WO2020011396A1

WO2020011396A1 - Method for operating a heat exchanger, arrangement comprising a heat exchanger, and air processing system comprising a corresponding arrangement

Info

Publication number: WO2020011396A1
Application number: PCT/EP2019/025222
Authority: WO
Inventors: Reinhold Hölzl; Pascal Freko; Alexander WOITALKA; Patrick Haider
Original assignee: Linde Aktiengesellschaft; Technische Universität München
Priority date: 2018-07-13
Filing date: 2019-07-11
Publication date: 2020-01-16
Also published as: EP3594596A1

Abstract

The invention relates to a method for operating a heat exchanger (100), which has a heat exchange zone (10), which extends between a first end (11) and a second end (12) and which has a plate stack comprising heat exchange plates (4), wherein a width of the heat exchange plates (4) and a height of the plate stack each equals one third to one fifth the length of the heat exchange plates (4) between the first end (11) and the second end (11). After decommissioning and reaching a temperature-compensated state, fluids, which are each directed through the heat exchange zone (10) at a first quantity per unit of time during normal operation, are first each directed through the first heat exchange zone (10) during restarting, up to a time of increase, at a second quantity per unit of time, which is lower than the first quantity per unit of time, and each directed through the first heat exchange zone (10) at the first quantity per unit of time only starting from the time of increase. The invention further relates to a corresponding arrangement, which is in particular designed as an air processing system.

Description

description

Method for operating a heat exchanger, arrangement with a heat exchanger and air processing system with a corresponding arrangement

The invention relates to a method for operating a heat exchanger and an arrangement with a correspondingly operable heat exchanger according to the preambles of the respective independent claims.

State of the art

Heat exchangers with cryogenic fluids, i.e. Operate fluids at temperatures significantly below 0 ° C, in particular significantly below -100 ° C. In the following, the present invention is mainly described with reference to the main heat exchangers (also referred to as “main heat exchangers” or “main heat exchangers”) of air separation plants, but in principle it is also suitable for use in others

Areas of application, for example for systems for storing and recovering energy using liquid air or natural gas liquefaction. The term "heat exchanger" is used routinely, even if strictly speaking no "exchange" of heat takes place in such an apparatus.

For the reasons explained below, the present invention is also particularly suitable in systems for liquefying gaseous air products, for example gaseous nitrogen. Corresponding plants can be supplied with gaseous nitrogen and liquefy it, in particular by air separation plants. The liquefaction is not like in a

Air separation plant, a rectification downstream. Therefore, when the problems described below are overcome, for example when there is no need for corresponding liquefaction products, these systems can be switched off completely and kept in standby until the next use.

For the construction and operation of main heat exchangers of air separation plants and other heat exchangers, reference is made to 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 in general can be found, for example, in 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".

Heat exchangers heat up without additional measures

Air separation plants and other heat exchangers flowed through with warm and cryogenic media when the associated plant and thus the

Decommissioning of the heat exchanger, or the temperature profile forming in a corresponding heat exchanger, cannot be maintained in such a case. If, for example, fluid is subsequently fed back into a heated or, as explained below, temperature-balanced heat exchanger, this fluid has a large temperature difference from the local one

Has metal temperature, this causes high thermal stresses due to the thermal expansion or contraction of the metal, which can lead to damage to the heat exchanger or require a disproportionately high cost of materials or manufacturing. This applies both when warm fluid meets colder metal and when cold fluid meets warmer metal.

In particular, when a heat exchanger is decommissioned before it heats up overall, due to the good heat conduction (longitudinal heat conduction) in its metallic material, the temperatures at the previously warm end and at the previously cold end are equalized. In other words, the previously warm end of the heat exchanger becomes colder over time and the previously cold end of the heat exchanger warmer until the temperatures mentioned are at or close to an average temperature. This is also illustrated again in the attached FIG. 1. The temperatures, which were around -175 ° C or +20 ° C at the time of decommissioning, converge over several hours and reach almost a medium temperature. However, this average temperature is still significantly below the ambient temperature, in particular if the heat exchanger as a whole is housed in a temperature-insulated housing. The heat exchanger only warms up to the ambient temperature over a much longer period. This case relates to the present invention. This behavior is observed in particular when the main heat exchanger, which is housed in a cold-insulated manner, is blocked together with the rectification unit when an air separation plant is switched off, ie when no more gas is supplied from the outside. In such a case, typically only gas that is produced due to thermal insulation losses is blown off cold. The same also applies if a system for liquefying a gaseous air product, for example liquid nitrogen, is switched off.

If there is a subsequent supply of warm fluid on

cooled warm end of the heat exchanger when it is restarted, the temperature suddenly increases there. The decreases accordingly

The temperature at the warmed up cold end when restarting, if appropriate cold fluid is fed in, suddenly. This leads to the material stresses already mentioned and thus possibly to damage.

According to US 2017/0292783 A1, a wound heat exchanger used in liquefying natural gas is slowly shut down in order to reduce temperature stresses. Both the temperature gradients and the

Temperature differences between the warm and the cold currents are kept within acceptable limits. US 2002/017468 A1, US 3,469,271 A and DE 10 2009 042994 A1 also relate to methods for operating heat exchangers or corresponding arrangements with heat exchangers.

The present invention therefore has as its object to provide measures which require certain heat exchangers to be restarted after a prolonged period

Enable decommissioning without the adverse effects mentioned, for use in cases in which the temperatures at the hot and cold ends of the heat exchanger have at least partially adjusted to one another after decommissioning, but still significantly below that

Ambient temperature.

Disclosure of the invention

Against this background, the present invention proposes a method for operating a heat exchanger and an arrangement with a correspondingly operable Heat exchanger, in particular as an air treatment plant, plant for storing and recovering electrical energy or plant for

Liquefaction of an air product can be designed with the features of the respective independent claims. Refinements are in each case

Subject of the dependent claims and the following description.

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

A "heat exchanger" in the parlance used here is an apparatus which is used for the indirect transfer of heat between at least two e.g. fluid flows guided in countercurrent to one another. A heat exchanger for use in the present invention may be formed from a single or a plurality of heat exchanger sections connected in parallel and / or in series, e.g. from one or more plate heat exchanger blocks. A heat exchanger has “passages” which are set up for fluid guidance and are fluidically separated from other passages or are only connected on the input and output sides via the respective headers. These are referred to below as "heat exchanger passages". The terms "heat exchanger" and "heat (exchanger)" are often used synonymously in the professional world. This also applies here.

The present invention relates to the apparatus referred to as plate fin heat exchangers in accordance with the German version of ISO 15547-2: 2005. If the term "heat exchanger" is used below, it is understood to mean a fin-plate heat exchanger. A finned plate heat exchanger has a plurality of superimposed flat

Chambers or elongated channels, which are each separated by corrugated or otherwise structured and interconnected, for example soldered plates, usually made of aluminum. The plates are stabilized by means of side bars and connected to each other. The structuring of the heat exchanger plates serves in particular to increase the heat exchange area, but also to increase the stability of the heat exchanger. The invention relates in particular to brazed aluminum fin-plate heat exchangers. As mentioned, the present invention can be used in air separation plants of known type, but also, for example, in plants for storing and recovering energy using liquid air and in plants for liquefying gaseous air products. The storage and recovery of energy using liquid air is also referred to as Liquid Air Energy Storage (LAES). A corresponding system is disclosed, for example, in EP 3 032 203 A1.

At times of high electricity supply, air is compressed, cooled, liquefied and stored in an insulated tank system in a first operating mode in a first operating mode. At times of low electricity supply, 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 stream obtained in this way is expanded in an expansion turbine which is coupled to a generator. The electrical energy obtained in the generator is

for example fed back into an electrical network.

Appropriate storage and recovery of energy is fundamentally not only possible using liquid air. Rather, other cryogenically formed using air can also be used in the first operating mode

Liquids are stored and used in the second operating mode for the generation of electrical energy. Examples of corresponding cryogenic

Liquids are liquid nitrogen or liquid oxygen or

Component mixtures consisting mainly of liquid nitrogen or liquid oxygen. In corresponding systems, external heat and fuel can also be coupled in in order to increase the efficiency and the output power, in particular using a gas turbine, the exhaust gas of which is expanded together with the pressure stream formed from the air product in the second operating mode. The invention is also suitable for such systems.

Classical can be used to provide appropriate cryogenic liquids

Air separation plants are used. If liquid air is used, it is also possible to use pure air liquefaction systems. As a generic term for Air separation plants and air liquefaction plants, the term "air treatment plants" is therefore also used below.

Advantages of the invention

Basically, a heat exchanger can be flowed through with cold gas from a tank or exhaust gas from the stationary system during a standstill of the associated system in order to avoid heating or the developed one

Keep temperature profile. However, such an operation is conventional

The process may only be complex to implement.

Especially with small amounts of corresponding cold gases or small

Flow velocities in the heat exchanger can result in an incorrect distribution within a heat exchanger block and in particular over several

Heat exchanger blocks cannot be excluded. In principle, however, it is desirable to keep the amounts of gas used low in order to

For example, to avoid product losses or the consumption of appropriate cryogenic media. Furthermore, implementation is more appropriate

Measures always require certain amounts of fluids that are additionally used to temper an appropriate heat exchanger.

The present invention proposes a method for operating a

Heat exchanger, which has a heat exchange zone, which extends between a first end and a second end, and which has a plate stack of heat transfer plates, the heat transfer plates, as is customary in this regard for fin-plate heat exchangers, structured (profiled, corrugated and, if necessary have perforated) sheets and corresponding edge bars (English sidebars). A parallelepiped-shaped block is formed by a corresponding plate stack, which block has corresponding headers for feeding and removing fluids, as is common practice. The heat exchanger operated according to the invention is, as mentioned, a fin-plate heat exchanger of a known type.

The present invention is applied to a heat exchanger in which a width of the heat transfer plates and a height of that formed therefrom

Plate stacks in the heat exchange zone between one fifth and one each Is a third of the length of the heat transfer plates between the first end and the second end. The width of the heat transfer plates is a dimension in a direction that is perpendicular to a main flow direction of the fluids through the heat exchanger or orthogonal to a shortest connection between the first and the second end and in a plane of the respective heat exchanger plates. The stack height denotes the added heights of the respective

Heat exchanger plates perpendicular to their plane.

The present invention thus already differs in this point from known methods for operating wound heat exchangers. In a wound heat exchanger, completely different temperature compensation phenomena occur than in a finned plate heat exchanger, because here the wound ones

Heat exchanger tubes or capillaries are also subjected to heat exchange with adjacent tubes or capillaries, but primarily with the surrounding jacket space, in which a gaseous medium to be heated typically flows. By wrapped in one

Heat exchangers present overall in a smaller proportion and in particular less rigid material transitions can be exposed to this, if necessary, significantly harsher temperature gradients. It is therefore not obvious to transfer suitable measures for a wound heat exchanger to a fin-plate heat exchanger. The specialist would have been prevented by the fundamentally different boundary conditions here.

In the context of the present invention, however, it was recognized that the measures proposed and explained below can also be used to operate a fin-plate heat exchanger with significantly reduced temperature voltages, provided that the dimensions are suitable for this purpose, even if none occurs during a standstill additional measures to

Maintenance of the temperature profile can be taken.

An appropriately dimensioned heat exchanger ensures that even with a significant reduction in the feed quantity, it is still sufficiently homogeneous

Temperature distribution over the entire cross-sectional area of the heat exchanger can adjust. In other words, even with reduced fluid feed, this can result in any cross-sectional plane between the first end and the second In the end, a temperature distribution can be achieved in which a maximum temperature and a minimum temperature do not differ by more than 20, 10 or 5 K.

The present invention proposes that, in a first operating mode, fluids are provided at different feed temperature levels and are each passed through the heat exchange zone in a first quantity per unit of time, thereby bringing the first end of the heat exchange zone to a first temperature level and the second end of the heat exchange zone to second temperature level, which is in particular below the first temperature level, is brought. The feed temperature levels are those at which the corresponding fluids are also fed into the heat exchanger or are fed to the heat exchanger at the first or second end. They comprise a first feed temperature level of a fluid to be cooled and a second feed temperature level of a fluid to be heated, the first feed temperature level in the case of an air separation plant in particular at ambient temperature or at 0 to 30 ° C. and the second

Feed temperature level at -100 to -200 ° C, for example at -120 to - 180 ° C. Further fluids can also be provided at this or further feed temperature levels at any time and passed through the heat exchanger in appropriate amounts.

The first temperature level, to which the first end of the heat exchange zone is brought, and the second temperature level, to which the second end of the heat exchange zone is brought, result in particular from the feed temperature levels mentioned. They are close to these, i.e. in particular, they reject them by no more than 20 ° C. or no more than 10 ° C.

Such a first operating mode corresponds to normal operation of the

Heat exchanger, which is used for the temperature control of corresponding fluids, which can be provided in the form of one or more identical or different fluid flows. As is customary in this respect, at least one first fluid to be cooled is passed through the heat exchange zone from the first to the second end and at least one second fluid to be heated is passed from the second to the first end. Corresponding temperature levels can in particular be at least partially in a cryogenic range. So the first temperature level in particular at 0 to 100 ° C, for example at about 20 ° C and the second temperature level in particular at -100 to -200 ° C, for example at about -175 ° C.

Within the scope of the method proposed according to the invention, in a second operating mode, the passage of the fluids, which are passed through the heat exchange zone in the first amount per unit time in the first operating mode, is at least partially prevented. A corresponding heat exchanger can also be completely "blocked in", i.e. it won't

Fluid flow more carried out and any existing, evaporating fluid is removed. A corresponding heat exchanger can be arranged in a so-called cold box, in particular together with other apparatus. A corresponding decommissioning can be particularly advantageous in the case of a plant for the liquefaction of a gaseous air product, for example gaseous nitrogen, since this is not connected to a rectification column system like an air separation plant.

By at least partially preventing the passage of the fluids, a temperature transition from the first end to the second end of the

Heat exchange zone or an increasing temperature compensation, as it has already been explained several times, causes. For further details, reference is made to FIG. 1 and the associated explanations below. The time period is selected in the context of the present invention such that a

Heat conduction between the first end and the second end of the

Heat exchange zone at the first end of the heat exchange zone set a third temperature level and at the second end of the heat exchange zone a fourth temperature level.

A difference between the first temperature level and the second

The temperature level in the case considered in the context of the present invention is always greater than a difference between the third

Temperature level and the fourth temperature level. In the second operating mode, therefore, a certain temperature compensation occurs, which can also have the effect that the third and fourth temperature levels are the same or at least do not differ by more than 50, 40, 30, 20 or 10 K. In particular, the invention does not relate to the fully heated state of a corresponding heat exchanger. Thus, an average value between the third temperature level and the fourth temperature level does not deviate by more than 50, 40, 30, 20 or 10 K from an average value between the first temperature level and the second temperature level. The two mean values are therefore similar or the same and differ only because of a temperature input (which is significantly slower than the heat balance between the warm and the cold end). In an air separation plant, the two mean values in particular both lie in the cryogenic range, in particular at less than -50 ° C. and up to -100 ° C. A temperature difference between the first and the second temperature level can be more than 150 K in particular. When operating fluids are fed in at regular temperatures, as explained above, this has the effect that they meet the heat exchanger or its first and second ends with a temperature difference of more than 50 or 75 K, which results from the respective feed temperature levels. In the context of the present invention, the mean value between the third and fourth, and thus also between the first and the second temperature level, deviates in particular by more than 50 K and up to 100 K from the closest feed-in temperature level (which may be above or below) ,

In the method, the system switches repeatedly from the first operating mode to the second operating mode and from the second operating mode to the first operating mode. Corresponding switching processes can in principle take place in different systems, but they are particularly important in systems in which an alternating mode of operation takes place routinely, for example systems for storing and recovering electrical energy using liquid air or other liquid air products. The present invention is particularly advantageous in plants of this type.

In principle, the present invention can be used in any system in which a heat exchanger can be operated accordingly. For example, plants for liquefaction and separation of natural gas, the aforementioned LAES plants, plants for air separation,

Liquefaction circuits of all kinds (especially for air and nitrogen) with and without air separation, ethylene plants (in particular separation plants that are set up to process gas mixtures from steamer racks), 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.

In the context of the present invention, it is provided that the switchover from the second operating mode to the first operating mode includes the fluids that flow through the first amount per unit time in the first operating mode

Heat exchange zone are to be conducted through the heat exchange zone in a second quantity per unit of time, which is less than the first quantity per unit of time, until a point in time of elevation and only through the first heat exchange zone in the first quantity per unit of time from the time of increase. It goes without saying that the switchover from the second operating mode can also take place in the form of a gradual or ramp-shaped transition. Even in such a case, the second quantity per unit of time (with the ramp-shaped increase) is less than the first quantity per unit of time (after the increase). Ramps with different gradients, gradients with ramps and plateaus and the like can also be used. The same applies to a ramp-like increase after the time of the increase.

The present invention is based on the knowledge that the thermally induced voltages when restarting in a suitable manner

dimensioned fin-plate heat exchanger from one

temperature-balanced state, as may be present in particular after longer phases of an explained second operating mode, can strongly depend on the speed of the restart. While high mass flows can lead to high thermal voltages, the thermal stress can be significantly reduced at low start-up speeds with sufficiently small mass flows. More is particularly below with reference to Figure 3

illustrated. As mentioned, the present invention exerts its effects in the heat exchangers explained above, since here a sufficiently balanced temperature profile can also be achieved in cross-section through the heat exchange zone by means of a sufficiently fast cross conduction.

Since cold and warm currents mostly in countercurrent to one another

appropriate heat exchanger are conducted, the temperature profile at Starting of the apparatus from the two ends starting with progressive time to the interior of the heat exchanger or its heat exchange zone. In sensitive areas, which are typically located in the terminal areas of a corresponding heat exchange zone, for example in a sensitive area of module connections, the heat exchanger already has the largest areas occurring during the transition to normal operation

If temperature changes are experienced, only reduced gradients and thus reduced thermal stresses occur in the further course. The present

The invention therefore proposes, with the above-mentioned measures, first to guide fluids through the heat exchange zone with a smaller amount per unit of time and only afterwards, namely to increase the amount or to increase the amount, if the temperature has already changed sufficiently in corresponding sensitive areas set maximum amount.

The present invention enables a significant service life optimization or improvement of fin-plate heat exchangers during restart processes from temperature-balanced conditions or at high temperature differences between incoming currents and metal temperatures of the heat exchanger.

Commissioning procedures proposed according to the invention are particularly also for existing topologies (possibly by retrofitting

Surface temperature measurements or sensors and / or corresponding sensors at entry and / or exit points of the heat exchanger, in particular in

Connection to turbines) feasible, since the present invention can be implemented essentially to optimize the dynamic approach.

In particular, the main heat exchangers of air separation plants can be operated in a load-flexible manner (for

Resist exploitation of e.g. electricity market prices) better over the life of the system. In this way, the present invention makes it possible to avoid unplanned downtimes, repair costs and procurement of spare parts.

The mode of operation of a corresponding system proposed according to the invention can be observed operationally, for example by means of surface temperature measurements. The start-up process can thus be monitored and the time at which the start-up process can be accelerated can be well predicted. A corresponding time of increase can therefore be determined in the context of the present invention at least in part on the basis of one or more temperature measurements at one or more points in the heat exchange zone.

It is particularly advantageous here if such temperature measurements relate to a sensitive zone such as the aforementioned area of the module connection. However, other sensitive areas resulting from the design of the heat exchanger can also be taken into account within the scope of the present invention. On

the corresponding area can be defined in particular by means of a longitudinal coordinate which corresponds to the end of a module connection. A measurement at another location is also possible in principle, provided that a temperature at a corresponding sensitive location can be inferred in this way, for example on the basis of known material properties and possibly

Model calculations regarding heat spread and fluid dynamics. In particular, one or more can be within the scope of the present invention

Surface temperature sensors are used that can be easily and inexpensively retrofitted in existing heat exchangers.

Is a corresponding heat exchanger, for example, characterized with sufficient accuracy with regard to material and thermal properties, and are

Known temperatures and fluid flows used, can possibly also on a

Temperature measurement can be dispensed with, because it can be assumed that after a certain time in the sensitive zones, a corresponding one

Temperature value is reached. Therefore, as an alternative or in addition, it is also possible to base the increase in time at least in part on the basis of a period of time that has elapsed since the switchover was initiated and / or on the basis of the start of the supply of the fluids that are used in the second operating mode in the second quantity per unit time to set the elapsed period. It is also possible, for example, to base the switchover time on a

To determine the total amount of fluids that are used in the second operating mode in the second amount per unit of time.

As mentioned several times, the present invention unfolds its particular advantages when the heat exchanger is designed as a fin-plate heat exchanger. Such a fin-plate heat exchanger can be made in particular of aluminum and / or stainless steel. A corresponding heat exchanger can also for example, be produced by means of 3D printing. Especially with such

Heat exchangers may experience the mentioned potentially high thermal stresses during repeated start-up processes.

The method according to the invention can be used particularly advantageously when the heat exchange zone has a first terminal partial zone extending from the first end, a second terminal partial zone extending from the second end and a central partial zone arranged between the first terminal partial zone and the second terminal partial zone has, the

The point in time of the increase is determined to be reached when it is determined or predicted that one or more temperature values in at least one of the terminal sub-zones will exceed or fall below a predetermined temperature.

In particular, the heat exchanger can have a number of modules which are connected to one another by means of module connections, one or more of the module connections being or being arranged in the terminal sub-zones, and the central sub-zone being free of the module connections. Due to the slow approach, the present invention permits targeted protection of the areas with the module connections or other sensitive zones, that is to say the first and second terminal partial zones, which are particularly critical with regard to rapid temperature changes. Module connections are particularly due to their

Notch effect particularly critical, but the terminal end zones are fundamentally sensitive to thermally induced stresses, even if none

Module connection are available. For details, please refer to the explanations above.

In the method according to the invention, as mentioned, the point in time of the increase can in particular be determined to be reached when it is determined or predicted that one or more temperature values in at least one of the terminal sub-zones will exceed or fall below a predetermined temperature. More precisely, in such a case, the time of the increase can be defined as reached if it is determined or predicted that one or more temperature values in the first terminal sub-zones exceed a predetermined temperature and / or if it is determined or predicted that one or more temperature values in the fall below a predetermined temperature in the second terminal sub-zones. The changeover between the first and the second quantity per unit of time can take place suddenly or gradually. In other words, in a particularly preferred embodiment of the present invention, switching from the second operating mode to the first operating mode may include an amount per unit time of the fluids that are conducted through the heat exchange zone in the first operating mode in the first amount per unit time the

Increase the time of increase continuously or gradually. In this way, temperature jumps can be further reduced.

For clarification, it is stated that in a method of the present invention, in particular in the first operating mode, one or more first fluids are fed to the heat exchange zone at its first end at the first temperature level, passed through the heat exchange zone and removed from the heat exchange zone at its second end at the second temperature level is or will be, and that in the first mode of operation one or more second fluids are supplied to the heat exchange zone at its second end at the second temperature level, passed through the heat exchange zone and removed from the heat exchange zone at its first end at the first temperature level.

The present invention also extends to an arrangement with a

Heat exchanger which has a heat exchange zone which extends between a first end and a second end and which has a plate stack of heat transfer plates, wherein a width of the

Heat transfer plates and a height of the plate stack in the

Heat exchange zone each a fifth to a third of a length of the

Heat transfer plates between the first end and the second end. According to the present invention, technical means are provided which are set up to operate different fluids in a first operating mode

Feed temperature levels are provided and each in a first amount per unit of time through the heat exchange zone, whereby the first end of the heat exchange zone to a first temperature level and the second end of the heat exchange zone to a second temperature level, which is in particular below the first temperature level, whereby technical Means are provided which are set up to operate the in a second operating mode The passage of the fluids, which are conducted through the heat exchange zone in the first operating mode in the first quantity per unit of time, at least partially and for a period of time which is dimensioned such that heat conduction between the first end and the second end of the

Heat exchange zone sets a third temperature level at the first end of the heat exchange zone and a fourth temperature level at the second end of the heat exchange zone, with a difference between the first

Temperature level and the second temperature level is greater than a difference between the third temperature level and the fourth temperature level and an average value between the third temperature level and the fourth temperature level does not deviate by more than 50 K from an average value between the first temperature level and the second temperature level. The invention provides that technical means are provided which are set up to switch several times in the method from the first operating mode to the second operating mode and from the second operating mode to the first operating mode.

The arrangement is characterized by technical means which are set up to carry out the switching from the second operating mode to the first operating mode in such a way that the fluids which are passed through the heat exchange zone in the first amount in each case in the first quantity per unit of time at a time of increase, are first passed through the first heat exchange zone in a second amount per time unit, which is less than the first amount per time unit, and are only passed through the first heat exchange zone in the first amount per time unit from the time of increase.

For features and advantages of a corresponding arrangement, which is set up in particular to carry out a method as explained above, reference is expressly made to the above statements. In particular, such a system has a control device which is designed, if necessary, for example according to a fixed switching pattern, on the basis of a sensor signal or

Request to switch between the first and the second operating mode. A corresponding arrangement can in particular have suitable sensors, in particular temperature and / or strain sensors. As mentioned, the present invention also extends to an arrangement which has means for the liquefaction and / or low-temperature separation of air and / or at least one gaseous air product. According to the invention, this is characterized in that it represents an arrangement with a heat exchanger, as has just been explained. In particular, the arrangement can be designed as an air separation plant. In this case, it comprises a distillation column system

fundamentally known type. A corresponding arrangement can in particular also be designed as a system for storing and recovering energy. A corresponding arrangement can also be designed as a plant for the liquefaction of nitrogen or as another plant of the type explained above. Regarding features and advantages, reference is made to the above explanations regarding the method according to the invention.

The invention is explained in more detail below with reference to the accompanying drawings, which illustrate an embodiment of the invention and corresponding

Show heat exchange diagrams.

Brief description of the drawings

Figure 1 illustrates temperature profiles at the warning and cold end of a heat exchanger operable according to the invention after decommissioning.

Figure 2 illustrates a finned plate heat exchanger that can be operated using a method according to an embodiment of the invention.

Figure 3 illustrates a relationship between fluid flows and thermal stresses in a fin-plate heat exchanger.

Figure 4 illustrates temperature gradients in a fin-plate heat exchanger at different times of flow.

FIG. 5 illustrates a nitrogen liquefaction plant that can be operated using a method according to an embodiment of the invention In the figures, elements that are identical or correspond to one another functionally or in terms of meaning are given identical reference numerals and are not explained repeatedly for the sake of clarity.

Detailed description of the drawings

Figure 1 illustrates temperatures in a heat exchanger, particularly a finned plate heat exchanger, after decommissioning, i.e. in a previously and subsequently also referred to as "second operating mode" operating mode, in which the passage of fluids through the heat exchanger is prevented, in the form of a temperature-time diagram.

The temperature-time diagram shown in FIG. 1 shows a temperature denoted by H (also referred to here as "first temperature level") at the warm end of the heat exchanger or its heat exchange zone ("first end") and a temperature denoted by C ( "second temperature level") at the cold end ("second end") each in ° C on the ordinate versus a time in hours on the abscissa.

As can be seen from FIG. 1, the temperature H at the first (warm) end of the heat exchange zone at the beginning of the decommissioning, and thus the temperature during regular operation of the heat exchanger or at the end of the operating mode referred to above and below as the "first operating mode", in the corresponding fluid is passed through the heat exchanger, approx. 20 ° C and the temperature C at the second (cold) end approx. -175 ° C. These temperatures become increasingly similar over time. The high thermal conductivity of the materials used in the heat exchanger is responsible for this. In other words, heat flows from the first (warm) end towards the second (cold) end. Together with the heat input from the environment, this results in a

Temperature level at the first end ("third temperature level") and a

Temperature level at the second end ("fourth temperature level") and an average temperature of approx. -90 ° C. The significant temperature increase at the second (cold) end of the heat exchange zone is largely due to the internal one

Temperature compensation in the heat exchanger and only to a lesser extent through external heat input. As mentioned several times, it can be too strong thermal in the case shown

Tensions arise when the first (warm) end of the heat exchanger is again exposed to a warm fluid of approximately 20 ° C. in the example shown after some time in the second operating mode.

The same applies to a second (cold) end.

FIG. 2 illustrates a fin-plate heat exchanger which can be operated using a method according to an embodiment of the invention, but which is only for illustration purposes with a significantly higher one

Plate stack is shown. This is designated by a total of 100 and is fundamentally designed in a known manner, as documented, for example, in the specialist literature mentioned at the beginning. The heat exchanger is designed for heat exchange between two fluids. However, the present invention can in particular also be designed to operate corresponding heat exchangers in which more than two fluids are subjected to heat exchange.

In the example shown, the heat exchanger 100 is constructed from two modules 1, 2, which can in principle be configured identically. Instead of two modules 1, 2, heat exchangers with more than two modules can also be used within the scope of the present invention. In the example shown, the modules 1, 2 are connected to one another by means of module connections, which, however, are only provided at the two ends of the two modules 1, 2. The module connections 1, 2 can be designed, for example, as elements which are each soldered to the modules 1, 2.

The modules 1, 2, alternatively also a corresponding heat exchanger 100 as a whole, are each constructed from heat exchanger plates 4, of which only one is specifically designated in the example shown. The heat exchanger plates 4 can in particular be soldered to one another. In particular, they are combined alternately in groups, which can be flowed through separately.

The two modules 1, 2 can be supplied with a warm or a cold fluid via headers 5 and 7, respectively. Corresponding fluids are fed into the respective headers by means of connecting pieces 51 and 71. A warm fluid is used of the header 5 distributed over a group of heat exchanger plates 4 of the modules 1, 2. After the fluid fed in by means of the header 5 has flowed through the modules 1, 2, it is collected by means of the header 6 and, in the cooled state, is discharged via a connection piece (not visible here). Correspondingly, a cold fluid is distributed to another group of heat exchanger plates 4 of the modules 1, 2 by means of the header 7. After the fluid fed in by means of the header 7 has flowed through the modules 1, 2, it is collected by means of the header 8 and, in the heated state, is discharged via the nozzle 81. As mentioned, a corresponding one

Heat exchanger 100 can also be set up to process further fluid flows. Corresponding groups of heat exchanger plates 4 and headers are provided for this.

For heat exchange, corresponding fluids flow through a heat exchange zone 10 of the heat exchanger 100, designated here as 10, which extends between a first end designated here as 11 and a second end designated here as 12. In a regular (“first”) operating mode, fluids at different temperature levels are passed through the heat exchange zone 10 in a specific (“first”) amount per unit of time in the manner previously explained. In this way, the first end 11 of the heat exchange zone 10 is brought to a certain ("first") temperature level and the second end 12 of the heat exchange zone 10 is also brought to a certain ("second") temperature level which is below the first temperature level.

If the heat exchanger 100 is taken out of operation (“second” operating mode), the passage of the fluids, which in the first operating mode are conducted in the first quantity per unit of time through the heat exchange zone 2, is at least partially prevented. In this way, a temperature transition is effected from the first end 11 to the second end 12 of the heat exchange zone 10. In one

corresponding method is repeated several times from the first operating mode to the second operating mode and from the second operating mode to the first

Operating mode switched. This can result in very strong thermal stresses without the use of the measures proposed within the scope of the present invention, as explained several times before. This applies in particular in the case of a heat exchanger 100 which is constructed from a plurality of modules 1, 2 and is connected to one another by means of corresponding module connections 3. The heat exchanger 100 shown here is characterized in particular by the fact that the heat exchange zone 10 has a first terminal sub-zone 13 extending from the first end 11 and a second terminal sub-zone 14 extending from the second end 12 and in the terminal sub-zones 13, 14 each of the module connections 3 are arranged. A central subzone of the heat exchange zone 10, however, is free of the module connections 3.

In the course of investigations, as also mentioned, it has been shown that the thermally induced voltages when restarting a corresponding heat exchanger 100, in particular a fin-plate heat exchanger, from a temperature-balanced state, i.e. if the second operating mode has been carried out for a long time, it may depend heavily on the speed of the restart. While high mass flows can lead to high thermal voltages, thermal stress can be almost completely avoided at low start-up speeds with sufficiently small mass flows.

Figure 3 illustrates a relationship between fluid flows and thermal stresses in a fin-plate heat exchanger. FIG. 3 shows a standardized cold mass flow in dimensionless units, that is to say an amount of cold fluid supplied to the heat exchanger per unit of time, on the

The abscissa and a normalized maximum thermal stress are plotted on the ordinate in dimensionless units.

As can be seen, the thermal induced at low mass flows

Voltages significantly lower than with higher mass flows. The present invention makes use of this knowledge and, in particular, proposes to start up a corresponding heat exchanger again using smaller amounts of fluid per unit of time. In particular, a quantity of fluid is only increased when the areas in which module connections of a finned-plate heat exchanger constructed from a plurality of modules, for example a heat exchanger as shown in FIG. 2, are arranged are sufficiently temperature-controlled, since such Areas particularly negative effects of thermal stresses. This is further explained with reference to FIG. 4. In other words, the present invention proposes to switch from the second operating mode to the first operating mode in such a way that the fluids which are conducted in the first operating mode in the first quantity per unit of time through the heat exchange zone of a corresponding heat exchanger up to an increase time first in a second quantity per unit time, which is less than the first quantity per unit time, to pass through the first heat exchange zone and only from the time of increase in the first quantity per unit time through the first heat exchange zone.

Since cold and warm currents are typically conducted in countercurrent to one another in a corresponding heat exchanger, as also in the example shown in FIG. 2, the temperature profile when starting, i.e. from the transition from the second to the first operating mode, starting from the two ends as time progresses to the inside of the heat exchanger or the

Heat exchange zone, set. If the heat exchanger, e.g. in a sensitive area of module connections, already experiencing the greatest temperature changes occurring during the transition to the first operating mode, only reduced gradients occur here, and thus greatly reduced

Thermal stresses in the further course. In the context of the present invention, the temperature changes of corresponding sensitive areas are brought about in particular with reduced amounts of fluid. Only then will one

appropriate heat exchanger operated with the full amounts of fluid.

4, diagrams 410 to 460 are shown, in each of which

Temperature profiles 401 to 406 in a heat exchange zone

Heat exchanger, for example the heat exchanger 100 shown in Figure 2 at different times. The times are each after a point in time at which a balanced temperature profile has been established due to a heat transfer from the warm to the cold end because the fluid supply has been cut off, that is to say after some time in the second operating mode. For better clarity and comparability with FIG. 2, the heat exchange zone and its sub-zones are also denoted here in the diagram 410 by 10, 13 and 14. At the time illustrated with diagram 410, there was only a slight change in temperature at the extreme ends of the

Heat exchange zone 10 result, which initially only affects the sub-zones 13 and 14. Temperature profiles 402 to 406 arise with increasing time. The highest voltages occur in particular when the one that arises

Temperature gradient is present at the inner end of the module connections here, which is approximately the case at the times indicated here with the diagrams 430 and 440.

In the context of the present invention, corresponding thermal voltages are reduced, in particular, by deliberately lowering those periods in which the areas of the module connections experience large temperature changes

Use mass flows (according to diagrams 410 to 440). Has the local temperature gradient already developed over the module connections

(according to diagram 550), the approach speed can be changed again if necessary

accelerated and thus based on common procedures without generating further significant voltage peaks.

FIG. 5 schematically illustrates a plant for nitrogen liquefaction, which can be operated using a method according to an embodiment of the invention, and is designated overall by 500.

The system 500 illustrated in FIG. 1 has in particular one

Heat exchanger 100 of the type explained above or a comparable

Heat exchanger on. Plants for nitrogen liquefaction are known in principle and are not restricted to the exemplary embodiment shown.

In the example shown, plant 500 is supplied with gaseous nitrogen (stream a), which can be provided, for example, by means of an air separation plant. The gaseous nitrogen is fed to a multi-stage compressor 510 and compressed. Part of the compressed gaseous nitrogen (stream b) is in

Turbine boosters 520, 530, which are each provided with aftercoolers, further compressed and fed to the heat exchanger 100 on the warm side. The rest (stream c) remains undensified and is also fed to the heat exchanger 100 on the warm side. A partial flow d of the flow b is taken from the heat exchanger 100 at an intermediate temperature level, in an expansion turbine

Turbine boosters 520 relaxed and fed into a container 540. Another partial stream e of stream c is taken from the heat exchanger 100 on the cold side and expanded into the tank 540 via a throttle (not specifically designated).

The stream c is taken from the heat exchanger 100 at an intermediate temperature level, expanded in a expansion turbine of the turbine booster 530, fed to the heat exchanger 100 at an intermediate temperature level and together with gaseous nitrogen from the container 540 as stream f at one

Intermediate pressure level returned to the compressor 510.

Liquid nitrogen from the container 540 is subcooled in a subcooler 550, which is cooled with a part of this nitrogen (stream g), and expanded into a storage tank 560 as stream h. Due to evaporation, gaseous nitrogen is now formed in the storage tank 560 and can be discharged unused as current i via a line and a valve if required. In addition, when the liquid nitrogen is transported from the subcooler 550 via the corresponding line (stream h) into the storage tank 200, flash gas is formed, which is also undesirable.

A further line can now be provided, via which gaseous and cold nitrogen can be fed back from the storage tank 560 as stream k into the liquefaction process. In the case shown here, this gaseous nitrogen is combined with the stream g upstream of the subcooler 550.

In this way, the cooling energy of the electricity k in the heat exchanger 100 can be used, as a result of which the entire liquefaction process becomes more efficient. A current I formed by combining the currents g and k can also be returned to the current a after heating, i.e. the amount carried in the stream k

gaseous nitrogen is fed via stream I to stream a and thus back to the liquefaction process.

As mentioned, the system 500 can, if the measures proposed according to the invention are implemented, be switched on and off as required, depending on the need for liquid nitrogen.

Claims

claims

1. A method of operating a heat exchanger (100), the one

Has heat exchange zone (10) which extends between a first end (1 1) and a second end (12), and which comprises a stack of plates

Has heat transfer plates (4),

- A width of the heat transfer plates (4) and a height of the

Plate stack in the heat exchange zone (10) is in each case one third to one fifth of a length of the heat transfer plates (4) between the first end (11) and the second end (11),

- In a first operating mode, fluids on different

Feed temperature levels are provided and each in a first amount per unit of time through the heat exchange zone (10), whereby the first end (11) of the heat exchange zone (10) to a first

Temperature level and the second end (12) of the heat exchange zone (10) is brought to a second temperature level,

- Wherein in a second operating mode, the passage of the fluids, which are passed in the first operating mode in each case in the first amount per unit of time through the heat exchange zone (2), is at least partially and for a period of time which is dimensioned such that by a Heat conduction between the first end (1 1) of the heat exchange zone (10) and the second end (12) of the heat exchange zone (10) at the first end (11) of the heat exchange zone (10) a third temperature level and at the second end (12) of the Heat exchange zone (10) a fourth

Sets temperature level,

- With a difference between the first temperature level and the

second temperature level is greater than a difference between the third temperature level and the fourth temperature level and an average value between the third temperature level and the fourth temperature level is not more than 50 K from an average value between the first

Temperature level and the second temperature level deviates, - In the method, multiple switching from the first operating mode to the second operating mode and from the second operating mode to the first operating mode, and

- Switching from the second operating mode to the first

Operating mode comprises, the fluids, which are conducted in the first operating mode in each case in the first amount per unit time through the heat exchange zone (10), up to a time of increase initially in a second amount per unit time, which is less than the first amount per

The unit of time is to pass through the first heat exchange zone (10) and to pass through the first heat exchange zone (10) in the first quantity per unit of time only from the time of the increase.

2. The method of claim 1, wherein the time of increase is determined based at least in part on one or more temperature measurements at one or more points of the heat exchange zone (10).

3. The method as claimed in claim 1 or claim 2, in which the time of increase is determined at least in part on the basis of a time period which has elapsed since the switching was initiated.

4. The method according to any one of the preceding claims, wherein the

Heat exchanger (100) is designed as a fin-plate heat exchanger.

5. The method according to any one of the preceding claims, wherein the

Heat exchange zone (10) a first terminal partial zone (13) extending from the first end (11), a second terminal partial zone (14) extending from the second end (12) and one between the first terminal partial zone (13) and of the second terminal subzone (14) arranged central subzone, the time of increase being determined as reached when it is determined or predicted that one or more temperature values in at least one of the terminal subzones (13, 14) will exceed or fall below a predetermined temperature ,

6. The method according to claim 5, wherein the heat exchanger (100) has a number of modules (1, 2) which are connected to one another by means of module connections (3), one or more of each in the terminal sub-zones (13, 14) Module connections (3) is or are, and wherein the central subzone is free of the module connections (3).

7. The method according to any one of the preceding claims, wherein switching from the second operating mode to the first operating mode comprises an amount per unit time of the fluids which are conducted in the first operating mode in the first amount per unit time through the heat exchange zone (10), to increase continuously or in stages up to the time of the increase.

8. The method according to any one of the preceding claims, in which in the first

Operating mode one or more first fluids of the heat exchange zone (10) at its first end (11) at the first temperature level, passed through the heat exchange zone (10) and removed from the heat exchange zone (10) at its second end (12) at the second temperature level or, and in which, in the first operating mode, one or more second fluids are fed to the heat exchange zone (10) at its second end (12) at the second temperature level, passed through the heat exchange zone (10) and to the heat exchange zone (10) at its first end (1 1) on the first

Temperature level is or will be taken.

9. Arrangement with a heat exchanger (100) which has a heat exchange zone (10) which extends between a first end (11) and a second end (12) and which has a plate stack of heat exchanger plates (4),

- A width of the heat transfer plates (4) and a height of the

Plate stack in the heat exchange zone is in each case one third to one fifth of a length of the heat transfer plates (4) between the first end and the second end, technical means being provided which are set up in a first operating mode to provide fluids on different levels

To provide feed temperature levels and each in a first amount per unit time through the heat exchange zone (10), whereby the first end (1 1) of the heat exchange zone (10) to a first

Temperature level and the second end (12) of the heat exchange zone (10) are brought to a second temperature level,

- wherein technical means are provided, which are set up in a second operating mode, the passage of the fluids in the first

Operating mode in each case in the first amount per unit of time through the

Heat exchange zone (2) are passed, at least partially and for a period that is dimensioned such that through

Heat conduction between the first end (1 1) of the heat exchange zone (10) and the second end (12) of the heat exchange zone (10) at the first end (11) of the heat exchange zone (10) a third temperature level and at the second end (12) of the Heat exchange zone (10) a fourth

Sets temperature level,

- Where technical means are provided, which are set up for the procedure several times from the first operating mode to the second

Operating mode and from the second operating mode to the first

Switch operating mode, and

technical means are provided which are set up to switch from the second operating mode to the first operating mode in such a way that the fluids which are passed through the heat exchange zone (10) in the first quantity per unit of time per unit time, up to an increase in time initially in a second quantity per unit of time, which is less than the first quantity per

Unit of time is passed through the first heat exchange zone (10) and is only passed through the first heat exchange zone (10) in the first quantity per unit of time from the time of the increase.

10. Arrangement according to claim 9, which has technical means set up to carry out a method according to one of claims 1 to 8.

11. The arrangement (100) according to claim 9 or claim 10, which has means for liquefying and / or low-temperature separation of air and / or one or more gaseous air products.

12. The arrangement (100) according to claim 1 1, wherein the means for liquefaction and / or

Cryogenic separation of air comprise a distillation column system (20).