Method for operating gas storage devices, and device for carrying out the method, comprising a pressure swing adsorption system and a membrane system

Abstract

The invention relates to a method for operating a gas storage device, wherein existing natural gas storage facilities or natural gas storage devices are used to store hydrogen as a stored gas; in the event of a mixture of hydrogen and natural gas, the removed production gas is separated in a gas separation system; the gas separation process is carried out in a pressure swing adsorption system (E02) having a connected membrane system (E03); the pressure swing adsorption system (E02) is supplied with the stored gas; the membrane system (E03) is then subjected to the desorption pressure originating from the pressure swing adsorption system (E02); the permeate gas is conducted from the membrane system (E03) back to the pressure swing adsorption system (E02) via a third control valve (V03); and the permeate pressure and the transmembrane flow, and thus the gas composition and the residual hydrogen content in the retentate of the membrane system (E03), are set by means of the third control valve (V03). The invention also relates to a device for carrying out the method.

Description

[0001] Method for operating gas storage systems and device for carrying out the method, comprising a pressure swing adsorption system and a membrane system

[0002] The invention relates to a method for operating gas storage facilities according to the preamble of claim 1 and to a device for carrying out the method.

[0003] It is known that in order to extract liquid raw materials from deposits, in particular natural gas or crude oil, these deposits are pressurised with a gas in order to ensure sufficient pressure for the extraction of even residual volumes.

[0004] Either nitrogen or carbon dioxide is used for this purpose, with the use of carbon dioxide now also being used to sequester carbon dioxide in depleted deposits, thus generating a double benefit.

[0005] An overview of Enhanced Gas Recovery, i.e. the removal of residual gas using CO2, is available from "Journal of Petroleum Science and Engineering", 196 (2021) "CO2 enhanced gas recovery and sequestration in depleted gas reservoirs: review", Ahmed Hamza et.al., in which an overview of the known processes and problems is presented.

[0006] Fundamentally, during a gas-gas exchange in a reservoir, physical and chemical processes take place that are not limited to the displacement of one gas by another. In addition, adsorption processes of the introduced displacement gas take place in pores and on the rocks forming the pores, and desorption processes of the gas to be displaced take place there. As is well known in these processes, equilibria are established.

[0007] Also from AT Turta, SSK Sim, AK Singhai, BF Hawkins, Alberta Research Council, Journal of Canadian Petroleum Technology, October 2008, Vol. 47, No. 10 is an overview of residual gas removal by gas-gas displacement, in particular using CO2 and N2 with CO2.

[0008] The same authors provide an overview of the factors that determine gas-to-gas displacement efficiency in the same journal, in the August 2009 issue, Vol. 48, No. 8. Here, too, nitrogen and carbon dioxide are used, as well as combustion gases.

[0009] The expulsion of residual natural gas by CO2 is also known from "Society of Petroleum Engineers, Enhanced Gas Recovery by CO2 Injection and Sequestration: Effect of Connate Water Salinity on Displacement Efficiency"; MK Abba et.al., 2017.

[0010] DE 10 2010 035 260 Al discloses the exploitation of natural gas deposits with hydrogen and its recovery.

[0011] DE 10 2010 034 711 Al discloses the extraction of natural gas using hydrogen extracted from the natural gas. In this process, the methane in the natural gas is reacted with water.

[0012] The storage of hydrogen in natural gas reservoirs is known from DE 10 2010 031 777 A1. This involves continuously analyzing the gas mixtures generated in the gas network and reacting to them at the point of consumption.

[0013] From DE 10 2010 020 762 A1 a method for the amplification and transport of renewable energies is known, in which electrolytically produced hydrogen is to be supplied to a natural gas pipeline and the gas mixture is supplied to a point of consumption.

[0014] EP 2 979 743 A1 discloses a device and a method for storing and distributing renewable energy, wherein natural gas is mixed with hydrogen produced by means of the renewable energy, the natural gas / hydrogen mixture thus obtained is distributed via a preferably already existing gas network, preferably a natural gas network, and the hydrogen is separated again from the natural gas / hydrogen mixture at a desired location by means of membrane separation, wherein the natural gas is mixed with the hydrogen produced by means of the renewable energy in a suitable storage facility and stored, wherein in the case of the withdrawal of natural gas and / or hydrogen, the stored gas mixture is separated by means of membrane separation into natural gas with a hydrogen content in accordance with the statutory provisions for feeding into the natural gas network on the one hand and a natural gas / hydrogen mixture with a hydrogen content of approximately 50% for return to the storage facility on the other.US Pat. No. 5,753,010 A discloses a process for increasing the product yield or reducing the size of steam methane reformers and pressure swing adsorption systems used for hydrogen production. A significant portion of the hydrogen in the PSA depressurization and purge gas, which would otherwise be burned as fuel in the reformer, is capped and recycled to the PSA system to produce additional high-purity hydrogen product. Selected portions of the depressurization and purge gas effluent are processed in adsorption membrane separators to increase the hydrogen content for recirculation to the PSA system. The remaining portions of the depressurization and purge gas effluent, which contain lower hydrogen concentrations, are used as fuel in the reformer.

[0015] Despite the now critically scrutinized use of fossil fuels, natural gas remains a highly valuable raw material, particularly for the chemical industry. Therefore, it is essential to effectively exploit existing natural gas reserves. However, it is important to keep costs low, which is why carbon dioxide is a cheap and, if sequestered, also a good raw material for extracting natural gas.

[0016] And, as explained in the aforementioned publications, carbon dioxide is also extracted along with the extracted natural gas, which must be separated from the natural gas and returned. This naturally also applies to gas mixtures with nitrogen or other gases. This is based on the described equilibrium processes. The necessary processes and equipment are known to those skilled in the art.

[0017] The equilibrium processes during adsorption / desorption mean that the displacement of natural gas is only possible up to a certain degree, or up to a degree where the separation of natural gas / displacement gas is no longer economical.

[0018] US Pat. No. 6,183,628 B1 discloses a process for separating hydrogen and hydrocarbons within refinery processes, which involves pressure swing adsorption and compression (cooling) steps, as well as the use of membranes. The membrane separation is intended to achieve a selectivity of 2.5 relative to methane and hydrogen. In total, a hydrogen stream, an LPG stream, and a methane-rich stream are to be produced.

[0019] US 2022 / 0219978 A1 addresses the problem that pressure swing adsorption and cryogenic separation processes in petrochemical processes have technological limitations regarding hydrogen yield. To remedy this, gas separation membranes are to be combined with the aforementioned processes. A hydrogen-containing gas stream is first fed to a pressure swing adsorption (PSA), with a membrane permeate stream also being fed to the PSA. The gas stream containing unseparated hydrogen is then fed to the membrane separation stage, where the membrane permeate stream containing hydrogen is fed to the PSA, and the residual gas stream is diverted.

[0020] US 4,238,204 deals with the separation of hydrogen or helium from a gas stream. A gas stream is fed to a selective adsorption unit in which the light gas is separated. A purge gas containing the light gas is obtained, which is then fed to a membrane separation unit, in which the light gas is recovered with higher purity. The permeate is returned to the selective adsorption unit. The gas, which contains adsorbed gases and a small amount of light gas, is to be disposed of or used for another purpose.

[0021] A similar process is known from US 4,229,188.

[0022] US Pat. No. 4,398,926 discloses a process in which a high-pressure gas stream containing up to 90 mol% hydrogen is fed to a separation device containing a membrane separation stage capable of selectively passing hydrogen. After a pressure reduction, the hydrogen is fed to a PSA adapted to the lower pressure. An offgas from the separation device is essentially obtained from the gas stream with the higher pressure, and a portion of this is brought to a lower pressure and additionally fed to the PSA to contribute to the recovery of the hydrogen and reduce operating costs.

[0023] The state of the art therefore shows that a separation task involving hydrogen and hydrocarbons can be accomplished using various processes / systems. To achieve the desired separation effect (which means sufficiently high gas purity and / or gas yield), a sufficient number of separation stages and / or process combinations are usually required, which, however, involves greater energy and equipment expenditure.

[0024] On the other hand, process design usually involves achieving the desired separation effects with the lowest possible equipment and energy expenditure. Furthermore, factors such as process stability and controllability play a significant role in process design.

[0025] The object of the invention is to create a process which separates hydrogen and natural gas more effectively and cheaply when operating a hydrogen storage system.

[0026] The problem is solved by a method having the features of claim 1.

[0027] Advantageous further training is indicated in the dependent subclaims.

[0028] A further object is to create a device that separates hydrogen and natural gas more effectively and cheaply when operating a hydrogen storage system.

[0029] The problem is solved by a device having the features of claim 14.

[0030] Advantageous further training is indicated in the dependent claims.

[0031] The invention is used in cases where existing natural gas deposits or existing natural gas storage facilities, in particular natural gas pore storage facilities, are supplied with hydrogen.

[0032] This is particularly the case if hydrogen is used as storage gas in an existing natural gas reservoir or storage facility in order to use a reservoir or an existing natural gas storage facility as a hydrogen storage facility.

[0033] https: / / www.geostockgroup.com / en / four-ways-to-store-large-quantities-of-hydrogen / argues that hydrogen would not mix with the gas present in the reservoir. "Estimation of Diffusion Losses of Hydrogen During the Creation of its Effective Storage in an Aquifer," Daniil Pavlovich Anikeev et al., SPE-206614-MS, 2021, particularly the first paragraph on page 11, also argues that hydrogen does not mix with natural gas, or rather, due to its lower density, it even separates and collects at the top of the reservoir.

[0034] Contrary to expert assumptions, tests conducted by the applicant have shown that, surprisingly, mixing of the introduced hydrogen (storage gas) with the residual natural gas does occur.

[0035] This mixing also allows the stored gas to penetrate more easily into less permeable regions of the reservoir, resulting in an increasing release of natural gas.

[0036] However, this also means that the mixed gases have to be separated again.

[0037] It should also be noted that the cushion gas, i.e., the gas remaining in the storage facility as a pressure reservoir, may, for example, consist of half hydrogen and half natural gas at the beginning of H2 storage operation for time and / or cost reasons. Therefore, the production of a gas mixture is expected for a longer period.

[0038] The above-mentioned effects occur both during the conversion of a natural gas reservoir into a hydrogen storage facility and during the conversion of a natural gas storage facility into a hydrogen storage facility, as well as over a longer period of operation of a hydrogen storage facility itself.

[0039] Contrary to popular belief that hydrogen and natural gas separate in the reservoir or that the two gases do not mix at all, field tests conducted by the applicant have shown that the hydrogen mixes into the natural gas both dispersively and diffusively.

[0040] When operating a hydrogen storage facility in a natural gas reservoir, or even when converting a reservoir into a storage facility or a natural gas storage facility into a hydrogen storage facility, it is to be expected that inconsistent gas composition conditions will persist over an extended period of time. Furthermore, it is well known in storage operations that pressure and volume flow conditions can fluctuate significantly depending on the fill level and the injection and withdrawal rates required by the market.

[0041] The present method is essentially intended for the operational phase of a hydrogen storage facility in a natural gas reservoir. However, it is not excluded that the method according to the invention could also be used during the conversion phase of a natural gas storage facility into a hydrogen storage facility, in which natural gas cushion gas is to be replaced by hydrogen cushion gas.

[0042] In any case, a system that processes the gas mixture must be very flexible with regard to input parameters such as pressure and gas composition.

[0043] Processes and systems for the separation of gases are, of course, already known, although known systems are designed for continuous processes, for example in refineries, where the volume flow, pressure conditions and gas composition are not subject to strong fluctuations.

[0044] Such known systems, if adapted to the conditions described above, would have to be designed to be unfavorably large to cope with all production conditions. Furthermore, the controllability and achievability of the desired separation effect for all production conditions of such gas separation systems are not guaranteed in the state of the art.

[0045] In order to create an economically viable configuration with high technical efficiency, the invention combines a pressure swing adsorption plant with a membrane separation, whereby the pressure in the plant is influenced, which allows the separation effect to be achieved even with strongly fluctuating input parameters.

[0046] The invention thus relates in particular to a method for operating a gas storage facility, wherein existing natural gas deposits or natural gas storage facilities are used to store hydrogen as storage gas, wherein the extracted production gas is separated in a gas separation plant when a mixture of hydrogen and natural gas is present, wherein the gas separation is carried out in a pressure swing adsorption plant with a connected membrane plant, wherein the pressure swing adsorption plant is directly subjected to the storage gas pressure and subsequently the membrane plant is subjected to the desorbate pressure originating from the pressure swing adsorption plant, wherein the permeate gas is fed from the membrane plant via a third control valve back to the pressure swing adsorption plant, wherein the third control valve is used to adjust the permeate pressure and the transmembrane flow and thus the gas composition and the residual hydrogen content in the retentate of the membrane plant.

[0047] A further development provides that the pressure swing adsorption system (E02) is directly pressurized with the storage gas pressure or with a preset pressure, whereby a pressure reduction system is arranged upstream of the pressure swing adsorption system (E02) in order to adjust the storage gas pressure to a maximum pressure of the system design.

[0048] A further development provides for the additional adjustment of the retentate pressure or the retentate gas quantity using a second control valve in the retentate gas line. This measure is used particularly when production conditions vary greatly with regard to the stored gas composition, or the storage pressure range exhibits large amplitudes, or the control options with the third control valve have been exhausted.

[0049] A further development provides that the permeate gas absolute pressure is set directly after the membrane system to 0.5 bar to 11 bar, in particular between 1 bar and 6 bar.

[0050] A further development provides that the pressure of the permeate is influenced by the third control valve and thus also the partial pressures of the hydrogen and the hydrocarbons in the membrane system, whereby the partial pressures affect the transmembrane flow of the hydrogen and the transmembrane flow of the hydrocarbons.

[0051] A further development provides that if too high a hydrogen content is detected in the retentate, the third control valve is opened to induce an increased transmembrane flow, whereby, since hydrogen permeates faster than hydrocarbons, the increase in the transmembrane flow is proportionally higher for hydrogen than for methane or hydrocarbons, whereby the proportion of hydrogen in the retentate is reduced, since relatively more hydrogen permeates from the retentate side to the permeate side than methane, whereby if the hydrogen content in the retentate is too low, the control is carried out in the opposite direction.

[0052] A further development provides that the partial pressures are intervened by closing the second control valve, causing a change in the transmembrane flow so that more hydrogen enters the permeate.

[0053] A further development provides that, in the case of particularly low amounts of desorbate, the functionality of the membrane system is maintained by damming the permeate and the methane is not recycled via the permeate but instead enters the retentate.

[0054] A further development provides for the permeate to be mixed with the storage gas via a gas mixer as a component of the feed gas to the pressure swing adsorption system.

[0055] A further development provides for the permeate gas to be recompressed to the current pressure of the storage gas via a compressor stage so that it can be mixed with the storage gas in the gas mixer.

[0056] A further development provides that the compressor stage is controlled via the suction pressure on the suction side, whereby a lower suction pressure is achieved by closing the third control valve, in particular with small permeate quantities and with low proportions of hydrocarbons in the storage gas.

[0057] A further development provides that when the storage gas pressure decreases, the compressor output is adjusted to the lower required feed pressure of the permeate into the gas mixer and is reduced, and when the proportion of hydrocarbons in the stored gas increases and the amount of desorbate increases accordingly, the pressure on the permeate side is reduced by opening the third control valve so that the membrane system can process larger gas quantities.

[0058] A further development provides that an increase in the pressure on the suction side of the compressor stage (E04) is brought about by opening the third control valve (V03), whereby this can compress higher quantities of permeate gas.

[0059] A further aspect of the invention relates to a device for separating natural gas and hydrogen when operating a gas storage facility, in particular for carrying out the method described above, wherein existing natural gas deposits or natural gas storage facilities are used to store hydrogen as storage gas, wherein the extracted production gas is separated in a gas separation plant when a mixture of hydrogen and natural gas is present, characterized in that a pressure swing adsorption plant with a connected membrane plant is provided for separating the gases, wherein a gas-conducting connection for the permeate gas from the membrane plant to the pressure swing adsorption plant is provided, wherein in one gas-conducting connection a third control valve for controlling the permeate pressure and the gas composition of the retentate is arranged in a fifth gas-conducting gas connection.

[0060] A further development provides for a second control valve in the fifth gas-carrying connection for the retentate gas from the membrane system.

[0061] A further development provides that a gas mixer is arranged in a first gas-conducting connection for the storage gas, wherein the gas-conducting connection for the permeate gas opens into the gas mixer and the gas mixer is designed to mix the storage gas and the permeate gas to form the feed gas for feeding into the pressure swing adsorption system.

[0062] A further development provides that a compressor stage for compressing the permeate gas is arranged in the sixth gas-conducting connection for the permeate gas before or after the third control valve.

[0063] The invention is explained by way of example with reference to a drawing. It shows:

[0064] Figure 1: highly schematic block diagram showing an inventive

[0065] Device with the process flow;

[0066] Figure 2: The natural gas content in the gas depending on the storage pressure.

[0067] The device is shown schematically in Figure 1.

[0068] The device according to the invention comprises one or more gas storage units E01 filled with a gas mixture consisting essentially of hydrogen and gaseous hydrocarbons (natural gas). The storage gas is fed to a gas mixer E05 via a first gas-conducting connection SO1 and from there, as feed gas, passes via a second gas-conducting connection SO2 to a pressure swing adsorption system E02. The pressure swing adsorption system E02 comprises one or more adsorption stages and / or adsorbers, control valves, and standard process accessories.

[0069] Via a gas-conducting fourth connection S04, gas passes from the low-pressure side of the pressure swing adsorption system E02 to a membrane system E03, comprising the desorbate gas of the pressure swing adsorption system E02 with a mixture of hydrogen and hydrocarbons.

[0070] Via a third gas connection S03 from the high-pressure side of the pressure swing adsorption plant E02, the product gas with the purified hydrogen is fed to the hydrogen network or to another hydrogen consumer or a hydrogen storage facility.

[0071] The membrane system E03 comprises in particular one or more membrane stages and / or membrane modules, fittings and accessories.

[0072] From a high-pressure side of the membrane plant E03, a fifth gas-conducting connection S05 leads to a natural gas network or another hydrocarbon consumer or storage facility comprising the retentate gas of the membrane plant with the enriched hydrocarbons.

[0073] A sixth gas connection S06 leads from a low-pressure side of membrane system E03 to gas mixer E05. This feeds the permeate gas from membrane system E03, a mixture of hydrogen and hydrocarbons, to gas mixer E05 and mixes it with the storage gas from gas line SO1 to form the feed gas for pressure swing adsorption system E02.

[0074] The permeate gas from the membrane system E03 is passed through a compressor stage E04, which consists of one or more compressors comprising one or more compression stages with the corresponding control valves and accessories.

[0075] In addition, the device according to the invention can comprise one, several or all devices from the following group: a first control valve V01 positioned in the connection which comprises product gas, a second control valve V02 in the connection which comprises the retentate gas, a third control valve V03 in the connection which comprises the permeate gas, - a first measuring device X001 for measuring the gas composition in the feed gas or storage gas,

[0076] - a second measuring device X002 for measuring the gas composition in the product gas,

[0077] - a third measuring device X003 for measuring the gas composition in the retentate gas,

[0078] - a first pressure measuring device P004 for measuring the pressure in the retentate gas or in the desorbate gas,

[0079] - one or more measuring devices F005 for the quantity measurement of the product gas flow or the storage gas flow.

[0080] The method according to the invention provides for firstly withdrawing a storage gas from a storage E01, comprising a hydrogen-natural gas mixture.

[0081] This storage gas is fed to a gas mixer E05, where it is mixed with the permeate gas from the membrane system E03. These two gases produce the feed gas, which is fed to the pressure swing adsorption system E02.

[0082] In the pressure swing adsorption plant E02, the feed gas is separated into the hydrogen-enriched product gas and the hydrogen-depleted desorbate gas.

[0083] The product gas is fed into a corresponding hydrogen gas network via a line S03 or stored again. Line S03 can contain both measuring devices F005 for measuring the quantity of product gas, as well as measuring devices X002 for measuring the gas composition, and at least one valve V01.

[0084] The desorbate gas is fed via line S04 to the membrane system E03 and is separated there into the retentate gas enriched in hydrocarbons and the permeate gas, which consists of hydrogen and hydrocarbon.

[0085] The permeate gas is fed to gas mixer E05 via line S06, where the pressure of the permeate gas is increased, if necessary, by compressor stage E04. This is particularly necessary for comparatively small permeate gas quantities. According to the invention, the pressure swing adsorption system can be directly pressurized with the storage pressure or storage gas pressure if this is within a range that corresponds to the pressure range of the system design. If the storage gas pressure is too high, i.e., if it exceeds the maximum pressure of the system design, a pressure reduction device can be installed upstream of the pressure swing adsorption system. The membrane system is pressurized with the desorbate pressure originating from the pressure swing adsorption system.

[0086] According to the invention, this avoids equipment and energy costs for increasing the pressure.

[0087] According to the invention, the stable and controllable operation of the device in combination with a gas storage device is achieved by measuring the product gas quantity with the measuring device F005 and, by means of this measured value, the stored quantity of the purified hydrogen is set to the predetermined value by adjusting the valve position of the valve V01.

[0088] Furthermore, according to the invention, the gas composition in the feed gas or in the storage gas is measured using the measuring device X001. Alternatively or additionally, the gas composition in the product gas is measured using the measuring device X002.

[0089] The valve switching times of the pressure swing adsorption system E02 are controlled using these measured values. This means that, for example, if the measured methane content in the feed gas increases, the adsorbers must be switched over earlier or the cycle times must be shortened because the adsorbers are used up more quickly.

[0090] As is well known, pressure swing absorption is operated in cycles, where every time the absorber is occupied, a change takes place in order to release the absorbed gas.

[0091] The lower the methane content in the gas (especially at the beginning of the withdrawal), the longer the cycles can be and the more they can be adjusted accordingly.

[0092] Furthermore, according to the invention, the gas composition in the retentate gas is measured using the measuring device X003. Using this measured value, the desired gas composition in the retentate gas is controlled by the valve position of the valve V03. Furthermore, according to the invention, the pressure in the retentate gas and / or the desorbate gas can be measured using the pressure measuring device P004. Using this measured value, the setting of a pressure range predefined in the process design can be ensured by adjusting the valve position of the valve V02.

[0093] The combination of pressure swing adsorption in conjunction with a membrane system and one, several or all of the previously outlined controls results in a surprising technical effect in that with little equipment expenditure such a system operates efficiently even under the constantly changing conditions in storage operation.

[0094] In order to circulate a small amount of hydrogen and repeatedly feed it to the pressure swing absorber, it makes sense to measure the feed gas for its methane content and adjust the cycle time accordingly.

[0095] During a typical withdrawal process from an underground storage facility filled with hydrogen and natural gas, the pressure gradually decreases along a ramp from a maximum storage pressure to the minimum permissible storage pressure. The gas composition in the withdrawn gas is subject to various fluctuations, which depend on a number of factors such as the withdrawal rate, the storage type, geological conditions and past operating procedures. According to the inventors' experience, the withdrawal process usually begins with a high hydrogen content, which then continuously decreases to a lower value. An example of such a process is shown in Figure 2. The withdrawal ramp begins at 65 bar and a natural gas content of approximately 4%. During withdrawal and the associated pressure reduction, the natural gas content initially increases relatively slowly. As withdrawal progresses, the natural gas content increases increasingly rapidly.At the end of the withdrawal process, at approximately 35 bar, the natural gas content in the withdrawn gas is already >12%. However, linear increases are also known.

[0096] In the case of the energy-saving direct application of the storage pressure to the pressure swing adsorption system according to the invention, but also when a pressure reduction is provided upstream, the difficulty in applying the process is that the driving force (pressure) available for the operation of the pressure swing adsorption system and the membrane system decreases, while the demand for it increases due to the increasing proportion of natural gas.

[0097] Despite this disadvantageous relationship, the plant according to the invention can be operated with the disclosed method over a wide range of production states if the control processes according to the invention are applied.

[0098] The normal storage operating pressure available for the operation of the system is in a range between 10 and 320 bar, in particular 10 and 150 bar, and frequently also between 20 and 80 bar.

[0099] The hydrogen content to be achieved in the product gas is >95%, but in particular >98% and preferably >99.999% if fuel cell applications are intended.

[0100] The hydrogen purity is adjusted during the design phase of the pressure swing adsorption and during the operating phase of the system by adjusting the valve switching times of the pressure swing adsorption system E02.

[0101] The control valve V01 is used for quantity control and releases the product gas to the downstream hydrogen consumer, whose operating pressure is normally below the lowest value of the storage pressure range.

[0102] The absolute pressure of the desorbate gas is typically between 2 bar and 30 bar, but most commonly between 4 and 11 bar. The desorbate pressure range has a significant influence on the separation efficiency of the pressure swing system and the membrane system and is selected during the process design phase.

[0103] During plant operation, the position of valve V02 controls the desorbate or retentate pressure. The valve releases the natural gas-enriched retentate gas to a natural gas consumer whose operating pressure is normally below the lowest value of the desorbate or retentate range.

[0104] The set residual hydrogen content in the retentate gas is normally < 10%, but usually < 2%. The specified hydrogen or natural gas content in the retentate gas is adjusted by the position of valve V03 by influencing the permeate pressure directly downstream of the membrane system E03. If the production conditions differ significantly in terms of the released gas composition or the storage pressure range, the position of valve V02 can also be used to adjust the retentate gas composition within a limited range.

[0105] Otherwise, it is sufficient to set a constant pressure using the position of the valve V02 in the retentate gas / desorbate gas.

[0106] The permeate gas absolute pressure directly after the membrane system E03 is normally between 0.5 bar and 11 bar, but mostly between 1 bar and 6 bar.

[0107] According to the invention, gas separation should be possible under changing conditions with regard to pressure and gas composition, which on the one hand results in the highest possible purity of the gas streams with the highest possible yield.

[0108] The device and method can be used to achieve constant gas compositions in the product gas and retentate gas, even when the storage gas pressure and composition are affected by large-amplitude fluctuations, using the pressure setting values ​​and pressure setting devices listed above for stable operation. This can be achieved with the lowest possible energy consumption.

[0109] The surprising effect is due to a special combination resulting from the nature of the two separation processes and the selection of optimized control processes.

[0110] During a withdrawal process, the natural gas content in the storage gas increases and directly leads to an increase in the natural gas content in the desorbate gas and an increase in the amount of desorbate gas.

[0111] For the membrane system that processes the desorbate gas, these two factors compensate each other to a certain extent. On the one hand, the membrane has to process an increased amount of desorbate gas, but the proportion of hydrogen to be separated is lower, which simplifies the separation effort for the membrane system to a certain extent. In any case, the pressure conditions of the membrane system must be adjusted for the fluctuations. This is primarily achieved by adjusting the third control valve V03, which regulates the permeate pressure and subsequently the transmembrane flow and the gas composition in the retentate. The third control valve V03 influences the permeate pressure and thus also the partial pressures of the hydrogen and the hydrocarbons or methane in the membrane system. These partial pressures affect the transmembrane flow of the hydrogen and the transmembrane flow of the hydrocarbons.

[0112] For example, if a desorbate with a specific gas composition and gas quantity is introduced into the membrane system and an excessively high hydrogen content is detected in the retentate using the third measuring device X03, opening the third control valve V03 results in an increased transmembrane flux. Since hydrogen permeates at least an order of magnitude faster than methane or hydrocarbons, the increase in transmembrane flux is proportionally higher for hydrogen than for methane or hydrocarbons. Subsequently, the proportion of hydrogen in the retentate decreases, since relatively more hydrogen permeates from the feed / retentate side to the permeate side than methane.

[0113] If the hydrogen content in the retentate is too low, the above-mentioned control and method can be carried out in the opposite direction.

[0114] In addition, the separation efficiency can be changed with the second control valve V02, which adjusts the desorbate pressure of the pressure swing adsorption system, which is why it should only be used when the control options with the third control valve V03 have been exhausted.

[0115] Increasing the pressure or closing the second control valve V02 on the retentate side has the same effect as opening the third control valve V03 or supports it. Here, too, the partial pressures are affected. Closing the second control valve V02 also causes a change in the transmembrane flow and affects the flow of hydrogen, which then increasingly enters the permeate.

[0116] The purpose of the V03 valve is also to maintain the functionality of the E03 membrane by backing up the permeate at particularly low desorbate quantities (especially at the beginning of the withdrawal process), and to prevent the methane from being recycled via the permeate but instead entering the retentate. The permeate contains hydrogen and methane and is added to the storage gas via the E05 gas mixer as a feed gas component.

[0117] Because the pressure drops from the desorbate to the permeate over the two separation stages, the permeate must be recompressed to the current pressure of the storage gas via the compressor stage E04 so that it can be mixed with the storage gas in the gas mixer E05.

[0118] Conventional compressors cannot be controlled across the entire gas flow variation. Therefore, the invention controls the compressor stage via the suction pressure on the suction side if the speed control is insufficient for the desired control range or is not even permissible. A lower suction pressure can be achieved by closing the third control valve V03, causing the compressor stage to draw in smaller gas volumes. This is particularly necessary for small permeate volumes, which result from low hydrocarbon content in the storage gas.

[0119] This approach has two advantages. Firstly, only a small portion of the permeate needs to be recompressed. Secondly, the storage gas pressure changes (decreases), allowing the compressor output to be adjusted to the lower required permeate feed pressure into the gas mixer. Since compressors in such plants account for a significant portion of energy consumption, this allows the plant to be operated energy-efficiently.

[0120] Conversely, if the proportion of hydrocarbons in the released gas increases, the amount of desorbate increases accordingly. Opening the third control valve V03 decreases the pressure on the permeate side immediately upstream of the third control valve V03, allowing the membrane system to process larger gas volumes. Opening the third control valve V03 simultaneously results in an increase in the pressure on the suction side of the compressor stage E04, allowing it to compress larger amounts of permeate gas, which was achievable with the disclosed control method.

[0121] The selection of the appropriate control ranges for the third control valve V03 with regard to the control of the permeate quantity and the interaction between the membrane system E03 and the compressor stage E04 is primarily carried out during the design phase. During operation, however, the position of the third valve V03 is primarily used to control the gas composition in the retentate. By correctly selecting the design parameters of all process units and control devices, the pressure values ​​upstream and downstream of the control valve V03 and the appropriate operation of the compressor stage E04 for varying permeate quantities can be correctly set. However, the overall control system must then be intelligently implemented as described above to control the pressure differences.Furthermore, it is surprising that such a process, involving a pressure swing absorber and a membrane stage, is particularly well-suited for hydrogen storage in porous storage systems, since any hydrogen sulfide formed enters the desorbate during pressure swing adsorption and from there into the separated CH4, where it causes comparatively few problems. The hydrogen sulfide in the discharged hydrogen is fed to pressure swing adsorption and then dried or enriched in the cycle, and if necessary, chemically separated, e.g., with activated carbon or metal oxides. This serves to prevent accumulation in the cycle.

[0122] List of reference symbols

[0123] E01 Gas storage

[0124] E02 Pressure swing adsorption plant

[0125] E03 Membrane system

[0126] E04 Compressor stage

[0127] E05 Gas mixer

[0128] 501 first gas-conducting connection

[0129] 502 second gas connection

[0130] 503 third gas-conducting connection

[0131] 504 fourth gas-conducting connection

[0132] 505 fifth gas-conducting connection

[0133] 506 sixth gas-conducting connection

[0134] V01 first control valve

[0135] V02 second control valve

[0136] V03 third control valve

[0137] X001 first measuring device

[0138] X002 second measuring device

[0139] X003 third measuring device

[0140] P004 fourth measuring device

[0141] F005 Flow Meter

Claims

Claims 1. A method for operating a gas storage facility, wherein existing natural gas deposits or natural gas storage facilities are used to store hydrogen as storage gas, wherein the extracted production gas is separated in a gas separation plant in the presence of a mixture of hydrogen and natural gas, characterized in that the gas separation is carried out in a pressure swing adsorption plant (E02) with a connected membrane plant (E03), wherein the pressure swing adsorption plant (E02) is pressurized with the storage gas and subsequently the membrane plant (E03) is pressurized with the desorbate pressure originating from the pressure swing adsorption plant (E02), wherein the permeate gas is fed from the membrane plant (E03) back to the pressure swing adsorption plant (E02) via a third control valve (V03),The third control valve (V03) adjusts the permeate pressure and the transmembrane flow and thus the gas composition and the residual hydrogen content in the retentate of the membrane system (E03).

2. Method according to claim 1, characterized in that the Pressure swing adsorption system (E02) is directly pressurized with the storage gas pressure or with a reduced storage gas pressure, whereby a pressure reduction system is arranged upstream of the pressure swing adsorption system (E02) in order to adjust the storage gas pressure to a maximum pressure of the system design.

3. Method according to claim 1 or 2, characterized in that the retentate pressure or the retentate gas quantity is additionally adjusted with a second control valve (V02) in the retentate gas line (S05).

4. Process according to one of the preceding claims, characterized in that the permeate gas absolute pressure directly after the membrane system (E03) is set to 0.5 bar to 11 bar, in particular between 1 bar and 6 bar.

5. Method according to one of the preceding claims, characterized in that the pressure of the permeate is influenced by the third control valve (V03) and thus also the partial pressures of the hydrogen and the hydrocarbons in the membrane system are influenced, wherein the partial pressures affect the transmembrane flow of the hydrogen and the transmembrane flow of the hydrocarbons.

6. Method according to one of the preceding claims, characterized in that if an excessively high hydrogen content is detected in the retentate, the third control valve (V03) is opened in order to bring about an increased transmembrane flow, wherein, since hydrogen permeates faster than hydrocarbons, the increase in the transmembrane flow is relatively higher for hydrogen than for methane or hydrocarbons, wherein the proportion of hydrogen in the retentate is reduced since relatively more hydrogen permeates from the retentate side to the permeate side than methane, wherein if the hydrogen content in the retentate is too low, the control is carried out in the opposite direction.

7. Method according to one of the preceding claims, characterized in that the partial pressures are intervened in by closing the second control valve (V02), whereby a change in the transmembrane flow is brought about, so that more hydrogen enters the permeate.

8. Process according to one of the preceding claims, characterized in that, at particularly low desorbate quantities, the functionality of the membrane system (E03) is maintained by damming the permeate and the methane is not recycled via the permeate but enters the retentate.

9. Process according to one of the preceding claims, characterized in that the permeate is mixed with the storage gas via a gas mixer (E05) as a component of the feed gas to the pressure swing adsorption plant (E02).

10. Method according to one of the preceding claims, characterized in that the permeate gas is compressed via a compressor stage (E04) to the current pressure of the Storage gas is recompressed so that it can be mixed with the storage gas in the gas mixer (E05).

11. Method according to one of the preceding claims, characterized in that the compressor stage (E04) is controlled via the suction pressure on the suction side, wherein a lower suction pressure is brought about by closing the third control valve (V03), in particular with small permeate quantities, with low proportions of hydrocarbons in the storage gas.

12. Method according to one of the preceding claims, characterized in that with decreasing storage gas pressure the compressor power is adapted to the lower required feed pressure of the permeate into the gas mixer and is reduced and with increasing proportion of hydrocarbons in the stored gas and correspondingly increasing amount of desorbate the pressure on the permeate side is reduced by opening the third control valve (V03) so that the membrane system (E03) can process larger gas quantities.

13. Method according to one of the preceding claims, characterized in that an increase in the pressure on the suction side of the compressor stage (E04) is brought about by opening the third control valve (V03), whereby the latter can compress higher quantities of permeate gas.

14. Device for separating natural gas and hydrogen when operating a gas storage facility, in particular for carrying out the method according to one of the preceding claims, wherein existing natural gas deposits or natural gas storage facilities are used for storing hydrogen as storage gas, wherein the extracted production gas is separated in a gas separation plant when a mixture of hydrogen and natural gas is present, characterized in that a pressure swing adsorption plant (E02) with a connected membrane plant (E03) is provided for separating the gases, wherein a sixth gas-conducting connection (S06) for the permeate gas from the membrane plant (E03) to the pressure swing adsorption plant (E02) is provided, wherein in the sixth gas-conducting connection (S06) a third control valve (V03) for controlling the permeate pressure and the gas composition of the retentate in the fifth gas-conducting gas connection (S05).

15. Device according to claim 14, characterized in that a second control valve (V02) is present in the fifth gas-carrying connection (S05) for the retentate gas from the membrane system (E03).

16. Device according to claim 14 or 15, characterized in that a gas mixer (E05) is arranged in a gas-conducting connection (SOI) for the storage gas, wherein the gas-conducting connection for the permeate gas (S06) opens into the gas mixer (E05) and the gas mixer (E05) is designed to mix the storage gas and the permeate gas to form the feed gas for feeding into the pressure swing adsorption plant (E02).

17. Device according to one of claims 14 to 16, characterized in that a compressor stage (E04) for compressing the permeate gas is arranged in the gas-conducting connection (S06) for the permeate gas before or after the third control valve (V03).

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