Forward osmosis system comprising solvent separation by means of membrane distillation

A system (10) for separating a product (14) contained as a solvent in a solution (12) to be processed, having at least one forward osmosis device (16) flowed through by the solution (12) to be processed and by a draw solution (20) and having a product recovery device (28) connected downstream thereof for recovering the product (14) from diluted draw solution (20′) exiting the forward osmosis device (16), wherein the forward osmosis device (16) comprises at least one flow passage (18) conducting the solution (12) to be processed and at least one flow passage (22) conducting the draw solution (20), wherein the inner space (24) of a respective flow passage (18) conducting the solution (12) to be processed is at least partly bounded by a semipermeable membrane wall (26) which is permeable for the solvent of the solution (12) to be processed, but not for the substance dissolved therein, and wherein at least one flow passage (22) conducting the draw solution (20) is bounded on mutually oppositely disposed sides by membrane walls (26) which are associated with two adjacent flow passages (18) conducting the solution (12) to be processed such that solvent from the solution (12) to be processed arrives in the adjacent flow passages (22) conducting the draw solution (20) through the membrane walls (26),

• wherein the product recovery device (28) has a heated desorber stage (56) which is flowed through by diluted draw solution (20′) exiting the forward osmosis device (16) and which comprises at least one gas space (58) as well as at least one flow passage (22) conducting the diluted draw solution (20′), wherein a respective gas space (58) is at least partly bounded by a vapor-permeable, liquid-tight membrane wall (38) and wherein at least one flow passage (22) is provided which is formed between such a gas space (58) and a heating unit (32) adjacent thereto and which conducts the diluted draw solution (20′) such that gas mixture (60) expelled from the diluted draw solution (20′) arrives in the gas space (58) through the membrane wall (38) and/or wherein the product (14) can be led off in the form of draw solution (120) exiting the heated desorber stage (56) and purified of the gas mixture (60);
• wherein the gas mixture (60) arising in the heated desorber stage (56) is supplied to a combined absorber/solution cooler stage (62) for generating regenerated draw solution (20), and/or wherein the regenerated draw solution (20) obtained through this absorber/solution cooler stage (62) is again supplied to the forward osmosis device (16);
• wherein the draw solution (20) is a solution which can be both separated and regenerated via the vapor pressure;
• wherein the absorber/solution cooler stage (62) comprises at least one gas space (58) and contains gas mixture (60) from the heated desorber stage (56) as well as at least one flow passage (22) conducting the purified or diluted draw solution (120 or 20′), wherein a respective gas space (58) is at least partly bounded by a vapor-permeable, liquid-tight membrane wall (38) and wherein at least one flow passage (22) is provided which is formed between such a gas space (58) and a cooling unit (52) adjacent thereto and which conducts the draw solution (20′) such that the gas mixture flows from the gas space (58) through the membrane wall (38) into the flow passage (22) conducting the purified or diluted draw solution (120 or 20′) and is dissolved in the purified or diluted draw solution (120 or 20′) cooled by the cooling unit (52);
• and
• wherein a device (66) for drying and cooling gas (68) by means of a hygroscopic solution (70) is provided for supplying the absorber/solution cooler stage (62) or its cooling units (52) with cooling fluid (64).