EP3614084A1 - Method and installation for cryogenic decomposition of air - Google Patents

Abstract

The invention relates to a method for the low-temperature separation of air using an air separation plant with a distillation column system (100) which has a first, a second, a third and a fourth separation unit (110-140). Compressed and cooled air is fed into the first separation unit (110), the first separation unit (110) is operated at a first pressure level of 4 to 6 bar absolute pressure, the second, the third and the fourth separation unit (120-140) are opened operated at a second pressure level of 1 to 2 bar absolute pressure, by means of the first separation unit (110) an oxygen-enriched and nitrogen-depleted, argon-containing first bottoms liquid and a nitrogen-enriched and oxygen-depleted first top gas are formed, the first bottoms liquid is at least partially transferred to the third separation unit (130), the first top gas is at least partially liquefied and returned to the first separation unit (110), by means of the second separation unit (120) an oxygen-rich second bottom liquid and a second top gas enriched with argon are formed, the second A first share of top gas is in the third door enn unit (130) and a second portion in the fourth separation unit (140), by means of the third separation unit (130) at least the majority of the argon, which is contained in a total amount of air supplied to the distillation column system (100), separated and by The third separation unit (130) is provided with a liquid return to the second separation unit (120), by means of the fourth separation unit (140) a fourth bottom liquid and a fourth top gas are formed, and the fourth bottom liquid is at least partially applied to the second separation unit (120 ) returned. The second separation unit (120) has 10 to 50 theoretical plates, the third separation unit (130) has 10 to 60 theoretical plates, and the third separation unit (130) is arranged above the second separation unit (120) and opens in a lower one Area opposite an upper area of the second separation unit (120). A corresponding system (200) is also the subject of the present invention.

Description

The invention relates to a method for the low-temperature separation of air and a corresponding system according to the preambles of the independent claims.

State of the art

The production of air products in a liquid or gaseous state by low-temperature separation of air in air separation plants is known and, for example, at H.-W. Häring (ed.), Industrial Gases Processing, Wiley-VCH, 2006, in particular Section 2.2.5, "Cryogenic Rectification ", described.

Air separation plants have distillation column systems which can be designed, for example, as two-column systems, in particular as classic Linde double-column systems, but also as three- or multi-column systems. In addition to the distillation columns for the production of nitrogen and / or oxygen in the liquid and / or gaseous state, that is to say the distillation columns for the nitrogen-oxygen separation, distillation columns for the production of further air components, in particular the noble gases krypton, xenon and / or argon, can be provided.

The distillation columns of the above-mentioned distillation column systems are operated at different pressure levels. Known double column systems have a so-called high pressure column (also referred to as a pressure column, medium pressure column or lower column) and a so-called low pressure column (also referred to as an upper column). The high-pressure column is typically operated at a pressure level of 4 to 7 bar, in particular approximately 5.3 bar. The low pressure column is operated at a pressure level of typically 1 to 2 bar, in particular approximately 1.4 bar. In certain cases, higher pressure levels can also be used in the low pressure column. The pressures specified here and below are absolute pressures at the top of the columns specified.

In known methods and systems for the low-temperature separation of air, an oxygen-enriched and an is enriched in a lower region of the high-pressure column Nitrogen-depleted liquid is formed and withdrawn from the high pressure column. This liquid, which in particular also contains argon, is at least partly fed into the low-pressure column and further separated there. It can be partially or completely evaporated before it is fed into the low-pressure column, it being possible for vaporized and unevaporated portions to be fed into the low-pressure column at different positions.

The present invention is based on a method or a corresponding system in which a high and a low pressure column is used. In the context of the present invention, however, the low-pressure column is not formed in one piece, but is divided into a first section and a second section, the first and the second section being arranged at different positions of the air separation plant and at different heights, and in particular not in a plan view of a longitudinal column axis project onto each other. However, the first and the second section of the low pressure column are operated at a common pressure level within the scope of the present invention. The low-pressure column used in the context of the present invention, which is divided into two sections, differs from also known arrangements, in which, in addition to the high-pressure and low-pressure column, a further column for separating nitrogen and oxygen is provided, which, however, is operated at a pressure level, that lies between the pressure levels at which the high pressure column and the low pressure column are operated.

Air separation plants with raw and pure argon columns can be used to obtain argon. An example is illustrated by Häring (see above) in Figure 2.3A and described from page 26 in the section "Rectification in the Low-pressure, Crude and Pure Argon Column" and from page 29 in the section "Cryogenic Production of Pure Argon". As explained there, argon accumulates at a certain height in the low-pressure column in corresponding plants. At this or at another convenient point, possibly also below the argon maximum, the so-called argon transition, argon-enriched gas with an argon concentration of typically 5 to 15 mol percent can be withdrawn from the low-pressure column and transferred to the crude argon column. A corresponding gas typically contains approx. 100 ppm nitrogen and otherwise essentially oxygen.

The crude argon column essentially serves to separate the oxygen from the gas drawn off from the low-pressure column. The separated oxygen in the crude argon column or a corresponding oxygen-rich fluid can be returned to the low-pressure column in liquid form. The oxygen or the oxygen-rich fluid is typically fed into the low-pressure column several theoretical or practical trays below the feed point for the liquid which has been drawn off from the high-pressure column, enriched with oxygen and depleted with nitrogen and possibly partially or completely evaporated. A gaseous fraction which remains in the crude argon column and essentially contains argon and nitrogen is separated further in the pure argon column to obtain pure argon. The crude and pure argon columns have top condensers, which can be cooled in particular with part of the liquid which has been drawn off from the high-pressure column and enriched with oxygen and nitrogen and which partially evaporates during this cooling. Other fluids can also be used for cooling.

In principle, a pure argon column can also be dispensed with in corresponding systems, it being typically ensured here that the nitrogen content at the argon transition is below 1 ppm. In this case, argon of the same quality as from a conventional pure argon column is drawn off from the raw argon column somewhat below the fluid conventionally transferred into the pure argon column, the bottoms in the section between the raw argon condenser, i.e. the top condenser of the raw argon column, and a corresponding deduction as barrier bottoms for Serve nitrogen.

As stated by Häring (see above) with reference to FIG. 2.4A, argon, although contained in atmospheric air with a content of less than 1 mole percent, has a strong influence on the concentration profile in the low pressure column. Thus the separation in the lowest separation section of the low pressure column, which typically comprises 30 to 40 theoretical or practical trays, can be regarded as an essentially binary separation between oxygen and argon. Only from the exit point for the gas transferred to the crude argon column does the separation within a few theoretical or practical soils change into a ternary separation of nitrogen, oxygen and argon.

Even if no argon is to be obtained in a corresponding plant or a corresponding method, it may prove advantageous to discharge argon from the low-pressure column. As mentioned, a corresponding argon discharge takes place when a crude argon column is used because argon-enriched gas is transferred from the low-pressure column to the crude argon column, but essentially only the oxygen contained in this gas is returned to the low-pressure column. The argon discharged with a correspondingly removed gas, however, is permanently withdrawn from the low pressure column.

An "argon discharge" is generally understood to mean a measure in which an argon-containing fluid is transferred from the low-pressure column to a further separation unit and, after depletion of argon, is partially or completely returned from the further separation unit to the low-pressure column. The classic way of evacuating argon is to use a crude argon column. However, argon discharge columns explained below can also be used.

The advantageous effect of the argon discharge is due to the fact that the separation of oxygen and argon is no longer necessary for the amount of argon discharged in the low pressure column, but this binary separation can be outsourced from the low pressure column. The separation of oxygen and argon in the low-pressure column itself is fundamentally complex and requires a corresponding "heating" performance of the main condenser. By removing argon from the low-pressure column, the heating capacity of the main condenser can be reduced. Therefore, with a constant yield of oxygen, for example, either more air can be blown into the low-pressure column or more pressurized nitrogen can be removed from the high-pressure column, which in turn can offer energetic advantages.

As explained, raw argon is obtained in a conventional raw argon column and processed into pure argon in a downstream pure argon column. An argon discharge column, on the other hand, is used primarily for argon discharge for the explained purpose of improving the separation in the low-pressure column. Basically, an "argon discharge column" can be understood here as a separation column for the separation of oxygen and argon, which is not used to obtain a pure argon product, but essentially serves to discharge argon from the low pressure column.

The structure of an argon discharge column differs only slightly from that of a classic crude argon column. However, an argon discharge column typically contains significantly fewer theoretical or practical trays, namely less than 40, in particular between 15 and 30. As with a conventional crude argon column, in particular the bottom area of an argon discharge column can be connected to an intermediate point of the low-pressure column. An argon discharge column can in particular be cooled by means of a top condenser in which the liquid drawn off from the high-pressure column, oxygen-enriched and nitrogen-depleted, is partially evaporated. An argon discharge column typically does not have a bottom evaporator. The present invention uses an argon purge column.

The object of the present invention is to improve the low-temperature separation of air using argon discharge columns and in particular to make the arrangement of the distillation columns used more advantageous.

Disclosure of the invention

Against this background, the present invention proposes a method for the low-temperature separation of air and a corresponding system with the features of the respective independent claims. Refinements are the subject of the dependent claims and the following description.

Before the features and advantages of the present invention are explained, some basics of the present invention are explained in more detail and terms used below are defined.

The devices used in an air separation plant are described in the cited technical literature, for example by Haering (see above) in Section 2.2.5.6, "Apparatus". If the following definitions do not deviate from this, express reference is made to the cited technical literature for the language used in the context of the present application.

Liquids and gases can, in the language used here, be rich or poor in one or more components, "rich" for a content of at least 50%, 75%, 90%, 95%, 99%, 99.5%, 99, 9% or 99.99% and "poor" for a maximum of 50%, 25%, 10%, 5%, 1%, 0.1% or 0.01% on a mole, weight or volume basis , The term "predominantly" can correspond to the definition of "rich". Liquids and gases can also be enriched or depleted in one or more components, these terms refer to a content in a starting liquid or gas from which the liquid or gas was obtained. The 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, and " depleted "if this or this contains at most 0.9 times, 0.5 times, 0.1 times, 0.01 times or 0.001 times the content of a corresponding component, based on the starting liquid or the starting gas. If, for example, "oxygen", "nitrogen" or "argon" is mentioned here, this should also be understood to mean a liquid or a gas which is rich in oxygen or nitrogen, but does not necessarily have to consist exclusively of it.

The present application uses the terms “pressure level” and “temperature level” to characterize pressures and temperatures, which is intended to express that corresponding pressures and temperatures in a corresponding system do not have to be used in the form of exact pressure or temperature values to realize the inventive concept. However, such pressures and temperatures are typically in certain ranges, for example ± 1%, 5%, 10%, 20% or even 50% around an average. Corresponding pressure levels and temperature levels can lie in disjoint areas or in areas that overlap one another. In particular, pressure levels include, for example, unavoidable or expected pressure drops. The same applies to temperature levels. The pressure levels given here in bar are absolute pressures.

The high-pressure column and the low-pressure column (or, in the context of the present invention, its first section) of an air separation plant are in heat-exchanging connection via a so-called main condenser. The Main condenser can in particular be arranged in a lower (sump) area of the low-pressure column (or its first section thereof). In this case, it is a so-called internal main condenser and the evaporation space of the main condenser is also the interior of the low-pressure column (or of its first section). However, the main condenser can basically be arranged outside the interior of the high-pressure column, that is to say a so-called external main condenser.

The main condenser and the top condenser of an argon discharge column which is used in the context of the present invention can each be designed as a condenser evaporator. A "condenser evaporator" is a heat exchanger in which a first, condensing fluid stream enters into indirect heat exchange with a second, evaporating fluid stream. Each condenser evaporator has a liquefaction space and an evaporation space which have liquefaction or evaporation passages. The condensation (liquefaction) of the first fluid flow is carried out in the liquefaction space, and the evaporation of the second fluid flow is carried out in the evaporation space. Evaporation and liquefaction space are formed by groups of passages that are in heat exchange relationship with each other. The main condenser can in particular be used as a single or multi-storey bath evaporator, in particular as a cascade evaporator (such as in the EP 1 287 302 B1 described), or be designed as a falling film evaporator. It can be formed by a single heat exchanger block or by a plurality of heat exchanger blocks which are arranged in a common pressure vessel. However, the present invention is expressly not limited to corresponding types of condenser evaporators or capacitors.

A distillation column system of an air separation plant is arranged in one or more cold boxes. A “cold box” is understood here to mean an insulating covering which completely encompasses a heat-insulated interior space with outer walls, except for bushings for lines and the like. Plant parts to be insulated are arranged in the interior, for example one or more distillation columns and / or heat exchangers. The insulating effect can be achieved by appropriate design of the outer walls and / or by filling the space between the system parts and the outer walls with an insulating material be effected. In the latter variant, a powdery material such as pearlite is preferably used. Both the distillation column system of a plant for the low-temperature separation of air as well as the main heat exchanger and other cold plant parts are enclosed in conventional air separation plants by one or more cold boxes. The external dimensions of the cold box usually determine the transport dimensions for prefabricated systems.

A "main heat exchanger" of an air separation plant is used to cool the feed air in indirect heat exchange with return flows from the distillation column system. It can be formed from a single or a plurality of heat exchanger sections connected in parallel and / or in series, for example from one or more plate heat exchanger blocks. Separate heat exchangers, which are used specifically for the evaporation or pseudo-evaporation of a single liquid or supercritical fluid, without heating and / or evaporation of another fluid, are not part of the main heat exchanger.

A "subcooler" or "subcooling counterflow" (the two terms are used fully interchangeably in the following) is a heat exchanger used here, through which gaseous and liquid material flows in an air separation plant are subjected to heat exchange, which is taken from the rectification column system and partially or completely returned to the rectification column system after the heat exchange.

The relative spatial terms "above", "below", "above", "below", "above", "below", "beside", "side by side", "vertically", "horizontally" etc. refer here to the spatial orientation of the distillation columns of an air separation plant in normal operation. An arrangement of two distillation columns or other components "one above the other" is understood here to mean that the upper end of the lower of the two parts of the apparatus is at a lower or the same geodetic height as the lower end of the upper of the two parts of the apparatus and the projections of the two parts of the apparatus are in intersect on a horizontal plane. In particular, the two parts of the apparatus are arranged exactly one above the other, that is to say the axes of the two parts of the apparatus run on the same vertical straight line. In other cases, especially if the apparatus parts have different diameters However, it can also be advantageous not to arrange the axes one above the other, for example to arrange the apparatus part with the smaller diameter closer to a cold box wall.

Advantages of the invention

The present invention is based on the knowledge that an arrangement of an argon discharge column in a distillation column system of an air separation plant, which has a two-part low-pressure column, which is significantly different from the state of the art, allows an air separation process to be designed particularly efficiently and, in particular, a corresponding air separation plant can be produced particularly simply and inexpensively.

The advantages achievable within the scope of the present invention include, in particular, a particularly advantageous arrangement of the respective components of a distillation column system proposed according to the invention in different cold boxes, which, even when argon discharge columns are used, enables them to be prefabricated and transported to the respective place of use in a prefabricated manner. However, the advantages of the present invention are not limited to the improved arrangement and transportability of the components in cold boxes, but in particular also include a simple construction of a corresponding air separation plant by dispensing with extensive piping, as is typically required in the case of a different, conventional arrangement of an argon discharge column.

An essential aspect of the present invention, in addition to the already mentioned division of the low-pressure column, is to place an argon discharge column in the open state on the underside of the lower section of a corresponding two-part low-pressure column. In general, in the context of these applications, the “lower” or “first” section of a two-part low-pressure column is understood to mean the section in the sump of which, as in the sump of a conventional one-piece low-pressure column, an oxygen-rich liquid is formed. The lower or first section of a corresponding two-part low-pressure column is in particular connected to the high-pressure column as a structural unit. The first or lower section of the two-part low-pressure column is located in particular also the main condenser connecting the high-pressure column and the low-pressure column in a heat-exchanging manner. The "second" or "upper" section of the two-part low-pressure column, on the other hand, is the one in which a nitrogen-rich head gas is formed on the top side, which can be designed as a corresponding (low-pressure) nitrogen product. In particular, the division of the low-pressure column in the context of the present invention is such that a maximum of the argon concentration results in an upper region or at the head of the first or lower section of the two-part low-pressure column, corresponding to the range of the maximum argon concentration in a conventional one-part low-pressure column. This is achieved in particular by an appropriate choice of the number of theoretical plates in the first part of the low pressure column and known structural measures.

Due to the arrangement of the high-pressure column, the first section of the low-pressure column and the argon discharge column proposed according to the invention, a correspondingly created structural unit can be introduced, in particular, into a still portable cold box, so a corresponding air separation unit is prefabricated and, if necessary, a corresponding cold box can be brought to the respective place of use. The remaining components in the cold part of the air separation plant, i.e. in particular the second section of the low-pressure column and possibly a subcooling counterflow can be outsourced to at least one second cold box, which likewise typically does not exceed the maximum sizes for any transport to the place of use. A particularly advantageous embodiment of the present invention results if the second section of the low-pressure column is moved into a cold box and the lines used for the piping of the separation units mentioned, in particular together with a subcooler, are moved to another cold box.

Overall, the present invention proposes a method for cryogenic air separation using an air separation plant with a distillation column system. In the context of the present invention, the distillation column system comprises a first separation unit (corresponding to the high-pressure column of a conventional air separation plant), a second separation unit (corresponding to the first or lower section of a two-part low-pressure column), a third separation unit (corresponding to the argon discharge column) and a fourth separation unit (corresponding to the second or upper section of a two-part low-pressure column). Compressed and cooled air is fed into the first separation unit, but not necessarily only into this, within the scope of the present invention. Corresponding air can be compressed using known measures, in particular using a main air compressor and possibly one or more secondary compressors, boosters and the like. In the context of the present invention, it is prepared by means of measures which are also known, that is, in particular freed of water and carbon dioxide. Within the scope of the present invention, different measures for air treatment and cooling as well as for the further treatment of this air can be used. In particular, one or more expansion valves, boosters, turbines and the like can also be used, as are known in principle from the field of air separation. For details, please refer to the relevant specialist literature, for example, Häring (see above).

In the context of the present invention, the first separation unit is operated at a first pressure level of 4 to 8 bar absolute pressure, for example a pressure level of approximately 5.3 bar absolute pressure, which corresponds to the normal operating pressure of a high-pressure column of an air separation plant. The second, the third and the fourth separation unit, however, are operated in the context of the present invention at a common second pressure level, which in the context of the present invention is 1 to 2 bar absolute pressure, that is to say corresponds to the typical pressure level of a low-pressure column of an air separation plant. The second pressure level can be, for example, approximately 1.4 bar absolute pressure.

In the context of the present invention, the first separation unit, as is known for high-pressure columns of air separation plants, forms an oxygen-enriched and nitrogen-depleted, argon-containing first bottoms liquid and a nitrogen-enriched and oxygen-depleted first overhead gas. For further details, reference is also made here to the relevant specialist literature on air separation or the operation of high-pressure columns of known air separation plants.

In the context of the present invention, the first bottom liquid is partially or completely transferred to the third separation unit and the first overhead gas is partially or completely liquefied and returned to the first separation unit. to Liquefaction of the first top gas or its portion returned to the first separation unit, in particular a main condenser is used, which in the present case connects the first separation unit and the second separation unit in a heat-exchanging manner. Further details on a corresponding main capacitor are explained below.

The present invention is not restricted to liquefying only the portion of the first overhead gas which is attributed to the first separation unit. Rather, within the scope of the present invention, further overhead gas can also be liquefied and, in particular as a liquid air product, without or with subsequent evaporation or conversion into the supercritical state, can be discharged as a product from the air separation plant. Furthermore, in the context of the present invention, further liquefied overhead gas from the top of the first separation unit, that is to say liquefied first overhead gas, can be fed in as a return to the fourth separation unit, in particular after corresponding liquefied overhead gas has previously been passed through a supercooling counterflow. Non-liquefied overhead gas can also be drawn off from the top of the first separation unit and, for example as a pressurized nitrogen product, can be carried out from the air separation plant. As already explained, the use of an argon discharge column can in particular achieve that the amount of top gas of the high pressure column discharged from the air separation plant can be increased accordingly.

In the context of the present invention, an oxygen-rich second bottom liquid and a second top gas enriched in argon are formed by means of the second separation unit. As mentioned, the second separation unit in the context of the present invention essentially corresponds to the lower section or first section of a two-part low-pressure column or the lower part of a classic, one-part low-pressure column up to the argon maximum. As already mentioned, this is achieved by the choice of appropriate release agents or the selection of the number of partitions. A corresponding design of the second separation unit enables advantageous argon removal in the third separation unit.

Within the scope of the present invention, a second portion of the second overhead gas is transferred to the third separation unit and a second portion to the fourth separation unit. While the fourth separation unit the conventional second or upper Section corresponds to a two-part low-pressure column, the third separation unit is essentially intended to carry out an argon discharge. As explained below, however, the third separation unit is designed as a structural unit together with the second separation unit within the scope of the present invention. It is therefore not necessary to remove the corresponding fluid from the low-pressure column and to transfer it to an argon discharge column. In contrast, the second overhead gas is in particular transferred to the third separation unit without deflection. The transfer takes place in particular without a wire.

At least the major part of the argon, which is contained in a total amount of air supplied to the distillation column system, is separated off by means of the third separation unit, wherein a liquid return is returned to the second separation unit by means of the third separation unit. For this purpose, the third separation unit has separation zones which can be formed using known separation devices, in particular ordered or disordered packings or trays. For the dimensioning of the third separation unit, reference is made to the explanations below. In principle, the third separation unit can be designed in a known manner, the third separation unit corresponding to an argon discharge column, which, however, is open in the lower area opposite the second separation unit.

In the context of the present invention, a fourth bottom liquid and a fourth top gas are formed by means of the fourth separation unit and the fourth bottom liquid is partly or completely returned to the second separation unit. In particular, if the fourth separation unit is arranged next to the second (and possibly the first and third) separation unit, a suitable pump is used for the transfer of the fourth bottom liquid to the second separation unit.

In the context of the present invention, it is provided in particular that the second separation unit, that is to say the first or lower section of the low-pressure column, has 10 to 50 theoretical plates, in particular 20 to 40 theoretical plates, and that the third separation unit 10 to 60 theoretical plates, in particular 15 to 30 theoretical plates. The second separation unit is therefore the section of a low-pressure column which comprises the typical oxygen section or corresponding separation devices of such an oxygen section. The the third separation unit, however, is, as already explained several times, as an argon discharge column.

Within the scope of the present invention, it is further provided that the third separation unit (in the sense of the above explanations) is arranged above the second separation unit, in particular exactly above this, and that the third separation unit is tapered in a lower area compared to an upper area of the second Separation unit opens. An “untapered” opening of the third separation unit is understood to mean that a column jacket of the third separation unit has no constriction compared to a column jacket of the second separation unit. In particular, in the context of the present invention there is no reduction in cross section compared to a cross section of the third separation unit. In particular, however, the third separation unit can have a smaller cross section than the second separation unit, and the entire cross section of the third separation unit can be available for an inflow of the first portion of the second top gas into the third separation unit. In contrast to conventionally found arrangements, in which an argon discharge column is arranged next to the distillation column system formed from high and low pressure column, no transfer of corresponding fluids by means of pumps, lines and the like is required in the context of the present invention. Rather, second overhead gas can rise from the second separation unit to the third separation unit essentially unimpeded, in particular without deflection or line, and liquid from the third separation unit can flow into the second separation unit essentially unhindered. Here too, as already mentioned, there is a particular advantage of the present invention.

As is known in this respect for argon discharge columns, the argon discharge column used in the context of the present invention, that is to say the third separation unit, can also have a top condenser which can be cooled with oxygen-enriched liquid from the high pressure column, in this case the first sump liquid. Corresponding liquid, which is partially evaporated during cooling, can then be fed into the fourth separation unit, in particular at different heights. The corresponding currents are advantageously divided outside the top capacitor so that they have different concentrations.

In the context of the present invention, as already mentioned, main capacitors, i.e. capacitors that connect the first separation unit and the second separation unit in a heat-exchanging manner, in particular falling film or cascade evaporators, in particular multi-storey cascade evaporators of the type explained above, can be used. This results in a particularly efficient liquefaction in a corresponding main condenser. However, the present invention is expressly not limited to such forms of condenser evaporators, but can be used with any type of main condenser.

In the context of the present invention, the compressed and cooled air which is fed into the first separation unit can in particular comprise a gaseous and a liquefied feed air stream, which are each fed into the first separation unit at the first pressure level. Here, a gaseous feed air stream at a first feed position and a liquid feed air stream at a second feed position can be fed into the first separation unit, the first feed position being below the second feed position, with no separation devices typically being provided in the first separation unit below the first feed position, whereby the second feed position is advantageously above a liquid retention device from which a liquid stream can be withdrawn from the first separation unit, and the second feed position lies above a separation unit or a separation area of the first separation device. It should be expressly emphasized that in the context of the present invention, feed air can also be fed into the first separation unit, for example in two phases, in a common line. The formation of appropriate material flows is known in the field of air separation.

In the context of the present invention, the first separating unit and the second separating unit are structurally connected to one another with particular advantage and can be arranged within a common column casing, the common column casing also being structurally connected to the third separating unit. A common column jacket in the sense of the present invention can in particular be a common cylindrical outer container, so that the first separating unit and the second separating unit can be produced with the same cross section within the scope of the present invention. Assigns the high pressure column or first Separation unit having a smaller diameter than the first section of the low-pressure column or the second separation unit, typically no accommodation is provided in a common column jacket; the column jacket of the high-pressure column is attached to the lower side of the column jacket of the foot section of the low-pressure column. Different cross sections can therefore also be used in principle. The third separation unit has in particular a smaller cross section than the first and / or the second separation unit and therefore does not have to be arranged within this common cylindrical column jacket, but can in particular be connected to it, for example welded to an opening in the upper region of the second separation unit. The fourth separation unit is advantageously not structurally connected to the first, the second and the third separation unit, but is only connected to the first, the second and the third separation unit via piping or lines. In this way, the first, the second and the third separation unit, on the one hand, and the fourth separation unit, on the other hand, can be arranged at different positions of a corresponding system and in particular can be accommodated in different cold boxes. The fourth separation unit can also have a smaller, but also a larger cross-section than the second separation unit. It can in particular have 18 to 65 theoretical plates and thus correspond to the rest of a corresponding two-part low-pressure column, the first section of which is formed by the second separation unit.

In the method proposed according to the invention, the first portion of the second top gas has in particular 20 to 50 percent by volume and the second portion of the second top gas has 50 to 80 percent by volume (ie in particular the rest) of the second top gas. This results in a particularly efficient argon discharge in the third separation unit within the scope of the present invention.

As already mentioned, in the context of the present invention, the fourth separation unit can be arranged in particular next to the second separation unit and in particular in a separate cold box. In this way, the overall height of a corresponding air separation plant is reduced overall. In such an embodiment, it is provided in particular that the fourth bottom liquid is returned to the second separation unit using a transfer pump or at least two transfer pumps arranged in parallel, and in particular at the top of the second separation unit to the second separation unit as liquid return is given up. In particular, two pumps can be operated in parallel and a third can be provided for reasons of redundancy. The use of two transfer pumps arranged in parallel enables a particularly simple construction because pumps of corresponding sizes are available as standard. A corresponding transfer pump is provided in order to overcome the height difference between the second separation unit and the fourth separation unit or vice versa. On the other hand, the second portion of the second top gas can advantageously flow into the fourth separation unit through a minimal pressure difference between the second separation unit and the fourth separation unit.

As already mentioned several times, the first separation unit, the second separation unit and the third separation unit are advantageously arranged in a common cold box and the fourth separation unit is arranged in a further cold box.

Within the scope of the present invention, the first separating unit, the second separating unit and the third separating unit on the one hand and the fourth separating unit on the other hand are connected to one another and / or to other devices by means of piping. At least part of this piping can run vertically. At least part of such piping can be separated from the two cold boxes, in which the first separation unit, the second separation unit and the third separation unit on the one hand and the fourth separation unit on the other hand are arranged, in an additional cold box, here as "piping cold box" referred to be arranged, which can be prefabricated. The provision of a corresponding piping cold box makes it possible to reduce the dimensions of the other two cold boxes accordingly and, in particular, to make them (better) transportable. A large part of the instrumentation, valves, etc. can also be accommodated in the piping gold box. For example, it can contain at least 50, 60, 70 or 80% of the line length of the lines forming the piping. The cold boxes are connected to one another at the location of the creation of an appropriate air separation plant and thus piping is also produced. It is particularly advantageous if a piping gold box also contains a subcooler or subcooling counterflow provided in the air separation plant, which can be arranged in a particularly favorable manner together with the piping.

In the context of the present invention, it can in particular be provided that the first sump liquid, regardless of whether it is arranged in a further cold box or not, is first passed through a corresponding countercooling counterflow and then fed into the fourth separation unit at a first feed position. It can further be provided to draw a liquid stream from the first separation unit in the vicinity, preferably directly below the feed position of a liquid feed air stream into the first separation unit, to lead it through the supercooling counterflow, and to feed it into the fourth separation unit at a second feed position. The second feed position in the fourth separation unit is advantageously above the first feed position in the fourth separation unit and is advantageously separated from the latter by at least one separation section.

In the context of the present invention, in particular a liquid air product can be removed from the distillation column system, increased in pressure in the liquid state, converted into the gaseous or supercritical state by heating, and discharged from the air separation plant. The present invention can therefore be used in particular in connection with a so-called internal compression of air products. For details on internal compression methods, reference is made to the cited prior art.

In the context of the present invention, further material flows can be taken from the distillation column system and made available as air products. In particular, a gaseous material stream can be removed from the fourth separation unit, passed through the supercooling countercurrent and carried out as so-called impure nitrogen from the distillation column system. A removal point from the fourth separation unit is advantageously above the second feed position in the fourth separation unit. Furthermore, in the context of the present invention, a liquid stream can be removed from an upper region of the fourth separation unit and made available as a liquid nitrogen product. It is also possible to remove a gaseous, nitrogen-rich stream in an upper region of the fourth separation unit, to pass it through the supercooling countercurrent and to provide it as a corresponding low-pressure nitrogen product.

The invention also extends to an air separation plant with a distillation column system which comprises a first separation unit, a second separation unit, a third separation unit and a fourth separation unit, as stated in the corresponding independent claim.

The air separation plant according to the invention, which is advantageously set up to carry out a method, as was explained above, benefits in the same way from the advantages of the method according to the invention in its explained configurations. We therefore expressly refer to the above explanations.

Brief description of the drawings

Figure 1 FIG. 13 illustrates a partial distillation column system of an air separation plant according to an embodiment of the present invention.

Detailed description of the drawings

Figure 1 shows a distillation column system of an air separation plant, which is set up for an operation according to an embodiment of the present invention, in a greatly simplified partial view. This in Figure 1 The distillation column system illustrated is designated 100 in total. It is provided in an air separation plant 200, which is only indicated here.

In the Figure 1 Illustrated components of the distillation column system 100 include a first separation unit 110, a second separation unit 120, a third separation unit 130 and a fourth separation unit 140, a main condenser 150, a supercooling counterflow 160, a transfer pump 170, an internal compression pump 180 and a top condenser 190.

The first separation unit 110 corresponds to a high-pressure column of a conventional air separation plant. The first separation unit is operated at a corresponding pressure level, referred to here as the "first pressure level". The second separation unit 120 and the fourth separation unit 140 correspond to a first section and a second section of a low pressure column of a conventional air separation plant. You will be on an appropriate joint Pressure level, here referred to as "second pressure level" operated. The third separation unit 130 represents an argon discharge column. It is also operated at the second pressure level.

In the in Figure 1 In the illustrated distillation column system 100, the first separation unit 110 and the second separation unit 120 are in heat-exchanging connection via the main condenser 150, as will also be explained below. The first separating unit 110 and the second separating unit 120 are furthermore arranged, in particular within a common column casing and above one another, in particular directly above one another, in the sense explained above. The top capacitor 190 is arranged at the upper end of the third separation unit 130.

With regard to further explanations of an air separation plant, of which the distillation column system 110 can be part, reference is made to relevant specialist literature, for example Haring (see above), in particular chapter 2.2.5 and figure 2.3A. In such an air separation plant, in particular a gaseous feed air stream 1 and a liquefied feed air stream 2 can be provided. In this context, in particular a main air compressor, cleaning and processing devices, turbines, expansion valves and a main heat exchanger of a known type can be used.

The feed air streams 1 and 2 are fed into the first separation unit 110 at feed positions 111 and 112, respectively. In the first separation unit 110, an oxygen-enriched and nitrogen-depleted and argon-containing bottoms liquid and a nitrogen-enriched and oxygen-depleted top gas are formed at the first pressure level. The bottom liquid is drawn off from the first separation unit 110 in the form of a stream 3. The top gas is drawn off from the first separation unit 110 in the form of a stream 4. Liquid in the form of a material flow 5 from the first separation unit 110 is carried out directly below the feed position 112 for the feed air flow 2.

The material flow 3 is passed through the supercooling counterflow 160 and partly fed into the fourth separation unit 140 in the form of a material flow 31 at a feed position 141. Another part is transferred in the form of a material flow 32 into an evaporation space of the top condenser 190. From the Evaporation space of the top condenser 190, a liquid stream 33 and a gaseous stream 34 are drawn off and likewise fed into the fourth separation unit 140, in particular at different heights. The stream 4 is also divided into two sub-streams 41 and 42. The first partial flow 41 is partially or completely liquefied in the main condenser 150. A first portion 411 of the first partial flow 41 is fed back to the first separation unit 110 at a feed position 113 as a return. A second portion 412 of the first partial flow 41 is passed through the supercooling counterflow 160 and is fed as return to the fourth separation unit 140. The partial stream 42 is carried out as a gaseous nitrogen pressure product from the distillation column system 100. The material flow 5 is passed through the supercooling counterflow 160 and fed into the fourth separation unit 140 at a feed position 142.

In the second separation unit 120, an oxygen-rich bottom liquid and an overhead gas enriched with argon are formed. The bottom liquid is drawn off from the second separation unit 120 in the form of a stream 6. A first partial flow 61 of the material flow 6 is increased in pressure in the internal compression pump 180 in the liquid state, and is converted into the gaseous or supercritical state by heating (in FIG Figure 1 not separately illustrated) and designed as an internally compressed oxygen pressure product. A second partial flow 62 of the material flow 6 is provided as a liquid oxygen product after partial passage through the supercooling counterflow 160 and corresponding tempering.

The top gas of the second separation unit 120 partly rises into the third separation unit 130, which is arranged above the second separation unit 120 and which opens in a lower region, in particular without a cross-sectional taper to the second separation unit 120. Another part of the top gas is drawn off in the form of a stream 7. The material flow 7 is fed into a lower region of the fourth separation unit 140 at a feed position 143.

A top gas is formed in the third separation unit 130, which contains at least the major part of the argon that was previously contained in the feed air supplied to the distillation column system 100. This overhead gas from the third separation unit 130 is drawn off in the form of a stream 8. Liquid trickling down from the third separation unit 130, which in this way is at argon is depleted or (essentially) free of argon, is returned directly to the second separation unit 120. In the third separation unit 130, argon is thus removed.

A sump liquid and a top gas are formed in the fourth separation unit 140. The bottom liquid is drawn off from the fourth separation unit 140 in the form of a material flow 9 and is returned as return to the second separation unit 120 by means of the transfer pump 170 and is thereby fed into the second separation unit 120 at a feed position 114. A material stream 10, so-called impure nitrogen, is removed from the fourth separation unit, passed through the supercooling counterflow 160 and carried out from the distillation column system 100. The same applies to a nitrogen-rich stream 11, which is provided as a gaseous low-pressure nitrogen product. Nitrogen-rich liquid in the form of a material flow 12 is drawn off from a liquid retention device at the head of the fourth separation unit (140) and made available as a liquid nitrogen product. If no gaseous low-pressure nitrogen product is required, a corresponding separation section in the fourth separation unit 14 can be omitted and all overhead gas can be drawn off as impure nitrogen in accordance with the material flow 10.

As illustrated here, but not mandatory for the present invention, the first separation unit 110, the second separation unit 120 and the third separation unit 130, on the one hand, and the fourth separation unit 140, on the other hand, are each provided in a cold box A or B and with one another and / or with others Devices such as the supercooling counterflow 160 and the main heat exchanger (not shown) are connected to one another by means of lines or piping, here combined with 20. The piping runs vertically, at least in sections. At least part of such piping 20 can be arranged separately from the two cold boxes A and B, in which the first separating unit 110, the second separating unit 120 and the third separating unit 130 on the one hand and the fourth separating unit 140 on the other hand, are arranged in an additional cold box C. , This additional cold box C for piping can also contain subcooler 160 in particular.

Claims (14)

Method for low-temperature separation of air using an air separation plant with a distillation column system (100), which has a first separation unit (110), a second separation unit (120), a third separation unit (130) and a fourth separation unit (140), wherein the first Separation unit (110) compressed and cooled air is fed, the first separation unit (110) is operated at a first pressure level of 4 to 8 bar absolute pressure, the second separation unit (120), the third separation unit (130) and the fourth separation unit (140) are operated at a second pressure level of 1 to 2 bar absolute pressure, by means of the first separation unit (110) an oxygen-enriched and nitrogen-depleted, argon-containing first bottoms liquid and a nitrogen-enriched and oxygen-depleted first top gas are formed, the first bottoms liquid partially or completely transferred to the third separation unit (130), the the first head gas is partially or completely liquefied and returned to the first separation unit (110), by means of the second separation unit (120) an oxygen-rich second bottom liquid and a second head gas enriched in argon are formed, the second head gas in a first proportion into the third separation unit ( 130) and a second portion is transferred to the fourth separation unit (140), by means of the third separation unit (130), the argon which is contained in a total amount of air supplied to the distillation column system (100) is partially or completely separated off by means of the third Separation unit (130) a liquid return to the second separation unit (120) is provided, by means of the fourth separation unit (140) a fourth bottom liquid and a fourth top gas are formed, and the fourth bottom liquid is partially or completely returned to the second separation unit (120) , characterized in that the second T racing unit (120) has 10 to 50 theoretical plates, that the third separating unit (130) has 10 to 60 theoretical plates, and that the third separating unit (130) is arranged above the second separating unit (120) and is opposite one another in a lower region upper area of the second separation unit (120) opens. Method according to one of the preceding claims, in which compressed and cooled air, which is fed into the first separation unit, comprises a gaseous and a liquefied feed air stream (1, 2). Method according to one of the preceding claims, in which the first separation unit (110) and the second separation unit (120) are arranged within a common column jacket or in two structurally connected column jackets, the common column jacket or the column jacket of the second separation unit (120) the third separation unit (130) is structurally connected. Method according to one of the preceding claims, in which the fourth separation unit has 18 to 55 theoretical plates. Method according to one of the preceding claims, wherein the first portion of the second head gas comprises 20 to 60 volume percent and the second portion of the second head gas 40 to 80 volume percent of the second head gas. Method according to one of the preceding claims, in which the fourth separation unit is arranged next to the second separation unit. Method according to one of the preceding claims, in which the fourth bottom liquid is returned to the second separation unit (120) using a transfer pump (170) or using two or more transfer pumps arranged in parallel. Method according to one of the preceding claims, in which the first separation unit (110), the second separation unit (120) and the third separation unit (130) are arranged in a common cold box (A). Method according to Claim 8, in which the fourth separation unit (140) is arranged in the common cold box (A) or in a further cold box (B). Method according to Claim 9, in which the first separation unit (110), the second separation unit (120) and the third separation unit (130) on the one hand and the fourth separation unit (140) on the other hand with one another and / or with further apparatus by means of piping (20) with one another connected in sections runs vertically, at least part of the piping (20) being arranged in a separate piping gold box (C). The method of claim 10, wherein a subcooler (120) is further arranged in the piping gold box (C). Method according to one of the preceding claims, in which a liquid air product is withdrawn from the distillation column system (100), pressure-increased in the liquid state, converted into the gaseous or supercritical state by heating and discharged from the air separation plant. Air separation plant with a distillation column system (100), which has a first separation unit (110), a second separation unit (120), a third separation unit (130) and a fourth separation unit (140), the air separation plant being set up into the first separation unit ( 110) feed compressed and cooled air, to operate the first separation unit (110) at a first pressure level of 4 to 8 bar absolute pressure, the second separation unit (120), the third separation unit (130) and the fourth separation unit (140) on a second To operate pressure level of 1 to 2 bar absolute pressure, by means of the first separation unit (110) to form an oxygen-enriched and nitrogen-enriched, argon-containing first bottoms liquid and a nitrogen-enriched and oxygen-depleted first top gas, the first bottoms liquid partially or completely to transfer to the third separation unit (130), the first head gas partially or completely to liquefy constantly and to be traced back to the first separation unit (110), by means of the second separation unit (120) to form an oxygen-rich second bottom liquid and a second head gas enriched in argon, the second head gas in a first proportion into the third separation unit (130) and to transfer a second portion into the fourth separation unit (140), by means of the third separation unit (130), to partially or completely separate the argon contained in a total amount of air supplied to the distillation column system (100) by means of the third separation unit (130) to provide liquid return to the second separation unit (120), by means of the fourth separation unit (140) to form a fourth bottom liquid and a fourth top gas, and to attribute the fourth bottom liquid at least partially to the second separation unit (120), characterized in that the second Separating unit (120) has 10 to 50 theoretical plates, the third separating unit (130) has 10 to 60 theoretical plates, and the third separating unit (130) is arranged above the second separating unit (120) and is located in a lower area compared to an upper area the second separation unit (120) opens. Air separation plant according to claim 13, which is set up to carry out a method according to any one of the preceding claims.

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