Patent ID: 8246791

Claim:
An apparatus for separating draw solution solutes and product solvent from a dilute draw solution, wherein the apparatus comprises: an osmotically driven membrane system comprising a source of dilute draw solution comprising thermally removable solutes; a first distillation column comprising: a first inlet coupled to the source of dilute draw solution for introducing a first portion of the dilute draw solution into a first end of the first distillation column; a first heat transfer means coupled to the first distillation column at a second end, said first heat transfer means having an inlet coupled to a first source of thermal energy and an outlet coupled to the first distillation column for directing the first source of thermal energy to the first distillation column to cause at least a portion of the dilute draw solution solutes in the first distillation column to vaporize; and a first outlet for removing the vaporized dilute draw solution solutes from the first distillation column; and a second distillation column comprising: a first inlet coupled to the source of dilute draw solution for introducing a second portion of the dilute draw solution into a first end of the second distillation column, wherein the first distillation column and the second distillation column are configured for parallel operation; a second heat transfer means coupled to the second distillation column at a second end, said second heat transfer means having an inlet coupled to the first outlet of the first distillation column for receiving the vaporized dilute draw solution solutes for use as a second source of thermal energy for the second distillation column, a first outlet coupled to the second distillation column for directing the second source of thermal energy to the second distillation column to cause at least a portion of the dilute draw solution solutes in the second distillation column to vaporize, and a second outlet coupled to the osmotically driven membrane system for reintroducing the vaporized dilute draw solution solutes from the first distillation column condensed within the second heat transfer means to the osmotically driven membrane system; and a first outlet for removing the vaporized dilute draw solution solutes from the second distillation column.