Method for operating an air separation plant and air separation plant

Abstract

The invention relates to a method for operating an air separation plant (100) having a distillation column system (110), a heat exchanger (1) and an adsorber (103), wherein a first operating mode is performed in a first time period and a second operating mode is performed in a second time period following the first time period. Provision is made for a third operating mode to be performed in a third time period between the second time period and the first time period, wherein in the third operating mode, compressed air is at least partially freed of water and carbon dioxide in the adsorber (103) and at least partially cooled in the heat exchanger (1), an air product is extracted from the distillation column system (110) and at least partially heated in the heat exchanger (1), and a settable portion of the compressed air cooled in the heat exchanger (1) or a settable amount of the further compressed air at least partially freed of water and carbon dioxide in the adsorber (103) but not cooled in the heat exchanger (1) is first fed to the air product and the air product is then heated in the heat exchanger (1). The subject matter of the invention also relates to a corresponding air separation plant (100).

Description

[0001] The invention relates to a method for operating an air separation plant having a distillation column system adapted for cryogenic rectification, having a heat exchanger and having an adsorber, and to a corresponding air separation plant. Background Art

[0002] The production of liquid or gaseous air products by cryogenic separation of air in an air separation plant is known and is described, for example, in Wiley-VCH Publishing Company in 2006 by H.-W. In the book "Industrial Gases Processing" edited and published by the American Society of Petroleum Exploration and Development, in particular in chapter 2.2.5 "Cryogenic Rectification", it is described. Further details of the corresponding methods and equipment specifically related to the present invention will be further described below.

[0003] In many fields of application, including also the field of air product production in air separation plants, heat exchangers (technically more correctly called: heat carriers) are operated with cryogenic fluids, i.e. fluids having a temperature well below 0° C., in particular well below −100° C. In the following, the invention is mainly described with reference to such main heat exchangers of air separation plants, i.e. those to which air which has already been dried and freed of carbon dioxide in an adsorber is supplied for cooling. In contrast, the invention does not relate to plants with such heat exchangers, i.e., heat exchangers which serve to freeze water and carbon dioxide from the air and which are therefore operated cyclically in order to remove frozen water and carbon dioxide from the heat exchanger from time to time. Such plants require operating modes specifically adapted to the cleaning purposes, which cannot be transferred to heat exchangers as used in the context of the present invention.

[0004] GB2126700A discloses a process and apparatus for producing nitrogen from air by cryogenic separation of air at superatmospheric pressure, which process and apparatus are capable of producing variable quantities of nitrogen from a constant supply of air by periodically distilling less than the entire supply of air in a column and expanding the air flow from the remaining supply in a turbine to perform work expansion, thereby providing additional refrigeration for the process and recovering the condensed nitrogen vapor thereby formed in excess of the amount required for reflux.

[0005] For the construction and operation of the main heat exchanger of an air separation plant, refer to (see above), Chapter 2.2.5.6, "Apparatus". For general details on heat exchangers, please see, for example, the publication "The Standards of the Brazed Aluminium Plate-Fin Heat Exchanger Manufacturers' Association", 2nd edition, 2000, in particular Chapter 1.2.1 "Components of an Exchanger". If "heat exchanger" is mentioned in the following description, this is always understood to be the main heat exchanger of the air separation plant.

[0006] Without additional measures, the heat exchangers of the air separation system are temperature-balanced and are heated when the system is shut down and thus when the heat exchangers are shut down, or in this case the temperature profile that is established in the respective heat exchangers during stationary operation cannot be maintained.

[0007] In particular, if the heat exchanger is stopped and then heated up as a whole due to the good thermal conductivity in its metal material (longitudinal heat conduction), this causes the temperature at the previously hot end and the temperature at the previously cold end to equilibrate. In other words, the previously hot end of the heat exchanger cools down over time and the previously cold end of the heat exchanger warms up over time until these temperatures are at or close to the average temperature. Figure 1 This is also shown again in FIG. 1 , where the temperatures in the figure, which were approximately −175° C. or +20° C. during shutdown, equilibrate to one another over several hours and reach almost the average temperature.

[0008] This behavior is observed in particular if, when shutting down an air separation plant, the cold-insulated main heat exchanger is blocked together with the rectification plant, i.e. no gas is fed in from the outside. In this case, typically only the gas generated by the loss of heat insulation is blown cold.

[0009] If, when the heat exchanger is subsequently restarted, hot air is then fed to the cooled hot end of the heat exchanger, the temperature there will suddenly increase. Correspondingly, when restarting, cold air product from a distillation column system of an air separation plant is fed to the heated cold end, the temperature there will suddenly drop. This leads to the material stresses already explained and thus to permanent damage if necessary.

[0010] The object of the present invention is therefore in particular to provide measures which make it possible to restart a heat exchanger of an air separation plant even after a long shutdown without the above-mentioned adverse effects occurring. Summary of the invention

[0011] Against this background, the invention proposes a method for operating an air separation plant having a distillation column system adapted for cryogenic rectification, having a heat exchanger and having an adsorber, and a corresponding air separation plant having the features of the invention.

[0012] First, some terms used to describe the present invention are explained and defined below.

[0013] "Heat exchanger" is a device used in the terminology used here, which is designed to transfer heat indirectly between at least two fluid flows, such as countercurrents, directed to each other. The heat exchanger used in the context of the present invention can be composed of a single or several parallel and / or series heat exchanger parts, such as one or several plate heat exchanger blocks. The heat exchanger has "channels" that are adapted for fluid guidance and separated from other channels by separation plates or connected only on the inlet and outlet sides via corresponding headers. The channels are separated from the outside world via side bars (English: SideBar). These channels are referred to as "heat exchanger channels" hereinafter. In the following, the terms "heat exchanger" and "heat carrier" are used as synonyms. Correspondingly, this also applies to the terms "heat exchange" and "heat exchange". The "main heat exchanger" of the air separation device is characterized in that at least most of the air to be separated and the air product formed are guided through the main heat exchanger.

[0014] In particular, the present invention relates to a device known as a plate-fin heat exchanger (English: Plate-Fin Heat Exchanger) according to the German document ISO 15547-2:2005. Therefore, if "heat exchanger" is mentioned below, it is particularly understood to be a plate-fin heat exchanger. A plate-fin heat exchanger has a large number of overlapping flat chambers or elongated channels, which are each separated from each other by corrugated or other structured and interconnected, for example brazed plates, usually aluminum plates. The plates are stabilized by means of side strips and connected to each other via these side strips. In particular, the structuring of the heat exchanger plates serves to increase the heat exchange area, but also to increase the stability of the heat exchanger. In particular, the present invention relates to a brazed aluminum plate-fin heat exchanger. In principle, the corresponding heat exchanger can also be made of other materials, for example stainless steel, or of a variety of different materials.

[0015] The air separation plant has a distillation column system which can generally be designed, for example, as a two-column system, in particular as a classic Linde two-column system, but can also be a three-column or multi-column system. In addition to distillation columns for extracting liquid and / or gaseous nitrogen and / or oxygen, i.e. distillation columns for nitrogen-oxygen separation, distillation columns for extracting other air components, in particular krypton, xenon and / or argon, can also be provided. The terms "rectification" and "distillation" as well as "tower" and "column" or terms formed therefrom are generally used as synonyms. The invention is applicable to air separation plants having any distillation column system which operates at low temperatures, i.e. at least partially below -100° C. For a detailed description, reference is made to the relevant professional literature.

[0016] The air supplied to the air separation plant is first compressed in a so-called main air compressor to a pressure level which depends on the specific operating mode of the air separation plant and which can typically be at or significantly above the highest operating pressure in the distillation column system. The air is heated during this compression process and is therefore subsequently first cooled in a direct contact cooler. This cooling reduces the moisture content of the water-saturated air and in this way reduces the subsequent drying effort.

[0017] In addition to water, air also contains, in particular, carbon dioxide. Water and carbon dioxide must be removed because solids are formed during the subsequent cooling in the main heat exchanger by desublimation or freezing, which gradually clog or block the heat exchanger. Hydrocarbons contained in the air can also cause problems, since they are less volatile than nitrogen and oxygen and can therefore accumulate in the liquid oxygen that forms, for example, in the bottom of the low-pressure column. To remove these components, at least in the newer types of air separation plants, adsorbers are used.

[0018] Adsorbers in air separation plants, such as As described in section 2.2.5.6 "Apparatus" (see above), typically there are adsorption vessels arranged in pairs, which switch between adsorption mode and regeneration mode. Zeolites that act as molecular sieves are generally used as adsorption materials. The adsorption cycle typically lasts from 1.5 hours to 6 hours and is carried out at the pressure level of compressed air. Before regeneration, the pressure is released to ambient pressure within typically about 10 minutes. Regeneration is carried out with a dry regeneration gas flow in countercurrent direction. Therein, the regeneration is divided into a heating phase, in which the regeneration gas flow is heated, and a subsequent cooling phase with cold regeneration gas. This is followed by a pressure build-up phase of about 20 minutes.

[0019] That is, gaseous compressed air that is essentially free of water and carbon dioxide is provided by means of the adsorber, which compressed air can be cooled in the main heat exchanger. In contrast, as explained, the present invention does not relate to such devices in which the corresponding components are removed from the compressed air used by refrigeration, as in US Pat. No. 3,469,271 A, for example.

[0020] If "air product" is mentioned here, it is understood to be a gas or liquid or medium in a supercritical state, which has one or more components contained in atmospheric air, but no other (air-independent) components. One or more components from atmospheric air can be present in the air product in the same or different absolute or relative proportions than in the atmospheric air.

[0021] The product air or another fluid is "free" of water and carbon dioxide as understood herein if the product air or another fluid has a water and carbon dioxide fraction which is not detectable. The product air or another fluid may also be "substantially" free of water and carbon dioxide as commonly understood, such that no significant amounts of water and carbon dioxide are contained. In particular, the product air or another fluid may contain residual contents of water and carbon dioxide of up to several ppm (parts per million) without the basic properties of the feed air or the corresponding product air being affected by the corresponding residual contents in terms of processing in the heat exchanger.

[0022] Advantages of the present invention

[0023] In principle, during the downtime of the relevant plant, it is possible to pass cold gas from a tank or waste gas from a vertical plant through the (main) heat exchanger of the air separation plant in order to avoid heating or to maintain the temperature profile that is established in stationary operation (i.e., in particular in normal production operation of the corresponding plant). However, such operation is only possible with conventional methods with considerable effort if appropriate.

[0024] In some cases, as also proposed in US Pat. No. 5,233,839 A, heat can also be introduced from the environment via a heat bridge to avoid cooling of the hot end of the corresponding heat exchanger. If, for example, there are no process units with a significant cold buffer capacity downstream of the heat exchanger (e.g. no rectification column system with cryogenic liquid accumulation), such heat retention can reduce excessive thermal stresses at the hot end when a hot process stream is suddenly supplied during restart. In this case, the supplied hot process stream can expand at the cold end of the heat exchanger after leaving and return as a cold stream via the cold end to the hot end, so that the heat exchanger can in this way slowly reach its normal temperature curve by Joule-Thomson cooling.

[0025] However, if there is a process unit downstream of the heat exchanger which has a significant cold buffer capacity (e.g. a distillation column system with a low-temperature liquid accumulation, as is the case in air separation plants), the occurrence of thermal stresses here can be minimized by means of the measures described above, but thermal stresses can occur at the cold end, which is heated at the same time, due to the sudden flow of colder fluid through, due to unreliably high (temporal and local) temperature gradients. In this case, the heat retention of the hot end can even lead to the formation of higher temperature differences at the cold end and thus increased thermal stresses.

[0026] The present invention now solves this problem as described in the corresponding technical solution. To this end, the present invention proposes a method for operating an air separation plant, which has a distillation column system adapted for cryogenic rectification, a heat exchanger and an adsorber. The heat exchanger is in particular the main heat exchanger of the air separation plant.

[0027] Among them, the invention also relates in particular to such measures, which avoid excessive thermal stresses at the cold end of the heat exchanger. However, such measures can be combined at any time with other measures that are intended to reduce the thermal stresses at the hot end of the heat exchanger.

[0028] Besides being combined with corresponding measures for temperature control on the hot side of the corresponding heat exchanger, the invention can also be combined at any time with other measures for temperature control on the cold side of the heat exchanger.

[0029] The present invention proposes: the method is performed in a first operating mode and a second operating mode, wherein the first operating mode is performed in a first time period, and the second operating mode is performed in a second time period, and the second time period is after the first time period. Wherein, the second time period and the first time period do not overlap each other in the context of the present invention and are performed alternately multiple times. Wherein, in the context of the present invention, the first time period or the first operating mode performed in the first time period corresponds to the production operation of the corresponding air separation device, that is, corresponds to such an operating time period, in which liquid and / or gaseous air products are provided. Correspondingly, the second operating mode performed in the second operating time period is represented as an operating time period in which the corresponding air product is not formed. The corresponding second time period or the second operating mode is particularly used to save energy or costs, for example when no air product is needed, when incentives from the energy market prove that production throttling is reasonable, or when maintenance work needs to be performed.

[0030] As mentioned above, in the second operating mode, preferably no gas flows through the heat exchanger, or flows through it to a significantly smaller extent than in the first operating mode. As already explained, the invention does not exclude that a certain amount of gas is also guided through the corresponding heat exchanger in the second operating mode, for example as a support for the measures proposed according to the invention to maintain the temperature of the heat exchanger or to bring it to temperature. However, the amount of fluid guided through the heat exchanger in the second operating mode is always significantly less than the amount of fluid guided through the heat exchanger in the conventional first operating mode. In the context of the present invention, the amount of fluid guided through the heat exchanger in the second operating mode is, for example, generally not more than 20%, 10%, 5% or 1% of the amount of fluid guided through the heat exchanger in the first operating mode.

[0031] In the context of the present invention, the first operating mode and the second operating mode are executed alternately with each other multiple times, that is, the first operating mode is always followed by the second operating mode, and the second operating mode is followed by the first operating mode again, and so on. However, this does not exclude in particular that further operating modes may be provided between the first and second operating modes or between the second and first operating modes, in particular a third operating mode provided according to the present invention is provided between the second and first operating modes. In the context of the present invention, the following sequence is particularly produced: first operating mode—second operating mode—third operating mode—first operating mode, and so on.

[0032] In the context of the present invention, in a first operating mode, water and carbon dioxide are at least partially removed from the compressed air in an adsorber and at least partially cooled in a heat exchanger. In addition, in the first operating mode, air product is extracted from the distillation column system and at least partially heated in a heat exchanger.

[0033] By operating the air separation plant, the first end of the heat exchanger is brought to a first temperature level, at which the compressed air to be cooled is conveyed and heated air product is extracted. The second end of the heat exchanger is brought to a second temperature level lower than the first temperature level, at which the air product to be heated is conveyed and cooled compressed air is extracted. The first temperature level corresponds in particular to the ambient temperature and, for example, comprises a temperature of 0 to 50° C. The second temperature level corresponds in particular to the extraction temperature of the air product from the distillation column system and is preferably at a significantly lower temperature, in particular at -50° C. to -200° C., for example at -100° C. to -200° C. or at -150° C. to -200° C.

[0034] If it is mentioned here that "the specifically mentioned compressed air or the specifically mentioned air product is cooled or heated, respectively", this of course does not exclude that other fluid streams can also be cooled or heated. The corresponding other fluid streams can have the same or different compositions. For example, the compressed air can be provided in the form of a total stream, from which several partial streams are formed and these partial streams can be cooled to the same or different temperatures. In addition, in the context of the present invention, it is also possible to extract several fluid streams from a distillation column system or a corresponding storage system, if appropriate, and heat them jointly or separately from one another in a heat exchanger.

[0035] It is also possible, for example, to divide the corresponding fluid flow in a heat exchanger into two or several partial flows, which are withdrawn from the heat exchanger at the same or different temperatures. It is naturally also possible to feed other fluid flows to the heat exchanger and to further heat the combined flow formed in this way in the heat exchanger. In any case, however, the compressed air and the air product (alone or together with other flows, as explained above) are cooled or heated in the heat exchanger.

[0036] In the second operating mode, in the context of the present invention, the cooling of the compressed air and the heating of the air product in the heat exchanger are partially or completely suspended. For example, instead of those fluids that are guided through the heat exchanger and cooled or heated in the heat exchanger in the first operating mode, no fluid may be guided through the heat exchanger. That is, the heat exchange channels of the heat exchanger used for cooling or heating in the first operating mode remain unflowed in this case. However, it is also feasible that, instead of the compressed air or air product that is guided through the heat exchanger and cooled or heated in the heat exchanger in the first operating mode, another fluid flow is guided through the heat exchanger, in particular in a significantly smaller amount. However, in the context of the present invention, the effect obtained during the second operating mode is that the hot end of the heat exchanger is cooled and / or the cold end of the heat exchanger is heated, wherein, as explained, the present invention particularly relates to measures to prevent excessive temperature stresses at the cold end of the heat exchanger.

[0037] One aspect of the invention is that in the second operating mode, the second end of the heat exchanger (to which the air product to be heated is supplied in the first operating mode and from which the cooled compressed air is extracted) is allowed to be heated from the second temperature level to a higher temperature level. This is particularly related to heating to a third temperature level, as also explained below with reference to the third operating mode. The third temperature level can be an average temperature between the first temperature level and the second temperature level, or in particular deviate from this average temperature by no more than 10K. As explained, the first end of the heat exchanger (to which the compressed air to be cooled is supplied in the first operating mode and from which the heated air product is extracted) can in particular also be cooled, however, the invention does not primarily relate to measures for temperature control of the heat exchanger at this first end, i.e. the "hot end".

[0038] According to the invention, it is now provided that a third operating mode is carried out in a third time period between the second time period and the first time period or in a plurality of alternating operations and following a further first time period following a preceding second time period. This third operating mode is used in particular for temperature control of the second end, i.e. the cold end, of the heat exchanger, which is heated to the third temperature level in the manner described during the second operating mode, since corresponding heating is permitted, for example, since no temperature control is carried out in this second operating mode. According to the invention, the third operating mode is carried out in particular for this purpose, so that the second end, i.e. the cold end, of the heat exchanger is brought back to the second temperature level or close to the second temperature level from the correspondingly increased third temperature level, so that the corresponding device can then be operated normally again in the first operating mode, i.e. a cryogenic fluid in the form of an air product and, if necessary, in the form of a further stream can be conveyed at the cold end of the heat exchanger without causing excessive temperature stresses. It is therefore advantageous to carry out the third operating mode directly before the immediately following new first time period.

[0039] According to the invention, in the third operating mode, more precisely in principle as in the first operating mode, water and carbon dioxide are at least partially removed from the compressed air in the adsorber and it is at least partially cooled in the heat exchanger. Likewise, in the third operating mode, product air is withdrawn from the distillation column system and at least partially heated in the heat exchanger. The same or different amounts can be used as in the first operating mode. According to the invention, a settable portion of the compressed air cooled in the heat exchanger or a settable amount of further compressed air at least partially freed from water and carbon dioxide in the adsorber but not cooled in the heat exchanger is first fed to the product air and then the product air is heated in the heat exchanger.

[0040] Since the compressed air is not yet cooled as much in the third operating mode as it would be later when the power is fully restored due to the gradual start-up of the cooling power of the heat exchanger, in particular due to the heat input from the surroundings and the temperature balance between the first end and the second end, the temperature to which the compressed air is cooled or can be cooled is significantly higher in the third operating mode than in the first operating mode. The cooled compressed air can therefore be used for temperature control in the third operating mode by feeding it in a settable amount to the product air at a significantly lower temperature. The compressed air that has not yet been cooled naturally has a significantly higher temperature again and can therefore also be used in a corresponding manner.

[0041] By using the measures according to the invention, as explained several times, it is possible that the cold end of the heat exchanger is not directly loaded with cryogenic fluid after a longer stop phase in which it has already heated up, but can be gradually cooled. In this case, as explained, the third operating mode is advantageously carried out until the first end is again at the first temperature level or sufficiently close to the first temperature level, and until the second end is again at the second temperature level or sufficiently close to the second temperature level. "Sufficiently close" can exist in particular when the temperature difference is below a predetermined threshold value, such as 30 K, 20 K, 10 K or 5 K, or can be derived from applicable regulations.

[0042] In the context of the present invention, the temperature level of the fluid flow formed by the air product and the portion of compressed air or other compressed air in the third operating mode can be continuously reduced. In the context of the present invention, a corresponding continuous reduction can include a gradual reduction and / or a stepwise reduction. The gradient of the reduction can be matched in particular in terms of its steepness to the current temperature or material characteristic parameters (e.g. thermal compatibility or pressure resistance). In this case, the gradual reduction or stepwise reduction does not need to be carried out continuously over the entire third time period, but rather, it is also possible to use reduction time periods with different gradients.

[0043] Therein, the continuous lowering can include setting the amount of compressed air fed in. Setting the amount advantageously includes using a control and / or regulating device, as has already been explained above.

[0044] The air product mentioned above may in particular be so-called impure nitrogen, i.e. a nitrogen-containing fluid having an oxygen content of, for example, up to 21% (typically up to 10%), which is extracted from the low-pressure column of a distillation column system, i.e. a distillation column operating at a pressure level of 1 bar to 2 bar (absolute pressure), in particular 1.1 bar to 1.3 bar.

[0045] The invention also relates to an air separation plant which is designed as described in the corresponding technical solution of the invention. With regard to the features and advantages of the corresponding air separation plant, which is particularly adapted to carry out the method as explained above, reference is explicitly made to the above discussion.

[0046] The invention is explained in more detail hereinafter with reference to the accompanying drawings, which show embodiments of the invention and corresponding heat exchange diagrams. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 The temperature curve of the heat exchanger after shutting down is shown without using the measures according to an embodiment of the invention.

[0048] Figure 2 An assembly with a heat exchanger is shown.

[0049] Figure 3 Other components with a heat exchanger are shown.

[0050] Figure 4 An assembly according to one embodiment of the present invention is shown.

[0051] Figure 5 An assembly according to one embodiment of the present invention is shown.

[0052] Figure 6 An air separation plant that may be operated in accordance with an embodiment of the present invention is shown.

[0053] Figure 7 Other components with a heat exchanger are shown.

[0054] In the figures, elements which are identical or which correspond to one another in function or meaning are provided with the same reference numerals and are not explained again for the sake of clarity. DETAILED DESCRIPTION

[0055] Figure 1 The temperature curve of the heat exchanger after shutting down is shown in the form of a temperature diagram without using the measures according to an advantageous embodiment of the invention.

[0056] exist Figure 1 In the diagram shown, the temperature at the hot end of the corresponding heat exchanger marked with H and the temperature at the cold end marked with C are each shown in ° C. on the ordinate, and the time in hours is shown on the abscissa.

[0057] like Figure 1As can be seen in Figure 1, at the start of the shutdown, the temperature H at the hot end of the heat exchanger is about +20°C, which also corresponds to the temperature of the normal operation of the heat exchanger, and the temperature C at the cold end is about –175°C. As time increases, these temperatures balance each other. The high thermal conductivity of the materials used in the heat exchanger is responsible for this. In other words, here the heat flows from the hot end in the direction of the cold end. Together with the heat input from the environment, an average temperature of about –90°C is generated. The significant increase in temperature at the cold end is mostly due to the internal temperature balance in the heat exchanger and only to a very small extent due to the external heat input.

[0058] As explained several times, if after a regeneration period the hot end of the heat exchanger is subjected to a hot fluid at about 20° C. in the example shown again without further measures, strong thermal stresses can occur in the case shown. However, corresponding thermal stresses can also occur when the plant connected downstream of the heat exchanger is immediately supplied with a cryogenic fluid again, for example cryogenic gas from a rectification column system of an air separation plant. The present invention solves the latter problem in particular.

[0059] exist Figure 2 , an assembly with a heat exchanger 1 is shown, in which the measures proposed according to the invention are not implemented. The heat exchanger 1 has a heat exchange region 10, to which a fluid is supplied and removed at a first end, i.e. the hot end 11, and likewise at a second end, i.e. the cold end 12. In the example shown, a fluid stream A, i.e. an air product from a distillation column system in an air separation plant, is supplied to the heat exchanger 1 at the cold end 12, heated in the heat exchange region 10 of the heat exchanger 1, and removed again at the hot end 11. The first fluid stream A is heated accordingly. In accordance with Figure 2 In the illustration of , a second fluid stream, namely compressed air from an adsorber in an air separation plant, is additionally fed to the heat exchanger 1 at the hot end 11 and is withdrawn at the cold end 12 .

[0060] In this way, different temperature levels occur at the hot end 11 and the cold end 12, here referred to as the "first" and "second" temperature levels. If the supply of fluid flows A and B is prohibited, the temperature changes accordingly, in particular the temperature at the cold end 12 increases to a "third" temperature level.

[0061] Therefore, as explained many times, if the first fluid flow A is to be supplied to the heat exchanger 1 again at a second temperature level, but the cold end 12 of the heat exchanger 1 has already been heated to a temperature level that is significantly higher than the first temperature level, temperature stresses may occur here, which may lead to damage to the heat exchanger 1 if necessary over a long period of time.

[0062] Therefore, in Figure 3In the figure, an assembly with a heat exchanger 1 is shown, which follows an embodiment that does not conform to the embodiment according to the invention. Figure 3 corresponding elements, wherein reference is made to Figure 2 Here, the heat exchanger 1 can also be fed with a fluid stream A formed from air products.

[0063] However, here, if necessary, the fluid flow A can be formed using the first output flow A1 and the second output flow A2. Figure 3 In the embodiment of the present invention, a first outlet flow A1 and a second outlet flow A2 are branched off from the basic flow A0, or the basic flow A0 is divided into outlet flows A1 and A2. In this case, the first fluid flow A is formed using the outlet flow A1 under the limitation of the regulating mechanism 14, which can be controlled in particular by a suitable control or regulating device 2, such as a controllable or adjustable valve.

[0064] In contrast, the outlet flow A2 is led through the heater 15 and heated therein. After heating, the partial flow A2 is combined with the partial flow A1. A settable mixing temperature is obtained. The mixing temperature can be set by setting the respective proportions of the first and second outlet flows A1, A2 or the amount of energy introduced via the heater 15. As explained, the temperature level in particular decreases gradually.

[0065] exist Figure 4 FIG. 4 shows an assembly with a heat exchanger 1 according to one embodiment of the invention. Figure 3 Unlike the components of the control device 14, the control device 14 is arranged in such a way that, if necessary, a part of the cooled compressed air in the form of the fluid flow B can be fed to the output flow A1 as the second output flow A2 and can thus be used to form the fluid flow A, which otherwise includes the air product. Here, too, the mixed temperature can be obtained in the manner explained by setting or regulating according to the conditions of the control device 2.

[0066] In accordance with Figure 5 In an embodiment of the invention, which also shows a component having a heat exchanger 1 according to an embodiment of the invention, a corresponding regulating device 14 is provided for forming a fluid flow A from uncooled compressed air, which is otherwise used to form a material flow B, so that a corresponding mixing temperature can also be obtained here.

[0067] Figure 6 An air separation plant with a heat exchanger is shown which can be operated using a method according to an advantageous embodiment of the invention.

[0068] An air separation plant of the type shown, as explained, has already been described elsewhere many times, for example in the publication by H.-W. In the book "Industrial Gases Processing" edited and published by the German Technical University, in particular in Chapter 2.2.5, "Cryogenic Rectification". Therefore, for a detailed explanation of the construction and the mode of operation, reference is made to the corresponding technical literature. The air separation plant using the invention can be designed in a very different way. The use of the invention is not limited to the Figure 6 implementation plan.

[0069] exist Figure 6 The air separation device shown in FIG. 1 is generally designated by 100. The air separation device mainly comprises a main air compressor 101, a precooling device 102, an adsorber 103, a recompression assembly 104, a main heat exchanger (such as Figures 2 to 5 1), an expansion turbine 106, a throttling device 107, a pump 108 and a distillation column system 110. In the example shown, the distillation column system 110 includes a classic double column assembly consisting of a high pressure column 111 and a low pressure column 112, as well as a crude argon column 113 and a pure argon column 114.

[0070] In the air separation plant 100, an inlet gas stream is sucked in and compressed via a filter (not shown) by means of a main air compressor 101. The compressed inlet gas stream is fed to a precooling device 102 which is operated by cooling water. The precooled inlet gas stream is purified in an adsorber 103. In the adsorber 103, water and carbon dioxide are largely removed from the precooled inlet gas stream.

[0071] Downstream of the adsorber 103, the inlet gas flow is divided into two partial flows. One of the partial flows is completely cooled in the main heat exchanger at the pressure level of the inlet gas flow. The other partial flow is recompressed in the recompression assembly 104 and likewise cooled in the main heat exchanger, but only to an intermediate temperature level. After cooling to the intermediate temperature level, the so-called turbine flow is expanded to the pressure level of the completely cooled partial flow by means of the expansion turbine 106, combined with the partial flow and fed to the high-pressure column 111.

[0072] An oxygen-rich liquid bottom fraction and a nitrogen-rich gaseous top fraction are formed in the high-pressure column 111. The oxygen-rich liquid bottom fraction f is extracted from the high-pressure column 111, partially used as a heating medium in the bottom evaporator of the pure argon column 114, and is respectively fed in defined portions to the top condenser of the pure argon column 114, the top condenser of the crude argon column 113, and the low-pressure column 112. Likewise, the fluid evaporated in the evaporation chambers of the top condensers of the crude argon column 113 and the pure argon column 114 is fed to the low-pressure column 112.

[0073] The gaseous nitrogen-rich top product is withdrawn from the top of the high-pressure column 111, liquefied in a main condenser which forms a heat exchange connection between the high-pressure column 111 and the low-pressure column 112, and is delivered to the high-pressure column 111 as reflux in proportion and expanded into the low-pressure column 112.

[0074] In the low-pressure column 112, an oxygen-rich liquid bottom fraction and a nitrogen-rich gaseous top fraction are formed. The former is partially pressurized in the pump 108 in liquid form, heated in the main heat exchanger 105 and provided as product. A nitrogen-rich liquid stream is withdrawn from a liquid holding device at the top of the low-pressure column 112 and conveyed out of the air separation plant 100 as liquid nitrogen product. The gaseous nitrogen-rich stream withdrawn from the top of the low-pressure column 112 is conducted through the main heat exchanger 105 and provided as nitrogen product at the pressure of the low-pressure column 112. In addition, a stream from the upper region is withdrawn from the low-pressure column 112 and, after heating in the main heat exchanger, is used in the precooling device 102 as so-called impure nitrogen or, after heating by means of an electric heater, is used in a purification system.

[0075] In particular, in the described embodiment of the invention, compressed air can be fed to the impure nitrogen in the third operating mode.

[0076] exist Figure 7 , other components not according to the present invention with a heat exchanger 1 are shown, which are generally designated by 700. For temperature control, a circulating flow C is used here, which is compressed on the hot side of the heat exchanger by means of a compressor 701, precooled in a cooler 702, supplied to the heat exchanger 1 at the hot end 11, withdrawn from the heat exchanger 1 at the cold end 12, expanded by means of a valve 703, supplied to the heat exchanger 1 again at the cold end 12, withdrawn from the heat exchanger 1 again at the hot end 11 and supplied to the compressor 701 again. The expansion at the valve 703 results in gradual cooling.

Claims

1. A method for operating an air separation plant (100) having a distillation column system (110), a heat exchanger (1) and an adsorber (103), wherein - a first operating mode is performed in a first time period, and a second operating mode is performed in a second time period that is located after the first time period, wherein: The first time period and the second time period are executed alternately multiple times, - in the first operating mode, the compressed air is at least partially freed of water and carbon dioxide in the adsorber (103) and at least partially cooled in the heat exchanger (1), - in the first operating mode, product air is extracted from the distillation column system (110) and is at least partially heated in the heat exchanger (1), - in the first operating mode, the first end (11) of the heat exchanger (1) is brought to a first temperature level and the second end (12) of the heat exchanger (1) is brought to a second temperature level which is lower than the first temperature level, - in the second operating mode, the cooling of the compressed air and the heating of the air product in the heat exchanger (1) are partially or completely suspended, and - in the second operating mode, the second end (12) of the heat exchanger (1) is allowed to heat up to a third temperature level which is higher than the second temperature level, characterized in that - executing a third operating mode in a third time period between the second time period and the first time period, - in the third operating mode, the compressed air is at least partially freed of water and carbon dioxide in the adsorber (103) and at least partially cooled in the heat exchanger (1), - in the third operating mode, the air product is extracted from the distillation column system (110) and is at least partially heated in the heat exchanger (1), and In the third operating mode, a settable portion of the compressed air cooled in the heat exchanger (1) or a settable amount of further compressed air at least partially freed of water and carbon dioxide in the adsorber (103) but not cooled in the heat exchanger (1) is first fed to the product air and then the product air is heated in the heat exchanger (1).

2. The method according to claim 1, wherein: The temperature level of the fluid flow (A) formed from the product air and the portion of the compressed air or of the further compressed air in the third operating mode decreases continuously in the third operating mode.

3. The method according to claim 2, wherein: The continuous reduction of the second temperature level comprises a continuous reduction of the portion of the compressed air or the amount of the further compressed air.

4. The method according to claim 3, wherein: Setting the portion of the compressed air or the amount of the further compressed air comprises using a control and / or regulating device (2).

5. The method according to one of the preceding claims, wherein: The third operating mode is carried out until the first end (11) of the heat exchanger (1) is again at the first temperature level or is so close to the first temperature level that the temperature difference is below a predetermined threshold value.

6. The method according to claim 5, wherein: The distillation column system (110) comprises a low-pressure column (113), and wherein a nitrogen-rich and oxygen-containing gas mixture extracted from the low-pressure column is used as the air product.

7. An air separation plant (100) comprising a distillation column system (110), a heat exchanger (1) and an adsorber (103), wherein the air separation plant (100) is adapted to: - executing a first operating mode in a first time period and executing a second operating mode in a second time period following the first time period, - in the first operating mode, the compressed air is at least partially freed of water and carbon dioxide in the adsorber (103) and at least partially cooled in the heat exchanger (1), - in the first operating mode, product air is extracted from the distillation column system (110) and is at least partially heated in the heat exchanger (1), - in the first operating mode, the first end (11) of the heat exchanger (1) is brought to a first temperature level and the second end (12) of the heat exchanger is brought to a second temperature level which is lower than the first temperature level, - in the second operating mode, partially or completely suspending the cooling of the compressed air and the heating of the air product in the heat exchanger (1), and - in the second operating mode, allowing the second end (12) of the heat exchanger (1) to heat up to a third temperature level higher than the second temperature level, It is characterized in that The device (100) is adapted to, - executing a third operating mode in a third time period between the second time period and the first time period, - in the third operating mode, the compressed air is at least partially freed of water and carbon dioxide in the adsorber (103) and at least partially cooled in the heat exchanger (1), - in the third operating mode, the air product is extracted from the distillation column system (110) and is at least partially heated in the heat exchanger (1), and In the third operating mode, a settable portion of the compressed air cooled in the heat exchanger (1) or a settable amount of further compressed air at least partially freed of water and carbon dioxide in the adsorber (103) but not cooled in the heat exchanger (1) is first fed to the product air and then the product air is heated in the heat exchanger (1).

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