Forward osmosis separation processes
Separation processes using engineered osmosis are disclosed generally involving the extraction of solvent from a first solution to concentrate solute by using a second concentrated solution to draw the solvent from the first solution across a semi-permeable membrane. Enhanced efficiency may result from using low grade waste heat from industrial or commercial sources.
1. A system for osmotic extraction of a solvent from a first solution, comprising:
a first chamber having an inlet fluidly connected to a source of the first solution;
a second chamber having an inlet fluidly connected to a source of a concentrated draw solution comprising ammonia and carbon dioxide in a molar ratio of at least 1 to 1;
a semi-permeable membrane system separating the first chamber from the second chamber;
a separation system fluidly connected downstream of the second chamber, the separation system comprising a distillation system, the separation system configured to receive a first portion of a dilute draw solution from the second chamber and to recover draw solutes and a solvent stream, wherein the distillation system is configured to vaporize the draw solutes out of the dilute draw solution;
a heat exchanger configured to receive the vaporized draw solutes to at least partially condense the vaporized draw solutes; and
a recycle system comprising an absorber configured to facilitate reintroduction of the draw solutes to the second chamber to maintain the molar ratio of ammonia to carbon dioxide in the concentrated draw solution, wherein the absorber is configured to receive the at least partially condensed draw solutes, wherein at least one of the heat exchanger and the absorber is configured to receive a second portion of the dilute draw solution, wherein the second chamber is configured to receive the condensed draw solutes, and wherein the distillation system comprises a distillation column or a membrane distillation apparatus.
2. The system of claim 1 , wherein the absorber comprises a packed column.
3. The system of claim 1 , wherein the absorber comprises a membrane contactor.
4. The system of claim 1 , wherein the recycle system further comprises a compression operation downstream of the absorber to enhance condensation of draw solute gases.
5. The system of claim 4 , wherein the compression operation comprises a gas compressor, a steam eductor, or a liquid stream eductor.
6. The system of claim 1 , wherein the semi-permeable membrane system comprises a membrane module immersed in the first solution, and wherein the concentrated draw solution flows through an interior of the membrane module.
7. The system of claim 1 , further comprising a downstream zero liquid discharge or other reduced discharge stream operation.
8. The system of claim 1 , wherein the membrane distillation apparatus is configured to strip draw solutes.
9. The system of claim 8 , wherein membranes in the membrane distillation apparatus are used for both separation of draw solutes and heat exchange in a module.