
Family ID | 54356501 |
Filed Date | 2018-07-26 |
United States Patent
Application |
20180209725 |
Kind Code |
A1 |
TERRIEN; Paul |
July 26, 2018 |
PRODUCTION OF HELIUM FROM A STREAM OF NATURAL GAS
Abstract
A method for producing a helium gas stream from a gas source
containing at least helium, methane, and nitrogen is provided. The
method includes introducing the gas into a double column nitrogen
rejection unit.
Inventors: |
TERRIEN; Paul; (Newton,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
L'Air Liquide, Societe Anonyme pour I'Etude et I'Exploitation des
Procedes Georges Claude |
Paris |
|
FR |
|
|
Family ID: |
54356501 |
Appl. No.: |
15/744987 |
Filed: |
July 12, 2016 |
PCT Filed: |
July 12, 2016 |
PCT NO: |
PCT/FR2016/051786 |
371 Date: |
January 15, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 3/0238 20130101;
F25J 2235/60 20130101; F25J 3/0257 20130101; F25J 3/0233 20130101;
F25J 3/0209 20130101; F25J 2290/34 20130101; F25J 2200/06 20130101;
F25J 2205/04 20130101; F25J 2205/02 20130101; F25J 3/029
20130101 |
International
Class: |
F25J 3/02 20060101
F25J003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 16, 2015 |
FR |
1556739 |
Claims
1.-14. (canceled)
15. A process for producing a helium gas stream from a source gas
stream comprising at least helium, methane and nitrogen, the
process comprising the following steps: step a): introducing the
source gas stream into a double-column nitrogen rejection unit, the
double column comprising a high-pressure distillation column, a
low-pressure distillation column and a condenser linking the
high-pressure column with the low-pressure column, the condenser
comprising an outlet, and the high-pressure column comprising a
top, and the low-pressure column comprising a top; step b):
extracting at the outlet of the condenser at least one part of a
mixture produced at the top of the high-pressure column; step c):
expanding the mixture resulting from step b) to an intermediate
pressure of between 8 bar and 20 bar absolute; step d): separating
the intermediate pressure mixture resulting from step c) in a first
phase separator vessel into a liquid phase and a helium-enriched
gas phase; step e): at least partially condensing the
helium-enriched gas phase in a heat exchanger; step f): separating
the at least partially condensed stream resulting from step e) in a
second phase separator vessel into a liquid phase and a gas phase
containing more than 50% by volume of helium.
16. The process of claim 15, further comprising a step g): using,
as refrigerant, the liquid phase after expansion resulting from
step f) in the heat exchanger used in step e).
17. The process of claim 16, wherein, during step g), the liquid
phase is vaporized at a pressure of between 0.1 bar and 3 bar
absolute.
18. The process of claim 15, wherein, during step a), the gas
stream is introduced into the high-pressure column at at least a
first feed level and a second feed level, the vapor fraction at the
first feed level being smaller than the vapor fraction at the
second feed level and the first feed level being introduced at a
higher level of the high-pressure column than the second feed
level.
19. The process of claim 16, further comprising a step h):
extracting the gas phase resulting from step f) as helium-rich
product containing at least 75% by volume of helium.
20. The process of claim 19, wherein the temperature at the outlet
of the condenser in step b) is between -150.degree. C. and
-165.degree. C.
21. The process of claim 20, wherein the pressure in the
high-pressure column is between 20 bar absolute and 50 bar absolute
and the pressure in the low-pressure column is between 1 bar
absolute and 5 bar absolute.
22. The process of claim 15, wherein the temperature at which step
c) is carried out is between -160.degree. C. and -180.degree.
C.
23. The process of claim 15, wherein the temperature at which step
e) is carried out is between -180.degree. C. and -210.degree.
C.
24. The process of claim 15, wherein the liquid phase resulting
from step d) is introduced into the low-pressure column.
25. The process of claim 15, further comprising an additional step
of producing a nitrogen-enriched stream comprising less than 2% by
volume of methane from a gas stream rom the top of the low-pressure
column.
26. The process of claim 15, wherein the source gas stream
comprises from 20% by volume to 80% by volume of methane, from 20%
by volume to 80% by volume of nitrogen and from 0% by volume to 2%
by volume of helium.
27. A facility for producing helium from a gas source mixture
comprising methane, helium and nitrogen, the facility comprising:
at least one nitrogen rejection unit equipped with a double column,
the double column comprising a high-pressure distillation column, a
low-pressure distillation column and a condenser linking the
high-pressure column with the low-pressure column, and a helium
extraction unit comprising a first phase separator vessel located
upstream of a heat exchanger which is itself located upstream of a
second phase separator vessel; wherein the nitrogen rejection unit
is located upstream of the helium extraction unit.
28. The facility of claim 27, wherein the helium extraction unit
contains neither a distillation column nor a rectification column
nor a phase separator vessel with multiple feeds.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a 371 of International Application
PCT/FR2016/051786, filed Jul. 12, 2016, which claims priority to
French Patent Application FR 1556739, filed Jul. 16, 2015, the
entire contents of which are incorporated herein by reference.
BACKGROUND
[0002] The present invention relates to a process for producing
helium from a source gas stream comprising at least helium, methane
and nitrogen.
[0003] Helium is commercially obtained virtually exclusively from a
mixture of volatile components of natural gas, this mixture
comprising, along with the helium, typically methane and nitrogen
and traces of hydrogen, of argon, and of other noble gases.
[0004] During the production of mineral oil, helium is made
available as a component of the gas which accompanies the mineral
oil, or in the context of the production of natural gas. It is
theoretically possible to obtain helium in the atmosphere, but it
is not economical because of the low concentrations (typical
concentration of helium in air of about 5.2 ppmv).
[0005] Crude natural gas can contain a large number of impeding
impurities that need to be removed. Nitrogen is one example of
this. Starting from a certain concentration of nitrogen in natural
gas, the latter is typically not saleable because of its low
calorific value. A cryogenic process carried out in a unit referred
to as a nitrogen rejection unit (NRU) is usually used to remove the
nitrogen.
[0006] If, in addition to the nitrogen, there is helium in the
natural gas, there is an economical benefit to extracting a
helium-rich stream separately in order to produce helium and to
sell it. Typically, the helium is concentrated in the cryogenic
process and is finally purified in a PSA (pressure-swing
adsorption) process.
[0007] Several solutions exist at the current time for extracting
helium in an NRU, in particular in a "double-column" NRU unit.
[0008] It is possible to add a column for distilling the nitrogen
and the helium, as is described in patent EP 0 633 437 B1 for
example, but this poses several problems: [0009] complexification
of the installation; [0010] energy consumption increased because of
the need for refrigeration (cycle) linked to this column.
[0011] Other solutions exist using successive partial condensations
and/or instantaneous (flash) vaporizations, but they do not
generally make it possible to have both a high helium content and a
high yield. One example is described in U.S. Pat. No. 4,701,201. In
said patent, the helium is recovered at the top of the
high-pressure (HP) column after partial condensation. This simple
partial condensation makes it necessary to choose between helium
yield and purity. In the patent, it is also indicated that it is
possible to achieve a reasonable yield (approximately 92%), but the
purity achieved for the helium-enriched stream is 37.2%.
[0012] There is thus a need to solve the problems described
above.
SUMMARY
[0013] For this reason, the subject of the present invention is a
process for producing a helium gas stream from a source gas stream
comprising at least helium, methane and nitrogen, comprising at
least the following steps:
[0014] step a): introducing said source gas stream into a
double-column nitrogen rejection unit, said double column
comprising a high-pressure distillation column, a low-pressure
distillation column and a condenser linking the high-pressure
column with the low-pressure column;
[0015] step b): extracting at the outlet of said condenser at least
one part of a mixture produced at the top of the high-pressure
column;
[0016] step c): expanding said mixture resulting from step b) to an
intermediate pressure of between 8 bar and 20 bar absolute;
[0017] step d): separating the mixture resulting from step c) in a
first phase separator vessel into a liquid phase and a
helium-enriched gas phase;
[0018] step e): at least partially condensing said helium-enriched
gas phase in a heat exchanger;
[0019] step f): separating the stream resulting from step e) in a
second phase separator vessel into a liquid phase and a gas phase
containing more than 50% by volume of helium.
[0020] According to other embodiments, the subject of the present
invention is also: [0021] A process as defined above, characterized
in that it comprises a step g): using, as refrigerant, the liquid
phase after expansion resulting from step f) in said heat exchanger
used in step e). [0022] A process as defined above, characterized
in that, during step g), said liquid phase is vaporized at a
pressure of between 0.1 bar and 3 bar absolute. [0023] A process as
defined above, characterized in that, during step a), the gas
stream is introduced into the high-pressure column at two or more
feed levels, the vapor fraction of the first feed being smaller
than the vapor fraction of the second and the first feed being
introduced at a higher level of said high-pressure column than the
second. [0024] A process as defined above, comprising a step h):
extracting the gas phase resulting from step f) as a helium-rich
product containing at least 75% by volume of helium. [0025] A
process as defined above, characterized in that the temperature at
the outlet of the condenser in step b) is between -150.degree. C.
and -165.degree. C. [0026] A process as defined above,
characterized in that the pressure in the high-pressure column is
between 20 bar absolute and 50 bar absolute and the pressure in the
low-pressure column is between 1 bar absolute and 5 bar absolute.
[0027] A process as defined above, characterized in that the
temperature at which step c) is carried out is between -160.degree.
C. and -180.degree. C. [0028] A process as defined above,
characterized in that the temperature at which step e) is carried
out is between -180.degree. C. and -210.degree. C. [0029] A process
as defined above, characterized in that the liquid phase resulting
from step d) is introduced into the low-pressure column of said
rejection unit. [0030] A process as defined above, comprising an
additional step of producing a nitrogen-enriched stream comprising
less than 2% by volume of methane from a gas stream from the top of
the low-pressure column. [0031] A process as defined above,
characterized in that the source gas stream comprises from 20% by
volume to 80% by volume of methane, from 20% by volume to 80% by
volume of nitrogen and from 0% by volume to 2% by volume of helium.
[0032] A facility for producing helium from a gas source mixture
comprising methane, helium and nitrogen, said facility comprising:
[0033] at least one nitrogen rejection unit equipped with a double
column, said double column comprising a high-pressure distillation
column, a low-pressure distillation column and a condenser linking
the high-pressure column with the low-pressure column, and [0034] a
helium extraction unit comprising a first phase separator vessel
located upstream of a heat exchanger which is itself located
upstream of a second phase separator vessel; [0035] characterized
in that the nitrogen rejection unit is located upstream of the
helium extraction unit. [0036] A facility as previously defined,
characterized in that said helium extraction unit contains neither
a distillation column nor a rectification column nor a phase
separator vessel with multiple feeds.
[0037] The solution which is the subject of the present invention
makes it possible to separate a stream composed of methane,
nitrogen and helium into three streams: a pure methane stream, a
pure nitrogen stream and a helium-rich stream.
[0038] The present invention makes it possible to solve the problem
of the solutions by partial condensation, by obtaining both a high
helium yield (>85%) and a high helium content (>50%), this
being without using a column dedicated to helium separation.
[0039] The integration of the helium extraction in an NRU unit with
a double-column scheme makes it possible to minimize the cost of
the equipment and the energy consumption of the helium extraction
unit (helium rejection unit, HRU) without penalizing the
consumption and the installation cost of the other pieces of
equipment of the NRU.
[0040] The process which is the subject of the invention consists
of a double-column NRU unit in which total condensation (or
virtually total condensation owing to the presence of uncondensable
compounds) is carried out at the level of the condenser of the
high-pressure HP column. The liquid produced at the top of this HP
column is partly used as reflux of the HP column and partly
intended to be used as reflux of the low-pressure LP column.
[0041] The particularity of the invention is the expansion of the
liquid produced and not used as reflux of the HP column, to an
intermediate pressure so as to thus "flash" or instantaneously
vaporize (the term "flash" gas is intended to mean: instantaneous
vapor) all the desired helium in a first helium separator vessel
(control of the yield) followed by a partial condensation of the
gas of said "flash" (or instantaneous vapor) so as to obtain a gas
having a high helium content in a second helium separator
vessel.
[0042] It will advantageously be possible to produce the cold
required for the partial condensation of the "flash" (instantaneous
vapor) from the first helium separator vessel by vaporizing at low
pressure the liquid from the bottom of the second helium separator
vessel.
BRIEF DESCRIPTION OF THE DRAWING
[0043] For a further understanding of the nature and objects for
the present invention, reference should be made to the following
detailed description, taken in conjunction with the accompanying
drawings, in which like elements are given the same or analogous
reference numbers and wherein:
[0044] FIG. 1 is a schematic representation of one embodiment of
the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0045] The process which is the subject of the present invention is
illustrated in FIG. 1.
[0046] In FIG. 1, a source gas stream 1 comprising at least helium,
methane and nitrogen is introduced at a pressure of approximately
50 bar absolute into a heat exchanger 2. The stream 3 at the outlet
of said exchanger 2 is expanded by means, for example, of a valve
4, before being introduced into a high-pressure column 5 of a
double-column unit 6 comprising a high-pressure distillation column
5, a low-pressure distillation column 7 and a condenser 8 linking
the high-pressure column 5 with the low-pressure column 7.
[0047] The source gas stream 1 comprises, for 100% by volume, for
example, from 20% by volume to 80% by volume of methane, from 20%
by volume to 80% by volume of nitrogen and from 1 ppm by volume to
1% by volume of helium.
[0048] The pressure of the high-pressure column is for example 30
bara and the pressure in the low-pressure column is for example 2
bara.
[0049] The principle of a double-column unit is widely described in
the technical art, for example in the document by Ruheman, "The
separation of gases" Oxford University press, 1949, chapter 7 or
else in the document by Barron, "Cryogenic systems", McGraw Hill,
Inc., 1996, p. 230, Air Separation Systems.
[0050] The term "nitrogen rejection unit" relates to a device in
which the nitrogen and the methane are separated by cryogenic
rectification.
[0051] In order to increase the helium yield, it is also possible
to carry out a multiple introduction into the high-pressure column
5: a part (3d) of the stream 3 being introduced mainly in liquid
form and a part (3c) is introduced mainly in gas form at the bottom
of column 5 so as to vaporize the helium that would otherwise be
entrained in the liquid methane.
[0052] A part 9 of the liquid stream 11 leaving the condenser 8
located in the bottom part of the low-pressure column 7 is used as
reflux in the top part 10 of the high-pressure column 5. In a
conventional double-column NRU scheme, the remainder of the liquid
11 is cooled and then expanded so as to be directly used as reflux
of the low-pressure column. The subject matter of the present
invention consists in using a part 12 of said liquid stream 11 for
extracting therefrom the helium before using it as reflux of the
low-pressure column.
[0053] This liquid stream 11 typically contains less than 2% by
volume of methane, more that 95% by volume of nitrogen and from
0.5% by volume to 3% by volume of helium.
[0054] The temperature of the liquid stream 12 is for example
between -150.degree. C. and -165.degree. C.
[0055] This liquid stream 12 is expanded to an intermediate
pressure by means, for example, of a valve 13. This intermediate
pressure is typically about 8 bara to 15 bara. It is for example 12
bara.
[0056] By virtue of this expansion, the liquid stream has been
vaporized, that is to say that gas has been instantaneously formed
(this is "flash" gas). The stream 14 thus produced contains a
majority of liquid and a minority of gas. This gas is enriched in
helium. This helium-enriched gas comprises at least 80% by volume
of the helium contained in the liquid stream 12. The two-phase
stream 14 is introduced into a first phase separator vessel 15. The
vessel 15 produces a liquid stream 16 and a gas stream 17. The gas
stream 17 contains more than 80% by volume of the helium contained
in the source stream 1.
[0057] Nevertheless, this gas stream 17 contains nitrogen. The
liquid stream 16 containing a majority of nitrogen, but also helium
and methane, is introduced into the top part 18 of the low-pressure
column 7 after having been expanded, for example by means of a
valve 19, in order to serve as reflux of the low-pressure column 7.
The stream 20 at the outlet of the top 21 of the column 7 is
introduced into a heat exchanger 22 or 2 in order to produce a
stream 23 which is rich in nitrogen or even pure with respect to
nitrogen, which does not contain helium and which contains less
than 1.5% by volume of methane.
[0058] The helium-enriched gas stream 17 typically contains more
than 70% by volume of nitrogen, more than 5% by volume of helium
and less than 2% by volume of methane, for example 90% by volume of
nitrogen, from 8% to 10% by volume of helium and less than 0.5% by
volume of methane. This gas stream 17 is introduced into a heat
exchanger 24 in order to be at least partially condensed. The
mixture 25 thus condensed is introduced into a second phase
separator vessel 26. A gas stream 27 is extracted at the top of the
separator 26. This gas stream 27 comprises more than 50% by volume
of helium, preferably more than 60% by volume of helium and more
particularly more than 70% by volume of helium. The gas stream 27
can optionally again pass through a heat exchanger 24.
[0059] The liquid phase 28 from the separator 26 serves to cool the
exchanger 24 after having been expanded to a pressure of less than
3 bara, for example by means of a pressure regulator such as a
valve 29. This liquid stream 28 is pure with respect to nitrogen,
for example it contains more than 99% by volume of nitrogen.
[0060] By virtue of the facility 31 comprising the nitrogen
rejection unit 6 and the helium extraction unit 30 as illustrated
in FIG. 1 and according to a process which is the subject of the
invention as previously described, with a source stream 1
containing approximately 50% by volume of nitrogen, 50% by volume
of methane and 0.3% by volume of helium, a helium purity in the
stream 27 of approximately 74% by volume and a helium yield of
approximately 91% are obtained.
[0061] It will be understood that many additional changes in the
details, materials, steps and arrangement of parts, which have been
herein described in order to explain the nature of the invention,
may be made by those skilled in the art within the principle and
scope of the invention as expressed in the appended claims. Thus,
the present invention is not intended to be limited to the specific
embodiments in the examples given above.
* * * * *