HYDRATE-BASED DESALINATION WITH HYDRATE-ELEVATING DENSITY-DRIVEN CIRCULATION

• US 20050247640A1
• Filed: 09/08/2003
• Published: 11/10/2005
• Est. Priority Date: 07/12/1999
• Status: Active Grant

• Current Assignee: Water Generating Systems I, LLC
• Original Assignee: Marine Desalination Systems LLC
• Inventors: Max, Michael D., Korsgaard, Jens
• Granted Patent: US 6,969,467 B1
• Time in Patent Office: Days
• US Class Current: 210/712
• CPC Class Codes: C02F 1/22 by freezing
• CPC Class Codes: C02F 1/26 by extraction
• CPC Class Codes: C02F 2103/08 Seawater, e.g. for desalination
• CPC Class Codes: Y02A 20/124 Water desalination

Abstract

In hydrate-based desalination or other water purification conducted using naturally buoyant or trapped-gas-assisted buoyancy hydrate in a hydrate fractionation column, a portion of fresh or purified product water is extracted from an upper, hydrate dissociation region of the fractionation column and reintroduced into a lower portion of the fractionation column at a point above but generally near a product water/saline water interface. The difference in density between the reintroduced product water and the fluid in the hydrate fractionation column above the point of reintroduction (water, hydrate, and gas) drives a natural circulation system which enhances the rate at which hydrate rises into the hydrate dissociation region.

Claims

1. A method of conducting hydrate-based desalination or water purification in a hydrate fractionation column, said method comprising:

introducing hydrate-forming substance into a lower, hydrate formation region of said hydrate fractionation column where saline or otherwise polluted water to be treated is present, said water to be treated being under temperature and pressure conditions sufficient for hydrate to form upon introduction of said hydrate-forming substance into said hydrate formation region, whereby positively buoyant or gas-assisted positively buoyant hydrate forms within said hydrate formation region,

allowing said hydrate to rise within said hydrate fractionation column toward a hydrate dissociation region of said hydrate fractionation column,

allowing said hydrate to dissociate to release fresh or purified water and said hydrate-forming substance, said fresh or purified water collecting in said upper, hydrate dissociation region of said hydrate fractionation column, and

collecting fresh or purified water product water,

wherein a fresh or purified water region of said hydrate fractionation column extends downwardly from said hydrate dissociation region to a level corresponding approximately to the top of a region where said hydrate is stable and a mixture of fresh or purified water, hydrate, and gaseous hydrate-forming substance is present within said fresh or purified water region of said hydrate fractionation column,

said method further comprising removing a portion of said fresh or purified water from an upper region of said hydrate fractionation column and reintroducing said removed portion of fresh or purified water into said hydrate fractionation column at a lower, reintroduction region thereof, said reintroduction region being located at a lower region of said fresh or purified water region of said hydrate fractionation column and above the level corresponding to the top of said region where hydrate is stable, whereby a fluid flow circuit is established that extends from said reintroduction region of said hydrate fractionation column, up along said fresh or purified water region of said hydrate fractionation column, and down along a fresh or purified water down-flow conduit through which said removed portion of fresh or purified water flows to said reintroduction region,

wherein the density of said mixture of fresh or purified water, hydrate, and gaseous hydrate-forming substance that is present in said fresh or purified water region of said hydrate fractionation column is less than the density of said removed and reintroduced portion of fresh or purified water such that a density-differential-driven circulatory system of fluid automatically rising at an enhanced rate within said fresh or purified water region of said hydrate fractionation column and flowing down along said fresh or purified water down-flow conduit is established.

4. The method of claim 1, further comprising controlling the rate of flow of said circulatory system so as to maintain a desired upward flow rate of hydrate within said fresh or purified water region of said fractionation column.

5. The method of claim 1, further comprising initiating the flow of fresh or purified water down along said fresh or purified water down-flow conduit using a pump.

6. The method of claim 5, further comprising generating electrical power as fluid automatically flows through said pump, as part of said circulatory system, due to the difference between the density of said mixture of fresh or purified water, hydrate, and gaseous hydrate-forming substance that is present in said fresh or purified water region of said hydrate fractionation column and the density of said removed portion of fresh or purified water that is in said fresh or purified water down-flow conduit.

7. The method of claim 1, wherein said portion of fresh or purified water is removed from said hydrate dissociation region.

8. The method of claim 1, wherein said portion of fresh or purified water is removed from said hydrate dissociation region via a degassification manifold that extends downwardly from said hydrate dissociation region.

9. The method of claim 8, wherein said portion of fresh or purified water is degassified in said degassification manifold.

10. The method of claim 8, wherein said fresh or purified product water is collected by being withdrawn from said degassification manifold.

11. The method of claim 1, further comprising recovering gaseous hydrate-forming substance, released upon dissociation from said hydrate, from said hydrate dissociation region of said hydrate fractionation column.

12. The method of claim 11, further comprising re-using said recovered hydrate-forming substance for further cycles of hydrate-based desalination or purification.

13. The method of any one of claims 1 and 4-12, wherein said hydrate fractionation column comprises a shaft formed in land, said hydrate formation region being formed at a lower portion of said in-land shaft, said method further comprising providing input water to be treated into said hydrate fractionation column at a location that is generally at or above the highest point within said hydrate formation region at which hydrate is formed.

14. The method of claim 13, wherein heated residual brine or other heated residue of said water to be treated is removed from a lower portion of said hydrate formation region of said hydrate fractionation column, thus removing heat of exothermic hydrate formation from said hydrate formation region.

15. The method of any one of claims 1 and 4-12, wherein the rate at which said removed portion of fresh or purified water is reintroduced into said hydrate fractionation column is controlled so as to maintain general separation between, and minimize mixing of, fresh or purified water in said fresh or purified water region of said hydrate fractionation column and seawater, residual brine, or other residual fluid below said fresh or purified water region of said hydrate fractionation column.

16. The method of claim 15, further comprising removing mixed salinity or mixed purity fluid that does result from mixing of said fresh or purified water in said fresh or purified water region of said hydrate fractionation column with said seawater, residual brine, or other residual fluid.

17. The method of any one of claims 1 and 4-12, wherein the manner in which said removed portion of fresh or purified water is reintroduced into said hydrate fractionation column is controlled so as to maintain general separation between, and minimize mixing of, fresh or purified water in said fresh or purified water region of said hydrate fractionation column and seawater, residual brine, or other residual fluid below said fresh or purified water region of said hydrate fractionation column.

18. The method of claim 17, further comprising removing mixed salinity or mixed purity fluid resulting from mixing of said fresh or purified water in said fresh or purified water region of said hydrate fractionation column and said seawater, residual brine, or other residual fluid.

19. The method of any one of claims 1 and 4-12, further comprising pre-treating said water to be treated with hydrate-forming substance without causing hydrate to form.

20. The method of claim 13, further comprising pre-treating said water to be treated with hydrate-forming substance without causing hydrate to form.

21. The method of claim 15, further comprising pre-treating said water to be treated with hydrate-forming substance without causing hydrate to form.

22. The method of claim 16, further comprising pre-treating said water to be treated with hydrate-forming substance without causing hydrate to form.

23. The method of claim 17, further comprising pre-treating said water to be treated with hydrate-forming substance without causing hydrate to form.

24. The method of claim 18, further comprising pre-treating said water to be treated with hydrate-forming substance without causing hydrate to form.

25. The method of claim 14, further comprising pre-treating said water to be treated with hydrate-forming substance without causing hydrate to form.

2. (canceled)

3. (canceled)