METHOD FOR OPERATING A HEAT EXCHANGER, ARRANGEMENT WITH A HEAT EXCHANGER, AND SYSTEM WITH A CORRESPONDING ARRANGEMENT

Abstract

A method for operating a heat exchanger, in which a first operating mode is carried out in first time periods, and a second operating mode is carried out in second time periods that alternate with the first time periods; in the first operating mode a first fluid flow is formed at a first temperature level, is fed into the heat exchanger in a first region at the first temperature level, and is partially or completely cooled in the heat exchanger; in the first operating mode a second fluid flow is formed at a second temperature level, is fed into the heat exchanger in a second region at the second temperature level, and is partially or completely heated in the heat exchanger. A corresponding arrangement and a system with such an arrangement are also covered by the present invention.

Claims

1-15. (canceled)

16. The method for operating a heat exchanger, in which a first operating mode is carried out in first time periods, and a second operating mode is carried out in second time periods that alternate with the first time periods, in the first operating mode, a first fluid flow is formed at a first temperature level, is fed into the heat exchanger in a first region at the first temperature level, and is partially or completely cooled in the heat exchanger, in the first operating mode, a second fluid flow is formed at a second temperature level, is fed into the heat exchanger in a second region at the second temperature level, and is partially or completely heated in the heat exchanger, and in the second operating mode, the feeding of the first fluid flow and of the second fluid flow into the heat exchanger is partially or completely halted, wherein in the second time period, the second region is cooled using cooling fluid that is conducted through passages in or on the heat exchanger in the second region, but not in the first region, which comprises the terminal 30% at the warm end of the heat exchanger.

17. The method according to claim 16, wherein the passages in the second region of the heat exchanger are evaporation passages through which flow occurs, and wherein the cooling fluid is a liquid that is extracted from a container and evaporated in the evaporation passages, wherein gas formed during the evaporation of the liquid is returned to the container, and wherein the liquid is pushed through the evaporation passages by a pressure, built up by the evaporation of the liquid, of the gas in the container.

18. The method according to claim 17, in which an amount to which the liquid in the evaporation passages is evaporated is adjusted by feeding the liquid into the container.

19. The method according to claim 17, in which the pressure, built up by the evaporation of the gas, in the container is adjusted by blowing off gas from the container.

20. The method according to claim 16, wherein the passages are in each case sections of heat exchanger passages running in the heat exchanger, wherein the sections comprise a length of not more than 50% or 40% of a total length of the heat exchanger passages, and wherein the cooling fluid is provided in gaseous form and conducted through the sections of the heat exchanger passages.

21. The method according to claim 16, in which heat is transferred to the first region in the second time period.

22. The method according to claim 21, in which the heat is provided by means of a heat source arranged outside the heat exchanger, and the heat is transferred from outside the heat exchanger to the first region.

23. The method according to claim 22, in which the provided heat is transferred by solid-state thermal conduction via a heat-conducting element contacting the first region.

24. The method according to claim 22, in which the provided heat is transferred to the first region via a gas chamber located outside the heat exchanger, wherein the heat is transferred to the first region via the gas chamber at least partially by convection and/or radiation.

25. The method according to claim 16, in which the heat exchanger is operated within the context of a gas separation method and in which, in the first operating mode, the first fluid flow is supplied at least partially to a rectification process after the partial or complete cooling in the heat exchanger.

26. The method according to claim 17, which uses, as the evaporation passages, at least part of the passages of the heat exchanger conducting the first fluid flow and/or the second fluid flow in the first operating mode, or uses passages formed on an outside of the heat exchanger separately from passages formed within the heat exchanger.

27. An arrangement having a heat exchanger, wherein the arrangement has means configured to carry out a first operating mode in first time periods and to carry out a second operating mode in second time periods that alternate with the first time periods, in the first operating mode, to form a first fluid flow at a first temperature level, to feed it into the heat exchanger in a first region at the first temperature level, and to cool it partially or completely in the heat exchanger, in the first operating mode, to form a second fluid flow at a second temperature level, to feed it into the heat exchanger in a second region at the second temperature level, and to heat it partially or completely in the heat exchanger, and in the second operating mode, to partially or completely halt the feeding of the first fluid flow and of the second fluid flow into the heat exchanger, wherein passages are provided in or on the heat exchanger in the second region, but not in the first region, which comprises the terminal 30% at the warm end of the heat exchanger, and means are provided that are configured to cool the second region in the second time period using cooling fluid that can be conducted through the passages in or on the heat exchanger in the second region, but not in the first region.

28. The arrangement according to claim 27, wherein the passages are provided as evaporation passages through which flow occurs in the second region of the heat exchanger, wherein a container is provided that is configured to receive a cryogenic liquid as the cooling fluid, and wherein means are provided that are configured to extract the liquid from the container and to evaporate it in the evaporation passages, wherein the means are configured to return gas formed during the evaporation to the container and to push the liquid through the evaporation passages by a pressure, built up by the evaporation, of the gas in the container.

29. The arrangement according to claim 27, wherein the passages are in each case sections of heat exchanger passages running in the heat exchanger, wherein the sections comprise a length of not more than 50%, 40%, 30%, or 20% of a total length of the heat exchanger passages, and wherein the cooling fluid can be provided in gaseous form and can be conducted through the sections of the heat exchanger passages.

30. A system, including the arrangement according to claim 27, wherein the system is designed as a gas separation system—in particular, as an air separation system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0078] FIG. 1 illustrates temperature profiles in a heat exchanger after it has been taken out of operation, without the use of measures according to an embodiment of the present invention.

[0079] FIG. 2 illustrates an arrangement with a heat exchanger according to a particularly preferred embodiment of the invention.

[0080] FIG. 3 illustrates an arrangement with a heat exchanger according to a further, particularly preferred, embodiment of the invention.

[0081] FIG. 4 illustrates an air separation system which can be equipped with an arrangement according to an embodiment of the invention.

[0082] In the figures, elements which are identical or correspond to one another in function or meaning are indicated by identical reference signs and, for the sake of clarity, are not explained repeatedly.

DETAILED DESCRIPTION OF THE DRAWINGS

[0083] FIG. 1 illustrates temperature profiles in a heat exchanger after it has been taken out of operation (through which heat exchanger no flow occurs), without the use of measures according to advantageous embodiments of the present invention, in the form of a temperature diagram.

[0084] In the diagram shown in FIG. 1, a temperature at the warm end of a corresponding heat exchanger, denoted by H, and a temperature at the cold end, denoted by C, are each shown in ° C. on the ordinate over a time in hours on the abscissa.

[0085] As can be seen from FIG. 1, at the beginning of the shutdown, the temperature H at the warm end of the heat exchanger, which still corresponds to the temperature in a regular operation of the heat exchanger, is approximately 20° C., and the temperature C at the cold end is approximately −175° C. These temperatures become more equal to each other over time. The high thermal conductivity of the materials installed in the heat exchanger is responsible for this. In other words, heat flows from the warm end towards the cold end here. Together with the heat input from the environment, a mean temperature of approx. −90° C. results. The significant temperature increase at the cold end occurs largely due to the internal temperature equalization in the heat exchanger, and only to a smaller extent due to external heat input.

[0086] As mentioned several times, in the case shown, severe thermal stresses may occur if the warm end of the heat exchanger, after some time of regeneration, is, without further measures, again subjected to a warm fluid of—in the example shown—approximately 20° C. However, thermal stresses may also, correspondingly, occur if a system downstream of the heat exchanger immediately delivers cryogenic fluids again—for example, cryogenic fluids from a rectification column system of an air separation system. However, the present invention relates less or not at all to systems in which the latter problem occurs.

[0087] In FIG. 2, an arrangement with a heat exchanger according to a particularly preferred embodiment of the present invention is illustrated and designated as a whole by 10. The embodiment according to FIG. 2 substantially corresponds to the first embodiment explained above.

[0088] The heat exchanger is provided with reference sign 1. It has a first region 11 and a second region 12, which are here not structurally distinguished from the rest of the heat exchanger 1. The first region 11 and the second region 12 are characterized in particular by the feeding or extraction of fluid flows.

[0089] In the example shown, two fluid flows A and B are conducted through the heat exchanger 1, wherein fluid flow A is previously referred to as the first fluid flow, and fluid flow B is previously referred to as a second fluid flow. The first fluid flow A is cooled in the heat exchanger 1, whereas the second fluid flow B is heated. The fluid flows A and B through the heat exchanger are typically conducted only during normal operation, i.e., the first time period or operating mode explained above. In contrast, the cooling explained below takes place in a second time period or operating mode.

[0090] For further details, reference is made to the explanations above. It should be emphasized in particular that, in the second operating mode explained several times, the corresponding fluid flows A and B do not flow through the heat exchanger, or do not flow through it to the same extent as in the first operating mode. For example, in the second operating mode, fluid flows other than fluid flows A and B can be used, or fluid flows A and B can be used in smaller quantities.

[0091] The heat exchanger 1 can be accommodated in the arrangement 10 in a cold box (not shown), which can, in particular, be partially filled with an insulating material—for example, perlite. A region which is free of the insulating material and simultaneously constitutes a gas chamber surrounding the first region 11 of the heat exchanger 1, is indicated by G.

[0092] In the arrangement 10, a heating device 3 is provided, which heats the first region 11 of the heat exchanger 1 during certain time periods of the second operating mode or during the entire second operating mode. For this purpose, heat H, illustrated here in the form of several arrows, can be transferred by means of the heating device 3 in the arrangement 10 to the first end 11 or the first region 11 of the heat exchanger 1. Although the transfer of heat is illustrated here via the gas chamber G, it can in principle also take place via a—for example, metallic—heat-conducting element if the heating device 3 is designed accordingly. In the first operating mode, no corresponding heat transfer typically takes place. According to the embodiment of the invention illustrated here, the second region 12 of the heat exchanger is cooled, or heat is actively dissipated therefrom, as explained below.

[0093] In the embodiment of the present invention illustrated here, the second region 12 of the heat exchanger 1 is cooled by evaporation of a liquid in evaporation passages 13, which are in heat contact with the second region 12. The liquid is extracted from a container 2, and gas formed during evaporation is partially or completely returned to the container 2. In the embodiment of the invention illustrated here, the liquid is pushed through the evaporation passages 13 by a pressure, built up by the evaporation, of the gas in the container 2. A natural circulation is thus established.

[0094] In the arrangement according to FIG. 2, an amount to which the liquid is evaporated in the evaporation passages 13 is adjusted by feeding the liquid into the container 2 via a feed line F. The feeding of the liquid into the container 2 is regulated by means of a temperature control TC on the basis of a value detected by means of a temperature transducer TI.

[0095] In the embodiment illustrated here, the pressure, built up by the evaporation of the gas, in the container 2 is, furthermore, adjusted by blowing off gas from the container 2, for which purpose a pressure regulation PC with a pressure transducer is used here. This acts on a valve, not separately designated, in an off-gas line O. An appropriate pressure setting furthermore adjusts the evaporation temperature and thus the cooling temperature.

[0096] FIG. 3 illustrates an arrangement with a heat exchanger according to a particularly preferred embodiment of the present invention. The embodiment according to FIG. 3 substantially corresponds to the second embodiment explained above.

[0097] Here as well, the arrangement is designated as a whole by 10. The heat exchanger is again provided with reference sign 1. It has a first region 11 and a second region 12. For further details, reference is made to the explanations relating to FIG. 2.

[0098] In the example shown, two fluid flows A and B are also conducted here through the heat exchanger 1, wherein fluid flow A was previously referred to as first fluid flow, and fluid flow B was previously referred to as second fluid flow. The first fluid flow A is cooled in the heat exchanger 1, whereas the second fluid flow B is heated. The fluid flows A and B through the heat exchanger are typically conducted only during normal operation, i.e., the first time period or operating mode explained above. In contrast, the cooling explained below takes place in a second time period or operating mode.

[0099] Heat exchanger passages 14, only indicated here, each run in the heat exchanger 1 between the first end 11 and the second end 12.

The passages each have sections 14′, which comprise a length of not more than 20% of a total length of the heat exchanger passages 14 between the first end 11 and the second end 12. A cooling fluid C is provided in gaseous form and conducted through the sections 14′ of the heat exchanger passages 14.

[0100] FIG. 4 illustrates an air separation system having an arrangement with a heat exchanger, which arrangement can be operated using a method according to an advantageous embodiment of the present invention.

[0101] As mentioned, air separation systems of the type shown are described many times elsewhere—for example, in H.-W. Häring (ed.), Industrial Gases Processing, Wiley-VCH, 2006—in particular, section 2.2.5, “Cryogenic Rectification.” For detailed explanations regarding structure and operating principle, reference is therefore made to corresponding technical literature. An air separation system for use of the present invention can be designed in a wide variety of ways. The use of the present invention is not limited to the embodiment according to FIG. 4.

[0102] The air separation system shown in FIG. 4 is designated as a whole by 100. It has, inter alia, a main air compressor 101, a pre-cooling device 102, a cleaning system 103, a secondary compressor arrangement 104, a main heat exchanger 105, which can be the heat exchanger 1 as explained above and is in particular part of a corresponding arrangement 10, an expansion turbine 106, a throttle device 107, a pump 108, and a distillation column system 110. In the example shown, the distillation column system 110 comprises a traditional double-column arrangement 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.

[0103] In the air separation system 100, an input air flow is sucked in and compressed by means of the main air compressor 101 via a filter (not labeled). The compressed input air flow is supplied to the pre-cooling device 102 operated with cooling water. The pre-cooled input air flow is cleaned in the cleaning system 103. In the cleaning system 103, which typically comprises a pair of adsorber containers used in alternating operation, the pre-cooled input air flow is largely freed of water and carbon dioxide.

[0104] Downstream of the cleaning system 103, the input air flow is divided into two subflows. One of the subflows is completely cooled in the main heat exchanger 105 at the pressure level of the input air flow. The other subflow is recompressed in the secondary compressor arrangement 104 and likewise cooled in the main heat exchanger 105, but only to an intermediate temperature. After cooling to the intermediate temperature, this so-called turbine flow is expanded by means of the expansion turbine 106 to the pressure level of the completely-cooled subflow, combined with it, and fed into the high-pressure column 111.

[0105] An oxygen-enriched, liquid bottom fraction and a nitrogen-enriched, gaseous top fraction are formed in the high-pressure column 111. The oxygen-enriched, liquid bottom fraction is withdrawn from the high-pressure column 111, partially used as heating medium in a bottom evaporator of the pure argon column 114, and fed, in each case, in defined proportions into a top condenser of the pure argon column 114, a top condenser of the crude argon column 113, and the low-pressure column 112. Fluid evaporating in the evaporation chambers of the top condensers of the crude argon column 113 and the pure argon column 114 is also transferred into the low-pressure column 112.

[0106] The gaseous, nitrogen-rich top product g is withdrawn from the top of the high-pressure column 111, liquefied in a main condenser which produces a heat-exchanging connection between the high-pressure column 111 and the low-pressure column 112, and, in proportions, is applied as a reflux to the high-pressure column 111 and expanded into the low-pressure column 112.

[0107] An oxygen-rich, liquid bottom fraction and a nitrogen-rich, gaseous top fraction are formed in the low-pressure column 112. The former is partially brought to pressure in liquid form in the pump 108, heated in the main heat exchanger 105, and provided as a product. A liquid, nitrogen-rich flow is withdrawn from a liquid-retaining device at the top of the low-pressure column 112 and discharged from the air separation system 100 as a liquid nitrogen product. A gaseous, nitrogen-rich flow withdrawn from the top of the low-pressure column 112 is conducted through the main heat exchanger 105 and provided as a nitrogen product at the pressure of the low-pressure column 112. Furthermore, a flow is withdrawn from an upper region of the low-pressure column 112 and, after heating in the main heat exchanger 105, is used as so-called impure nitrogen in the pre-cooling device 102 or, after heating by means of an electric heater, is used in the cleaning system 103.