Adsorber

Abstract

Adsorber element for helium purification in cryogenic systems is disclosed, comprising an end cap to be inserted in or connected to an adsorber housing; a first filter element comprising a layer of a first filter material connected to the end cap and extending from the end cap in an axial direction, wherein the first filter element is formed as hollow cylinder; and a second filter element comprising a second filter material connected to the end cap and extending from the end cap in the axial direction, wherein the second filter element has a cylindrical shape and is nested with the first filter element. The adsorber removes oil from the helium. Also disclosed is a method of operating an adsorber for helium purification in cryogenic systems comprising determining a pressure drop over the adsorber and if the pressure drop exceeds a threshold generating a warning signal indicative of oil saturation of the adsorber.

Description

The present invention relates to an adsorber element for helium purification in cryogenic systems, an adsorber comprising such an adsorber element, preferably employed in a cryogenic system and a cryogenic system including such an adsorber. Further, the present invention relates to a method for operating such an adsorber for helium purification. Cryogenic system consists of a compressor and a cryogenic device such as Gifford-McMahon (GM) cooler and connection lines to supply and return the refrigerant in the hermetically sealed system. As refrigerant Helium is used. For Helium supply compressors with internal oil recirculation for cooling and lubrication are state of the art. To remove oil contained in a Helium flow a separation system is used which consist of a pre-separator and a fine separator to eliminate any oil emissions. Additionally, an adsorber is installed downstream of the fine separator which is frequently replaced by regular maintenance. To avoid the contamination of cryogenic devices any impurities in the system must be removed. Typically, different kind of contaminants are known such as oil aerosols and oil vapor, water vapor, air, other gases and volatile solvents. The adsorber must be able to remove these contaminants from the Helium flow to suppress contamination and malfunction of the cryogenic device. Typically, adsorbers for Helium purification are designed as packed bed adsorber inside of a shell with a filling consisting of activated carbon or char coal respectively. Inlet and outlet connection of the adsorber is designed with hermetically sealed connectors so that the adsorber can be stored and dispatched with pressurized Helium filling. The pressurized adsorber can be connected to the pressurized cryogenic system by hermetically sealed connectors without any loss of Helium. However, oil can still pass the separation system with a constant oil carry-over rate. This might be influenced by pulsation of the GM cooler, discontinuous operation and frequently activation / shutdown of the system. It is an object of the present invention to provide a versatile adsorber for improved helium purification. The problem is solved by an adsorber element according to claim 1, an adsorber according to claim 11, a cryogenic system according to claim 18 and a method for operating such an adsorber according to claim 19. In as aspect of the present invention, an adsorber element for helium purification in cryogenic systems is provided. The adsorber element comprises an end cap to be inserted into or connected to an adsorber housing such as a pressurized container. Further, the adsorber element comprises a first filter element comprising a layer of a first filter material as adsorber connected to the end cap and extending from the end cap in an axial direction. The first filter element is formed as hollow cylinder. Further, the adsorber element comprises a second filter element comprising a second filter material as adsorber connected to the end cap and extending from the end cap in the axial direction. The second filter element has a cylindrical shape and is nested with the first filter element. Thus, by the first filter element and the second filter element, specific contaminants such as oil aerosol and oil vapor of helium can be filtered out by the adsorber in order to reduce contamination of the helium in the cryogenic system. Due to building the first filter element as hollow cylinder, radial flow through the first filter element is enabled. Thereby pressure drop over the adsorber element is reduced. By analysis of adsorbers after long time of continuous operation it was found by the inventors that typical oil emissions which come from the fine separator to the adsorber consist of droplets of size less than 1.5 micron and even below 0.1 micron with a main spectrum 0.1 to 0.3 micron which can be classified as aerosol. Indeed, it shows that oil emissions consist of both gaseous oil vapor and liquid oil aerosol which must be eliminated by the adsorber. Furthermore, by the inventors it was found that these oil emissions do not appear when the saturation level of the fine separator is lower than 30 % up to 85% by mass compared to the mass of oil which is stored in the fine separator in saturation equilibrium in steady state operation. This indicate that these oil emissions are not caused by any defects or leakages in the fine separator. Thus, the fine separator tends to re-entrain oil aerosol if a certain saturation level is exceeded, i.e. when the saturation equilibrium of the fine separator is reached after a certain operation time. That means the presence of both liquid oil aerosol and gaseous oil vapor after the fine separator can be considered as normal operation mode. Furthermore, the formation of both liquid oil aerosol and gaseous oil vapor after the fine separator might be affected by change of pressure by commissioning and / or switch-on and / or switch-off, process-related pressure change, inadvertent change of pressure, malfunction of fine separator. Thus, for the adsorber it is not sufficient to foresee a packed filter bed of char coal since this would only eliminate oil vapor. By choosing char coal type with sufficient selectivity for gaseous contaminants such as oil vapor, water vapor, air, other gases, volatile solvents, etc. a sufficient purification of Helium can be achieved. A char coal bed with adapted grain size with its porous structure cannot effectively eliminate oil aerosol with main spectrum 0.1 to 0.3 micron which can be considered as a very stable aerosol because this is the range of the most penetrating particle size. Furthermore, the porous structure of the char coal might be plugged by liquid oil. However, by the present invention additional filter elements are implemented in order to reliably remove oil aerosol from the gas flow to prevent contamination of the helium. Here and in the following, axial direction of the adsorber or adsorber element is defined as the axial direction of the hollow cylinder of the first filter element. The radial direction is defined here and in the following as direction perpendicular to the axial direction towards or away from the center axis of the hollow cylinder of the first filter element. Here and in the following gas flow through the filter elements is in the order of the filter elements itself. Thus, gas such as helium entering the adsorber flows first through the first filter element, subsequently through the second filter element and then through each additional filter element. Preferably, the second filter element surrounds the first filter element in particular in a radial direction. In this case, flow through the first filter element is from the center of the adsorber element radially outwards. Alternatively, the second filter element is arranged radially within the first element. In this case, the flow is radially inwards towards the center of the adsorber element through the first filter element. Preferably, the first filter element and the second filter element are arranged concentric. Preferably, the second filter element is formed as hollow cylinder. In particular if the second filter element surrounds the first filter element, the second filter element is formed as hollow cylinder such that the first filter element can be placed radially within the first filter element. Alternatively, the second filter element is formed as full cylinder. In particular, the second filter element is formed as full cylinder if the second filter element is arranged radially within the first filter element. Preferably, the first filter element and the second filter element are built as cartridge. Thus, replacement of these filter elements can be simplified. In particular, the cartridge provides a preassembled first filter element and second filter element. Therein, implementing only a single cartridge in the adsorber element may have the benefit of simplifying the overall design and reducing the number of individual parts which need to be maintained or replaced. Preferably, the adsorber element comprises a third filter element having a third filter material as adsorber and extending in the axial direction, wherein the third filter element is nested with the first filter element and / or the second filter element. Therein, the third filter element may surround the first filter element and the second element, only the first filter element or only the second filter element. Preferably, the third filter element is connected to the end cap. Thus, the first filter element, the second filter element and the third filter element are built as a single cartridge. Alternatively, the third filter element may be connected to a separate cap element. Thereby the first filter element and the second filter element are built as a first cartridge and the third filter element (and any further filter element) may be built as second cartridge. Thus, replacement of the first and second filter element independent from the third filter element is feasible by simply replacing the first cartridge or the second cartridge only, respectively. Preferably, the second filter element or the third filter element is built as packed filter bed. In particular, the packed filter bed can be built as active charcoal filter. Alternatively, the last filter element may contain other filter materials or adsorbent material such as a molecular sieve or zeolite. Preferably, the last filter element is built as packed filter bed. In particular, the packed filter bed can be built as active charcoal filter. Alternatively, the last filter element may contain other filter materials or adsorbent material such as a molecular sieve or zeolite. Preferably, the last filter element, in particular when built as charcoal filter comprises a filter layer to remove coal dust, wherein the filter layer is arranged downstream of the respective filter material, i.e the charcoal. In one embodiment the filter layer is directly attached to the filter material of the last filter element or, in another embodiment, is placed apart and separate from the filter material of the last filter element, e.g. arranged in the outlet of the adsorber, close to the outlet or within the outlet channel of the adsorber element. Preferably, the adsorber element may comprise more than three filter elements, wherein the additional filter elements may have the features as described above with respect to the second filter element and / or the third filter element. And the last filter layer might be a wrapped layer for dust removal. Preferably, the first filter element is a radially separated from the second filter element. Similar, the second filter element may be spaced apart from the third filter element in a radial direction. In particular if the helium flows through the first filter element and the second filter element in a radial direction, by the clearance or gap between the first filter element and the second filter element, the pressure is equalized between the individual filter elements and the helium is distributed over the full surface of the subsequent respective filter element. Preferably, the gas flow through the first filter element is in a radial direction. This is in particular enabled through the hollow cylinder shape of the first filter element. Preferably, gas flow through the second filter element and / or the third filter element is in the axial direction or a radial direction. Thus, gas flow through the second filter element may be in an axial direction or a radial direction. Alternatively or additionally, gas flow through the third filter element is in the axial direction or a radial direction. Thus, the gas flow through the second filter element and the third filter element may differ or is equal. Thus, most efficient use of the respective filter material can be achieved by adapting the direction of flow adequately. Preferably, the adsorber element comprises a baffle extending in the axial direction and is preferably also connected to the end cap. Therein, the baffle is arranged between the first filter element and the second filter element. Alternatively or additionally, the baffle is arranged between the second filter and the third filter element. By the baffle, direction of the gas flow within the adsorber element can be directed. In particular, by the baffle a change of a radial gas flow into an axial gas flow is enabled. Preferably, the adsorber element comprises an inlet channel. In particular, the inlet channel is axially centered or axially arranged relatively to the filter elements. Alternatively, the inlet channel surrounds the first filter element. Preferably, the adsorber element comprises an outlet channel. In particular, the outlet channel is axially centered or axially arranged relatively to the filter elements. Alternatively, the outlet channel surrounds the first filter element. Preferably, all filter elements are directly connected to the end cap such that the adsorber element comprises only one end cap. In other words, the adsorber element is built as a single cartridge which can be inserted into an adsorber housing. Alternatively, the adsorber element comprises more than one end cap, wherein different filter elements are connected to different end caps such that the adsorber element comprises more than one cartridge which are nested with each other to be inserted into an adsorber housing. Therein, implementing more than one cartridge may have the benefit that individual filter elements can be replaced without the need to replace all filter elements together. Preferably, the first filter element is configured to remove liquid oil aerosol. Alternatively or additionally, the second filter element is configured to remove water vapor and / or oil vapor. Alternatively or additionally, the third filter element is configured to remove oil vapor. Thus, by implementing the first filter element and the second filter element and preferably also a third filter element, different contaminants of the helium can be filtered out, wherein the filter material of each filter element can be tailored to the specific contaminant to be filtered out or adsorbed. Preferably, the first filter element is configured to store more than 100 g oil, preferably more than 50 g and more preferably more than 20 g oil without release of oil aerosol. Thus, the first filter element is able to filter out liquid oil aerosol. Therein, the first filter element has a high saturation amount of oil stored in the first filter material. Therein, despite the stored oil in the first filter material, the first filter element does not release aerosol which may contaminate the helium and also may contaminate the second filter element or a third filter element and reduce their filter performance. Preferably, the first filter material and the second filter material are equal or different. In particular, if a third filter element is implemented, the first filter material, the second filter material and the third filter material are equal or different. In particular if more than three filter elements are implemented, each of the filter elements may have a different filter material. Preferably, the second filter material or the third filter material is active charcoal. Active charcoal is known to be able to filter out oil vapor and is thus implemented preferably as last filter element of the adsorber element. Preferably, the first filter element and / or the second filter element is a fibrous filter material such as filter paper, nonwoven, felt, or a porous filter material. Preferably, the first filter material has a basis weight between 50 g / m2 and 110 g / m2 and preferably between 60 g / m2 and 95 g / m2. Therein, the basis weight might be determined according to ISO 596:2012-07. Preferably, the first filter material has an air permeability at 200 Pa of between 30 I / m2 / s to 250 I / m2 / s and preferably between 35 I / m2 / s to 120 I / m2 / s. In particular the permeability is determined according to ISO 9237:1995-06. Preferably, the maximum pore size of the filter material is between 6 pm and 35 pm and preferably between 9 pm and 30 pm. Therein, the pore size is determined according to ASTM F316. Preferably, the mean flow pore size of the first filter material is between 1 pm and 12 pm and more preferably between 3 pm and 10 pm. Therein, the mean flow pore size is determined according to ASTM F316. By the aforementioned parameters of the basis weight and I or the impermeability and I or the max pore size and / or the mean flow pore size, a sufficient filter effect for liquid oil aerosol is provided without excessive pressure drop over the first filter element. At the same time, storage of oil is enabled without release of liquid oil aerosol towards the second filter element and preferably the third filter element. In another aspect of the present invention, an adsorber for helium purification in cryogenic systems is provided. The adsorber comprises an adsorber housing such as a pressurized container, having an inlet and an outlet. Therein, the inlet of the adsorber may be connected to a helium supply, i.e. a compressor and / or connected to a separator of such and helium supply, and the outlet of the adsorber may be connected to a cryopump. Further, the adsorber comprises an adsorber element as described before. Therein, the adsorber element is arranged within the adsorber housing. Preferably, the inlet of the adsorber housing is arranged radially, axially or tangentially. Additionally or alternatively, the outlet of the adsorber housing is arranged radially, axially or tangentially. In particular by arranging one or both of the inlet and the outlet radially, flow through at least the first filter element in the radial direction is enabled. Preferably, a differential pressure of the adsorber or pressure drop over the adsorber during first use is 30 mbar or below, preferably 10 mbar or below in operation. Thus, sufficiently low pressure drops over the adsorber can be achieved. During operation and collecting of oil in the filter elements, the differential pressure increases. Preferably, the differential pressure of the adsorber or pressure drop over the adsorber is 180 mbar or below, preferably 120 mbar or below and most preferably 80 mbar or below in operation after reaching a certain saturation level. Thus, sufficiently low pressure drops over the adsorber can be achieved during operation of the adsorber element. Preferably, the adsorber comprises a pressure sensor connected to the inlet and / or the outlet to determine a differential pressure drop over the adsorber. In particular, the pressure sensor may be connected to an inlet channel of the adsorber element or an outlet channel of the adsorber element. By determining the pressure drop over the adsorber, saturation of the adsorber element can be determined. In particular, the pressure sensor or both pressure sensors are connected to an evaluation unit, wherein in the evaluation unit the differential pressure is compared to a predetermined threshold. If the differential pressure exceeds the predetermined threshold, a warning signal is generated indicative of oil saturation of the adsorber or a level of saturation of the adsorber before start of the adsorber to re-entrain oil aerosol which would otherwise contaminate the helium. Replacement of the adsorber element or at least one of the filter elements is then necessary in order to maintain the filter performance of the adsorber and prevent re-entrainment of any oil. Preferably, the predetermined threshold is between 30 mbar and 200 mbar, more preferably between 80 mbar and 150 mbar. Preferably, the end cap has a flange connected to a flange of the adsorber housing. Thus, by the flange a connection between the end cap and the adsorber housing can be generated which is releasably in order to maintain or service the adsorber element to replace one or more cartridges of the adsorber element. Alternatively, the end cap of the adsorber element can be welded, glued or otherwise connected to the adsorber housing. Preferably, the adsorber housing comprises a packed filter bed. Thus, by the adsorber housing also a filter element can be provided. In particular, a third filter element can be employed and directly connected by the adsorber housing, wherein the first filter element and the second filter element are provided by the adsorber element inserted into the adsorber housing. Preferably, the adsorber comprises a baffle which are directly and preferably irremovably connected to the adsorber housing for example by welding. Thus, by inserting the adsorber element into the adsorber housing, the baffle may be placed between the first filter element and the second filter element and / or the second filter element and the third filter element in order to direct the gas flow through the adsorber. In another aspect of the present invention, a cryogenic system is provided. The cryogenic system comprises a helium supply including a compressor and a heat exchanger to supply helium for cooling to a cryopump connected to the helium supply. Preferably, the helium supply may further include at least one separator to separate oil from the helium flow. Therein, an adsorber as previously described is arranged between the helium supply and the cryopump. As previously described the inlet of the adsorber may be connected to the helium supply, wherein the outlet of the adsorber may be connected to the cryopump. Contaminated helium from the helium supply may enter the adsorber which removes the contaminants and provides contaminant free helium to the cryopump. In particular, helium supplied to the cryopump by the adsorber according to the present invention may have less than 50 mg per year of oil vapor and less than 100 mg water per year during operation. In another aspect of the present invention, a method for operating an adsorber for helium purification in cryogenic systems is provided. The method includes the steps of determining a pressure drop over the adsorber or one or more of the filter elements during operation and if the pressure drop exceeds a predetermined threshold generating a warning signal indicative of oil saturation of the adsorber. It has been found that the differential pressure or pressure drop over the adsorber is connected to the saturation of the filter material. Thus, by providing a predetermined threshold and measuring the pressure drop over the adsorber, oil saturation can be determined, and a warning signal can be generated prior to a saturation level of the adsorber with oil starting from which oil aerosols are re-entrained in the gas flow. Hence, release of oil aerosols from the saturated first filter element can be prevented, and service intervals can be optimized for the adsorber. Thereby, in the present invention differential pressure of the whole adsorber can be used to determine saturation level. Alternatively, the differential pressure is determined only over one or more but not all filter elements of the adsorber, wherein only the differential pressure of the one or more filter elements is used to determine a saturation level. For example, differential pressure might be determined only of the first filter element to determine the saturation level of the first filter element. Preferably, the predetermined threshold corresponds to a pressure drop caused by an oil saturation of the first filter element of less than 85%, preferably less than 50% and more preferably less than 30% of the oil mass stored in an equilibrium state, i.e. maximum saturation of the first filter material. Preferably, the adsorber of the method is further built along the features as described for the adsorber and / or the adsorber element above. In the following the present invention is described in more detail with reference to the accompanying figures. The figures show: Fig. 1 a cryogenic system according to the present invention, Fig. 2A and 2B an adsorber element and an adsorber according to an embodiment of the present invention, Fig. 3A and 3B an adsorber element and an adsorber according to an embodiment of the present invention, Fig. 4A and 4B an adsorber element and an adsorber according to an embodiment of the present invention, Fig. 5A and 5B an adsorber element and an adsorber according to an embodiment of the present invention, Fig. 6A and 6B an adsorber element and an adsorber according to an embodiment of the present invention, Fig. 7A and 7B an adsorber element and an adsorber according to an embodiment of the present invention, Fig. 8 an adsorber according to an embodiment of the present invention, Fig. 9 an adsorber according to an embodiment of the present invention and Fig. 10 an absorber according to an embodiment of the present invention. Referring to Fig. 1 showing a cryogenic system 100 including a cryopump 102 which is connected to a helium supply 104. Therein, the helium supply may include a compressor, a heat exchanger and an oil separator to supply helium to a coldhead of the cryopump 102. Therein, in a connection line between the helium supply 104 and the cryopump 102 an adsorber 10 is arranged in order to remove contaminants in the helium such as oil vapor, oil aerosol, water and / or other gases. Referring to Figs. 2A and 2B showing an embodiment of an adsorber element 12 in Fig. 2A and an adsorber 10 containing such adsorber element 12 in Fig. 2B. The adsorber element 12 is built as cartridge to be inserted into a housing 24 of the adsorber 10. The adsorber element 12 comprises an end cap 14. Connected to the end cap 14 and extending in an axial direction from the end cap 14 are a first filter element 16, a second filter element 18 and in the example of Figs. 2A and 2B a third filter element 20. Therein, the first filter element 16, the second filter element 18 and the third filter element 20 are nested with each other. In other terms, the first filter element 16 is built as hollow cylinder surrounding the second filter element 18 and the third filter element 20. Similarly, in the example of Fig. 2A and 2B the second filter element 18 is built as hollow cylinder surrounding the third filter element 20. Similarly, the third filter element 20 is built as hollow cylinder surrounding the center of the cartridge 12 building a central outlet channel 34. The first cylinder element 16 is built by a first filter material. The second filter element 18 is built by a second filter material and the third filter element 20 is built by a third filter material. Therein, the first filter material, the second filter material and the third filter material may be the same or may be different. In particular, the third filter material can be char coal, wherein in particular the third filter element 20 may be built as packed filter bed to contain the char coal. Preferably, the first filter material and the second filter material may be built as fibrous filter material such as felt, nonwoven fibres or filter media, such as filter paper. In particular, the first filter element 16 is configured to remove liquid oil aerosol from a gas stream. The second filter element 18 may be configured to remove water vapor from the gas stream and the third filter element 20 may be configured to remove oil vapor. Different configurations of the filter elements are also possible and the present invention may not be limited to the specific filter ability of the respective filter elements. In particular, more filter elements can be implemented in the adsorber element 12. Figs. 2A and 2B and the following figures only showing examples of the adsorber element 12 and the adsorber 10 with three filter elements. However, the adsorber as well as the adsorber element may have just two filter elements or may have more than three filter elements. Also, the size and thickness of the individual filter elements is only indicated as an example in the figures and may differ for other configurations of adsorber element 12 and the adsorber 10. For example, the second filter element 18 is illustrated in the figures to be thicker in the radial dimension compared to the first filter element 16. The situation may be reversed or alternatively the thickness of the first element 16 and the second filter element 18 may be equal. The same applies to the third filter element and any further filter element in relation to each other and in particular in relation to the first filter element 16 and the second filter element 18. The first filter element 16, the second filter element 18 and the third filter element 20 have an equal extension in the axial direction. In particular, the ends of the filter elements opposite to the end cap 14 are also connected to a cap element 22. Therein, the cap element 22 has an opening 29 as lead through for the gas flow as indicated by arrows 30. Thus, by the end cap 14 and the cap element 22, the individual filter elements of the adsorber element 12 are preassembled as cartridge. The adsorber element 12 can be inserted into a housing 24 of the adsorber 10 preferably inserted into the housing by an axial relative movement. The housing 24 of the adsorber 10 has an inlet 26, wherein in the example of Fig. 2B the inlet 26 is arranged radially. Further, the housing 24 has an outlet 28, wherein in the example of Fig. 2B the outlet 28 is arranged axially. The outlet 28 is in communication with the opening 29 of the cap element 22 in order to allow a gas to leave the cartridge towards the outlet 28 as indicated by arrows 30. By the housing 24 and the adsorber element 12, an inlet channel 32 is formed which is radially outmost arranged, surrounding the first filter element 16. As depicted in Fig. 2B and in particular by arrows 30, a gas flow from the inlet 26 flows through the first filter element 16, the second filter element 18 and the third filter element 20 in a radial direction towards an outlet channel 34 formed in the center of the adsorber element 12 and from there towards the outlet 28 of the housing 24. As shown in the Figs. 2A and 2B, the first filter element 16 is radially separated from the second filter element. Similar, the second filter element 18 is radially apart from the third filter element 20. Thus, between the individual filter elements voids are created in order to distribute the gas flow over the complete radial surface of the subsequent filter element, as well as pressure equalizing. Due to the construction of the adsorber 10, liquid oil aerosol is captured in the first filter element 16, wherein oil vapor in the example of Figs. 2A and 2B may be captured in the third filter element 20. Thus, oil is reliably removed from the helium flow through the adsorber 10 and cannot reach the coldhead of the cryopump 102. Further, blocking of the second filter element 18 and third filter element 20 by oil is minimized. In particular, the arrangement of the adsorber 10 is such that less than 50 mg oil per year is achieved during operation. At the same time pressure drop over the adsorber 10 is minimized due to radial flow within the adsorber 10 and increased filter element surface. In the following figures same or similar elements are indicated with the same reference number. Therein, in the Figs. 2A - 10 different modifications of the adsorber 10 and the adsorber element 12 are shown, wherein modifications of individual figures can be freely combined. The embodiments of the figures must not be understood as limiting embodiments. For example, the embodiment of Fig. 10 can be freely combined with each of the adsorbers 10 of Figs. 2B, 3B, 4B, 5B, 6B, 7B, 8 and 9. Similar, this applies to other features and configurations of the adsorber element 12 and the adsorber 10. Referring to Figs. 3A and 3B. In the embodiment of Figs. 3A and 3B the third filter element 20 is built as packed filter bed in the center of the adsorber element 12. The third filter element 20 is separated from the second filter element 20 in a radial direction by a baffle 36 surrounding the third filter element 20 in a radial direction. If the adsorber element 12 of Fig. 3A is inserted into a housing 24 as depicted by arrows 30 in Fig. 3B, the flow direction through the first filter element 16 and the second filter element 18 is in a radial direction towards the center of the adsorber. Due to the baffle 36 the flow direction is changed and gas flow through the third filter element 20 is in an axial direction. In the embodiment of Figs. 4A and 4B, the configuration of the first filter element 16, the second filter element 18 and the third filter element 20 is similar to the configuration of Figs. 3A and 3B. However, the adsorber element 12 of Fig. 4A comprises an additional cap element 23 and an additional end cap 15, wherein the third filter element 20 is held between the additional end cap 15 and the additional cap element 23. Therein, the additional cap element 23 contains an opening 29 in fluid communication with the outlet 28 of the housing 24. Thus, the adsorber element 12 of Fig. 4A contains a first cartridge 38 including the third filter element 20 and a second cartridge 40 including the first filter element 16 and the second filter element 18. Therein, the first cartridge 38 and the second cartridge 40 are nested with each other such that the first cartridge 38 is placed in a central opening of the second cartridge 40. Afterwards, the adsorber element 12 containing the first cartridge 38 and the second cartridge 40 may be inserted into the adsorber housing 24. Implementing more than one cartridge in the adsorber element may have the benefit that individual filter elements can be replaced. For example, if the first filter element 16 and / or the second filter element 18 may reach saturation by oil or other contaminants, these filter elements can be replaced independently from the third filter element 20 by simply removing the second cartridge 40 and replacing the second cartridge 40 with a new one and returning the refurbished adsorber element 12 into the housing 24 of the adsorber 10. Referring to the embodiment of Figs. 5A and 5B showing a similar configuration of the first filter element 16, a second filter element 18 and a third filter element 20 compared to the embodiment of Figs. 2A and 2B. However, in the embodiment of Figs. 5A and 5B the third filter element 20 is built as first cartridge 38, wherein the first filter element 16 and the second filter element 18 are combined to a second cartridge 40. Referring to the embodiment of Figs. 6A and 6B, the radial order of the first filter element 16, the second filter element 18 and the third filter element 20 is reversed. The inlet channel formed by the adsorber element 12 is in the center of the adsorber element 12 and gas flow is radially outwards. Therein, between the adsorber element 12 and the housing 24, an outlet channel 34' is established. In addition, in the embodiment of Figs. 6A and 6B, the housing 24 comprises an inlet 26' which is arranged axially and is in communication with an opening 29 of a cap element 22. By reversing the order of the filter elements, the available surface of the respective filter elements can be adapted. In particular, the surface of the radially outermost filter element is larger than the surface of any radially inner filter element. Thus, in dependence on the necessity, adapting the available surface of the first filter element 16, second filter element 18 and / or third filter element 20 is feasible. Referring to the embodiments of Figs. 7A and 7B. The embodiment of Figs. 7A and 7B shows a similar configuration of the first filter element 16, the second filter element 18 and the third filter element 20 compared to the embodiment as shown in Figs. 6A and 6B. However, the first filter element 16 and the second filter element 18 are combined to a second cartridge 40, wherein the third filter element 20 is built as first cartridge 38. Referring to the embodiment of Fig. 8. In the embodiment of Fig. 8 gas flow is in a radial direction as indicated by arrows 30 through the first filter element 16 and the second filter element 18. The first filter element 16 and the second filter element 18 are radially surrounded by a baffle 36. By the baffle 36 direction of the gas flow is changed. The third filter element 20 surrounds radially the first filter element 16 and the second filter element 18. The third filter element 20 is arranged radially outer the baffle 36. Gas flow through the third filter element 20 is in the axial direction. In particular, in the embodiment of Fig. 8 the third filter element 20 is directly connected to the housing 24. Hence, the adsorber element 12 only contains a first filter element 16 and a second filter element 18 which is inserted into a central opening established by the third filter element 20. By the adsorber element 12 together with the third filter element 20, an axially arranged outlet channel 34' is created in communication with an outlet 28. Referring to the embodiment of Fig. 9 the third filter element 20 is directly connected to a housing 24. Similar, baffle 36' is directly connected to the housing 24 and radially surrounding the third filter element 20. The adsorber element 12 in the embodiment of Fig. 9 only contains the first filter element 16 and the second filter element 18. As indicated by arrows 30 gas flow through the first filter element 16 and the second filter element 18 is in the radial direction toward the center, wherein gas flow through the third filter element 20 is in the axial direction. The adsorber element 12 is built as cartridge, wherein by the first filter element 16 and a second filter element 18 a central opening is established to receive the third filter element 20 upon inserting the adsorber element 12 into the housing 24 of the adsorber 10. Referring to the embodiment of Fig. 10 showing an adsorber 10. In particular, the adsorber 10 can be built along with any of the embodiments shown before. A pressure sensor 39 is connected to the inlet 26 and the outlet 28 in order to determine a pressure difference or a differential pressure over the adsorber 10. Therein, the pressure sensor may be directly connected to the inlet 26 and the outlet 28 as illustrated in the Fig. 10. Alternatively, the pressure sensor 39 may be connected instead to one or both of the inlet channel 32 and the outlet channel 34 of the adsorber 10. By the pressure sensor 39, a pressure drop over the adsorber 10 is determined. The pressure sensor 39 may be connected to an evaluation unit or control unit (not shown). The differential pressure is compared to a predetermined threshold, wherein a warning signal is generated by the evaluation unit if the differential pressure measured by the pressure sensor 39 exceeds this predetermined threshold. Preferably, the predetermined threshold is between 30 mbar and 200 mbar, more preferably between 80 mbar and 150 mbar. It has been shown by the inventors that the saturation of the filter elements and in particular saturation by liquid oil aerosols of the filter elements is in direct connection with an increase of the differential pressure or pressure drop over the adsorber 10. Hence, as long as the differential pressure is below the predetermined threshold, the saturation level of one or more of the filter elements is sufficiently low in order to reliably reduce contaminants of the gas flow. If the differential pressure exceeds the predetermined threshold, the filter material of one or more of the filter elements approaches saturation and need to be replaced. Thus, service intervals can be optimized, and unnecessary replacement of any filter elements can be prevented. At the same time, contamination and damage of the cryopump due to oil from the compressor can be prevented. Thus, by the present invention, an adsorber is provided which can reliably remove oil and oil aerosols from the gas flow. At the same time, pressure drop over the adsorber is low. This leads to a reliable operation of more than 20.000 hours and preferably more than 30.000 hours without service. Reference List 10 adsorber 12 adsorber element / cartridge 14 end cap 15 additional end cap 16 first filter element 18 second filter element 20 third filter element 22 cap element 23 additional cap element 24 housing 26, 26' inlet 28 outlet 29 opening 30 arrows 32 inlet channel 34, 34' outlet channel 36, 36' baffle 38 first cartridge 39 pressure sensor 40 second cartridge 100 cryogenic system 102 cryopump 104 helium supply

Claims

1. Adsorber element for helium purification in cryogenic systems, comprising:an end cap to be inserted in or connected to an adsorber housing;a first filter element comprising a layer of a first filter material connected to the end cap and extending from the end cap in an axial direction, wherein the first filter element is formed as hollow cylinder; anda second filter element comprising a second filter material connected to the end cap and extending from the end cap in the axial direction, wherein the second filter element has a cylindrical shape and is nested with the first filter element.

2. Adsorber element according to claim 1, wherein the second filter element surrounds the first filter element or the second filter element is arranged within the first filter element.

3. Adsorber element according to claim 1 or 2, wherein the second filter element is formed as hollow cylinder or full cylinder.

4. Adsorber element according to any of claims 1 to 3, comprising a third filter element having third filter material and extending in the axial direction, wherein the third filter element is nested with the first filter element and / or the second filter element.

5. Adsorber element according to any of claims 1 to 4, wherein the second filter element or third filter element is built as packed filter bed.

6. Adsorber element according to any of claims 1 to 5, wherein gas flow through the first filter element is in a radial direction.

7. Adsorber element according to any of claims 1 to 6, wherein gas flow through the second filter element and / or the third filter element is in the axial direction or a radial direction.

8. Adsorber element according to any of claims 1 to 7, comprising a baffle extending in the axial direction and preferably connected to the end cap, wherein the baffle is arranged between the first filter element and the second filter element and / or between second filter element and the third filter element.

9. Adsorber element according to any of claims 1 to 8, wherein the first filter element is configured to remove liquid oil aerosol and / or the second filter element is configured to remove water vapor and / or the third filter element is configured to remove oil vapor.

10. Adsorber element according to any of claims 1 to 9, wherein the first filter element is configured to store more than 100g oil, preferably more than 50g oil and more preferably more 20g oil without release of oil aerosol.

11. Adsorber for helium purification in cryogenic systems, comprising:an adsorber housing having an inlet and an outlet andan adsorber element according to any of claims 1 to 10 arranged within the adsorber housing.

12. Adsorber according to claim 11, wherein the adsorber housing has a radial or axial inlet and / or wherein the adsorber housing has a radial or axial outlet.

13. Adsorber according to claim 11 or 12, comprising a differential pressure of the adsorber of 180mbar or below, preferably 120mbar or below and most preferably 80mbar or below.

14. Adsorber according to any of claims 11 to 13, comprising a pressure sensor connected to the inlet and / or the outlet to determine a differential pressure / pressure drop over the adsorber or one or more filter elements.

15. Adsorber according to any of claims 11 to 14, wherein the end cap has flange connected to a flange of the adsorber housing.

16. Adsorber according to any of claims 11 to 15, wherein the adsorber element is axially insertable into the adsorber housing.

17. Adsorber according to any of claims 11 to 16, wherein the adsorber housing comprises a packed filter bed.

18. Cryogenic system comprising a helium supply including a compressor and a heat exchanger to supply helium for cooling to a cryopump connected to the helium supply, wherein an adsorber according to any of claims 11 to 17 is arranged between the helium supply and the cryopump.

19. Method for operating an adsorber for helium purification in cryogenic systems, including:Determining a pressure drop over the adsorber during operation; andIf the pressure dop exceeds a predetermined threshold, generating a warning signal indicative of oil saturation of the adsorber.

Images