Patent ID: 7563370

Claim:
A plant for providing elevated osmotic pressure through use of pressure retarded osmosis, wherein the plant comprises at least one semipermeable membrane or membrane module where the membrane or membrane module comprises a non-porous material as a diffusion skin, and at least one layer of a porous material, wherein the porous layer has, when water wetted, a porosity φ, thickness x, and tortuosity τ related to one another as given by the expression: x·τ=φ·S Equation(1) wherein S has a value of 0.0015 meter or lower, the porosity φ has an average value of more than 50%, the tortuosity τ is less than 2.5, a water permeability of the porous layer is greater than 1×10 −11 m/s/Pa, and a salt permeability of the porous layer is less than 3×10 −8 m/s, and a pressure exchange arrangement connected to an outlet of the membrane or membrane module configured to receive direct hydraulic transfer of osmotic pressure at elevated pressure branched off therefrom to provide increased pressure to water delivered to an inlet of the membrane or membrane module at a diffusion skin side.