Separating method for alternative gas mixtures for use as insulating media

Abstract

The invention relates to a method for recovering a useful gas from a gas mixture consisting of a useful and at least one secondary gas, wherein the gas mixture is first compressed and transferred into a pressure vessel (93). Then, from the pressure vessel (93), a secondary-gas containing gas phase is removed and condensed useful gas is transferred into a purification vessel (95). In the purification vessel (95), 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. The most suitable drawing: Fig. 1

Description

[0001] Separation methods for alternative gas mixtures for use as insulating media

[0002] 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 to a pressure vessel where it is cooled. A secondary-containing gas phase is then extracted from the pressure vessel, and the liquefied useful gas is transferred to a purification vessel. In the purification vessel, the liquefied useful gas is then heated and purified by extracting a further gas phase. The invention further 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.

[0003] Gas mixtures are frequently used in technical applications. After these mixtures have been used, it is usually necessary to separate them into their individual gas components in order to dispose of or reuse the components.

[0004] Gas mixtures are used, for example, as protective gases for electrical switchgear. In the past, SF6 was a very common protective gas, which has excellent insulating properties. However, SF6 is harmful to the climate, so other protective or insulating gases have been developed in recent years that have technically similar properties to SF6 and are also more environmentally friendly. These alternative protective or insulating gases are formed from gas mixtures. For example, such gas mixtures are based on C4 nitrile (2,3,3,3-tetrafluoro-2-(trifluoromethyl)propaninitrile) or C5 ketone (1,1,1,3,4,4,4-heptafluoro-3-(trifluoromethyl)butan-2-one). These gases, on which gas mixtures for the formation of a protective or insulating gas are based, are referred to below as utility gases. To form a gas mixture as a protective or insulating gas, one or more so-called secondary gases are added to the main gas.These secondary gases can be, for example, nitrogen or carbon dioxide. The mixing ratios between the primary gas and the secondary gas are adjusted to the application in which the gas mixture is used. When using such a gas mixture, for example as insulating gas in a switchgear, it can happen that these gas mixtures become contaminated, for example, if air is unintentionally mixed in. In this case, a gas mixture with other, unwanted components is formed, which are also referred to as secondary gases.

[0005] There is therefore a need for solutions to separate gas mixtures consisting of a primary gas and at least one secondary gas back into their individual gas components. Firstly, it is necessary to remove impurities from unintentionally contaminated gas mixtures. Secondly, there is also a need to separate uncontaminated gas mixtures back into their individual components in order to create new gas mixtures from these components, for example, with different mixing ratios. There is a particularly high demand for such solutions in the area of ​​protective and insulating gases for electrical switchgear. However, reliable separation of gas mixtures and recovery of primary gases from gas mixtures are also required in other technical fields.

[0006] The object of the invention is therefore to propose solutions for reliably separating gas mixtures into their individual components.

[0007] This problem of the invention is solved 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 of

[0008] A) Compression of the gas mixture in a compressor,

[0009] B) Transfer of the compressed gas mixture into a pressure vessel,

[0010] C) Cooling the compressed gas mixture in the pressure vessel until the useful gas transitions into the liquid phase and a secondary gas-containing gas phase remains, whereby the pressure in the pressure vessel is adjusted 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,

[0011] D) Extraction of the secondary gas-containing gas phase from the pressure vessel,

[0012] E) Transfer of the liquefied utility gas from the pressure vessel to a purification vessel,

[0013] F) Heating of the liquefied feed gas in the purification vessel,

[0014] G) Extraction of the gas phase from the purification vessel until the internal pressure in the purification vessel corresponds to the vapor pressure of the feed gas at the current temperature in the purification vessel.

[0015] The process according to the invention is designed to separate a gas mixture and recover a useful gas from it. The gas mixture consists of a useful gas and at least one secondary gas. Typically, however, the gas mixture contains several secondary gases. By recovering the useful gas from the mixture, at least one secondary gas remains, thus separating the gas mixture. In a first process step, the gas mixture is compressed using a compressor. The gas mixture is compressed to a suitable pressure. The process according to the invention aims to liquefy the useful gas while retaining the secondary gas(es) in the gaseous phase. This makes separation by extracting either the gaseous secondary gas or the liquid useful gas particularly simple.A suitable pressure, set by compression in the first process step, must therefore be selected such that the target gas is liquefied in a subsequent process step, while the secondary gas(es) remain unliquefied. Ideally, this suitable pressure is set solely by the initial compression in the compressor. Alternatively, an additional pressure adjustment, for example by further compression or expansion, can be provided between the compressor and the pressure vessel or within the pressure vessel itself.

[0016] In a second process step, the compressed gas mixture is transferred to a pressure vessel. The pressure vessel is where the gas mixture undergoes its initial separation into its individual components. The gas mixture is transferred to the pressure vessel under the pressure previously generated during compression and temporarily stored there. Valves and devices for cleaning the gas mixture, such as filters, are installed along the path between the compressor and the pressure vessel. The pressure vessel includes a cooling unit that cools both the vessel and the gas mixture within it. The gas mixture in the pressure vessel is then cooled. A specific pressure and temperature combination is maintained within the pressure vessel at which the primary gas, which typically has a significantly lower vapor pressure than the secondary gas, liquefies.Simultaneously, the combination of pressure and temperature is adjusted so that the secondary gas in the pressure vessel remains gaseous. Whether a gas exists in a gaseous or liquid state depends on whether the prevailing pressure is above or below the vapor pressure of the gas in question. The vapor pressure, in turn, depends on the prevailing temperature. The condition or state at which a gas transitions from a liquid to a gaseous state can be described as its vapor pressure. Conversely, this condition is also the condensation point, at which a gas transitions from a gaseous to a liquid state. The term vapor pressure is commonly used when a liquid and a gaseous phase coexist in an environment. Below the vapor pressure, a gas exists in a gaseous state in such an environment; above the vapor pressure, it exists in a liquid state.The term "condensation point" does not necessarily require a mixture of liquid and gaseous phases. Above the condensation point, a gas always exists in the gaseous state. In this case, no liquid phase is required. Therefore, the property below the vapor pressure can be equated with the property above the condensation point when a purely gaseous phase is present. According to the invention, the gaseous gas mixture is compressed in the first step to a pressure that, 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, with all components of the gas mixture in gaseous form. The temperature is then reduced in the pressure vessel. This reduction in temperature lowers the vapor pressure of the gas components.Inside the pressure vessel, the temperature is reduced until the pressure inside is significantly higher than the vapor pressure of the gas at the set temperature. At this pressure and temperature combination, the gas liquefies. The pressure vessel is set so that it is at least twice the gas pressure of the gas under the prevailing conditions. The pressure is set significantly higher than the gas pressure of the gas to ensure complete liquefaction. In practice, it has been found that this complete liquefaction is most easily achieved at pressures inside the vessel that are 3-5 times higher than the vapor pressure of the gas.The pressure and temperature combination in the pressure vessel is simultaneously set so that it is at least 5% lower than the vapor pressure of the secondary gas. This margin ensures that the secondary gas remains completely and safely in the gaseous phase and does not partially liquefy. Depending on the type of secondary gas, it may not even have a vapor pressure under the prevailing conditions in the pressure vessel. This is the case, for example, with a secondary gas formed from 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, do 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%, and particularly preferably between 10 and 30%, lower than the vapor pressure of the secondary gas. This pressure setting already separates a very large proportion of the secondary gas from the gas mixture. However, some residues of the primary gas remain in the gaseous phase within the pressure vessel, and conversely, some residues of the secondary gas remain in the liquid phase, which consists largely of primary gas.

[0017] After the initial separation of the gas mixture in the pressure vessel, the gas phase containing the secondary gas is extracted from the pressure vessel. Ideally, a suitable extraction line equipped with a valve is provided in the upper part of the pressure vessel for this purpose.

[0018] In a further process step, the liquefied process gas is transferred from the pressure vessel to a purification vessel. In this purification vessel, the process gas undergoes a second purification process to remove any remaining traces of the secondary gas. This transfer of the process gas to the purification vessel is typically driven by the pressure prevailing in the pressure vessel.

[0019] The purification vessel includes at least one heating element that heats the vessel and the liquefied feed gas within it. This heating increases the vapor pressure of the gases in the purification vessel relative to the conditions in the pressure vessel. Due to the rising vapor pressure, any remaining secondary gas in the liquefied feed gas transitions into the gaseous phase and escapes from the liquefied feed gas. Simultaneously, the rising temperature in the purification vessel reduces the solubility of the secondary gas(es) in the liquefied feed gas, causing them to transition into the gaseous phase, leave the liquefied feed gas, and thus purify the feed gas. In a further process step, the gaseous phase, along with the separated secondary gas residues, is extracted from the purification vessel. This extraction process can reduce the pressure within the purification vessel.Extraction continues until the internal pressure in the purification vessel reaches a minimum value equal to the vapor pressure of the feed gas at the current temperature. The prevailing pressure in the purification vessel is therefore always greater than or equal to the vapor pressure of the feed gas at the current temperature within the vessel. To ensure thorough separation of the feed gas and secondary gas, the internal pressure in the purification vessel is reduced during extraction until it reaches the vapor pressure of the feed gas. This effectively separates any remaining secondary gas from the feed gas. At pressures very close to the vapor pressure of the feed gas, the feed gas also begins to transition into the gaseous state. The gas phase extracted from the purification vessel may therefore also contain a proportion of feed gas.According to the invention, however, maintaining an internal pressure in the purification vessel very close to the vapor pressure of the feed gas is essential for achieving high purity of the separated or recovered feed gas, which is collected in liquefied form in the purification vessel. After completion of this process step, the feed gas is present in the purification vessel in liquid form with a very high purity. Recovery of the remaining feed gas, which is extracted from the purification vessel, is possible through optional embodiments of the process, as described below.

[0020] In a particularly preferred embodiment, the method according to the invention is carried out exactly in the sequence of the individual process steps as described above. However, it is also possible to modify the sequence of the process steps if this leads to more favorable results in the application.

[0021] Furthermore, the proposal advantageously provides that the gas mixture is extracted from a container containing the gas mixture in the application by means of a suction pump before compression (A). In this embodiment, the gas mixture is extracted from the container in which it is used technically before compression. For example, such a container could 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 extraction pressure. This low extraction pressure ensures that the usable gas, which typically has a very low vapor pressure, remains safely in the gaseous phase during extraction. Filters for cleaning the extracted gas mixture can be installed before or after the suction pump during extraction from the container.Gas mixtures used in switchgear as protective or insulating gases can be extracted directly from the switchgear and then subjected to compression for the process according to the invention. Alternatively, extraction from the switchgear or the container can also be carried out using the suction pump into a buffer tank. In this case, the gas mixture can be subjected to compression for the process according to the invention in this buffer tank. An advantage of the intermediate storage of the gas mixture in a buffer tank is that the system for carrying out the process 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 integrated with the buffer tank or designed separately from it.In a preferred embodiment of the proposal, the gas mixture is cleaned, in particular filtered, after extraction by the suction pump. In this embodiment, the gas mixture is cleaned after extraction, before compression by the compressor. Various types of filters can be used for cleaning.

[0022] Furthermore, it is provided that after the gas phase is extracted (G) from the purification vessel, the purified gas remaining in liquid form in the purification vessel is transferred to a storage container. In this embodiment, the purified gas, which collects at the bottom of the purification vessel after the gas phase has been extracted, is taken from the purification vessel and transferred to a storage container, such as a gas cylinder. The recovered gas can then be used in a new application. For example, the storage container can be connected to a mixing system where the recovered gas is added to a new gas mixture.

[0023] In an advantageous embodiment, the gas mixture is dried and / or cleaned, in particular filtered, between compression (A) and transfer (B). In this embodiment, the gas mixture is cleaned and / or dried between compression and the pressure vessel. This cleaning and / or drying can be carried out before or during transfer (B) into the pressure vessel. Drying means the removal of moisture or dampness contained in the gas mixture. Cleaning is usually carried out using filters. A two-stage cleaning process is also possible, with a first cleaning step before compression and a second cleaning step after compression.

[0024] It is cleverly designed that the gas mixture is compressed to a pressure of 5-20 bar, particularly 10 bar, during compression A). This pressure range is especially suitable for carrying out a process in which C4 or C5 is to be recovered from a gas mixture as the feed gas. At the temperatures prevailing in the pressure vessel, this pressure is significantly higher than the vapor pressure of the feed gas, but significantly lower than the vapor pressure of the secondary gas. Thus, this pressure range is particularly suitable for the initial separation of the feed gas and the secondary gas.

[0025] In a further preferred embodiment, the gas mixture is cooled to a temperature of -30 to -60 °C, and in particular to a temperature of -45 to -50 °C, during cooling (C) in the pressure vessel. This temperature range during cooling in the pressure vessel, especially in combination with the previously described preferred pressure range, is particularly suitable for recovering C4 or C5 from a gas mixture. As already described, these parameters result in cooling conditions in the pressure vessel where the pressure is significantly higher than the vapor pressure of the feed gas, but simultaneously lower than the vapor pressure of the secondary gas. Under these conditions, the feed gas reliably transitions into the liquid state, while the secondary gas assumes a gaseous state.

[0026] Furthermore, it is advantageously provided that cooling (C) is carried out for between 5 and 20 minutes, particularly 10 minutes. Cooling in the pressure vessel is usually performed periodically. This means that gas mixture is first transferred from the compression into the pressure vessel. This transfer is then interrupted, and cooling is initiated. A time period of between 5 and 20 minutes has proven particularly effective in creating conditions within the pressure vessel where the primary gas is liquid, while the secondary gas is gaseous. Of course, cooling can also be performed for a shorter or longer period than this range.

[0027] Advantageously, the transfer (B) of the gas mixture into the pressure vessel is carried out periodically, and a settling period is observed before (D) the secondary gas-containing gas phase is withdrawn from the pressure vessel. Ideally, the transfer of the gas mixture into the pressure vessel is not continuous but periodic. This means that, in a first step, the gas mixture is transferred from the compression point into the pressure vessel. In a second step, the transfer is interrupted, and cooling takes place in the pressure vessel without further filling. After the desired parameters in the pressure vessel have been set, a settling period is observed. During this settling period, the secondary gas contained in the liquefied feed gas escapes upwards and collects in gaseous form above the liquid feed gas.Without a settling period, larger amounts of gaseous secondary gas would be present in the liquid feed gas. After the settling period has elapsed and the secondary gas has dissipated, the gas phase containing the secondary gas is then extracted from the pressure vessel.

[0028] Furthermore, the proposal advantageously provides for the disposal or destruction of the secondary gas-containing gas phase extracted during extraction D). Particularly in the case of protective or insulating gases, the secondary gas is not harmful to the environment or climate and is also inexpensive to obtain. In this specific case, it is not cost-effective to reuse the secondary gas for further applications. Disposal or destruction is therefore simpler and more cost-effective.

[0029] In a preferred embodiment of the proposal, the transfer (E) of the liquefied feed gas occurs when the pressure vessel is filled with a gas mixture exceeding 0.75 ± 20% kg / L. The filling and emptying, or transfer of the liquefied feed gas, into the purification vessel preferably occur periodically. Advantageously, the transfer of the liquefied feed gas takes place when the pressure vessel has a filling density of 0.75 ± 20% kg / L, or 0.75 kg / L with a tolerance of ± 20%. At a higher filling density, insufficient space remains in the pressure vessel to collect the gas phase containing secondary gases. At a lower filling density, only a small amount of liquid feed gas phase is contained in the pressure vessel, making the transfer inefficient. The aforementioned filling densities have proven suitable in practice.However, if the shape or size of the pressure vessel is changed, other areas of filling density may also be optimal for initiating the transfer of the liquefied utility gas.

[0030] Furthermore, it is provided that the purification vessel is evacuated before the transfer (E) of the liquefied feed gas. In this embodiment, the purification vessel is emptied or evacuated before the liquid feed gas phase is transferred from the pressure vessel. This results in no or only very low back pressure in the purification vessel, allowing the liquid feed gas phase to be transferred into the purification vessel without obstruction. Moreover, this ensures that the transferred feed gas phase is not contaminated by residual gas present in the purification vessel.

[0031] In an advantageous embodiment, the heating F) of the liquefied feed gas in the purification vessel is carried out by an electrically operated heating device. In this embodiment, the heating is performed by an electric or electronic heating device. Such heating devices are particularly easy to regulate in terms of their power, which simplifies the design of the conditions inside the purification vessel. Typically, one or more temperature sensors are provided inside the purification vessel and are integrated into a control loop for regulating the heating device.

[0032] In a further preferred embodiment, the heating F) of the liquefied feed gas in the purification vessel is carried out by a heat exchanger acting as a heating device. This heat exchanger utilizes the waste heat generated during the cooling C) of the compressed gas mixture in the pressure vessel and transfers it to the purification vessel. A heat pump is typically used to cool the gas mixture in the pressure vessel. This process generates waste heat outside the pressure vessel, which can then advantageously be used to heat the feed gas in the purification vessel. Such a heat exchanger significantly reduces the overall energy consumption for carrying out the process according to the invention and makes a system for carrying out this process very energy-efficient.

[0033] Furthermore, it is advantageously provided that heating is achieved both by the heat exchanger and additionally by the electric heater. In this embodiment, heating is accomplished through a combination of a heat exchanger and an electric heater. Advantageously, a significant portion of the heating is performed by the particularly energy-efficient heat exchanger. Fine temperature control in the purification vessel is achieved by an electric heater, which is adjustable almost in real time and with very precise control. This fine control is important for establishing conditions in the purification vessel where the prevailing pressure is very close to the vapor pressure of the feed gas. A combination of heat exchanger and electric heater is therefore both energy-efficient and highly effective for the separation or recovery of the feed gas.

[0034] Advantageously, the gas phase extracted from the purification vessel during extraction (G) is returned to the pressure vessel. The gas phase extracted from the purification vessel consists largely of secondary gas but also contains residual useful gas. To recover this residual useful gas, the gas phase is advantageously reintroduced into the process. Preferably, this is achieved by reintroducing the gas phase into the pressure vessel via a compressor or pump. Any remaining useful gas in the gas phase is then recovered in a second process cycle. This return of the gas phase from the purification vessel to the process results in a particularly effective recovery of the useful gas.

[0035] Furthermore, the proposal advantageously provides that the extraction (G) of the gas phase from the purification vessel is carried out by a compressor. In this embodiment, the extraction from the purification vessel is performed by a compressor that additionally compresses the extracted gas phase. Either the same compressor used for the initial compression (A) can be used for this extraction, or alternatively, a different or additional compressor can be used. By using the same compressor as for the initial compression (A), it is used twice, which simplifies the design of a system for carrying out the process.

[0036] In a preferred embodiment of the proposal, it is provided that during filling (H) the purified feed gas remaining in liquid phase in the purification vessel is filled into an evacuated pressure vessel. The prior evacuation of the pressure vessel into which the purified feed gas is to be filled ensures that the feed gas is not recontaminated. At the same time, in this embodiment, there is no or only very low back pressure in the pressure vessel intended for filling, making the filling process simple and efficient.

[0037] Furthermore, it is provided that the vapor pressure curve of the feed gas lies below the vapor pressure curve of the secondary gas. The process according to the invention is particularly suitable for separating gas mixtures in which the feed 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, gas mixtures containing C4 or C5 as the feed gas are often used as protective or insulating gases. 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 above its critical temperature. In this case, the condensation point of the feed gas is higher than the condensation point of nitrogen.

[0038] In an advantageous embodiment, the internal pressure and temperature of the purification vessel are continuously measured by sensors during the extraction process (G) of the gas phase from the purification vessel. A control system, based on these sensor readings, terminates the extraction process (G) as soon as the vapor pressure of the feed gas in the purification vessel is reached. The gas phase is extracted from the purification vessel until the internal pressure in the vessel corresponds to the vapor pressure of the feed gas under the prevailing conditions. For the recovery of the purest possible feed gas, it is important that the internal pressure in the purification vessel is brought as close as possible to the vapor pressure of the feed gas. Therefore, automatic, electronic control of the internal pressure is advantageous. For this purpose, one or more pressure and / or temperature sensors are provided in the purification vessel.The measured values ​​from these sensors are used for electronic control of the extraction of the gas phase as well as for controlling the heating device and the temperature in the processing tank.

[0039] It is advantageously planned that the transfer (B) of the compressed gas mixture into the pressure vessel occurs either periodically or continuously. As previously described, this transfer is preferably carried out periodically. At one time, the pressure vessel is filled, and at another time, when no filling is taking place, the contents of the pressure vessel are cooled, thus separating the gas mixture. Alternatively, however, it is also possible to make the filling of the pressure vessel, and therefore also the removal of the separated gas phases, continuous. Such a continuous process increases the temporal efficiency of the corresponding systems. Since a continuous process generates additional costs, it is primarily economically viable for large-scale plants.

[0040] In a further preferred embodiment, the transfer E) is driven by the pressure prevailing in the pressure vessel. In this embodiment, the transfer of the liquefied feed gas from the pressure vessel to the purification vessel is driven by the pressure prevailing in the pressure vessel. This embodiment is particularly effective in combination with prior evacuation of the purification vessel. No additional system components, such as pumps or the like, are required for the transfer of the liquid feed gas phase. Due to the heating in the purification vessel, the vapor pressure of the feed gas there increases compared to the vapor pressure at room temperature. Thus, the feed gas in its liquid phase can be transferred from the cooled pressure vessel to the heated purification vessel.Alternatively, it is of course possible to include supporting system components that facilitate the transfer into the purification tank. For example, the existing compressor could be used to assist in transferring the liquid phase into the purification tank.

[0041] The object of the invention is also achieved by a system for recovering a useful gas from a gas mixture, wherein the system comprises at least the following components:

[0042] a compressor for compressing the gas mixture,

[0043] a pressure vessel to hold the compressed gas mixture,

[0044] wherein the pressure vessel has a cooling unit for cooling the compressed gas mixture, and the pressure vessel has a withdrawal line for the secondary gas-containing gas phase, and the pressure vessel is connected via a transfer line to a purification vessel which serves to transfer the liquefied useful gas,

[0045] the purification vessel includes a heating device for heating the liquefied feed gas, and an extraction unit on an extraction line that extracts the gas phase from the purification vessel.

[0046] as well as a filling line is provided and

[0047] purified usable gas can be filled via the filling line.

[0048] An apparatus according to the invention is suitable and designed to carry out the process according to the invention and thereby recover a usable gas from a gas mixture. It should be expressly noted here that disclosures relating to the apparatus components within the description of the process according to the invention are also disclosed in connection with the apparatus according to the invention.

[0049] The system according to the invention comprises a compressor designed to compress the gas mixture and 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 designed to cool its contents. Furthermore, the pressure vessel includes a discharge line designed to remove the secondary gas-containing gas phase from the pressure vessel. The discharge line is connected in the upper region of the pressure vessel, with this connection located above the liquid level of the liquefied usable gas phase. The pressure vessel also includes a transfer line that carries purification tanks.The transfer line is designed to extract the liquid gas phase from the pressure vessel and transfer it to the purification vessel. The transfer line is connected to the lower section of the pressure vessel, below the liquid level of the gas phase. The system according to the invention further comprises the aforementioned purification vessel, which is designed to perform a second separation of the gas mixture. The gas transferred from the pressure vessel still contains residual secondary gas, the vast majority of which is removed from the gas in the purification vessel. With a system according to the invention, a purity of more than 99% of the recovered gas is possible. The purification vessel includes a heating device designed to heat the contents of the purification vessel.This heating device can also comprise several components, for example, an electrically operated component and a component connected to a heat exchanger that utilizes the waste heat from the cooling process in the pressure vessel. Furthermore, the purification vessel includes at least one extraction unit with at least one extraction line. The extraction unit is designed to remove the secondary gas-containing gas phase from the purification vessel. At least one filling line is connected to the purification vessel for the removal of the recovered, purified usable gas. The recovered usable gas is extracted from the system according to the invention via this filling line.

[0050] A system according to the invention consists of reliable technical components and has a simple design. Therefore, a system according to the invention is very reliable and enables the recovery of usable gas with very high purity.

[0051] Advantageously, the extraction unit is equipped with a control unit that extracts the gas phase from the purification vessel until the internal pressure in the purification vessel equals the vapor pressure of the target gas at the current temperature in the purification vessel. In this embodiment of the system, an electronic or computer-controlled control unit is provided that regulates the conditions, in particular the pressure and temperature in the purification vessel. This control unit uses as input measured values ​​from sensors located inside the purification vessel. As output, the control unit influences the extraction of the gas phase from the purification vessel. For example, the control unit can influence the opening of a valve in the extraction line. An analogous control unit can also be provided on the pressure vessel to regulate the extraction of the secondary gas-containing gas phase from there.The control unit can be formed by a plant control system or be part of a plant control system.

[0052] 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 unit. In this embodiment, at least one pressure or temperature sensor is arranged on the pressure vessel, and advantageously also on the purification vessel, which is connected to a system control unit or a control unit. Advantageously, several pressure and temperature sensors are provided, which transmit their measured values ​​as input to an automatic control system for the conditions in the pressure vessel and / or in the purification vessel.

[0053] A system for recovering a usable gas from a gas mixture can be operated particularly efficiently using a system controller. This controller is designed 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 example, flow sensors can be installed in the lines from the compressor to the pressure vessel, from the pressure vessel to the purification tank, and / or from the purification tank back to the compressor. These sensors measure the mass flow rates and communicate them to the system controller. Furthermore, sensors can be installed to determine the mass or weight of the gas mixture in the pressure vessel and the purification tank. Using the measured values ​​from these sensors, the system controller can then automatically determine the density in the tanks.The system control is also designed to calculate the vapor pressures of the individual components in real time, particularly within the pressure vessel and the purification vessel, and to regulate the internal pressures and temperatures according to the process specifications. Furthermore, the system control can act on the various valves required for the passage of the gas mixture through the system or for the extraction of the gas from separate components. Finally, sensors can be integrated to determine the moisture content and particle contamination of the gas mixture. Based on the signals from these sensors, the system can then automatically control whether the gas mixture should be dried or purified, adjusting filters and / or drying units accordingly.

[0054] In a further embodiment, sensors can be arranged in the extraction line for removing the secondary gas-containing gas phase from the pressure vessel. These sensors monitor the remaining amount of usable gas in this extracted gas phase. Based on the signals from these sensors, the extracted gas phase can then be released into the atmosphere for disposal if the usable gas concentration is low. If the usable gas concentration is too high, the gas phase can also be reintroduced into the process to remove or at least reduce the remaining traces of usable gas.

[0055] Furthermore, sensors can be arranged downstream of the connection through which the gas mixture to be separated is fed into the system or process. These sensors determine the composition of the gas mixture, in particular the proportion of the target 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 into the system or process for purification. This determination of the gas composition can, of course, also be performed continuously, and the system control can continuously regulate the amount of gas mixture fed in based on the determined signals.The object of the invention is also achieved by using a system according to one of the previously described embodiments for recovering the useful gas C4-nitrile (2,3,3,3-tetrafluoro-2-(trifluoromethyl)propaninitrile) 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 by carrying out or using the process according to one of the previously described embodiments. A system according to the invention is particularly well suited for carrying out a process according to the invention. The useful gases C4-nitrile, also known by CAS number 42532-60-5, and C5-ketone, also known by 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 used as protective or insulating gases, such as nitrogen or carbon dioxide. A system according to the invention is constructed from simple components and is very well suited to efficiently and with high purity separating gas mixtures in which the individual components have differing vapor pressures. Furthermore, a system according to the invention can be constructed very compactly, so that it can be operated as a mobile system.

[0056] In this context, it is particularly emphasized that all features and properties described in relation to the system, as well as procedures, are analogously transferable and interchangeable with regard to the formulation of the inventive method and are considered to be co-disclosed. The same applies in reverse, meaning that structural features, i.e., device-related features, mentioned only in relation to the method can also be considered and claimed within the scope of the device or system claims and are likewise part of the disclosure.

[0057] The invention is schematically illustrated in the drawings, particularly in one exemplary embodiment. The drawings show:

[0058] Fig. 1 shows a schematic representation of an embodiment of a system according to the invention,

[0059] Fig. 2 shows a block diagram of an embodiment of a method according to the invention.

[0060] In the figures, identical or corresponding elements are designated with the same reference numerals and are therefore not described again unless expedient. The disclosures contained in the entire description are transferable analogously to identical parts with the same reference numerals or component designations. Furthermore, the positional designations chosen in the description, such as top, bottom, side, etc., refer to the directly described and illustrated figure and are to be applied analogously to the new position if the position changes. Individual features or combinations of features from the different 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.At the bottom right is a connection 101, through which a gas mixture to be separated can be supplied to the system. Connection 101 can be directly connected to an application, such as an electrical switchgear. Alternatively, a transport container for a gas mixture, such as a gas cylinder, can also be connected to connection 101. A connecting line leads from connection 101 to the suction pump 21. This connecting line can be opened and closed by valve 132. A bypass line runs from connection 101, bypassing the suction pump 21. This bypass line allows the suction pump 21 to be bypassed. The bypass line can be opened and closed by valve 131.The system thus offers the possibility of drawing in the gas mixture from port 101 using the suction pump 21, or alternatively, of supplying the gas mixture to the next system components or process steps via the bypass line, driven by pressure present outside the system. The setting for which path from port 101 is to be selected can be made via valves 132 and 131. A filter 122 is located downstream of the suction pump 21 or the bypass line. The gas mixture can be cleaned in this filter, for example, by removing suspended solids. The compressor 11 is located downstream of the filter 122. This compressor 11 draws in the gas mixture from the line upstream of it and compresses it.During operation of the system, the compressor 11 is preferably controlled such that the pressure downstream of the compressor 11 is already set to ensure that the desired liquefaction of the usable gas occurs after the gas mixture is fed into the pressure vessel 93. In practice, a set outlet pressure of 5–20 bar, preferably 10 bar, has proven particularly suitable for the compressor 11. Downstream of the compressor, a further valve 201 and a further filter 121 are arranged in a connecting line. The valve 201 allows the line leading away from the compressor 11 to be opened and closed. The filter 121 is designed to clean the already compressed gas mixture. A drying unit can also be provided in the line running downstream of the compressor 11 to remove moisture from the gas mixture.

[0061] A connecting line runs from filter 121 to pressure vessel 93, which can be opened and closed by valve 139. This valve 139 thus determines whether or not a gas mixture is supplied to pressure vessel 93. The pressure vessel is typically filled periodically, meaning that valve 139 is sometimes open and sometimes closed. Valve 139 can be controlled by a system controller. Of course, valve 139 can also be opened or closed manually. Pressure vessel 93 is elongated, with its longest dimension oriented essentially vertically. The line running from valve 139 to pressure vessel 93 is connected to the vessel in its upper section, specifically in the upper third. Pressure vessel 93 is pressure-tight and pressure-resistant.The pressure vessel 93 comprises a cooling unit 931, which cools the pressure vessel and the gas mixture contained therein. In the illustration, the cooling unit 931 is shown in a zigzag shape. In reality, helical or spiral cooling lines are advantageously arranged in the pressure vessel 93 over a large portion of its length. This ensures that the pressure vessel 93 and its contents are cooled uniformly and effectively. The cooling unit 931 preferably cools the contents of the pressure vessel 93 to a temperature between -30 and -60 °C, particularly preferably to a range of -45 to -50 °C. A withdrawal line 1401 is also connected to the pressure vessel 93 in its upper third. This withdrawal line 1401 serves to extract the secondary gas-containing gas phase that forms in the pressure vessel 93.To control or regulate this extraction, valve 140 is located in the extraction line 1401. The extraction line 1401 terminates at connection 105. Connection 105 is designed to be connected to a container through which the secondary gas-containing gas phase can be removed from the system. The extracted secondary gas-containing gas phase can then either be disposed of or reused. A transfer line 1351 is connected to the lowest point of the pressure vessel 93, which can be opened and closed via the two valves 135 and 134. The transfer line 1351 connects the pressure vessel 93 to the purification vessel 95 shown to its 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 functions optimally when the pressure vessel and purification vessel 95 are approximately the same size.The liquefied gas is transferred from pressure vessel 93 to purification vessel 95 via transfer line 1351. A first separation step to separate the gas from the secondary gas is carried out in pressure vessel 93. However, the gas taken from pressure vessel 93 still contains traces of secondary gas, which are removed in purification vessel 95. A second separation step between the gas and the secondary gas therefore takes place in purification vessel 95.

[0062] The purification vessel 95 comprises a heating device 951, which heats the purification vessel 95 and the gas contained therein. The heating device 951 is preferably controlled by a system controller. In the illustrated embodiment, the heating device 951 is designed as an electric heating device. Alternatively, however, other types of heating devices 951 can also be used, such as a heat exchanger that utilizes the waste heat from the cooling unit 931 of the pressure vessel 93. The pre-purified, liquid feed gas is heated in the purification vessel 95. The pressure in the purification vessel 95 is regulated such that this internal pressure is very close to the vapor pressure of the feed gas under the prevailing conditions in the purification vessel 95. The internal pressure is selected to be slightly higher than this vapor pressure.This ensures that residual secondary gases present in the liquid feed gas escape from the liquid feed gas due to their significantly higher vapor pressure. These residual secondary gases then collect in gaseous form in the upper section of the purification vessel 95. A suction line 1331 is connected to the top of the purification vessel 95 for the extraction of this collected secondary gas. This suction line 1331 can be opened and closed via the valve 133. When the gaseous secondary gas is extracted from the purification vessel 95, the pressure inside the purification vessel 95 decreases. The system is regulated so that the internal pressure in the purification vessel 95 is at least equal to the vapor pressure of the feed gas. A filling line 1361 is connected to the bottom of the purification vessel 95 and can be opened and closed via the valve 136. Connection 103 is provided at the end of this filling line 1361.At port 103, the previously recovered and purified gas, obtained in two stages, is removed from the system. For this purpose, a pressure vessel, into which the liquid gas is filled, can be connected to port 103. Using this pressure vessel, the recovered gas can then be supplied for further use. The extraction line 1331 connects the purification vessel 95 to the line that connects the suction pump 21 and the bypass line around the suction pump 21 to the compressor 11. The gas phase extracted from the purification vessel 95 can be fed back to the compressor 11 via the extraction line 1331. The extracted gas phase contains residual gas. By returning the extracted gas phase from the purification vessel 95 to the compressor 11, this gas phase, which is also a gas mixture, is fed back to the separation stages in the pressure vessel 93 and the purification vessel 95.This recirculation ensures that even the residual usable gas remaining in the gas phase after initial purification is recovered in a subsequent process cycle. This enables virtually complete recovery of the usable gas from the gas mixture. Valves 133, 131, and 132 allow the system to select whether compressor 11 draws in, compresses, and delivers to pressure vessel 93 either the gas mixture supplied via connection 101, the recirculated gas phase via suction line 1331, or a mixture of both. Conveniently, this setting—which determines which gas mixtures are compressed and conveyed by compressor 11—is automatically performed by a system controller. The system controller utilizes signals from several different sensors located at various points within the system.

[0063] Fig. 2 shows a block diagram of an embodiment of a method according to the invention. Fig. 2 presents an embodiment of the method according to the invention as a flowchart. At the beginning of the method, an extraction 30 takes place from the application containing the gas mixture to be separated. This extraction can be carried out either directly from the application or from a buffer tank, which transports the gas mixture from the actual application to the system in which the method according to the invention is carried out. The extraction 30 can, for example, be carried out via a suction pump 21, as described above. After extraction, a cleaning process 31 is provided, in which contaminants and moisture are removed from the gas mixture. This cleaning process...

[0064] Step 31 is an optional process step that can be omitted if the gas mixture is sufficiently pure. The next step involves compression A, preferably performed by a compressor. During compression A, the gas mixture is compressed, preferably to a pressure of approximately 10 bar. During this compression A, all components, i.e., the feed gas and secondary gas(es), leave the compressor 11 in gaseous form, and no liquefaction has yet occurred. However, in the direction of flow downstream of the compressor 11, which contains lines and components at room temperature, it is possible that some of the feed gas may already liquefy and enter the pressure vessel 93 in liquefied form. After compression A, a further optional drying / cleaning step takes place.

[0065] 32. This drying / cleaning step 32 can also be omitted if the gas mixture is sufficiently pure. Advantageously, the purity of the gas mixture is determined by sensors during extraction 30 and before or after compression A, and based on the sensor signals, the cleaning steps 31 and drying / cleaning 32 are only carried out if necessary. Subsequently, the gas mixture is transferred B into the pressure vessel 93, where an initial separation of the gas mixture takes place. This separation is achieved via cooling 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 so that it is significantly higher, in particular at least twice as high, as the vapor pressure of the feed gas and simultaneously significantly lower, in particular 5–40% lower, than the vapor pressure of the secondary gas. This causes the vast majority of the secondary gas to transition into the gaseous phase, while the feed gas liquefies and collects in pressure vessel 93. The secondary gas-containing phase is removed from pressure vessel 93 by extraction D. This separates the vast majority of the secondary gas from the gas mixture. The extracted secondary gas-containing phase is then removed from the process by disposal / disposal 33. Subsequently, or concurrently with extraction D, the liquid feed gas is transferred E from pressure vessel 93 to purification vessel 95.This transfer E preferably occurs solely due to the pressure prevailing in the pressure vessel 93, which forces the liquid feed gas further into the purification vessel 95. The subsequent heating F of the liquid feed gas is carried out by a heating device 951 in the purification vessel 95. The liquid feed gas is thereby heated to a temperature of approximately 0 to 20 °C. After or during the heating F, the gas phase is extracted G from the purification vessel 95. The heating F and extraction G are controlled such that the internal pressure in the purification vessel 95 is slightly higher than the vapor pressure of the feed gas under the conditions prevailing in the purification vessel 95. The internal pressure in the purification vessel 95 is thus significantly closer to the vapor pressure of the feed gas than the internal pressure in the pressure vessel 93.Due to this internal pressure in the purification vessel 95, which is close to the vapor pressure, the last traces of secondary gas, which are still present in liquid form in the feed gas, are effectively converted into the gaseous phase and removed from the gas mixture by the extraction unit F. The feed gas thus remains in liquid form at the bottom of the purification vessel 95 with a very high purity. A purity of >99% can be achieved using the process according to the invention. The purified, liquid feed gas is drawn from the purification vessel 95 by the filling unit H. The gas phase drawn from the purification vessel 95 by the extraction unit G still contains traces of feed gas. To recover these last traces of feed gas, the gas phase is fed back to the compression unit A and the subsequent process steps via the recirculation unit 34.The last remaining traces of usable gas are thus recovered in a second process cycle, resulting in a very high recovery rate for the process.

[0066] Claims submitted now with the application and subsequently shall not prejudice the obtaining of further protection.

[0067] Should closer examination, particularly of the relevant prior art, reveal that one or more features are advantageous but not essential for the objective of the invention, a formulation is naturally being sought that no longer includes such a feature, especially in the main claim. Such a sub-combination is also covered by the disclosure of this application.

[0068] It should further be noted that the embodiments and variants of the invention described in the various embodiments and shown in the figures can be combined with one another in any way. Individual or multiple features are freely interchangeable. These combinations of features are also disclosed. The cross-references in the dependent claims indicate the further development of the subject matter of the main claim by the features of the respective dependent claim. However, these are not to be understood as a waiver of the right to obtain independent, pecuniary protection for the features of the cross-referenced dependent claims.

[0069] Features disclosed only in the description, or individual features from claims comprising multiple features, may at any time be incorporated into the independent claim(s) as being essential to the invention for the purpose of distinguishing it from the prior art, even if such features were mentioned in connection with other features or achieve particularly favorable results in connection with other features.

[0070] Reference numeral list

[0071] 11 Compressor

[0072] 21 Suction pump

[0073] 30 Extraction

[0074] 31 Cleaning

[0075] 32 T drying / cleaning

[0076] 33 Disposal / Destruction

[0077] 34 Repatriation

[0078] 93 pressure vessels

[0079] 95 purification containers

[0080] 101 connection

[0081] 103 connection

[0082] 105 connection

[0083] 121 filters

[0084] 122 filters

[0085] 131 Valve

[0086] 132 Valve

[0087] 133 Valve

[0088] 134 Valve

[0089] 135 valve

[0090] 136 Valve

[0091] 139 Valve

[0092] 140 valve

[0093] 201 Valve

[0094] 931 Cooling unit

[0095] 951 Heater

[0096] 1331 Suction line / Extraction line

[0097] 1351 Transfer line

[0098] 1361 Filling line

[0099] 1401 Extraction line

Claims

Patenta ns prüche 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 of A) Compression of the gas mixture in a compressor (11), B) Transfer of the compressed gas mixture into a pressure vessel (93), C) Cooling the compressed gas mixture in the pressure vessel (93) until the useful gas transitions into the liquid phase and a secondary gas-containing gas phase remains, whereby the pressure in the pressure vessel (93) is 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 (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) Extraction of the secondary gas-containing gas phase from the pressure vessel (93), E) Transfer of the liquefied utility gas from the pressure vessel (93) to a purification vessel (95), F) Heating of the liquefied feed gas in the purification vessel (95), G) Extraction of the gas phase from the purification vessel (95) until the internal pressure in the purification vessel (95) corresponds to the vapor pressure of the useful gas at the current temperature in the purification vessel (95), 2. Method according to claim 1, characterized in that the transfer B) of the gas mixture into the pressure vessel (93) is carried out periodically and a settling time is observed before the withdrawal D) of the secondary gas-containing gas phase from the pressure vessel (93).

3. Method according to one of the preceding claims, characterized in that the transfer E) of the liquefied utility gas takes place when the pressure vessel is filled with gas mixture to a density of 0.75 + / - 20 % kg / L.

4. Method according to one of the preceding claims, characterized in that the heating F) of the liquefied feed gas in the purification vessel (95) is carried out by a heat exchanger as a heating device, which utilizes the waste heat generated during the cooling C) of the compressed gas mixture in the pressure vessel and supplies it to the purification vessel (95).

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

6. Method according to one of the preceding claims, characterized in that the vapor pressure curve of the feed gas lies below the vapor pressure curve of the secondary gas.

7. Method according to one of the preceding claims, characterized in that during the extraction G) of the gas phase from the purification vessel (95) the internal pressure and temperature in the processing vessel are continuously measured by sensors and a control system, based on the measured values ​​of these sensors, terminates the extraction G) as soon as the vapor pressure of the useful gas in the purification vessel (95) is reached.

8. Plant for recovering a useful gas from a gas mixture, wherein the plant comprises at least the following components: a compressor (11) for compression of 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 secondary gas-containing gas phase, and the pressure vessel (93) is connected via a transfer line (1351) to a purification vessel (95) which serves to transfer the liquefied useful gas, wherein a heating device (951) for heating the liquefied useful gas is attached to the purification vessel (95), a suction unit on a suction line (1331) that extracts the gas phase from the purification container (95), as well as a filling line (1361) is provided and purified usable gas can be filled via the filling line (1361).

9. System according to claim 8, characterized in that a control unit is provided on the extraction unit, which extracts the gas phase from the purification vessel (95) until the internal pressure in the purification vessel (95) corresponds to the vapor pressure of the useful gas at the current temperature in the purification vessel (95).

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)propaninitrile) 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 by carrying out or using the process according to one of the preceding claims 1 to 7.