EP3101374A2 - Method and installation for cryogenic decomposition of air - Google Patents

Abstract

A method is proposed for the distillative cryogenic separation of feed air in a distillation column system (10) of an air separation plant at different distillation pressures, wherein the total feed air is compressed in a total amount of air to a first pressure level which is at least 4 to 5 bar above the highest of the distillation pressures, and From the total amount of air, a first partial air quantity is first cooled to a first temperature level of 130 to 170 and then compressed to a second pressure level which is at least 10 bar above the first pressure level, and a second partial air amount is first cooled to a second temperature level of 110 to 150 K. and then released to a third pressure level that is below the first pressure level. It is contemplated that a compression / expansion assembly (30, 40) is used with a transmission in which a drive wheel (38) is engaged with a gear (39) and the gear (39) is engaged with a driven gear (37). wherein with the drive wheel (38) the blades of two or more turboexpanders (33, 34) and the output gear (37) the blades of two or more turbo compressors (31, 32) are coupled, and the first partial air quantity for compression to the second pressure level successively through the turbo-compressor (31, 32) and the second partial air quantity for relaxation to the third pressure level in parallel through the turboexpander (33, 34) is guided. A corresponding air separation plant (100, 200) is also the subject of the invention.

Description

The invention relates to a method and a plant for the cryogenic separation of air according to the preambles of the independent claims.

State of the art

The production of air products in the liquid or gaseous state by cryogenic separation of air in air separation plants is known and, for example at H.-W. Haring (ed.), Industrial Gases Processing, Wiley-VCH, 2006, especially Section 2.2.5, "Cryogenic Rectification The present invention is particularly suitable for air separation plants with internal compression, as described above, Section 2.2.5.2, "Internal Compression" explained.

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-column or multi-column systems. In addition to the distillation columns for the recovery of nitrogen and / or oxygen in the liquid and / or gaseous state (for example, liquid oxygen, LOX, gaseous oxygen, GOX, liquid nitrogen, LIN and / or gaseous nitrogen, GAN), so the distillation columns for nitrogen-oxygen Separation, distillation columns can be provided for obtaining further air components, in particular the noble gases krypton, xenon and / or argon.

The distillation column systems of air separation plants are operated at different operating pressures in their distillation columns. Known double column systems have, for example, a so-called (high) pressure column and a so-called low-pressure column. The operating pressure of the high-pressure column is, for example, 4.3 to 6.9 bar, in particular about 5.5 bar. The low-pressure column is operated at an operating pressure of, for example, 1.2 to 1.7 bar, in particular about 1.4 bar. The pressures given here are absolute pressures in the bottom of corresponding distillation columns. The pressures mentioned below are also referred to as "distillation pressures", because in them the fractional distillation the respectively fed air takes place within the distillation columns. This does not exclude that other pressures may be present elsewhere in a distillation column system.

In the distillation column systems cooled compressed air (feed air) is fed, which is brought by means of different compressors or combinations of different compressors (for example, main air compressors and booster) to pressure. Products obtained in a corresponding air separation plant can also be pressurized with compressors (product compressors) or corresponding combinations of compressors.

The operating costs (OPEX) of an air separation plant are mainly determined by energy consumption, which in turn depends mainly on the energy consumption of the compressors (main air compressors, booster and product compressor, if any). The investment costs (CAPEX) are also significantly determined by the cost of providing the compressors.

In the air separation processes can be used in which the feed air by means of a main air compressor (English Main Air Compressor, MAC) brought about the pressure of the high pressure column and only a portion of the feed air by means of a booster compressor (Booster Air Compressor, BAC) recompressed and used for internal compression of oxygen (see below) or for cooling. These more conventional methods are also referred to as MAC / BAC methods.

Recently, instead of the MAC / BAC methods, increasingly so-called HAP (High Air Pressure) methods are used, since these can offer advantages in comparison to the MAC / BAC methods. HAP processes are particularly advantageous in coal gasification or coal liquefaction (coal to gas, coal to liquids, CTX) or the gasification of heavy oil. The air separation plants used here usually have exclusively or almost exclusively gas products (gaseous, internally compressed pressure oxygen, GOXIC or pressure nitrogen, PGAN) supply, with no need for a significant flexibility in the process management.

In a HAP process, the total feed air is compressed in a main air compressor to a pressure that is well above the distillation pressure in the high pressure column. The pressure difference used is at least 4 bar and preferably between 6 and 16 bar. Such HAP methods are for example from EP 2 466 236 A1 , of the EP 2 458 311 A1 and the US 5,329,776 A known, MAC / BAC method, for example, from the literature cited above.

The US 5 901 579A shows a coupled via a gearbox turbo compressor and turboexpander for use in a HAP process. From the EP 2 634 517 A1 and the EP 2 520 886 A1 Arrangements are known in which so-called cold compressors or cold booster (see below) are used.

Air separation plants can, as mentioned, be operated with so-called internal compression. In the internal compression, for example, to provide the above-mentioned gaseous, internally compressed oxygen pressure, a liquid stream is removed from the distillation column system and at least partially brought to liquid pressure. The liquid brought to pressure is heated in a main heat exchanger of the air separation plant against a heat transfer medium and evaporated. The liquid stream may in particular be liquid oxygen, but also nitrogen or argon. The internal compression is thus used to obtain appropriate gaseous printed products. Among other things, the advantage of internal compression processes is that corresponding fluids do not have to be compressed outside the air separation plant in a gaseous state, which often proves to be very complicated and / or requires expensive safety measures.

The term "evaporation" includes, as also explained below, in the internal compression cases in which there is a supercritical pressure and therefore no phase transition takes place in the true sense. The liquid pressurized stream is then "pseudo-evaporated". A heat transfer medium is liquefied (or pseudo-liquefied if it is under supercritical pressure) against a (pseudo) vaporising stream. The heat carrier is usually formed by a partial flow of the compressed feed air, which is referred to as inductor current. In a warmer area of the used in the evaporation or pseudo-vaporization Heat exchanger can be introduced additional heat of vaporization by the so-called turbine flow (or by multiple turbine streams).

In order to efficiently heat and vaporize the stream brought to liquid pressure, this heat transfer medium must have a relatively high pressure due to thermodynamic conditions. Therefore, a correspondingly high-density power must be provided. If, for example, for use in the aforementioned CTX method or the gasification of heavy oil, but also in other scenarios, internally compressed pressure oxygen with high or very high pressures (for example, 50 bar and more) are provided, this is particularly true.

This can lead to problems that can not or only with disadvantageous means with conventional measures, as explained in detail below. The present invention therefore has as its object to provide possibilities that allow to carry out a corresponding compression in a simple and efficient manner in a HAP process.

Disclosure of the invention

Against this background, the present invention proposes a method and an installation for the cryogenic separation of air with the features of the independent claims. Embodiments are each the subject of the dependent claims and the following description.

Before explaining the features and advantages of the present invention, its principles and the terms used will be explained.

In air separation plants, turbo compressors are used to compress the air. This applies, for example, to the "main (air) compressor", which is characterized by the fact that through this the total amount of air fed into the air separation plant, ie the entire "feed air", is compressed. A "secondary compressor", in which a part of the air quantity compressed in the main air compressor is brought to an even higher pressure in MAC / BAC process, is likewise typically designed as a turbocompressor. For (subsequent) compression of partial air volumes Typically, additional turbo compressors are provided, which are also referred to as boosters.

At several points in air separation plants air is also relaxed, including turboexpander can be used. This applies in particular to the relaxation of a so-called turbine flow, as explained below. Turboexpanders can also be coupled with turbo compressors (boosters) and drive them. If one or more turbocompressors without externally supplied energy, i. driven only by one or more turboexpander, the term "turbine booster" is used for such an arrangement.

The mechanical structure of turbocompressors and turboexpanders is known to those skilled in principle. In a turbo compressor, the compression of the air by means of blades, which are arranged on an impeller or directly on a shaft, a turbo-compressor forms a structural unit, however, which may have a plurality of "compressor stages". A compressor stage typically includes an impeller or a corresponding array of blades. All of these compressor stages can be driven by a common shaft. A turboexpander is basically designed to be comparable, but the blades are driven by the expanding air. Again, several expansion stages can be provided. Turbo compressor and turboexpander can be designed as radial or axial machines.

The following is the speech that "the blades" of a turbocompressor or turboexpander are "non-rotatably coupled" with another element, such as a drive wheel or output gear, this means that there is a mechanical connection between the blades and the other element. The blades are, as mentioned, attached to one or more impellers or rotatably connected to a shaft, or directly to a shaft, so that a direct torque transmission between the shaft and blades is possible. In this way, each rotatably coupled to the shaft member is also rotatably coupled to the blades. Such a "rotationally fixed coupling" causes a rotational speed equal and the same direction of rotation of the blades and the other element, such as the drive wheel or the driven wheel, about the axis of the Wave. A coupling across a gear engagement is not a "non-rotatable coupling" in the sense explained.

A "drive wheel" is understood below to mean a gear which is acted on by a shaft with a torque, in particular by being coupled to the rotor blades of a turboexpander. On the other hand, a "driven wheel" is a toothed wheel which in turn applies a torque to a shaft, in particular the shaft of a turbocompressor.

The present application uses the terms "pressure level" and "temperature level" to characterize pressures and temperatures, thereby indicating that corresponding pressures and temperatures need not be used in the form of exact pressure and temperature values, respectively, to the inventive concept realize. However, such pressures and temperatures typically range in certain ranges that are, for example, ± 1%, 5%, 10%, 20% or even 50% about an average. Corresponding pressure levels and temperature levels can be in disjoint areas or in areas that overlap one another. In particular, for example, pressure levels include unavoidable or expected pressure drops. The same applies to temperature levels. The pressure levels indicated here in bar are absolute pressures.

In order to be able to efficiently design a HAP process, or to be able to efficiently provide internally compressed gaseous pressure oxygen at high pressures, an air flow at comparatively high pressure is required, as mentioned at the outset. This pressure is again significantly higher than the HAP method already high pressure of the total compressed air and is typically produced by means of so-called cold booster. A cold booster is understood to mean a turbocompressor which is charged with air at low temperatures, generally below 0 ° C. This is advantageously driven by means of a turboexpander.

A single stage compression of said current, also referred to as inductor current, is merely a hypothetical example for illustration in the accompanying drawings FIG. 1 shown. A single-stage compression is not sufficient to achieve the required pressures, since the achievable pressure ratio of the cold booster is limited (the pressure ratio Π in corresponding turbocompressors is usually not higher than 1.8 to 2.0). In addition, the flow rate of the correspondingly high air flow to be compressed (in an energy-optimized design, a second air flow is used at a lower pressure level) is much lower than the mass flow of the air, which is expanded in a usable for driving turboexpander. This would lead to very different specific speeds, which is why a corresponding unit is currently not buildable.

In principle, this problem could be circumvented by using a two-stage arrangement instead of a single-stage cold booster which is at least partially driven externally, for example by electrical energy. However, this is not desirable as a rule, since this would cause additional costs both by the required provision of an electric motor and by the dimensioning of the local medium-voltage network. In particular, HAP methods can, as explained below, manage completely without the use of electric motors for compression, so that the provision of an electric motor and the required infrastructure would be particularly disadvantageous here. In particular, in large CTX projects or in processes for the gasification of heavy oil, in which air separation plants are operated using HAP processes, and for which the present invention is particularly suitable, must be used in any case at the high air volumes used turboexpander (the entire gaseous air for rectification is relaxed in a HAP process via appropriate turboexpander), so that it is recommended that the compression of the throttle current over this, ie without external electrical energy.

Another arrangement, also for purposes of illustration only, is FIG. 2 shown and explained below. Although a corresponding arrangement has not been considered in the cold part of a corresponding system so far, but is known per se and has already been used in "warm" turbine booster, if there are very different flow rates. Would such an arrangement in the "cold" part of a corresponding system used, as in FIG. 2 However, in the case of the second cold booster, where a final pressure of about 57 bar (at similar pressure of internally compressed oxygen) is produced, the ratios of the volumetric flows remained too unbalanced, so that such a unit because of too different specific speeds currently also not buildable. In order to make the described units constructible, the amount of inductor current would have to be increased and the amount of turbine flow reduced. As a result, however, the method loses efficiency because the final pressure of the throttle current would be lower.

The present invention was therefore based on the search for an arrangement which allows a two-stage compression of the throttle flow at optimum proportions by means of a turbine drive.

According to the invention, it has been recognized that a compression / expansion arrangement, in which several (ie two or more) driving turboexpanders are connected in parallel and two or more turbo compressors are connected in series, solves the problems explained above. Instead of a direct drive or a direct transmission via a shaft, an intermediate transmission is used as explained below in the context of the invention. The use of such an intermediate gear allows the decoupling of specific speeds and allows the desired drive. The inventively proposed arrangement is similar to a so-called Compander, in which a turbo compressor is coupled with a turboexpander via an intermediate gear. According to the invention, however, neither a generator nor an engine are needed.

The present invention proposes a process for the distillative cryogenic separation of feed air in a distillation column system of an air separation plant at different distillation pressures. As part of the process of the invention, the total feed air is compressed in a total amount of air to a first pressure level, which is at least 4 to 5 bar above the highest of the distillation pressures. In the context of the present invention, therefore, an HAP method explained at the outset is used. As mentioned, the highest of the operating pressures in a corresponding distillation column system, ie the operating pressure in the (high) pressure column, for example, at 4.3 to 6.9 bar, for example, at 5.2 bar lie. In the context of the method according to the invention, therefore, the total feed air is compressed to a pressure level which is at least 4 to 5 bar above such pressure, that is, for example at least 11, 12, 13, 14, 15 or 16 bar. Specific values are explained below.

In the context of the method according to the invention, a first partial air quantity of the mentioned total air quantity is first cooled to a first temperature level of 130 to 170 K, typically in a main heat exchanger of a corresponding air separation plant, and then compressed to a second pressure level which is at least 10 bar above the first pressure level , The present invention is thus used in HAP processes in which comparatively high pressures are generated, for example in order to be able to provide internally compressed printed products at correspondingly high pressures, as explained below.

Furthermore, in the context of the present invention, a second partial air quantity is first cooled to a second temperature level of 110 to 150 K and then released to a third pressure level which is below the first pressure level and, for example, at the highest of the distillation pressures, ie the operating pressure of the high pressure column can. The cooling to the second temperature level can also be done in a main heat exchanger of the air separation plant.

As explained above, problems arise in the simultaneous compression and expansion of corresponding partial air quantities, in particular when the compaction is to be carried out by work released during the expansion, i. if the supply of external (electrical) energy is to be dispensed with. This is especially true if the first and the second partial air quantity differ significantly, because this, as mentioned, leads to significant speed differences.

The present invention contemplates using a compression / expansion assembly with a transmission in which a drive wheel is engaged with a gear and the gear is engaged with a driven gear. With the drive wheel, the blades of two or more turboexpander and the driven wheel, the blades of two or more turbocompressors in the above-described sense are rotatably coupled. The first partial air quantity is performed for compression to the second pressure level in succession by the turbo-compressor and the second partial air volume for relaxation to the third pressure level in parallel through the turboexpander. A "parallel" guiding by a plurality of turboexpanders is understood to mean that the second partial air quantity is divided into two or more partial flows and each of the partial flows is guided through one of the turboexpanders. By using the compression / expansion arrangement can solve the problem explained above, by means of the transmission used, the speeds of each turbo compressor and turboexpander used are adapted to each other. Through a serial use of several turbocompressors very high pressure differences can be generated, which would not be achieved with only one compressor unit. The invention also allows the use of first and second partial air quantities in significantly different orders of magnitude, since the use of the transmission speed differences can be compensated. The guided through the turbo compressor first partial air amount is present at the first temperature level explained. Therefore, the turbocompressors are operated as a cold booster.

Because several turboexpanders are connected in parallel in the context of the present invention, the mechanical loads that occur can be distributed symmetrically and the individual turboexpanders can be made smaller and less expensive. Particular advantages arise when two turbocompressors are used, the blades are coupled on both sides of the driven gear each with a driven shaft coupled to the first shaft. In this way, asymmetric loads can be reduced and wear reduced.

Advantageously, a torque transmitted to the gear wheel by means of the drive wheel is greater than or equal to a torque transmitted to the output gear by means of the gear wheel. So there is no need to provide additional drives such as an electric motor, the turbocompressors can only be driven by the turboexpander.

A further advantage of the compression / expansion arrangement according to the invention is that flexible additional driving or driven gears can be brought into engagement with the gear wheel and therefore the method can be expanded as desired. For example, in this way one or more further turboexpanders driving via a drive wheel and / or one or more turbo compressors driven by the turbine wheel via a driven wheel can be used. The gear itself is preferably not rotatably coupled with turbo expanders and / or turbo compressors, but preferably transmits only torques between drive and driven wheels. In other words, in one Compression / expansion arrangement according to the present invention, the gear on the one hand and the driving or driven units on the other hand (for example, the blades of turboexpanders and turbocompressors) speed operated differently. However, this does not rule out that the driving or driven units can be operated with equal speed to each other.

Advantageously, in the context of the present invention, the first pressure level at 10 to 17 bar, in particular 13 to 16 bar and / or the second pressure level at 40 to 70 bar, in particular at 50 to 60 bar. The second pressure level is thus at comparatively high values, which make the use of a single booster no longer possible, since in this, as explained, the achievable pressure difference is too low. This problem is solved by the serial use of several turbocompressors, which are coupled according to the invention with a transmission.

As mentioned, the third pressure level, which is below the first pressure level, may, for example, be at the highest of the distillation pressures in the distillation column arrangement, for example the pressure level at which a high pressure column is operated. By stating that the third pressure level is "at" the highest of the distillation pressures, it is meant that the third pressure level does not deviate by more than 1 bar from the highest of the distillation pressures of the distillation column arrangement.

As explained, the present invention is particularly suitable when the respective partial air volumes differ significantly from one another. This is the case in particular if the first partial air quantity corresponds to 0.2 times to 0.6 times the second partial air quantity and / or if the first and the second partial air quantities together are 0.3 times to 0.6 times correspond to the total amount of air. The ratios mentioned relate in each case to standard volumes per unit time, ie standard volume flows, for example standard cubic meters per hour (Nm ³ / h). The differences in the actual volumetric flows present are much higher because there are widely differing pressures. In particular, at significantly different first and second partial air volumes, which lead to a comparatively small amount of air must be compressed, but a relatively large amount of Air can be relaxed, the method of the present invention is due to the use of the illustrated transmission.

Advantageously, in the context of the present invention, the second partial air quantity before cooling to the second temperature level is compressed from the first pressure level to an intermediate pressure level which is below the second pressure level. For this purpose, for example, another turbo-compressor can be used. This can be powered by a (for the purpose of providing the necessary cooling capacity for the entire process) turboexpander, which relaxes another stream.

The process of the invention develops particular advantages when the distillation column system is taken from a liquid, oxygen-rich air product, increased in pressure and then transferred by heating from the liquid to the supercritical or gaseous state, ie for internal compression processes. In such internal compression processes, in the context of the present invention, the liquid, oxygen-rich air product can be liquid-pressure-elevated to the first pressure level or another high pressure level. The invention is therefore particularly suitable for processes in which corresponding internal compression products are to be provided at high pressures.

By combining an internal compression process with a HAP process, particular advantages are achieved in the context of the present invention. Conventional MA / BAC processes sometimes reach their capacity limits with large volumes of air. For example, in air separation plants for oxygen capacities above 130,000 Nm ³ / h, the limits of conventional plant components have been reached. Due to the low pressure of the feed air present here, for example adsorber stations with diameters of more than 6 meters are needed and sometimes driven at the limit. Even assembly work for pipelines and flaps with very large diameters, which are required at such high air flow rates, lead to high costs. By using a HAP process such problems are significantly mitigated due to significantly lower volume flows, the entire "warm" part of an air separation plant is much smaller.

In MAC / BAC processes as well as HAP processes, the air compressors are typically driven by steam turbines. The steam turbines used in this case are typically twin-shaft turbines, which are set up for the simultaneous drive of main and secondary compressors (MAC and BAC in MAC / BAC method) by means of one of the shafts in each case. A typically additionally required nitrogen product compressor requires its own drive in the form of an electric motor in a MAC / BAC method. This causes additional costs, as explained above. Therefore, HAP methods are particularly advantageous because here the product compressor can be driven directly via one of the shafts of the steam turbine (the booster falls away). Such systems therefore benefit particularly from solutions that do not require electric drives.

The present invention further relates to an air separation plant, which is set up for the distillative cryogenic separation of feed air in a distillation column system at different distillation pressures. This plant has means which are adapted to compress the total feed air in a total amount of air to a first pressure level which is at least 4 to 5 bar above the highest of the distillation pressures, from the total amount of air a first partial air amount initially to a first temperature level of 130 to cool to 170 K and thereafter to compress to a second pressure level which is at least 10 bar above the first pressure level, and to first cool a second partial air volume to a second temperature level of 110 to 150 K and thereafter to relax to a third temperature level below that first pressure levels.

The system is characterized by a compression / expansion arrangement with a transmission, in which according to the invention a drive wheel with a gear and the gear is in engagement with a driven gear. With the drive wheel, the blades of two or more turboexpander and the driven wheel, the blades of two or more turbo compressors are coupled. Means are provided which are adapted to lead the first partial air quantity for compression to the second pressure level in succession through the turbo-compressor and the second partial air volume for expansion to the third pressure level in parallel through the turboexpanders.

Advantageously, an arrangement is used in the context of the present invention, in which at least one further drive wheel and / or at least one further output gear is in engagement with the gear wheel. In this way, further driving or driven units can be coupled with a corresponding compression / expansion arrangement in a simple and flexible manner.

In particular, the present invention is suitable for air separation plants, in which the compression / expansion arrangement comprises two turbocompressors, the blades are coupled on both sides of the driven gear with a driven shaft coupled to the first shaft, and / or two turboexpander, the blades on both sides of the drive wheel with a coupled to the drive wheel coupled second shaft. In this way, as already explained, asymmetric loads can be reduced. With a "two-sided" arrangement is here as above meant that the drive or driven gear is disposed on a shaft which extends axially on both sides of the drive or driven gear. On each of the two sides, a corresponding turbocompressor or turboexpander or its rotor blades can be arranged.

For features and advantages of such air separation plants, which are set up in particular for carrying out a method, as previously explained in detail, reference is made to the above explanations. Corresponding systems benefit from the advantages explained with regard to the method.

The invention will be explained in more detail below with reference to the accompanying drawings which show preferred embodiments of the invention.

Brief description of the drawings

• In FIG. 1 an air separation plant to illustrate the underlying task of the invention in the form of a schematic process flow diagram is illustrated.
• In FIG. 2 an air separation plant to illustrate the underlying task of the invention in the form of a schematic process flow diagram is illustrated.
• In FIG. 3 a compression / expansion arrangement according to an embodiment of the invention is schematically illustrated.
• In FIG. 4 is a non-inventive compression / expansion arrangement illustrated schematically.

Detailed description of the drawings

In the figures, corresponding elements carry identical reference numerals and will not be explained repeatedly for the sake of clarity.

In FIG. 1 an air separation plant for illustrating the underlying object of the invention in the form of a schematic process flow diagram is illustrated and designated 100 in total.

The air separation plant 100 is fed via a filter 1 feed air (AIR), which is compressed by means of a main air compressor 2. The compression of the feed air in the main air compressor 2 takes place at pressure level, which is referred to in this application as "first" pressure level and which is significantly higher than the maximum operating pressure of a below explained distillation column system 10 of the air separation plant 100. The process performed in the air separation plant 100 So is a HAP method as explained above. The first pressure level is for example about 14.5 bar. The compressed by the main air compressor 2 amount of air flow c is referred to here as "total air amount". This is, for example, about 655,000 Nm ³ / h.

A compressed air flow a provided in this way is precooled in a direct contact cooler 3, which is charged inter alia with a cooled water flow b from an evaporative cooler 4. The operation of the direct contact cooler 3 and the evaporative cooler 4 will not be explained in detail. After cooling in the direct contact cooler 3, a correspondingly cooled compressed air flow, now denoted by c, is fed to an adsorber 5, which in the illustrated example comprises two adsorber vessels filled with a suitable adsorption material and operated in alternating operation and whose operation is likewise not explained in detail. In the evaporative cooler 4 and the Adsorbersatz 5 can be used for cooling or regeneration, for example, a stream d, which is taken from the distillation column system 10 as a so-called impure nitrogen and processed in a suitable manner. In this context, for example, a steam heater 6 is used.

A dried in the Adsorbersatz 5 compressed air flow is denoted by d. This is divided in the example shown in two sub-streams e and f. The partial flow e is then divided again into two partial flows g and h and fed to a main heat exchanger 7 on the hot side. The partial flow g is the explained turbine flow, the partial flow h is a (second) throttle flow with lower pressure. The partial flow f is further compressed in a booster turbine 8, cooled in a not separately designated aftercooler, split again into two partial flows i and k and fed to the main heat exchanger 8 on the hot side. The partial flow i is a higher pressure (first) throttle flow to be compressed, and the partial flow k is a flow to be expanded to provide cooling power.

All sub-streams e to k thus each comprise partial air quantities of the total air quantity of the stream a, c or d. The partial air quantity encompassed by stream i, for example approx. 102,000 Nm ³ / h, is referred to here as the "first" partial air quantity, the partial air quantity comprised by stream g, for example approx. 307,000 Nm ³ / h, as the "second" partial air quantity of the total air quantity. The partial air volume of the total amount of air comprised by stream h is, for example, approximately 55,000 Nm ³ / h. The division is arbitrary and can, in deviation from the specific example, also be carried out in a different order.

The partial flows g, i and k are taken from the main heat exchanger 7 respectively to intermediate temperature levels, the intermediate temperature level at which the partial flow i is taken from the main heat exchanger 7, taken here as the "first" temperature level and the intermediate temperature level at which the partial flow g from the main heat exchanger 7 is referred to as the "second" temperature level. The partial flow h is removed from the main heat exchanger 7 cold side.

In the FIG. 1 shown air separation plant is to provide internally compressed pressure oxygen at a high pressure level, for example, to about 57 bar, and set in an amount of, for example, about 135,000 Nm ³ / h. For this purpose, the distillation column system 10, a liquid, oxygen-rich stream I is removed, increased pressure by means of a pump 9 and transferred in the Hautpwärmetauscher 7 from the liquid to the supercritical state at the mentioned pressure.

Due to the comparatively high pressure at which the internally compressed pressure oxygen of the stream I in the skin heat exchanger 7 is transferred or vaporized into the supercritical state, a heat carrier at high pressure is accordingly required. This heat carrier is formed here by the partial flow i, which must be further compressed for this purpose.

It should be understood that the in FIG. 1 For this purpose, and for the simultaneous relaxation of the partial flow g, used booster turbine 101 could only theoretically be used, due to the mentioned limits of achievable in a corresponding booster pressure ratios, however, structurally currently not feasible. At the same time, it is to be expected that the driving turboexpander is currently structurally unrealizable.

The partial flow i would have to be compressed after removal from the main heat exchanger 7 at the first intermediate temperature level by means of the booster turbine 101, starting from the achieved in the booster turbine 8 pressure level of, for example, about 17 bar to a pressure level of, for example, about 57 bar. A corresponding pressure level is referred to herein as a "second" pressure level.
In the example shown, the partial flow i is fed to the main heat exchanger 7 at an intermediate temperature level and removed from it on the cold side. The partial flows h and i are in the example shown downstream of the main heat exchanger 7 to a lower pressure level, for example, the pressure level of a pressure column in the distillation column assembly 10 of about 5.2 bar, relaxed. For this purpose, for example, in the FIG. 1 shown, but not separately designated valves or so-called Dense Liquid Expander are used. Relaxation to such a pressure level can also take place for the partial flows g and k in the respective expansion turbines of the booster turbines 8 and 101, respectively.

The partial streams g to k are fed into the distillation column system 10 mentioned a number of times, which here is represented in a highly schematized and miniaturized manner and typically comprises a plurality of distillation columns operated at different operating pressures. In the example shown, a high-pressure column 11 and a low-pressure column 12 are shown, which are in heat exchanging connection via a main capacitor 13. The high-pressure column 11 is operated, for example, at the pressure level to which the currents g to k are relaxed. The streams g to k are typically fed into the high pressure column 11, but it can also be partially fed into the low pressure column 12. The interconnection of the high-pressure column 11 and the low-pressure column 12 is not shown in detail, as well as additional columns, valves, pumps, heat exchangers and the like.

The distillation column system 10 may comprise any number of corresponding columns and may be configured to recover different products of air. In addition to the above-mentioned liquid, oxygen-rich stream I to provide internally compressed pressure oxygen (GOX IC), the distillation column system 10, for example, a nitrogen-rich, liquid stream m can be removed, which also by means of a pump (without reference numerals) pressure-increased and in the main heat exchanger 7 in gaseous or supercritical state can be transferred. Further nitrogen-rich streams n and o can be taken from the high-pressure column 11, for example in gaseous form, heated in the main heat exchanger 7 and used as gaseous nitrogen product (GAN) or sealing gas for pumps (seal gas). The stream d, which can also be partly blown off to the atmosphere, has already been mentioned.

In FIG. 2 an air separation plant to illustrate the underlying task of the invention in the form of a schematic process flow diagram is illustrated and indicated generally at 200.

On the basis of in FIG. 2 illustrated air separation plant 200, which incidentally the in FIG. 1 illustrated air separation plant 100, it is explained that even a use of serial booster or parallel turboexpander alone does not solve the problems explained above or is not technically feasible.

According to FIG. 2 For example, the partial flow i in the boosters of two booster turbines 201 and 202 would be compressed via an intermediate pressure level of, for example, about 31 bar to the previously described second pressure level of, for example, about 57 bar. The partial flow i can, as in FIG. 2 not illustrated, after exiting the boosters of the booster turbine 201 and before entering the boosters of the booster turbine 202, for example, are cooled in the main heat exchanger 7, so that its inlet temperature in the boosters of the booster turbines 201 and 202 is the same or similar. Correspondingly, the partial flow g would be divided into two partial flows and expanded in the turboexpanders assigned to the booster turbines 201 and 202. The turboexpander would only have to process half of the "second" partial air quantity of the stream g, ie in the example shown, in each case, for example, about 153,000 Nm ³ / h. Nevertheless, the volume flow through the booster of the booster turbine 202 would still be too small for the volume flow through the corresponding turboexpander and thus the specific speeds are too different, so that this solution is also not feasible.

In FIG. 3 a compression / deflation arrangement according to an embodiment of the invention is schematically illustrated and indicated generally at 30. The compression / expansion arrangement 30, instead of the booster turbine 101 and the booster turbines 201 and 202 in an air separation plant 100 and 200, respectively, according to the FIGS. 1 and 2 to be involved. The integration results from the corresponding designation of the partial flows g and i. These are in each case the streams g and i downstream of the main heat exchanger 7.

The mentioned first partial air quantity of the total amount of air, as mentioned, for example, about 102,000 Nm ³ / h at a pressure level of about 17 bar, in the form of the partial flow i is successively guided by two turbo compressors 31 and 32 and thereby to the mentioned second pressure level of for example approx 57 bar compressed. The pressure of the partial flow i between the turbocompressors 31 and 32 is for example about 31 bar. Between the turbocompressors 31 and 32, a cooling of the current i in the main heat exchanger 7 or otherwise take place. The second partial air amount of the total amount of air, as mentioned, for example, about 307,000 Nm ³ / h at a pressure level of about 14.5 bar is divided in the form of the partial flow g on two partial streams and relaxed in parallel in two turboexpanders 33 and 34, as mentioned for example, about 5.2 bar.

The turbocompressors 31 and 32 and the turboexpanders 33 and 34 are connected to each other via shafts 35 and 36, respectively. On the shaft 35 of the turbocompressors 31 and 32, a driven gear 37 is mounted on the shaft 37 of the turboexpander 33 and 34, a drive wheel 38. Both with the driven gear 37 and the drive wheel 38 is a gear 39 is engaged.

A torque introduced into the shaft 36 by the parallel relaxation of the partial flows of the flow g in the turboexpanders 33 and 34 can be introduced via the drive wheel 38 to the gear wheel 39 and from there via the output gear 37 into the shaft 35. By a suitable choice of the number of teeth and the geometry of the drive wheel 38, the gear 39 and the driven gear 37 can be ensured that, as mentioned, greatly different volume flows in the turboexpanders 31 and 32 on the one hand and in the turbocompressors 33 and 34 on the other hand copes easily can be.

In FIG. 4 a compression / expansion arrangement not according to the invention is illustrated schematically and designated 40 as a whole. Compression / expansion arrangement 40 can also be used instead of the booster turbine 101 or the booster turbines 201 and 202 in an air separation plant 100 or 200 in accordance with FIGS. 1 and 2 to be involved. The integration also results here by the corresponding designation of the partial flows g and i. These are in each case the streams g and i downstream of the main heat exchanger 7.

Already with reference to the compression / expansion assembly 30 of FIG. 3 Illustrated elements of the compression / expansion assembly 40 are identified by identical reference numerals. Notwithstanding the in FIG. 3 However, the compression / expansion arrangement 30 illustrated in FIG FIG. 4 only a turboexpander 33 on. This reduces the number of components to be provided, but requires that a corresponding turboexpander 33 in the required size and against the background of the mechanical loads occurring technically feasible.

Claims (14)

Process for the distillative cryogenic separation of feed air in a distillation column system (10) of an air separation plant at different distillation pressures, wherein the total feed air is compressed in a total amount of air to a first pressure level which is at least 4 to 5 bar above the highest of the distillation pressures, and of the total amount of air - A first partial air quantity is first cooled to a first temperature level of 130 to 170 K and then compressed to a second pressure level, which is at least 10 bar above the first pressure level, and - A second partial air quantity is first cooled to a second temperature level of 110 to 150 K and then released to a third pressure level, which is below the first pressure level, wherein - A compression / expansion assembly (30, 40) is used with a transmission in which a drive wheel (38) with a gear (39) and the gear (39) with a driven gear (37) is engaged, wherein - With the drive wheel (38), the blades of two or more turboexpander (33, 34) and the output gear (37), the blades of two or more turbo compressors (31, 32) are rotatably coupled, and - The first partial air quantity for compression to the second pressure level in succession by the turbo-compressor (31, 32) and the second partial air amount for relaxation to the third pressure level in parallel through the turboexpander (33, 34) is performed. Method according to Claim 1, in which a torque transmitted to the gear (39) by means of the drive wheel (38) is greater than or equal to a torque transmitted to the output gear (37) by means of the gear wheel. The method of claim 1 or 2, wherein as the turbo compressors (31, 32) two turbo compressors (31, 32) are used, the blades on both sides of the Output gear (37) are each coupled to a driven shaft (37) coupled to the first shaft (35). Method according to one of the preceding claims, wherein the first pressure level at 10 to 17 bar, in particular 13 to 16 bar, and / or in which the second pressure level at 40 to 70 bar, in particular at 50 to 60 bar, is located. A process according to any one of the preceding claims, wherein the third pressure level does not deviate by more than 1 bar from the highest of the distillation pressures in the distillation column assembly (10). Method according to one of the preceding claims, in which a standard volume flow of the first partial air quantity corresponds to 0.2 times to 0.5 times a standard volume flow of the second partial air quantity and / or together with the standard volume flows of the first and second partial air quantities to 0.4 times corresponds to 0.6 times a standard volume flow of the total amount of air. A method according to any one of the preceding claims, wherein the second partial air amount is compressed prior to cooling to the second temperature level from the first pressure level to an intermediate pressure level which is below the second pressure level. Method according to one of the preceding claims, in which the distillation column system, a liquid, oxygen-rich air product removed, liquid pressure increased and then transferred by heating from the liquid to the supercritical or gaseous state. The method of claim 8, wherein the liquid, oxygen-rich air product is pressure-increased liquid to the first pressure level. Air separation plant (100, 200) adapted for distillative cryogenic separation of feed air in a distillation column system (10) at different distillation pressures, wherein means are provided which are adapted to the total feed air in a total amount of air to a first To compress the pressure level that is at least 5 bar above the highest of the distillation pressures, and of the total amount of air first to cool a first partial air quantity to a first temperature level of 130 to 170 K and then to compress it to a second pressure level which is at least 10 bar above the first pressure level, and - To cool a second partial air amount first to a second temperature level of 110 to 150 K and then to relax to a third pressure level, which is below the first pressure level, wherein - A compression / expansion assembly (30, 40) with a transmission in which a drive wheel (38) with a gear (39) and the gear (39) with a driven gear (37) is engaged, wherein - With the drive wheel (38), the blades of two or more turboexpander (33, 34) and the output gear (37), the blades of two or more turbo compressors (31, 32) are rotatably coupled, and - Means are provided which are adapted to the first partial air quantity for compression to the second pressure level successively through the turbo-compressors (31, 32) and the second partial air amount for relaxation to the third pressure level in parallel through the turboexpander (33, 34) to lead. Air separation plant (100, 200) according to claim 10, wherein at least one further drive wheel and / or at least one further output gear with the gear (39) is engaged. Air separation plant (100, 200) according to claim 10 or 11, are provided in the two turbocompressors (31, 32), the blades on both sides of the driven gear (37) in each case with a driven gear (37) coupled to the first shaft (35) are coupled. Air separation plant (100, 200) according to one of Claims 10 to 12, in which two turbo expanders (33, 34) are provided, the rotor blades of which are provided on both sides of Drive wheel (38) are each coupled to a with the drive wheel (38) coupled to the second shaft (36). Air separation plant (100, 200) according to any one of claims 10 to 13, which is adapted to carry out a method according to one of claims 1 to 9.

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