KR20210077687A - Method and unit for cold air separation - Google Patents

Abstract

The present invention relates to an air separation unit (100, 200) having a distillation column system (10) having a high pressure column (11) operated at a first pressure range and a low pressure column (12) operated at a second pressure range below the first pressure range. ) is used for the method for cold air separation. A first sump liquid having a higher content of oxygen and a lower content of nitrogen than atmospheric air, and a first head gas having a lower content of oxygen and a higher nitrogen content than atmospheric air are subjected to high pressure using a low temperature rectification process. formed in column 11; A second sump liquid having a higher content of oxygen and a lower content of nitrogen than the first sump liquid, and a second head gas having a higher content of nitrogen and a lower content of oxygen than the first sump liquid are subjected to a low temperature rectification process. formed in the low pressure column 12 using A second head gas or a component thereof is drawn from the low pressure column 12 in the form of crude nitrogen. A fraction of crude nitrogen in return form is heated, compressed to a pressure level within a first pressure range, cooled and fed successively to the high pressure column 11 . The invention likewise relates to an air separation unit ( 100 , 200 ).

Description

Method and unit for cold air separation

The invention relates to a method and a unit for cold air separation according to the preamble of the independent claims.

(editor), Industrial Gases Processing, Wiley-VCH, 2006] - 특히, Section 2.2.5, "Cryogenic Rectification"에 기재되어 있다.The production of air products in liquid or gaseous state by cold air separation in air separation units is known, for example as described in H.-W.

(editor), Industrial Gases Processing, Wiley-VCH, 2006] - in particular, Section 2.2.5, "Cryogenic Rectification".

The air separation unit has a distillation column system, which can be designed, for example, as a two-column system, in particular as a classic Linde double-column system, but also as a three-column or multi-column system can be designed In addition to a distillation column for extracting nitrogen and/or oxygen in liquid and/or gaseous state, i.e. a distillation column for nitrogen-oxygen separation, for extracting further air components, in particular the noble gases krypton, xenon, and/or argon A distillation column may be provided.

The distillation columns of the mentioned distillation column systems are operated at different pressure levels. Known dual-column systems have what are known as high pressure columns (also referred to as pressure columns, medium pressure columns, or bottom columns) and those known as low pressure columns (also referred to as top columns). High pressure columns are typically operated at pressure levels of 4 to 7 bar, in particular approximately 5.3 bar. The low pressure column is typically operated at a pressure level of 1 to 2 bar, in particular approximately 1.4 bar. In some cases, even higher pressure levels may be used in both rectification columns. The pressures shown here and below are absolute pressures at the head of each column indicated.

Depending on the required product spectrum (ie the amounts of different liquid and gaseous air products produced absolutely and relative to one another), different unit configurations of the air separation unit have different suitability. If, for example, predominantly gaseous nitrogen is required at a pressure level of, for example, an absolute pressure of 9.5 bar, the method described, for example, in EP 2 789 958 A1 and the further patent literature cited therein may be advantageous. have. It can also be used with so-called pure oxygen columns and/or combined with (vacuum) pressure swing adsorption. In this way, oxygen of different purities can also be provided. However, in some cases a need exists for further optimization.

DE 821 654 B discloses a method in which nitrogen is fed into a high-pressure column. This nitrogen is previously used to boil the sump of the high pressure column. His source is not explained.

CN 106123489 A discloses, in one embodiment, a method in which a portion of the feed air fed into the high pressure column is liquefied in a condenser evaporator downstream of the main heat exchanger.

DE 198 03 437 A1 describes a method for cold air separation in which nitrogen is recycled from the top of the low-pressure column into the high-pressure column, which in an embodiment is referred to as an “enrichment circuit”. For recycle, such nitrogen is compressed together with additional nitrogen from the head of the low pressure column, where that additional nitrogen is withdrawn as pressure nitrogen from the air separation unit.

It is an object of the present invention that an air separation unit, for example, at a pressure level of absolute pressure of 9.5 bar (with an oxygen content typically in the ppm or ppb range, based on molar concentration, for example approximately 1 ppm or 80 ppb or less) is relatively Optimized for the case of supplying high purity nitrogen, but at the same time also "impure" oxygen (oxygen content of eg 85-98 mol%, preferably 90-98 mol%) to provide a solution.

This object is achieved by a method and a unit for cold air separation having the respective features of the independent claims. Advantageous embodiments include the subject matter of the following description and each dependent claim.

In the following, some terms used to describe the present invention and its advantages as well as the underlying technical background will first be described in more detail.

, Section 2.2.5.6, "Apparatus"]에 설명되어 있다. 따라서, 하기 정의들이 다르지 않다면, 본 출원의 체제 내에서 사용되는 용어의 목적을 위해 인용된 기술 문헌은 명시적으로 언급된다.The apparatus used in the air separation unit is described in the cited technical literature, for example [

, Section 2.2.5.6, "Apparatus"]. Accordingly, unless the following definitions differ, technical literature cited for the purpose of terms used within the framework of this application is expressly recited.

“Condenser evaporator” refers to a heat exchanger in which a first condensing fluid stream engages in indirect heat exchange with a second evaporative fluid stream. Each condenser evaporator has a liquefaction chamber and an evaporation chamber. The liquefaction and evaporation chambers have a liquefaction or evaporation passage. Condensing (liquefaction) of the first fluid stream is performed in the liquefaction chamber and evaporation of the second fluid stream is performed in the evaporation chamber. Evaporation and liquefaction chambers are formed by groups of passages in heat exchange relationship with each other.

In particular, the so-called main condenser, which makes the heat exchange connection of the high-pressure column and the low-pressure column of the air separation unit, is designed as a condenser evaporator. The main condenser is in particular a single-level or multi-level bath evaporator, in particular a cascade evaporator (eg as described in EP 1 287 302 B1), but can also be designed as a falling film evaporator. . It may be formed by a single heat exchanger block or by a plurality of heat exchanger blocks arranged in a common pressure vessel.

In a “forced flow” condenser evaporator, a stream of liquid is forced through an evaporation chamber by its own pressure, where it is partially evaporated. This pressure is created, for example, by a liquid column in the supply line to the evaporation chamber. The height of this liquid column here corresponds to the pressure loss in the evaporation chamber. In "once-through" condenser evaporators of this type, the gas-liquid mixture coming out of the evaporation chamber separated by the phases is passed either directly to the next process step or to a downstream device, in particular the remaining liquid fraction is sucked back again. The condenser will not be introduced into the liquid bath of the evaporator.

An “expansion turbine” or “expansion machine” that can be coupled via a common shaft to an energy converter or additional expansion turbine such as a generator, compressor, or oil brake is set up to relieve a gas or at least partially liquid stream. In particular, the expansion turbine for use in the present invention may be designed as a turbo expander. If the compressor is driven by one or more expansion turbines, but without any energy supplied externally, for example by an electric motor, the term "turbine driven" compressor or alternatively "booster" is used. The arrangement of a turbine driven compressor and expansion turbine is also referred to as a “boost turbine”.

A multi-stage turbocompressor, referred to herein as a "main air compressor", is used in the air separation unit to compress the supply air to be separated. The mechanical design of turbocompressors is generally known to those skilled in the art. In turbocompressors, the medium to be compressed is compressed by means of turbine blades arranged on the turbine wheel or directly on the shaft. In this case, the turbocompressor forms, however, in the case of a multi-stage turbocompressor, a structural unit which can have a plurality of compressor stages. The compressor stage generally comprises a corresponding arrangement of turbine blades. All of these compressor stages can be driven by a common shaft. However, it may also be provided for the compressor stage to be driven as a group by different shafts, wherein the shafts may also be connected to one another via gears.

The main air compressor is further characterized by the fact that it compresses the total amount of air fed into the distillation column system and used for the production of the air product, ie the total feed air. Accordingly, a “boost” may also be provided, which, however, brings only a fraction of the amount of compressed air in the main air compressor to a higher pressure. It can also be designed as a turbocompressor. The use of a common compressor or compressor stage of such a compressor as booster and main air compressor may also be provided. In order to compress some amount of air, an additional turbocompressor in the form of a booster described above is typically provided in the air separation unit, however, which, as a rule, results in only a relatively small degree of compression as compared to the main air compressor or booster.

Liquids and gases, as used herein, may be rich or low in one or more components, wherein "enriched" means at least 50%, 75%, 90%, 95%, 99%, 99.5%, 99.9%, or 99.99%, and “low” may refer to a content of up to 50%, 25%, 10%, 5%, 1%, 0.1%, or 0.01%, where % is molar; By weight, or by volume. The term “mostly” may correspond to the definition of “abundant”. Liquids and gases may also be enriched or depleted of one or more components, where these terms refer to the content in the starting liquid or gas from which the liquid or gas has been extracted. A liquid or gas is "enriched" if it contains at least 1.1 times, 1.5 times, 2 times, 5 times, 10 times, 100 times, or 1,000 times the content of the corresponding component, based on the starting liquid or starting gas. , is "depleted" if it contains up to 0.9x, 0.5x, 0.1x, 0.01x, or 0.001x. By way of example, when reference is made herein to “oxygen” or “nitrogen”, it is also understood to mean a liquid or gas enriched in oxygen or nitrogen, but not necessarily exclusively.

[Effects of the Invention]

), 특히 도 2.3A 및 수반하는 설명을 참조한다. 본 발명은, (몰 농도를 기준으로, 산소 함량이 전형적으로 ppm 또는 ppb 범위, 예를 들어 대략 1 ppm 또는 80 ppb 이하인) 비교적 높은 순도의 질소가, 예컨대, 8 내지 12 bar, 특히 9.5 bar의 절대 압력의 압력 수준에서 제공되게 하지만, 동시에 또한 (산소 함량이, 예컨대, 85 내지 98 몰%, 바람직하게는 90 내지 98 몰%인) "비순수" 산소가 공급되게 하는 방법 및 공기 분리 유닛에 관한 것이다.The invention advantageously uses the double-column system known per se, comprising a high-pressure column and a low-pressure column, in particular taking into account the above-mentioned requirements which apply to the product spectrum of air separation units. For example of a corresponding unit, the technical literature cited at the beginning (

), see in particular FIG. 2.3A and the accompanying description. The present invention provides that nitrogen of a relatively high purity (with an oxygen content typically in the range of ppm or ppb, for example up to approximately 1 ppm or 80 ppb, based on molar concentration), e.g. 8 to 12 bar, in particular 9.5 bar to the air separation unit and to a method which allows to be provided at a pressure level of absolute pressure, but at the same time also to be supplied with "impure" oxygen (with an oxygen content of, for example, 85 to 98 mol%, preferably 90 to 98 mol%) it's about

In a conventional double-column system of the type described, the high-pressure column and the low-pressure column are connected to each other in a heat exchange manner by a so-called main condenser. A common form of the embodiment of the corresponding double-column system comprises a so-called internal main condenser, ie a corresponding device arranged in the sump region of the low-pressure column. However, it is also possible to use a so-called external main condenser, into which the fluid is fed, the fluid is taken via a line from the sump region of the low pressure column and fed into the main condenser. In the main condenser of the known double-column system or comparable apparatus, the sump liquid of the low-pressure column is evaporated while the overhead gas of the high-pressure column is at least partially liquefied. A corresponding device is therefore a condenser evaporator of the type described.

In a conventional double-column system in an air separation unit, the high-pressure column and the low-pressure column are further arranged vertically and have a common column shell or connected column shells. In particular, the column shells of the high-pressure column and the low-pressure column can be welded to each other, or the high-pressure column and the low-pressure column can be arranged in a common outer shell, which is then housed in a so-called cold box. However, the present invention can also use high-pressure and low-pressure columns, two-part low-pressure columns, etc., arranged separately from one another, if this is convenient, for example for reasons of installation space. In other words, the present invention is not limited to use with conventional dual-column systems in which the high pressure column and the low pressure column are permanently connected to each other. Additionally, the present invention is not limited to single piece high and low pressure columns.

의 도면 2.3A 및 p. 23 참조) 비순수 질소 스트림에 특히 유리하다는 발견에 기초한다.The present invention also relates to the extraction of feed air drawn from the low pressure column of the corresponding distillation column system, i.e., to be extracted from the air separation unit, not so exclusively or permanently, as is known from the prior art, and, for example, to be used for regeneration of adsorbers serving as purification (in the prior art also referred to as "waste gas";

Figure 2.3A and p. 23) is based on the finding that it is particularly advantageous for pure nitrogen streams.

Rather, within the framework of the present invention, it is true that the corresponding impure nitrogen is partially returned to the high-pressure column. Here, a corresponding part of the impure nitrogen is heated, in particular in the main heat exchanger of the air separation unit, compressed in the hot part of the air separation unit, then cooled again and fed into the high-pressure column. It is understood that not all of the impure nitrogen drawn from the low pressure column can be treated accordingly. Rather, the present invention uses only a fraction of the corresponding impure nitrogen in the manner described, so that additional impure nitrogen can be used, for example for generating refrigeration, for regeneration of adsorbers, as sealing gas for compressors, etc. It is true that it can be, or it can simply be blown off to atmosphere.

As used herein and hereinafter, "impure nitrogen" or "pure nitrogen stream" is understood to mean a gas mixture consisting primarily of nitrogen, but may also have significant impurities of oxygen and lower amounts of noble gases. have. The gas mixture referred to within the framework of the present invention as "impure nitrogen" contains according to the invention from 8 to 15 mol% oxygen, in particular from 10 to 13 mol% oxygen. The argon content is typically comparable to that of air and is typically 0.6 to 1.4 mol%, in particular 0.7 to 1.3 mol%, depending on the process parameters.

Overall, to achieve the described advantages, the present invention provides a distillation column system having a condenser evaporator and a high pressure column operated within a first pressure range and a low pressure column operated within a second pressure range below the first pressure range. We propose a method for cold air separation in which an air separation unit having For further explanations regarding the corresponding pressure ranges, reference is made to the preceding description. The “first pressure range” can in particular be, for example, from 7 to 13 bar, and the “second pressure range” can in particular be from 2 to 4 bar (in each case absolute pressure). Thus, such a pressure range exceeds the typical pressure range in which the high and low pressure columns of conventional air separation units are normally operated. This is achieved by the measurement according to the invention as explained further below.

As is known in this regard, a sump liquid, referred to herein as a “first” sump liquid, is formed in the high pressure column of the air separation unit by low temperature rectification. It has a higher oxygen content and a lower nitrogen content than atmospheric air. A typical oxygen content of the corresponding first sump liquid is typically from 25 to 35 mol %, employing a measurement according to the invention discussed further below. Additionally, the top gas, referred to herein as the “first” top gas formed in the high pressure column, has a lower oxygen content and a higher nitrogen content than atmospheric air. The nitrogen content of this first overhead gas is typically greater than 95 mol %, in particular greater than 99 mol %.

In the low-pressure column of the corresponding air separation unit, a sump liquid is likewise formed by low-temperature rectification, which is referred to herein as a “second” sump liquid. It has a higher oxygen content and a lower nitrogen content than the first sump liquid. The oxygen content is typically greater than 90 mole %. Additionally, in the low pressure column, a top gas is formed, referred to herein as a “second” top gas. It has a lower oxygen content and a higher nitrogen content than the first sump liquid. It contains oxygen and nitrogen, in particular in the concentration ranges previously described for "impure nitrogen".

The basic operation of high-pressure and low-pressure columns is known. Compressed and cooled air in the form of one or more feed air streams is fed into the high pressure column, and the first sump liquid, or a portion thereof, is transferred into the low pressure column and further rectified there. The first overhead gas or a portion thereof may be liquefied or partially liquefied in a main condenser connecting the high pressure column and the low pressure column in a heat exchange manner, thereby returning the liquid to the high pressure column and possibly also to the low pressure column. may be provided. A portion of the first overhead gas may also be extracted from the air separation unit in non-liquefied or liquefied form as the corresponding product. The feeding and delivery of additional mass flows into or between high and low pressure columns are likewise known, but are not described in all embodiments for reasons of clarity.

Within the framework of the present invention, as is likewise known from the prior art, the second overhead gas is taken partially or completely as impure nitrogen from the low pressure column. Thus, the low pressure column is designed in such a way and operated in such a way that the corresponding impure nitrogen is formed in its head. Reference is made to the technical literature cited for further use of such impure nitrogen in the prior art. As mentioned, the corresponding impure nitrogen can be used, for example, for regeneration of the adsorption unit and/or to be blown off to atmosphere.

Within the framework of the present invention, a portion of the impure nitrogen is continuously heated as a return quantity, compressed to a pressure within a first pressure range, cooled, and then fed into a high pressure column. The return amount is typically heated to a temperature within a temperature range greater than 0°C, typically within a temperature range of 0°C to 50°C. As will also be explained below, the main heat exchanger of the corresponding air separation unit is typically used for this purpose. If the return amount is supposed to be heated, this does not exclude the fact that the return amount can possibly also be cooled before being heated. Such cooling may in particular be due to an expansion of the return amount. After compression and cooling, no further cooling will occur, in particular downstream thereof, if the latter is carried out in the main heat exchanger.

Compression to pressure in the first pressure region is typically achieved in such a way that the return amount can be fed directly into the high pressure column after cooling has occurred, for that reason the corresponding pressure is at least equal to the pressure into the high pressure column at the feed point. chosen to correspond. In other words, the pressure in the first pressure region at which the return amount is compressed is a pressure that is at least as high as the pressure at the feed point where the return amount is fed into the high-pressure column. However, the pressure advantageously does not exceed the pressure range in which the high pressure column is operated.

Within the framework of the present invention, the corresponding treatment of a portion of the impure nitrogen in return form leads to the formation of a (positive) enrichment circuit for the high-pressure column. In this way, in addition to the nitrogen product, it is also possible to efficiently feed the (impurity) oxygen product directly from the cooling part of the air separation unit at a relatively high pressure of 2 to 12 bar without any boosting. Within the framework of the invention, as a whole, a combination of dual columns operated under elevated pressure with further advantageous refinements described below is carried out.

As mentioned, DE 821 654 B discloses a method in which nitrogen is fed into the high-pressure column 6 (the reference numerals given therein) according to FIG. 1 . This nitrogen was previously used to boil the sump of the high pressure column (6). His source is not explained. In any case, however, as explicitly stated in line 35 , pure nitrogen is removed here from the head of the low pressure column 8 . The only other stream taken here from the low pressure column (8) is, along line 58, an argon containing prefraction (16). Thus, no impure nitrogen is available to boil the sump of the high pressure column 6 . The fact that the nitrogen of the mass stream 13 must be pure nitrogen is also made clear by the fact that it is fed through a valve 15 at the head of the high-pressure column 6 , if it is pure nitrogen, the person skilled in the art takes this into account won't do it However, the enrichment circuit in the sense of the present invention cannot be implemented with pure nitrogen.

In this example from the prior art, the pressure column is not rich in gas, but liquid (pure nitrogen) to be dispensed at the head of the column. In order to realize this type of rectification, the gaseous nitrogen to be compressed must have a corresponding purity and a corresponding pressure. The pressure must be significantly higher than the pressure in the pressure column to allow condensation on the sump liquid. Within the framework of the present invention, there are no external/internal sources for such streams of nitrogen. There is no nitrogen compressor, and no pure low pressure nitrogen is produced in the low pressure column. To produce this, a liquid scrubbing nitrogen stream from the high pressure column and at least one additional rectification section to the low pressure column are required. Removal of scrubbing nitrogen to the low pressure column will in turn reduce the effectiveness of rectification in the high pressure column.

DE 198 03 437 A1 describes a method for cold air separation in which the return of nitrogen from the head of the low-pressure column into the high-pressure column takes place, as mentioned, in an embodiment, referred to as an “enrichment circuit”. For recycle, such nitrogen is compressed together with additional nitrogen from the head of the low pressure column, where that additional nitrogen is withdrawn as pressure nitrogen from the air separation unit. This fact already shows that it (“PGAN”) thereby comprises a nitrogen-rich product, ie pure nitrogen. Impure nitrogen is explicitly indicated as such in DE 198 03 437 A1, for example in FIG. 5 (“N2U”). Additionally, as can be seen from the figure, the nitrogen cycled in the circuit is discharged at the head of the high pressure column, which would not occur if the nitrogen cycled was impure nitrogen. Therefore, also here, an enrichment circuit without departing from the meaning of the invention cannot be realized with the advantages described. See the detailed description above.

As already mentioned, the heating of the return amount can take place in particular in the main heat exchanger of the corresponding air separation unit. Thus, in this embodiment, it is provided that the air separation unit has a main heat exchanger in which at least a majority of the total amount of air fed into the distillation column system is cooled, wherein the heating and cooling of the return amount is at least partially within the main heat exchanger. is carried out As already mentioned, within the framework of the present invention, not all of the impure nitrogen is heated, compressed and fed into the high pressure column. Rather, in particular, it is true that a further portion of the impure nitrogen can be extracted from the air separation unit. Such additional components may, inter alia, be partially heated in the main heat exchanger, may be expanded by a turbine or expansion machine, which may typically be braked by a generator, or may be further heated in the main heat exchanger to separate the air It may be withdrawn from the unit, or may be used as regeneration gas in the manner described.

Within the framework of the present invention, a portion of the compressed and cooled air passes through a condenser evaporator, is at least partially liquefied therein, and is fed into the distillation column system. Furthermore, a further portion of the compressed and cooled air is fed into the distillation column system here, without passing through the condenser evaporator. In embodiments not according to the invention, such a condenser evaporator may be arranged in a liquid container to which part or all of the second sump liquid is supplied. This will result in a particularly simple arrangement. In such a case, the gas evaporating from the vessel may be taken as the gaseous oxygen product and heated in the main heat exchanger, while the non-evaporating portion from the cooling portion of the air separation unit may be taken in liquid form without being heated as the liquid oxygen product. .

However, the present invention unfolds certain advantages when used in conjunction with an arrangement in which a corresponding condenser evaporator is coupled to another mass exchange column, as detailed below. According to the invention, in the condenser evaporator, a liquid having an inlet oxygen content of 15% to 45%, in particular 20% to 40%, is evaporated, as it emerges from the corresponding mass exchange column and accumulates there as a sump liquid, in particular. In particular, the condenser evaporator used within the framework of the present invention may take the form of a forced flow condenser evaporator, in particular having a once-through configuration as described above. Thus, in the method according to the invention, the condenser evaporator can be designed so that the liquid specified in each case is forced by its own pressure through the evaporation chamber and partially evaporated there, which evaporates during partial evaporation. The unfinished portion can be prevented from flowing back through the evaporation chamber.

Within the framework of the invention, in particular, the part of the compressed and cooled air that is fed into the distillation column system without passing through the condenser evaporator is at least partially fed into the high-pressure column at a first feed point as gaseous compressed air, At the second feeding point, which is 1 to 10 theoretical plates above the feeding point, the return amount is advantageously fed. This is particularly advantageous, since the return amount has a higher nitrogen content than atmospheric air and for this reason the feed at the second feed point is particularly good.

In the process according to the invention, at least a portion of the first sump liquid can be fed into the low pressure column at a first point, possibly after supercooling but without any measures affecting its composition. In contrast, air liquefied or partially liquefied in the condenser evaporator may be fed into the low pressure column at a second point. In this case, the second point is arranged above the first point, in particular at the head of the low pressure column.

In a particularly preferred embodiment of the invention, a portion of the compressed and cooled air passing through the condenser evaporator and at least partially liquefied therein and fed into the distillation column system is fed entirely into the low pressure column. In contrast, a further portion of the compressed and cooled air fed into the distillation column system can be fed partially, but advantageously likewise entirely, into the high-pressure column without passing through the condenser evaporator.

Advantageously, in one embodiment of the process according to the invention, as already mentioned, a first portion of the stream of impure nitrogen in return form can be continuously heated and compressed to a pressure within the first pressure range. may be cooled, may be fed into a high pressure column; However, a further portion of the unpure nitrogen stream may be continuously partially heated, expanded in the expansion turbine, reheated, and discharged from the air separation unit. Cooling can take place by using a corresponding expansion turbine.

In one embodiment of a variant of this method, the oxygen-enriched gas may also be taken from the lower region of the low pressure column and combined with a further portion of the impure nitrogen, prior to partial heating thereof. Cooling can also take place in this way, especially if the corresponding oxygen is not required.

Within the framework of the present invention, combined machines may be used for compression. Thus, the return amount of feed air and impure nitrogen supplied to the distillation column system can be compressed in particular in different compressor stages of a single compressor (see previous section) or in compressors mechanically coupled to each other.

Where, at least not exclusively, pure oxygen is required for industrial applications, the air separation unit can be optimized with respect to its manufacturing and operating costs, in particular with regard to its energy consumption. For a detailed description, see expert literature, such as F.G. Kerry, Industrial Gas Handbook: Gas Separation and Purification, CRC Press, 2006, Section 3.8, "Development of low oxygen-purity processes"]. For example, an air separation unit with a so-called mixing column can be used to obtain lower purity gaseous compressed oxygen. In this regard, reference is made, for example, to EP 3 179 186 A1 and the references therein.

In a conventional mixing column, conventionally, an oxygen-enriched liquid is supplied near gaseous compressed air near the head and sump - so-called mixing column air, and undergoes mass exchange. Thus, so-called "impure" oxygen can be drawn off at the head of the mixing column and taken from the air separation unit as a gaseous product. The liquid underlying within the sump of the mixing column may be fed into the distillation column system used at a suitable point with regard to energy considerations or separation techniques. By using a mixing column, in particular, the energy required to increase the pressure of the oxygen product can be reduced at the expense of the purity of the oxygen product.

It may be advantageous to use, instead of a conventional mixing column, a mass exchange column into which another mass stream is fed instead of a feed air stream. It may in particular be an oxygen-rich liquid from a high-pressure column, in particular its sump liquid. Such liquid, which is already enriched in oxygen compared to atmospheric air, is fed into the mass exchange column, in particular in liquid form, and in a sump is mixed with the liquid flowing down in the mass exchange column. By means of the condenser evaporator, the formed mixed liquid is evaporated as described below, and the formed vapor rises in the mass exchange column. Thus, according to the invention, the gas phase in the corresponding mass exchange column is not formed by means of compressed air, as in a conventional mixing column, but rather in this alternative way.

In a conventional air separation unit with a mixing column, the maximum usable so-called injection equivalent is largely limited for reasons explained in more detail below. However, this also limits the possible energy savings by increasing the injection equivalents in the air separation unit. By the described operation of the mass exchange column, this disadvantage is eliminated.

The term “injection equivalent” refers to compressed air that is expanded by a typical Lachmann turbine (“injection turbine”) and fed into (“injected into”) a low pressure column. The air expanded into the low pressure column thus impedes rectification, which is why the amount of air that can be expanded in the injection turbine and thus the cooling that can be generated in this way for the corresponding unit is limited. The nitrogen-rich air product taken from the high-pressure column and discharged from the air separation unit also affects the rectification in a corresponding manner. The amount of nitrogen removed from the high pressure column and withdrawn from the air separation unit in addition to the air supplied in the low pressure column can be specified in relation to the total air supplied to the distillation column system. The values obtained are "infusion equivalents".

Thus, the injection equivalent can be taken from the high pressure column plus the amount of compressed air compressed with respect to the total compressed air fed into the distillation column system and expanded by the injection turbine into the low pressure column of the air separation unit and liquid return It is defined as the amount of nitrogen that is neither returned to the high pressure column itself nor fed to the low pressure column as liquid return. The nitrogen taken from the high pressure column may be pure or essentially pure nitrogen from the head of the high pressure column, ie the first overhead gas mentioned above, but also nitrogen which may be withdrawn from the high pressure column from the region below the head with a lower nitrogen content. may be an enriched gas.

In the corresponding air separation unit an injection turbine is used and compressed air of quantity M1 is expanded therein, nitrogen of quantity M2 is taken from the high pressure column and taken as liquid and/or gaseous nitrogen product, ie high and/or low pressure If, not used as return to the column, both M3 of compressed air are fed to the distillation column system as a whole, the injection equivalent E in the corresponding unit occurs as follows:

E = (M1 + M2) / M3. (One)

For example, it goes without saying that M1 can also be zero.

Compared to other methods for cold air separation, the lower available injection equivalents by the conventional mixed column method is that, in particular, the air stream fed into the mixing column does not optimally participate in the rectification process in the dual column. True. In particular, the oxygen present in this air stream completely bypasses the high and low pressure columns. This oxygen is taken from the air separation unit in the form of the head product of the mixing column. On the other hand, the nitrogen contained in the air stream to the mixing column remains almost completely in the sump liquid of the mixing column (after the exchange process in the mixing column). This sump liquid typically has an oxygen content of about 65% and, in known methods, is fed into the low pressure column at a feed point corresponding to that oxygen content.

However, from a separate point of view, such a feed point is located in the region of the low pressure column at a relatively remote below, ie at a point where the oxygen content is still relatively high. The rectification or separation section lying below the feed point can already be considered an oxygen section, since no further feed into the low pressure column takes place below the feed point for the sump product of the mixing column. Thus, from a separate point of view, the nitrogen into the mixing column from the air stream (which enters the low pressure column in the form of the sump liquid of the mixing column) must be separated very far from below. However, such separation is extremely complex under the given conditions and requires a relatively high performance of the main condenser. Accordingly, the amount of injection into the low-pressure column or the stated equivalent of injection must be reduced correspondingly, in order to achieve a satisfactory separation.

A significant advantage of the modified operation of the mass exchange column described above is that the feed air is fed entirely into the distillation column system and is correspondingly pre-separated there. As mentioned, in conventional methods, the air flow fed into the mixing column does not optimally participate in the rectification process in the dual column, and in particular, the oxygen present in such an air stream completely bypasses the high and low pressure columns. pass However, it does so within the framework of the aforementioned operation of the mass exchange column. In this way, it is possible to greatly improve the commutation ratio or reduce the effort required for commutation. Thus, first of all, molecular oxygen does not bypass the rectification column (all oxygen is treated in the rectification column by a separation technique), as in conventional processes, and excess nitrogen does not occur in the low pressure column, which must be separated with greater effort. does not The performance of the main condenser can be greatly reduced in this way, or a significant increase in injection equivalents with the associated energy savings is possible in the corresponding unit.

Within the framework of the present invention, the air supplied into the distillation column system passes partially through the condenser evaporator, which, as already mentioned, is also fed into the distillation column system without passing through the condenser evaporator.

According to the invention, the condenser evaporator is operated with a mass exchange column, in particular in such a way that the mixed liquid is partially evaporated in the condenser evaporator, the mixed liquid being formed using a sump liquid taken from the mass exchange column, the mass exchange column A portion of the first sump liquid is supplied at the first supply point and a portion of the second sump liquid is supplied at a second supply point above the first supply point. Thus, in the manner described above, the mixed liquid in the sump of the mass exchange column can be obtained and, in particular, partially evaporated into the condenser evaporator by being diverted into this condenser evaporator.

Within the framework of the invention, a portion of the first sump liquid fed into the mass exchange column at the first feed point is in particular injected into the mass exchange column unheated. "Unheated" feed is understood to mean that a portion of which is not subjected to any specific temperature increasing measures. This applies at least in the case considered here when the operating pressure of the mass exchange column is below the operating pressure of the high pressure column. Subcooling of a portion of the first sump liquid may also be advantageous in certain instances. In contrast to the described embodiment of the present invention, the portion of the second sump liquid fed into the mass exchange column at the second feed point is heated in the main heat exchanger prior to being fed into the mass exchange column. In particular, this portion is taken from the main heat exchanger at an intermediate temperature level.

Mixed liquid refers to those liquids described above that are evaporated in the condenser evaporator. Within the framework of the present invention, the portion of the mixed liquid not evaporated in the condenser evaporator is, as mentioned, in particular partially or preferably entirely fed into the low-pressure column. Within the framework of the invention, the liquid may also be taken from the mass exchange column described, at an extraction point between the first and second feed points, and may be fed partially or preferably entirely into the low pressure column. The same applies also to the further portion of the first sump liquid fed directly into the low pressure column, ie without being fed to the mass exchange column.

In the process according to the invention, it can in particular be provided that a heat exchanger of the form of a so-called supercooled countercurrent heat exchanger is used, wherein the fractional amount of a portion of the second sump liquid fed into the mass exchange column at the second feed point. or the entire amount is heated before being heated in the main heat exchanger and/or a partial amount or the total amount of the return amount is heated before further heating in the main heat exchanger and/or passed through a condenser evaporator and is at least partially therein The partial amount or the total amount of a portion of the compressed and cooled air that is liquefied into a mixture and fed into the distillation column system is cooled before being fed into the distillation column system, and/or the partial amount or the total amount of a portion of the non-evaporative portion of the mixed liquid is A partial or total amount of liquid that is cooled before being partially or wholly fed into the distillation column system and/or taken from the mass exchange column at an extraction point between the first feed point and the second feed point is partially or wholly introduced into the low pressure column. It is cooled prior to being fed, and/or a partial amount or the entire amount of a further portion of the first sump liquid is cooled before being fed into the low pressure column. As mentioned, a part of the material stream mentioned above can in each case also be used correspondingly, ie cooled or heated. The material streams mentioned may be fed to or taken from the corresponding heat exchangers at points corresponding to their respective temperatures.

Within the framework of the invention, it may in particular be provided for the overhead gas to be removed from the mass exchange column, heated and withdrawn from the air separation unit. This overhead gas has a lower oxygen content than the second sump liquid and can therefore be provided at a corresponding pressure as usable process product in addition to the supplied nitrogen. The first overhead gas from the high pressure column can also be taken as product in the manner described.

As mentioned, the air separation unit according to an embodiment not according to the invention can be operated without a mass exchange column in the manner described above. In this regard, it may be provided that in the condenser evaporator the second sump liquid or a portion thereof, ie the sump liquid from the high-pressure column, is partially evaporated to an unchanged composition, wherein the vaporized and non-evaporated portions thereof are separated from the air separation system. partially or wholly extracted as oxygen products from

The invention also leads to an air separation unit. For the features and advantages of such an air separation unit, reference is made to the corresponding independent claims. In particular, such an air separation unit is designed for carrying out the method in one or more of the previously described embodiments and has correspondingly designed means for this purpose. Accordingly, for features and advantages, reference is made explicitly to the above description.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be described in more detail below with reference to the accompanying drawings illustrating preferred embodiments of the present invention.

1 shows in a simplified schematic representation an air separation unit according to an embodiment of the invention;
2 shows an air separation unit according to an embodiment of the invention in a simplified schematic representation;
3 shows in a simplified schematic representation an air separation unit not according to the invention;
In the drawings, elements that functionally or structurally correspond to each other are denoted by the same reference numerals and are not described repeatedly for the purpose of clarity. In the figure, the liquid material stream is indicated by (filled) black flow arrows, while the gaseous stream of material is indicated by (unfilled) white flow arrows.

1 , an air separation unit according to an embodiment of the present invention is shown in the form of a schematic process flow diagram, which is generally indicated by 100 .

In unit 100 , supply air A is drawn through filter 1 by means of a main air compressor 2 . After precooling in a heat exchanger (not shown) and in a direct contact condenser, the correspondingly compressed air is fed to an adsorber station 3 , where it is freed from unwanted components such as water and carbon dioxide. The air is then fed to the main heat exchanger 4 of the air separation unit 100 in the form of a feed air stream a, from which it is extracted at the cooling end. The feed air stream, also initially designated a, is then split into two partial streams (b) and partial streams (c). Partial stream (b) is at least liquefied or partially liquefied in the condenser evaporator (5), still denoted b, and passes through a supercooled countercurrent heat exchanger (6), which is then followed by a low pressure column (12) in addition to a high pressure column ( 11) is fed into the low pressure column 12 of the distillation column system 10 . On the other hand, the partial stream c is fed directly into the high-pressure column 11 .

In the high-pressure column 11 , using a partial flow c fed into the high-pressure column 11 and a further material stream - described below - a material having a higher oxygen content and a lower nitrogen content than atmospheric air. One sump liquid and a first overhead gas having a lower oxygen content and higher nitrogen content than atmospheric air are formed by low temperature rectification. The first sump liquid exits the high pressure column 11 and is split into two partial streams (d) and partial streams (e). The partial stream d is fed into the mass exchange column 7 at a first feed point. Partial stream (e) passes through a subcooled countercurrent heat exchanger (6) and is fed into a low pressure column (12). The first overhead gas is a first portion in the form of a partial stream (f) partially or completely liquefied in a high-pressure column and a main condenser 13 connecting the high-pressure column 11 and the low-pressure column 12 in a heat exchange manner. is taken from A part of this (see link X) can then be withdrawn from the air separation unit 100 as liquid nitrogen product (HPLIN); The other portion is returned to the high pressure column 11 in the form of reflux (not indicated separately). The portion of the first overhead gas that has not passed through the main condenser 13 can be heated in the main heat exchanger 4 in the form of a mass stream g, for example compressed nitrogen product (PGAN) Alternatively, it may be provided as the sealing gas SG.

In the low pressure column 12, using the material stream fed into the low pressure column 12, a second sump liquid having a higher oxygen content and a lower nitrogen content than the first sump liquid, and a lower than the first sump liquid. A second overhead gas having an oxygen content and a higher nitrogen content is formed by low temperature rectification. A first sump liquid is at least partially extracted in the form of mass stream (h) from the sump of low pressure column 12 by means of a pump (not shown separately) and is partially provided as liquid nitrogen product in the form of mass stream (i) do. Another portion, shown here in the form of mass stream k, passes through a subcooled countercurrent heat exchanger 6 , is partially heated in the main heat exchanger 4 , and at a second feed point into mass exchange column 7 . is supplied

By feeding the mass stream (d) and the mass stream (k) into the mass exchange column 7, as previously described, a mixed liquid is formed in the sump. It is discharged and evaporated, in particular in a condenser evaporator 5 , which may take the form of a forced flow condenser evaporator. The non-evaporative portion of the mixed liquid in the form of mass stream 1 may be passed through a supercooled countercurrent heat exchanger 6 and then fed into a low pressure column 12 . A liquid in the form of a mass stream m is withdrawn from the mass exchange column 7 at an extraction point between a first feed point (material stream d) and a second feed point (material stream k), the liquid being likewise , which may be fed into the low pressure column 12 after it has previously passed through a supercooled countercurrent heat exchanger 6 .

The overhead gas from the head of the mass exchange column 7 may pass through the main heat exchanger 4 in the form of a mass stream n and may be provided as gaseous nitrogen pressure product GOX.

Within the framework of the embodiment of the present invention shown in FIG. 1 , a second overhead gas is withdrawn as unpure nitrogen from the head of the low pressure column 12 in the form of a mass stream o and a supercooled countercurrent heat exchanger 6 . is then heated in the main heat exchanger (4), compressed by the compressor (8), cooled by an aftercooler (not shown separately), and in the main heat exchanger (4). It is cooled further and returned to the high-pressure column 11 , now denoted p. This is the fraction of the "return amount" mentioned several times, ie impure nitrogen. However, a partial stream of material stream o - ie a further portion of impure nitrogen, here denoted q - is branched from mass stream o and, like the conventional impure nitrogen stream, the main heat exchanger 4 ), expanded by the generator turbine 9 , further heated in the main heat exchanger 4 , and used in a suitable manner, for example in the adsorber station 3 , as regeneration gas. . In this way, cooling can occur.

1 and the figures that follow, here the mass flow referred to is fed to or taken from a supercooled countercurrent heat exchanger in each case at the warm or cold end and vice versa, but in another corresponding to the respective temperature of the mass flows It is also possible to provide feed or extraction at the point.

2 shows an air separation unit, generally designated 200, according to another embodiment of the present invention; While the air separation unit 100 according to FIG. 1 is particularly suitable for a full production amount of oxygen, the embodiment 200 according to FIG. 2 is particularly advantageous where lower oxygen production is desired. The air separation unit 200 according to FIG. 2 is characterized in that an oxygen-enriched gas is drawn from the high-pressure column in the form of a mass stream r, passed through a supercooled countercurrent heat exchanger 6 and the mass stream q described in FIG. 1 . ) differs essentially from the air separation unit 100 according to FIG. 1 in that it is combined with

3 shows an air separation unit not according to the invention and generally designated 300; The embodiments shown herein by way of example are only intended to facilitate understanding of the present invention. In contrast to the embodiment described above, the mass exchange column 7 is not provided in this case. Instead, a second sump liquid in the form of a mass stream (h) is fed directly into a vessel 20 , a so-called secondary condenser, in which a condenser evaporator denoted 5a is arranged. In contrast, the first sump liquid is not supplied. The second sump liquid is supplied, in particular with respect to the material, in an unchanged composition. The vaporized portion of the supplied second sump liquid is extracted in the form of a mass stream (s) and a non-evaporative portion in the form of a mass stream (t).

Claims (15)

having a condenser evaporator (5) and a distillation column system (10) having a high pressure column (11) operated within a first pressure range and a low pressure column (12) operated within a second pressure range below the first pressure range A method for cold air separation in which an air separation unit (100, 200) is used, comprising:
- a first sump liquid having a higher oxygen content and a lower nitrogen content than atmospheric air, and a first overhead gas having a lower oxygen content and a higher nitrogen content than atmospheric air, by low temperature rectification in said high pressure column (11) is formed within,
- a second sump liquid having a higher oxygen content and a lower nitrogen content than the first sump liquid, and a second overhead gas having a higher nitrogen content and lower oxygen content than the first sump liquid by low temperature rectification formed in the low pressure column (12),
- said second overhead gas or a portion of said second overhead gas is taken from said low pressure column (12) as impure nitrogen having an oxygen content of 8 to 15 mol %;
- a portion of said impure nitrogen is continuously heated as a return quantity, compressed to a pressure within said first pressure range, cooled and fed into said high-pressure column (11);
- a portion of the compressed and cooled air passes through the condenser evaporator (5), is liquefied or partially liquefied therein, and is fed into the distillation column system (10),
- a liquid having an inlet oxygen content of 15% to 45%, in particular 20% to 40%, is evaporated or partially evaporated in said condenser evaporator (5),
- a further part of the compressed and cooled air is fed into the distillation column system (10) without passing through the condenser evaporator (5). The high-pressure column (11) according to claim 1, wherein the portion of compressed and cooled air that is fed into the distillation column system (10) without passing through the condenser evaporator (5) is gaseous compressed air into the high-pressure column (11) at a first feed point. at least partially fed, wherein the return amount of impure nitrogen is fed at a second feeding point that is 1 to 10 theoretical or practical trays above the first feeding point. 3. The method of claim 1 or 2,
- a portion of said first sump liquid is fed into said low pressure column (12) at a first point,
- air liquefied or partially liquefied in the condenser evaporator (5) is fed into the low pressure column (12) at a second point,
- the second point is arranged above the first point, in particular at the head of the low pressure column (12). 4. A portion of the compressed and cooled air passing through the condenser evaporator (5) and at least partially liquefied therein and fed into the distillation column system (10) is wholly according to any one of the preceding claims. A further portion of the compressed and cooled air fed into the low pressure column (12) and fed into the distillation column system (10) without passing through the condenser evaporator (5) is partially or wholly the high pressure column (11) fed into, the way. 5. The method according to claim 3 or 4, wherein a forced flow condenser evaporator is used as said condenser evaporator (5). 6. The high-pressure column according to any one of claims 3 to 5, wherein the first portion of the impure nitrogen as the return amount is continuously heated, compressed to the pressure within the first pressure range, cooled, and (11) a further portion of the impure nitrogen is continuously partially heated, expanded in an expansion turbine (9), reheated and discharged from the air separation unit (100, 200) . 7. The method of claim 6, wherein an oxygen rich gas is taken from the lower region of the low pressure column (12) and combined with a further portion of the impure nitrogen prior to partial heating thereof. 8. Compressor according to any one of claims 3 to 7, wherein the feed air supplied to the distillation column system (10) and the return amount of the impure nitrogen are in different compressor stages of a single compressor or mechanically coupled to each other. compressed in the field, the method. 6. A liquid mixture according to any one of claims 3 to 5, wherein a mixed liquid is partially evaporated in the condenser evaporator (5), the mixed liquid being formed using a sump liquid taken from a mass exchange column (7), A portion of the first sump liquid is fed into the mass exchange column 7 unheated at a first feed point and a portion of the second sump liquid heated at a second feed point above the first feed point. Supplied by the method. 2. The low pressure column (12) according to claim 1, wherein said mixed liquid is partially evaporated in said condenser evaporator (5), and a portion of said mixed liquid not evaporated in said condenser evaporator (5) is at least partially into said low pressure column (12). Supplied method. 11. A liquid according to claim 9 or 10, wherein liquid is taken from the mass exchange column (7) at an extraction point between the first feed point and the second feed point and is partially or wholly fed into the low pressure column (12). and a further portion of the first sump liquid is fed into the low pressure column (12). 12. The method of claim 11,
- the partial amount or the total amount of the part of the second sump liquid fed into the mass exchange column (7) at the second feed point is heated before being fed into the main heat exchanger (4);
- a partial amount or the entire amount of said return amount is heated prior to further heating in said main heat exchanger (4) and/or;
- a partial amount or a total amount of a portion of the compressed and cooled air passing through the condenser evaporator (5) and at least partially liquefied therein and fed into the distillation column system (10) into the distillation column system (10) cooled before being fed and/or
- the partial amount or the total amount of the non-evaporative portion of the mixed liquid is cooled before being partially or wholly fed into the low pressure column ( 12 );
- at the extraction point between the first feed point and the second feed point the partial amount or the total amount of liquid taken from the mass exchange column 7 is cooled before being partially or wholly fed into the low pressure column 12 and/or
- a heat exchanger (6) is used, wherein a partial amount or the total amount of a further portion of the first sump liquid is cooled before being fed into the low pressure column (12). 13. A top gas according to any one of claims 9 to 12, wherein top gas is taken from the mass exchange column (7), heated, discharged from the air separation unit (100, 200) and/or a first top gas is taken from the high pressure column (11), heated and discharged from the air separation unit (100, 200). 9. The method of any preceding claim, wherein oxygen is obtained at a product pressure above the second pressure range. A distillation column system (10) having a condenser evaporator (5) and a high pressure column (11) set to operate within a first pressure range and a low pressure column (12) set to operate within a second pressure range below the first pressure range As an air separation unit (100, 200) having a,
- a first sump liquid having a higher oxygen content and a lower nitrogen content than atmospheric air, and a first overhead gas having a lower oxygen content and a higher nitrogen content than atmospheric air, by low-temperature rectification into said high-pressure column ( 11) to form within,
- a second sump liquid having a higher oxygen content and a lower nitrogen content than the first sump liquid, and a second overhead gas having a lower oxygen content and a higher nitrogen content than the first sump liquid, to low temperature rectification By, formed in the low pressure column 12,
- extraction of said second overhead gas or a portion of said second overhead gas from said low pressure column (12) as impure nitrogen having an oxygen content of 8 to 15 mol%;
- a portion of said impure nitrogen is continuously heated as a return amount, compressed to a pressure within said first pressure range, cooled and fed into said high-pressure column (11);
- passing a portion of said compressed and cooled air through said condenser evaporator (5), liquefied or partially liquefied therein and fed into said distillation column system (10),
- in the condenser evaporator (5) evaporating or partially evaporating a liquid having an inlet oxygen content of 15% to 45%, in particular 20% to 40%,
- an air separation unit (100, 200) configured to feed a further portion of the compressed and cooled air into the distillation column system (10) without passing through the condenser evaporator (5).

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