Method for heating a process loop and a process loop

Abstract

The invention relates to a method for heating a process loop (10) with a plurality of components connected to one another via lines through which a gaseous fluid flows, wherein at least one of the components is a compressor (1) and another component is a process unit (2). A pressure level (psetpoint) at which the dew point of the fluid is below a temperature of the plurality of components of the process loop (2) is determined (S110), and the first fluid is compressed by the compressor (1) (S120) such that the outlet pressure level of the fluid discharged on the pressure side of the compressor (1) is less than or equal to the determined pressure level (psetpoint). The invention further relates to a process loop (10) designed to carry out the method for heating the process loop (10).

Description

[0001] The invention relates to a method for heating a process loop and a process loop for carrying out the method. background

[0002] If the temperature of a gas mixture or pure substance in a process loop, which may include compressors, lines, heat exchangers such as air coolers or condensers, and other components, falls below the dew point temperature of a gaseous fluid compressed by the compressor, the fluid begins to condense. Condensation can occur when the temperature of the fluid drops below the dew point temperature, or when the fluid is compressed to a higher pressure level by starting a compressor, with lines, air coolers, and other components still at the temperature prevailing before startup, which is below the dew point temperature of the fluid at elevated pressure.

[0003] Condensation of the gaseous fluid must be avoided for several reasons. Firstly, condensation of the compressed fluid leads to a loss of gaseous fluid in the compressor, which may necessitate compressor shutdown due to insufficient suction and / or discharge pressure levels, thereby increasing the start-up time of the process loop. Secondly, liquids, especially in the compressor suction lines, should be avoided, as liquid droplets can penetrate the compressor machine and cause compressor damage. Furthermore, after the compressor has started up, condensation can occur in the lines, air coolers, or other equipment on the discharge side, and liquid fluid can be transferred to the suction side via an anti-surge line.

[0004] This not only increases the compressor's start-up time, but can also cause damage if the compressor's suction bottle's separation efficiency is insufficient or the reservoir isn't emptied sufficiently. Furthermore, condensed liquids can damage the anti-surge valve.

[0005] To prevent such scenarios, special measures are taken for so-called winterization. Traditionally, pipes and other components are insulated and equipped with trace heating to heat them to a temperature level above the dew point of the gaseous fluid before commissioning, or to maintain the temperature level above the dew point. Air coolers require a housing with additional heating coils. The heating coils are traditionally heated with steam or hot oil, which requires additional operating materials, as well as their installation and handling.

[0006] Such winterization measures not only incur additional costs for installation, operation and maintenance, but also require, especially in the case of air coolers, additional installation space, which may be limited, for example on oil production platforms, ships, barges (floats) or when the available space is already occupied by other process components.

[0007] Therefore, there is a need to improve the efficiency and costs of winterization measures. Disclosure of the invention

[0008] Against this background, the present invention proposes a method for heating a process loop and a corresponding process loop for implementing the method with the features of the independent claims. Preferred embodiments are the subject of the dependent claims and the following description.

[0009] Before explaining the advantages of the present invention, some terms used in describing the invention are defined in more detail below.

[0010] This application uses the terms "pressure level" and "temperature level" to characterize pressures and temperatures. This is intended to express that corresponding pressures and temperatures in a corresponding system do not have to be used in the form of exact pressure or temperature values. However, such pressures and temperatures typically fluctuate within certain ranges, for example, within ± 1%, 5%, 10%, 20%, or 25% of a mean value. Corresponding pressure levels and temperature levels can lie in disjoint ranges or in ranges that overlap. The same pressure level can, for example, still exist when unavoidable pressure losses occur. The same applies to temperature levels. The pressure levels specified here in bar are absolute pressures.Furthermore, the pressure levels specified are only example values ​​that apply to the gas mixtures shown as examples.

[0011] It is understood that when we talk about "winterization" here, the corresponding measures do not have to be limited to the winter season, but can be used whenever lower temperatures prevail and / or a corresponding process loop is out of operation.

[0012] The process loop comprises a plurality of components that are connected to one another via lines through which a gaseous fluid flows. The components of the process loop comprise at least one compressor, one heat exchanger, in particular an air cooler, and one process unit. Furthermore, the process loop can comprise, for example, further heat exchangers, liquid separators and / or filters. When the term "components of the process loop" is used below, this also refers in particular to the lines of the process loop. In the method, a pressure level for the fluid is determined such that the dew point of the fluid lies below a temperature level of the process loop. In particular, an outside temperature in a region in which the plurality of components of the process loop are arranged can be used as the temperature level of the process loop.Furthermore, it is possible to use the temperature of individual or several, especially all, components of the process loop as the temperature level of the process loop. The first fluid is then compressed by the compressor so that the outlet pressure of the fluid discharged on one pressure side of the compressor is less than or equal to the specified pressure level.

[0013] The fluid is compressed by the compressor, passed through the downstream system, and throttled to the suction pressure level via the gas return line. Compression heats the temperature of the gaseous fluid to a temperature level that exceeds the temperature level of the process loop, transferring heat to the lines and other components of the process loop, thereby heating them. The temperature of the gaseous fluid drops in the process.

[0014] By selecting the specific pressure level created in the fluid by the compressor so that the dew point of the fluid is below the temperature level of the process loop, condensation of the gaseous fluid in the process loop does not occur. This shortens the start-up time of the process loop, as the warm-up prevents downstream problems that would otherwise occur and would be time-consuming to resolve. This also prevents damage to the compressor and eliminates the need for winterization measures such as enclosing and heating one or more heat exchangers in the process loop, thus saving additional costs for their installation, operation, and maintenance. Furthermore, the required installation space, especially for air coolers, can be saved, allowing the process loop to be designed to save space.

[0015] Furthermore, the process can be used flexibly in systems with different types of heat exchangers and devices or components, as it increases the temperature of the connected components. The process can also be applied in process loops where warm-up rates need to be limited to reduce thermal stress during start-up, as the heat supplied to the fluid can be flexibly adjusted by the selected pressure level.

[0016] In one embodiment, the temperature level of the process loop is determined by measuring a temperature level of at least one of the plurality of components of the process loop. In particular, in a case where the temperature levels of multiple components are measured, the temperature level of the process loop can be determined based on the lowest measured temperature level. The temperature level of the process loop can, in particular, be or include a temperature level of an inner wall of the conduit at one or more locations.

[0017] By determining and using a measured temperature level, the pressure level at which the dew point of the fluid lies below the temperature level can be determined more precisely. This can further shorten the start-up time of the process loop while still preventing condensate from the gaseous fluid in the process loop.

[0018] In one embodiment, the outlet pressure level of the gaseous fluid at a pressure-side outlet of the compressor is further compared with a first pressure threshold value, and if it is determined that the pressure level is less than a first pressure threshold value, the determination of the pressure level is repeated such that the dew point of the gaseous fluid is below a temperature of the plurality of components of the process loop, wherein the determined pressure level is greater than the previously determined pressure level. The first pressure threshold value corresponds in particular to the pressure level, and thus indirectly to a target temperature of the process loop, at which the process in the process unit can be carried out or which is necessary for the process in the process unit. Once the required pressure level or the required temperature level has been reached, the winterization measures can be deactivated.

[0019] Because the temperature level of the process loop is heated by compressing the fluid, the pressure level of the fluid also rises, at which the dew point of the fluid is below the temperature level of the process loop. By repeatedly determining the pressure level to which the fluid is compressed, the temperature of the process loop can be successively increased until the fluid reaches a pressure level (first pressure threshold) required for the process in the process unit. Furthermore, this accelerates the heating process, as the heat input into the compressed gas via the compressor increases with increasing pressure.

[0020] This allows the start-up time of the process loop to be further shortened and thus the previously mentioned advantages to be achieved in a particularly advantageous manner.

[0021] In one embodiment, if the determined pressure level is below a predetermined second pressure threshold, the method is carried out first with a gaseous first fluid and subsequently with a gaseous second fluid, wherein the first fluid is used up to a predetermined third pressure threshold and the second fluid is used after the third pressure threshold is exceeded. The dew point of the first fluid is, in particular, below the dew point of the fluid, at least in a pressure range between the second and third pressure thresholds, at the same pressure level. The second pressure threshold is, in particular, the minimum pressure level that can be generated by the compressor.

[0022] At very low outside temperatures or temperatures of the components of the process loop, the pressure level at which the dew point of the gaseous fluid (second fluid), which is used in particular for operating the process loop, lies above the temperature level of the plurality of components of the process loop, is so low that the fluid cannot be compressed to this pressure level by the compressor, which is intended to compress the gaseous fluid to an increased pressure level, for example 20 bar, during normal operation. As a result, the gaseous fluid cannot be compressed and thus the components of the process loop cannot be heated. In this case, the method is initially carried out with a first fluid whose dew point lies below the dew point of the second fluid, at least in a predetermined pressure range between a second (minimum) pressure threshold and a third (maximum) pressure threshold.The first fluid can be compressed to a higher pressure level without the dew point rising above the temperature of the plurality of components. After the pressure level of the first fluid has reached the third pressure threshold, it is replaced in the lines by the second fluid and the method is again carried out until the pressure level of the second fluid reaches or exceeds the first pressure threshold. The pressure level of the second fluid can in particular be lower than the pressure level to which the first fluid was compressed. The second fluid can in particular be the fluid used to operate the process loop. However, it is also conceivable that the second fluid is only an intermediate fluid in order to increase the temperature level of the process loop before the fluid used for operation is introduced.

[0023] This means that the process can also be applied at very low temperatures and the aforementioned advantages can be achieved over a wide temperature range.

[0024] In one embodiment, the first fluid and / or the second fluid contain at least one of the following components: methane, nitrogen, helium, hydrogen, argon, ethane, ethane derivatives, propane, propane derivatives, butane, butane derivatives, and carbon dioxide. The term "derivatives" in this context refers to mono- or polysubstituted (functionalized) alkanes with carbon chain lengths corresponding to those of the original alkane. The exact composition of the second gaseous fluid depends in particular on the ambient conditions and the specifications of the compressor. The first fluid contains, in particular, pure components or mixtures of components with a high dew point to prevent condensation. Ideally, these components are also present in the refrigeration circuit during normal operation, which means that these components do not need to be vented later.The remaining components required in the second fluid can be added to the circuit later while the compressor's final power is being built up. The components of the make-up fluid and the fill rates are selected to achieve the desired composition for normal operation.

[0025] The second fluid used as the operating fluid can, for example, have a composition of 2 mol% methane, 71 mol% ethane, 13 mol% propane, and 14 mol% butane. At an outside temperature of -40°C, the pressure level at which the dew point is below the temperature level of the process loop cooled to the outside temperature is 1.2 bar. In this case, a first fluid can initially be used that has a composition of, for example, 10 mol% methane and 90 mol% ethane. The pressure level at which the dew point exceeds the temperature level of the process loop is approximately 8.5 bar for this composition. Therefore, the process can initially be carried out with the first fluid until the temperature level of the process loop has reached a temperature level at which the second fluid can be used. When selecting the first fluid, the properties of the compressor in particular must be taken into account.Based on these, the pressure and temperature levels that can and / or must be achieved are determined. Based on these pressure and temperature levels, the composition of the first fluid (heating fluid) can be selected.

[0026] The addition of additional components does not necessarily have to result in a sudden change in the composition of the fluid. It is also conceivable that additional components could be added gradually until the composition of the fluid used to operate the process unit is reached.

[0027] This allows the process to be carried out simply and efficiently at low temperatures.

[0028] In one embodiment, the process loop has a first bypass that connects an outlet of the compressor to a compressor inlet, and wherein the flow of fluid through the first bypass can be regulated by a first valve. The method begins with the operation of the compressor being started, with the first valve being opened so wide that a minimum flow occurs through the first bypass. The minimum flow is a minimum flow, depending on the type of compressor, that is necessary to safely start operation of the compressor. The first bypass must, in particular, connect the outlet of the compressor directly to the inlet, but can also comprise other components of the process loop. The first bypass is, in particular, the anti-surge line of the compressor.Therefore, the first valve cannot conventionally be closed completely, as it is necessary for the stable and safe operation of the compressor and is controlled by a control unit of the compressor so that it is at least minimally open at all times (minimal opening degree).

[0029] In one embodiment, the process loop further comprises a second bypass that connects an inlet of the process unit to an outlet of the process unit and can be opened and closed via a second valve. The second bypass is configured to be opened when the process unit is not to be heated and closed when the process unit is to be heated.

[0030] The second valve can be opened successively, i.e., step by step. Alternatively, it is also possible to initially keep the second valve closed until the part of the process loop connected by the anti-surge line—i.e., the compressor, the heat exchanger, and the anti-surge line itself—has reached a temperature level equal to or above the second temperature threshold. The first valve can then be closed to the minimum opening required for safe compressor operation, and the second valve of the second bypass can be opened to heat the remaining components of the process loop.If, in particular, the process unit is also to be heated subsequently, the second valve can be closed again after the temperature level of the other components has reached or exceeded the second temperature threshold, bringing the process unit to a temperature level equal to or above the second temperature threshold. If the process unit is not to be heated at all, the second valve is closed as soon as the temperature level of all components in the process loop except the process unit has reached or exceeded the second temperature threshold.

[0031] This makes it possible to decouple the process unit, which is located, for example, in an interior space and therefore does not require heating, from the circuit while heating the remaining components of the process loop by opening the second valve and thus the second bypass. If, however, the second bypass is not opened, even a potentially cold process unit can be warmed up to a certain degree, thus preventing condensation within the process unit. This allows the heating of the process loop to be flexibly adapted to the current situation, and the aforementioned advantages can be achieved particularly efficiently. Furthermore, the process loop can be heated in stages.

[0032] The proposed process loop is configured to perform a method according to one of the variants presented. For further features and advantages of such a process loop and its embodiments, reference is therefore expressly made to the above explanations regarding the method and embodiments proposed according to the invention, as these apply equally to this. Short description of the drawings

[0033] Figure 1 shows a block diagram of an embodiment of a process loop which is configured to carry out an embodiment of the method, Figure 2 shows a flow diagram of an embodiment of the method, Figure 3 shows a curve of the dew point temperature of a fluid with pressure, and Figure 4 shows the curve of the dew point temperature of two different fluids with pressure. Embodiments of the invention

[0034] The embodiments described below are provided for the purpose of assisting the reader in understanding the claimed and previously discussed features. They are merely representative examples and are not intended to be exhaustive and / or limiting with regard to the features of the invention. It is to be understood that the advantages, embodiments, examples, functions, features, structures, and / or other aspects described above and below are not to be considered limitations on the scope of the invention as defined in the claims or limitations on equivalents to the claims, and that other embodiments may be utilized and changes may be made without departing from the scope of the claimed invention.

[0035] Figure 1shows a block diagram of an embodiment of a process loop 10 that is configured to carry out an embodiment of the method. The process loop 10 has a process unit 2 in which a process is to be carried out. In order to carry out this process, the gaseous fluid must have a certain target pressure p target. The pressure level in the fluid is built up by a compressor 1, which is driven by a compressor machine or a compressor motor 1a. Alternatively, the compressor 1 can also be driven by a gas or steam turbine. The process loop 10 further has a heat exchanger 5, which is in particular an air cooler 5, in which the compressed gaseous fluid can be cooled after compression.The process loop 10 may have further components 6, 7 that are not described in detail here, for example, further heat exchangers, in particular condensers, moisture separators, and / or filters. The individual components of the process loop 10 are connected to one another via lines, in particular such that the gaseous fluid flows into the compressor 1 on the suction side, is compressed by the compressor, and is discharged to the air cooler 5 on the pressure side of the compressor 1. From the air cooler 5, the fluid flows into the process unit 2 via the inlet of the process unit 2, passes through the process unit 2, and leaves the process unit 2 via its outlet, returning to the pressure side of the compressor 1.

[0036] The process loop 10 further comprises a first and a second bypass 3, 4. In the first bypass 3, the pressure side of the compressor 1 is connected to the suction side of the compressor 1. The first bypass 3 has a first valve 3a, via which the flow of the fluid through the first bypass 3 can be regulated. The first bypass 3 does not have to start directly after the compressor 1, but can, as in Figure 1 shown, can also be branched off after the air cooler 5. The first bypass 3 also serves as an anti-surge line.

[0037] In the second bypass 4, the inlet of the process unit 2 is connected to the outlet of the process unit 2. The second bypass 4 is controlled by a second valve 4a, which can be opened and closed. If the process unit 2 is not to be heated during the process, for example, because it is located indoors and has therefore not cooled down, the second bypass 4 can be opened by opening the second valve 4a so that the fluid does not flow into the process unit 2. If, however, the process unit 2 is to be heated, the second valve 4a, and thus the second bypass 4, remains closed.

[0038] One or more of the components of the process loop 10 may further include temperature sensors with which the temperature level of the respective components can be determined. Furthermore, it is possible for one or more temperature sensors to be arranged at various points along the lines to measure the temperature level at these points in the process loop 10.

[0039] Figure 2 shows a flowchart of an embodiment of the method, Figure 3 shows a curve of the dew point temperature of a fluid with pressure, and Figure 4 shows the dew point temperature of two different fluids versus pressure. These figures are described together below.

[0040] In step S90, the compressor 1 is started by providing it with a minimum flow of fluid via the first bypass 3, wherein the minimum flow depends on the type of compressor. Since the first bypass 3 is the anti-surge line of the compressor 1, a minimum opening degree of the first valve 3a is controlled, for example, by a control unit of the compressor 1 (not shown), wherein the minimum opening degree depends on the operating state of the compressor 1, in particular the distance from the surge line. Therefore, it is possible that the first valve 3a cannot be fully closed during normal operation.

[0041] In step S100, the temperature level of process loop 10 is determined. For this purpose, for example, the outside temperature can be measured and determined as the temperature level of process loop 10. Furthermore, it is possible to measure the temperature level of one or more of the components and / or various sections of the lines and use this to determine the temperature level of the process loop. In particular, the lowest measured value can be determined as the temperature level of process loop 10.

[0042] Based on the temperature level of the process loop 10, a pressure level p is determined in step S110 such that the dew point of the fluid is below the temperature level of the process loop 10.

[0043] Figure 3 and 4 show two different applications for heating the process loop 10. In Figure 3the temperature level of the process loop 10 is, for example, positive, i.e. above 0°C. However, the method can also be applied in cases where the temperature level of the process loop 10 is initially below 0°C. In this case, the dew point temperature of the gaseous fluid (solid line) lies in a range operable by the compressor 1 between the minimum second pressure threshold p min that can be generated by the compressor 1 and a maximum third pressure threshold p max that can be generated by the compressor 1, below the initial temperature level T Start (dashed line, for example 40°C) of the process loop 10. In this case, the method can be carried out with the fluid used for operating the process unit 2.For example, the intersection point of the initial temperature level T Start and the dew point temperature curve is at 7 bar, i.e. the specific pressure level p at which the dew point is below the temperature level of the process loop 10 must be below 7 bar.

[0044] In Figure 4the initial temperature level T start (dashed line) of the process loop 10 is very low (for example -40°C). The dew point temperature (solid line) of the second fluid used for the operation of the process unit 2 is always above the temperature level of the process loop 10 in the operable range of the compressor 1 (between p min and p max ). In this case, the compressor 1 cannot compress the fluid in such a way that condensation does not occur in the process loop 10. If, in such a case, the pressure level p is determined based on the temperature level of the process loop 10 (S110), the pressure level p is below a minimum first pressure threshold value p min .In this case, the second fluid is replaced by a first fluid that has a dew point temperature, at least in a pressure range between the second pressure threshold p min and the third pressure threshold p max , that is below the dew point temperature of the fluid used to operate the process unit 2. An exemplary dew point temperature profile of the first fluid is shown in . Figure 4shown by way of example as a dash-double dot curve. The dew point of the first fluid is, for example, at the second pressure threshold value p min at -46°C and is therefore below the initial temperature level T Start . As can be seen, a pressure level p can be determined for the first fluid which can be generated by the compressor 1 and at which the dew point temperature is below the initial temperature level T Start of the process loop 10. The first fluid can preferably contain components which are also contained in the second fluid used for the operation of the process unit 2, in particular only components which are also contained in the second fluid used for the operation of the process unit 2, but in a mixing ratio that is different from that in the second fluid. This makes it easier to adjust the composition of the fluid subsequently. However, it is also possible for the first fluid to contain components which are not contained in the second fluid.In this case, these components must first be removed from the process loop before the composition of the second fluid can be created in the process loop. For example, the fluid used to operate process unit 2 can be a mixture containing 2 mol% methane, 71 mol% ethane, 13 mol% propane, and 14 mol% butane, while the first fluid can be a mixture containing 10 mol% methane and 90 mol% ethane. This eliminates the need to pump out the first fluid when the second fluid is to be introduced into process loop 10; instead, the other components can simply be added to achieve the composition of the second fluid.

[0045] Subsequently, in step S120, the fluid is compressed by compressor 1 to a pressure level corresponding to the determined pressure level p. During compression, the fluid continues to heat up. This heat is then transferred to the lines and other components as the fluid flows through them, thereby increasing the temperature level of process loop 10 in general and of the individual components and line sections in particular.

[0046] In particular, once the compressor 1 is running stably and the fluid is compressed to the specific pressure level p, the first valve 3a can initially be opened further to further heat the lines of the first bypass 3 and the other components connected in the first bypass 3, such as the air cooler 5, in particular until the temperature level reaches or exceeds the second temperature threshold. Subsequently, the first valve 3a is closed to the minimum opening degree, and the other components of the process loop 10 can be heated.

[0047] If the process unit 2 is not to be heated, the second valve 4 can be opened to open the second bypass 4. The opening can occur gradually, while the first valve 3a has not yet been set to its minimum opening degree. It is also conceivable that the second valve 4a is fully opened as soon as the compressor 1 is running at a stable level. This can occur after the components of the first bypass 3 have reached a temperature level above the first temperature threshold or directly after the compressor 1 has reached stable operation.

[0048] In step S130, an outlet pressure level of the gaseous fluid on the pressure side of the compressor 1 is determined and compared with a first pressure threshold value p desired. The first pressure threshold value p desired corresponds to the working pressure of the process unit 2. Once the gaseous fluid has reached this pressure level, the process in the process unit 2 can be carried out and further heating of the process loop 10 is not necessary. However, this is only checked if the fluid used to operate the process unit 2 flows through the process loop. If the pressure level on the pressure side of the compressor 1 is below the first pressure threshold value p desired, the method begins again by determining (S110) a pressure level p` at which the dew point of the fluid is below the temperature level of the process loop 10, wherein the newly determined pressure level p` is higher than the previously determined pressure level p.This is possible because the temperature level of the process loop 10 no longer corresponds to the initial temperature level T start , but has risen to a higher temperature level T 1 due to the heat transferred from the fluid to the components and lines of the process loop 10. This process is repeated until the pressure level of the fluid on the pressure side of the compressor reaches or exceeds the first pressure threshold value p setpoint.

[0049] In the case where a first fluid is initially used to heat the process loop 10, the process is carried out with the first fluid up to the third pressure threshold value p max . The second fluid is then introduced into the process loop (for example by adding further components, see above) and the process is carried out with the second fluid. The determined pressure level for the second fluid is in particular lower than the pressure level last determined for the first fluid. If the pressure level of the second fluid subsequently reaches or exceeds the first pressure threshold value p setpoint, the process is terminated and the process in the process unit 2 can be started.

Claims

1. A method for heating a process loop (10) having a plurality of components which are connected to one another via lines through which a gaseous fluid flows, wherein the plurality of components (1, 2, 5, 6, 7) comprise at least one compressor (1), a heat exchanger (5), in particular an air cooler, and a process unit (2), the method comprising: determining (S110) a pressure level (p) such that the dew point of the fluid is below a first temperature level of the process loop (10), compressing (S120) the first fluid by the compressor (1) such that an outlet pressure level of the fluid discharged on a pressure side of the compressor (1) is less than or equal to the determined pressure level (p).

2. The method according to claim 1, wherein determining (S110) a pressure level (p) further comprises: determining (S100) the temperature level of the process loop (10), in particular by measuring a temperature level of at least one of the plurality of components of the process loop (10).

3. The method according to claim 1 or 2, wherein the method after compressing (S120) further comprises: comparing (S130) the outlet pressure level of the gaseous fluid with a first pressure threshold value (p Soll ), and if it is determined that the pressure level is less than the first pressure threshold (p Soll ), repeating the determination (S110) of the pressure level such that the dew point of the gaseous fluid is below a temperature of the plurality of components of the process loop (2), wherein the determined pressure level (p`) is greater than the previously determined pressure level (p).

4. Method according to one of the preceding claims, wherein, if the determined pressure level (p) is below a predetermined second pressure threshold value (p min ), the method is carried out first with a gaseous first fluid and then with a gaseous second fluid, used in particular for the operation of the process unit (2), wherein the first fluid is heated up to a predetermined third pressure threshold value (p max ) is used and the second fluid is released after exceeding the third pressure threshold (p max ) is used.

5. Method according to the preceding claim, wherein a dew point of the first fluid, at least in a pressure range between the first and the second pressure threshold value (p min , p max ), at the same pressure level is below the dew point of the fluid.

6. The method according to claim 4 or 5, wherein the second fluid contains at least one of the following components: methane, nitrogen, helium, hydrogen, argon, ethane, ethane derivatives, propane, propane derivatives, butane, butane derivatives and carbon dioxide.

7. The method according to any one of claims 4 to 6, wherein the first fluid contains at least one of the following components, in particular in a different composition than the second fluid: methane, nitrogen, helium, hydrogen, argon, ethane, ethane derivatives, propane, propane derivatives, butane, butane derivatives and carbon dioxide.

8. The method according to any one of the preceding claims, wherein the process loop (10) has a first bypass (3) which connects an output of the compressor (1) to an input of the compressor (1) and can be controlled via a first valve (3a), and wherein the method further comprises: starting (S90) the operation of the compressor (1), wherein during starting the first valve (3a) is opened so wide that a minimum flow through the first bypass (3) takes place.

9. The method according to any one of the preceding claims, wherein the process loop (10) further comprises a second bypass (4) which connects an inlet of the process unit (2) to an outlet of the process unit (2) and can be opened and closed via a second valve (4a), wherein the second bypass (4) is configured to be opened when the process unit (2) is not to be heated and to be closed when the process unit (2) is to be heated.

10. Process loop (10) comprising a plurality of components which are connected to one another via lines through which a gaseous fluid flows, wherein at least one of the components is a compressor (1) and a further component is a process unit (2), wherein the process loop (10) is designed to carry out the method according to one of the preceding claims.

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