EP4003571A1

EP4003571A1 - Separating method for alternative gas mixtures for use as insulating media

Info

Publication number: EP4003571A1
Application number: EP20732108.4A
Authority: EP
Inventors: Sebastian GLOMB; Mathias GESTLE
Original assignee: Dilo Armaturen und Anlagen GmbH
Current assignee: Dilo Armaturen und Anlagen GmbH
Priority date: 2019-07-22
Filing date: 2020-05-18
Publication date: 2022-06-01
Also published as: WO2021013403A1; US20220266190A1; DE102019119741A1; CA3142980A1; JP2022541040A; CN114007723A; KR20220052906A

Abstract

The invention relates to a method for recovering a useful gas from a gas mixture consisting of a useful gas and at least one secondary gas, wherein the gas mixture is first compressed and transferred into a pressure vessel. Then, from the pressure vessel, a secondary-gas containing gas phase is removed and condensed useful gas is transferred into a purification vessel. In the purification vessel, the condensed useful gas is then purified. The invention further relates to a plant for recovering a useful gas from a gas mixture. Finally, the invention relates to the use of a plant to carry out a method for recovering a useful gas from a gas mixture.

Description

Separation process for alternative gas mixtures for use as insulation media

The invention relates to a method for recovering a useful gas from a gas mixture consisting of a useful gas and at least one secondary gas, the gas mixture first being compressed and transferred to a pressure vessel, where cooling takes place. A secondary gas phase is then removed from the pressure vessel and liquefied useful gas is transferred to a purification vessel. The liquefied useful gas is then heated in the purification container and purified by sucking off a further gas phase. The invention also relates to a system for recovering a useful gas from a gas mixture. Finally, the invention relates to the use of a system for carrying out a method for recovering a useful gas from a gas mixture.

Gas mixtures are often used in technical applications. After using these mixtures, it is usually necessary to break them down again into their individual gas components in order to dispose of the components or to reuse them.

Gas mixtures are used, for example, as protective gas for electrical switchgear. In the past, a very common protective gas was SF6, which has very good insulating properties. However, SF6 is harmful to the climate, so that in the recent past other protective or insulating gases have been developed that have technically similar properties to SF6 and are more environmentally friendly at the same time. These alternative protective or insulating gases are formed by gas mixtures. For example, such gas mixtures are based on C4-nitrile (2,3,3,3-tetrafiuoro-2- (trifluoromethyl) propanenitrile) or C5-ketone (1, 1, 1, 3,4,4,4-heptafluoro-3 - (trifluoromethyl) butan-2-one). These gases, on which gas mixtures are based to form a protective or insulating gas, are referred to below as useful gases. One or more so-called secondary gases are added to the useful gas to form a gas mixture as a protective or insulating gas. These secondary gases can be nitrogen or carbon dioxide, for example. The mixing ratios between useful gas and secondary gas are adapted to the application in which the gas mixture is used. When using such a gas mixture, for example as an insulating gas in a switchgear, it can happen that these gas mixtures are contaminated, for example if air is inadvertently mixed in. In this case, a gas mixture is created with other, unwanted components, which are also referred to as secondary gases.

There is thus a need for solutions to break down gas mixtures consisting of a useful gas and at least one secondary gas back into their individual gas components. On the one hand, it is necessary to unintentionally free contaminated gas mixtures from the contaminants. In addition, there is also a need to break down uncontaminated gas mixtures again into their individual components in order to generate new gas mixtures from the individual components, for example with different mixing ratios of the individual components to one another. There is a great need for such solutions in particular in the field of protective and insulating gases for electrical switchgear. However, in other technical areas too, gas mixtures must be reliably separated and useful gases recovered from gas mixtures.

The object of the invention is therefore to propose solutions to be able to reliably separate gas mixtures into their individual components.

This object of the invention is achieved by a method for recovering a useful gas from a gas mixture consisting of a useful gas and at least one secondary gas, comprising at least the steps

A) Compression of the gas mixture in a compressor,

B) transferring the compressed gas mixture into a pressure vessel,

C) Cooling of the compressed gas mixture in the pressure vessel until the useful gas changes into the liquid phase and a secondary gas-containing gas phase remains, the pressure in the pressure vessel being set so that it is at least twice as high as the vapor pressure of the useful gas at the current temperature in the pressure vessel and the pressure in the pressure vessel is at least 5% lower than the vapor pressure of the secondary gas at the current temperature in the pressure vessel,

D) Removal of the secondary gas-containing gas phase from the pressure vessel,

E) transferring the liquefied useful gas from the pressure vessel to a purification vessel,

F) heating of the liquefied useful gas in the purification tank,

G) suction of the gas phase from the purification container until the internal pressure in the purification container corresponds to the vapor pressure of the useful gas at the current temperature in the purification container.

The method according to the invention is intended to separate a gas mixture and to recover a useful gas from it. The gas mixture consists of a useful gas and at least one secondary gas. However, the gas mixture usually has several secondary gases. By recovering the useful gas from the mixture, the at least one secondary gas remains, so that the gas mixture is separated. In a first process step, the gas mixture is compressed, for which a compressor is used. The gas mixture is compressed to a suitable pressure. The aim of the method according to the invention is to liquefy the useful gas, but to keep the secondary gas or gases in the gaseous phase. A separation by removing either the gaseous secondary gas or the liquid useful gas is particularly simple. A suitable pressure, which is set by the compression in the first process step, is therefore to be selected so that the useful gas is suitably liquefied in a later process step, but the secondary gas or gases are not. Ideally, such a suitable pressure is set exclusively by the initial compression in the compressor. Alternatively, an additional adjustment of the pressure can be provided between the compressor and the pressure vessel or in the pressure vessel, for example by means of further compression or relaxation.

In a second process step, the compressed gas mixture is transferred to a pressure vessel. The pressure vessel is the place where the gas mixture is first broken down into its individual components. The gas mixture is transferred to the pressure vessel under the pressure previously generated during compression and is initially stored there. On the way between the compressor and the pressure vessel, valves and devices for cleaning the gas mixture, such as filters, are provided. The pressure vessel comprises a cooling unit with which the pressure vessel and the gas mixture located therein can be cooled. The gas mixture in the pressure vessel is now cooled. A combination of pressure and temperature is set in the pressure vessel at which the useful gas, which usually has a significantly lower vapor pressure than the secondary gas, liquefies. At the same time, the combination of pressure and temperature is set so that the secondary gas remains gaseous in the pressure vessel. Decisive for whether a gas is gaseous or liquid, whether the prevailing pressure is above or below the vapor pressure of the corresponding gas. The vapor pressure, in turn, depends on the prevailing temperature. The condition or the state from which a gas changes from the liquid to the gaseous state can on the one hand be referred to as the vapor pressure of this gas. In other words, this condition also corresponds to the condensation point from which a gas changes from a gaseous to a liquid state in the other direction. The term vapor pressure is commonly used when a liquid and a gaseous phase coexist in one environment. Below the vapor pressure a gas is in gaseous form in such an environment, above the vapor pressure it is in liquid form. A mixture of liquid and gaseous phases is not absolutely necessary for the use of the term condensation point. Above the condensation point, a gas is always in a gaseous state. In this case there does not have to be a phase of liquid gas. The property below the vapor pressure can thus be equated with the property above the condensation point when a purely gaseous phase is present. According to the invention, the gas mixture present in gaseous form is compressed by the compression in the first step to a pressure which, at the prevailing temperature, is below the vapor pressure of all gas components. In this state, the gas mixture is introduced into the pressure vessel, all components of the gas mixture being in gaseous form. The temperature is then reduced in the pressure vessel. This reduction in temperature reduces the vapor pressure of the gas components. The temperature in the pressure vessel is reduced until the pressure prevailing in the pressure vessel is significantly higher than the vapor pressure of the useful gas at the set temperature. With this combination of pressure and temperature in the pressure vessel, the useful gas changes to the liquid state. The pressure vessel is set so that it is at least twice as high as the gas pressure of the useful gas under the prevailing conditions in the pressure vessel. The pressure in the pressure vessel is therefore set significantly higher than the gas pressure of the useful gas to ensure that the useful gas is actually completely liquefied. In practice it has been found that this complete liquefaction can be achieved particularly well at pressures in the pressure vessel that are 3-5 times as high as the vapor pressure of the useful gas. The combination of pressure and temperature in the pressure vessel is set at the same time so that it is at least 5% lower than the vapor pressure of the secondary gas. This distance from the vapor pressure of the secondary gas ensures that this secondary gas remains safely and completely in the gaseous phase and does not already partially liquefy. Depending on the type of secondary gas, it may not have any vapor pressure under the prevailing conditions in the pressure vessel. This is the case, for example, with a secondary gas which is formed by nitrogen. If such a secondary gas has no vapor pressure under the prevailing conditions, the pressure in the pressure vessel is low enough to ensure that the secondary gas remains in the gaseous phase. Other secondary gases, such as carbon dioxide, have a vapor pressure under the prevailing conditions in the pressure vessel. For such secondary gases, the pressure inside the pressure vessel is preferably set between 5 and 40%, particularly preferably between 10 and 30% lower than the vapor pressure of the secondary gas. As a result of this set state, a very large part of the secondary gas is already separated from the gas mixture. However, residues of the useful gas also remain in the gaseous phase in the pressure vessel; conversely, residues of the secondary gas still remain in the liquid phase, which largely consists of useful gas.

After the first separation of the gas mixture in the pressure vessel, the secondary gas-containing gas phase is removed from the pressure vessel. For this purpose, a corresponding extraction line provided with a valve is expediently provided in the upper region of the pressure vessel.

In a further process step, the liquefied useful gas is transferred from the pressure vessel to a purification vessel. A second purification of the useful gas is carried out in this purification tank with the aim of removing residues of the secondary gas still contained therein. This transfer of the useful gas into the purification vessel is usually driven by the pressure prevailing in the pressure vessel.

The purification container comprises at least one heating device which heats the purification container and the liquefied useful gas located therein. As a result of this heating in the purification vessel, the vapor pressure of the gases contained therein increases relative to the conditions in the pressure vessel. As a result of the increasing vapor pressure, the residues of the secondary gas still contained in the liquefied useful gas pass into the gaseous phase and thus escape from the liquefied useful gas. At the same time, the increasing temperature in the purification tank reduces the solubility of the secondary gas or gases in the liquid useful gas, so that they pass into the gas phase, leave the liquid useful gas and the useful gas is thus purified. In a further process step, the gas phase with the removed residues of the secondary gas is then sucked out of the purification container. With this suction, the pressure in the purification tank can be reduced. The suction is carried out until the internal pressure in the purification tank corresponds as a minimum value to the vapor pressure of the useful gas at the current temperature. The prevailing pressure in the purification container is therefore always greater than or equal to the vapor pressure of the useful gas at the current temperature in the container. In order to ensure a thorough separation of the useful gas and the secondary gas, the internal pressure in the purification tank is reduced during the suction down to the vapor pressure of the useful gas. In this way, residues of secondary gas are also effectively separated from the useful gas. At pressures that are very close to the vapor pressure of the useful gas, the useful gas also begins to change into the gaseous state. The gas phase sucked out of the purification container can thus also contain a proportion of useful gas. According to the invention, however, setting an internal pressure in the purification vessel very close to the vapor pressure of the useful gas is essential for good purity of the useful gas which has been separated out or recovered and which is collected in liquefied form in the purification vessel. After completing this process step, the useful gas is in liquid form with a very high purity in the purification tank. A recovery of the residues of the useful gas, which are sucked off from the purification container, is possible by means of optional embodiments of the method, as described further below.

In a particularly preferred embodiment, the method according to the invention is carried out precisely in the sequence of the individual method steps as described above. However, it is also possible to change the sequence of the process steps if this leads to more favorable results in the application.

Furthermore, it is advantageously provided in the proposal that the gas mixture is sucked off by means of a suction pump from a container in which the gas mixture is in use, prior to compression A). In this embodiment, before compression, the gas mixture is withdrawn from the container in which it is used technically. For example, such a container can be the housing of an electrical switchgear, in which the gas mixture is used as a protective or insulating gas. A suction pump enables a very low suction pressure. Such a low suction pressure ensures that the useful gas, which usually has a very low vapor pressure, remains safely in the gaseous phase during suction. When the gas mixture is sucked out of the container, filters can be installed upstream or downstream of the suction pump to clean the extracted gas mixture. Gas mixtures used in a switchgear, which are used as protective or insulating gas, can be sucked off directly from the switchgear and then fed to the compression for carrying out the method according to the invention. Alternatively, the suction from the switchgear or the container can also take place in a buffer container by means of the suction pump. In this case, the gas mixture can be supplied to compression for the method according to the invention in this buffer container. The advantage of the intermediate storage of the gas mixture in a buffer container is that the system for carrying out the method according to the invention can be located at a different location than where the gas mixture is used. In this case, the suction pump can be structurally combined with the buffer container or it can also be designed separately from it. In a preferred embodiment of the proposal it is provided that the gas mixture is cleaned, in particular filtered, after the suction, which takes place by the suction pump. In this embodiment, the gas mixture is cleaned before the compression by the compressor, after the suction. Various types of filters can be provided for cleaning.

Furthermore, it is provided that after the suction G) of the gas phase from the purification container, the purified useful gas remaining in the purification container in the liquid phase is filled. In this embodiment, the purified useful gas, which collects at the bottom of the purification container after the gas phase has been suctioned off, is removed from the purification container and filled. Such filling can take place in storage containers, such as gas bottles. The recovered useful gas can then be supplied to a new application in the storage container. For example, the storage container can be connected to a mixing system in which the recovered useful gas is mixed with a new gas mixture.

In an advantageous embodiment it is provided that the gas mixture between the compression A) and the transfer B) is dried and / or cleaned, in particular filtered. In this embodiment, the gas mixture is cleaned and / or dried between the compression and the pressure vessel. This cleaning and / or drying can be carried out before or during transfer B) into the pressure vessel. Drying is understood to mean that moisture or moisture contained in the gas mixture is removed. Cleaning is usually done with the help of filters. It is also possible to carry out a two-stage cleaning in which a first cleaning step takes place before the compression and a second cleaning step takes place after the compression.

It is cleverly provided that the gas mixture is compressed to a pressure of 5-20 bar, in particular 10 bar, during compression A). This pressure range is particularly suitable for carrying out a process in which C4 or C5 is to be recovered from a gas mixture as useful gas. At the temperatures prevailing in the pressure vessel, this pressure is significantly higher than the vapor pressure of the useful gas, but well below the vapor pressure of the secondary gas. This pressure range is therefore particularly suitable for a first separation of useful gas and secondary gas.

In a further preferred embodiment it is provided that the gas mixture is cooled to a temperature of -30 to -60 ° C, in particular to a temperature of -45 to -50 ° C, during cooling C) in the pressure vessel. This temperature range when cooling in the pressure vessel is particularly suitable in combination with the preferred pressure range described above for the recovery of C4 or C5 from a gas mixture. As already described above, when cooling in the pressure vessel, these parameters create conditions in which the pressure is significantly higher than the vapor pressure of the useful gas, but at the same time the pressure is lower than the vapor pressure of the secondary gas. Under these conditions, the useful gas safely turns into the liquid state of aggregation, whereas the secondary gas assumes a gaseous state.

Furthermore, it is advantageously provided that the cooling C) is carried out between 5 and 20 minutes, in particular 10 minutes. Usually, the cooling in the pressure vessel takes place periodically. This means that the gas mixture is first transferred from the compression to the pressure vessel. This transfer is then interrupted and cooling is initiated. A period of time between 5 and 20 minutes has proven to be particularly good at generating states in the pressure vessel in which the useful gas is liquid, but the secondary gas is in gaseous form. Of course, cooling can also be carried out for a shorter or longer period than the mentioned range.

It is advantageously provided that the transfer B) of the gas mixture into the pressure vessel takes place periodically and a settling time is waited for before the removal of D) of the secondary gas-containing gas phase from the pressure vessel. Advantageously, the transfer of the gas mixture into the pressure vessel is not carried out continuously, but periodically. This means that in a first step the gas mixture is transferred from the compression to the pressure vessel. In a second step, the transfer is interrupted and the pressure vessel is cooled without further filling the pressure vessel. After setting the desired parameters in the pressure vessel, a settling time is awaited. During this settling time, the secondary gas contained in the liquefied useful gas escapes upwards and collects in gaseous form above the liquid useful gas. Without a settling time, larger residues of gaseous secondary gas would be contained in the liquid useful gas. After waiting for the settling time and the outgassing of the secondary gas, the secondary gas-containing gas phase is then withdrawn from the pressure vessel.

Furthermore, it is advantageously provided in the proposal that the secondary gas-containing gas phase removed during removal D) is disposed of or destroyed. In the case of protective or insulating gases in particular, the secondary gas is not harmful to the environment or the climate and, at the same time, can be obtained inexpensively. In this case in particular, it is not profitable to reuse the secondary gas for other applications. Disposal or destruction is easier and cheaper here.

In a preferred embodiment of the proposal it is provided that the transfer E) of the liquefied useful gas takes place when the pressure vessel is filled with a gas mixture above 0.75 +/- 20% kg / L. The filling and also the emptying or the transfer of the liquefied useful gas into the purification container preferably takes place periodically. The transfer of the liquefied useful gas takes place advantageously when the pressure vessel has a filling density of 0.75 +/- 20% kg / L, 0.75 kg / L with a tolerance of plus or minus 20%. With a higher filling density, there is not enough space left in the pressure vessel to collect the secondary gas-containing gas phase. At a lower filling density, the pressure vessel only contains a small amount of liquid useful gas phase and the transfer is therefore not efficient. The mentioned filling densities have proven to be suitable in practice. If the shape or size of the pressure vessel is changed, however, other areas of the filling density can also be optimal for initiating the transfer of the liquefied useful gas.

It is also provided that the purification container is evacuated before the transfer E) of the liquefied useful gas. In this embodiment, the purification container is emptied or evacuated before the liquid useful gas phase is transferred from the pressure container. As a result, there is no or only very little counterpressure in the purification tank and the liquid useful gas phase can prevented from being transferred into the purification tank. This also ensures that the transferred useful gas phase is not contaminated by residual gas in the purification tank.

In an advantageous embodiment it is provided that the heating F) of the liquefied useful gas in the purification container takes place by an electrically operated heater. In this embodiment, the heating is carried out by an electrical or electronic heater. Such heating devices are particularly easy to regulate in terms of their output, which makes it particularly easy to design the conditions inside the purification container. Usually, one or more temperature sensors are provided in the interior of the purification container, which are integrated into a control loop for controlling the heater.

In a further preferred embodiment, it is provided that the heating F) of the liquefied useful gas in the purification vessel is carried out by a heat exchanger as a heating device which uses the waste heat generated during cooling C) of the compressed gas mixture in the pressure vessel and feeds it to the purification vessel. A heat pump is usually used to cool the gas mixture in the pressure vessel. This creates waste heat outside the pressure vessel, which in turn can be used in a favorable manner to heat the useful gas in the purification vessel. Such a heat exchanger significantly reduces the total energy consumption for carrying out the method according to the invention and makes a system for carrying out this method very energy-efficient.

Furthermore, it is advantageously provided that the heating takes place on the one hand by the heat exchanger and on the other hand additionally by the electrical heater. In this embodiment, the heating takes place by a combination of a heat exchanger with an electrical heater. A basic proportion of the heating is advantageously carried out by the particularly energy-efficient heat exchanger. The fine control of the temperature in the purification container is carried out by an electric heater, which can be controlled almost in real time and very precisely. This fine control is important in order to set conditions in the purification tank at which the prevailing pressure is very close to the vapor pressure of the useful gas. A combination of heat exchanger and electric heater is therefore energy-efficient on the one hand and very effective for a pure separation or recovery of the useful gas.

It is advantageously provided that the gas phase removed from the purification container during the suction G) is returned to the pressure container. The gas phase sucked out of the purification container consists largely of secondary gas, but also contains residues of useful gas. To recover these residues of useful gas, the gas phase is advantageously fed back into the process. This is preferably done in that the gas phase is fed back to the pressure vessel via a compressor or a pump. Any useful gas still contained in the gas phase is then recovered in a second process run. This return of the gas phase from the purification tank into the process results in a particularly effective recovery of the useful gas.

Furthermore, it is advantageously provided in the proposal that the suction G) of the gas phase from the purification container is carried out by a compressor. In this embodiment, the suction from the purification tank by a compressor that additionally compresses the extracted gas phase. Either the same compressor that is used for the initial compression A) can be used for this suction, or a different or additional compressor can alternatively be used. By using the same compressor as for the initial compression A) This is used twice, which simplifies the design of a system for carrying out the method.

In a preferred embodiment of the proposal, it is provided that during the filling H) of the purified useful gas remaining in the liquid phase in the purification container, this is filled into an evacuated pressure container. The previous evacuation of the pressure vessel into which the purified useful gas is to be filled ensures that the useful gas is not contaminated again. At the same time, in this embodiment there is no or only a very low counterpressure in the pressure vessel provided for filling, which makes filling simple and efficient.

It is also provided that the vapor pressure curve of the useful gas runs below the vapor pressure curve of the secondary gas. The process according to the invention is particularly suitable for the separation of gas mixtures in which the useful gas to be recovered has a lower vapor pressure and / or a higher condensation point than the secondary gas. The recovery or separation of the gas mixture is based on this difference in vapor pressure. In the field of electrical switchgear, protective or insulating gases often use gas mixtures that contain C4 or C5 as useful gas. These two gases both have a very low vapor pressure, which is significantly lower than the vapor pressure of commonly used secondary gases such as nitrogen or carbon dioxide. Nitrogen has no vapor pressure at all above the critical temperature. In this case, the condensation point of the useful gas is higher than the condensation point of nitrogen.

In an advantageous embodiment it is provided that during the suction G) of the gas phase from the purification container, the internal pressure and the temperature in the processing container are continuously measured by sensors and a control, based on the measured values of these sensors, ends the suction G) as soon as the vapor pressure of the useful gas in the purification tank is reached. The gas phase is sucked out of the purification container until the internal pressure in the container corresponds to the vapor pressure of the useful gas under the conditions there. For the recovery of a useful gas that is as pure as possible, it is important that the internal pressure in the purification tank is brought as close as possible to the vapor pressure of the useful gas. Automatic, electronic regulation of the internal pressure is therefore advantageous. For this purpose, one or more pressure and / or temperature sensors are provided in the treatment container. The measured values of these sensors are used for an electronic regulation of the extraction of the gas phase as well as to regulate the heater and the temperature in the treatment tank.

It is cleverly provided that the transfer B) of the compressed gas mixture into the pressure vessel takes place periodically or continuously. As already shown, this transfer is advantageously carried out periodically. The pressure vessel is filled at one time and the contents of the pressure vessel are cooled at another time when no filling takes place, thus separating the gas mixture. Alternatively, however, it is also possible to make the filling of the pressure vessel and thus also the removal of the separated gas phases continuous. Such a continuous process increases the temporal efficiency of corresponding systems. Since a continuous process generates additional effort, it is economically profitable mainly for large systems.

In a further preferred embodiment it is provided that the transfer E) is driven by the pressure prevailing in the pressure vessel. In this embodiment, the liquefied useful gas is transferred from the pressure vessel to the purification vessel, driven by the pressure prevailing in the pressure vessel. This embodiment is particularly effective in combination with a previously performed evacuation of the purification container. No additional system components, such as pumps or the like, have to be provided for the transfer of the liquid useful gas phase. As a result of the heating in the purification tank, the vapor pressure of the useful gas increases there compared to the vapor pressure at room temperature. In this way, the useful gas can be transferred in the liquid phase from the cooled pressure vessel to the heated purification vessel. Alternatively, it is of course possible, in particular, to provide support system components which carry out the transfer into the purification container. For example, the compressor that is already present could be used to support the transfer of the liquid phase into the purification container.

The object of the invention is also achieved by a system for recovering a useful gas from a gas mixture, the system having at least the following components:

a compressor for compressing the gas mixture,

a pressure vessel for receiving the compressed gas mixture,

wherein the pressure vessel has a cooling unit for cooling the compressed gas mixture, and the pressure vessel has an extraction line for the secondary gas-containing gas phase, and the pressure vessel is connected via a transfer line to a purification vessel which is used to transfer the liquefied useful gas,

with a heater on the purification tank for heating the liquefied useful gas, a suction unit on a suction line that sucks the gas phase out of the purification tank,

and a filling line is provided and

purified useful gas can be filled via the filling line.

A system according to the invention is suitable for and intended to carry out the method according to the invention and thereby to recover a useful gas from a gas mixture. At this point it should be expressly pointed out that disclosures that are made about the system components in the context of the description of the method according to the invention are also disclosed in connection with the system according to the invention.

The system according to the invention has a compressor which is provided to compress the gas mixture and to supply it to the pressure vessel. The compressor is connected to the pressure vessel via at least one connecting line. The first separation of the gas mixture takes place in the pressure vessel. The pressure vessel includes a cooling unit, which is provided for the content of the To cool the pressure vessel. In addition, the pressure vessel comprises a removal line, which is provided to remove the secondary gas-containing gas phase from the pressure vessel. The extraction line is connected in the upper area of the pressure vessel, this connection being located above the liquid level of the liquefied useful gas phase. In addition, the pressure vessel comprises a transfer line which leads to the purification vessel. The transfer line is provided to remove the liquid useful gas phase from the pressure vessel and to transfer it into the purification vessel. The transfer line is connected to the pressure vessel in the lower area below the liquid level of the useful gas phase. The system according to the invention further comprises the already mentioned purification container, which is intended to perform a second separation of the gas mixture. The useful gas transferred from the pressure vessel still contains residues of secondary gas, most of which are removed from the useful gas in the purification vessel. With a system according to the invention, a purity of the recovered useful gas of more than 99% is possible. The purification container comprises a heater which is provided to heat the contents of the purification container. This heater can also have several components, for example an electrically operated component and a component that is connected to a heat exchanger that uses the waste heat of the cooling from the pressure vessel. Furthermore, the purification container comprises at least one suction unit with at least one suction line. The suction unit is intended to remove the secondary gas-containing gas phase from the purification container. At least one filling line is connected to the purification tank to remove the recovered, purified useful gas. The recovered useful gas is removed from the system according to the invention via this filling line.

A system according to the invention consists of reliable technical components and has a simple structure. Thus, a system according to the invention is very reliable and enables useful gas to be recovered with a very high degree of purity.

It is advantageously provided that a control unit is provided on the suction unit which sucks the gas phase from the purification container until the internal pressure in the purification container corresponds to the vapor pressure of the useful gas at the current temperature in the purification container. In this embodiment of the system, an electronic or computer-controlled control unit is provided which controls the conditions, in particular pressure and temperature, in the purification container. This control unit uses, as input, measured values from sensors arranged inside the purification container. As an output, the control unit influences the extraction of the gas phase from the purification container. For this purpose, the control unit can, for example, influence the opening of a valve in the suction line. An analog control unit can also be provided on the pressure vessel in order to regulate the withdrawal of the secondary gas-containing gas phase there. The control unit can be formed by a system control or it can also be part of a system control.

Furthermore, it is advantageously provided that at least one pressure or temperature sensor is arranged on the pressure vessel, which is / are connected to a system control. In this embodiment, at least one pressure or temperature sensor is arranged at least on the pressure vessel, but advantageously also on the purification vessel, which with a system control or a Control unit is connected. A number of pressure and temperature sensors are advantageously provided, which forward their measured values as input into an automatic regulation of the conditions in the pressure vessel and / or in the purification vessel.

A system for recovering a useful gas from a gas mixture can be operated particularly efficiently using a system control. This system control is intended to operate the system at least partially automatically. In addition to the sensors already described for determining pressure or temperature, further sensors are optionally provided for this purpose. For example, flow sensors can be provided in the lines from the compressor to the pressure vessel, from the pressure vessel to the purification vessel and / or from the purification vessel back to the compressor, which determine the mass flows flowing through and communicate them to the system control. In addition, sensors can be provided to determine the mass or weight of the gas mixture in the pressure vessel and in the purification vessel. The system control can then automatically determine the density in the containers using the measured values of these sensors. The system control is also intended to calculate the vapor pressures of the individual components in real time, especially in the pressure vessel and in the purification vessel, and to regulate the internal pressures and temperatures according to the specifications of the method. In addition, the system control can act on the various valves that are required when the gas mixture is passed through the system or when the separate components are removed. Finally, sensors can be provided which determine the humidity and the contamination of the gas mixture by particles. Based on the signals from these sensors, the system can then automatically regulate whether drying or cleaning of the gas mixture should take place and, for this purpose, influence the filter and / or drying units.

In a further embodiment, sensors can be arranged in the withdrawal line for withdrawing the secondary gas-containing gas phase from the pressure vessel, which monitor the remaining amount of useful gas in this withdrawn gas phase. Based on the signals from these sensors, if the useful gas concentration is low, the withdrawn gas phase can be released into the atmosphere for disposal. If the useful gas concentration is too high, the gas phase can also be fed back into the process in order to remove or at least reduce the remaining useful gas residues.

Furthermore, sensors can be arranged in the flow direction after the connection via which the gas mixture to be separated is fed to the system or the method, which determine the composition of the gas mixture, in particular the proportion of the useful gas, the proportion of the secondary gas and the purity of these gases. Based on the signals from these sensors, the system control can then determine the maximum amount of gas mixture that can be fed to the system or the purification process. This determination of the gas composition can of course also be carried out continuously and the system control can also continuously regulate the amount of gas mixture taken up based on the signals determined. The object of the invention is also achieved by using a system according to one of the embodiments described above for recovering the useful gas C4-nitrile (2,3,3,3-tetrafluoro-2- (trifluoromethyl) propanenitrile) and / or C5-ketone (1, 1, 1, 3,4,4,4-heptafluoro-3- (trifluoromethyl) butan-2-one) from a gas mixture with at least one or more of the following secondary gases: oxygen, nitrogen and / or carbon dioxide, in particular below Implementation or use of the method according to one of the embodiments described above. A plant according to the invention is particularly well suited for carrying out a method according to the invention. The useful gases C4-nitrile, also designated with the CAS number 42532-60-5, and C5-ketone, also designated with the CAS number 756-12-7, both have a very low vapor pressure. This vapor pressure is significantly lower than the vapor pressure of typical secondary gases in gas mixtures that are used as protective or insulating gas, such as nitrogen or carbon dioxide. A system according to the invention is made up of simple components and is very well suited for separating gas mixtures in which the individual components have differing vapor pressures efficiently and with great purity. A system according to the invention can also be constructed very compactly so that it can be operated as a mobile system.

In this context, it is pointed out in particular that all the features and properties described in relation to the system, but also procedures, can also be applied analogously with regard to the formulation of the method according to the invention and are replaceable in the sense of the invention and are also disclosed. The same also applies in the opposite direction, that is, structural features, ie features according to the device, only mentioned in relation to the method can also be taken into account and claimed within the scope of the device or system claims and are also included in the disclosure.

In the drawings, the invention is shown schematically in particular in one embodiment. Show it:

1 shows a schematic representation of an embodiment of a system according to the invention,

2 shows a block diagram of an embodiment of a method according to the invention.

In the figures, elements that are the same or that correspond to one another are each designated by the same reference symbols and are therefore not described again unless appropriate. The disclosures contained in the entire description can be applied analogously to the same parts with the same reference symbols or the same component names. The position details chosen in the description, such as for example above, below, to the side, etc., refer to the figure immediately described and shown and are to be transferred accordingly to the new position in the event of a change in position. Furthermore, individual features or combinations of features from the different exemplary embodiments shown and described can also represent independent, inventive or inventive solutions. Fig. 1 shows a schematic representation of an embodiment of a system according to the invention. A connection 101 can be seen at the very bottom right, via which a gas mixture to be separated can be fed to the system. The connection 101 can be connected directly to an application, for example an electrical switchgear. Alternatively, a transport container for a gas mixture, for example a gas bottle, can also be connected to the connection 101. A connecting line leads from the connection 101 to the suction pump 21. This connecting line can be opened and closed by the valve 132. Starting from connection 101, a bypass line leads past the suction pump 21. The suction pump 21 can be bypassed via this bypass line. The bypass line can be opened and closed by the valve 131. The system thus offers the possibility of sucking in the gas mixture from the connection 101 with the aid of the suction pump 21 or, alternatively, of feeding the gas mixture to the next system components or process steps via the bypass line, driven by pressure outside the system. The setting of which route should be selected starting from connection 101 can be made via valves 132 and 131. A filter 122 can be seen in the direction of flow after the suction pump 21 or the bypass line. The gas mixture can be cleaned in this filter and, for example, suspended matter in the gas mixture can be removed. The compressor 11 is arranged in the direction of flow after the filter 122. This compressor 11 sucks in gas mixture from the line in front of it in the flow direction and compresses it. When the system is in operation, the compressor 11 is preferably regulated in such a way that the pressure downstream of the compressor 11 is already set so that the desired liquefaction of the useful gas takes place after the gas mixture has been continued into the pressure vessel 93. In practice, a set output pressure of the compressor 11 of 5-20 bar, preferably 10 bar, has proven to be particularly suitable. In the direction of flow after the compressor, a further valve 201 and a further filter 121 are arranged in a connecting line. The valve 201 enables the line leading away from the compressor 11 to be opened and closed. The filter 121 is provided to clean the already compressed gas mixture. In the line running in the direction of flow after the compressor 11, a drying unit can additionally be provided with which moisture is removed from the gas mixture.

A connecting line to the pressure vessel 93, which can be opened and closed by the valve 139, runs from the filter 121. This valve 139 can thus be used to determine whether or not the gas mixture is supplied to the pressure vessel 93. The pressure vessel is usually filled periodically, that is to say the valve 139 is opened at times and closed at times. This valve 139 can be controlled by a system controller. Of course, the valve 139 can also be opened or closed manually. The pressure vessel 93 is elongated, the longest dimension of which is oriented essentially vertically. The line running from the valve 139 to the pressure vessel 93 is connected to the pressure vessel 93 in the upper region, in particular in the upper third thereof. The pressure vessel 93 is designed to be pressure-tight and pressure-resistant. The pressure vessel 93 comprises a cooling unit 931, which cools the pressure vessel and the gas mixture located therein. In the illustration, the cooling unit 931 is shown in a zigzag shape. In reality, helically or spirally running cooling lines are advantageously arranged in the pressure vessel 93 over a large area of the length of the pressure vessel 93. This ensures that the pressure vessel 93 and its contents are cooled uniformly and effectively. The cooling unit 931 cools the contents of the pressure vessel 93 preferably to a temperature between -30 and -60 ° C., particularly preferably to a range from -45 to -50 ° C. A removal line 1401 is also connected in the upper third to the pressure vessel 93. This removal line 1401 serves to remove the secondary gas-containing gas phase forming in the pressure vessel 93 from the pressure vessel 93. In order to control or regulate this extraction, the valve 140 is arranged in the extraction line 1401. The extraction line 1401 ends at the connection 105. The connection 105 is provided to be connected to a container via which the secondary gas-containing gas phase can be removed from the system. The withdrawn secondary gas-containing gas phase can then either be disposed of or reused. At the lowest point of the pressure vessel 93, a transfer line 1351 is connected, which can be opened and closed via the two valves 135 and 134. The transfer line 1351 connects the pressure vessel 93 with the purification vessel 95 shown to the right. In the schematic view in FIG. 1, the purification vessel 95 is shown smaller than the pressure vessel 93. In practice, however, it has been found that the system works optimally when pressure vessels and purification vessel 95 are approximately the same size. The liquefied useful gas is transferred from the pressure vessel 93 into the purification vessel 95 via the transfer line 1351. A first separation step for separating useful gas and secondary gas is carried out in the pressure vessel 93. The useful gas removed from the pressure vessel 93, however, still has residues of secondary gas, which are removed in the purification vessel 95. A second separation step of useful gas and secondary gas thus takes place in the purification container 95.

The purification container 95 comprises a heater 951 which heats the purification container 95 and the gas contained therein. The heater 951 is preferably controlled or regulated via a system control. In the embodiment shown, the heater 951 is designed as an electrical heater. Alternatively, however, other types of heating devices 951 can also be used, such as a heat exchanger that uses the waste heat from the cooling unit 931 of the pressure vessel 93. The already pre-cleaned, liquid useful gas is heated in the purification tank 95. The pressure in the purification container 95 is regulated in such a way that this internal pressure is very close to the vapor pressure of the useful gas under the conditions prevailing in the purification container 95. The internal pressure is selected to be slightly higher than this vapor pressure. This ensures that residues of secondary gas which are in the liquid useful gas are outgassed from the liquid useful gas due to their significantly higher vapor pressure. The residues of secondary gas then collect in gaseous form in the upper region of the purification container 95. A suction line 1331 is connected to the top of the purification container 95 to remove this collected secondary gas. This suction line 1331 can be opened and closed via the valve 133. When the gaseous secondary gas is sucked out of the purification container 95, the pressure inside the purification container 95 is reduced. The system is regulated so that the internal pressure in the purification container 95 corresponds minimally to the vapor pressure of the useful gas. A filling line 1361, which can be opened and closed via the valve 136, is connected to the bottom of the purification container 95. The connection 103 is provided at the end of this filling line 1361. At connection 103, the useful gas previously recovered and cleaned in two stages is removed from the system. For this purpose, a pressure vessel, for example, into which the liquid useful gas is filled, can be connected to the connection 103. With the help of this pressure vessel, the recovered useful gas can then be used for further use. The suction line 1331 connects the purification container 95 to the line which connects the suction pump 21 and the bypass line around the suction pump 21 to the compressor 11. The gas phase drawn off from the purification container 95 can be fed back to the compressor 11 via the suction line 1331. The extracted gas phase contains residues of useful gas. As the extracted gas phase is returned from the purification container 95 to the compressor 11, this gas phase, which also represents a gas mixture, is again fed to the separation steps in the pressure container 93 and in the purification container 95. This recycling ensures that the residues of useful gas that remain in the gas phase after a first purification are also recovered in a further process run. This enables almost complete recovery of the useful gas from the gas mixture. The valves 133, 131 and 132 can be used to set whether the compressor 11 sucks in gas mixture supplied via connection 101, gas phase returned via suction line 1331 or a mixture of both, compresses it and supplies it to pressure vessel 93. This setting, which gas mixtures are compressed and conveyed by the compressor 11, is advantageously made automatically by a system control. The system control uses the signals from several different sensors that are located at different points in the system.

2 shows a block diagram of an embodiment of a method according to the invention. In Fig. 2, an embodiment of the method according to the invention is shown as a flow chart. At the beginning of the process there is a suction 30 from the application in which the gas mixture to be separated is located. This suction can either take place directly from the application or from a buffer container with the aid of which the gas mixture is transported from the actual application to the system in which the method according to the invention is carried out. The suction 30 can, for example, as described above, take place via a suction pump 21. After the suction, cleaning 31 is provided in which dirt and moisture are removed from the gas mixture. This purification

31 represents an optional process step which can also be omitted if the gas mixture is appropriately pure. In the next step, compression A took place, which is preferably carried out by a compressor. During compression A, the gas mixture is compressed, preferably to a pressure of about 10 bar. With this compression A, all the components, that is to say useful gas and secondary gas (s), leave the compressor 11 in gaseous form and no liquefaction takes place yet. In the direction of flow after the compressor 11, in which there are lines and components which are at room temperature, it is possible, however, that parts of the useful gas are already liquefied and reach the pressure vessel 93 already liquefied. After compression A, there is another optional drying / cleaning

32 instead. This drying / cleaning 32 can also be omitted with a correspondingly pure gas mixture. In a favorable manner, the purity of the gas mixture is determined via sensors during the suction 30 and before or after the compression A and, based on the sensor signals, the cleaning 31 and drying / cleaning 32 steps are only carried out when required. The gas mixture is then transferred B into the pressure vessel 93, in which the gas mixture is first separated. This separation is carried out via the cooling system C in the pressure vessel 93. The gas mixture in the pressure vessel 93 is cooled to a preferred temperature between -45 ° and -50 ° C. At this temperature and the pressure previously set by compression A, the useful gas is then liquefied. The useful gas can be, for example, C4-nitrile or C5-ketone, both of which have a very low vapor pressure. During cooling C, the internal pressure in pressure vessel 93 is set or regulated in such a way that it is significantly greater, in particular at least twice as great like the vapor pressure of the useful gas and at the same time significantly lower, in particular 5-40% lower than the vapor pressure of the secondary gas. As a result, the vast majority of the secondary gas already changes into the gaseous phase, while the useful gas liquefies and collects in the pressure vessel 93. The gas phase containing the secondary gas is removed from the pressure vessel 93 by the withdrawal D. As a result, most of the gas is separated from the gas mixture as secondary gas. The withdrawn phase containing secondary gas is then withdrawn from the process by disposal / destruction 33. Subsequently or parallel to the withdrawal D, the liquid useful gas is transferred E from the pressure vessel 93 to the purification vessel 95. This transfer E is preferably carried out solely by the pressure prevailing in the pressure vessel 93, which drives the liquid useful gas further into the purification vessel 95. The subsequent heating F of the liquid useful gas takes place by a heater 951 in the purification container 95. The liquid useful gas is heated to a temperature of approximately 0 to 20 ° C. After or during the heating F, the gas phase is sucked out of the purification container 95. The heating F and the suction G are regulated so that the internal pressure in the purification container 95 is slightly higher than the vapor pressure of the useful gas under the conditions prevailing in the purification container 95. The internal pressure in the purification tank 95 is thus significantly closer to the vapor pressure of the useful gas than the internal pressure in the pressure vessel 93. This internal pressure in the purification container 95, which is close to the vapor pressure, effectively removes the last residues of secondary gas, which is still present in the useful gas in liquid form the gaseous phase is transferred and removed from the gas mixture by the suction system F. The useful gas with a very high purity thus remains in liquid form at the bottom in the purification container 95. A purity of> 99% can be achieved using the process according to the invention. The purified, liquid useful gas is removed from the purification container 95 by the filling H. The gas phase removed from the purification container 95 during the suction G still contains residues of useful gas. In order to recover these last residues of useful gas, the gas phase is fed back to compression A and the subsequent process steps through return 34. The last residues of useful gas are thus recovered in a second process run, whereby the process has a very high degree of recovery.

The claims filed now with the application and later do not prejudice the attainment of further protection.

If, on closer examination, in particular of the relevant prior art, it should be found that one or the other feature is favorable for the aim of the invention, but not crucially important, a formulation is of course already sought which has such a feature , in particular in the main claim, no longer has. Such a sub-combination is also covered by the disclosure of this application.

It should also be noted that the configurations and variants of the invention described in the various embodiments and shown in the figures can be combined with one another as desired. Individual or multiple features can be interchanged with one another as required. These combinations of features are also disclosed. The references given in the dependent claims indicate the further development of the subject matter of the main claim through the features of the respective subclaim. However, these are not to be understood as a waiver of the achievement of an independent, objective protection for the features of the dependent claims.

Features that were only disclosed in the description or also individual features from claims that comprise a plurality of features can at any time be adopted as being of essential importance for the invention to delimit them from the state of the art in the independent claim (s), even then, if such features are mentioned in connection with other features or if they achieve particularly favorable results in connection with other features.

List of reference symbols

11 compressor

21 suction pump

30 suction

31 Cleaning

32 Drying / cleaning

33 Disposal / destruction

34 repatriation

93 pressure vessels

95 Purification container

101 connection

103 connection

105 connection

121 filters

122 filters

131 valve

132 valve

133 valve

134 valve

135 valve

136 valve

139 valve

140 valve

201 valve

931 cooling unit

951 heater

1331 suction line / suction line

1351 overpass line

1361 filling line

1401 sampling line

Claims

Patent claims

1. A method for recovering a useful gas from a gas mixture consisting of a useful gas and at least one secondary gas, comprising at least the steps

A) Compression of the gas mixture in a compressor (11),

B) transferring the compressed gas mixture into a pressure vessel (93),

C) cooling the compressed gas mixture in the pressure vessel (93) until the useful gas changes into the liquid phase and a secondary gas-containing gas phase remains, the pressure in the pressure vessel (93) being set so that it is at least twice as high as the vapor pressure of the useful gas in the the current temperature in the pressure vessel (93) and the pressure in the pressure vessel (93) is at least 5% lower than the vapor pressure of the secondary gas at the current temperature in the pressure vessel (93),

D) Removal of the secondary gas-containing gas phase from the pressure vessel (93),

E) transferring the liquefied useful gas from the pressure vessel (93) to a purification vessel (95),

F) heating of the liquefied useful gas in the purification tank (95),

G) suction of the gas phase from the purification container (95) until the internal pressure in the purification container (95) corresponds to the vapor pressure of the useful gas at the current temperature in the purification container (95),

2. The method according to claim 1, characterized in that the transfer B) of the gas mixture into the pressure vessel (93) takes place periodically and a settling time is awaited before the removal D) of the secondary gas-containing gas phase from the pressure vessel (93).

3. The method according to any one of the preceding claims, characterized in that the transfer E) of the liquefied useful gas takes place when the pressure vessel is filled to over 0.75 +/- 20% kg / L with gas mixture.

4. The method according to any one of the preceding claims, characterized in that the heating F) of the liquefied useful gas in the purification tank (95) takes place by a heat exchanger as a heating device, which uses the waste heat generated during cooling C) of the compressed gas mixture in the pressure vessel and the purification tank ( 95) supplies.

5. The method according to any one of the preceding claims, characterized in that the gas phase removed from the purification container (95) during the suction G) is returned to the pressure container (93).

6. The method according to any one of the preceding claims, characterized in that the vapor pressure curve of the useful gas runs below the vapor pressure curve of the secondary gas.

7. The method according to any one of the preceding claims, characterized in that during the suction G) of the gas phase from the purification container (95), the internal pressure and the temperature in the processing container are continuously measured by sensors and a controller based on the measured values of these sensors, which Suction G) ends as soon as the vapor pressure of the useful gas in the purification tank (95) is reached.

8. Plant for the recovery of a useful gas from a gas mixture, the plant having at least the following components:

a compressor (11) for compressing the gas mixture,

a pressure vessel (93) for receiving the compressed gas mixture,

wherein the pressure vessel (93) has a cooling unit (931) for cooling the compressed gas mixture,

and the pressure vessel (93) has a withdrawal line (1401) for the gas phase containing secondary gas,

and the pressure vessel (93) is connected to a purification vessel (95) via a transfer line (1351), which is used to transfer the liquefied useful gas, a heater (951) on the purification vessel (95) for heating the liquefied useful gas,

a suction unit on a suction line (1331) which sucks the gas phase out of the purification tank (95),

and a filling line (1361) is provided and

purified useful gas can be filled via the filling line (1361).

9. Plant according to claim 8, characterized in that a Re gel unit is provided on the suction unit, which sucks the gas phase out of the purification container (95) until the internal pressure in the purification container (95) equals the vapor pressure of the useful gas at the current temperature in the purification container (95) corresponds.

10. Use of a plant according to one of the preceding claims 8 or 9 for recovering the useful gas C4-nitrile (2,3,3,3-tetrafluoro-2- (trifluoromethyl) propanenitrile) and / or C5-ketone (1, 1 , 1, 3,4,4,4-heptafluoro-3- (trifluoromethyl) butan-2-one) from a gas mixture with at least one or more of the following secondary gases: oxygen, nitrogen and / or carbon dioxide, in particular when carrying out or using the Method according to one of the preceding claims 1 to 7.