Thermal desalination
A thermal desalination process comprising: introducing a feed solution into a thermal separation unit, distilling the feed solution in the thermal separation unit to produce a distillate stream and a residual stream having a higher solute concentration than the feed solution, contacting a portion of the residual stream from the thermal separation unit with one side of a selectively permeable membrane, contacting the opposite side of the selectively permeable membrane with a portion of the feed solution, such that water flows across the membrane to dilute the residual stream by direct osmosis, and introducing at least a portion of the diluted residual stream into the thermal separation unit.
1. A thermal desalination process comprising:
introducing a feed solution into a thermal separation unit,
distilling the feed solution in the thermal separation unit to produce a distillate stream and a residual stream having a higher solute concentration than the feed solution,
removing and discarding a first portion of the residual stream from the thermal separation unit as blowdown;
first contacting, after the removing and discarding, a second portion of the residual stream from the thermal separation unit with one side of a selectively permeable membrane;
second contacting the opposite side of the selectively permeable membrane with a portion of the feed solution, such that water flows across the membrane to dilute the residual stream by direct osmosis;
removing, after the second contacting, a concentrated feed solution from the opposite side of the selectively permeable membrane; and
introducing at least a portion of the diluted residual stream, with the feed solution, into the thermal separation unit.
2. A process as claimed in claim 1 , wherein the feed solution is seawater or brackish water.
3. A process as claimed in claim 1 , wherein the thermal separation unit is selected from the group consisting of multistage flash distillation apparatus, a multi-effect distillation apparatus and a vapour compression apparatus.
4. A process as claimed in claim 1 , which comprises heating the portion of feed solution prior to contact with the selectively permeable membrane.
5. A process as claimed in claim 1 , wherein the portion of feed solution is treated with an anti-scaling agent and/or an anti-microbial agent prior to contact with the selectively permeable membrane.
6. A process as claimed in claim 1 , wherein the portion of the residual solution is treated with an anti-scaling agent and/or an anti-microbial agent prior to contact with the selectively permeable membrane.
7. A process as claimed in claim 1 , wherein the portion of the residual stream is treated to remove particulate or organic substances prior to introduction to the membrane.
8. A process as claimed in claim 1 , wherein the portion of the feed solution is treated to remove particulate, or organic substances prior to introduction to the membrane.
9. A process as claimed in claim 1 , wherein the selectively permeable membrane has an average pore size of 10 to 40 Angstroms.