EP3312533A1 - Method for air separation and air separation plant - Google Patents

Abstract

The invention relates to a method for air separation, in which a part of compressed feed air, which is to be decomposed in an air separation plant (200), is cooled and liquefied by means of a main heat exchanger (150), wherein the liquid air in the course of a Joule-Thomson Turbine (170) is expanded and then fed to a high pressure column (111) of the air separation plant (200), the liquefied air having left the main heat exchanger (150) and before it is fed to the Joule-Thomson turbine (170) , is cooled, and an air separation plant (200).

Description

The invention is in the field of air separation plants and relates to a method for air separation and an air separation plant 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. Häring (ed.), Industrial Gas Processing, Wiley-VCH, 2006, especially Section 2.2.5, "Cryogenic Rectification" s.

Air separation plants have distillation column systems which include, for example, two or three column arrangements for providing nitrogen and oxygen rich air products. Typically, at least one so-called (high) pressure column and a so-called low pressure column are present. The operating pressure of the high-pressure column is, for example, 4.3 to 6.9 bar, preferably about 5.0 bar. The low-pressure column is operated at an operating pressure of, for example, 1.3 to 1.7 bar, preferably about 1.5 bar. The stated pressure values are present in the bottom of corresponding columns. It is also possible, for example, to provide so-called medium-pressure columns which are operated at an operating pressure which lies between the stated values. In particular, the low-pressure column may also be formed in two parts. For details refer to the literature.

An air separation plant air, so-called feed air, fed, which can be removed for example from the environment. In the course of the air supply in the air separation plant, the air is compressed and then subjected to various processes in order to purify and cool it, for example, before it is fed to the high-pressure column. In particular, the compressed feed air can be divided into sub-streams, possibly recompressed, and treated in different ways. If here and in the following of air is mentioned, should including both ambient air and air that has already undergone various processes, even if the composition deviates from the usual ambient air.

The present invention has as its object to make a process for air separation, in particular the air supply, more energy efficient.

Disclosure of the invention

This object is achieved by a method for air separation and an air separation plant with the features of the independent claims. Embodiments are the subject of the dependent claims and the following description.

Advantages of the invention

The present invention is based on a per se known method for air separation, as explained in more detail, from. In this case, a proportion of the compressed air, which is to be decomposed in total in an air separation plant, ie a part of the total feed air, cooled and liquefied by means of a main heat exchanger of the air separation plant, said liquefied air in the course of a Joule-Thomson turbine relaxed and in the further course of a high-pressure column of the air separation plant, in particular the lower region, is supplied.

So-called. Joule-Thomson turbines (also called Joule-Thomson expanders, liquid turbines or DFE or "Dense Fluid Expander") can be used in air separation plants instead of or in addition to throttle valves. In this case, the high-pressure liquid (ie, here, liquid air, usually with a pressure of more than 20 bar) to a medium pressure (for example, about 6 bar) relaxed, which corresponds to the pressure in the high pressure column (also referred to as high pressure column) of the air separation plant or differs only slightly, for example by less than 1 bar, from this. For further details, please refer to the cited literature. The task of the Joule-Thomson turbine is at Häring especially in the sections "Cold Section ( Fig. 2 .3A) "on page 24 and" Cryogenic Losses are Mainly Covered by the Turbine "on page 27.

The use of Joule-Thomson turbines instead of Joule-Thomson (throttle) valves makes it possible to reduce the Joule-Thomson current by as much as 6%, depending on the situation, resulting in energy leaks, for example, to the booster air compressor (Booster Air Compressor or BAC) for so-called MAC-BAC processes, on the nitrogen cycle compressor for air separation plants with nitrogen circulation or on the main air compressor (Main Air Compressor or MAC) for so-called high-pressure air or HAP (High Air Pressure) air separation process means.

A MAC-BAC process differs from a HAP process in that only a portion of the feed air is compressed to a pressure that is substantially, i. is at least 3 bar above the operating pressure of the high pressure column. The remaining feed air is only compressed to the operating pressure of the high-pressure column or a pressure typically deviating from it by not more than 1 to 2 bar and fed thereinto into the high-pressure column. The compressed to the higher pressure portion of the feed air can be performed in a MAC-BAC process after cooling at least in part by the Joule-Thomson turbine.

In a HAP process, however, the entire feed air is compressed to a pressure which is substantially, ie by at least 3 bar, above the operating pressure of the high pressure column. The pressure difference used is at least 3 bar, but may also be significantly higher, for example at 4, 5, 6, 7, 8, 9 or 10 bar and up to 14, 16, 18 or 20 bar. HAP methods are for example from EP 2 980 514 A1 and the EP 2 963 367 A1 known. In a HAP process, typically no booster is provided, the main compressor is the only compressor device driven by external energy. However, boosters driven by expansion turbines can be provided, which compress the air streams to an even higher pressure. Even in a HAP process, a part of this air is passed through the Joule-Thomson turbine. The remaining air is also released before being fed into the distillation column system.

During the relaxation of the turbine flow, the expansion process ends in a two-phase region, that is part of the liquid, here the liquid air, is thereby evaporated. The resulting vapor is also referred to as flash gas. The Joule-Thomson turbine, like all turbomachines, is sensitive to phase changes in the fluid to be expanded - in fact, flash gas in the machine itself can cause major mechanical damage, including destruction of the machine.

Therefore, it can be provided to make the relaxation in the Joule-Thomson turbine procedurally two-stage. First, the high pressure liquid can not be relaxed to the medium pressure but to a slightly higher intermediate pressure (for example, about 10 to 16 bar). The main criterion here is that the vapor content at the exit from the Joule-Thomson turbine remains as low as possible. The remaining relaxation of this intermediate pressure on the medium pressure can then be done in a throttle valve.

For this purpose, however, usually a control system is necessary, which must be able to not only allow regular operation, but also to avoid dangerous situations that can occur especially when adjusting the system. It is expedient in this case that the intermediate pressure is maintained higher than a procedurally optimal pressure, so that there is always a certain safety margin. However, the existing energy-saving potential in such a system is usually not exhausted.

For so-called "flexible" air separation plants, i. Air separation systems, which are often adjusted, can lead to the disadvantage that the use of Joule-Thomson turbines, especially with respect to throttle valves, no longer worthwhile. It is also possible to design impellers of the Joule-Thomson turbines with special geometry, so that the turbine can be used for a higher proportion of flash gas, but this requires a high manufacturing outlay. The mentioned control system would be unchanged. As a rule, the method is more efficient the lower the intermediate pressure is selected. However, the lower the intermediate pressure, the higher the risk that the two-phase area will occur during relaxation. A good regulatory system is almost inevitable.

According to the invention, however, now the liquid air, after it has left the main heat exchanger and before the Joule-Thomson turbine is fed, further cooled. It is advisable to cool down to a temperature between 98 and 105 K.

With the proposed method it can be achieved that the state of the air at the exit from the Joule-Thomson turbine is in a "safe area", i. that no or at least sufficiently little flash gas is formed or the two-phase region is not reached, since the conditions during the expansion are correspondingly changed by the cooling before entering the Joule-Thomson turbine. A special regulation, as mentioned above, is therefore no longer necessary. Furthermore, instrumentation costs as well as commissioning costs for the air separation plant are significantly reduced. Even during operation of the air separation plant can be ensured that the Joule-Thomson turbine is operated as optimally as possible. In addition, the rectification in the lower portion of the high pressure column can be improved. Likewise, a throttle valve - depending on the cooling of the air - no longer absolutely necessary. It is understood that a throttle valve between the Joule-Thomson turbine and the supply to the high-pressure column - depending on the additional cooling of the air - can still be provided, but even then no regulation is necessary.

Preferably, the liquefied air, after leaving the heat exchanger and before it is fed to the Joule-Thomson turbine, is passed through an evaporator in which the air is further cooled by evaporation of a cryogenic liquid. The use of an evaporator allows a particularly efficient cooling of the air. The evaporator can be arranged particularly advantageous in the bottom of the high-pressure column of the air separation plant and serve here as a bottom evaporator for the evaporation of the oxygen-enriched liquid which separates in the bottom of the high-pressure column. In this way, heat can be introduced into the sump of the high-pressure column for evaporation, which is removed from the liquefied air.

Alternatively, it is preferred if the evaporator is arranged separately, in particular outside the high-pressure column of the air separation plant. This allows variable positioning of the evaporator and does not require changes in the high pressure column.

In the separate arrangement of the evaporator, it is advantageous if a part of the air leaving the Joule-Thomson turbine, fed to the evaporator for its operation and then discharged from the evaporator and separately from the remaining air, the Joule-Thomson Turbine leaves, the high-pressure column is supplied. The necessary for the operation of the evaporator cold can therefore be diverted or removed directly from the flow of cooled air.

Alternatively, however, it is also preferred if the air leaving the Joule-Thomson turbine is subsequently fed completely to the evaporator for its operation and subsequently removed from the evaporator and fed to the high-pressure column. Thus, the cooled air can be fully used to provide the necessary for the operation of the evaporator cold. Depending on the situation, one or the other variant may be more energy efficient. In both cases, a part of the still liquid air taken from the Joule-Thomson turbine is vaporized by the liquefied air supplied to the Joule-Thomson turbine, and the former is cooled down at the same time.

Another preferred way to cool the liquid air is that the liquefied air, after leaving the heat exchanger and before it is fed to the Joule-Thomson turbine, is passed through another heat exchanger or subcooler to cool the air , Also in this way the necessary cooling of the liquid air can be achieved. It is particularly expedient if the further heat exchanger or the subcooler is used for at least one further cooling operation in the air separation plant, i. if the further heat exchanger or subcooler is present anyway, since then the integration of the proposed method, an existing air separation plant is particularly simple and fast.

In an air separation plant according to the invention a part of the compressed air to be decomposed in the air separation plant, so a part of the feed air through a main heat exchanger so feasible that this portion of the feed air is cooled and liquefied, in the course of a Joule-Thomson Turbine is provided by which this liquefied air is feasible so that it is relaxed. In addition, a high-pressure column is provided, which this air can be supplied in the further course. Here is a cooling unit, ie in particular an evaporator, a another heat exchanger or a subcooler, provided by means of which this liquid air, after it has left the main heat exchanger and before it is fed to the Joule-Thomson turbine, can be cooled.

Concerning. advantageous embodiments and the advantages of the air separation plant according to the invention is made to avoid repetition of the above statements to the method, which apply accordingly.

The invention will be explained in more detail below with reference to the accompanying drawing, which shows various parts of the installation, by means of which the measures according to the invention will be explained.

Figur 1

zeigt eine nicht erfindungsgemäße Luftzerlegungsanlage in Form eines schematischen Prozessflussdiagramms.

Figur 2

zeigt eine Luftzerlegungsanlage gemäß einer Ausführungsform der Erfindung in Form eines schematischen Prozessflussdiagramms.

Figur 3

zeigt ein T-S-Diagramm zur Erläuterung der Erfindung.

Figur 4

zeigt eine Luftzerlegungsanlage gemäß einer weiteren Ausführungsform der Erfindung in Form eines schematischen Prozessflussdiagramms.

Figur 5

zeigt eine Luftzerlegungsanlage gemäß einer weiteren Ausführungsform der Erfindung in Form eines schematischen Prozessflussdiagramms.

Short description of the drawing

FIG. 1

shows a non-inventive air separation plant in the form of a schematic process flow diagram.

FIG. 2

shows an air separation plant according to an embodiment of the invention in the form of a schematic process flow diagram.

FIG. 3

shows a TS diagram for explaining the invention.

FIG. 4

shows an air separation plant according to another embodiment of the invention in the form of a schematic process flow diagram.

FIG. 5

shows an air separation plant according to another embodiment of the invention in the form of a schematic process flow diagram.

Detailed description of the drawing

In FIG. 1 An air separation plant of known type is shown, with which, among other air products, for example, gaseous (GAN) and liquid nitrogen (LIN) and liquid oxygen (LOX), in particular using an internal compression (ICLIN, ICLOX) can be provided. Air separation plants of the type shown are often described elsewhere, for example at H.-W. Haring (ed.), Industrial Gases Processing, Wiley-VCH, 2006, especially Section 2.2.5, "Cryogenic Rectification Reference should therefore be made to the corresponding specialist literature for detailed explanations on the structure and mode of operation An air separation plant for use of the present invention may be designed in many different ways.

From the in FIG. 1 shown air separation plant 100 are shown substantially only the high-pressure column 111 and the low-pressure column 112 as part of a distillation column system. While distillation columns for crude argon and pure argon are indicated only as block 113, components such as main air compressor and pre-cooler are not shown. A main heat exchanger 150 is only partially shown, namely insofar as air of a flow a (JT-AIR) is passed through the main heat exchanger 150 for cooling and liquefaction. The other illustrated streams or media (UN2, GAN, FEED, ICLIN, ICLOX) can also be passed through the main heat exchanger 150, such as in FIG. 1 of the WO 2016/015850 A1 shown.

The apparatus provided upstream of the main heat exchanger 150 is also explicitly stated FIG. 1 of the WO 2016/015850 A1 and the related explanations. As shown and explained there, feed air can be sucked in via a main air compressor, cooled in a pre-cooling unit and cleaned in a cleaning unit. A partial flow can first be fed to a booster for recompression. From this, in turn, a part in the form of the flow a (JT-AIR) is recompressed in the after-compressor to a Nachverdichterenddruck warm supplied to the main heat exchanger 150 and taken this cold side.

After the air of the flow a has passed through the main heat exchanger 150, it is fed to a Joule-Thomson turbine 170, in which the air is expanded, as mentioned above. For this purpose, a control system 171 is provided, which is indicated only schematically. After the Joule-Thomson turbine 170, a throttle valve may be provided, which passes through the air before it is fed to the high-pressure column 111.

Furthermore, a subcooler 160 is provided for subcooling liquid or gaseous air products, which are guided from the high-pressure column 111, inter alia, into the low-pressure column 112.

In the air separation plant 100 shown here, as described above, the liquefied air through the main heat exchanger 150 in the Joule-Thomson turbine 170 is performed, for example, with a pressure of about 20 bar or higher. In the Joule-Thomson turbine 150, the air is then depressurized, for example, to a pressure of about 10 to 16 bar to avoid the formation of flash gas. For this purpose, in particular the control system 171 is necessary.

In FIG. 2 Now, an air separation plant according to an embodiment of the invention in the form of a schematic process flow diagram is shown. The air separation plant 200 corresponds in its basic structure of the air separation plant 100 according to FIG. 1 , In contrast, however, an evaporator 180 is now provided here, through which the air of the flow a, after it has been liquefied by the main heat exchanger 150, is guided.

The evaporator 180 is disposed in the sump of the high-pressure column 111 in order to obtain the for the operation and thus the cooling of the performed air. As it passes through the evaporator 180, heat of the stream a is transferred to the liquid bottom product of the high-pressure column 111, which is thereby partly vaporized. The air of the stream a cooled in this way in the evaporator 180 is then fed to the Joule-Thomson turbine 150, in which the air is expanded. Anschießend then the air - as well as according to FIG. 1 - The high-pressure column 111 fed.

In FIG. 3 a TS diagram is shown for a more detailed explanation of the invention. Here, the temperature T is plotted against the entropy S. In a conventional air separation plant with Joule-Thomson turbine, as in FIG. 1 As shown, the relaxation of the air proceeds from point P1, which corresponds to a state in which the air leaves the main heat exchanger and enters the Joule-Thomson turbine (neglecting any conduction effects) via the point P2 to the point P3.

In the air separation plant according to FIG. 2 or the corresponding procedure is the air, starting from the point P1 first by means of Evaporator further cooled without significant pressure change, that is, the point P4 is reached in the diagram, which corresponds to the state in which the air then enters the Joule-Thomson turbine. There, the air is then released to point P5. The pressure at point P5 corresponds to that at point P3, which can be seen on the isobar, but less or no flash gas is generated. This means that no complex control is required.

In FIG. 4 an air separation plant according to a further embodiment of the invention in the form of a schematic process flow diagram is shown. The air separation plant 300 corresponds in its basic structure of the air separation plant 200 according to FIG. 2 ,

In contrast to this, however, the evaporator 180 is now provided separately outside the high-pressure column 111. Again, the air is passed through the evaporator 180 after being liquefied by the main heat exchanger 150 (flow a).

After the air has left the evaporator 180, it is - as well as according to FIG. 2 - Guided by the Joule-Thomson turbine 170, in which the air is released. However, after leaving the Joule-Thomson turbine 170, the air is now first again passed through the evaporator 180, this time not for cooling but for the operation or cooling of the evaporator 180 itself. Subsequently, the liquid air from the bottom of the evaporator 180 of the high-pressure column fed.

Any resulting gaseous air from the upper portion of the evaporator 180 may also be supplied to the high-pressure column 111 at a corresponding location.

In FIG. 5 an air separation plant according to a further embodiment of the invention in the form of a schematic process flow diagram is shown. The air separation plant 400 corresponds in its basic structure of the air separation plant 300 according to FIG. 4 ,

In contrast to this, however, the relaxed and liquid air in the Joule-Thomson turbine 170 is not conducted completely into the evaporator 180, but instead only partially. The rest of the part will be similar to FIG. 2 - Performed directly in the high pressure column 111. In this way, cooling and thus operation of the evaporator 180 are possible.

With everyone in the Figures 2 . 4 and 5 shown embodiments of the air separation plant and the corresponding method for air separation is now no complex control system for the Joule-Thomson turbine longer necessary.

Claims (15)

Process for air separation, in which a part of compressed feed air which is decomposed in an air separation plant (200, 300, 400) is first cooled and liquefied by means of a main heat exchanger (150), the liquefied air being subsequently fed by means of a Joule-Thomson Turbine (170) is expanded and subsequently fed to a high-pressure column (111) of the air separation plant (200, 300, 400), characterized in that the liquefied air, after leaving the main heat exchanger (150) and before it is fed to the Joule-Thomson turbine (170), is further cooled. The method of claim 1, wherein the liquefied air, after leaving the heat exchanger (150) and before it is fed to the Joule-Thomson turbine (170), is cooled to a temperature of between 98 and 105K. A method according to claim 1 or 2, wherein the liquefied air, after having left the heat exchanger (150) and before being fed to the Joule-Thomson turbine (170), is passed through an evaporator (180) in which the air passes through Transfer of heat to a cryogenic liquid is cooled. The method of claim 3, wherein the evaporator (180) is disposed in a sump of the high pressure column (150) of the air separation plant (200). Method according to claim 3, wherein the evaporator (180) is arranged separately, in particular outside the high-pressure column (111) of the air separation plant (300, 400). The method of claim 5, wherein a portion of the air exiting the Joule-Thomson turbine (170) is fed to the evaporator (180) for operation and then discharged from the evaporator (180) and separated from the remaining air containing the evaporator (180) Joule-Thomson turbine (170) leaves, the high-pressure column (111) is supplied. The method of claim 5, wherein the air leaving the Joule-Thomson turbine (170), in the further course completely to the evaporator (180) supplied to its operation and then discharged from the evaporator (180) and fed to the high-pressure column (111) becomes. The method of claim 1 or 2, wherein the liquefied air, after leaving the heat exchanger (150) and before it is fed to the Joule-Thomson turbine (170), is passed through another heat exchanger or subcooler (160) the air is cooled. The method of claim 8, wherein the further heat exchanger or subcooler (160) is used for at least one further cooling operation in the air separation plant. Air separation plant (200, 300, 400), in which a part of compressed feed air, which is decomposed in the air separation plant (200, 300, 400), first by a main heat exchanger (150) is feasible so that the air is cooled and liquefied, wherein further comprising a Joule-Thomson turbine (170) is provided, through which the liquefied air is guided so that it is relaxed, and wherein a high-pressure column (111) is provided, to which the air is supplied in the further course, characterized in that a cooling unit is provided, by means of which the liquefied air, after it has left the main heat exchanger (150) and before it is fed to the Joule-Thomson turbine (170), can be cooled. Air separation plant (200, 300, 400) according to claim 10, wherein the cooling unit is designed as an evaporator (180) which is arranged in particular in a sump of the high-pressure column (111) of the air separation plant (200). Air separation plant (200, 300, 400) according to claim 10, wherein the cooling unit is designed as an evaporator (180), which is arranged separately, in particular outside the high-pressure column (111) of the air separation plant (300, 400) Air separation plant (400) according to claim 12, which is designed such that a part of the air leaving the Joule-Thomson turbine (170) can be supplied to the evaporator (180) for its operation and subsequently discharged from the evaporator (180) and separately from the remaining air leaving the Joule-Thomson turbine (150), the high-pressure column (111) can be fed. Air separation plant (300) according to claim 12, which is designed such that the air leaving the Joule-Thomson turbine, in the further course completely to the evaporator for its operation can be fed and subsequently discharged from the evaporator and the high-pressure column can be fed. Air separation plant (200, 300, 400) according to claim 10, wherein the cooling unit as a further heat exchanger or as a subcooler (160) of the air separation plant (200, 300, 400), which is provided in particular for at least one further cooling operation in the air separation plant.

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