U.S. patent application number 16/755821 was filed with the patent office on 2020-10-22 for method and device for separating air by cryogenic distillation.
The applicant listed for this patent is L'Air Liquide, Societe Anonyme pour I'Etude et I'Exploitation des Precedes Georges Claude. Invention is credited to Richard DUBETTIER-GRENIER, Patrick LE BOT.
Application Number | 20200333069 16/755821 |
Document ID | / |
Family ID | 1000004955527 |
Filed Date | 2020-10-22 |
United States Patent
Application |
20200333069 |
Kind Code |
A1 |
DUBETTIER-GRENIER; Richard ;
et al. |
October 22, 2020 |
METHOD AND DEVICE FOR SEPARATING AIR BY CRYOGENIC DISTILLATION
Abstract
A method for separating air by cryogenic distillation, wherein
air is compressed in a first compressor, cooled in a heat exchanger
and then separated in a system of columns, liquid oxygen is
vaporized in the heat exchanger countercurrent to a flow of
pressurized gas which pseudo-condenses, a flow of gas which is air
or a gas delivered from the system of columns is expanded in a
cryogenic expansion turbine having a single wheel, the turbine
having an inlet temperature lower than -100.degree. C., a gas which
is air or a gas delivered from the system of columns is compressed
in a first booster compressor having a single wheel, with an inlet
temperature higher than -50.degree. C., a gas which is air or a gas
delivered from the system of columns.
Inventors: |
DUBETTIER-GRENIER; Richard;
(La Varenne Saint Hilaire, FR) ; LE BOT; Patrick;
(Vincennes, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
L'Air Liquide, Societe Anonyme pour I'Etude et I'Exploitation des
Precedes Georges Claude |
Paris |
|
FR |
|
|
Family ID: |
1000004955527 |
Appl. No.: |
16/755821 |
Filed: |
August 30, 2018 |
PCT Filed: |
August 30, 2018 |
PCT NO: |
PCT/FR2018/052130 |
371 Date: |
April 13, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 2240/04 20130101;
F25J 2230/20 20130101; F25J 3/04412 20130101; F25J 3/04024
20130101; F25J 3/04393 20130101; F25J 3/04309 20130101; F25J 3/0406
20130101; F25J 3/0409 20130101; F25J 3/04381 20130101; F25J 3/04054
20130101; F25J 3/04351 20130101 |
International
Class: |
F25J 3/04 20060101
F25J003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 13, 2017 |
FR |
1701070 |
Claims
1.-15. (canceled)
16. A method for separating air by cryogenic distillation, wherein
air is compressed in a first compressor, cooled in a heat exchanger
and then separated in a system of columns, liquid oxygen is
vaporized in the heat exchanger countercurrent to a flow of
pressurized gas which pseudo-condenses, a flow of gas which is air
or a gas delivered from the system of columns is expanded in a
cryogenic expansion turbine having a single wheel, the turbine
having an inlet temperature lower than -100.degree. C., a gas which
is air or a gas delivered from the system of columns is compressed
in a first booster compressor having a single wheel, with an inlet
temperature higher than -50.degree. C., a gas which is air or a gas
delivered from the system of columns, this gas having already been
compressed in the first booster compressor, is compressed in a
second booster compressor having a single wheel with an inlet
temperature lower than -100.degree. C., the gas compressed in at
least the first booster compressor cools in the heat exchanger,
contributes to the vaporization of liquid oxygen by exchange of
heat in the exchanger, and is pseudo-liquefied on leaving the cold
end of the heat exchanger, wherein: a) the work generated by the
expansion turbine is used for the compression step in the first
booster compressor and for the compression step in the second
booster compressor, b) the operating conditions for the wheel of
the expansion turbine, the wheel of the first booster compressor
and the wheel of the second booster compressor are defined such
that these three wheels have the same rotational speed, c) i) the
wheel of the first booster compressor, the wheel of the second
booster compressor and the wheel of the turbine are mounted on the
same rotation shaft, or ii) the first and the second booster
compressor are connected to the wheel of the expansion turbine,
each by a rotation shaft, these shafts rotating at the same
rotational speed, or iii) the first booster compressor and the
wheel of the expansion turbine are connected to the second booster
compressor, each by a rotation shaft, these shafts rotating at the
same rotational speed, and d) the first compression step allows
work to be generated outside the cold box, and this generates
cooling power for the air separation method.
17. The method as claimed in claim 16, comprising a second
expansion turbine, wherein the first expansion turbine and the
second expansion turbine operate in parallel and the flow of gas
which is air or a gas delivered from the system of columns is
divided into two fractions, each being expanded in one of the two
turbines.
18. The method as claimed in claim 17, wherein, of the expansion
wheel, the wheel of the second expansion turbine, the wheel of the
first booster compressor and the wheel of the second booster
compressor, at least one has an efficiency lower than that which it
would have, under the same operating conditions, at another
rotational speed.
19. The method as claimed in claim 16, wherein the gas compressed
in the first and the second booster compressor is air used for
distillation.
20. The method as claimed in claim 16, wherein at least some of the
air, or even all of the air or at least some of the gas, or even
all of the gas, compressed in the first booster compressor is then
compressed in the second booster compressor.
21. The method as claimed in claim 16, wherein the work produced by
the turbine is not transferred to a generator, to an oil brake or
to a compressor other than the first and second booster
compressors.
22. The method as claimed in claim 16, wherein the inlet
temperature of the turbine is lower than the inlet temperature of
the second booster compressor and/or the inlet temperature of the
first booster compressor.
23. The method as claimed in claim 16, wherein the air is
compressed first in the first booster compressor and then in the
second booster compressor.
24. The method as claimed in claim 23, wherein all the air
compressed in the first booster compressor is then compressed in
the second booster compressor.
25. The method as claimed in claim 16, wherein the air expanded in
the turbine has been compressed in the first booster
compressor.
26. The method as claimed in claim 25, wherein the air expanded in
the turbine has already been compressed in the first booster.
27. The method as claimed in claim 16, wherein the air expanded in
the turbine has not been compressed in the first or the second
booster compressor.
28. A apparatus for separating air by cryogenic distillation,
comprising a heat exchanger, a pipe for sending air compressed in a
first compressor to be cooled in the heat exchanger, a system of
columns, a pipe for sending the air cooled in the heat exchanger to
be separated in the system of columns, a pipe for sending liquid
oxygen from the system to be vaporized in the heat exchanger, a
pipe for sending a flow of pressurized gas into the heat exchanger,
a cryogenic expansion turbine having a single wheel, a pipe
connected to an intermediate point of the heat exchanger for
sending a flow of gas which is air or a gas delivered from the
system of columns from the heat exchanger to be expanded in the
cryogenic expansion turbine, the turbine having an inlet
temperature lower than -100.degree. C., a first single-stage
booster compressor with an inlet temperature higher than
-50.degree. C., a pipe for sending a gas which is air or a gas
delivered from the system of columns, to be compressed in the first
booster compressor, a second single-stage booster compressor with
an inlet temperature lower than -100.degree. C., a pipe connected
to an intermediate point of the heat exchanger for sending a gas
which is air or a gas delivered from the system of columns to be
compressed in the second booster compressor, a means for sending at
least some of the gas, or even all of the gas, compressed in the
first booster compressor to be compressed in the second booster
compressor), a pipe for sending the gas compressed in at least the
first booster compressor to be cooled in the heat exchanger and
thus contribute to the vaporization of liquid oxygen by exchange of
heat in the exchanger, wherein: a) the wheel of the expansion
turbine, possibly the wheel of the second turbine, the wheel of the
first booster compressor and the wheel of the second compressor are
connected to one another in such a way that each wheel can have the
same rotational speed, and b) i) the wheel of the first booster
compressor, the wheel of the second booster compressor and the
wheel of the turbine is mounted on the same rotation shaft, or ii)
the first and the second booster compressor are connected to the
wheel of the expansion turbine, and possibly to the wheel of the
second turbine, each by a rotation shaft, these shafts being
capable of rotating at the same rotational speed, or iii) the first
booster compressor and the wheel of the expansion turbine are
connected to the second booster compressor, each by a rotation
shaft, these shafts being capable of rotating at the same
rotational speed.
29. The apparatus as claimed in claim 28, wherein the gas
compressed in the first and the second booster compressor is air
intended for distillation.
30. The apparatus as claimed in claim 28, comprising a means for
sending at least some of the air, or even all of the air,
compressed in the first booster compressor to be compressed in the
second booster compressor.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a 371 of International Application
PCT/FR2018/052130, filed Aug. 30, 2018, which claims priority to
French Patent Application No. 1701070, filed Oct. 13, 2017, the
entire contents of which are incorporated herein by reference.
BACKGROUND
[0002] The present invention relates to a method and an apparatus
for separating air by cryogenic distillation.
[0003] Air separation units (ASU) for separating air by cryogenic
distillation using cryogenic compression of a gas are known. One
known means for implementing this cold compression is to drive a
cryogenic-compression wheel using a cryogenic expansion turbine.
Nevertheless, such equipment does not generate the production of
coldness needed for the operation of air separation units because
no work is extracted from the cold box. For that reason, such
systems are always coupled to an additional means for producing
cold. The known means are: [0004] Oil brake: The work is extracted
by the viscous friction between the rotational shaft and a film of
pressurized oil contained in a cavity around the shaft. This
friction causes the oil to heat up, which oil is cooled outside of
the system in order to remove the work. This system has the
disadvantage of implementability and efficiency. Specifically, the
work generated is lost and detracts from the efficiency of the
whole. Furthermore, the system is limited in terms of the extracted
power (approx. 100 kW) and is therefore not suitable for ASUs that
require a higher cooling power. [0005] Compressor brake and
refrigerant: In this method, another assembly comprising another
turbine coupled to a compressor is used to supplement the assembly
of a turbine having a cryogenic outlet temperature coupled to a
compressor having a cryogenic booster inlet temperature. The
turbine is therefore coupled to a compressor the intake temperature
of which is ambient or slightly below ambient. Compressing the gas
heats same and the gas is cooled in a heat exchanger (typically
against water) in order to extract heat, and therefore work,
therefrom. This is the means most commonly used in the field of
ASUs. [0006] Generator: The expansion turbine may also be coupled
to a generator which extracts work by generating electrical energy
which is sent to a network. The rotational speed of this generator
is most often very much lower than the rotational speed of the
turbine, requiring a reduction gearbox between the two elements.
This component is expensive and generates friction losses.
Generators with high rotational speeds are also found. This
generator is then integrated onto the turbine shaft and generates
electricity without the need for an intermediate reduction gearbox.
A system for processing the electric signal (frequency, etc. . . .
) is then needed in order to make it compatible with the
specifications of the electrical networks to which it can then be
sent on. These systems are very expensive and also limited in terms
of generated power (approx. 250 kW) and are unable to fully meet
the needs of the ASUs.
[0007] Furthermore, it is also known practice to be able to couple
a combination of compressors and turbines on the one same shaft.
Drives will be encountered for example where compressors are driven
by a gas turbine, having a hot gas turbine driving its air
compressor and another product compressor. However, these
arrangements, however complex they might be, are not applicable to
cryogenic use: different types of turbines, below-ambient
temperatures, no criticality regarding thermal losses.
SUMMARY
[0008] According to the invention, in an air separation unit
separating air by cryogenic distillation, two compressed flows are
generated, characterized in that: [0009] each compression is
achieved in a single-stage compression stage, [0010] the two
compression stages are driven by the one same cryogenic expansion
turbine, [0011] the first compression step, from a temperature
close to ambient temperature, allows work to be generated outside
the cold box, and this generates cooling power for the air
separation method, [0012] the second compression step is a
cryogenic compression, which compresses a gas drawn off from an
intermediate level of the main exchanger at a first temperature
which is a cryogenic temperature, and returned to the main
exchanger at a temperature higher than the first temperature.
[0013] In one preferred implementation, the two compression steps
will be arranged in series on the same flow. As a preference, this
flow will be part of the total airflow, which will first of all be
compressed from ambient temperature, then when cold. This flow,
after having been reintroduced into the main exchanger, will travel
as far as the cold end of the exchanger where it will be (pseudo)
liquefied.
[0014] According to the invention, the turbine wheel and the wheels
of the booster compressors rotate at the same rotational speed.
[0015] Surprisingly, that makes it possible to maintain acceptable
thermodynamic efficiencies in the compression steps and in the
expansion step, despite the three wheels having the same rotational
speed. By comparison with the prior art which consisted in using
two turbine and booster assemblies, it becomes possible thanks to
the invention to reduce the investment costs thereof without
dramatically penalizing the efficiency of the method.
[0016] The invention will be described in more detail with
reference to the figures which depict methods according to the
invention.
[0017] One subject matter of the invention provides a method for
separating air by cryogenic distillation, wherein air is compressed
in a first compressor, cooled in a heat exchanger and then
separated in a system of columns, liquid oxygen is vaporized in the
heat exchanger countercurrent to a flow of pressurized gas which
(pseudo) condenses, a flow of gas which is air or a gas delivered
from the system of columns is expanded in a cryogenic expansion
turbine having a single wheel, having an inlet temperature lower
than -100.degree. C., a gas which is air or a gas delivered from
the system of columns, this gas having already been compressed in
the first booster compressor, is compressed in a first booster
compressor having a single wheel with an inlet temperature higher
than -50.degree. C., a gas which is air or a gas delivered from the
system of columns is compressed in a second booster compressor
having a single wheel with an inlet temperature lower than
-100.degree. C., the gas compressed in at least the first booster
compressor cools in the heat exchanger, contributes to the
vaporization of liquid oxygen by exchange of heat in the exchanger,
and is (pseudo) liquefied on leaving the cold end of the heat
exchanger, wherein: [0018] a) the work generated by the expansion
turbine is used for the cryogenic compression step in the first
booster compressor and for the compression step in the second
booster compressor, and [0019] b) the operating conditions for the
wheel of the expansion turbine, the wheel of the first booster
compressor and the wheel of the second booster compressor are
defined to allow these three wheels to have the same rotational
speed, and [0020] c) i) the wheel of the first booster compressor,
the wheel of the second booster compressor and the wheel of the
turbine are mounted on the same rotation shaft, or [0021] ii) each
booster compressor is connected to the wheel of the turbine by a
rotation shaft, these shafts rotating at the same rotational speed,
or [0022] iii) the first booster compressor and the wheel of the
expansion turbine are connected to the second booster compressor,
each by a rotation shaft, these shafts rotating at the same
rotational speed, and [0023] d) the first compression step allows
work to be generated outside the cold box, and this generates
cooling power for the air separation method.
[0024] According to other optional aspects: [0025] of the expansion
wheel, the wheel of the first booster compressor and the wheel of
the second booster compressor, at least one has an efficiency lower
than that which it would have, under the same operating conditions,
at another rotational speed. [0026] the gas compressed in the first
and the second booster compressor is air intended for distillation.
[0027] at least some of the air, or even all of the air or at least
some of the gas, or even all of the gas, compressed in the first
booster compressor is then compressed in the second booster
compressor. [0028] the work produced by the turbine is not
transferred to a generator, to an oil brake or to a compressor
other than the first and second booster compressors. [0029] the
inlet temperature of the turbine is lower than the inlet
temperature of the second booster compressor and/or the inlet
temperature of the first booster compressor. [0030] the air is
compressed first of all in the first booster compressor and then in
the second booster compressor. [0031] all of the air compressed in
the first booster compressor is then compressed in the second
booster compressor. [0032] the air expanded in the turbine has been
compressed in the first booster compressor. [0033] the air expanded
in the turbine has been compressed in the first booster compressor
and possibly in the second booster compressor. [0034] the air
expanded in the turbine has not been compressed in the first or the
second booster compressor.
[0035] Another aspect of the invention provides an apparatus for
separating air by cryogenic distillation, comprising a heat
exchanger, a pipe for sending air compressed in a first compressor
to be cooled in the heat exchanger, a system of columns, a pipe for
sending the air cooled in the heat exchanger to be separated in the
system of columns, a pipe for sending liquid oxygen from the system
to be vaporized in the heat exchanger, a pipe for sending a flow of
pressurized gas into the heat exchanger, a cryogenic expansion
turbine having a single wheel, a pipe connected to an intermediate
point of the heat exchanger for sending a flow of gas which is air
or a gas delivered from the system of columns from the heat
exchanger to be expanded in the cryogenic expansion turbine, having
an inlet temperature lower than -100.degree. C., a first
single-stage booster compressor with an inlet temperature higher
than -50.degree. C., a pipe, possibly connected to an intermediate
point of the heat exchanger, for sending a gas which is air or a
gas delivered from the system of columns, to be compressed in the
first booster compressor, a second single-stage booster compressor
with an inlet temperature lower than -100.degree. C., a pipe
connected to an intermediate point of the heat exchanger for
sending a gas which is air or a gas delivered from the system of
columns to be compressed in the second booster compressor, where
appropriate, means for sending at least some of the gas, or even
all of the gas, compressed in the first booster compressor to be
compressed in the second booster compressor, a pipe for sending the
gas compressed in at least the first booster compressor to be
cooled in the heat exchanger and thus contribute to the
vaporization of liquid oxygen by exchange of heat in the exchanger,
wherein: [0036] a) the wheel of the expansion turbine, the wheel of
the first booster compressor and the wheel of the second compressor
are connected to one another in such a way that each wheel can have
the same rotational speed, and [0037] b) the wheel of the first
booster compressor, the wheel of the second booster compressor and
the wheel of the turbine being mounted on the same rotation shaft
or each booster compressor is connected to the wheel of the turbine
by a rotation shaft, these shafts being designed to rotate at the
same rotational speed.
[0038] According to other optional aspects: [0039] the method uses
the second expansion turbine, the two turbines operating in
parallel and the flow of gas which is air or a gas delivered from
the system of columns is divided into two fractions, each being
expanded in one of the two turbines. [0040] the gas compressed in
the first and the second booster compressor is air intended for
distillation. [0041] the apparatus comprises means for sending at
least some of the air, or even all of the air or at least some of
the gas, or even all of the gas, compressed in the first booster
compressor to be compressed in the second booster compressor.
[0042] the turbine is not coupled to a generator, to an oil brake
or to a compressor other than the first and second booster
compressors. [0043] the apparatus comprises just one single
turbine. [0044] the apparatus comprises means for sending air from
the first booster compressor and possibly from the second booster
compressor to the turbine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] 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:
[0046] FIG. 1 is a symbolic representation of a method for
separating air by cryogenic distillation in a double column having
an optional minaret, in accordance with one embodiment of the
present invention.
[0047] FIG. 2 is a symbolic representation of a method of
separating air by cryogenic distillation in a double column system
wherein two booster compressors are used, in accordance with one
embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0048] A flow of air compressed to the pressure of the first
column, denoted by the reference MP, from the double column is
split into two. A flow 3 is cooled in a main heat exchanger E1 and
is sent to the first column MP. The rest 5 of the air is compressed
in an auxiliary booster compressor S and cooled in a cooler R
before being split into two. A part, 7, of the air is sent to the
main heat exchanger E1 where it is cooled down to an intermediate
temperature of this exchanger which is lower than -100.degree. C.
At this temperature, the flow 7 is sent to a turbine T where it is
expanded to the pressure of the first column before being mixed
with the flow 3 and sent to the first column.
[0049] Another part, 9, of the air from the booster compressor S is
sent to a first booster compressor B1 without having been cooled in
the heat exchanger E1. The air 9 is then cooled in a cooler before
being sent to the hot end of the heat exchanger where it is cooled
to an intermediate temperature of the heat exchanger which is
nevertheless higher than the inlet temperature of the turbine T.
The air 9 leaves the exchanger E1 at this intermediate temperature
and is compressed in a second booster compressor B2. The compressed
air is returned to the exchanger E1 at a temperature higher either
than the intermediate temperature or the inlet temperature of the
turbine T. The air compressed in B2 continues to be cooled in the
heat exchanger E1 as far as the cold end and is expanded in a valve
V to return to the column MP in liquid or pseudo-condensed form. A
part of this expanded liquid may also be returned to the
low-pressure column BP.
[0050] The first and second booster compressors are both
single-stage booster compressors having just one compression
wheel.
[0051] The wheel of the first booster compressor B1, the wheel of
the second booster compressor B2 and the wheel of the turbine T are
mounted on the same rotation shaft, or on securely connected
shafts.
[0052] The turbine T is not coupled either to a generator or to an
oil brake. It drives only the first and second booster compressors
B1, B2.
[0053] The first booster compressor B1 has an inlet temperature
higher than -50.degree. C., possibly higher than 0.degree. C.,
preferably higher than 10.degree. C. The second booster compressor
B2 has an inlet temperature lower than -100.degree. C.
[0054] A liquid enriched in oxygen and a liquid enriched in
nitrogen are sent from the first column MP to the second column,
denoted by the reference BP, as reflux liquids. An overhead gas of
the first column condenses in a bottom condenser of the second
column and is condensed and returned to the first column.
[0055] In the method of FIG. 2, just two booster compressors are
used. The air flow 1 compressed to a pressure at least 5 bar higher
than the pressure of the first column is divided into two parts 7,
9. The part 7 is sent to the main heat exchanger E1 where it is
cooled down to an intermediate temperature of this exchanger which
is lower than -100.degree. C. At this temperature, the flow 7 is
sent to a turbine T where it is expanded to the pressure of the
first column. The part 9 of the air is compressed in a second
booster compressor B2. The compressed air is sent, after having
been cooled in a water refrigerant, to the hot end of the heat
exchanger E1 where it is cooled to an intermediate temperature of
the exchanger which is nevertheless higher than or equal to the
inlet temperature of the turbine T. The air 9 leaves the exchanger
E1 at this intermediate temperature and is compressed in a second
booster compressor B2. The compressed air is returned to the
exchanger E1 at a temperature higher than the inlet temperature of
the turbine T. The air compressed in B2 continues to be cooled in
the heat exchanger E1 as far as the cold end and is expanded in a
valve to return to the column MP in liquid or pseudo-condensed
form. A part of this expanded liquid may also be returned to the
low-pressure column BP.
[0056] The first and second booster compressors are both
single-stage booster compressors B1, the wheel of the second
booster compressor B2 and the wheel of the turbine T are mounted on
the same rotation shaft, or on securely connected shafts.
[0057] The turbine T is not coupled either to a generator or to an
oil brake. It drives only the first and second booster compressors
B1, B2.
[0058] The first booster compressor B1 has an inlet temperature
higher than 0.degree. C. The second booster compressor B2 has an
inlet temperature lower than -100.degree. C.
[0059] In the two figures, the work generated by the expansion
turbine is used for the cryogenic compression step in the first
booster compressor and for the compression step in the second
booster compressor.
[0060] The operating conditions for the wheel of the expansion
turbine T, the wheel of the first booster compressor B1 and the
wheel of the second booster compressor B2 are defined to allow
these three wheels to have the same rotational speed.
[0061] The wheel of the first booster compressor B1, the wheel of
the second booster compressor B2 and the wheel of the turbine T are
mounted on the same rotation shaft in the figures.
[0062] Otherwise, each booster compressor may be connected to the
wheel of the turbine by a rotation shaft, these shafts rotating at
the same rotational speed.
[0063] Of the expansion wheel, the wheel of the first booster
compressor and the wheel of the second booster compressor, at least
one has an efficiency lower than that which it would have, under
the same operating conditions, at another rotational speed.
[0064] At least one, or even at least two, or even all of the
wheels do not operate at their optimal efficiency.
[0065] It will be appreciated that the invention also applies to
instances in which a flow of nitrogen or another gas originating
from distillation is compressed in a first booster compressor
having an inlet temperature higher than -50.degree. C. and a second
booster compressor having an inlet temperature lower than
-100.degree. C.
[0066] 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.
* * * * *