Submerged water desalination system with remote pump

Abstract

A submersible water desalination apparatus includes a plurality of water separation membrane elements that when supplied with salinated water under pressure at a first depth will produce at least partially desalinated product water and concentrate or brine; a product water collector that receives product water from the membrane elements; and a permeate conduit that transports product water from the collector downwardly to a motorized submersible pump remotely located from the membrane elements and collector at a second depth greater than the first depth. The second depth is sufficiently greater than the first depth so that the height of a standing column of product water in the product water collector and permeate conduit between the membrane elements and the suction side of the pump maintains a net positive suction head that prevents inlet side cavitation during pump startup and operation.

1 . A submersible water desalination apparatus comprising:
 i) a plurality of water separation membrane elements that when supplied with salinated water under pressure will produce at least partially desalinated product water and concentrate or brine;   ii) a product water collector that receives product water from the membrane elements;   iii) a permeate conduit that transports product water from the collector to a motorized submersible pump remotely located from the membrane elements and collector; and   iv) the submersible pump having a suction side that receives product water from the permeate conduit and a discharge side that pumps product water away from the desalination apparatus through a product water conduit for surface or subsurface use;   wherein when the apparatus is submerged and the pump receives product water from the membrane elements, the pump suction side maintains a net positive suction head that prevents inlet side cavitation during pump startup and operation.   
     
     
         2 . An apparatus according to  claim 1 , wherein the water separation membrane elements are reverse osmosis elements. 
     
     
         3 . An apparatus according to  claim 1 , wherein the pump comprises a multistage pump. 
     
     
         4 . An apparatus according to  claim 1 , wherein the pump comprises a positive displacement, centrifugal or axial-flow pump. 
     
     
         5 . An apparatus according to  claim 1 , wherein the pump comprises a piston pump. 
     
     
         6 . An apparatus according to  claim 1 , wherein the pump comprises a plunger pump. 
     
     
         7 . An apparatus according to  claim 1 , wherein the pump comprises a rotary pump. 
     
     
         8 . An apparatus according to  claim 1 , wherein the pump comprises a centrifugal pump. 
     
     
         9 . An apparatus according to  claim 1 , wherein the permeate conduit transports the product water downwardly to the pump. 
     
     
         10 . An apparatus according to  claim 1 , wherein the apparatus is submerged, and there is a standing column of product water in the product water collector and permeate conduit between the membrane elements and the pump suction side, the standing column of product water having a height. 
     
     
         11 . An apparatus according to  claim 10 , wherein the membrane elements are supplied with salinated water under pressure at a first depth, the pump is at a second depth greater than the first depth, and the second depth is sufficiently greater than the first depth so that the height of the standing column of product water maintains the net positive suction head. 
     
     
         12 . An apparatus according to  claim 11 , wherein the height is at least about 3 meters. 
     
     
         13 . An apparatus according to  claim 11 , wherein the height is at least about 5 meters. 
     
     
         14 . An apparatus according to  claim 11 , wherein the height is at least about 10 meters. 
     
     
         15 . An apparatus according to  claim 1 , wherein the apparatus is submerged at a depth, and that depth is adjustable to increase or decrease hydrostatic pressure on the apparatus and the net positive suction head. 
     
     
         16 . An apparatus according to  claim 1 , wherein the pump is affixed to a seabed. 
     
     
         17 . An apparatus according to  claim 1 , wherein the pump is suspended above a seabed. 
     
     
         18 . An apparatus according to  claim 1 , wherein the water separation membrane elements are operated at a recovery ratio of product water volume to feedwater volume that is no greater than 40%. 
     
     
         19 . An apparatus according to  claim 1 , wherein the water separation membrane elements are operated at a recovery ratio of product water volume to feedwater volume that is no greater than 20%. 
     
     
         20 . A method for operating a submerged water desalination apparatus, the method comprising the steps of:
 i) producing at least partially desalinated product water and concentrate or brine from a plurality of submerged water separation membrane elements;   ii) collecting product water in a product water collector that receives product water from the membrane elements; and   iii) pumping product water from the product water collector through a permeate conduit that transports product water from the collector to a motorized submersible pump remotely located from the membrane elements and collector, the submersible pump having a suction side that receives product water from the permeate conduit and a discharge side that pumps product water away from the desalination apparatus through a product water conduit for surface or subsurface use;   wherein when the apparatus is submerged and the pump receives product water from the membrane elements, the pump suction side maintains a net positive suction head that prevents inlet side cavitation during pump startup and operation.