HELIUM RECOVERY PROCESS

Abstract

A process for recovery of helium from one or more than one helium-containing off-gas streams comprises preconditioning off-gas through a multi-stage preconditioning device, cryogenically separating a helium-enriched gas fraction from the preconditioned off-gas received from the preconditioning device a cryogenic separation device, and purifying the helium-enriched gas fraction received from the cryogenic separation device using a purification device so as to obtain purified helium gas with a higher helium content than the helium-enriched gas.

Claims

1. A process for recovery of helium from one or more than one helium-containing off-gas streams, wherein the off-gas streams are treated successively by preconditioning, cryogenic separation and purification in an installation, the process comprising, in order of succession: preconditioning off-gas using a multi-stage preconditioning device so as to obtain preconditioned off-gas, the preconditioning device comprising n stages S1 to Sn, with n≥2, each stage S1 to Sn being adapted to precondition off-gas by at least partially chemically converting at least one component other than helium in the off-gas and/or by at least partially removing at least one component other than helium from the off-gas, the preconditioning device optionally comprising means for adjusting the temperature and/or pressure of the off-gas upstream of one or more of the stages S1 to Sn; cryogenically separating a helium-enriched gas fraction from the preconditioned off-gas received from the preconditioning device using a cryogenic separation device; and purifying the helium-enriched gas fraction received from the cryogenic separation device using a purification device so as to obtain purified helium gas with a higher helium content than the helium-enriched gas, wherein: the preconditioning device has multiple off-gas inlets, each off-gas inlet corresponding to one of the stages S1 to Sn so that the off-gas of an off-gas stream introduced into the preconditioning device via one of the off-gas inlets is thereafter preconditioned in the corresponding stage, the stage S1 to Sn are in linear fluid succession so that off-gas which has been preconditioned in stage Sx, with 1≤x<n, is sent to stage Sx+1 for further preconditioning, whereas off-gas which has been preconditioned in stage Sn is sent as the preconditioned off-gas to the cryogenic separation device, wherein for each off-gas stream from which helium is to be recovered, components other than helium which are present in the off-gas and which are to be chemically converted and/or removed therefrom in the preconditioning device are determined and the off-gas inlet via which said off-gas stream is introduced into the preconditioning device is selected in function of said determined components.

2. The process for recovery of helium of claim 1, wherein the preconditioned off-gas consists: for between 99.0000% vol and 100.0000% vol of helium and air gases; and/or for 78.0000% vol to 100.0000% vol of helium and nitrogen.

3. The process for recovery of helium of claim 1, wherein the helium-enriched gas fraction has a helium content of at least 95.0000% vol, preferably at least 99.0000% vol but less than 100.0000% vol, in particular s 99.9700% vol or s 99.9500% vol.

4. The process for recovery of helium of claim 1, wherein the purified helium gas is has a helium content of at least 99.9900% vol and up to 100% vol, preferably at least 99.9990% vol, more preferably at least 99.9999% vol.

5. The process for recovery of helium of claim 1, wherein the one or more off-gas streams include or consist of off-gas which has been generated during semiconductor manufacturing in a semiconductor manufacturing installation, the one or more off-gas streams preferably including off-gases generated by one or more than one semiconductor factoring tools.

6. The process for recovery of helium of claim 5, wherein at least part of the purified helium gas is recycled to and used in the semiconductor manufacturing installation, at least part of the purified helium being preferably recycled to and used in the one or more semiconductor factoring tools.

7. A process for manufacturing semiconductors, the process comprising the steps of: producing semiconductors in a semiconductor production installation, during which helium-containing off-gas is generated; collecting one or more streams of helium-containing off-gas from the semiconductor production installation; and recovering purified helium from the collected off-gas streams by means of the process of claim 1.

8. The process for recovery of helium of claim 1, wherein the stages S1 to Sn include one or more stage selected from off-gas combustion devices, off-gas washing devices, condensation devices, activated-carbon devices, catalytic oxidation devices, adsorption devices and off-gas filter devices.

9. The process for recovery of helium of claim 1, wherein the stages S1 to Sn include at least one of the following devices: off-gas combustion stages selected from: electrically heated combustor with or without oxidant injection, natural gas heated combustors with or without oxidant injection; off-gas washing stages selected from: fresh-water washers, KOH washers, NaOH washers or a succession of at least two of these washers with a fresh water washer as the final washer; condensation stages selected from coolant-cooled heat exchanger and separator devices; off-gas catalytic oxidation stages selected from: heterogeneous catalytic oxidation devices with palladium and or silver as catalytic active component; and adsorption stages selected from: adsorption devices with aluminum oxide adsorbents and/or molecular sieve adsorbents.

10. The process for recovery of helium of claim 1, wherein the preconditioning device comprises means for adjusting the temperature and/or pressure of the off-gas upstream of one or more of the stages S1 to Sn.

11. The process for recovery of helium of claim 1, wherein the preconditioning device comprises means for adjusting the temperature of the off-gas upstream of one or more of the stages S1 to Sn selected from electrical gas heating devices, gas/gas heat exchange devices, gas/liquid heat exchange devices and adiabatic compression heaters.

12. The process for recovery of helium of claim 1, wherein the preconditioning device comprises at least one compressor or expander for adjusting the pressure of the off-gas upstream of one or more of the stages S1 to Sn.

13. The process for recovery of helium of claim 1, wherein the gas-preconditioning device comprises: an off-gas combustion stage and an off-gas washer downstream of the off-gas combustion stage; an off-gas washer, a condensation stage downstream of the off-gas washer and an activated-carbon stage downstream of the condensation stage; an adiabatic compression heater, a catalytic oxidation stage downstream of the adiabatic compression heater, an off-gas cooling device downstream of the catalytic oxidation device and an adsorption stage downstream of the off-gas cooling device; an off-gas heating device and a catalytic oxidation stage downstream of the off-gas heating device; or an adsorption stage and an off-gas filter stage downstream of the adsorption stage.

14. The process for recovery of helium of claim 1, wherein in the cryogenic separation device the helium-enriched gas fraction is separated from the preconditioned off-gas using one or more cryogenic separation processes selected from the group consisting of: cryogenic distillation; and cryogenic condensation.

15. The process for recovery of helium of claim 1, wherein in the purification device, the helium-enriched gas fraction is purified into the purified helium gas using one or more purification processes selected from the group consisting of: adsorption processes; and processes comprising catalytic oxidation followed by adsorption.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0080] The present invention and its advantages are illustrated in the following non-limiting examples, reference being made to FIG. 1 and FIG. 2, whereby:

[0081] FIG. 1 is a schematic representation of the succession of steps in the process according to the invention; and

[0082] FIG. 2 is a more detailed schematic representation of an embodiment of the process according to the present invention and a corresponding helium-recovery installation.

DETAILED DESCRIPTION OF THE INVENTION

[0083] As illustrated in FIG. 1, according to the present invention, the one or more helium-containing off-gas streams are subjected successively to preconditioning, cryogenic separation and purification in corresponding units specifically designed for the purpose.

[0084] During the preconditioning step, components other than helium are removed from the one or more helium-containing off-gas streams, for example by means of one or more of the following processes: combustion, chemical (e.g., KOH or NaOH) and/or water washing, filtration, etc. The main purpose of the preconditioning step is to ensure stable and efficient process conditions for the subsequent cryogenic separation step by removing components from the off-gas stream(s) that are liable to affect the cryogenic separation.

[0085] Preferably, at the end of the preconditioning step, the preconditioned off-gas consists essentially of helium and air gases, more preferably of helium, nitrogen, oxygen and argon. The term “air gases” refers to the gases present in atmospheric air. In the present context, the term “essential consisting of” means that the preconditioned gas consists for between 99.0000 and 100.0000% vol of helium and air gases, in particular of helium, nitrogen, oxygen and argon.

[0086] Preferably, at the end of the preconditioning step, the preconditioned off-gas consists for 70.0000% vol to 100.0000% vol, or even 78.0000% vol to 100.0000% vol of helium and nitrogen.

[0087] During the cryogenic separation step (step 2), a helium-enriched gas fraction is separated off from the preconditioned gas by cryogenic separation. Typically, in said cryogenic separation step, a liquefied nitrogen phase is separated from a helium-enriched fraction in gaseous form.

[0088] During the purification step (step 3) the helium-enriched fraction is further purified so as to obtain purified helium gas with a level of purity which meets the requirements of the intended subsequent use of the helium gas. In particular, if the purified helium gas is to be recycled back to the installation(s) or one of the installations which generate the one or more helium-containing off-gas streams, the helium-enriched fraction is purified to the level of purity required for its use in said installation.

[0089] A useful example of a purification step or substep which may be used in the process according to the invention is purification with activated carbon, in particular cryogenic purification with activated carbon, which permits the removal of traces of inter alia nitrogen from the helium-enriched fraction.

[0090] After purification, the purified helium may be stored in containers for storage or transport or may immediately be directed to its point or points of use via a pipeline or manifold. The pipeline or manifold may comprise elements such as valves for directing and controlling the flow of the purified helium, compressors and/or expanders for regulating the pressure of the purified helium and coolers and/or heaters for controlling the temperature of the purified helium.

[0091] It is an essential aspect of the process according to the present invention, that the preconditioning of the one or more helium-containing off-gas streams takes place in a multi-stage preconditioning unit which comprises n stage units S1 to Sn, with n≥2, in linear succession. Each one of said units S1 to Sn is adapted to convert at least one component other than helium in the off-gas and/or to remove at least one component other than helium from the off-gas.

[0092] FIG. 2 shows an embodiment of the present invention, whereby the preconditioning unit comprises a succession of six stage units S1 to S6.

[0093] The installation used for recovering helium from helium-containing off-gas streams comprises a preconditioning unit 10, a cryogenic separation unit 20 and a purification unit 30.

[0094] Each of the six stage units S1 to S6 is designed to remove and/or chemically convert a non-helium component of the off-gas treated therein.

[0095] In the illustrated embodiment, stage unit S1 is an off-gas combustor or incinerator. Stage unit S1 may be heated by the combustion of fuel, such a natural gas or hydrogen therein. Other means may also be used to raise the temperature in stage unit S1 so as to ensure that combustible substances, such as organic halogenics, volatile combustible toxic gases, hydrocarbons and organometallic compounds, present in the off-gas are combusted/incinerated/oxidized.

[0096] Off-gas which has thus been preconditioned in stage unit S1 is sent to stage unit S2. In stage unit S2, off-gas coming from preceding stage unit S1 and/or off-gas supplied directly to stage unit S2 is subjected to chemical washing with a KOH and/or NaOH solution. During the chemical washing, oxides, such as those generated by oxidation in stage unit S1, are removed from the off-gas. Other non-helium compounds, such as halogenic acid(s) can also be removed from the off-gas by this preconditioning method. Stage unit S3 is a cold drying unit, in which moisture is removed from the off-gas treated therein. Moisture may be present in the helium-containing off-gas streams from which helium is to be recovered. Moisture may also be generated in the off-gas or be absorbed by the off-gas during preconditioning in preceding stage units. For example, moisture may be generated during off-gas oxidation in a preceding combustion or incineration stage unit (such as S1) and/or absorbed in a preceding washing stage unit (such as S2). Off-gas preconditioned in stage unit S3 is sent to stage unit S4. In stage unit S4, the off-gas is treated with activated carbon. In this manner, toxic metals present, such as Ar and Ge, can be removed from the off-gas. The next stage unit, in the embodiment illustrated in FIG. 2, is catalytic oxidation unit S5. In catalytic oxidation unit S5, components in the off-gas, such as H.sub.2 and CO, which are difficult to separate from helium by cryogenic separation are oxidized by catalytic oxidation. Catalysts suitable for this purpose are known in the art. One particular such catalyst contains 0.5% wt Pd and 5% wt Ag as catalytically active substances. Such catalytic oxidation is effective within a specific temperature range and requires heating of the off-gas upstream of catalytic oxidation unit S5. In the illustrated embodiment, the off-gas is heated by compression in compressor 11. Following the catalytic oxidation in stage unit S5, the off-gas is cooled in cooler 12. Cooler 12 may be a cooler-condenser, in which case part of the moisture generated by catalytic oxidation in stage unit S5 is removed from the off-gas in cooler-condenser 12. Thus, when cooler 12 is a cooler-condensor, cooler 12 de facto constitutes a further preconditioning stage unit, in that the cooler-condensor removes moisture, i.e. a non-helium component, from the off-gas cooled therein. It will be appreciated that preconditioning unit 10 may comprise several stage units of the same type, such as multiple moisture removal stage units or multiple filter stage units at different positions along the succession of stage units. In the illustrated embodiment, the next stage unit S6 is an adsorption unit in which substantially all CO.sub.2 and moisture, such as, in particular, the CO.sub.2 and moisture (or remaining fraction thereof) generated by catalytic oxidation in preceding stage unit S5, is removed from the off-gas. Stage unit S6 is an alternating bed adsorption unit. Alumina and/or molecular sieves may be used as adsorption medium in stage unit S6.

[0097] The off-gas leaving final stage unit S6, i.e. the preconditioned off-gas, consists almost entirely of helium and nitrogen and is sent to cryogenic separation unit 20.

[0098] In the illustrated embodiment, cryogenic separation unit 20 comprises heat exchanger 21, distillation column 22, a head condenser 23 and a phase separator 24.

[0099] To separate the helium from the nitrogen in the preconditioned off-gas, the preconditioned off-gas is cooled to a cryogenic temperature in heat exchanger 21 and sent to the bottom of distillation column 22. In column 22, the cooled preconditioned off-gas is separated so as to form a nitrogen-rich liquid with a reduced helium content at the bottom of column 22 and a nitrogen-rich gas with an increased helium content at the top of column 22. The nitrogen-rich gas is completely condensed in head condenser 23 at the top of column 22 by heat exchange with the nitrogen-rich liquid, thereby vaporizing the nitrogen rich liquid to form a waste gas which is used to cool down the preconditioned off-gas in heat exchanger 21. Extraneous liquid nitrogen LN is used as a cold source for column 22.

[0100] Head condenser 23 is operated at a temperature which is insufficient to condense helium. A phase separator 24 is installed on the highest piping point of the outlet side of head condenser 23.

[0101] Phase separator 24 is fed with the non condensable helium and the liquefied nitrogen In the steady state of the process there will be an equilibrium between a helium-enriched gas fraction and a liquid nitrogen phase in phase separator 24.

[0102] The level in the phase separator 24 can be controlled by releasing the helium-enriched gas fraction from phase separator 24, using, for instance, a constant setpoint as main control strategy. A secondary control strategy maintains a constant pressure in phase separator 24 so that helium gas collects in head condenser 23.

[0103] The nitrogen gas condensed in head condenser 23 is sent back to the top of column 22 as reflux, so that column 23 operates as a total reflux column.

[0104] The helium-enriched fraction leaving helium separator 24 consists mainly of helium, but may still contain traces of nitrogen, which may have to be removed before the helium can be reused. Thereto, the helium-enriched fraction is sent from cryogenic separation unit 20 to purification unit 30.

[0105] In the illustrated embodiment, purification unit 30 comprises a cryogenic alternating activated-carbon adsorption unit 31 capable of removing essentially all nitrogen from the helium-enriched fraction. Liquid nitrogen LN is used as cooling medium.

[0106] The purified helium leaving purification unit 30 has a purity of 99.9999% vol and is therefore suitable for substantially all industrial uses of helium gas. The purified helium is obtained in gaseous form at a gage pressure of more than 750 kPa (7.5 barg).

[0107] In the illustrated embodiment, the off-gas streams from which helium is to be recovered are produced in a semiconductor plant 40. Plant 40 contains multiple semiconductor facturing tools, at least some of which use helium He in their semiconductor production process and generate a helium-containing off-gas stream. Three such semiconductor tools 41, 42, 43 are shown in FIG. 2 for illustration purposes, though the number of these semiconductor facturing tools may be much larger. As mentioned earlier, in such a semiconductor production plant 40, the use of helium is not necessarily limited to semiconductor facturing tools and helium-containing off-gas streams may also be generated by other units (not shown) of semiconductor production plant 40.

[0108] Plant 40 is connected to a factory exhaust system 51, which collects exhaust gas streams from plant 40, whereafter the collected exhaust gas is subjected to the necessary emission-reduction measures in cleaning unit 52, before the thus cleaned exhaust gas is released into the atmosphere via stack 53.

[0109] When helium-containing off-gas streams from plant 40 are sent to exhaust system 51, the helium contained therein is lost when the off-gas is released into the atmosphere.

[0110] The aim of the present invention is to avoid, or at least to minimize, such losses.

[0111] Thereto, the semiconductor tools 41, 42, 43 (and other equipment) which produce helium-containing off-gas are fluidly connected to preconditioning unit 10.

[0112] Whereas in FIG. 2, each off-gas stream is generated by one single tool 42, 43, 44, an off-gas stream may also be collected from a set of semiconductor facturing tools of plant 40 (not shown), in particular when identical or substantially identical processes, generating substantially identical off-gases, take place in the tools of said set.

[0113] In the illustrated embodiment, semiconductor facturing tools 41, 42, 43 are also fluidly connected to exhaust system 51. However, the flue gas streams from said tools 41, 42, 43 are only sent to exhaust system 51 when the helium recovery system is down for maintenance or when the off-gas stream generated by said tools 41, 42, 43 contain no or only insignificant levels of helium, so that sending the corresponding off-gas stream to the helium recovery system would result in a loss of efficiency of the latter. Indeed, the composition of the off-gas stream generated by a given tool can vary over time depending on the process taking place in tools 42, 43, 44, or even the stage of a given process, making said off-gas stream suitable or unsuited for the recovery of helium therefrom. Valves A and B are used to direct a given off-gas stream to preconditioning unit 10 or to exhaust system 51. Valve C is used to open or close the access to exhaust system 51 for off-gas from semiconductor plant 40.

[0114] In accordance with the present invention, for each off-gas stream from which helium is to be recovered, components other than helium which are present in the off-gas and which are to be chemically converted and/or removed therefrom in the preconditioning unit are determined. Such determination may be achieved by real-time measurements and/or calculations. Alternatively, the information regarding the presence of these components in the generated off-gas stream may be derived from earlier measurements and/or calculations with respect to the performance of identical or highly similar processes in the tool or in tools of the same type.

[0115] Also in accordance with the present invention, preconditioning unit 10 has off-gas inlets which are associated with different stage units of preconditioning unit 10.

[0116] In FIG. 2, an off-gas inlet 61 is shown, which feeds into and is thus associated with stage unit S1, as well as a second off-gas inlet 62, located downstream of stage unit S1 (in the succession of stage units) and feeding into stage unit S2 with which inlet 62 is associated. In a similar manner, further off-gas inlets (not shown) may be present, which are associated with other stage units of preconditioning unit 10. For example, for maximum flexibility, each stage unit S1 to S6 of preconditioning unit 10 may have its own off-gas inlet associated therewith.

[0117] Thus, when, as is the case for tools 41 and 43, the off-gas stream generated by a given tool (or other equipment) contains, in addition to helium, combustible substances which need to be oxidised in stage unit S1, said off-gas stream is introduced into preconditioning unit 10 via inlet 61 associated with stage unit S1 and the corresponding off-gas is subjected to preconditioning in each stage unit S1 to S6, in succession. If, as is the case for tool 42, the off-gas stream generated by said tool does not contain components which must be oxidised in stage unit S1, but does contain one or more components which must be removed therefrom by chemical washing in stage unit S2, then said off-gas stream is introduced into preconditioning unit 10 via off-gas inlet 62 associated with stage unit S2, so that the corresponding off-gas is subjected to preconditioning in stage units S2 to S6, but not in stage unit S1. Although not illustrated in FIG. 2, a similar approach may be applied to off-gas inlets associated with the other stage units S3 to S6.

[0118] To the extent that semiconductor factoring tools 41, 42, 43 (or other equipment's) may produce helium-containing off-gas streams, the composition of which varies over time, in particular with respect to the presence of components other than helium, a tool (or equipment), may be fluidly connected to several off-gas inlets of preconditioning unit 10. A valve system (not shown) directs said off-gas stream to one of off-gas inlets 61, 62 in function of the composition of the off-gas at the given moment in time.

[0119] As shown in FIG. 2, compressors 71, 72, 73 are provided to pressurize the off-gas streams and to transport them to the appropriate off-gas inlet 61, 62 of preconditioning unit 10. It will be appreciated that, before being introduced into preconditioning unit 10, the off-gas streams may also be subjected to other measures, such as particle separation (filtering) in order to protect the valves from erosion or corrosion or for heating in order to prevent condensation in the pipe(s)/manifold(s) transporting the off-gas stream(s) to preconditioning unit 10.

[0120] The process according to the present invention thus optimizes the helium recovery from the one or more helium-containing off-gas streams in that it enables, for each off-gas stream, to determine the number of preconditioning stages to which the corresponding off-gas must be subjected, as opposed to systematically subjecting the off-gas stream or all of the off-gas streams to all of the preconditioning stages of the preconditioning units.

[0121] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0122] The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

[0123] “Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of “comprising.” “Comprising” is defined herein as necessarily encompassing the more limited transitional terms “consisting essentially of” and “consisting of”; “comprising” may therefore be replaced by “consisting essentially of” or “consisting of” and remain within the expressly defined scope of “comprising”.

[0124] “Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0125] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0126] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

[0127] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.