Water desalination process using ion selective membranes

• US 6,998,053 B2
• Filed: 08/18/2004
• Issued: 02/14/2006
• Est. Priority Date: 08/20/1999
• Status: Expired due to Fees

• Current Assignee: Let Leading Edge Technologies Limited
• Original Assignee: Let Leading Edge Technologies Limited
• Inventors: Awerbuch, Leon
• Primary Examiner(s): Fortuna, Ana M.
• Application Number:
  US10/920,860
• Publication Number:
  US 20050011832A1
• Time in Patent Office: 545 Days
• Field of Search: 210/652, 210/195.2, 210/641, 210/653, 210/170, 210/257.2, 210/175, 210/180, 203/12
• US Class Current: 210/652
• CPC Class Codes: B01D 1/26 Multiple-effect evaporating
• CPC Class Codes: B01D 2311/04 Specific process operations in the feed stream; Feed pretreatment
• CPC Class Codes: B01D 2311/18 pH control
• CPC Class Codes: B01D 2311/268 Water softening
• CPC Class Codes: B01D 3/065 Multiple-effect flash distillation (more than two traps)
• CPC Class Codes: B01D 61/026 comprising multiple reverse osmosis steps
• CPC Class Codes: B01D 61/027 Nanofiltration
• CPC Class Codes: B01D 61/0271 comprising multiple nanofiltration steps
• CPC Class Codes: B01D 61/029 Multistep processes comprising different kinds of membrane processes selected from reverse osmosis, hyperfiltration or nanofiltration
• CPC Class Codes: B01D 61/04 Feed pretreatment
• CPC Class Codes: C02F 1/04 by distillation or evaporation
• CPC Class Codes: C02F 1/042 Prevention of deposits
• CPC Class Codes: C02F 1/06 Flash evaporation
• CPC Class Codes: C02F 1/441 by reverse osmosis
• CPC Class Codes: C02F 1/442 by nanofiltration
• CPC Class Codes: Y02A 20/124 Water desalination
• CPC Class Codes: Y02A 20/131 Reverse-osmosis

Abstract

The invention is directed to an improved desalination process to produce potable water. The process represents an improvement of hybrid of membrane and desalination technologies. The improvement of the invention comprises the operation of an ion selective membrane at a variable pressure as a function of the cost of electricity to form a softened salt water that is blended in variable proportions, to increase the top operating temperature of the desalination system and increase recovery of potable water, with untreated salt water.

Claims

1. A desalination process using a membrane system to produce potable water which comprises:

(a) passing a first stream of water containing a high concentration of hardness ions through an ion selective membrane to form softened water having a reduced content of hardness ions;

(b) blending the softened water with a second stream of water containing a higher concentration of hardness ions than the softened water to form a feed;

(c) passing the feed through a reverse osmosis membrane system to form a water product of potable quality,

wherein the softened water content of the feed is at least 15%;

and wherein the proportions of the softened water and second stream of water forming the feed are varied to increase the top operating temperature of the desalination process and increase recovery of potable water.

2. The desalination process according to claim 1, wherein the ion selective membrane comprises one or more nanofiltration membranes.

3. The desalination process according to claim 1, wherein the first stream of water is subjected to a deaeration pre-treatment step after passing through said one or more nanofiltration membranes.

4. The desalination process according to claim 3, wherein the first stream of water and the feed is pre-heated before deaeration.

5. The desalination process according to claim 1, wherein the ion selective membrane is operated at a variable pressure of 5–

80 bar.

6. The desalination process according to claim 5, wherein the ionic content and quantity of the softened water varies with the operating pressure of the ion selective membrane.

7. The desalination process according to claim 1, wherein the softened water is stored in a buffer system for blending with the second stream of water to form the feed.

8. The desalination process according to claim 1, wherein the softened water of step (a) is fed by a cluster system to two or more reverse osmosis membranes.

9. The desalination process according to claim 1, wherein reject of the RO membrane is partially subjected to a nanofiltration.

10. The desalination process according to claim 1, wherein a stoichiometric amount of acid is added to the first stream before that stream passes through the ion selective membrane.

11. The desalination process according to claim 1, wherein the ion selective membrane is operated at a variable pressure as a function of the cost of electricity.

12. The desalination process of claim 1, wherein the first stream of water is selected from the group consisting of salt water, seawater, brackish water, waste water and impaired water.

13. The desalination process of claim 12, wherein the impaired water contains soluble salts having an ionic content of harness ions in excess of 1,500 mg/liter.

14. The desalination process of claim 1, further comprising the step:

(d) passing reject water of step (c) through at least one thermal distillation process which is part of a hybrid system.

15. The desalination process of claim 14, wherein the thermal distillation process is selected from the group consisting of multiflash distillation, multieffect distillation and vapor compressor distillation.