CN106931721B

CN106931721B - Method for the cryogenic separation of air and air separation plant

Info

Publication number: CN106931721B
Application number: CN201611273154.3A
Authority: CN
Inventors: T·劳滕施莱格
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2015-12-07
Filing date: 2016-12-06
Publication date: 2020-12-01
Anticipated expiration: 2036-12-06
Also published as: RU2016147700A; RU2721195C2; CN106931721A; TR201905990T4; EP3179185A1; RU2016147700A3; EP3179188B1; EP3179188A1

Abstract

The application proposes a method for the cryogenic separation of air using an air separation plant (100) having a distillation column system (10) comprising a higher pressure column (11) operating at a higher pressure column pressure level and a lower pressure column (12) operating at a lower pressure column pressure level. The invention also relates to a corresponding air separation plant (100).

Description

Method for the cryogenic separation of air and air separation plant

Technical Field

The present invention relates to a method for the cryogenic separation of air in an air separation plant and to an air separation plant for carrying out such a method.

Background

It is known to produce air products in liquid or gaseous form by cryogenic separation of air in an air separation plant, for example in h.

(Hrsg.), Industrial Gases Processing, Wiley-VCH, 2006, especially section 2.2.5, "Cryogenic Rectification".

For a series of industrial uses of gaseous oxygen it is necessary to use air separation plants with so-called internal compression. A corresponding air separation plant is also set forth in the above-mentioned citation and reference may be made to fig. 2.3A thereof. In the corresponding air separation plant, the pressure is applied to the ultralow temperature liquid, in particular to the liquid oxygen at the ultralow temperature, and the liquid oxygen is evaporated relative to the heat conductor to finally obtain a gaseous product. Internal compression has advantages in energy conversion over additional compression of gaseous products at low pressure.

The same applies to other products, such as nitrogen or argon, which can likewise be obtained by internal compression in the gaseous state and which are discharged from the distillation column system beforehand as a cryogenic liquid. If the corresponding cryogenic liquid is subjected to a pressure exceeding the critical pressure, no vaporization in the usual sense takes place, but a transition to the supercritical state takes place. This is called "pseudo-evaporation".

The internal compressed oxygen, which is also a cryogenic liquid product, can be achieved by the so-called High-Air-Pressure (HAP-) method. By "cryogenic liquid product" is herein understood that the corresponding air separation plant can only provide a small amount of liquid product, for example less than 2% of the total air introduced into the distillation system.

The HAP process may be understood as an air separation process in which all air introduced into the distillation system (also referred to herein as "air feed") is first compressed in a main air compression chamber to a pressure that is significantly greater than the maximum operating pressure in the distillation system. In particular in the HAP process air is first compressed to a pressure which is at least 4 to 5 bar, and at most 20 bar higher than the operating pressure in the distillation system. In a conventional two-column system having a higher pressure column and a lower pressure column, the "maximum operating pressure" in the distillation column system is the operating pressure of the higher pressure column. The investment costs of the air separation plant of the HAP process are particularly low, since only one compressor is required.

In order to optimize the HAP process in terms of energy, a so-called throttle flow may be used. As is known in principle, such a throttling stream is a substream of the compressed feed air, which can be further boosted in pressure, cooled and depressurized via a depressurization device, in particular a throttling valve, into the distillation column system or its higher pressure column.

In the HAP process, such a throttling flow may begin with an already high initial pressure exerted by all the feed air, with the boosting continuing with hot and cold boosters. The air is fed to the respective "hot booster" without or only after a comparatively low cooling, for example in a water cooler downstream of the main air compressor. The feed end temperature of such hot boosters is therefore significantly above 0 ℃. The feed temperature of the "cold booster" is significantly lower than 0 ℃ due to the previous cooling of the air introduced into the cold booster.

Most HAP processes have an advantageous Q/T profile in the main heat exchanger, when the oxygen pressure generated by internal compression is greater than 25 bar, which means compression to a certain pressure level in ultra low temperature liquid state by means of a corresponding turbine. The capacity conversion efficiency of the Q/T characteristic is relatively unfavorable for the HAP process when the pressure required for internal compression of oxygen drops to well below 25 bar. The conventional method with a primary compressor and a secondary compressor appears to be more advantageous when the pressure is between 6 and 25 bar.

In the process known as the MAC/BAC process (Main Air Compressor/Booster Air Compressor), part of the Air fed to the distillation system is compressed only to the maximum working pressure in the distillation system or optionally less, while another part of the Air is compressed to a higher pressure by means of a secondary Compressor. Such a process is particularly advantageous when no or only very small amounts of liquid air products, such as liquid oxygen, are produced. If, in such cases, the demand for gaseous nitrogen-enriched air products is also low, in particular MAC/BAC processes are proposed, in which a so-called blowing turbine is used, i.e. a turbine which depressurizes compressed air into the lower pressure column of the distillation column system.

However, the corresponding MAC/BAC method is opposite to the HAP method in that the investment cost is higher due to the higher cost of the compression apparatus. There is therefore a need for a process which combines the low cost advantages of the HAP process with the above-mentioned advantages of the MAC/BAC process, particularly with a blow turbine.

Disclosure of Invention

Against this background, a method for the cryogenic separation of air in an air separation plant and an air separation plant for carrying out such a method are proposed. Preferred embodiments are described below.

The present application uses the terms "pressure level" and "temperature level" to characterize pressure and temperature, thereby expressing that pressure and temperature need not be used in the form of precise pressure or temperature values in the respective devices to implement aspects of the present invention. Such pressures and temperatures typically fluctuate within a certain range, for example ± 1%, 5%, 10%, 20% or even 50% around the median value. The respective pressure and temperature levels can be in discrete ranges or in overlapping ranges. For example, the pressure level includes, in particular, unavoidable pressure losses or expected pressure losses, which are caused, for example, by cooling effects or transmission losses. The same applies to the temperature level. The pressure levels given in bar here relate to absolute pressure.

A turbo compressor is used in an air separation plant for compressing air. Such as a "main air compressor", characterized in that all the air introduced into the distillation column system, i.e. all the air feed, is compressed by it. Correspondingly, the "secondary compressor" can also be a turbo compressor, in which a part of the air introduced into the main compressor is compressed to a higher pressure in the MAC/BAC process. For compressing the partial air, further turbo compressors, also referred to as superchargers, are usually provided, which compress only to a relatively small extent compared to the main air compressor or the secondary compressor.

In many locations of the air separation plant, the air can furthermore be depressurized, wherein a pressure reducer in the form of a turboexpander, also referred to as "turbine", can be used. The turbo expander can also be connected to and drive a turbo compressor or booster. Such an arrangement may also be referred to as a "turbocharger" when the turbocompressor or (es) are not driven by external energy, i.e. are driven solely by the turbocompressor (es). In the case of turbochargers, the turbo expander is mechanically connected to the turbo compressor or supercharger.

The rotary units, for example, a pressure reducer or a pressure reducing turbine, a compressor or a compression stage, a booster or a booster, the rotors of an electric motor or similar devices, can generally be mechanically connected to one another in a suitable manner. "mechanically coupled" is understood in the context herein to mean that a fixed or mechanically adjustable rotational speed relationship is achieved between these rotating components by mechanical components, such as gears, belts, transmissions, and the like. The mechanical connection is usually achieved by two or more parts which are each in engagement with one another, for example in form-fitting or frictional engagement, for example gears or pulleys, with a belt or other rotationally fixed connection. The rotationally fixed connection can in particular be realized by a common shaft on which the rotary units are mounted in each case rotationally fixed. The rotational speed of the rotary unit is the same in such cases.

In contrast, the unit "mechanically decoupled" means that there is no fixed or mechanically adjustable speed relationship between the respective components. It is of course also possible to preset specific speed relationships, for example between a plurality of electric motors, in particular by suitable electronic control, or between a plurality of turbines, in particular by selecting suitable feed and final pressures. This is not achieved, however, by one or more individual interengagement, for example with positively or frictionally engaging parts or by a rotationally fixed connection.

The mechanical construction of turbocompressors and turboexpanders is well known to the skilled person. The compression of air is carried out in turbo compressors by means of rotor blades, which are arranged on the rotor or directly on the shaft. The turbocompressor forms a structural unit here, but it has a plurality of "compression stages". The compression stage typically includes a rotor or corresponding rotor blade arrangement. All compression stages may be driven by the same shaft. The turboexpander is in fact designed to be referenced, but here the rotor blades are driven by the expanding air. Here too, a plurality of expansion stages are involved. Turbocompressors and turboexpansions can be designed as radial or axial machines.

It is discussed within the scope of the present application to obtain an air product, in particular an oxygen or nitrogen product. The "product" leaves the apparatus and is arranged, for example, in a tank or is used therein. This is not only a concern for the circulation within the device, but can also be used before leaving the device, for example as a coolant in a heat exchanger. The term "product" therefore does not include such distillates or streams, which are themselves stored in the plant and are used there only as reflux, coolant or purge gas.

Advantages of the invention

The invention is based on the recognition that the use of superchargers arranged in series, between which the air to be compressed of the throttling flow is not cooled, makes it possible to provide the HAP process with the advantages of the conventional MAC/BAC process in terms of particular efficiency or at least energy conversion. The heat exchange effect in the main heat exchanger installed in the air separation plant according to the invention is more advantageous than that of the usual method in which intermediate cooling is carried out between cold superchargers. The invention is based on the recognition that the use of a hot turbocharger upstream of a cold turbocharger is particularly advantageous. In this case, a total of three superchargers can compress the throttle flow several times, but not the other flows. Cooling takes place between the heat exchangers on the one hand and the superchargers arranged in series on the other hand, and downstream of the cold superchargers, in particular in the main heat exchanger.

The invention relates to a method for the cryogenic separation of air using an air separation plant, comprising a distillation column system comprising a high-pressure column operating at a high-pressure column pressure level and a low-pressure column operating at a low-pressure column pressure level. The high-pressure column pressure level is, for example, between 4 and 7 bar, the level which is customary in corresponding air separation plants. The low-pressure column pressure level is slightly above atmospheric pressure, in particular 1.2 to 1.8 bar, so that, for example, a high separation efficiency is ensured without the use of additional pumps and the air product entering the low-pressure column is conducted away.

The HAP process according to the invention first comprises the step of first compressing all the air fed to the distillation column system to an initial pressure level which is at least 4 and at most 20 bar higher than the high pressure column pressure. It is within the scope of the invention to compress the air used to a pressure level of 10 to 23 bar in the main air compressor used. Compressed air can also be dried and purified at this pressure level by means of molecular sieves.

A portion of the air compressed to the initial pressure level and correspondingly dried and purified is then subjected to a first pressure increase process at a first temperature level greater than 0 ℃, followed by two further pressure increase processes at a temperature level lower than the first temperature level. The air subjected to the first pressure increase process can in this case be cooled in particular after the first pressure increase process in a main heat exchanger of the respective air separation plant. The respective air therefore carries out further pressure boosting processes at correspondingly lower temperature levels.

The air subjected to the two other pressure boosting processes is then depressurized into the higher pressure column. A throttle valve is used for pressure reduction. The air which has thus undergone the two other pressure boosting processes and the first pressure boosting process before is called the so-called "throttle flow", a term which is already well known in the air separation field.

The low-temperature oxygen-enriched liquid is discharged from the low-pressure column, subjected to pressure increase in a low-temperature state, subsequently heated and evaporated, and discharged from the air separation plant as an air product. The process according to the invention is therefore an air separation process in which the oxygen or a corresponding oxygen-enriched air product is subjected to so-called internal compression.

According to the invention, a first booster (i.e. a "hot" booster, as mentioned several times above) is used for the first pressure boosting process, wherein the first booster is driven with a first pressure reducer, in which another part of the air compressed to the initial pressure level is depressurized from the initial pressure level to a second pressure level and subsequently fed into the low-pressure column. The other parts are cooled in particular before. The first depressurizer is, according to its function, a so-called "jet turbine" or "rahmen turbine", which is also known in the field of air separation. The energy efficiency can be improved by the corresponding injection of air into the lower pressure column. Specific details can be found in The specialist literature, for example f.g. kerry, Industrial Gas Handbook Gas separation and Purification, CRC Press, 2006, in particular section 3.8.1, "The Lachmann Principle".

According to the invention, the second and third booster (i.e. the two "cold" boosters) are also used for two further boosting processes, through which air is conducted successively in order to carry out the two further boosting processes, wherein the air is fed into the third booster at the temperature level at which it leaves the second booster. In other words, within the scope of the invention, no intermediate cooling between the cold superchargers takes place, as is known according to the invention, as a better heat exchange effect can be achieved in the heat exchanger used than in the usual methods.

The amounts of air which are each led through the first, second and third turbocharger and optionally through the throttle differ from one another by not more than 10% according to the invention. In particular, the air quantities differ by no more than 5% or are substantially or completely identical. In other words, the amount of air that is subjected to the first and the two additional boosting processes, respectively, and the amount of air that is optionally depressurized in the throttle valve are similar or identical within the mentioned ranges.

This means that the first, second and third booster and the optionally used pressure reduction valve are used only to provide a throttle flow and not to provide a further air portion or flow into the distillation column system. The advantages of the invention are particularly pronounced if the low-temperature oxygen-rich liquid discharged from the low-pressure column is pressurized to 6 to 25 bar in the low-temperature state. According to the invention, a corresponding pressure increase is therefore provided. As mentioned at the outset, the conversion efficiency of conventional MAC/BAC processes is advantageous, typically in the pressure range of the internally compressed oxygen product. However, the invention also achieves corresponding advantages in the HAP process by using the above-described turbochargers which are not intercooled and are connected in series.

As mentioned above, the invention is particularly advantageous if the liquid throughput is small, i.e. the air product is led out of the air separation plant in liquid form in a proportion of at most 1% or 0% based on the total amount of air fed to the distillation column system. The above design is therefore made according to the present invention. In addition, a relatively small amount of nitrogen-enriched air product is produced. The nitrogen-enriched air product is withdrawn near the top or near the top of the higher pressure column of the distillation column system and is no longer refluxed to the higher pressure column or the lower pressure column. Thus, in particular within the scope of the present invention, a proportion of up to 2% of the nitrogen-enriched air product is withdrawn from the higher pressure column and conducted off the air separation plant in the gaseous state, based on the total amount of air fed to the distillation column system.

Within the scope of the invention, the second booster and the third booster are advantageously each driven by means of a pressure reducer, in which a further portion of the air, which has been cooled beforehand and then introduced into the distillation column system after pressure reduction in the pressure reducer, is compressed to the initial pressure level, is depressurized. For driving the second turbocharger, the second pressure reducer is used here, and for driving the third turbocharger, the third pressure reducer is used. In contrast to superchargers which are designed for two other boosting processes and are operated in series, the respective pressure reducers are arranged in parallel (parallel), which means that the air used to drive the pressure reducers is divided beforehand into two partial flows. In this way, the amount of air to be depressurized can be adapted to the desired pressure increase in the respective cold booster connected to the pressure reducer or vice versa.

In particular, the cold booster is driven by the respective pressure reducer via a suitable mechanical connection. Corresponding mechanical connections can be referred to above. In practice, the respective pressure booster can also be driven by a motor, but it is particularly advantageous from the standpoint of the investment costs and the heat transfer to the respective plant to be driven by the respective pressure booster.

The air is advantageously depressurized in a depressurization machine driving the second and third superchargers to a high-pressure column pressure level. Partial liquefaction of the air can be achieved by a corresponding pressure reduction. The gaseous part can here be fed directly into the higher pressure column, while the liquefied part is depressurized into the lower pressure column. The liquefied fraction can be refluxed to the lower pressure column in this way and the separation efficiency improved there, for example as mentioned in the "Theoretical Analysis of the Claude Cycle" in the document section 2.6 of Kerry.

The invention allows further optimization and improvement. In particular, a portion of the air compressed to the initial pressure level can be cooled and, starting from the initial pressure level, depressurized into the higher-pressure column without additional pressurization by means of a booster or the like. This can be achieved in particular by means of a further pressure relief valve.

The air fed to the second booster can in particular be pre-cooled in the main heat exchanger to a temperature level of 130 to 200K. The air depressurized in the depressurization machine driving the second and third superchargers is in particular cooled beforehand to a temperature level of 120 to 190K. The air depressurized in the first decompressor driving the first supercharger is in particular pre-cooled to a temperature level of 150 to 230K. The air boosted in the third booster is advantageously cooled to a temperature level of 97 to 105K, i.e. the lowest temperature level, after this boosting and before its depressurization into the higher-pressure column, which can be achieved by means of a corresponding main heat exchanger. The pressure is advantageously increased by 10 to 25 bar by means of a second pressure booster and by 5 to 20 bar by means of a third pressure booster.

The invention also relates to an air separation plant for the cryogenic separation of air having a distillation column system comprising a higher pressure column operating at a higher pressure column pressure level and a lower pressure column operating at a lower pressure column pressure level.

The air separation plant comprises here means designed for first compressing all the air fed to the distillation column system to an initial pressure level which is at least 4 and at most 20 bar higher than the high pressure column pressure level; a portion of the air compressed to an initial pressure level is subjected to a first pressure boosting process at a first temperature level greater than 0 ℃, followed by two other pressure boosting processes at a temperature level lower than the first temperature level, followed by pressure reduction with a throttle valve into the higher pressure column; the low-pressure column is drained of a low-temperature oxygen-enriched liquid which is subjected to pressure increase in a low-temperature state, is subsequently heated and evaporated, and is discharged from the air separation plant. According to the invention, a first booster is provided for the first warm-up process, which is mechanically connected to the first pressure reducer, wherein means are provided for reducing another part of the air compressed to the initial pressure level in the first pressure reducer from the initial pressure level to the low-pressure column pressure level and subsequently feeding it into the low-pressure column. According to the invention, a second and a third turbocharger are provided for two further pressure boosting processes, and means are provided for the purpose of successively conducting air through the second and third turbochargers for the two further pressure boosting processes, where the air is fed into the third turbocharger at a temperature level at which it leaves the second turbocharger. Means are provided for the purpose that the respective amounts of air which are conducted through the first, second and third turbocharger in total differ from one another by not more than 10%. Furthermore, means are provided for the purpose of setting the pressure increase to 6 to 25 bar, which is carried out in the cold state, of the low-temperature oxygen-enriched liquid discharged from the low-pressure column.

The air separation plant is designed to supply in liquid form an air product in a proportion of at most 1% based on the amount of air fed to the distillation column system, advantageously to discharge from the higher pressure column and in gaseous form a nitrogen-enriched air product in a proportion of at most 2% based on the amount of air fed to the distillation column system.

Such air separation plants are particularly designed for carrying out the above-described process. Reference is therefore made to the corresponding features and advantages.

The invention will be further elucidated with reference to the appended drawings, and specific details will be described by way of structural form of the invention.

Drawings

Fig. 1 shows an air separation plant according to the invention in the form of a flow diagram.

Fig. 2 shows a Q/T diagram of a heat exchanger using a form of construction according to the invention.

Fig. 3 shows a Q/T diagram of a heat exchanger using a form of construction according to the invention.

Detailed Description

Fig. 1 shows an air separation plant according to the invention in a particularly advantageous embodiment in a flow diagram and is designated 100.

The air separation plant 100 is fed with a compressed air stream a by means of an air compression and purification unit 1, comprising a main air compressor and a suitable purification system, of which only a rough illustration is given. The air separation plant shown in fig. 1 is designed for the so-called HAP process. This means that the compressed air stream a, comprising all the air fed to the distillation column system 10 of the air separation plant 100, is compressed to a pressure level at least 4 to 20 bar higher than the pressure level of the higher pressure column 11 of the distillation column system 10.

The pressure level of stream a is referred to herein as the "initial pressure level" and the pressure level of higher pressure column 11 is referred to as the "higher pressure column pressure level". A total of 4 substreams are produced at the initial pressure level from the compressed air stream a, denoted by b, c, d and e.

The air of the partial stream b is initially pressurized in the booster 2. The pressure increase in booster 2 is referred to herein as the "first pressure increase process" which is carried out at a temperature above 0 ℃, and therefore booster 2 is also commonly referred to as a "hot booster".

The air of the substream b is cooled in the aftercooler 3 after having been boosted in the booster 2 and is subsequently fed on the hot side to the main heat exchanger 4 of the air separation plant 100. The air of substream b is discharged from the main heat exchanger 4 (see connection a) at an intermediate temperature level significantly below 0 ℃. The correspondingly cooled air of the substream b is followed by two further pressure boosting processes. For this purpose, the air of the partial stream b is passed first through a booster 5 and subsequently through a booster 6. Supercharger 5 is referred to herein as the "second" supercharger, and supercharger 6 is also referred to as the "third" supercharger. Both superchargers 5, 6 are operated at a temperature level significantly below 0 ℃, in particular at a temperature level below the first temperature level of supercharger 2. They are therefore also referred to as "cold superchargers".

The air of the substream b is fed to the third booster 6 at the temperature level at which it leaves the second booster 5. No intermediate cooling takes place between the second supercharger 5 and the third supercharger 6. After the pressure increase in the booster 6, the air of the partial stream b is reintroduced into the main heat exchanger 4 at the temperature level at which it leaves the third booster 6 and is discharged on the cold side.

The superchargers 5 and 6 are driven by the depressurization machines 7 and 8, in which the air of the substream c is used, which for this purpose is divided into substreams f and g. The air of substream c is here first fed to the hot side of the main heat exchanger and discharged at an intermediate temperature level, before it is divided into the substreams f and g mentioned and fed to the depressurizers 7, 8.

The air of branch d is sent to the hot side of the main heat exchanger 4 and discharged on the cold side, and the air of branch e is sent to the hot side of the main heat exchanger 4, discharged at an intermediate temperature level and used in the decompressor 9 for driving the supercharger 2.

The depressurized air of substreams f and g is converted in a separator 13, in which the liquid phase is separated off. The liquid phase (see connection B) is depressurized into the lower pressure column 12 in the form of a stream h. The part of the air of streams f and g which remains gaseous is fed to the higher pressure column 11 in the form of stream i. The air of substreams b and d is depressurized via

valves

14 and 15 into the higher pressure column 11. The liquid fraction in the form of stream q can be obtained from the higher-pressure column 11 by depressurization directly below the feed openings for streams b and d, guided through the supercooling inverter 16 and depressurized into the lower-pressure column 12 together with stream h.

The air of streams b, d and i is utilized in higher pressure column 11 to form an oxygen-enriched liquid bottoms and a nitrogen-enriched gaseous overhead. The oxygen-enriched liquid bottoms is withdrawn at least partially in the low pressure column 11 as stream k, directed through a subcooled inverter 16 and depressurized into low pressure column 12. At least a portion of the nitrogen-enriched gaseous overhead product is withdrawn as stream 1. A portion of which can be warmed in main heat exchanger 4 in stream m and exported from air separation plant 100 as a nitrogen-rich pressure product, or used as a dense gas (seal gas Dichtgas), for example, in the main air compressor of air compression and purification unit 1.

Another portion of stream 1 may be at least partially liquefied in a main condenser 17 in heat exchange communication with the higher and lower pressure columns. The corresponding partially liquefied product can be refluxed to the higher pressure column 11 and another portion is directed as stream n through a subcooled inverter 16 and depressurized into the lower pressure column 12.

An oxygen-rich liquid bottoms and a gaseous overhead are formed in lower pressure column 12. The oxygen-rich liquid column bottoms of lower pressure column 12 can be obtained at least in part as stream o from higher pressure column 12 and converted to a liquid by raising the pressure with pump 18, warmed and vaporized in main heat exchanger 4 and exported from air separation plant 100 as an internally compressed oxygen-rich product.

The gaseous overhead product of the lower pressure column 12 can be discharged at least partly in the form of stream p as so-called impure nitrogen, guided through a sub-cooled inverter 16, heated in the main heat exchanger 4, for example as regeneration gas for the adsorber in the air compression and purification unit 1.

A particularly advantageous heat exchange can be achieved in the main heat exchanger 4 by the work flow of the air separation plant 100 illustrated in fig. 1, provided that the other conditions described above are met. This will be illustrated by means of the Q/T diagrams shown in fig. 2 and 3.

In fig. 2, a corresponding Q/T diagram is shown, the oxygen enriched air of stream o being compressed in pump 18 of the air separation plant 100 to a pressure level of about 15.0 bar, and in fig. 3, a corresponding Q/T diagram at a pressure of about 10.0 bar is shown. The abscissa here denotes the temperature in K and the ordinate denotes the enthalpy (total) of the heat exchanger in MW. 201 denotes the heat state change curve or the total curve and 202 denotes the coolant state change curve or the total curve, in which the oxygen-enriched air of the flow o to be heated is present. As can be seen from fig. 2 and 3, the state change curves or

total curves

201 and 202 are very close due to the use of the corresponding air separation plant curves according to the invention.

The closer the total curves of heat and cold in the main heat exchanger are, the less energy conversion losses due to heat transfer are, since the energy conversion losses due to heat transfer are related to 1/T²Proportional, in particular temperature differences at "low temperatures" from the viewpoint of energy conversionDisadvantageously. T above denotes the temperature level of the local heat transfer.

Thus, as shown, when the total heat and cold curves are in the range of 200 to 100K, then the working process in the main heat exchanger is very advantageous in the sense described or the energy conversion efficiency of the whole system can be improved in such cases.

Claims

1. A method for the cryogenic separation of air using an air separation plant (100) having a distillation column system (10) comprising a higher pressure column (11) operating at a higher pressure column pressure level and a lower pressure column (12) operating at a lower pressure column pressure level, wherein the method comprises:

-first compressing all air fed to the distillation column system (10) to an initial pressure level at least 4 and at most 20 bar higher than the high pressure column pressure level,

-a portion of the air compressed to the initial pressure level is subjected to a first pressure boosting process at a first temperature level greater than 0 ℃, followed by two other pressure boosting processes at a temperature level lower than the first temperature level, followed by pressure reduction into the higher pressure column (11) with a throttle valve (14),

-discharging a low temperature oxygen-rich liquid from the low pressure column (12), said low temperature oxygen-rich liquid being subjected to pressure increase, heating and evaporation in a low temperature state, being conducted out of the air separation plant (100),

it is characterized in that the preparation method is characterized in that,

-using a first booster (2) for the first boosting process, which is driven by means of a first decompressor (9), in which a further portion of the air compressed to the initial pressure level is decompressed from the initial pressure level to the low-pressure column pressure level and subsequently fed into the low-pressure column (12),

-using a second booster (5) and a third booster (6) through which air is conducted successively for two other boosting processes, wherein the air is fed into the third booster (6) at a temperature level at which it leaves the second booster (5),

-the respective amounts of air which are led through the first supercharger (2), the second supercharger (5) and the third supercharger (6) in total differ from one another by not more than 10%,

-the pressure increase of the low-temperature oxygen-enriched liquid discharged from the low-pressure column (12) is carried out at low temperature to 6 to 25 bar,

-withdrawing from the air separation plant (100) in liquid form a proportion of air product of at most 1%, based on the total amount of air fed to the distillation column system (10).

2. The process according to claim 1, wherein a proportion of nitrogen-enriched air product of at most 2%, based on the total amount of air fed to the distillation column system (10), is withdrawn from the high-pressure column (11) and conducted out of the air separation plant (100) in gaseous state.

3. The process according to claim 1 or 2, wherein the second booster (5) and the third booster (6) are each driven by means of a pressure reducer (7, 8) in which the pressure reduction is carried out in parallel with another portion of the air which has been previously cooled and then fed into the distillation column system (10) and compressed to the initial pressure level.

4. A method according to claim 3, wherein the air is depressurized to a high-pressure column pressure level in a depressurizer (7, 8) driving the second booster (5) and the third booster (6).

5. Process according to claim 4, wherein the air is partially liquefied by reducing the pressure in the depressurizers (7, 8) driving the second booster (5) and the third booster (6) to the pressure level of the higher pressure column, wherein the portion remaining in the gaseous state is fed into the higher pressure column (11) and the liquefied portion is fed into the lower pressure column (12).

6. A process according to claim 1 or 2, wherein a further portion of the air compressed to the initial pressure level is cooled and depressurized into the higher pressure column (11) starting from the initial pressure level.

7. A process according to claim 1 or 2, wherein the air fed to the second booster (5) is pre-cooled to a temperature level of 130 to 200K.

8. A method according to claim 3, wherein the air depressurized in the depressurization machines (7, 8) driving the second booster (5) and the third booster (6) is cooled to a temperature level of 120 to 190K before depressurization thereof.

9. A method according to claim 1 or 2, wherein the air depressurized in the first depressuriser (9) is pre-cooled to a temperature level of 150 to 230K.

10. A process according to claim 1 or 2, wherein the air boosted in the third booster (6) is cooled to a temperature level of 97 to 105K before its depressurization into the higher-pressure column (11).

11. A process according to claim 1 or 2, wherein the pressure increase in the second booster (5) is a pressure increase of 10 to 25 bar and the pressure increase in the third booster (6) is a pressure increase of 5 to 15 bar.

12. Air separation plant (100) for the cryogenic separation of air having a distillation column system (10) comprising a higher pressure column (11) operating at a higher pressure column pressure level and a lower pressure column (12) operating at a lower pressure column pressure level, wherein the air separation plant (100) comprises means designed for:

-discharging a low-temperature oxygen-rich liquid from the low-pressure column (12), said low-temperature oxygen-rich liquid being subjected to pressure increase in a low-temperature state, and subsequently heated and evaporated, leading out from the air separation plant (100),

it is characterized in that the preparation method is characterized in that,

-providing a first booster (2) for the first warm-up process, which is mechanically connected to the first pressure reducer (9), wherein means are provided for reducing another part of the air compressed to the initial pressure level in the first pressure reducer (9) from the initial pressure level to the low-pressure column pressure level and subsequently into the low-pressure column (12),

-a second supercharger (5) and a third supercharger (6) are provided for two further pressure boosting processes, and means are provided for the purpose of successively conducting air through the second supercharger (5) and the third supercharger (6) for the two further pressure boosting processes, where the air is fed into the third supercharger (6) at a temperature level at the time of leaving the second supercharger (5),

-means are provided for the purpose that the respective amounts of air which are led through the first supercharger (2), the second supercharger (5) and the third supercharger (6) in total differ from one another by not more than 10%,

-means are provided for the purpose of setting the pressure increase process, carried out in the cold state, of the low-temperature oxygen-enriched liquid discharged from the low-pressure column (12) to a pressure increase of 6 to 25 bar,

-the air separation plant (100) is designed to provide the air product in liquid form in a proportion of at most 1% based on the amount of air fed into the distillation column system (10).

13. Air separation plant (100) according to claim 12, designed for carrying out a method according to one of claims 1 to 11.