DE102016006714A1 - Multi-column method and apparatus for cryogenic decomposition - Google Patents

Abstract

The method is for the cryogenic separation of air in a distillation column system with a first two-column system having a first high pressure column (11), a first low pressure column (12) and a first main condenser (13), and a second column system comprising a second high pressure column (21), a second low-pressure column (22) and a second main condenser (23), Gaseous feed air (1) is introduced into the lower region of the first high-pressure column (11). From the bottom of the first low pressure column (12), a first liquid oxygen product (16) is withdrawn, from the top of the first low pressure column (12) a gaseous nitrogen product (18). The head of the second high-pressure column (21) is operated with a higher nitrogen concentration than the head of the first high-pressure column (11). The sump of the first low-pressure column (12) is operated at a higher pressure than the sump of the second low-pressure column (22).

Description

The invention relates to a multi-column method for the cryogenic separation of air according to the preamble of claim 1. Methods and apparatus for the cryogenic separation of air are, for example Hausen / Linde, Tiefftemperaturtechnik, 2nd edition 1985, chapter 4 (pages 281 to 337) known.

A corresponding column system can be designed as a two-column system (for example as a classic Linde double column system), or as a three-column or multi-column system. It may in addition to the columns for nitrogen-oxygen separation, further devices for obtaining high purity products and / or other air components, in particular of noble gases, for example, an argon production and / or a krypton-xenon recovery.

The main condenser and the remaining boilers in the separation columns used in the invention are designed as condenser-evaporators. The term "condenser-evaporator" refers to a heat exchanger in which a first condensing fluid stream undergoes indirect heat exchange with a second evaporating fluid stream. Each condenser-evaporator has a liquefaction space and an evaporation space, which consist of liquefaction passages or evaporation passages. In the liquefaction space, the condensation (liquefaction) of the first fluid flow is performed, in the evaporation space the evaporation of the second fluid flow. Evaporation and liquefaction space are formed by groups of passages that are in heat exchange relationship with each other.

It is known to combine two two-pillar systems within a plant or a plant strand in order to achieve a higher capacity per strand for given transport widths. An example is in EP 2489968 A1 shown.

The invention has for its object to achieve in such a method in addition to the increase in capacity and energy savings.

This object is solved by the features of patent claim 1.

Although they can basically be the same or similar, the two double columns are operated differently, namely with different nitrogen concentration at the heads of the high-pressure columns. This makes it possible to set different pressures despite the same or similar oxygen concentration in the bottom of the low-pressure columns there, without having to install the particularly high heating surface on one of the main capacitors. This results in a particularly favorable energy system.

The effect is exploited that impure nitrogen condenses at higher temperatures than pure nitrogen. On the evaporating side, the law of Clausius-Clapeyron is exploited in parallel; this states that the boiling temperature of a liquid increases with the increase of the pressure or decreases with the reduction of the pressure. The pressure in the first low-pressure column must be set so high that the pressure losses of the impure and pure nitrogen streams are compensated for the atmosphere. The operating pressure in the bottom of the first low-pressure column is, for example, 1.2 to 1.6 bar, preferably 1.3 to 1.4 bar. The pressure of the second low pressure column can be chosen to be lower, that the overhead gas must be discharged usually to a lower pressure. The operating pressure in the bottom of the second low-pressure column is, for example: 1.05 to 1.4 bar, preferably 1.1 to 1.2 bar.

Both high-pressure columns are fed from the same air flow. In this case, the second high-pressure column can be supplied indirectly with feed gas by a gas stream from the first high-pressure column is removed and forms a feed stream for the second high-pressure column, which is supplied in particular to the second high-pressure column at the bottom.

The oxygen concentration in the bottoms of the low pressure columns may be the same or different within the given range of values. By "equal concentration" is meant here a situation in which the two concentration values deviate by less than 1 mol%, preferably by less than 0.2 mol%. At such similar concentrations, liquid oxygen from both sumps can be combined, for example, by liquid oxygen from the bottom of one of the two low-pressure columns introduced into the bottom of the other low-pressure column and the two sump fractions are taken from there together. Alternatively, the bottoms liquids may be separately withdrawn from the low pressure columns, pooled outside the columns, and finally continued through a common pipeline.

From the top of the first low-pressure column, a pure or impure nitrogen product is preferably withdrawn.

The second low-pressure column can also be operated as a crude argon column or argon discharge column. Then she gets involved in her head recovered argon enriched product. This argon product may be pure or impure and recovered in gaseous or liquid state.

Particularly in the latter case, the second low-pressure column preferably has a top condenser (argon condenser), which is designed as a condenser-evaporator and is cooled by liquid crude oxygen from one of the high-pressure columns or from both high-pressure columns.

Above the low-pressure column top condenser, one or more mass transfer sections can be arranged which are supplied with rising steam from the evaporation space of the low-pressure column top condenser.

In a first variant, the two high-pressure columns are connected in parallel. Both high pressure columns are then pressurized with air or a gas of similar composition at the bottom. In a second variant, however, the first high-pressure column and the second high-pressure column are connected in series, as described in claim 8.

Here, the two high-pressure columns are connected in series. No air is introduced directly into the second high-pressure column, but the entire gaseous feed air flows into the first high-pressure column. There, the air is not rectified to pure nitrogen, but only to impure nitrogen with a nitrogen concentration of, for example, 90 to 95%, preferably 91 to 93%. This impure nitrogen is fed to the bottom region of the second high-pressure column and only there distilled to pure nitrogen having a purity of, for example, greater than 99.9%, preferably greater than 99.99%. All percentages in this application are to be understood molar, unless otherwise stated in a particular case.

As a result, the pressure in the first high pressure column is particularly low, the air pressure can be lowered accordingly and thus energy saved.

In order to achieve the object according to the invention and also to incorporate an argon column, the second column system is designed as a triple column comprising from the top an additional column for oxygen-nitrogen separation, the second low-pressure column, the argon condenser, the argon column, the high-pressure column overhead condenser and the second high-pressure column. In principle, the columns of the second column system and those of the first two-column system can also be arranged side by side.

The argon column may be designed as an argon discharge column, as a full-strength crude argon column or as any other type of argon-oxygen separation column. An "argon discharge column" here refers to a separation column for argon-oxygen separation, which is not used for obtaining a pure argon product but for discharging argon of the air to be separated into the high-pressure column and low-pressure column. Their circuit differs only slightly from that of a classical crude argon column, but it contains significantly less theoretical plates, namely less than 40, especially between 15 and 30. Like a crude argon column, the sump region or an intermediate region of an argon discharge column is connected to an intermediate point of the low pressure column and the Argon discharge column is cooled by a top condenser, on the evaporation side of which relaxed bottom liquid is introduced from the high-pressure column.

In the context of the invention, the argon column is preferably designed as an argon discharge column which has less than 40 theoretical plates, in particular 15 to 30 theoretical plates.

The mean temperature difference at the high pressure column top condenser may be lower than at the main condenser. Alternatively, it may be equal to or higher than the average temperature difference on the main condenser.

If the argon is to be recovered as a valuable product and, for example, further purified in a pure argon column and, in particular, freed of nitrogen, a separate crude argon column can be used in addition to the argon discharge column. (The second low-pressure column is then in the form of a split column and consists of the combination of argon discharge column and crude argon column.) The gas from the top of the argon discharge column is led down into the crude argon column to further remove the oxygen there. The liquid obtained in the bottom of the crude argon column is added as reflux to the argon discharge column. The crude argon column is placed parallel to the argon discharge column (which is installed above the second high pressure column). As a result, total coldbox height is saved in this embodiment of the invention and the overall concept can be ideally modular. This is particularly advantageous when several parallel strands are to be operated with and without argon recovery. Such a system is claimed in claim 12.

The impure nitrogen liquid from the main condenser or from the top of the first high-pressure column can be fed to the first low-pressure column at an intermediate point. Pure nitrogen is inventively not generated in the first high-pressure column, but only in the second high-pressure column.

While the first part is applied to the top of the second low-pressure column, a second part of the nitrogen-rich bottoms liquid from the second high-pressure column can be introduced into the first low-pressure column.

In addition, an intermediate liquid can be withdrawn from the second high-pressure column and fed to the first low-pressure column at an intermediate point. Due to the nitrogen-rich liquid, oxygen losses in the impure nitrogen flow from the first low-pressure column can be reduced.

In the method according to the invention, the pressure at the top of the second high pressure column is preferably equal to or lower than at the top of the first high pressure column. The pressure difference is, for example, 0.0 to 0.2 bar, preferably 0.05 to 0.10 bar and in a specific example is 0.10 bar. The absolute numbers are in the following areas:

Head of the first high-pressure column:
For example, 4.8 to 5.5 bar, preferably 4.9 to 5.1 bar

Head of the second high-pressure column:
For example, 4.78 to 5.49 bar, preferably 4.8 to 5.0 bar

It is also advantageous if the pressure at the bottom of the second low-pressure column is lower than at the bottom of the first low-pressure column. The pressure difference is for example 0.1. to 0.3 bar, preferably 0.15 to 0.25 bar and is 0.20 bar in a specific example. The absolute numbers are for example in the following areas:
First low-pressure column 1.3 to 1.6 bar
Second low-pressure column 1.05 to 1.4 bar

The invention and further details of the invention are explained in more detail below with reference to an embodiment schematically illustrated in the drawing. Hereby show:

1 a first embodiment with four separation columns,

2 a second embodiment with five columns and separation

3 a third embodiment with divided second low-pressure column.

In the simplified drawings, in particular air compression, pre-cooling, air cleaning and main heat exchanger with turbine (s) have been omitted.

In the process of 1 flows cooled, purified air 1 as gaseous feed air into the bottom of the first high-pressure column 11 , Next to the first high pressure column 11 form the first low-pressure column 12 and the main capacitor 13 the "first two-pillar system". The head of the first high-pressure column is in heat-exchanging connection with the bottom of the first low-pressure column via the first main condenser

A second airflow 2 which is wholly or partially liquid, the first high-pressure column ( 11 ) at a lower intermediate point. Oxygen rich bottoms liquid 3 from the first high-pressure column (oxygen content about 35%) is in the evaporation chamber of a low-pressure column top condenser or argon condenser 25 initiated. The argon capacitor 25 is part of the "second column system", which also has a second high-pressure column 21 , a second main capacitor 23 and a second low pressure column 22 includes.

From the bottom of the first low-pressure column 12 becomes a first liquid oxygen product 16 subtracted, at their head a gaseous nitrogen product 18 which has a purity of 99.9% in the example.

Part of the gaseous feed air 1 becomes the first high-pressure column 11 taken immediately again and via line 34 the bottom of the second high-pressure column 21 fed. The administration 34 does not contain a throttling device, so that at the bottom of both high-pressure columns 11 . 21 practically the same pressure prevails. "Practically equal" are two pressures here if their difference is less than 50 mbar. In the second high pressure column 21 pure nitrogen is obtained with a purity of 99.99% (at the top).

From the head of the second high-pressure column 21 becomes liquid nitrogen 5 deducted. The liquid pure nitrogen 5 gets upside down the first low-pressure column 12 given up. The nitrogen-containing bottoms liquid 6 from the second high pressure column 21 contains about 35% oxygen; it will be shared with the bottoms liquid 3 from the first high-pressure column 11 into the evaporation space of the low-pressure column overhead condenser (argon condenser) 25 fed. Steam formed in the evaporation space 9 as well as the remaining liquid there fraction 32 be in the first low-pressure column 12 initiated.

The bottom of the second low-pressure column 22 is above the second main capacitor 23 with the head of the second high-pressure column 21 in heat exchanging connection. An argon-containing liquid 30 from the first low-pressure column 12 becomes the second low-pressure column 22 initiated. From the head of the second low-pressure column 22 becomes one Argon-rich faction 31 withdrawn as gas with an argon concentration of 96%.

The liquid oxygen in the bottom of the second low-pressure column 22 has an oxygen content of 99.5%. He will be lead over 26 deducted and either together with the bottoms liquid 16 the first low-pressure column 12 (also 99.5% oxygen) over the product line 36 dissipated or alternatively separated from this. In both cases, it is advantageous if the oxygen liquid (s) are subjected to internal compression, that is brought to an elevated pressure in the liquid state, optionally evaporated in the main heat exchanger, but in any case heated and finally withdrawn as a gaseous pressure product.

From the head of the first low-pressure column 12 becomes pure gaseous nitrogen 18 deducted, from an intermediate point gaseous impure nitrogen 19 with a nitrogen content of 98%.

Via wire 17 becomes liquid impure nitrogen from the first high-pressure column 11 or from the liquefaction space of the first main capacitor 13 the first low-pressure column 12 supplied at an intermediate point.

Liquid impure nitrogen 33 a purity of 98 to 99% is at an intermediate point of the second high-pressure column 21 taken and an intermediate point of the first low-pressure column 12 fed.

• – 4,9 bar am Kopf der ersten Hochdrucksäule 11
• – 4,8 bar am Kopf der zweiten Hochdrucksäule 21
• – 1,4 bar am Sumpf der ersten Niederdrucksäule 12
• – 1,2 bar am Sumpf der zweiten Niederdrucksäule 22

The pressures in the columns are in the embodiment:

• - 4.9 bar at the top of the first high-pressure column 11
• - 4.8 bar at the top of the second high-pressure column 21
• - 1.4 bar at the bottom of the first low-pressure column 12
• - 1.2 bar at the bottom of the second low-pressure column 22

In the process of 2 flows cooled, purified air 1 as gaseous feed air into the bottom of the first high-pressure column 11 , Next to the first high pressure column 11 form the first low-pressure column 12 and the main capacitor 13 the "first two-pillar system". The head of the first high-pressure column is in heat-exchanging connection with the bottom of the first low-pressure column via the first main condenser

A second airflow 2 which is wholly or partially liquid, the first high-pressure column ( 11 ) at a lower intermediate point. Oxygen rich bottoms liquid 3 from the first high-pressure column (oxygen content about 35%) is in the evaporation chamber of a low-pressure column top condenser or argon condenser 25 initiated. The argon capacitor 25 and the additional column arranged above 24 are part of the "second column system", which also has a second high-pressure column 21 , a second main capacitor 23 and a second low pressure column 22 includes.

From the bottom of the first low-pressure column 12 becomes a first liquid oxygen product 16 subtracted, at their head a gaseous nitrogen product 18 which has a purity of 99.9% in the example.

As the top product of the first high-pressure column 11 becomes impure nitrogen gas 4 taken with a purity of 92% and the bottom of the second high-pressure column 21 fed. Basically, this feed fraction of the second high-pressure column 21 not from the head of the first high-pressure column 11 be deducted, but from an intermediary; however, their removal from the first high-pressure column requires more than 10 practical or theoretical plates above the sump of the first high-pressure column 11 be performed; Also in this case, the (impure) gaseous nitrogen fraction becomes the bottom region of the second high-pressure column 21 fed. In the second high pressure column 21 the nitrogen purity is further increased up to 99.99% (at the head).

From the head of the second high-pressure column 21 becomes liquid nitrogen 5 deducted, which has a higher nitrogen concentration than the impure nitrogen gas 4 namely 99.99%. The liquid pure nitrogen 5 gets upside down the first low-pressure column 12 given up. The nitrogen-rich bottoms liquid 6 from the second high pressure column 21 contains 4% oxygen; she becomes a first part 7 on the head of the additional column 24 abandoned and a second part 8th the first low-pressure column 12 supplied at an intermediate point. The nitrogen-rich overhead gas (nitrogen content 95%) of the additional column 24 is also in the first low-pressure column 12 initiated. The oxygen-enriched bottom liquid of the additional column 24 has an oxygen content of 40%. She is being lead 32 the first low-pressure column 12 also forwarded to an intermediate body.

About the argon capacitor 25 , which is designed as a condenser-evaporator, is the head of the second low-pressure column 22 with the sump of the additional column 24 in heat exchanging connection. The bottom of the second low-pressure column 22 is above the second main capacitor 23 with the head of the second high-pressure column 21 in heat exchanging connection. An argon-containing liquid 30 from the first low-pressure column 12 becomes the second low-pressure column 22 initiated. From the head of the second low-pressure column 22 becomes an argon rich fraction 31 withdrawn as gas with an argon concentration of 96%.

The liquid oxygen in the bottom of the second low-pressure column 24 has an oxygen content of 99.5%. He will be lead over 26 deducted and either together with the bottoms liquid 16 the first low-pressure column 12 (also 99.5% oxygen) over the product line 36 dissipated or alternatively separated from this. In both cases, it is advantageous if the oxygen liquid (s) are subjected to internal compression, that is brought to an elevated pressure in the liquid state, optionally evaporated in the main heat exchanger, but in any case heated and finally withdrawn as a gaseous pressure product.

From the head of the first low-pressure column 12 becomes pure gaseous nitrogen 18 deducted, from an intermediate point gaseous impure nitrogen 19 with a nitrogen content of 98%.

Via wire 17 becomes liquid impure nitrogen from the first high-pressure column 11 or from the liquefaction space of the first main capacitor 13 the first low-pressure column 12 supplied at an intermediate point.

Liquid impure nitrogen 33 a purity of 98 to 99% is at an intermediate point of the second high-pressure column 21 taken and an intermediate point of the first low-pressure column 22 fed.

• – 4,9 bar am Kopf der ersten Hochdrucksäule 11
• – 4,8 bar am Kopf der zweiten Hochdrucksäule 21
• – 1,4 bar am Sumpf der ersten Niederdrucksäule 12
• – 1,1 bar am Sumpf der zweiten Niederdrucksäule 22

The pressures in the columns are in the embodiment:

• - 4.9 bar at the top of the first high-pressure column 11
• - 4.8 bar at the top of the second high-pressure column 21
• - 1.4 bar at the bottom of the first low-pressure column 12
• - 1.1 bar at the bottom of the second low-pressure column 22

3 corresponds largely 1 , however, is the second low-pressure column 22 as a split column with two sections 22a . 22b educated. This can cause an argon-rich faction on her head 31 be obtained with a particularly low oxygen content of, for example, 1 ppm. In the embodiment, the second low-pressure column contains 22 about 150 theoretical plates.

The swamp of the first section 22a is above the second main capacitor 23 with the head of the second high-pressure column 21 in heat exchanging connection. The second section 22b has the low pressure column top condenser 25 on, which acts as an argon condenser and is designed as a condenser-evaporator. He will be like in 1 of oxygenated bottoms liquid 6 cooled from the two high-pressure columns. Likewise in 1 becomes an argon-containing liquid 30 from the first low-pressure column 12 in the second low-pressure column 22 initiated. About the gas line 22c becomes head-steam of the first section 22a in the second section 22b initiated. Conversely, the bottom liquid of the second section, possibly conveyed by a pump, flows via the liquid line 22d back to the head of the first section 22a ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2489968 A1 [0004]

Cited non-patent literature

• Hausen / Linde, Tiefftemperaturtechnik, 2nd Edition 1985, Chapter 4 (pages 281 to 337) [0001]

Claims (12)

A process for the cryogenic separation of air in a distillation column system comprising - a first two-column system comprising a first high-pressure column ( 11 ), a first low-pressure column ( 12 ) and a first main capacitor ( 13 ), which is designed as a condenser-evaporator, - a second column system, the second high-pressure column ( 21 ), a second low-pressure column ( 22 ) and a second main capacitor ( 23 ), which is designed as a condenser-evaporator, wherein - gaseous feed air ( 1 ) in the lower region of the first high-pressure column ( 11 ), - the head of the first high-pressure column ( 11 ) via the main capacitor ( 13 ) in heat exchanging connection with the bottom of the first low pressure column ( 12 ), - from the bottom of the first low-pressure column ( 12 ) a first liquid oxygen product ( 16 ), - from the top of the first low-pressure column ( 12 ) a gaseous nitrogen product ( 18 ), characterized in that - an argon-containing liquid ( 30 ) from the first low-pressure column ( 12 ) in the second low-pressure column ( 22 ) is initiated. The head of the second high-pressure column ( 21 ) is operated with a higher nitrogen concentration than the head of the first high-pressure column ( 11 ), - the bottom of the first low-pressure column ( 12 ) is operated with an oxygen concentration of more than 95%, in particular of more than 99%, - the bottom of the second low-pressure column ( 22 ) is operated with an oxygen concentration of more than 95%, in particular more than 99%, - the bottom of the first low-pressure column ( 12 ) at a higher pressure than the bottom of the second low-pressure column ( 22 ) is operated. Process according to claim 1, characterized in that a gas stream ( 34 ; 4 ) from the first high-pressure column ( 11 ) and a feed stream for the second high-pressure column ( 21 ), in particular the second high-pressure column ( 21 ) is fed to the sump. A method according to claim 1 or 2, characterized in that the oxygen concentrations in the sumps of the first and the second low-pressure column ( 12 . 22 ) the same oxygen concentration prevails and liquid oxygen from both marshes is brought together. Method according to one of claims 1 to 3, characterized in that from the head of the first low-pressure column ( 12 ) a pure or impure nitrogen product ( 18 ) is deducted. Method according to one of claims 1 to 4, characterized in that at the top of the second low-pressure column ( 22 ) an argon-enriched or argon-rich fraction ( 31 ) is won. Method according to one of claims 1 to 5, characterized in that - from the head of the first high-pressure column ( 11 ) impure nitrogen gas ( 4 ) and the bottom of the second high-pressure column ( 21 ), - liquid nitrogen ( 5 ), which has a higher nitrogen concentration than the impure nitrogen gas ( 4 ), from the high pressure column top condenser ( 23 ) or from the head of the second high-pressure column ( 21 ) and to the top of the first low-pressure column ( 12 ), and in particular - nitrogen-rich bottoms liquid ( 6 ) from the second high pressure column ( 21 ) at least to a first part ( 7 ) on the head of an additional column ( 24 ), - nitrogen-rich top gas ( 9 ) of the additional column ( 24 ) in the first low-pressure column ( 12 ), - the second low-pressure column ( 22 ) a low pressure column top condenser ( 25 ), which is used as argon condenser ( 25 ) acts as a condenser-evaporator is formed and via which the head of the second low-pressure column ( 22 ) with the sump of the additional column ( 24 ) is in heat-exchanging connection, - an argon-containing liquid ( 30 ) from the first low-pressure column ( 12 ) in the second low-pressure column ( 22 ), - from the top of the second low-pressure column ( 22 ) an argon-rich fraction ( 31 ), - the bottom of the second low-pressure column ( 22 ) via the second main capacitor ( 23 ) with the head of the second high-pressure column ( 21 ) is in heat exchanging connection and - oxygen-enriched bottoms liquid ( 26 ) of the second low-pressure column ( 22 ) as a second liquid oxygen product ( 26 ) is discharged. Method according to one of claims 1 to 6, characterized in that impure nitrogen liquid ( 17 ) from the main capacitor ( 13 ) or from the first high-pressure column ( 11 ) and the first low-pressure column ( 12 ) is supplied at an intermediate point. Method according to one of claims 1 to 7, characterized in that a second part ( 8th ) of the nitrogen-rich bottoms liquid ( 6 ) from the second high pressure column ( 21 ) in the first low-pressure column ( 12 ) is initiated. Method according to one of claims 1 to 8, characterized in that a Intermediate liquid ( 33 ) from the second high pressure column ( 21 ) and the first low-pressure column ( 12 ) is supplied at an intermediate point. Method according to one of claims 1 to 9, characterized in that the average temperature difference at the high-pressure column head capacitor ( 23 ) is lower than at the main capacitor ( 13 ). Method according to one of claims 1 to 10, characterized in that oxygen-rich bottoms liquid ( 3 ) from the first high-pressure column ( 11 ) directly or indirectly into the second low-pressure column ( 22 ) is initiated. Method according to one of claims 1 to 11, characterized in that - the second low-pressure column 22 as a split column with at least two sections ( 22a . 22b ), wherein - the sump of the first section ( 22a ) via the second main capacitor ( 23 ) with the head of the second high-pressure column ( 21 ) is in heat exchanging connection, - the second section ( 22b ) a low pressure column top condenser ( 25 ), which is used as argon condenser ( 25 ) and is designed as a condenser-evaporator, - an argon-containing liquid ( 30 ) from the first low-pressure column ( 12 ) in the second low-pressure column ( 22 ), and - from the top of the second low-pressure column ( 22 ) an argon-rich fraction ( 31 ) is deducted.

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