Coiled membrane filtration system

Abstract

A method and apparatus for achieving reverse osmosis, microfiltration, nanofiltration and ultrafiltration, produces Dean vortices against a membrane surface which is advantageously in a form of a wound helical membrane tube.

What is claimed is:  
     
       1. A method of defouling and depolarizing  an inner surface of a hollow curved tubular membrane which comprises , comprising the step of: 
       moving a fluid containing a liquid component and a fouling component, said fouling component selected from the group consisting of a solute,  solid particles and a mixture of a solute and solid particles, through the curved tubular membrane, said membrane having an inner surface and an outer surface, whereby a portion of the liquid component is filtered by passing from the inner surface to the outer surface of said membrane, said fluid being directed through the curved tubular membrane at a rate sufficient to produce Dean vortices in the fluid which move across said inner surface of said tubular membrane and at least partially defoul the inner surface of the membrane of solid particles filtered from the liquid component.  
     
     
       2. A method according to  claim 1  wherein said curved tubular membrane comprises coils which progress axially. 
     
     
       3. A method according to  claim 2  wherein there is little or no spacing between adjacent coils as they progress axially. 
     
     
       4. A method according to  claim 1  wherein said curved tubular membrane comprises coils that are wound to progress both axially and radially. 
     
     
       5. A method according to  claim 1 , wherein said curved tubular membrane comprises coils that are wound to progress radially. 
     
     
       6. A method according to  claim 1 , including producing Dean vortices using a sufficiently high Dean number for cleaning the membrane and depolarizing a concentration polarization of the membrane without excessive pressure drop in the wound  curved tubular membrane, and maximizing a ratio between the sufficiently high Dean number and a critical Dean number, the critical Dean number being a function of fluid flow rate, the inner diameter of the tube, the membrane thickness and a radius of a winding of the wound  curved tubular membrane. 
     
     
       7. A method according to  claim 6 , including moving the fluid solution past the inner surface at a velocity greater than a critical velocity according to the equation 
       
         
           ν c =Re o μ/dρ,  
         
       
       where Re c  is the critical Reynolds number for the fluid, μ is the viscosity of the fluid, d is the inner diameter of the curved tubular membrane and ρ is the density of the fluid. 
     
     
       8. An apparatus for effecting a pressure-driven filtration process which comprises: 
       a)  an outer shell having a feed inlet, a feed outlet, and a permeate outlet;    
         b ) a  one or more hollow curved tubular membrane  membranes having a curved inner surface and outer surface within said outer shell, wherein said tubular membranes are connected to said feed inlet and feed outlet to allow flow of a fluid from the feed inlet to the feed outlet through the tubular membrane across the inner surface, wherein a portion of the fluid can pass from the inner surface to the outer surface of the tubular membranes; wherein said outer surface is in communication with the permeate outlet; wherein said permeate outlet allows a pressure drop from the inner surface of the membrane to the outer surface of the membrane and wherein the tubular membrane includes a tubular diameter and a radius of curvature that allows Dean vortices to form in the fluid above a critical velocity; and  
       c) means for moving a fluid containing a component selected from the group consisting of a solute, solid particles and a mixture of a solute and solid particles to produce Dean vortices in the fluid which move across said curved inner surface. 
     
     
       9. An apparatus according to  claim 8 , wherein the curved tubular membrane is a helical coil  membranes are spiral coils. 
     
     
       10. An apparatus according to  claim 9 , wherein the spiral coil is a helical coil and has  spiral coils are helical tubes and have turns which progress axially. 
     
     
       11. An apparatus according to  claim 8 , including means for moving the fluid past the membrane inner surface at a rate above a critical velocity according to the equation 
       
         
           ν c =Re o μ/dρ;  
         
       
       where Re c  is the critical Reynolds number of the fluid, μ is the viscosity of the fluid, d is the inner diameter of the curved tubular membrane  membranes and ρ is the density of the fluid. 
     
     
       12. The An apparatus according to  claim 8  wherein said curved tubular membrane comprises  membranes comprise coils that are wound to progress both axially and radially. 
     
     
       13. The  An apparatus according to  claim 8  wherein said curved tubular membrane comprises  membranes comprise coils that are wound to progress radially. 
     
     
       14. An apparatus according to  claim 8  wherein said tubular membranes number two or more. 
     
     
       15. A method of defouling an inner surface of a hollow curved tubular membrane, comprising the step of: 
       
         moving a fluid having a liquid component and a macromolecule component through the curved tubular membrane, said membrane having an inner surface and an outer surface, whereby a portion of the liquid component is filtered by passing from the inner to the outer surface of said membrane, said fluid being directed through the curved tubular membrane at a rate sufficient to produce Dean vortices in the fluid which moves across said inner surface of said tubular membrane and at least partially defoul the inner surface of the membrane of the macromolecule component filtered from the liquid component. 
       
     
     
       16. A method of defouling an inner surface of a hollow curved tubular membrane, comprising the step of: 
       
         moving a fluid having a liquid component and a particulate or colloid component through the curved tubular membrane, said membrane having an inner surface and an outer surface, whereby a portion of the liquid component is filtered by passing from the inner to the outer surface of said membrane, said fluid being directed through the curved tubular membrane at a rate sufficient to produce Dean vortices in the fluid which move across said inner surface of said tubular membrane and at least partially defoul the inner surface of the membrane of the particulate or colloid component filtered from the liquid component. 
       
     
     
       17. An apparatus for effecting a pressure-driven filtration process, comprising: 
         a )  an outer shell having feed inlet, a feed outlet, and a permeate outlet; and    
         b )  a plurality of curved hollow tubular membranes having an inner surface and outer surface within said outer shell, wherein said tubular membranes are connected to said feed inlet and feed outlet to allow flow of a fluid from the feed inlet to the feed outlet through the tubular membranes across the inner surface of the membranes, wherein the tubular membrane includes a tubular diameter and radius of curvature such that, at a critical velocity, Dean vortices are formed and defoul the inner surface of said membranes, wherein a portion of the fluid can pass from the inner surface to the outer surface of the tubular membranes, and wherein said outer surface is in communication with the permeate outlet.   
     
     
       18. An apparatus of  claim 17 , wherein said curved tubular membranes include coils which progress axially. 
     
     
       19. An apparatus of  claim 18 , wherein said curved tubular membranes progress along the same axis. 
     
     
       20. An apparatus of  claim 18 , wherein said curved tubular membranes include essentially no spacing between adjacent coils as the coils progress axially. 
     
     
       21. An apparatus of  claim 17 , wherein said curved tubular membranes include coils that are wound to progress axially and radially. 
     
     
       22. An apparatus of  claim 17 , wherein said curved tubular membranes include coils that are wound to progress radially. 
     
     
       23. The apparatus of  claim 17 , wherein said tubular membranes are suitable for reverse osmosis, nanofiltration, ultrafiltration or microfiltration. 
     
     
       24. An apparatus for effecting a pressure-driven filtration process, comprising: 
         a )  an outer shell having a feed inlet, a feed outlet, and a permeate outlet; and    
         b )  a plurality of spiral hollow tubular membranes having an inner surface and outer surface within said outer shell, wherein said tubular membranes are connected in parallel to said feed inlet and feed outlet to allow flow of a fluid from the feed inlet to the feed outlet through the tubular membranes across the inner surface of the membranes, wherein the tubular membrane includes a tubular diameter and radius of curvature such that, at a critical velocity, Dean vortices are formed and defoul the inner surface of said membranes wherein a portion of the fluid can pass from the inner surface to the outer surface of the tubular membranes, and wherein said outer surface is in communication with the permeate outlet.   
     
     
       25. An apparatus according to  claim 8  wherein said permeate outlet is open.