Apparatus and process for desalination of seawater

• US 5,102,550 A
• Filed: 11/01/1990
• Issued: 04/07/1992
• Est. Priority Date: 11/01/1990
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Pizzino, Joseph F., Patchett, David B.
• Primary Examiner(s): Dawson, Robert A.
• Assistant Examiner(s): FORTUNA, ANA M
• Application Number:
  US07/607,936
• Time in Patent Office: 523 Days
• Field of Search: 210/640, 210/651, 210/650, 210/653, 210/500.27, 210/500.21, 210/500.41, 210/652, 210/323.2, 210/321.8, 210/321.89, 203/10, 202/180, 202/163, 202/172, 55/16
• US Class Current: 210/640
• CPC Class Codes: B01D 61/364 Membrane distillation
• CPC Class Codes: C02F 1/447 by membrane distillation distillation and evaporation without the use of membranes C02F1/04
• CPC Class Codes: C02F 2103/08 Seawater, e.g. for desalination
• CPC Class Codes: Y02A 20/131 Reverse-osmosis

Abstract

An apparatus and process for desalination of seawater using a hydrophobic por permeable membrane. Heated seawater is passed across one surface of a membrane at rates which cause the flow to be turbid such that its turbidity is characterized by Reynolds numbers in excess of 1000. Fresh water is passed across the other surface of the membrane to act as a condenser and collector of vapor which passes through the membrane.

Claims

1. An apparatus for obtaining fresh water from seawater, comprising:

a membrane distillation module further comprising a shell having a saline inlet port, a saline outlet port, a fresh water inlet port and a fresh water outlet port, said fresh water ports fluidly isolated from said saline ports by at least one tubular porous hydrophobic membrane;

means for flowing heated seawater through said seawater ports so that said seawater passes the interior surface of said at least one tubular membrane with a flow rate exceeding laminar flow corresponding to a Reynolds number in excess of 1000; and

,

means for flowing fresh water through said fresh water ports so that said fresh water passes over the exterior of said tubular membrane, said fresh water collecting and condensing water vapor that passes through said permeable membranes;

whereby the pressure difference between said fresh water and said seawater is maintained in the range of -2.5 psi to +2.5 psi.

2. A process for obtaining fresh water from seawater, comprising:

passing fresh water along a first surface of a vapor permeable hydrophobic membrane; and

passing heated seawater along a second surface of said membrane at a turbulent flow corresponding to a Reynolds number in excess of 1000.

3. A process as claimed in claim 2 wherein said turbulent flow corresponds to a Reynolds number of at least 2000.

4. A process as claimed in claim 2 wherein said turbulent flow corresponds to a Reynolds number in the range of 2000 to 5000.

5. A process as claimed in claim 2 wherein said membrane is expanded porous polytetrafluoroethelene.

6. A process as claimed in claim 5 wherein the maximum membrane pore size is within the range of 2.0 to 3.5 microns.

7. A process as claimed in claim 2 wherein said membrane is tubular.

8. A process as claimed in claim 2 wherein the flow direction of said seawater and said fresh water are in the same direction along opposed surfaces of said membrane.

9. A process as claimed in claim 2 wherein the flow direction of said seawater is opposite the flow direction of said fresh water along opposed surfaces of said membrane.

10. A process as claimed in claims 2 wherein said seawater is heated to a temperature in the range of 150 to 210 degrees F.

11. A process as claimed in claim 10 wherein said seawater is heated to a temperature in the range of 190 to 200 degrees F.

19. A process as claimed in claim 2 wherein the pressure difference between said fresh water and said seawater is maintained in the range of -2.5 psi to +2.5 psi.

12. An apparatus for obtaining fresh water from seawater, comprising:

a membrane distillation module further comprising a shell having a saline inlet port, a saline outlet port, a fresh water inlet port and a fresh water outlet port, said fresh water ports fluidly isolated from said saline ports by at least one tubular porous hydrophobic membrane having a ratio of length to diameter of about 19;

means for flowing heated seawater through said seawater ports so that said seawater passes the interior surface of said at least one tubular membrane with a flow rate exceeding laminar flow corresponding to a Reynolds number in excess of 1000; and

means for flowing fresh water through said fresh water ports so that said fresh water passes over the exterior of said tubular membrane, said fresh water collecting and condensing water vapor that passes through said permeable membrane.

17. An apparatus as claimed in claim 12 wherein the pressure difference between said fresh water and said seawater is maintained in the range of -1.0 psi to +1.0 psi.

18. An apparatus as claimed in claim 12 wherein the pressure difference between said fresh water and said seawater is maintained in the range of -2.5 psi to +2.5 psi.

13. A process for obtaining fresh water from seawater, comprising:

passing fresh water along a first surface of a vapor permeable, tubular hydrophobic membrane having a ratio of length to diameter of about 19; and

passing heated seawater along a second surface of said membrane at a turbulent flow corresponding to a Reynolds number in excess of 1000.

14. A process for obtaining fresh water from seawater, comprising:

passing fresh water along a first surface of a vapor permeable hydrophobic membrane; and

passing heated seawater along a second surface of said membrane at a turbulent flow corresponding to a Reynolds number in excess of 1000;

whereby the pressure difference between said fresh water and said seawater is maintained in the range of -1.0 psi to +1.0 psi.

15. A process as claimed in claim 14 wherein said membrane is tubular.

16. A process as claimed in claim 15 wherein said membrane has a ratio of length to diameter of about 19.