Method for extracting and sequestering carbon dioxide

• US 6,890,497 B2
• Filed: 01/11/2001
• Issued: 05/10/2005
• Est. Priority Date: 08/18/1998
• Status: Active Grant

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: United States Department of Energy
• Inventors: Caldeira, Kenneth G., Rau, Gregory H.
• Primary Examiner(s): Langel, Wayne A.
• Application Number:
  US09/759,781
• Publication Number:
  US 20010022952A1
• Time in Patent Office: 1,580 Days
• Field of Search: 423/232, 423/415.1, 423/419.1, 423/421, 423/422, 423/430, 423/437.R, 423/438
• US Class Current: 423/220
• CPC Class Codes: B01D 2251/402 of magnesium
• CPC Class Codes: B01D 2251/404 of calcium
• CPC Class Codes: B01D 53/62 Carbon oxides
• CPC Class Codes: Y02C 20/40 of CO2

Abstract

A method and apparatus to extract and sequester carbon dioxide (CO₂) from a stream or volume of gas wherein said method and apparatus hydrates CO₂, and reacts the resulting carbonic acid with carbonate. Suitable carbonates include, but are not limited to, carbonates of alkali metals and alkaline earth metals, preferably carbonates of calcium and magnesium. Waste products are metal cations and bicarbonate in solution or dehydrated metal salts, which when disposed of in a large body of water provide an effective way of sequestering CO₂ from a gaseous environment.

Claims

1. A method of extracting and sequestering CO₂ from a gas stream, said method comprising the steps of:

hydrating said CO₂ in said gas stream with an aqueous solution to form carbonic acid, thereby resulting in a CO₂-depleted gas stream;

reacting said carbonic acid with carbonate to form a waste stream solution of metal ions and bicarbonate, wherein said carbonate is of the form X(CO₃)_m wherein X is any element or combination of elements that can chemically bond with a carbonate group or its multiple, wherein at least one said element is a group IA, IIA, IIIA, IVA, IB, IIB, IIIB, IVB, VB, VIB, VIIB, or VIIIB element of the periodic table, and

wherein m is a stoichiometrically determined positive integer;

pre-treating said waste stream solution to reduce the amount of CO₂ outgassing and carbonate precipitation that may occur after said waste stream solution is released into a disposal site; and

releasing said pre-treated waste stream solution into said disposal site, wherein said disposal site comprises a large body of water.

2. The method as recited in claim 1 wherein:

said pre-treating step comprises a CO₂ degassing step selected from the group consisting of allowing said waste stream solution to degas CO₂ to an overlying headspace whose pCO₂ is less than that of said waste stream solution;

purging said waste stream with a gas stream whose pCO₂ is less than that of the waste stream;

and applying a partial vacuum to the headspace above the waste stream.

3. The method as recited in claim 1 wherein:

said pre-treating step comprises diluting said waste steam solution with a second solution that is undersaturared with respect to CO₂, carbonate ions, or both CO₂ and carbonate ions.

4. The method as recited in claim 1 wherein:

said pre-treating step comprises adding chemical additives which impede carbonate precipitation, said chemical additives being selected from the group consisting of phosphate, metals, and organic compounds, said organic compounds being selected from the group consisting of EDTA, humic substances, aromatic acids, citrate, malate, pyruvate, glycelglycerine, glycogen, arginine, glutamate, glycine, glycoprotein succinate, taurine, chondroitin sulfate, galactose, dextrose and acetate.

5. The method as recited in claim 1 wherein:

said pre-treating step comprises exchanging at least a portion of the Ca²⁺ cations present in said waste solution with exchange cations which when balanced by the CO₃²⁻

anions exhibit greater solubility and less propensity for precipitation than does CaCO₃.

6. The method as recited in claim 5 wherein:

said cation exchanging step comprises passing said waste stream solution through an ion exchange column, with said column contaimng Na⁺ exchange ions.

7. The method as recited in claim 1 wherein:

said pre-treating step comprises exchanging at least a portion of the CO₃²⁻

anions present in said waste solution with other anions.

8. The method as recited in claim 7 wherein:

said anion step comprises passing said waste solution through an ion exchange column containing Cl⁻

anions.

9. The method as recited in claim 1 wherein:

said pre-treating step comprises increasing the density of said waste stream solution.

10. The method as recited in claim 1 wherein:

said disposal site comprises a large body of water that is either freshwater or seawater.

11. The method as recited in claim 10 wherein:

the pCO₂ of said body of water at the point of release of waste stream solution is less than that of said waste stream solution.

12. The method as recited in claim 10 wherein:

said releasing step comprises releasing said waste stream solution at a depth sufficient for mixing of said waste stream solution with said body of water to occur.

13. The method as recited in claim 10 wherein:

said releasing step comprises releasing said waste stream solution at a depth wherein the pressure and temperature existent at said depth is sufficient to impede CO₂ outgassing to the atmosphere and carbonate precipitation.

14. The method as recited in claim 10 wherein:

said large body of water is either a sea or ocean; and

said releasing step comprises releasing said waste stream solution below the pycnocline.

15. The method as recited in claim 10 wherein:

said large body of water is either a sea or ocean; and

said releasing step comprises releasing said waste stream solution in the vicinity of a reef, above the pycnocline.

16. The method as recited in claim 10 wherein:

said disposal site is a body of surface seawater having sufficient constituents that serve to impede carbonate precipitation, said constituents being phosphate, Mg²⁺ ions, or phosphate and Mg²⁺ ions.

17. The method as recited in claim 10 wherein:

said disposal site is a body of surface seawater having sufficient organic compounds that serve to impede carbonate precipitation, said organic compounds selected from the group consisting of humic substances, aromatic acids, citrate, malate, pyruvate, glycelglycerine, glycogen, arginine, glutamate, glycine, glycoprotein succinate, taurine, chondroitin sulfate, galactose, dextrose and acetate.

18. The method as recited in claim 10 wherein:

said large body of water is either a sea or ocean; and

said releasing step comprises releasing said waste stream solution at a depth below the carbonate compensation depth (CCD).