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Title:
METHOD AND INSTALLATION FOR COOLING A MEDIUM
Document Type and Number:
WIPO Patent Application WO/2018/115087
Kind Code:
A1
Abstract:
The invention relates to a method for cooling a medium (a) by a plurality of heat exchangers (110, 120), in which at least one heat exchanger (110) is operated in an active state, wherein, in the active state, the medium (a) is passed through the heat exchanger (110, 210) and cooled, and at least one component (c) of the medium (a) is frozen out in the heat exchanger (110), wherein at least one heat exchanger (120) is at the same time operated in an inactive state, wherein, in the inactive state, the medium (a) is not passed through the heat exchanger (120) and the heat exchanger (120) is freed of the at least one frozen-out component (c), if present, and wherein a heat exchanger (110) that is being operated in the active state is brought into the inactive state as soon as at least one predetermined criterion is satisfied, and also relates to an installation (100) for cooling a medium (a).

Inventors:
BAUER, Heinz (Gartenstraße 12, Ebenhausen, 82067, DE)
BRAUN, Konrad (Sylvensteinstr. 7B, Lenggries, 83661, DE)
DEICHSEL, Florian (Lenaustr. 1, München, 81373, DE)
JUNGFER, Bernd (Gartenstrasse 13, Achmühle, 82547, DE)
KROBOTH, Markus (Centa-Herker-Strasse 3, München, 80797, DE)
LAMUELA CALVO, Ana-Maria (Max-Friedlaender-Bogen 25, München, 80339, DE)
LEL, Viacheslav (Zugspitzstr 5, Grünwald, 82031, DE)
OBERMEIER, Andreas (Buchgraben 5, Egmating, 85658, DE)
SPREEMAN, Jürgen (Prinzregentenstraße 57, Rosenheim, 83022, DE)
STEINBAUER, Manfred (Ledergasse 20, Raisting, 82399, DE)
WINDMEIER, Christoph (Marienburgweg 10, Geretsried, 82538, DE)
Application Number:
EP2017/083748
Publication Date:
June 28, 2018
Filing Date:
December 20, 2017
Export Citation:
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Assignee:
LINDE AKTIENGESELLSCHAFT (Klosterhofstrasse 1, Munich, 80331, DE)
International Classes:
F25J3/00; B01D53/00; B01D53/26; F25J3/06; F25J5/00; F28D7/00; F28F17/00; F28F27/02
Foreign References:
DE1056635B1959-05-06
DE102013008535A12014-11-20
US3450105A1969-06-17
US20120318017A12012-12-20
US3318103A1967-05-09
Other References:
None
Attorney, Agent or Firm:
RICHMOND, Sarah (The Preistley Centre, 10 Priestley Road the Surrey Research Park, Guildford Surrey GU2 7XY, GU2 7XY, GB)
Download PDF:
Claims:
Claims

Method for cooling a medium (a) using a plurality of heat exchangers (1 10, 120, 210, 220), wherein at least one heat exchanger (1 10, 210) is operated in an active state,

wherein, in the active state, the medium (a) is passed through the respective heat exchanger (1 10, 210) and cooled, and at least one component (c) of the medium (a) is frozen out in the respective heat exchanger (1 10, 210),

characterized in that at least one heat exchanger (120, 220) is at the same time operated in an inactive state,

wherein, in the inactive state, the medium (a) is not passed through the respective heat exchanger (120, 220) and the respective heat exchanger (120, 220) is freed of the at least one frozen-out component (c), if present, and

wherein at least one of the heat exchangers (1 10, 210) that are being operated in the active state is brought into the inactive state, and at least one of the heat exchangers (120, 220) that are being operated in the inactive state is brought into the active state, as soon as at least one predetermined criterion is satisfied.

Method according to Claim 1 , wherein, the medium (a) is natural gas.

Method according to Claim 1 or Claim 2, wherein in the inactive state, the respective heat exchanger (120, 220) is freed of the at least one frozen-out component (c) by the respective heat exchanger (120, 220) being warmed and/or by a pressure of medium located in the respective heat exchanger (120, 220) being reduced.

Method according to Claim3, wherein the respective heat exchanger (120, 220) is warmed by a further medium (d), in particular at a temperature that is higher than a current temperature of the respective heat exchanger (120, 220), being passed through the respective heat exchanger (120, 220), in particular on the shell side.

Method according to one of the preceding claims, wherein the at least one predetermined criterion comprises the reaching of a minimum throughflow rate of medium (a) through the respective heat exchanger (1 10, 210) operating in the active state and/or a maximum pressure loss and/or a maximum outlet

temperature of the medium from the respective heat exchanger (a).

6. Method according to one of the preceding claims, wherein at least one of the

plurality of heat exchangers (210, 220) has a number of channels (21 1 , 212, 213,

221 , 222, 223) through which the medium (a) can be passed,

wherein, if one of the heat exchangers (210) with the number of channels (21 1 , 212, 213) is operated in the active state, the medium (a) is passed through at least one of the channels (21 1 ) and the medium (a) is not passed through at least one other (212, 213) of the channels, and

wherein the at least one channel (21 1 ) through which the medium (a) is passed is changed as soon as at least one predetermined further criterion is satisfied.

7. Method according to Claim 6, wherein, after a change of the at least one channel (21 1 ) through which the medium (a) is passed, the medium (a) is passed through at least one channel (212, 213) through which it has not yet been passed during a current uninterrupted active state.

8. Method according to Claim 6 or 7, wherein, when one of the heat exchangers (220) with the number of channels (221 , 222, 223) is being operated in the inactive state, the number of channels (221 , 222, 223) of the respective heat exchanger (220) are at the same time freed of the at least one frozen-out component (c), if present. 9. Method according to one of the preceding claims, wherein the at least one

component (c) is selected from a group comprising at least one high-boiling hydrocarbon component with six to sixteen, preferably six to ten, carbon atoms, carbon dioxide, water, and a sulfur compound from the group of thiols or hydrides. 10. Installation (100, 200) for cooling a medium (a), comprising a plurality of heat exchangers (1 10, 120, 210, 220) through which the medium (a) can be passed and which can be operated in an active state, in which

the medium (a) for cooling can be passed through the respective heat exchanger (1 10, 210) and at least one component (c) of the medium (a) can be frozen out in the respective heat exchanger (1 10, 210),

characterized in that the plurality of heat exchangers (1 10, 120, 210, 220) can also be operated in an inactive state, in which the medium (a) cannot be passed through the respective heat exchanger (120, 220) and the respective heat exchanger (120, 220) can be freed of the at least one frozen-out component (c), if present,

wherein the installation (100, 200) is configured in such a way that: at least one heat exchanger (1 10, 210) can be operated in the active state; and at the same time at least one heat exchanger (120, 220) can be operated in the inactive state, and

wherein the installation (100, 200) is also configured in such a way that: at least one of the heat exchangers (1 10, 210) that are being operated in the active state can be brought into the inactive state; and that at least one of the heat exchangers (120, 220) that are being operated in the inactive state can be brought into the active state.

Installation (100, 200) according to Claim 10, wherein the medium (a) is natural gas.

Installation (100, 200) according to Claim 1 1 , wherein the installation (100, 200) is also configured in such a way that:

in the inactive state, a respective heat exchanger (120, 220) can be heated to free it of the at least one frozen-out component (c): and/or that,

in the inactive state, a pressure of a medium located in the respective heat exchanger (120, 220) can be reduced to free it of the at least one frozen-out component (c).

13. Installation (100, 200) according to Claim 12, wherein the respective heat

exchanger (120, 220) can be warmed by a further medium (d), in particular at a temperature that is higher than a current temperature of the respective heat exchanger (120, 220), being able to be passed through the respective heat exchanger (120, 220), in particular on the shell side.

14. Installation (200) according to one of Claims 10 to 13, wherein at least one of the plurality of heat exchangers (210, 220) has a number of channels (21 1 , 212, 213, 221 , 222, 223) through which the medium (a) can be passed,

wherein, in the case of the at least one heat exchanger (210) with the number of channels (21 1 , 212, 213), whenever it is being operated in the active state, the medium (a) can be passed through at least one (21 1 ) of the channels and the medium (a) cannot be passed through at least one other (212, 213) of the channels, and

wherein the at least one heat exchanger (210) with the number of channels (21 1 , 212, 213) is formed in such a way that the at least one channel (21 1 ) through which the medium (a) can be passed at least during the active state can be changed.

Description:
Description

Method and installation for cooling a medium

The invention relates to a method and an installation for cooling a medium, in particular for cooling a natural gas.

Apart from methane as the main component, natural gas generally also consists of components with a higher boiling point, such as for example ethane, propane and higher alkanes, and also components with a lower boiling point, such as for example nitrogen, hydrogen and helium.

When treating natural gas, the content of high boilers (also referred to hereinafter as "high-boiling hydrocarbon components") must be considered in particular. Within the scope of this application, these are understood as meaning in particular hydrocarbons with more than six, and in particular up to sixteen, carbon atoms, but also carbon dioxide or sulfur components, in particular sulfur-containing components such as mercaptans, and hydrogen sulfide. Examples of high boilers are hexane, octane and benzene. These high boilers may for example be separated during the liquefaction of natural gas (also referred to in the liquid state as LNG - Liquid Natural Gas). A process known as cryogenic rectification may be used for example for this.

Cryogenic rectification for the separation of high-boiling hydrocarbon components (also referred to as heavy hydrocarbons or HHC for short) during natural gas liquefaction in natural gas liquefaction processes (LNG processes) is generally necessary whenever a concentration of the high-boiling hydrocarbon components exceeds about 1 to 3 ppm by mole. The separation of high-boiling hydrocarbon components generally requires additional equipment and has an adverse effect on the efficiency of the process.

Furthermore, depending on the pressure of the gas supplied, throttling of the natural gas to lower pressures may be necessary to allow the separation to be carried out. For further liquefaction, in some circumstances the natural gas must subsequently be compressed again to higher pressures, for which further equipment is again required. Against this background, the present invention has the object of providing an improved, and in particular more energy-efficient, possible way of cooling a medium, certain components being frozen out during the cooling. Advantages of the invention

The present invention is based on a method and an installation for cooling a medium, such as for example natural gas, by means of a heat exchanger or subcooler, at least one component of the medium, in the case of natural gas in particular the high-boiling hydrocarbon components mentioned, such as hexane, octane and benzene, being frozen out in the heat exchanger. Freezing out should be understood here as meaning the transformation of vapor or liquid into a solid state by cooling in the range of low temperatures to the sublimation point (desublimation) or to the solidification point or below. When reference is made here and hereinafter to the cooling of natural gas and the freezing out of high-boiling hydrocarbon components, this is only for purposes of explaining the invention. It goes without saying that the invention envisaged can also be used for other cooling processes in which one or more components are frozen out or are to be frozen out in the heat exchanger. If the freezing out of high-boiling hydrocarbon components takes place in the heat exchanger, over the course of time there is an increase in the pressure loss as a result of the growing layer of frozen-out high-boiling hydrocarbon components. At the same time, the effectiveness of the heat transfer falls. As soon as the pressure loss exceeds a limit value or the necessary heat can no longer be transferred, the heat exchanger laden with frozen-out high-boiling hydrocarbon components must be cleaned.

Consequently, continuous operation of the installation used for natural gas liquefaction is not possible.

Thus, a plurality number of heat exchangers (also described as "a number of heat exchangers) are used, at least one heat exchanger being operated in an active state. In the active state, the medium is passed through the respective heat exchanger and cooled, and at least one component of the medium is frozen out in the respective heat exchanger. Thus, according to the invention, at least one heat exchanger is at the same time operated in an inactive state. In the inactive state, the medium is not passed through the respective heat exchanger, but instead the respective heat exchanger is freed of the at least one frozen-out component, if present, i.e. if such a component has previously been frozen out in this at least one heat exchanger. At least one of the heat exchangers that are being operated in the active state can in this case be brought into the inactive state. Correspondingly, at least one of the heat exchangers that are being operated in the inactive state can be brought into the active state. Such a change from the active state to the inactive state may be made dependent on a criterion, such as for example the reaching of a minimum throughflow rate of medium through the heat exchanger operated in the active state, a maximum pressure loss or a maximum outlet temperature of the medium from the heat exchanger. Since at least one heat exchanger in the active state and at least one heat exchanger in the inactive state are always provided (possibly with the exception of a short period of time while switching over between different heat exchangers), it goes without saying that, when switching over a heat exchanger from the active state to the inactive state, if necessary a heat exchanger is switched over from the inactive state to the active state. In the simplest case with a total of two heat exchangers, these two can therefore be switched alternately back and forth between the active state and the inactive state. During the process of changing from active to inactive, or vice versa, it is conceivable for two heat exchangers to be (briefly) operated in parallel in the active state.

It goes without saying that, in order to achieve the cooling of the medium, a coolant is respectively passed through the heat exchangers in the active state. For this purpose, the heat exchangers may for example have one or more channels or tubes through which the medium is passed. These channels or tubes may then be surrounded by a shell, thereby forming a channel through which the coolant can be passed.

In this way there is therefore always one heat exchanger which is used for cooling, and possibly liquefying, the medium and also for freezing out one or more components of the medium, while at the same time there is a further heat exchanger, in which already frozen-out components can be removed again. This makes continuous cooling of the medium and continuous operation of the installation possible. Freeing the respective heat exchanger of the at least one frozen-out component in the inactive state preferably takes place by the respective heat exchanger being warmed. For this purpose, in particular, a further medium, in particular one at a temperature that is higher than the current temperature of the heat exchange, may be passed through the respective heat exchanger. This further medium that is used for the warming is also referred to in the case of gas as a de-riming gas. In this way, easy warming of the respective heat exchanger is possible. The warming has the effect that the frozen-out components become liquid or gaseous and can escape or be flushed out from the heat exchanger. A further possible way of removing the frozen-out components is that a pressure of medium located in the heat exchanger is reduced. In this way too, the frozen-out components can be detached.

It is also of advantage if at least one among the plurality of heat exchangers has a number of channels (or tubes) through which the medium can be passed. If at least one of the heat exchangers with the number of channels is operated in the active state, the medium may be passed through at least one of the channels and not through at least one other of the channels. The at least one channel through which the medium is passed may then be changed. Such a change may in this case be made dependent on a predetermined further criterion, such as for example the reaching of a minimum throughflow rate of medium through the current at least one channel and/or a maximum pressure loss. In other words, various channels or tubes, through which the medium is passed at different times, may thus be used within a heat exchanger. It is expedient in this respect if, after a change of the at least one channel through which the medium is passed, the medium is passed through at least one channel through which it has not yet been passed during a current uninterrupted active state. In this way, different channels can therefore be used one after the other for passing through the medium.

It is also conceivable in this case that a number of channels (or tubes) are in each case used simultaneously. In the case of a tube bundle heat exchanger, it is therefore possible for example for a number of tubes to be used simultaneously in the sense of what is known as a tube fraction, and then also changed. Depending on the number of tube fractions, for example two, three or four, the time period for which the heat exchanger can be operated in the active state can consequently be extended. The reason for this is that the channels or tube fractions can always be changed whenever the current channel or the current tube fraction is clogged by the frozen-out components. In comparison with only one channel or only one tube fraction, the time period in the active state can consequently be multiplied correspondingly. A further advantage in this case is that - in particular if further such heat exchangers with numbers of channels are also used - the time period for which the respective heat exchanger can remain in the inactive state also becomes correspondingly longer. More time is therefore available for warming up the inactive heat exchanger, so that the heat exchanger is stressed less, which can result in a longer overall service life.

Furthermore, as a result of the less frequent switching over between different heat exchangers, the heat exchangers are subjected to lower stresses that are caused by the changing. This likewise allows the service life to be extended.

In the inactive state, the number of channels of the corresponding heat exchanger can then preferably also at the same time be freed of the at least one frozen-out component, if present. The time period that is necessary for freeing the heat exchanger of the frozen-out components is consequently not longer than in the case of a heat exchanger with only one channel or only one tube fraction. Correspondingly, the warming can be drawn out over a longer time in order to reduce the stressing.

An installation according to the invention for cooling a medium correspondingly has a number of heat exchangers through which the medium can be passed and which can in each case be operated in an active state, in which the medium for cooling can be passed through the respective heat exchanger and at least one component of the medium can be frozen out in the respective heat exchanger. Furthermore, the number of heat exchangers can in each case also be operated in an inactive state, in which the medium cannot be passed through the respective heat exchanger and the respective heat exchanger can be freed of the at least one frozen-out component, if present. The installation is thus formed in such a way that at least one heat exchanger can be operated in the active state and at the same time at least one heat exchanger can be operated in the inactive state, the installation also being formed in such a way that at least one of the heat exchangers that are being operated in the active state can be brought into the inactive state and that at least one of the heat exchangers that are being operated in the inactive state can be brought into the active state.

Preferably, at least one among the number of heat exchangers has a number of channels through which the medium can be passed. In the case of the at least one heat exchanger with the number of channels, whenever it is being operated in the active state, the medium can be passed through at least one of the channels and cannot be passed through at least one other of the channels. Moreover, the at least one heat exchanger with the number of channels is formed in such a way that the at least one channel through which the medium can be passed at least during the active state can be changed.

With respect to the advantages and further advantageous design embodiments of the installation according to the invention, to avoid repetition reference should be made to the above statements with respect to the method according to the invention, which apply correspondingly.

The invention is explained in more detail below with reference to the appended drawings, which show various parts of the installation, on the basis of which the measures according to the invention are explained.

Brief description of the drawing

Figure 1 shows an installation for cooling a medium according to a preferred

embodiment of the invention.

Figure 2 shows an installation for cooling a medium according to a further preferred embodiment of the invention. In Figure 1 , an installation 100 for cooling and also for liquefying a medium such as natural gas is represented. On the basis of the installation 100, there follows a more detailed explanation not only of the installation itself but also of a sequence of a method according to the invention in a preferred embodiment. In the present case, the installation 100 has two heat exchangers 1 10 and 120. Each of the two heat exchangers 1 10 and 120 has a channel 1 1 1 and 121 , respectively, through which medium to be cooled can be passed. Even though reference is made here in each case to a channel, it is also possible that a number of channels or tubes through which the medium can be passed simultaneously are used in parallel. Furthermore, each of the two heat exchangers 1 10 and 120 has in each case a channel 1 15 and 125, respectively, by which a coolant or a refrigerant can be precooled before it is cooled further by expansion and then, on the shell side of the heat exchangers 1 10 and 120, gives off its cold, flowing in the opposite direction to the media flowing in the channels 1 1 1 and 121 .

The medium to be cooled, as stream a, may thus in principle be supplied to each of the two heat exchangers 1 10 and 120 or the corresponding channels 1 1 1 and 121 and passed through them. The use of suitable valves allows the stream a of the medium to be passed according to choice through the heat exchanger 1 10 or the heat exchanger 120. In the example shown, the stream a is only passed through the heat exchanger 1 10, but not through the heat exchanger 120, which is indicated by dashed lines. In the case of a change from one heat exchanger to the other, the two may also be (briefly) operated, i.e. flowed through by the medium, in parallel.

The coolant, as stream b, may likewise in principle be supplied to each of the two heat exchangers 1 10 and 120 or the corresponding channels 1 15 and 125 and passed through them. The use of suitable valves allows the stream b of the coolant to be passed according to choice through the heat exchanger 1 10 or the heat exchanger 120. In the example shown, the stream b is only passed through the heat exchanger 1 10, but not through the heat exchanger 120, which is indicated by dashed lines. In the case of a change from one heat exchanger to the other, the two may also be (briefly) operated, i.e. flowed through by the coolant, in parallel. In this way, the heat exchanger 1 10 is therefore operated in the active state, the heat exchanger 120 on the other hand in the inactive state. This means that the medium is cooled or liquefied by means of the heat exchanger 1 10, while - by suitably controlling the temperature or the flow of the coolant - one or more components are frozen out in the heat exchanger 1 10, there in particular in the channel 1 1 1. In the case of natural gas as the medium, these components may be in particular high-boiling hydrocarbons, water, carbon dioxide and sulfur-containing components (mercaptans, hydrogen sulfide), as explained at the beginning.

On the other hand, the heat exchanger 120 can be warmed up, for example by the setting of the flow of the coolant through the heat exchanger or else in addition by other suitable measures such as pressure adjustments or passing through a further medium at a greater temperature. Components that have been frozen out in the heat exchanger 120, there in particular in the channel 121 , because the heat exchanger 120 was previously operated in the active state - as the heat exchanger 1 10 is now - can as a result of this warming be made to thaw and discharged or removed from the heat exchanger 120 as stream c. For the warming, for example a further medium may be supplied, as stream d. It goes without saying that, with the function of the heat exchangers changed over correspondingly, such a stream d may be supplied to the heat exchanger 1 10 and a stream c let out.

A change from the active state to the inactive state may take place whenever for example a throughflow rate of medium through the heat exchanger that is being operated in the active state falls below a minimum value or a threshold value, below which for example efficient operation is no longer possible. Another or further criterion may be for example the reaching of a maximum pressure loss, from which efficient operation is no longer possible.

It should in this respect be ensured that, by the time the heat exchanger that is first being operated in the active state, here the heat exchanger 1 10, changes to the inactive state, the heat exchanger that is being operated in the inactive state, here the heat exchanger 120, is operational again, i.e. can be operated in the active state. This means in particular that, as far as possible, the frozen-out components have by that time been removed, and the heat exchanger has also cooled down again to operating temperature.

With the installation 100 shown, continuous operation for the cooling of a medium is consequently possible, it being possible for components to be frozen out in the heat exchanger, or alternately in one of the two heat exchangers. In Figure 2, an installation 200 for cooling and also for liquefying a medium such as natural gas is represented. On the basis of the installation 200, there follows a more detailed explanation not only of the installation itself but also of a sequence of a method according to the invention in a further preferred embodiment. The installation 200 corresponds in its basic construction to the installation 100 according to Figure 1 , but in the present case each of the two heat exchangers 210 and 220 has not only one channel through which the medium can be passed. Rather, each of the two heat exchangers 210 and 220 has in each case three channels 21 1 , 212 and 213 and 221 , 222 and 223, respectively, through which in each case a medium to be cooled can be passed.

Furthermore, each of the two heat exchangers 210 and 220 has in each case a channel 215 and 225, respectively, through which a coolant can be passed. These channels may be formed as in the case of the installation 100 according to Figure 1. Even though reference is made here in each case to a channel, it is also possible that a number of channels or tubes through which the medium can be passed

simultaneously are used in parallel in the sense of a tube fraction. In the case of each of the two heat exchangers 210 and 220, the medium to be cooled, which is supplied as stream a, can thus in principle be passed through each of the three channels 21 1 , 212 and 213 and 221 , 222 and 223. The use of suitable valves allows the stream a of the medium to only be passed however, according to choice, through one of the three channels in each case. In the example shown, the stream a is on the one hand only passed through the heat exchanger 210, which here is being operated in the active state, and there on the other hand is only passed through the channel 21 1 , but not through the channels 212 and 213, which is indicated by dashed lines. In this state, the operation of the installation 200 corresponds at first to that of the installation 100 according to Figure 1 , but then, after a certain time, instead of through the channel 21 1 the stream a can be passed through the channel 212.

Correspondingly, a further change can take place to the channel 213. Parallel operation of for example the channels 21 1 and 212 is also conceivable. Such a change may for example always take place whenever a throughflow rate of medium through the channel that is currently being used falls below a minimum value or a threshold value, below which for example efficient operation is no longer possible. Another or further criterion may be for example the reaching of a maximum pressure loss, from which efficient operation is no longer possible. This means that the heat exchanger 210 can be operated in the active state until all the channels, here three channels, are clogged with frozen-out components. Only then is a change to the inactive state necessary. In comparison with the installation 100 according to Figure 1 , operation in the active state is consequently possible for a longer time, therefore in the case shown with three channels for example approximately three times as long.

This also means furthermore that the heat exchanger 220 can be operated in the inactive state for a correspondingly longer time period. This makes slower warming of the heat exchanger possible, which means less stressing of the heat exchanger and of its components or component parts. As can be seen from the heat exchanger 220, the individual channels, here the channels 221 , 222 and 223, can at the same time be freed of the frozen-out components (stream c). For the warming, for example a further medium may be supplied, as stream d. It goes without saying that, with the function of the heat exchangers changed over correspondingly, such a stream d may be supplied to the heat exchanger 210 and a stream c let out.

With the installation 200 shown, consequently, it is not just that continuous operation for the cooling of a medium is possible, it being possible for components to be frozen out in the heat exchanger, or alternately in one of the two heat exchangers, but that a single cycle, during which a heat exchanger is in an active or inactive state, can last for a correspondingly longer time, which contributes to a longer service life of the installation as a whole, or can make it possible for a greater amount of solid matter to be frozen out in a cycle of the same length.