U.S. patent application number 11/571131 was filed with the patent office on 2008-08-07 for method and installation for the emergency back-up supply of a gas under pressure.
Invention is credited to Jean-Marc Peyron.
Application Number | 20080184736 11/571131 |
Document ID | / |
Family ID | 34946246 |
Filed Date | 2008-08-07 |
United States Patent
Application |
20080184736 |
Kind Code |
A1 |
Peyron; Jean-Marc |
August 7, 2008 |
Method And Installation For The Emergency Back-Up Supply Of A Gas
Under Pressure
Abstract
In a method for the emergency back-up supply of a gas under
pressure by vaporization of a pressurized liquid, this gas normally
being supplied by vaporization of liquid (33) in a first exchanger
(1) of a pumped air separation unit, during the step of operating a
second exchanger (2) in order to produce the make-up gas,
pressurized liquid (33) and high-pressure air (8) continue to be
sent to the first exchanger.
Inventors: |
Peyron; Jean-Marc; (Creteil,
FR) |
Correspondence
Address: |
AIR LIQUIDE;Intellectual Property
2700 POST OAK BOULEVARD, SUITE 1800
HOUSTON
TX
77056
US
|
Family ID: |
34946246 |
Appl. No.: |
11/571131 |
Filed: |
June 28, 2005 |
PCT Filed: |
June 28, 2005 |
PCT NO: |
PCT/EP2005/053014 |
371 Date: |
November 15, 2007 |
Current U.S.
Class: |
62/643 |
Current CPC
Class: |
F25J 3/04824 20130101;
F25J 2240/42 20130101; F25J 3/0409 20130101; F25J 3/04478 20130101;
F25J 3/04412 20130101; F25J 2250/50 20130101; F25J 2235/50
20130101; F25J 2290/62 20130101 |
Class at
Publication: |
62/643 |
International
Class: |
F25J 3/04 20060101
F25J003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 29, 2004 |
FR |
04/51354 |
Claims
1-12. (canceled)
13. A method for the emergency back-up supply of a gas under
pressure, by vaporization of a pressurized liquid in which: i)
during a first step: a) a first stream of air is compressed by
means of a compressor (3) and purified in a purification unit (5);
b) at least one portion of the air is compressed to a high
pressure, which allows vaporization of the pressurized liquid; c)
at least one portion of the air at the high pressure is sent to a
first exchanger (1); d) at least one portion of the air cooled in
the first exchanger is sent to a system of distillation columns
(15, 17); and e) at least one liquid (27) is withdrawn from one of
the columns of the system, the liquid is pressurized and sent to
the first exchanger, where it vaporizes to form a gas under
pressure; ii) during a second step a stream of the said liquid is
sent to a second exchanger (2) where it vaporizes to form a make-up
stream of the gas under pressure, characterized in that, during the
second step, at least initially, air at the high pressure and
pressurized liquid coming from one column of the system are sent to
the first exchanger and then the stream of high-pressure air sent
to the first exchanger is reduced, possibly to zero, and the stream
of pressurized liquid sent to the first exchanger is reduced,
possibly to zero.
14. The method of claim 13, in which, during at least part of the
second step, air is sent from a gaseous air storage tank (5, 9) to
the first exchanger and then to the system of columns and,
optionally during the first step, supercharged air is sent to the
air storage tank where it is stored in gaseous form.
15. The method of claim 14, in which all the air is compressed to
the high pressure and then purified in the purification unit (5),
the purification unit constituting the air storage tank.
16. The method of claim 15, in which, as high-pressure air
passages, only passages of the first exchanger (1) dedicated to
high-pressure air are used, these passages being closest to the
passages for vaporizing the said liquid, this being achieved by
separation of the liquid air output boxes at the cold end of the
main exchanger and by the addition of a liquid air valve per
additional liquid air output box, which makes it possible to expand
this liquid into the columns.
17. The method of claim 13, in which all the liquid to be
pressurized is stored in a second storage tank (19).
18. The method of claim 13, in which, during the first step, a
stream of the said liquid, smaller than the stream sent during the
second step, is sent to the second exchanger (2) where it vaporizes
to form gas under pressure.
19. The method of claim 13, in which at least one of the liquids
(27) to be pressurized is rich in oxygen, argon, nitrogen,
hydrogen, helium, methane or carbon monoxide.
20. The method of claim 13, in which the liquid is pressurized by
means of at least one pump (39).
21. The method of claim 13, in which, during the second step, air
is sent directly from the first storage tank (5, 9) to the first
exchanger (1).
22. The method of claim 13, in which, during a third step,
pressurized liquid is sent only to the second exchanger (2) and air
is no longer sent to the first exchanger (1).
23. The method of claim 13, in which, during the second step, at
least some of the heat needed to vaporize the liquid comes from the
thermal inertia of the first exchanger (1).
24. An installation for the emergency back-up supply of a gas under
pressure, by vaporization of a pressurized liquid, comprising: i) a
first storage tank (5, 9); ii) a pump (39); iii) a first exchanger
(1); iv) a second exchanger (2); v) a compressor (3); vi) a
purification unit (5); vii) a supercharger (7); viii) means for
sending air to the compressor, means for sending compressed air to
the purification unit and means for sending at least one portion of
the purified air to the supercharger; ix) means for sending air to
a column of a system of columns (17, 19); x) means for withdrawing
at least one liquid (27) from the system of columns optionally
after having stored it in a storage tank; xi) means for sending the
liquid to the pump in order to pressurize it; xii) means for
sending the pressurized liquid to the first exchanger; xiii) means
for withdrawing the vaporized liquid from the first exchanger; xiv)
means for sending the pressurized liquid to the second exchanger;
and xv) a tank (9) for storing gaseous air under pressure, the tank
being connected to the outlet of the air supercharger,
characterized in that the storage tank (9) is connected to the
outlet of the air supercharger via an expansion valve.
Description
[0001] This invention relates to methods and installations for the
emergency back-up supply of a gas under pressure, by vaporization
of cryogenic liquids, in particular those used for supplying
customers with gaseous products (nitrogen, oxygen, argon) when the
industrial installations (such as air separation units) can ensure
only partial supply of the product, or even no supply at all (f or
example in the event of trip-out, load reduction for an electricity
tariff constraint, etc.). The invention also applies to the storage
of other cryogenic liquids, such as hydrogen, helium and carbon
monoxide.
[0002] An emergency back-up vaporizer is illustrated in EP-A-0 452
177 in which liquid nitrogen coming from a storage tank is
vaporized in an exchanger by heat exchange with the ambient
air.
[0003] EP-A-0 628 778 discloses a cryogenic liquid storage tank in
which the liquid is pumped and then vaporized in a vaporizer before
being sent to the customer.
[0004] "Large Oxygen Plant Economics and Reliability" by W. J.
Scharle, Bulletin Y-143, National Fertilizer Division Center,
Tennessee Valley Authority, Muscle Shoals, Ala. and "Oxygen
Facilities for Synthetic Fuel Projects" by W. J. Scharle and K.
Wilson, Journal of Engineering for Industry, November 1981, Vol.
103, pp. 409-417 describe an emergency back-up oxygen production
system composed of:
[0005] a storage tank containing a quantity of product in liquid
form;
[0006] several pumps (here, two pumps for reliability reasons) that
withdraw the liquid contained in the storage tank in order to
compress it to the pressure normally delivered to customers
(pressure in the line); and
[0007] an exchanger, the function of which is to vaporize the
liquid under pressure.
[0008] On leaving this equipment, the gas is in general close to
the ambient temperature and is sent to the customer. Depending on
the energy sources available on the site and their costs, this
exchanger may use as heat source to vaporize the liquid under
pressure, for example air, steam, hot water or combustion flue
gas.
[0009] One of the main features of these emergency back-up
installations is their start-up time. This is particularly
important as it determines the quality and the continuity of the
gas supply to customers. An excessively long start-up time after
tripping of the production unit may cause too great a pressure drop
in the line and may generate malfunctions in customer processes and
installation shut-down.
[0010] In the case of the oxygen production systems described in
the above articles, a gaseous oxygen buffer tank is provided in
order to supply the pressurized product during the time needed to
bring the pump into operation if the pump has to be operated cold
(about 15 to 20 minutes according to the abovementioned articles by
W. J. Scharle).
[0011] Conventionally, if the vaporization pump is permanently
maintained at cryogenic temperature and if the distance between the
pump and the vaporization hairpin is very short, the time needed
for the emergency back-up system to reach 100% of its capacity in a
stable manner is around 2 minutes, made up by 1 minute for the pump
to start up and 1 minute for the vaporization exchanger to come up
to speed. In certain cases, this time of 2 minutes is still too
long as regards permitted pressure fluctuation constraints in the
line--in this case, as described above, one solution consists in
installing, downstream of the exchanger, gas buffer tanks (for
example at 200 bar) designed to supply the production for 1 to 3
minutes, the time that the system made up of the pump and the
vaporizer requires to reach its normal operating speed. The
drawback of this solution is its high price (large volume, high
pressure, pump for filling the buffer tanks, etc.).
[0012] FR-A-2 825 136 describes a method for the emergency back-up
supply of a gas under pressure by vaporization of a pressurized
liquid in which the liquid to be pressurized is stored in a storage
tank, liquid is withdrawn from the storage tank and pressurized,
and at least some of the pressurized liquid is vaporized in a
vaporizer in order to produce the emergency back-up gas under
pressure and, if the flow of gas under pressure is not required,
liquid is withdrawn from the storage tank and pressurized, some of
the pressurized liquid is vaporized in a vaporizer and the rest of
the pressurized liquid is returned to the storage tank after
depressurization.
[0013] Partial oxidation reactors require a supply of oxygen at
high pressure (70 bar and higher) with the pressure stabilized to
.+-.1% of the nominal value. Air separation units supplying the
oxygen must therefore comply with this constraint whatever their
operating mode and in particular in the event of the air separation
unit being shut down.
[0014] During the time to bring the emergency back-up vaporization
unit into service, the pressure in the customer's network will
drop, following a curve whose slope depends on the volume of water
in the network and on the flow consumed. Therefore the low pressure
limit (-1%) may be rapidly reached (in less than 5 seconds) if the
length of the customer's network is less than one kilometre.
[0015] It is therefore necessary to have an oxygen supply system
that provides the necessary flow to the customer during start-up of
the vaporization hairpin, the pumps already being in operation.
[0016] It is an object of the invention to provide a method for the
emergency back-up supply of a gas under pressure, by vaporization
of a pressurized liquid in which:
[0017] i) during a first step: [0018] a) a first stream of air is
compressed by means of a compressor and purified in a purification
unit; [0019] b) at least one portion of the air is compressed to a
high pressure, which allows vaporization of the pressurized liquid;
[0020] c) at least one portion of the air at the high pressure is
sent to a first exchanger; [0021] d) at least one portion of the
air cooled in the exchanger is sent to a system of distillation
columns; [0022] e) at least one liquid is withdrawn from one of the
columns of the system, the liquid is pressurized and sent to the
exchanger, where it vaporizes to form a gas under pressure;
[0023] ii) during a second step: [0024] a stream of the said liquid
is sent to a second exchanger where it vaporizes to form a make-up
stream of the gas under pressure, characterized in that, during the
second step, at least initially, air at the high pressure and
pressurized liquid coming from one column of the system are sent to
the first exchanger and then the stream of high-pressure air sent
to the first exchanger is reduced, possibly to zero, and the stream
of pressurized liquid sent to the first exchanger is reduced,
possibly to zero.
[0025] According to other optional aspects:
[0026] during at least part of the second step, air is sent from a
gaseous air storage tank to the first exchanger and then to the
system of columns and, optionally during the first step,
supercharged air is sent to an air storage tank where it is stored
in gaseous form;
[0027] all the air is compressed to the high pressure and then
purified in the purification unit, the purification unit
constituting the air storage tank;
[0028] all the liquid to be pressurized is stored in a second
storage tank;
[0029] during the first step, a stream of the said liquid, smaller
than the stream sent during the second step, is sent to the second
exchanger where it vaporizes to form gas under pressure;
[0030] at least one of the liquids to be pressurized is rich in
oxygen, argon, nitrogen, hydrogen, helium, methane or carbon
monoxide;
[0031] the liquid is pressurized by means of at least one pump;
[0032] during the second step, air is sent directly from the first
storage tank to the first exchanger; and
[0033] during a third step, pressurized liquid is sent only to the
second exchanger and air is no longer sent to the first
exchanger.
[0034] It is another object of the invention to provide an
installation for the emergency back-up supply of a gas under
pressure, by vaporization of a pressurized liquid, comprising:
[0035] i) a first storage tank; [0036] ii) a pump; [0037] iii) a
first exchanger; [0038] iv) a second exchanger; [0039] v) a
compressor; [0040] vi) a purification unit; [0041] vii) a
supercharger; [0042] viii) means for sending air to the compressor,
means for sending compressed air to the purification unit and means
for sending at least one portion of the purified air to the
supercharger; [0043] ix) means for sending air to a column of a
system of columns; [0044] x) means for withdrawing at least one
liquid from the system of columns, optionally after having stored
it in a storage tank; [0045] xi) means for sending the liquid to
the pump in order to pressurize it; [0046] xii) means for sending
the pressurized liquid to the first exchanger; [0047] xiii) means
for withdrawing the vaporized liquid from the first exchanger;
[0048] xiv) means for sending the pressurized liquid to the second
exchanger; and [0049] xv) a tank for storing gaseous air under
pressure, the tank being connected to the outlet of the air
supercharger, characterized in that it includes means for sending
the air from the supercharger to the storage tank.
[0050] The invention will be described in greater detail with
reference to FIGS. 1 to 5. FIGS. 1 and 5 show an air separation
unit according to the invention and FIGS. 2 to 4 show the air and
oxygen streams during various steps of the method according to the
invention.
[0051] The Figures denoted A show the streams of high-pressure air
and pressurized oxygen in the first exchanger, while the figures
denoted B show the pressurized oxygen stream in the second
exchanger.
[0052] FIG. 1 shows an air separation unit with a double column 15,
17, the medium-pressure and low-pressure columns being thermally
coupled by a condenser 21.
[0053] An air stream is compressed to the medium pressure by a
compressor 3 and then purified in the purification unit 5. The
purified stream is divided into two. One portion is sent to a
supercharger 7 where it is supercharged to a high pressure of
between 20 and 100 bar. The rest of the air 13 is sent to the first
exchanger 1, where it cools before being sent to the
medium-pressure column 15.
[0054] The reflux streams are not shown in order to simplify the
figure.
[0055] A liquid oxygen stream 27 is withdrawn from the bottom of
the low-pressure column 17 and sent to the storage tank 19.
[0056] A gaseous nitrogen stream 23 is withdrawn from the top of
the low-pressure column 17 and used to regenerate the purification
unit 5.
[0057] During a first step, which constitutes the ordinary
operation of the air separation unit, a small portion of the
supercharged air is sent to the storage tank 9 so as to fill it via
the line 25.
[0058] Otherwise, the remaining supercharged air is sent to the
first exchanger 1 where it condenses before being sent to the
double column.
[0059] Air withdrawn from the storage tank 19 is pressurized by the
pump 39 and sent to the first exchanger 1 via the line 33, where it
vaporizes to form gaseous oxygen under pressure.
[0060] Optionally, a small stream of oxygen may be permanently sent
during the first step to the second exchanger 2, where it vaporizes
by heat exchange with a heat-transfer fluid independent of the air
separation unit, such as steam or the ambient air.
[0061] When it is desired to shut down the air separation unit, the
operation switches to the second step and the stream of liquid
oxygen sent to the first exchanger 1 is progressively reduced,
while the stream sent to the second exchanger 2 is increased
progressively so as to ensure a gentle transition towards the
second exchanger 2. To vaporize the liquid oxygen in the first
exchanger 1, the liquid air valve 41 on the line 11 remains open,
controlled according to the oxygen flow rate and the air pressure.
This air pressure drops gently from the nominal pressure at the
outlet of the supercharger 7 down to a value close to that of the
medium-pressure column 15.
[0062] FIG. 2A shows the oxygen and supercharged air streams sent
to the first exchanger during the second step, in the case in which
no oxygen stream is sent to the second exchanger during the first
step.
[0063] Air in the storage tank 9 is sent to the first exchanger 1
immediately after the compressor 3 and/or the supercharger 7 are/is
stopped. The supercharged air stream is instantly increased, to
compensate for the other heat-supplying streams absent (as there is
no longer any medium-pressure air 13), by opening the liquid air
valve 41. Thus, firstly the supercharged air stream increases to
above the nominal value during the first step (100%) and then
progressively reduces as the stream of vaporized oxygen is reduced,
and likewise the pressure in the supercharged air passage of the
exchanger decreases, this pressure being controlled by the make-up
from the gas storage tank, likewise the pressure in the air storage
tank decreases. The supercharged air stream is linearly reduced, by
closing the liquid air valve 41, according to the stream of
high-pressure gaseous oxygen which is itself also linearly reduced
when the oxygen stream sent to the second exchanger is itself
linearly increased. One minute passes between the triggering of the
air stream coming from the storage tank and the reduction to zero
of the supercharged air sent to the first exchanger. Some of the
heat needed to vaporize the liquid oxygen comes from the thermal
inertia of the main exchanger.
[0064] FIG. 3A shows the oxygen and supercharged air streams sent
to the first exchanger during the second step in the case in which
an oxygen stream is sent to the second exchanger during the first
step.
[0065] FIG. 3B shows that, during the second step, the oxygen
stream vaporized in the second exchanger 2 starts from a value of Y
%, which is the value of the stream sent during the first step, and
rises to 100% with a transition time of only 15 seconds.
[0066] FIG. 4A shows that no air or oxygen stream is sent to the
first exchanger 1 during the third step. FIG. 4B shows that all the
pressurized oxygen is sent to the second exchanger during the third
step.
[0067] In the examples of FIGS. 1 to 4, the first air storage tank
9 is at a higher pressure than the output pressure of the
supercharger 7--it has therefore been increased by an auxiliary
system, for example a small compressor. With this higher-pressure,
for example 150 bar, system, it is possible to maintain the
pressure in the supercharged passage at the nominal value or to
allow it to drop.
[0068] In the installation shown in FIG. 5, which is less expensive
than that of FIG. 1, there is no system for increasing the pressure
of the first storage tank 9. The first storage tank 9 is connected
to the outlet of the supercharger 7. When the compressor 3 and/or
the supercharger 7 are/is stopped, the method of supplying make-up
gas is the same as that described previously--the supercharged air
stream is immediately increased by opening the HP liquid air valve
41, and then it is reduced as the oxygen stream reduces and the air
pressure reduces.
[0069] Of course, it is possible for the installation to be of the
type described in EP-504 029 with all the air intended for
distillation being compressed to a single pressure, purified, sent
to the first exchanger, where it exchanges heat with the oxygen,
and is then sent partly to the distillation unit, the rest of the
air being expanded in a Claude turbine.
* * * * *