U.S. patent application number 17/500877 was filed with the patent office on 2022-04-28 for method and apparatus for producing high-pressure nitrogen.
This patent application is currently assigned to L'Air Liquide, Societe Anonyme pour l'Etude et l?Exploitation des Procedes Georges Claude. The applicant listed for this patent is L'Air Liquide, Societe Anonyme pour l'Etude et l?Exploitation des Procedes Georges Claude. Invention is credited to Jianwei CAO, Eric DAY, Baptiste FARA, Lin XU.
Application Number | 20220128301 17/500877 |
Document ID | / |
Family ID | 1000005956117 |
Filed Date | 2022-04-28 |
United States Patent
Application |
20220128301 |
Kind Code |
A1 |
CAO; Jianwei ; et
al. |
April 28, 2022 |
METHOD AND APPARATUS FOR PRODUCING HIGH-PRESSURE NITROGEN
Abstract
A method and apparatus for producing a high-pressure gas from an
air separation unit is provided, in which the method includes the
steps of introducing a cold air feed into a distillation column
system under conditions effective for separating the cold air feed
into a first air gas and a second air gas; withdrawing the first
and second air gases from the distillation column system and
warming said first and second air gases in a main heat exchanger,
wherein the first air gas is withdrawn from the distillation column
system at a medium pressure; splitting the first air gas into a
first fraction and a second fraction; expanding the first fraction
in a turbine; and compressing the second fraction in a booster to a
pressure that is higher than the medium pressure, wherein the
booster is powered by the turbine
Inventors: |
CAO; Jianwei; (Hangzhou,
CN) ; XU; Lin; (Hangzhou, CN) ; DAY; Eric;
(Hangzhou, CN) ; FARA; Baptiste; (Hangzhou,
CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
L'Air Liquide, Societe Anonyme pour l'Etude et l?Exploitation des
Procedes Georges Claude |
Paris |
|
FR |
|
|
Assignee: |
L'Air Liquide, Societe Anonyme pour
l'Etude et l?Exploitation des Procedes Georges Claude
Paris
FR
|
Family ID: |
1000005956117 |
Appl. No.: |
17/500877 |
Filed: |
October 13, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 2240/12 20130101;
F25J 2210/40 20130101; F25J 3/04381 20130101; F25J 3/04412
20130101; F25J 2270/04 20130101; F25J 3/04309 20130101; F25J
2200/06 20130101; F25J 2215/42 20130101 |
International
Class: |
F25J 3/04 20060101
F25J003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 26, 2020 |
CN |
CN 202011155756.5 |
Claims
1. A method for producing a high-pressure gas from an air
separation unit, the method comprising the steps of: introducing a
cold air feed into a distillation column system under conditions
effective for separating the cold air feed into a first air gas and
a second air gas; withdrawing the first and second air gases from
the distillation column system and warming said first and second
air gases in a main heat exchanger, wherein the first air gas is
withdrawn from the distillation column system at a medium pressure;
splitting the first air gas into a first fraction and a second
fraction; expanding the first fraction in a turbine; and
compressing the second fraction in a booster to a pressure that is
higher than the medium pressure, wherein the booster is powered by
the turbine.
2. The method as claimed in claim 1, further comprising the step of
warming the expanded first fraction.
3. The method as claimed in claim 2, wherein the expanded first
fraction is warmed in a second heat exchanger against the boosted
second fraction.
4. The method as claimed in claim 2, wherein the expanded first
fraction is warmed in the main heat exchanger.
5. The method as claimed in claim 4, wherein the boosted second
fraction is cooled to ambient temperature using a dedicated
cooler.
6. The method as claimed in claim 5, wherein the dedicated cooler
is a water cooler.
7. The method as claimed in claim 1, wherein the first fraction and
the second fraction are withdrawn at an intermediate location of
the heat exchanger, such that the first fraction and the second
fraction are partially warmed in the main heat exchanger.
8. The method as claimed in claim 7, further comprising the step of
warming the expanded first fraction in the main heat exchanger, and
wherein the boosted second fraction is at ambient temperature at an
outlet of the booster.
9. The method as claimed in claim 1, wherein the second fraction is
withdrawn at an intermediate location of the heat exchanger and the
first fraction is withdrawn at a warm end of the heat exchanger,
such that the first fraction is fully warmed and the second
fraction is partially warmed.
10. The method as claimed in claim 9, further comprising the step
of warming the expanded first fraction in the main heat exchanger,
and wherein the boosted second fraction is at ambient temperature
at an outlet of the booster.
11. The method as claimed in claim 1, wherein the distillation
column system comprises at least one distillation column.
12. The method as claimed in claim 1, wherein the distillation
column system comprises a double column.
13. The method as claimed in claim 1, wherein the first air gas is
nitrogen and the second air gas is oxygen.
14. An apparatus for producing a high-pressure gas from an air
separation unit, the apparatus comprising: a main heat exchanger
having a warm end and a cold end; a distillation column system in
fluid communication with the cold end of the main heat exchanger,
wherein the distillation column system is configured to receive a
cold air feed from the cold end of the main heat exchanger and
separate the cold air feed into a first air gas and a second air
gas, wherein the distillation column system is also configured to
send the first air gas to the cold end of the main heat exchanger;
a turbine in fluid communication with the main heat exchanger,
wherein the turbine is configured to receive a first fraction of
the first air gas after warming in the main heat exchanger; a warm
booster in fluid communication with the main heat exchanger,
wherein the warm booster is configured to receive a second fraction
of the first air gas after warming in the main heat exchanger
thereby providing a high-pressure gas that is at a pressure greater
than an operating pressure of a column within the distillation
column system, wherein the turbine is configured to power the warm
booster.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn. 119 (a) and (b) to Chinese patent application No.
CN202011155756.5, filed Oct. 26, 2020, the entire contents of which
are incorporated herein by reference
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention relates to a method and apparatus for
producing high-pressure nitrogen from a cryogenic air separation
unit.
BACKGROUND OF THE INVENTION
[0003] Cryogenic air separation units (ASUs) produce pure nitrogen
and oxygen streams by taking atmospheric air and separating it into
nitrogen and oxygen using distillation, most commonly using a
double distillation column having a low pressure and a
medium-pressure column, at cryogenic temperatures. Under normal
circumstances, the ASU will produce a low-pressure nitrogen stream
from the low-pressure column and a medium-pressure stream from the
medium-pressure column.
[0004] If high-pressure nitrogen is desired (e.g., at a pressure
greater than the pressure of the medium-pressure column, for
example at 7 to 11 bara), there are normally two ways to achieve
this goal: (1) internal compression and (2) external compression.
With internal compression, liquid nitrogen (LIN) is withdrawn from
the medium-pressure column and sent to a liquid pump for
pressurization to the desired high pressure. This pressurized LIN
is then vaporized in the main heat exchanger. With external
compression, a medium-pressure or low-pressure gas is withdrawn
from the medium-pressure column or low-pressure column,
respectively, before it is warmed in the main heat exchanger. After
warming in the main heat exchanger, the warmed gas is then
compressed in a dedicated compressor.
[0005] Unfortunately, when retrofitting an existing ASU using
internal compression, a new LIN pump is required and the operation
of the heat exchanger and the main air compressor (and/or booster
air compressor) will also be affected. In fact, in some
circumstances, the existing heat exchanger might not be designed to
handle LIN vaporization, and therefore, a new heat exchanger could
be required. Additionally, operating expenses will increase as
well.
[0006] With respect to external compression, both CAPEX and OPEX
will be increased due to the dedicated nitrogen compressor used to
compress the nitrogen downstream the heat exchanger.
SUMMARY OF THE INVENTION
[0007] The present invention is directed to a device and a method
that can provide pressurized nitrogen without increasing both the
CAPEX and OPEX. In one embodiment, the invention can include
splitting the medium-pressure GAN from the main heat exchanger into
two parts, with one part going to a turbine to produce low-pressure
GAN, while the other portion goes to a nitrogen booster. While the
CAPEX is increased, the OPEX is largely unchanged, as the turbine
can be used to drive the booster.
[0008] In another embodiment, the invention can include an
additional heat exchanger that is used to exchange heat between the
resulting high-pressure nitrogen from the booster and the
low-pressure nitrogen from the turbine.
[0009] In certain embodiments of the invention, there is no need to
extract any extra streams from the column system to warm up, which
means there is no impact on the existing heat exchanger and column
system. Furthermore, because the nitrogen booster is powered by the
nitrogen turbine, little to no additional power is needed, which
means OPEX remain largely unchanged.
[0010] In one embodiment, a method for producing a high-pressure
gas from an air separation unit is provided. In this embodiment,
the method can include the steps of: introducing a cold air feed
into a distillation column system under conditions effective for
separating the cold air feed into a first air gas and a second air
gas; withdrawing the first and second air gases from the
distillation column system and warming said first and second air
gases in a main heat exchanger, wherein the first air gas is
withdrawn from the distillation column system at a medium pressure;
splitting the first air gas into a first fraction and a second
fraction; expanding the first fraction in a turbine; and
compressing the second fraction in a booster to a pressure that is
higher than the medium pressure, wherein the booster is powered by
the turbine.
[0011] In optional embodiments of the method for producing a
high-pressure gas: [0012] the method can also include a step of
warming the expanded first fraction; [0013] the expanded first
fraction is warmed in a second heat exchanger against the boosted
second fraction; [0014] the expanded first fraction is warmed in
the main heat exchanger; [0015] the boosted second fraction is
cooled to ambient temperature using a dedicated cooler; [0016] the
dedicated cooler is a water cooler; [0017] the first fraction and
the second fraction are withdrawn at an intermediate location of
the heat exchanger, such that the first fraction and the second
fraction are partially warmed in the main heat exchanger; [0018]
the method can also include a step of warming the expanded first
fraction in the main heat exchanger, and wherein the boosted second
fraction is at ambient temperature at an outlet of the booster;
[0019] the second fraction is withdrawn at an intermediate location
of the heat exchanger and the first fraction is withdrawn at a warm
end of the heat exchanger, such that the first fraction is fully
warmed and the second fraction is partially warmed; [0020] the
method can also include a step of warming the expanded first
fraction in the main heat exchanger, and wherein the boosted second
fraction is at ambient temperature at an outlet of the booster;
[0021] the distillation column system comprises at least one
distillation column; [0022] the distillation column system
comprises a double column; and/or [0023] the first air gas is
nitrogen and the second air gas is oxygen.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] These and other features, aspects, and advantages of the
present invention will become better understood with regard to the
following description, claims, and accompanying drawings. It is to
be noted, however, that the drawings illustrate only several
embodiments of the invention and are therefore not to be considered
limiting of the invention's scope as it can admit to other equally
effective embodiments.
[0025] FIG. 1 represents an embodiment of the present
invention.
[0026] FIG. 2 represents a second embodiment of the present
invention.
[0027] FIG. 3 represents a third embodiment of the present
invention.
[0028] FIG. 4 represents a fourth embodiment of the present
invention.
DETAILED DESCRIPTION
[0029] While the invention will be described in connection with
several embodiments, it will be understood that it is not intended
to limit the invention to those embodiments. On the contrary, it is
intended to cover all the alternatives, modifications and
equivalence as may be included within the spirit and scope of the
invention defined by the appended claims.
[0030] In FIG. 1, air feed 2, which is already compressed and
purified, is cooled in main heat exchanger 10 and introduced into
distillation column system 20. Those of ordinary skill in the art
will recognize that distillation column system can be any system
that is suitable for separating air into its constituent components
(e.g., nitrogen, oxygen, argon). In the embodiment shown in FIG. 1,
a gaseous nitrogen stream 22, which is preferably at medium
pressure (i.e., pressure matching the medium-pressure column of a
double column system), is withdrawn from the distillation column
system 20 and warmed in heat exchanger 10. After warming, gaseous
nitrogen stream 22 is preferably split into a first fraction 24 and
a second fraction 26. First fraction 24 is expanded across turbine
30 to produce low-pressure nitrogen 32. Second fraction 26 is
compressed in booster 40 to produce high-pressure nitrogen 42. The
heat of compression can be removed from high-pressure nitrogen 42
by cooling it against low-pressure nitrogen 32 in supplemental heat
exchanger 50 to yield both low-pressure nitrogen product stream 34
and high-pressure nitrogen product stream 44.
[0031] The embodiment shown in FIG. 1 is particularly useful in
instances with an existing plant in that there is no need to modify
the existing heat exchanger 10. Instead, supplemental heat
exchanger 50 is used to provide the appropriate cooling for stream
42.
[0032] In FIG. 2, the setup can be largely the same, with the
exception of the cooling and warming of streams 42 and 32,
respectively. In this embodiment, high-pressure nitrogen 42 can be
cooled via cooling water cooler 45, and low-pressure nitrogen 32
can be warmed in main heat exchanger 10. An advantage of the
embodiment shown in FIG. 2 is that the cooling provided by
expansion of stream 32 can be used to further cool the incoming
air, thereby allowing for additional flexibility in the main
process (e.g., increased liquid production and/or lower operating
expenses).
[0033] In the embodiment shown in FIG. 3, high-pressure nitrogen 42
does not require any additional cooling to get to ambient
temperatures after compression, since gaseous nitrogen stream 22 is
only partially warmed within heat exchanger 10.
[0034] FIG. 4 provides an additional embodiment similar to that of
FIG. 3; however, in the embodiment of FIG. 4, first fraction 24 is
fully warmed in heat exchanger 10 prior to being expanded in
turbine 30. Stream 42 for both FIG. 3 and FIG. 4 is preferably at
ambient temperature following compression in booster 40. By fully
warming first fraction 24 to ambient temperature, either more power
can be produced within expansion turbine 30 due to a higher
enthalpy change or a lower flow rate for stream 24 can be used to
achieve the same pressure for stream 42. Therefore, the embodiment
of FIG. 4 allows for the potential of power savings and/or
increased HP GAN production.
[0035] The tables below show comparative flows, temperatures and
pressures of the various streams for each figure.
TABLE-US-00001 TABLE I Comparative Data for FIG. 1 2 22 24 32 34 26
42 44 F (Nm3/h) 158550 36360 18000 18000 18000 18360 18360 18360
P(bar a) 5.967 5.748 5.535 1.220 1.106 5.535 10.262 10.162 T (C.)
26.0 -177.4 15.6 -60.7 20.0 15.6 89.6 11.4
TABLE-US-00002 TABLE II Comparative Data for FIG. 2 2 22 24 32 34
26 42 44 F (Nm3/h) 159170 36360 17990 17990 17990 18370 18370 18370
P(bar a) 5.961 5.742 5.544 1.320 1.197 5.544 10.034 9.934 T (C.)
26.0 -177.4 8.1 -63.3 8.1 8.1 77.2 29.0
TABLE-US-00003 TABLE III Comparative Data for FIG. 3 2 22 24 32 34
26 42 F (Nm3/h) 159750 36360 17840 17840 17840 18520 18520 P(bar a)
5.969 5.750 5.552 1.290 1.176 5.552 10.031 T (C.) 26.0 -177.3 -50.0
-107.7 17.2 -50.0 4.7
TABLE-US-00004 TABLE IV Comparative Data for FIG. 4 2 22 24 32 34
26 42 F (Nm3/h) 158400 31300 12800 12800 12800 18500 18500 P(bar a)
5.988 5.773 5.750 1.190 1.171 5.576 10.068 T (C.) 26.0 -177.3 17.1
-62.1 17.1 -50.0 4.7
[0036] While the embodiments above have been disclosed with
reference to stream 22 being medium-pressure nitrogen, those of
ordinary skill in the art will recognize that stream 22 could also
be low-pressure oxygen.
[0037] While the invention has been described in conjunction with
specific embodiments thereof, it is evident that many alternatives,
modifications, and variations will be apparent to those skilled in
the art in light of the foregoing description. Accordingly, it is
intended to embrace all such alternatives, modifications, and
variations as fall within the spirit and broad scope of the
appended claims. The present invention may suitably comprise,
consist or consist essentially of the elements disclosed and may be
practiced in the absence of an element not disclosed. Furthermore,
language referring to order, such as first and second, should be
understood in an exemplary sense and not in a limiting sense. For
example, it can be recognized by those skilled in the art that
certain steps can be combined into a single step.
[0038] The singular forms "a", "an", and "the" include plural
referents, unless the context clearly dictates otherwise.
[0039] Optional or optionally means that the subsequently described
event or circumstances may or may not occur. The description
includes instances where the event or circumstance occurs and
instances where it does not occur.
[0040] Ranges may be expressed herein as from about one particular
value, and/or to about another particular value. When such a range
is expressed, it is to be understood that another embodiment is
from the one particular value and/or to the other particular value,
along with all combinations within said range.
* * * * *