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EP 1 797 384 B1 |
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EUROPEAN PATENT SPECIFICATION |
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Mention of the grant of the patent: |
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22.07.2009 Bulletin 2009/30 |
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Date of filing: 10.08.2005 |
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International Patent Classification (IPC):
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International application number: |
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PCT/EP2005/053938 |
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International publication number: |
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WO 2006/048341 (11.05.2006 Gazette 2006/19) |
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AIR SEPARATION PROCESS USING CRYOGENIC DISTILLATION
KRYOGENE DESTILLATION VERWENDENDER LUFTTRENNPROZESS
PROCEDE DE SEPARATION DE L'AIR PAR DISTILLATION CRYOGENIQUE
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Designated Contracting States: |
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AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IS IT LI LT LU LV MC NL PL PT RO SE
SI SK TR |
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Priority: |
21.09.2004 FR 0452099
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Date of publication of application: |
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20.06.2007 Bulletin 2007/25 |
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Proprietor: L'AIR LIQUIDE, Société Anonyme pour l'Etude
et l'Exploitation des Procédés Georges Claude |
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75007 Paris (FR) |
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Inventors: |
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- BRUDER, Olivier
F-75321 PARIS CEDEX 07 (FR)
- LE BOT, Patrick
F-94300 VINCENNES (FR)
- DUBETTIER-GRENIER, Richard
F-94210 LA VARENNE SAINT-HILAIRE (FR)
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Representative: Mercey, Fiona Susan |
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L'Air Liquide SA,
Département Propriété Intellectuelle,
75 quai d'Orsay 75321 Paris Cedex 07 75321 Paris Cedex 07 (FR) |
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References cited: :
EP-A- 0 930 097 US-A- 5 349 827 US-A- 6 128 921
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FR-A- 2 686 405 US-A- 5 396 772
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Note: Within nine months from the publication of the mention of the grant of the European
patent, any person may give notice to the European Patent Office of opposition to
the European patent
granted. Notice of opposition shall be filed in a written reasoned statement. It shall
not be deemed to
have been filed until the opposition fee has been paid. (Art. 99(1) European Patent
Convention).
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[0001] The present invention relates to an air separation process using cryogenic distillation.
In particular, it relates to air separation processes for the production of large
quantities of oxygen with a content of greater than 90 mol% with a yield of greater
than 90% in a unit comprising at least one column operating at low pressure and at
least one column operating at high pressure, at least one column of which containing
at least one section of structured packings of the cross-corrugated type.
[0003] US-A-5653126 describes the use of cross-corrugated structured packings having a density of at
least 500 m
2/m
3 with a low HETP for the separation of air.
[0004] Typically, cross-corrugated packings have corrugations at 45° with the axis of the
column in which they are installed. The packings may or may not be perforated and
are generally formed by folded metal foil strips.
[0005] The increase in demand for gas separation units of large capacity (production greater
than 2000 tonnes of gas produced per day) has led to the need to design distillation
columns of increasing diameter, despite the frequent use of pressurized distillation
processes (with columns operating at pressures above 2 bar abs).
[0006] Transport problems become significant when the diameter of the elements exceeds 3m,
or even 4.5m, and these are sometimes insurmountable for columns greater than 6m in
diameter. If it was desired to increase the ratio of oxygen production (in t/d of
pure product) to cross section (in m
2) of the low-pressure column, that is to say to reduce the diameter of the low-pressure
column for constant oxygen production (or given air throughput), for a unit comprising
a medium-pressure column thermally coupled to a low-pressure column or for a unit
comprising three columns, including a medium-pressure column thermally coupled to
a low-pressure column and an intermediate-pressure column fed from the medium-pressure
column, the only solutions were:
[0007] In an air separation unit producing large quantities of oxygen and nitrogen, if it
was desired to reduce the diameter of this column, the only solutions were:
- to increase the withdrawal of lean liquid and of liquid nitrogen, but above a certain
ratio it is found that the purity of the nitrogen and of the lean liquids dramatically
drops and that the oxygen yield of the unit collapses;
- to increase the flow of blown air, but above a certain ratio the performance of the
unit is greatly degraded - reduction in oxygen yield (or in oxygen purity), reduction
in medium-pressure gaseous nitrogen (or in purity of medium-pressure gaseous nitrogen);
- to increase the liquid air flow, but this flow is set by the production of pumped
products and the production of liquid products (liquid oxygen, liquid nitrogen, liquid
argon), or a substantial loss of energy;
- to increase the pressure of the unit (with a medium pressure > 8 bar abs), but this
is highly disadvantageous from the energy standpoint if the pressure of the waste
nitrogen is not utilized (that is to say by expansion in order to make liquid, or
as product pressure).
[0008] The object of the present invention is to alleviate the problems of the prior art
by allowing the column diameters to be reduced for a given oxygen production.
[0009] One object of the invention is to provide a process according to Claim 1.
[0010] The yield is the percentage number of oxygen molecules in all the oxygen-rich products
relative to the number of oxygen molecules in the feed air for the separation unit.
[0011] The capacity per unit area of the column is the ratio of the molar volume of gas
sent into the column to the mean cross section of the column.
[0012] According to other optional features:
- the largest-diameter column of the column system contains at least one section filled
with a gas/liquid contactor allowing material exchange between the gaseous phase and
the liquid phase such that its effectiveness is defined by a TUH (Transfer Unit Height)
of less than 350 mm (preferably less than 300 mm);
- the gas/liquid contactor is composed of cross-corrugated structured packings having
a density of less than 500 m2/m3, preferably less than 400 m2/m3;
- the column system comprises at least one double column formed by a medium-pressure
column and a low-pressure column, the medium-pressure column being thermally coupled
to the low-pressure column, and the low-pressure column constituting the largest-diameter
column;
- the ratio of the oxygen produced to the cross section of the low-pressure column is
greater than or equal to 150 t/d/m2;
- the ratio of the flow rate of air sent to the column system to the cross section of
the low-pressure column is not less than 22153 Nm3/h/m2 (21000 Sm3/h/m2), preferably not less than 24263 Nm3/h/m2 (23000 Sm3/h/m2) and even more preferably not less than 26372 Nm3/h/m2 (25000 Sm3/h/m2);
- the ratio of the gaseous air sent to the medium-pressure column to the cross section
of the low-pressure column is not less than 18988 Nm3/h/m2 (18000 Sm3/h/m2) (preferably not less than 21098 Nm3/h/m2 (20000 Sm3/h/m2) and even more preferably not less than 23208 Nm3/h/m2 (22000 Sm3/h/m2)); and
- at least one section of the medium-pressure column contains cross-corrugated structured
packings with a density not exceeding 500 m2/m3, or even 400 m2/m3.
[0013] A fluid will be called a "product" if it is output from the air separation unit with
the content of one of its constituents being:
- greater than 85 mol%, if the constituent is oxygen;
- greater than 95 mol%, if the constituent is nitrogen.
[0014] The extraction efficiency of a constituent will be defined by the ratio of the molar
quantity of the said constituent entering the separation unit via the feed fluids
to the molar quantity of the same constituent leaving via the product(s), the content
of this constituent being greater than or equal to those mentioned above.
[0015] Cross-corrugated structured packings with a density not exceeding 500 m
2/m
3, or even 400 m
2/m
3, may be installed in the medium-pressure column and/or the low-pressure column of
a double column, in the medium-pressure column and/or the low-pressure column and/or
the intermediate-pressure column of a triple (Etienne) column, an argon column, a
mixing column or any other type of air gas separation column.
[0016] A packing has a density of less than 500 m
2/m
3 if its mean density (without deducting the area of any perforations) does not exceed
500 m
2/m
3.
[0017] The invention will be described in greater detail with reference to the figure.
[0018] Figure 1 shows a process according to the invention.
[0019] In a unit according to the invention, a double column comprises a medium-measure
column 1 operating at between 5 bar abs and 20 bar abs and a low-pressure column 3
operating at apressure between 1.2 bar abs and 8 bar abs. The low-pressure column
is larger in diameter than the medium-pressure column, but it is possible in some
cases for the medium-presure column to be larger in diameter than the low pressure
column. The two columns are thermally coupled to each other by a reboiler/condensor
5, for example of the bath type.
[0020] The low-pressure column 3 contains only sections of structured packings 2 having
a density not exceeding 500 m
2/m
3, for example having a density of 400 m
2/m
3.
[0021] The medium-pressure column 1 contains only sections of structured packings 2 having
a density close or identical to the above values.
[0022] A stream of cooled and purified air 7 is sent to the medium-pressure column 1 and
oxygen-enriched and nitrogen-enriched liquid streams 9, 11 are sent from the medium-pressure
column to the low-pressure column after an expansion step.
[0023] Withdrawn from the bottom of the low-pressure column is a stream of gaseous oxygen
13 as product, with an oxygen yield of greater than 90% (preferably greater than 95%).
The oxygen purity is greater than 90 mol% oxygen (preferably greater than 95 mol%
oxygen or even 99 mol% oxygen).
[0024] At the top of the low-pressure column, gaseous nitrogen 15 is withdrawn with a nitrogen
yield of greater than 85% (preferably greater than 90%). The purity of the nitrogen
is greater than 99 mol% nitrogen (preferably greater than 99.99 mol% nitrogen or even
99.999 mol% nitrogen).
[0025] A stream of waste nitrogen 17 is withdrawn from an upper level of the low-pressure
column.
[0026] The diameter (in metres) of the low-pressure column is less than:

where:
Qair is the sum of the flow rates in Sm3/h of the air feeding the column system;
K is the capacity per unit area of the column and equals at least 22153 Nm3/m2 (21000 Sm3/m2) (preferably at least 24263 Nm3/m2 (23000 Sm3/m2) or even at least 26372 Nm3/m2 (25000 Sm3/m2)); and
P0 is equal to 2 bar abs.
[0027] To give a numerical example, it will be assumed that an installation has to treat
an air throughput of 527450 Nm
3/h (500000 Sm
3/h). According to the invention, if the low-pressure column is operated at a pressure
below 2 bar abs, the cross section of the low-pressure column will therefore be less
than:

(preferably less than (500000/23000) m
2 or even less than (500000/25000) m
2)
and the diameter less than:

i.e. 5.5m (preferably 5.26m, or even at most 5.05m).
[0028] If the low-pressure column is operated at 3 bar abs, the cross section of the low-pressure
column will therefore be less than:

(preferably less than (500000/23000) m
2 or even less than (5000000/25000) m
2)
and the diameter less than:

i.e. 5.13m (preferably 4.9 m, or even at most 4.7 m).
1. Process for the separation of air into at least one constituent by cryogenic distillation
of air in a system of columns (1, 3) comprising at least one column (1, 3)
a) for producing at least gaseous oxygen as product, such that the oxygen yield is
greater than 90% (preferably 95%) and the oxygen purity is greater than 90 mol% oxygen
(preferably 95 mol% oxygen or even 99 mol% oxygen) and/or
b) for producing at least nitrogen such that the nitrogen yield is greater than 85%
(preferably greater than 90%) and the nitrogen purity is greater than 99 mol% nitrogen
(preferably 99.99 mol% nitrogen or even 99.999 mol% nitrogen)
characterized in that:
• if the operating pressure of the largest-diameter column (3) is P<2 bar abs, then
the diameter (in metres) of this column is less than:

if the operating pressure of the largest-diameter column is P > 2 bar abs, then the
diameter (in metres) of this column is less than:

where:
Qair is the sum of the flow rates in Nm3/h of the air feeding the column system;
K is the capacity per unit area of the column and equals at least 22153 Nm/m2 (21000 Sm3/m2) (preferably at least 24263 Nm3/m2 (23000 Sm3/m2) or even at least 26372 (25000 Nm2/m2 Sm3/m2)); and
P0 is equal to 2 bar abs.
2. Process according to Claim 1, in which the largest-diameter column (3) of the column
system contains at least one section (2) filled with a gas/liquid contactor allowing
material exchange between the gaseous phase and the liquid phase such that its effectiveness
is defined by a TUH (Transfer Unit Height) of less than 350 mm (preferably less than
300 mm).
3. Process according to Claim 2, in which the gas/liquid contactor is composed of cross-corrugated
structured packings having a density of less than 500 m2/m3, preferably less than 400 m2/m3.
4. Process according to Claim 1, 2 or 3, in which the column system comprises at least
one double column formed by a medium-pressure column (3) and a low-pressure column
(1), the medium-pressure column being thermally coupled to the low-pressure column,
and the low-pressure column constituting the largest-diameter column.
5. Process according to Claim 4, producing oxygen in which the ratio of the oxygen produced
to the cross section of the low-pressure column is greater than or equal to 150 t/d/m2.
6. Process according to Claim 4 or 5, in which the ratio of the flow rate of air sent
to the column system to the cross section of the low-pressure column is not less than
22153 Nm3/h/m2 (21000 sm3/h/m2), preferably not less than 24263 Nm3/h/m2 (23000 Sm3/h/m2) and even more preferably not less than 26372 Nm3/h/m2 (25000 Sm3/h/m2).
7. Process according to Claim 4, 5 or 6, in which the ratio of the gaseous air sent to
the medium-pressure column (1) to the cross section of the low-pressure column is
not less than 18988 Nm3/h/m2 (18000 Sm3/h/m2) (preferably not less than 21098 Nm3/h/m2 (20000 Sm3/h/m2) and even more preferably not less than 23208 Nm3/h/m2 (22000 Sm3/h/m2)).
8. Process according to Claim 7, in which at least one section (2) of the medium-pressure
column (1) contains cross-corrugated structured packings with a density not exceeding
500 m2/m3, or even 400 m2/m3.
1. Verfahren zur Zerlegung von Luft in mindestens einen Bestandteil durch Tieftemperaturdestillation
von Luft in einem System von Säulen (1, 3) mit mindestens einer Säule (1, 3)
a) zur Herstellung von mindestens gasförmigem Sauerstoff als Produkt mit einer Sauerstoffausbeute
von mehr als 90% (vorzugsweise 95%) und einer Sauerstoffreinheit von mehr als 90 Mol-%
Sauerstoff (vorzugsweise 95 Mol-% Sauerstoff oder sogar 99 Mol-% Sauerstoff) und/oder
b) zur Herstellung von mindestens Stickstoff mit einer Stickstoffausbeute von mehr
als 85% (vorzugsweise mehr als 90%) und einer Stickstoffreinheit von mehr als 99 Mol-%
Stickstoff (vorzugsweise 99,99 Mol-% Stickstoff oder sogar 99,999 Mol-% Stickstoff),
dadurch gekennzeichnet, daß:
■ dann, wenn der Betriebsdruck der den größten Durchmesser aufweisenden Säule (3)
P < 2 bar abs. beträgt, der Durchmesser (in Meter) dieser Säule kleiner als:

ist,
dann, wenn der Betriebsdruck der den größten Durchmesser aufweisenden Säule P > 2
bar abs. beträgt, der Durchmesser (in Meter) dieser Säule kleiner als:

ist,
wobei:
QLuft die Summe der Strömungsraten der das Säulensystem speisenden Luft in Nm3/h ist;
K die Kapazität der Säule pro Flächeneinheit ist und gleich mindestens 22153 Nm3/m2 (21.000 Sm3/m2) (vorzugsweise mindestens 24263 Nm3/m2 (23.000 Sm3/m2) oder sogar mindestens 26372 Nm3/m2 (25.000 Sm3/m2) ist und
P0 gleich 2 bar abs. ist.
2. Verfahren nach Anspruch 1, bei dem die den größten Durchmesser aufweisende Säule (3)
des Säulensystems mindestens einen Abschnitt (2) enthält, der mit einem Stoffaustausch
zwischen der Gasphase und der Flüssigphase erlaubenden Gas/Flüssigkeit-Kontaktor gefüllt
ist, so daß seine Effektivität durch eine TUH (Höhe einer Übertragungseinheit) von
weniger als 350 mm (vorzugsweise weniger als 300 mm) definiert ist.
3. Verfahren nach Anspruch 2, bei dem der Gas/Flüssigkeit-Kontaktor aus gekreuzt-gewellten
geordneten Packungen mit einer Dichte von weniger als 500 m2/m3, vorzugsweise weniger als 400 m2/m3, besteht.
4. Verfahren nach Anspruch 1, 2 oder 3, bei dem das Säulensystem mindestens eine aus
einer Mitteldrucksäule (3) und einer Niederdrucksäule (1) gebildete Doppelsäule umfaßt,
wobei die Mitteldrucksäule thermisch mit der Niederdrucksäule gekoppelt ist und die
Niederdrucksäule die Säule mit dem größten Durchmesser darstellt.
5. Verfahren nach Anspruch 4, das Sauerstoff produziert, bei dem das Verhältnis des produzierten
Sauerstoffs zum Querschnitt der Niederdrucksäule größer gleich 150 t/d/m2 ist.
6. Verfahren nach Anspruch 4 oder 5, bei dem das Verhältnis von Strömungsrate der dem
Säulensystem zugeführten Luft zu Querschnitt der Niederdrucksäule mindestens 22153
Nm3/h/m2 (21. 000 Sm3/h/m2), vorzugsweise mindestens 24263 Nm3/h/m2 (23.000 Sm3/h/m2) und noch weiter bevorzugt mindestens 26372 Nm3/h/m2 (25.000 Sm3/h/m2) beträgt.
7. Verfahren nach Anspruch 4, 5 oder 6, bei dem das Verhältnis von der Mitteldrucksäule
(1) zugeführter gasförmiger Luft zu Querschnitt der Niederdrucksäule mindestens 18988
Nm3/h/m2 (18.000 Sm3/h/m2) (vorzugsweise mindestens 21098 Nm3/h/m2 (20.000 Sm3/h/m2) und noch weiter bevorzugt mindestens 23208 Nm3/h/m2 (22.000 Sm3/h/m2)) beträgt.
8. Verfahren nach Anspruch 7, bei dem mindestens ein Abschnitt (2) der Mitteldrucksäule
(1) gekreuztgewellte geordnete Packungen mit einer Dichte von höchstens 500 m2/m3 oder sogar 400 m2/m3 enthält.
1. Procédé de séparation d'air en au moins un constituant par distillation cryogénique
de l'air dans un système de colonnes (1, 3) comprenant au moins une colonne (1, 3)
a) pour produire au moins de l'oxygène gazeux comme produit tel que le rendement en
oxygène est supérieur à 90 % (préferablement 95 %) et la pureté d'oxygène est supérieure
à 90 % mol. d'oxygène (préférablement 95 % mol. d'oxygène, voire 99 % mol. d'oxygène)
et/ou
b) pour produire au moins de l'azote tel que le rendement en azote est supérieur à
85 % (préférablement supérieur à 90 %) et la pureté de l'azote est supérieure à 99
% mol. d'azote (préférablement à 99.99 % mol. d'azote, voire à 99,999 % mol. d'azote)
caractérisé en ce que :
• si la pression de fonctionnement de la plus large des colonnes (3) est P < 2 bars
abs, alors le diamètre (en mètres) de cette colonne est inférieur à :

si la pression de fonctionnement de la plus large des colonnes est P > 2 bars abs,
alors le diamètre (en mètres) de cette colonne est inférieur à :

où :
Qair est la somme des débits d'air alimentant le système de colonnes, en Nm3/h ;
K est la capacité surfacique de la colonne et vaut au moins 22 153 Nm3/m2 (21 000 Nm3/m2) (préférablement au moins 24 263 Nm3/m2 (23 000 Nm3/m2), voire au moins 26 372 Nm3/m2 (25 000 Nm3/m2); et
P0 est égale à 2 bars abs.
2. Procédé selon la revendication 1 dans lequel la colonne de plus grand diamètre (3)
du système de colonnes contient au moins un tronçon (2) rempli avec un contacteur
gaz/liquide permettant l'échange de matière entre la phase gazeuse et la phase liquide
tel que son efficacité sera définie par une hauteur par unité de transfert (HUT) inférieure
à 350 mm (préférablement à 300 mm).
3. Procédé selon la revendication 2 dans lequel le contacteur gaz/liquide est composé
de garnissages structurés ondulés-croisés ayant une densité de moins de 500 m2/m3, de préférence de moins de 400 m2/m3.
4. Procédé selon la revendication 1, 2 ou 3 dans lequel le système de colonnes comprend
au moins une double colonne constituée par une colonne moyenne pression (3) et une
colonne basse pression (1), la colonne moyenne pression étant thermiquement reliée
à la colonne basse pression et la colonne basse pression constituant la colonne la
plus large.
5. Procédé selon la revendication 4 produisant de l'oxygène dans lequel le rapport entre
l'oxygène produit et la section de la colonne basse pression est supérieur ou égal
à 150 t/j/m2.
6. Procédé selon la revendication 4 ou 5 dans lequel le rapport entre le débit d'air
envoyé au système de colonnes et la section de la colonne basse pression est supérieur
ou égal à 22 153 Nm3/m2 (21 000 Nm3/h/m2), préférablement à 24 263 Nm3/m2 (23 000 Nm3/h/m2) et encore plus préférablement à 26 372 Nm3/m2 (25 000 Nm3/h/m2).
7. Procédé selon la revendication 4, 5 ou 6 dans lequel le rapport entre l'air gazeux
envoyé à la colonne moyenne pression (1) et la section de la colonne moyenne pression
est supérieur ou égal à 18 988 Nm3/h/m2 (18 000 Nm3/h/m2) (préférablement à 21 098 Nm3/h/m2 (20 000 Nm3/h/m2), encore plus préférablement à 23 208 Nm3/h/m2 (22 000 Nm3/h/m2).
8. Procédé selon la revendication 7 dans lequel au moins un tronçon (2) de la colonne
moyenne pression (1) contient des garnissages structurés ondulés-croisés de densité
inférieure à 500 m2/m3, voire à 400 m2/m3.

REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader's convenience only.
It does not form part of the European patent document. Even though great care has
been taken in compiling the references, errors or omissions cannot be excluded and
the EPO disclaims all liability in this regard.
Patent documents cited in the description