Method for separating gases

Abstract

The invention relates to a special apparatus, in particular linkage of gas separation membrane modules, and a special method for separating gas mixtures containing helium.

1 : Method for separating gases containing helium, characterized in that it is carried out in an apparatus which has a feed stream separation stage ( 1 ), a retentate separation stage ( 2 ) and a permeate separation stage ( 3 ), as well as at least one compressor ( 4 ) and/or at least one, preferably one or two, vacuum pump(s) ( 15 ),
 the feed stream separation stage ( 1 ) separates a feed stream ( 5 ) consisting of helium and at least one other component into a first permeate stream ( 6 ) enriched with regard to helium compared to the feed stream ( 5 ), and a first retentate stream ( 7 ) depleted with regard to helium compared to the feed stream ( 5 ),   the retentate separation stage ( 2 ) separates the first retentate stream ( 7 ) into a second permeate stream ( 9 ) enriched with regard to helium compared to the first retentate stream ( 7 ), and a second retentate stream ( 8 ) depleted with regard to helium compared to the first retentate stream ( 7 ),   the permeate separation stage ( 3 ) separates the first permeate stream ( 6 ) into a third retentate stream ( 10 ) depleted with regard to helium compared to the first permeate stream ( 6 ), and a third permeate stream ( 11 ) enriched with regard to helium compared to the first permeate stream ( 6 ),   the third permeate stream ( 11 ) is removed as product or processed further and optionally the second retentate stream ( 8 ) is removed as a first further product or processed further or discarded,   the second permeate stream ( 9 ) and the third retentate stream ( 10 ) are fed to the feed stream ( 5 ) or discarded,   the first permeate stream ( 6 ) is not subjected to a recompression,   upon recycling the second permeate stream ( 9 ) and the third retentate stream ( 10 ), the control of the gas volume recycled with the second permeate stream ( 9 ) and the third retentate stream ( 10 ) to the feed stream ( 5 ) is adjusted such that, in total, less than 50% by volume, preferably 5 to 40% by volume, very particularly preferably 5 to 30% by volume and especially preferably 10 to 25% by volume, of the volume of the crude gas stream ( 17 ) are recycled,   and   upon recycling the second permeate stream ( 9 ) and the third retentate stream ( 10 ), the helium concentration after the first recycling of the second permeate stream ( 9 ) and of the third retentate stream ( 10 ) in the feed stream ( 5 ) is increased, preferably by at least 2%, particularly preferably by at least 3%, particularly preferably by 4 to 10% and very particularly preferably by 5 to 10%, in each case compared to the concentration in the crude gas stream ( 17 ).   
     
     
         2 : Apparatus for separating gases containing helium, characterized in that
 it has a feed stream separation stage ( 1 ), a retentate separation stage ( 2 ) and a permeate separation stage ( 3 ), as well as at least one compressor ( 4 ) and/or at least one, preferably one or two, vacuum pump(s) ( 15 ),   the feed stream separation stage ( 1 ) is designed such that it separates a feed stream ( 5 ) consisting of helium and at least one other component into a first permeate stream ( 6 ) enriched with regard to helium compared to the feed stream ( 5 ), and a first retentate stream ( 7 ) depleted with regard to helium compared to the feed stream ( 5 ),   the retentate separation stage ( 2 ) is designed such that it separates the first retentate stream ( 7 ) into a second permeate stream ( 9 ) enriched with regard to helium compared to the first retentate stream ( 7 ), and a second retentate stream ( 8 ) depleted with regard to helium compared to the first retentate stream ( 7 ),   the permeate separation stage ( 3 ) is designed in such a way that it separates the first permeate stream ( 6 ) into a third retentate stream ( 10 ) depleted with regard to helium compared to the first permeate stream ( 6 ), and a third permeate stream ( 11 ) enriched with regard to helium compared to the first permeate stream ( 6 ),   the apparatus is designed such that the third permeate stream ( 11 ) can be removed as a product or processed further and optionally the second retentate stream ( 8 ) can be removed as a further product or processed further or discarded,   the apparatus is designed such that the second permeate stream ( 9 ) and the third retentate stream ( 10 ) can be fed to the feed stream ( 5 ) or be discarded,   the apparatus is designed in such a way that the first permeate stream ( 6 ) is not subjected to a recompression,   upon recycling the second permeate stream ( 9 ) and the third retentate stream ( 10 ), the recycling of the gas volume recycled with the second permeate stream ( 9 ) and with the third retentate stream ( 10 ) to the feed stream ( 5 ) is regulated in such a way that, in total, less than 50% by volume, preferably 5 to 40% by volume, very particularly preferably 5 to 30% by volume and especially preferably 10 to 25% by volume, of the volume of the crude gas stream ( 17 ) are recycled,   and   upon recycling the second permeate stream ( 9 ) and the third retentate stream ( 10 ), the recycling of the second permeate stream ( 9 ) and of the third retentate stream ( 10 ) is regulated such that the helium concentration after the first recycling of the second permeate stream ( 9 ) and of the third retentate stream ( 10 ) in the feed stream ( 5 ) is increased, preferably by at least 2%, particularly preferably by at least 3%, particularly preferably by 4 to 10% and very particularly preferably by 5 to 10%, in each case compared to the concentration in the crude gas stream ( 17 ).   
     
     
         3 : Method according to  claim 1 ,
 characterized in that, at least in the feed stream separation stage ( 1 ), but preferably in the feed stream separation stage ( 1 ), the retentate separation stage ( 2 ) and the permeate separation stage ( 3 ), gas separation membrane modules with a mixed-gas selectivity for helium/methane or for helium/nitrogen of at least 40, preferably 50 to 400, particularly preferably 150 to 300, are used.   
     
     
         4 : Method according to  claim 3 ,
 characterized in that   the material used for the separation-active layer of the membranes is a polyimide of the general formula   
       
         
           
           
               
               
           
         
         R is selected from the group consisting of 
       
       
         
           
           
               
               
           
         
         x, y: mole fraction where 0<x<0.5 and 1>y>0.5. 
       
     
     
         5 : Method according to  claim 4 ,
 characterized in that   the material used for the separation-active layer of the membranes is a polyimide comprising 10 to 90% by weight, preferably 15 to 25% by weight and very particularly preferably 20% by weight of   
       
         
           
           
               
               
           
         
         and 90 to 10% by weight, preferably 85 to 75% by weight and very particularly preferably 80% by weight of 
       
       
         
           
           
               
               
           
         
       
     
     
         6 : Method according to  claim 1 ,
 characterized in that   the second permeate stream ( 9 ) and the third retentate stream ( 10 ) on the suction side of the compressor ( 4 ) are passed for reprocessing.   
     
     
         7 : Method according to  claim 1 ,
 characterized in that   a multistage compressor ( 4 ) is used.   
     
     
         8 : Method according to  claim 7 ,
 characterized in that   the second permeate stream ( 9 ) and/or the third retentate stream ( 10 ) is/are introduced into the compressor ( 4 ) between two compression stages.   
     
     
         9 : Method according to  claim 1 ,
 characterized in that   the first retentate stream ( 7 ) and/or the second retentate stream ( 8 ) and/or the third retentate stream ( 10 ) are passed through a pressure relief valve.   
     
     
         10 : Method according to  claim 1 ,
 characterized in that   at least one of the membrane separation stages ( 1 ) to ( 3 ) comprises more than one gas separation membrane module which are connected in parallel and/or in series.   
     
     
         11 : Method according to  claim 1 ,
 characterized in that   the gas separation membrane module(s) consist(s) of hollow fibre membranes and/or flat membranes.   
     
     
         12 : Method according to  claim 1 ,
 characterized in that   at least 95%, preferably at least 97%, particularly preferably at least 99% and very particularly preferably at least 99.5%, of the helium introduced into the apparatus with the crude gas stream ( 17 ) are removed from the system via the third permeate stream ( 11 ).   
     
     
         13 : Method according to  claim 1 ,
 characterized in that   the pressure of the permeate side ( 6 ) of the feed stream separation stage ( 1 ) is adjusted preferably by means of a pressure relief valve ( 14 ) on the retentate side of the permeate separation stage ( 3 ) to 1 to 30 bar, preferably to 2 to 20 bar and particularly preferably to 2 to bar.   
     
     
         14 : Method according to  claim 1 ,
 characterized in that   the pressure of the first and second retentate stream ( 7 ) and ( 8 ) is adjusted preferably by means of a pressure relief valve ( 13 ) in the second retentate stream ( 8 ) to 1 to 100 bar, preferably to 5 to 80 bar and particularly preferably to 10 to 70 bar.   
     
     
         15 : Method according to  claim 1 ,
 characterized in that   the driving force used for the separation task is a partial pressure difference between the retentate side and the permeate side in the respective membrane separation stages, the partial pressure difference being generated by a compressor in the feed stream ( 5 ) and/or by a vacuum pump ( 15 ) in the second and/or third permeate stream ( 9 ) and/or ( 11 ) and/or by a permeate-side flushing-gas stream.   
     
     
         16 : Method according to  claim 14 ,
 characterized in that   the pressure of the permeate of the feed stream separation stage ( 1 ) is identical or increased compared with the ambient pressure, meaning that there is still a partial pressure difference between retentate and permeate of the permeate separation stage ( 3 ) and therefore a driving force is present for the case when the permeate of the permeate separation stage ( 3 ) is at ambient pressure or subatmospheric pressure is applied.   
     
     
         17 : Apparatus according to  claim 2 ,
 characterized in that, at least in the feed stream separation stage ( 1 ), but preferably in the feed stream separation stage ( 1 ), the retentate separation stage ( 2 ) and the permeate separation stage ( 3 ), gas separation membrane modules with a mixed-gas selectivity for helium/methane or for helium/nitrogen of at least 40, preferably 50 to 400, particularly preferably 150 to 300, are used.   
     
     
         18 : Apparatus according to  claim 17 ,
 characterized in that   the material used for the separation-active layer of the membranes is a polyimide of the general formula   
       
         
           
           
               
               
           
         
         R is selected from the group consisting of 
       
       
         
           
           
               
               
           
         
         x, y: mole fraction where 0<x<0.5 and 1>y>0.5. 
       
     
     
         19 : Apparatus according to  claim 18 ,
 characterized in that   the material used for the separation-active layer of the membranes is a polyimide comprising 10 to 90% by weight, preferably 15 to 25% by weight and very particularly preferably 20% by weight of   
       
         
           
           
               
               
           
         
         and 90 to 10% by weight, preferably 85 to 75% by weight and very particularly preferably 80% by weight of 
       
       
         
           
           
               
               
           
         
       
     
     
         20 : Apparatus according to  claim 2 ,
 characterized in that   the second permeate stream ( 9 ) and the third retentate stream ( 10 ) on the suction side of the compressor ( 4 ) are passed for reprocessing.   
     
     
         21 : Apparatus according to  claim 2 ,
 characterized in that   a multistage compressor ( 4 ) is used.   
     
     
         22 : Apparatus according to  claim 21 ,
 characterized in that   the second permeate stream ( 9 ) and/or the third retentate stream ( 10 ) is/are introduced into the compressor ( 4 ) between two compression stages.   
     
     
         23 : Apparatus according to  claim 2 ,
 characterized in that   the first retentate stream ( 7 ) and/or the second retentate stream ( 8 ) and/or the third retentate stream ( 10 ) are passed through a pressure relief valve.   
     
     
         24 : Apparatus according to  claim 2 ,
 characterized in that   at least one of the membrane separation stages ( 1 ) to ( 3 ) comprises more than one gas separation membrane module which are connected in parallel and/or in series.   
     
     
         25 : Apparatus according to  claim 2 ,
 characterized in that   the gas separation membrane module(s) consist(s) of hollow fibre membranes and/or flat membranes.   
     
     
         26 : Apparatus according to  claim 2 ,
 characterized in that   at least 95%, preferably at least 97%, particularly preferably at least 99% and very particularly preferably at least 99.5%, of the helium introduced into the apparatus with the crude gas stream ( 17 ) are removed from the system via the third permeate stream ( 11 ).   
     
     
         27 : Apparatus according to  claim 2 ,
 characterized in that   the pressure of the permeate side ( 6 ) of the feed stream separation stage ( 1 ) is adjusted preferably by means of a pressure relief valve ( 14 ) on the retentate side of the permeate separation stage ( 3 ) to 1 to 30 bar, preferably to 2 to 20 bar and particularly preferably to 2 to bar.   
     
     
         28 : Apparatus according to  claim 2 ,
 characterized in that   the pressure of the first and second retentate stream ( 7 ) and ( 8 ) is adjusted preferably by means of a pressure relief valve ( 13 ) in the second retentate stream ( 8 ) to 1 to 100 bar, preferably to 5 to 80 bar and particularly preferably to 10 to 70 bar.   
     
     
         29 : Apparatus according to  claim 2 ,
 characterized in that   the driving force used for the separation task is a partial pressure difference between the retentate side and the permeate side in the respective membrane separation stages, the partial pressure difference being generated by a compressor in the feed stream ( 5 ) and/or by a vacuum pump ( 15 ) in the second and/or third permeate stream ( 9 ) and/or ( 11 ) and/or by a permeate-side flushing-gas stream.   
     
     
         30 : Apparatus according to  claim 28 ,
 characterized in that   the pressure of the permeate of the feed stream separation stage ( 1 ) is identical or increased compared with the ambient pressure, meaning that there is still a partial pressure difference between retentate and permeate of the permeate separation stage ( 3 ) and therefore a driving force is present for the case when the permeate of the permeate separation stage ( 3 ) is at ambient pressure or subatmospheric pressure is applied.