EP3719428A1 - Method for operating a heat exchanger, assembly with heat exchanger and system with corresponding assembly - Google Patents

Abstract

The invention relates to a method for operating a heat exchanger (1), in which a first operating mode is carried out in first periods of time and a second operating mode is carried out in second periods of time that alternate with the first periods of time, in the first operating mode a first fluid flow ( A) formed at a first temperature level, fed into the heat exchanger (1) in a first area (2) at the first temperature level, and in the heat exchanger (1) is partially or completely cooled, in the first operating mode a second fluid flow (B) formed at a second temperature level, fed into the heat exchanger (1) in a second area (3) at the second temperature level, and partially or completely heated in the heat exchanger (1), and in the second operating mode the feed of the first fluid flow (A ) and the second fluid flow (B) is partially or completely suspended in the heat exchanger (1). Either in the second period of time or in a third period of time that lies between at least one of the second periods of time and the subsequent first period of time, heat is supplied to the first area (2) by means of a heating device ( 7) is provided and in that the heat is transferred from outside the heat exchanger (1) to the first region (2). The second area (3) is operated without active heat dissipation, while the heat is simultaneously supplied to the first area (2) in the second period or in the third period. A corresponding arrangement (10) and a system (100) with such an arrangement (10) are also the subject of the present invention.

Description

The invention relates to a method for operating a heat exchanger, an arrangement with a heat exchanger that can be operated accordingly, and an installation with a corresponding arrangement according to the preambles of the respective independent claims.

State of the art

In a large number of areas of application, heat exchangers (technically more correct: heat exchangers) are used with cryogenic fluids, i.e. Fluids operated at temperatures well below 0 ° C, in particular well below -100 ° C. In the following, the present invention is mainly described with reference to the main heat exchangers of air separation plants, but it is basically also suitable for use in other areas of application, for example for plants for storing and recovering energy using liquid air or natural gas liquefaction or plants in the petrochemical industry.

For the reasons explained below, the present invention is also particularly suitable in plants for liquefying gaseous air products, for example gaseous nitrogen. Corresponding systems can be supplied with gaseous nitrogen, in particular by air separation systems, and liquefy it. The liquefaction is not followed by a rectification, as in an air separation plant. Therefore, when the problems explained below are overcome, these systems can be completely switched off and kept on standby until the next use, for example when there is no need for corresponding liquefaction products.

For the construction and operation of main heat exchangers in air separation plants and other heat exchangers, refer to the relevant specialist literature, for example H.-W. Häring (Ed.), Industrial Gases Processing, Wiley-VCH, 2006 , in particular Section 2.2.5.6, "Apparatus". Details on heat exchangers are general for example the publication " The Standards of the Brazed Aluminum Plate-Fin Heat Exchanger Manufacturers' Association, "2nd Edition, 2000 , in particular Section 1.2.1, "Components of an Exchanger".

Without additional measures, heat exchangers from air separation plants and other heat exchangers through which warm and cryogenic media flow, achieve temperature equalization and heat up when the associated plant is shut down and the heat exchanger is shut down, or the temperature profile that develops in a corresponding heat exchanger in stationary operation can be in such a Case not be held. If, for example, cryogenic gas is then fed into a heated heat exchanger when it is restarted, or vice versa, there are high thermal stresses as a result of different thermal expansion due to differential temperature differences, which can damage the heat exchanger or require a disproportionately high amount of material and manufacturing costs to avoid such To avoid damage.

In particular, when a heat exchanger is shut down before it heats up overall, the temperatures at the previously warm end and at the previously cold end are equalized due to the good thermal conduction (longitudinal heat conduction) in its metallic material. In other words, the previously warm end of the heat exchanger becomes colder over time and the previously cold end of the heat exchanger becomes warmer until the said temperatures are at or near an average temperature. This is also in the attached Figure 1 illustrated again. The temperatures, which were around -175 ° C or +20 ° C at the time of shutdown, equalize over several hours and almost reach an average temperature.

This behavior is observed in particular when, when an air separation plant is switched off, the main heat exchanger, which is housed insulated from the cold, is blocked together with the rectification unit, ie when no more gas is supplied from the outside. In such a case, typically only gas that arises from thermal insulation losses is blown off cold. The same also applies when a system for liquefying a gaseous air product, for example liquid nitrogen, is switched off.

If warm fluid is subsequently fed in at the cooled, warm end of the heat exchanger when it is restarted, the temperature there rises suddenly. Correspondingly, the temperature at the heated, cold end decreases suddenly when the system is restarted if the corresponding cold fluid is fed in there. This leads to the material stresses already mentioned and thus possibly to damage.

The present invention therefore has the object of specifying measures which enable a corresponding heat exchanger, in particular in one of the aforementioned systems, to be restarted after a long period of shutdown without the aforementioned disadvantageous effects occurring.

Disclosure of the invention

Against this background, the present invention proposes a method for operating a heat exchanger, an arrangement with a heat exchanger that can be operated accordingly, and a system with a corresponding arrangement with the features of the respective independent claims.

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

In the parlance used here, a “heat exchanger” is an apparatus which is designed for the indirect transfer of heat between at least two fluid flows, for example, which are guided in countercurrent to one another. A heat exchanger for use in the context of the present invention can be formed from a single or several parallel and / or serially connected heat exchanger sections, for example from one or more plate heat exchanger blocks. A heat exchanger has “passages” which are set up to guide fluid and are separated from other passages by metal dividers or only connected on the inlet and outlet side via the respective headers. The passages are separated from the outside by means of side bars. The passages mentioned are referred to below as “heat exchanger passages”. In the following, following the common usage, the two The terms "heat exchanger" and "heat exchanger" are used synonymously. The same applies to the terms “heat exchange” and “heat exchange”.

The present invention relates in particular to the apparatus referred to in the German version of ISO 15547-2: 2005 as plate-fin heat exchangers. If a “heat exchanger” is used below, this should therefore be understood to mean, in particular, a fin-plate heat exchanger. A fin-plate heat exchanger has a large number of flat chambers or elongated channels lying one above the other, each of which is formed by corrugated or otherwise structured and interconnected, for example soldered plates, usually. made of aluminum, are separated from each other. The panels are stabilized by means of side bars and connected to one another via these. The structuring of the heat exchanger plates serves in particular to enlarge the heat exchange surface, but also to increase the stability of the heat exchanger. The invention particularly relates to brazed fin and plate heat exchangers made of aluminum. In principle, however, corresponding heat exchangers can also be made from other materials, for example from stainless steel, or from various different materials.

As mentioned, the present invention can be used in air separation plants of a known type, but also, for example, in plants for storing and recovering energy using liquid air. The storage and recovery of energy using liquid air is also known as Liquid Air Energy Storage (LAES). A corresponding system is, for example, in the EP 3 032 203 A1 disclosed. Systems for liquefying nitrogen or other gaseous air products are also known from the technical literature and also with reference to the Figure 3 described. In principle, the present invention can also be used in any further systems in which a heat exchanger can be operated accordingly. It can be, for example, plants for natural gas liquefaction and separation of natural gas, the LAES plants mentioned, plants for air separation, liquefaction cycles of all kinds (especially for air and nitrogen) with and without air separation, ethylene plants (i.e. in particular separation plants that process gas mixtures Steam crackers are set up), plants in which cooling circuits, for example with ethane or ethylene on different Pressure levels are used, and systems in which carbon monoxide and / or carbon dioxide cycles are provided act.

At times of high electricity supply, air in LAES systems is compressed, cooled, liquefied and stored in an insulated tank system in a first operating mode with corresponding electricity consumption. At times when the electricity supply is low, the liquefied air stored in the tank system is heated in a second operating mode, in particular after a pressure increase by means of a pump, and thus converted into the gaseous or supercritical state. A pressure flow obtained in this way is expanded in an expansion turbine, which is coupled to a generator. The electrical energy obtained in the generator is fed back into an electrical network, for example.

Corresponding storage and recovery of energy is fundamentally not only possible using liquid air. Rather, other cryogenic liquids formed using air can also be stored in the first operating mode and used in the second operating mode to generate electrical energy. Examples of corresponding cryogenic liquids are liquid nitrogen or liquid oxygen or component mixtures which predominantly consist of liquid nitrogen or liquid oxygen. In corresponding systems, external heat and fuel can also be coupled in to increase efficiency and output power, in particular using a gas turbine, the exhaust gas of which is expanded together with the pressure flow formed from the air product in the second operating mode. The invention is also suitable for such systems.

Classic air separation plants can be used to provide the corresponding cryogenic liquids. If liquid air is used, it is also possible to use pure air liquefaction systems. The term "air processing systems" is therefore also used below as a generic term for air separation systems and air liquefaction systems. The present invention relates in particular to known so-called nitrogen liquefiers.

Advantages of the invention

In principle, cold gas from a tank or exhaust gas from the stationary system can flow through a heat exchanger during a shutdown of the associated system in order to avoid heating or to maintain the temperature profile developed in stationary operation (i.e. in particular the usual production operation of a corresponding system) . Such an operation can, however, only be implemented with great effort in conventional methods.

In certain cases, such as in the U.S. 5,233,839 A proposed that, in order to avoid the cooling of the warm end of a corresponding heat exchanger, an introduction of heat from the environment via thermal bridges can be made there. If there is no process unit downstream of the heat exchanger with a significant buffer capacity for cold (e.g. no rectification column system with the accumulation of cryogenic liquids), such as in a pure air liquefaction system, this type of warming can result in excessive thermal stresses occurring when warm process streams are suddenly supplied to the warm end when restarting be reduced. In this case, for example, after exiting the cold end of the heat exchanger, the supplied warm process streams can be at least partially relaxed in an expansion machine and transferred as cold streams (which in this case, however, do not yet have the low temperature that is present at the cold end in normal operation) the cold end can be returned to the warm end. In this way, the heat exchanger can be slowly brought to its normal temperature profile by means of Joule-Thomson cooling. The present invention relates in particular to this case, that is to say processes in which, after restarting, the cold end of the heat exchanger is not directly acted upon by cold process streams (at the final temperature present in normal operation).

If, however, as is preferably not the case in the context of the present invention, downstream of the heat exchanger there is a process unit with a significant buffer capacity for cold (e.g. a rectification column system with accumulation of cryogenic liquids, as is the case in an air separation plant), then one can use the above-described Measures to minimize the occurrence of thermal voltages at this point, at the same time warmed cold In the end, however, the sudden onset of the flow of colder fluid can lead to the occurrence of thermal stresses due to impermissibly high (temporal and local) temperature gradients. Keeping the warm end warm even promotes the formation of higher temperature differences at the cold end and thus the occurrence of increased thermal stresses.

As mentioned, the present invention relates in particular to the first case explained above. In other words, within the scope of the present invention (in addition to the always provided heating at the warm end of the heat exchanger), the cold end of the heat exchanger is operated without being cooled during standstill phases.

Against this background, the present invention proposes a method for operating a heat exchanger. As will also be explained in detail below, the heat exchanger can in particular be part of a corresponding arrangement, which in turn can be designed as part of a larger system. The present invention can be used in particular in air processing systems of the type explained in detail above and below. In principle, however, it can also be used in other areas of application in which a flow through a corresponding heat exchanger is prevented during certain times and the heat exchanger heats up during these times or a temperature profile formed in the heat exchanger is equalized. In particular, the present invention can be used less in an air separation plant and more in a pure condenser, since in the latter there is no corresponding buffer capacity at the cold end and therefore it is not necessary to keep the cold end cold during standstill phases.

The present invention relates to those measures which avoid excessive thermal stress on the warm end of a heat exchanger. In the context of the present invention, measures of this kind are not combined with further measures aimed at reducing thermal stresses at the cold end of the heat exchanger. Thus, the measures proposed according to the invention and corresponding configurations can offer particular advantages by dispensing with fluidic or non-fluidic cooling of the cold end of the heat exchanger, for example by dispensing with a flow through the cold part of the heat exchanger or its cold end using corresponding cold gas flows. The present invention is based on the knowledge that such cooling is not necessary in the cases mentioned. The operation of the heat exchanger proposed according to the invention offers advantages by dispensing with the measures mentioned, because it reduces the consumption of cold fluids and does not have to be laboriously provided with the corresponding hardware and control technology.

In contrast to temperature control of the warm and cold ends of a corresponding heat exchanger using measures such as those mentioned above U.S. 5,233,839 A are disclosed, the proposed according to the invention keeping the warm end of the heat exchanger warm without cooling at the cold end can be done more easily and inexpensively. This keeping warm can take place within the scope of the present invention using appropriate control and / or regulation strategies on the basis of one or more measured temperatures at the heat exchanger. In the context of the present invention, there is in particular no provision for evaporating gas from one or more storage tanks of the system to flow through a cold end of the heat exchanger or the heat exchanger as a whole during a standstill phase of the system, of which the heat exchanger is part of, as mentioned in the above U.S. 5,233,839 A described. Therefore, corresponding evaporating gas, if present, can be used for other purposes within the scope of the present invention.

The present invention proposes carrying out the method in a first operating mode in first time periods and in a second operating mode in second time periods which alternate with the first time periods. The first time periods and the second time periods do not overlap within the scope of the present invention. The first periods of time or the first operating mode carried out in this first period corresponds within the scope of the present invention to the production operation of a corresponding plant, in the case of an air gas liquefaction plant that is to the operating period in which a liquefaction product is provided, or in the case of an air separation plant would correspond to the according to the invention is less in focus, that Operating mode in which liquid and / or gaseous air products are provided by air separation. Correspondingly, the second operating mode, which is carried out in the second operating time periods, represents an operating mode in which corresponding products are not formed. Corresponding second periods of time or a second operating mode serve in particular to save energy, for example in systems for liquefying and re-evaporation of air products for energy generation or in the previously mentioned LAES systems.

As already mentioned, the heat exchanger is preferably not flowed through in the second operating mode or is flowed through to a significantly lesser extent than in the first operating mode. However, the present invention does not fundamentally rule out that certain quantities of gases are also passed through a corresponding heat exchanger in the second operating mode, although the cold end of the heat exchanger is not cooled, i.e. without an active dissipation of heat. The amount of fluids passed through the heat exchanger in the second operating mode is always well below the amounts of fluids that are passed through the heat exchanger in a regular first operating mode. The amount of fluids passed through the heat exchanger in the second operating mode is within the scope of the present invention, for example, no more than 20%, 10%, 5% or 1% or 0.1%, based on the fluids through the heat exchanger in the first operating mode amount of fluid carried.

In the context of the present invention, the first operating mode and the second operating mode are carried out alternately in the respective periods of time, as mentioned, that is, on a respective first period in which the first operating mode is carried out, a second period in which the second operating mode is always followed is carried out and on the second period or the second operating mode then again a first period with the first operating mode, etc. However, this does not preclude in particular that further periods with further operating modes can be provided between the respective first and second periods, in particular one according to the invention possibly provided third time period with a third operating mode. In the context of the present invention, in the case of a third operating mode, the following sequence results in particular: first operating mode - second operating mode - third operating mode - first operating mode, etc.

In the context of the present invention, in the first operating mode, a first fluid flow is formed at a first temperature level, fed into the heat exchanger in a first area at the first temperature level, and partially or completely cooled in the heat exchanger. In the context of the present invention, in particular a gas or gas mixture that is only to be liquefied and rather less a gas mixture to be broken down by a gas mixture decomposition process can be used as a corresponding first fluid flow, since the invention is more the operation of liquefaction systems for air gases or corresponding air products and less the Operation of (air) separation plants concerns.

Furthermore, in the first operating mode, a second fluid flow is formed at a second temperature level, fed into the heat exchanger in a second area at the second temperature level and partially or completely heated in the heat exchanger. The formation of the second fluid flow can in particular represent the formation of a return flow in a gas liquefaction system. To cool the gas to be liquefied, a part of the pressure flow is expanded to perform work in gas liquefaction systems, is thereby cooled, and used as a refrigerant in a heat exchanger. A second part of the pressure flow, which has not been correspondingly expanded, is liquefied in the heat exchanger due to the pressure and quantity difference present. This is also referring to Figure 3 explained again below.

The second temperature level corresponds in particular to the temperature at which a corresponding return flow is formed in a liquefaction plant. It is preferably at cryogenic temperatures, in particular from -50 ° C to -200 ° C, for example from -100 ° C to -200 ° C or from -150 ° C to -200 ° C. In contrast, the first temperature level is at the first fluid flow is formed and fed to the heat exchanger in the first region, preferably at bypass temperature, but in any case typically at a temperature level well above 0 ° C, for example from 10 ° C to 50 ° C.

If it is mentioned here that a first or second fluid flow is formed at the first or second temperature level, this does not, of course, apply excluded that further fluid flows are formed at the first or second temperature level. Corresponding further fluid flows can have the same or a different composition as or than the fluid of the first or second fluid flow. For example, a total flow can initially be formed, from which the second fluid flow is formed by branching off. Furthermore, within the scope of the present invention, a plurality of fluid flows can optionally also be formed and then combined with one another and used in this way to form the second fluid flow.

If it is said here that a fluid flow in the heat exchanger is "partially or completely" cooled, this is understood to mean that either the entire fluid flow is passed through the heat exchanger, either from a warm end or an intermediate temperature level to the cold end or an intermediate temperature level or vice versa, or that the corresponding fluid flow in the heat exchanger is divided into two or more partial flows that are taken from the heat exchanger at the same or different temperature levels. Of course, it is also possible to feed a further fluid flow to the respective fluid flow in the heat exchanger and to further cool or heat a collective flow formed in this way in the heat exchanger. In any case, however, a corresponding fluid flow is fed into the heat exchanger, specifically at the first or second temperature level, and this is cooled or heated in the heat exchanger (alone or together with other flows as explained above).

It is also understood that in addition to the first and second fluid streams, further fluid streams can also be cooled or heated in the heat exchanger, namely to the same or different temperature levels and / or starting from the same or different temperature levels as the first or the second fluid stream . Corresponding measures are customary and known in the field of air separation, so that reference can be made in this regard to the relevant specialist literature, as cited at the beginning.

In the second operating mode, within the scope of the present invention, the first fluid flow and the second fluid flow are fed into the heat exchanger and the respective cooling or heating in the heat exchanger partially or fully exposed. For example, instead of the first fluid flow, which is passed through the heat exchanger in the first operating mode and is cooled in the heat exchanger, no fluid can be passed through the heat exchanger. The heat exchanger passages of the heat exchanger, which are used in the first operating mode to cool the first fluid flow, remain impervious to flow in this case. However, it is also possible, instead of the first fluid flow, which is passed through the heat exchanger and cooled in the first operating mode, to pass a different fluid flow through the heat exchanger, in particular in a significantly smaller amount. The same also applies to the second fluid flow, which can be replaced by another gas in the second operating mode, but without causing cooling at the cold end of the heat exchanger, i.e. the mentioned second area, within the scope of the present invention.

If the cold end of the heat exchanger is being cooled down, this occurs in particular to the second temperature level at which this cold end is present in the first operating mode. This second temperature level can be set slowly in the context of the present invention, where there is no significant buffer capacity for fluid at the cold end.

According to the invention, it is now provided that in the second or in a third period of time, which lies between at least one of the second periods of time and the subsequent first period of time, heat is supplied to the first area in that this heat is provided by means of a heating device and applied from outside the heat exchanger the first area is transferred. For example, this heat can be provided by means of the heating device and transferred to the first area via a gas space located outside the heat exchanger, or this heat can be fed to the heat exchanger block via a component that contacts the heat exchanger, for example via metallic or non-metallic supports, suspensions or fastenings Solid contact electrical heating tapes can also be used within the scope of the present invention. The heat transfer takes place in the configuration in which the heat is transferred via the gas space, predominantly or exclusively without solid body contact, ie predominantly or exclusively in the form of heat transfer in the gas space, ie without or predominantly without heat transfer by solid heat conduction. The term "predominantly" here denotes a proportion of the amount of heat of less than 20% or less than 10%. In the case of the use of other heating devices such as electrical heating strips, these ratios will of course vary accordingly.

The present invention therefore provides for active heating of the warm end of a corresponding heat exchanger to be carried out in the second period or in a separate further period. The term “outside of the heat exchanger” distinguishes the present invention from alternatively likewise possible heating by means of a targeted fluid flow through the heat exchanger passages. The heating does not take place here by the transfer of heat from a fluid guided through the heat exchanger passages.

In this context, it should be pointed out in particular that when a “region” of a heat exchanger (the first region or the second region) is mentioned, such regions do not refer to the direct feed point of the first or second fluid flow into the heat exchanger must restrict, but that these areas can also in particular represent terminal sections of a corresponding heat exchanger, which can extend a predetermined distance in the direction of the center of the heat exchanger. Corresponding areas can in particular include the terminal 10%, 20% or 30% of a corresponding heat exchanger. Corresponding areas are typically not structurally delimited from the rest of the heat exchanger.

According to the invention, the second area of the heat exchanger is operated without active heat dissipation and thus without being cooled, while the heat is supplied to the first area in the second period or in the third period. The term "active heat dissipation" is intended to denote an intentionally brought about heat dissipation to the environment, for example in that the second area is exposed to, ie contacted or flowed through, a fluid that has a lower temperature than the second area at the time of the fluid exposure. Heat can also be dissipated here, for example, in that heat flows off to colder areas. However, there is no flow of fluid that causes the second region to cool down.

In the context of the present invention, in particular, heating of the second area is permitted, while the heat is simultaneously supplied to the first area in the second period or in the third period. The permitted heating can in particular be more than 10 K, more than 20 K, more than 30 K, more than 40 K or more than 50 K. With a corresponding duration, it can in particular also take place at a temperature to which the first end is heated by the supply of heat in the second period or in the third period. The heating of the second area can in particular also take place at least partially by active heating of the first area and an inflow of heat by conduction. In particular, heat can also be introduced through the surroundings.

In the context of the present invention, the heat transfer by means of the heating device can be transferred to the heat exchanger from outside the heat exchanger passages by solid-state heat conduction via a heat conducting element contacting the first area. This can be done, for example, as already mentioned, via supports or metallic or non-metallic elements as heat conducting elements which contact the heat exchanger and which in turn are heated, for example, by means of a resistive or inductive heater. A corresponding arrangement can in principle as in U.S. 5,233,839 A proposed to be formed. It should be emphasized, however, that the present invention proposes to operate the second region of the heat exchanger in the second time periods or, if necessary, in the third time periods without being cooled. The present invention therefore proposes a new and unobvious method compared to this prior art.

As an alternative to the heat transfer by solid-state heat conduction, the heat provided by the heating device can also be transferred to the first area via a gas space located outside the heat exchanger, as explained, namely at least partially convectively and / or radiatively.

The present invention in the embodiment in which heat is transferred from the heating device to the first region via the gas space located outside the heat exchanger, the particular advantage that, for example in contrast to the one mentioned U.S. 5,233,839 A no suspension of a corresponding area is required, which is provided there for the transfer of heat. In this embodiment, the present invention allows temperature control even in cases in which a heat exchanger block is stored in other areas, for example at the bottom or in the middle, in order in this way to relieve the stresses on the lines that connect a corresponding heat exchanger to the environment to decrease. The method presented in the prior art, on the other hand, can only be used if a corresponding heat exchanger block is suspended from the top. Another disadvantage of the method described in the mentioned prior art compared to the mentioned embodiment of the invention is that heat is only introduced there to a limited extent at the supports and not over the entire surface of a heat exchanger in a corresponding area. This can, for example, lead to icing at the sheet metal jacket transitions of a corresponding heat exchanger. In contrast, the present invention in the mentioned embodiment enables an advantageous introduction of heat and in this way an effective temperature control without the disadvantages described above.

In particular, within the scope of the present invention, as mentioned, it can be provided that the heat is at least partially convective and / or radiative to the first region via the gas space. In particular, gas turbulence can be induced for convective heat transfer, so that heat build-up can be avoided. Pure radiant heating, on the other hand, can act directly on the first area of the first heat exchanger via the corresponding infrared radiation.

As mentioned several times, the method of the present invention is particularly suitable for use in the context of a gas liquefaction process, for example in the context of a process for liquefying nitrogen, air or natural gas, in which a correspondingly liquefied gas mixture is not fed to any decomposition. In other words, the gas liquefaction process provides for the first fluid stream to be at least partially liquefied and undivided, that is to say, in particular, to be provided as a process product in an essentially unchanged material composition. Certain changes, albeit minor changes compared to decomposition, can result from the liquefaction itself due to the different condensation temperatures.

The present invention extends to an arrangement with a heat exchanger, the arrangement having means which are set up to carry out a first operating mode in first periods of time and to carry out a second operating mode in second periods of time which alternate with the first periods of time, in which first operating mode to form a first fluid flow at a first temperature level, to feed it into the heat exchanger in a first area at the first temperature level, and to cool partially or completely in the heat exchanger, in the first operating mode to further form a second fluid flow at a second temperature level, in to feed a second region at the second temperature level into the heat exchanger, and to partially or completely heat it in the heat exchanger, and partially or completely to feed the first fluid flow and the second fluid flow into the heat exchanger in the second operating mode etting.

According to the invention, a heating device is provided which is set up to supply heat to the first area either in the second time period or in a third time period that lies between at least one of the second time periods and the subsequent first time period by providing the heat by means of a heating device and is transferred from outside the heat exchanger to the first area. According to the invention, it is further provided that the second area is operated without active heat dissipation, while the heat is simultaneously supplied to the first area in the second period or in the third period.

For further aspects of such an arrangement, express reference is made to the above explanations relating to the method according to the invention and its configurations. The arrangement according to the invention benefits from the advantages that have been described for corresponding methods and method variants. In the context of the present invention, the heat exchanger is advantageously arranged in a cold box, a gas space through which the heat can be transferred being formed by an area within the cold box free of insulating material. In this case, the first area of the heat exchanger can be arranged in the gas space within the coldbox in particular without suspensions contacting the first area. Reference is also made to the above explanations regarding the relevant advantage.

In the context of the present invention, the heating device can be designed as a radiant heater that can be heated electrically or using heating gas, for example. The heating device can, however, also be designed, in particular, as a resistive or convective heating device, which heats up a heat-conducting element that contacts the first region of the heat exchanger.

The present invention also extends to a plant, which is characterized in that it has an arrangement here as explained above. The plant can in particular be designed as a gas liquefaction plant or, less preferably, as a gas mixture separation plant. It is also distinguished in particular by the fact that it is set up to carry out a method, as was previously explained in embodiments.

The invention is explained in more detail below with reference to the accompanying drawings, which show an embodiment of the invention and corresponding heat exchange diagrams.

Brief description of the drawings

• Figure 1 illustrates temperature profiles in a heat exchanger after shutdown without the use of measures according to an embodiment of the present invention.
• Figure 2 illustrates an arrangement with a heat exchanger according to a particularly preferred embodiment of the invention.
• Figure 3 Fig. 10 illustrates an air liquefaction system that can be equipped with an arrangement according to an embodiment of the invention.

In the figures, identical or functionally or meaningfully corresponding elements are indicated with identical reference symbols and are not explained repeatedly for the sake of clarity.

Detailed description of the drawings

Figure 1 illustrates temperature profiles in a heat exchanger after shutdown (through which there is no flow) without the use of measures according to advantageous embodiments of the present invention in the form of a temperature diagram.

In the in Figure 1 The diagram shown in the diagram shows a temperature labeled H at the warm end of a corresponding heat exchanger and a temperature labeled C at the cold end, each in ° C on the ordinate versus a time in hours on the abscissa.

How out Figure 1 As can be seen, the temperature H at the warm end of the heat exchanger at the start of decommissioning, which still corresponds to the temperature in regular operation of the heat exchanger, is approx. 20 ° C and the temperature C at the cold end is approx. -175 ° C. These temperatures gradually equalize over time. The high thermal conductivity of the materials built into the heat exchanger is responsible for this. In other words, here heat flows from the warm end towards the cold end. Together with the heat input from the environment, this results in an average temperature of approx. -90 ° C. The significant temperature increase at the cold end is largely due to the internal temperature compensation in the heat exchanger and only to a lesser extent due to external heat input.

As mentioned several times, in the case shown there can be strong thermal stresses if the warm end of the heat exchanger is exposed to a warm fluid of approx. 20 ° C. in the example shown after regeneration for some time without further measures. Correspondingly, however, thermal stresses can also arise if a system downstream of the heat exchanger immediately supplies cryogenic fluids again, for example cryogenic liquids from a rectification column system of an air separation system. However, the present invention relates to plants in which the latter problem occurs less or not at all.

In Figure 2 an arrangement with a heat exchanger according to a particularly preferred embodiment of the present invention is illustrated and overall labeled 10. The heat exchanger is provided with the reference number 1. It has a first area 2 and a second area 3, which are each illustrated here by dotted lines, but in reality are not structurally differentiated from the rest of the heat exchanger 1. The first area 2 and the second area 3 are characterized, in particular, by the supply and withdrawal of fluid flows. In the example shown, two fluid flows A and B are passed through the heat exchanger 1, the fluid flow A previously being referred to as the first fluid flow and the fluid flow B being previously referred to as the second fluid flow. The first fluid flow A is cooled in the heat exchanger 1, while the second fluid flow B is heated. For further details, please refer to the explanations above. It should be emphasized in particular that in the second operating mode, which has been explained several times, the heat exchanger is not flowed through by the corresponding fluid flows A and B or not to the same extent as in the first operating mode. For example, in the second operating mode, other than fluid flows A and B or fluid flows A and B can be used in a smaller amount.

The heat exchanger 1 is accommodated in the arrangement 10 in a cold box 4 which is partially filled with an insulating material, for example perlite, which is arranged up to a filling level 6 in the cold box 4 and is illustrated here by hatching. An area free on the insulating material, which at the same time represents a gas space surrounding the first area 2 of the heat exchanger 1, is indicated by 5.

A heating device 7 is provided in the arrangement 10, which heats the first region 2 of the heat exchanger 1 during certain periods of the second operating mode, during the entire second operating mode or, as mentioned, in separate periods of time in a third operating mode. For this purpose, heat, illustrated here in the form of a wavy arrow 8, can be transferred to the first end 2 or the first region 2 of the heat exchanger 1 by means of the heating device 7 in the arrangement 10. Although the transfer of heat via the gas space 5 is illustrated here, this can in principle also take place via a, for example, metallic heat conducting element, if the heating device 7 is designed accordingly. In the first operating mode, there is typically no corresponding heat transfer. The second area 3 of the heat exchanger remains uncooled or no heat is actively dissipated from it.

In Figure 3 an air liquefaction system 100 with an arrangement 10 which has a heat exchanger 1 is illustrated schematically. A corresponding system is also referred to as a "nitrogen liquefier". For further details with regard to the arrangement 10, refer in particular to the one explained above Figure 2 referenced. The air liquefaction system 100 is used, for example, to provide liquid nitrogen or to liquefy gaseous nitrogen. For example, an air separation plant can be provided to provide the gaseous nitrogen.

As explained several times above, the present invention is particularly suitable for use in connection with systems for liquefying gaseous air products, since no further rectification system is connected to them themselves, they can therefore be simplified and put out of operation more frequently if necessary, and after Restarting, there is still no cold fluid available with which the cold end of the heat exchanger 1 is directly applied.

The heat exchanger 1 is also illustrated here with the first area 2 and the second area 3. However, these areas are only indicated here. As explained in detail below, in a first operating mode the heat exchanger 1 is supplied with several first fluids to be cooled in the first area 2 at a first temperature level and passed through the heat exchanger 1, and in the first operating mode several second fluids to be heated are supplied to the heat exchanger 1 fed to the second area 3 at a second temperature level below the first temperature level and passed through the heat exchanger 1. The first fluids are cooled and the second fluids are heated.

The heat exchanger 1 here has a number of heat exchanger passages, which are designated by W to Z. In the first operating mode, which is shown in Figure 3 and which corresponds to normal operation of the liquefaction plant 100, ie a production operation, a gaseous nitrogen stream a is compressed to a liquefaction pressure level together with a nitrogen stream b in a multi-stage compressor arrangement 101, to which a further nitrogen stream c is fed at an intermediate stage. The correspondingly compressed nitrogen is divided into two substreams d and e, of which substream d is fed to the heat exchanger 1 or its first region 2. The partial flow e is divided into two Turbine boosters 102 and 103 are further compressed and then likewise fed to heat exchanger 1 or its first region 2.

In the second region 3, liquefied nitrogen, which is part of the substream e, is withdrawn from the heat exchanger 1. This liquefied nitrogen is flashed into a container 105 via a valve 104. Liquid nitrogen withdrawn from the bottom of the container 105 can be fed in the form of a liquid nitrogen flow f to the warm end of a subcooler 106, which is cooled using a partial flow g of the liquid nitrogen flow f, the amount of which is adjusted via a valve 107. After evaporation in the subcooler 106, the partial flow g is further heated in the heat exchanger 1 and returned to the compression in the form of the nitrogen flow b already mentioned. The remainder of the liquid nitrogen flow f, illustrated here in the form of a liquid nitrogen flow h, can, for example, be delivered as a product or stored in a tank 108.

The turbine boosters 102 and 103 are driven using the partial flow d and a further partial flow of the partial flow e, which is denoted here by i. The substreams d and i are withdrawn from the heat exchanger 1 at suitable intermediate temperatures. The correspondingly relaxed substream d is fed to the heat exchanger 1 at an intermediate temperature, in the heat exchanger 1 with nitrogen, which is withdrawn in gaseous form from the top of the container 106 and fed to the heat exchanger 1 at the cold end, combined, heated and in the form of the already mentioned nitrogen flow c returned to compression. The partial flow i is fed into the container 105 after a corresponding expansion.

It goes without saying that in a second operating mode in which the feeding of the mentioned fluid flows into the heat exchanger 1 is suspended Figure 1 explained temperature compensation begins. Hence they become Figure 2 the measures explained. Since there is no cold-buffering rectification column system on the cold side of the heat exchanger 1, the second area 3 is not immediately exposed to cold fluid when it is restarted, but this can be successively cold-run by the expansion in the valves 104 and 107. Warming up at the warm end is therefore sufficient.

Claims (14)

Method for operating a heat exchanger (1), 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 (A) is formed at a first temperature level, is fed into the heat exchanger (1) in a first area (2) at the first temperature level, and is partially or completely cooled in the heat exchanger (1), - In the first operating mode, a second fluid flow (B) is formed at a second temperature level, is fed into the heat exchanger (1) in a second area (3) at the second temperature level, and is partially or completely heated in the heat exchanger (1), and - In the second operating mode, the feeding of the first fluid flow (A) and the second fluid flow (B) into the heat exchanger (1) is partially or completely suspended, characterized in that - either in the second period of time or in a third period of time, which lies between at least one of the second periods of time and the subsequent first period of time, heat is supplied to the first area (2) by the heat by means of a heating device arranged outside the heat exchanger (1) (7) is provided and by transferring the heat from outside the heat exchanger (1) to the first region (2), and - The second area (3) is operated without active heat dissipation, while the heat is simultaneously supplied to the first area (2) in the second period or in the third period. Method according to Claim 1, in which the second region (3) is allowed to be heated while the heat is simultaneously supplied to the first region (2) in the second period or in the third period. Method according to Claim 1 or 2, in which the heat provided by means of the heating device (7) is transferred by solid-state heat conduction via a heat-conducting element in contact with the first region (2). Method according to Claim 1 or 2, in which the transfer of the heat provided by means of the heating device (7) is transferred to the first region (2) via a gas space located outside the heat exchanger (1), the heat via the gas space (3) at least is transmitted partially convectively and / or radiatively to the first area (2). Method according to one of the preceding claims, in which the heat exchanger (1) is operated as part of a gas liquefaction process. Process according to Claim 5, in which the gas liquefaction process comprises at least partially liquefying the first fluid stream (A) and providing it as a process product without being broken down. Arrangement (10) with a heat exchanger (1), the arrangement (10) having means which are set up for - 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, - to form a first fluid flow (A) at a first temperature level in the first operating mode, to feed it into the heat exchanger (1) in a first region (2) at the first temperature level, and to cool it partially or completely in the heat exchanger (1), - To form a second fluid flow (B) at a second temperature level in the first operating mode, in a second area (3) at the second To feed the temperature level into the heat exchanger (1) and to partially or completely heat it in the heat exchanger (1), and - in the second operating mode, partially or completely suspend the feeding of the first fluid flow (A) and the second fluid flow (B) into the heat exchanger (1), characterized in that - A heating device (7) arranged outside the heat exchanger (1) is provided, which is set up for the first range either in the second time period or in a third time period that lies between at least one of the second time periods and the subsequent first time period (2) supplying heat by providing heat by means of the heating device (7) and transferring it from outside the heat exchanger (1) to the second region (2), and - The second area (3) is operated without active heat dissipation, while the heat is simultaneously supplied to the first area (2) in the second period or in the third period. Arrangement (10) according to Claim 7, in which the heat exchanger (1) is arranged in a coldbox (4), a gas space (5) being formed by an area within the coldbox (4) free of insulating material. Arrangement (10) according to Claim 8, which is set up to transfer the heat provided by means of the heating device (7) via the gas space (5) to the second region (2). Arrangement (10) according to one of Claims 7 to 9, in which the first area (2) of the heat exchanger (1) is arranged in the gas space (5) within the coldbox (4) without suspensions contacting the first area. Arrangement (10) according to Claim 7 or 8, in which the heating device (7) is coupled to the first region (2) via a heat-conducting element. Arrangement (10) according to one of Claims 7 to 11, in which the heating device (7) is designed as a radiant heater and / or as a resistive and / or inductive heater. Plant (100), characterized by an arrangement according to one of Claims 9 to 12, the plant (100) being designed as a gas liquefaction plant. Installation (100) according to claim 13, characterized in that it is set up to carry out a method according to one of claims 1 to 6.

Images