METHOD FOR OPERATING AN AIR SEPARATION PLANT, HAVING A DISTILLATION COLUMN SYSTEM, A HEAT EXCHANGER AND AN ADSORBER, AND AIR SEPARATION PLANT

Abstract

A method for operating an air separation plant having a distillation column system, a heat exchanger, and an adsorber, wherein, in a first time period, a first operating mode is carried out and, in a second time period following the first time period, a second operating mode is carried out. In a third time period between the second time period and the first time period, a third operating mode is carried out, in which third operating mode compressed air is at least partially freed of water and carbon dioxide in the adsorber and at least part of said compressed air is cooled in the heat exchanger, an air product is removed from the distillation column system and at least part of said air product is heated in the heat exchanger.

Claims

1-7. (canceled)

8. A method for operating an air separation plant which comprises: a distillation column system; a heat exchanger; and an adsorber, in which in a first time period, a first operating mode is carried out and, in a second time period following the first time period, a second operating mode is carried out, the first and second time periods being carried out multiple times alternately, in the first operating mode, compressed air is at least partially freed of water and carbon dioxide in the adsorber and at least part of said compressed air is cooled in the heat exchanger, in the first operating mode, an air product is removed from the distillation column system and at least part of said air product is heated in the heat exchanger, in the first operating mode, a first end of the heat exchanger is brought to a first temperature level and a second end of the heat exchanger is brought to a second temperature level below 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 are partially or completely suspended, and in the second operating mode, heating of the second end of the heat exchanger to a third temperature level above the second temperature level is allowed, wherein in a third time period between the second time period and the first time period, a third operating mode is carried out, in the third operating mode, compressed air is at least partially freed of water and carbon dioxide in the adsorber and at least part of said compressed air is cooled in the heat exchanger, in the third operating mode, the air product is removed from the distillation column system and at least part of said air product is heated in the heat exchanger, and in the third operating mode, an adjustable portion of the compressed air cooled in the heat exchanger or an adjustable amount of additional compressed air, which is at least partially freed of water and carbon dioxide in the adsorber but is not cooled in the heat exchanger, is fed to the air product before the air product is heated in the heat exchanger.

9. The method according to claim 8, in which a temperature level at which a fluid flow, which is formed from the air product and the portion of the compressed air or the additional compressed air in the third operating mode, is reduced successively in the third operating mode.

10. The method according to claim 9, in which the successive reduction of the second temperature level comprises successively decreasing the portion of the compressed air or the amount of the additional compressed air.

11. The method according to claim 10, in which the adjustment of the portion of the compressed air or the amount of the additional compressed air comprises using an open- and/or closed-loop control device.

12. The method according to claim 8, in which the third operating mode is carried out until the first end of the heat exchanger is again at or close to the first temperature level such that a temperature difference is below a predetermined threshold.

13. The method according to claim 12, in which the distillation column system comprises a low-pressure column and in which a nitrogen-rich and oxygen-containing gas mixture removed from the low-pressure column is used as the air product.

14. An air separation plant which comprises: a distillation column system; a heat exchanger; and an adsorber, the air separation plant being designed to carry out a first operating mode in a first time period and a second operating mode in a second time period which is after the first time period, in the first operating mode, to free compressed air at least partially of water and carbon dioxide in the adsorber and to cool at least part of said compressed air in the heat exchanger, in the first operating mode, to remove an air product from the distillation column system and to heat at least part of said air product in the heat exchanger, in the first operating mode, to bring a first end of the heat exchanger to a first temperature level and a second end of the heat exchanger to a second temperature level below the first temperature level, in the second operating mode, to partially or completely suspend the cooling of the compressed air and the heating of the air product in the heat exchanger, and in the second operating mode, to allow heating of the second end of the heat exchanger to a third temperature level above the second temperature level, wherein the plant is designed in a third time period between the second time period and the first time period, to carry out a third operating mode, in the third operating mode, to free compressed air at least partially of water and carbon dioxide in the adsorber and to cool at least part of said compressed air in the heat exchanger, in the third operating mode, to remove the air product from the distillation column system, and to heat at least part of said air product in the heat exchanger, and in the third operating mode, to feed an adjustable portion of the compressed air cooled in the heat exchanger or an adjustable amount of additional compressed air which is at least partially freed of water and carbon dioxide in the adsorber, but is not cooled in the heat exchanger, to the air product before the air product is heated in the heat exchanger.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] 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.

[0046] FIG. 2 illustrates an arrangement with a heat exchanger.

[0047] FIG. 3 illustrates a further arrangement with a heat exchanger.

[0048] FIG. 4 illustrates an arrangement according to an embodiment of the invention.

[0049] FIG. 5 illustrates an arrangement according to an embodiment of the invention.

[0050] FIG. 6 illustrates an air separation plant which can be operated according to an embodiment of the invention.

[0051] FIG. 7 illustrates a further arrangement with a heat exchanger.

[0052] 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

[0053] FIG. 1 illustrates temperature profiles in a heat exchanger after it has been taken out of operation without the use of measures according to advantageous embodiments of the present invention, in the form of a temperature graph.

[0054] 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.

[0055] 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 converge 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 toward the cold end here. Together with the heat input from the environment, an average temperature of approximately −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.

[0056] As mentioned several times, in the case shown, severe thermal stresses may occur if the warm end of the heat exchanger is again subjected to a warm fluid of approximately 20° C. in the example shown after some time of regeneration without further measures. However, thermal stresses may also correspondingly occur if a plant downstream of the heat exchanger immediately delivers cryogenic fluids again, for example cryogenic gases from a rectification column system of an air separation plant. The present invention addresses in particular the latter problem.

[0057] FIG. 2 illustrates an arrangement with a heat exchanger 1 in which the measures proposed according to the invention are not realized. The heat exchanger 1 has a heat exchange region 10 to which fluids are supplied and from which fluids are removed at a first, i.e. warm end 11 and to which fluids are likewise supplied and from which fluids are removed at a second, i.e. cold end 12. In the example shown, a fluid flow A, in an air separation plant an air product from a distillation column system, is fed to the heat exchanger 1 at the cold end 12, is heated in the heat exchange region 10 of the heat exchanger 1, and is removed again at the warm end 11. The first fluid flow A heats up accordingly. In the illustration according to FIG. 2, a second fluid flow (in an air separation plant compressed air from an adsorber) is also fed to the heat exchanger 1 at the warm end 11 and removed at the cold end 12.

[0058] In this way, different temperature levels, here referred to as “first” and “second” temperature level, result at the warm end 11 and the cold end 12. If the supply of the fluid flows A and B is prevented, the temperatures therefore change correspondingly and in particular the temperature at the cold end 12 increases correspondingly to a “third” temperature level.

[0059] As mentioned several times, when the first fluid flow A is to be fed back to the heat exchanger 1 at the second temperature level, but the cold end 12 of the heat exchanger 1 has been heated to a temperature level significantly above the first temperature level, temperature stresses here would therefore possibly lead to damage to the heat exchanger 1 over a relatively long time.

[0060] FIG. 3 therefore illustrates an arrangement with a heat exchanger 1 according to a non-inventive embodiment of the present invention. For the designation of the respective elements of FIG. 3, reference is made here to the explanations relating to FIG. 2. Here too, a fluid flow A which is formed from an air product can be fed to the heat exchanger 1.

[0061] However, this fluid flow A can be formed as needed using a first output flow A1 and a second output flow A2. In the embodiment according to FIG. 3, the first output flow A1 and the second output flow A2 are branched off from a base flow A0, or the base flow A0 is divided into the output flows A1 and A2. The output flow A1 is used to form the first fluid flow A by restriction by means of a control element 14, which can be actuated in particular by a suitable open- and/or closed-loop control device 2, for example a valve under open- or closed-loop control.

[0062] By contrast, the output flow A2 is guided through and heated in a heater 15. After the heating, the subflow A2 is combined with the subflow A1. An adjustable mixing temperature results. This mixing temperature can be adjusted by adjusting the respective portions of the first and second output flows A1, A2 or an amount of the energy introduced above the heater 15. As mentioned, the temperature level is in particular reduced gradually.

[0063] FIG. 4 illustrates an arrangement with a heat exchanger 1 according to an embodiment of the present invention. In a departure from the arrangement according to FIG. 3, in this case a control element 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 is fed as a second output flow A2 to an output flow A1 and can thus be used to form the fluid flow A which otherwise comprises an air product. Here too, a mixing temperature can be obtained in the manner explained by adjustment or regulation according to a control unit 2.

[0064] In the embodiment according to FIG. 5, in which an arrangement with a heat exchanger 1 according to an embodiment of the present invention is also illustrated, a corresponding control element 14 is provided so that the fluid flow A can be formed from uncooled compressed air, which otherwise is used to form substance flow B, so that here too a corresponding mixing temperature can be obtained.

[0065] FIG. 6 illustrates an air separation plant having a heat exchanger, which can be operated using a method according to an advantageous embodiment of the present invention.

[0066] As mentioned, air separation plants of the type shown are described multiple times elsewhere, for example in H.-W. Haring (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 plant 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. 6.

[0067] The air separation plant shown in FIG. 6 is designated as a whole with 100. It has, inter alia, a main air compressor 101, a pre-cooling device 102, an adsorber 103, a secondary compressor arrangement 104, a main heat exchanger, denoted by 1 like the heat exchanger of FIGS. 2 to 5, 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.

[0068] In the air separation plant 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 adsorber 103. In the adsorber 103, the pre-cooled input air flow is largely freed of water and carbon dioxide.

[0069] Downstream of the adsorber 103, the input air flow is divided into two subflows. One of the subflows is completely cooled in the main heat exchanger 1 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 1, 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.

[0070] 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 f is removed 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.

[0071] The gaseous nitrogen-rich top product is removed 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, applied as a reflux to the high-pressure column 111 and expanded into the low-pressure column 112.

[0072] 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 plant 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 removed from an upper region of the low-pressure column 112 and, after heating in the main heat exchanger 1, 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.

[0073] It is this impure nitrogen, in particular, to which the compressed air can be fed in the third operating mode in the explained embodiments of the invention.

[0074] FIG. 7 shows a further non-inventive arrangement with a heat exchanger 1 which is denoted as a whole by 700. For temperature control, a circulation flow C is used here, which is compressed on the warm side of the heat exchanger by means of a compressor 701, pre-cooled in a cooler 702, fed to the heat exchanger 1 at the warm end 11, removed from the heat exchanger 1 at the cold end 12, expanded by means of a valve 703, fed back to the heat exchanger 1 at the cold end 12, removed again from the heat exchanger 1 at the warm end 11, and fed again to the compressor 701. The expansion at the valve 703 results in gradual cooling.