ELECTROCHEMICAL CELL, METHOD AND APPARATUS FOR CAPTURING CARBON DIOXIDE FROM FLUE GAS AND DECOMPOSING NITROSAMINE COMPOUNDS

Abstract

An apparatus for capturing CO.sub.2 from flue gas includes (a) an absorber, (b) a stripper, (c) a heat exchanger, (d) an amine absorbent circulating through the absorber, the stripper and the heat exchanger, (e) a water washing unit downstream from the flue gas outlet of the absorber, and (f) an electrochemical cell. The electrochemical cell is connected to the water washing unit and is adapted to adsorb and decompose nitrosamine compounds present in liquid separated by the water washing unit.

Claims

1. An electrochemical cell, comprising: an anode including a first carbon xerogel electrode and a first current collector; a cathode including a second carbon xerogel electrode and a second current collector; a separator made from an insulating material; and a current source applying an electrical current to said anode and said cathode.

2. The electrochemical cell of claim 1, including a first endplate including a solution inlet and a second endplate including a solution outlet.

3. The electrochemical cell of claim 2, wherein said first current collector and said second current collector are made of titanium.

4. The electrochemical cell of claim 3, wherein said anode is adjacent said first endplate, said cathode is adjacent said second endplate and said separator is porous.

5. The electrochemical cell of claim 3, wherein said cathode is adjacent said first endplate, said anode is adjacent said second endplate and said separator is porous.

6. The electrochemical cell of claim 1, including a first endplate having a first solution inlet and a first solution outlet and a second endplate having a second solution inlet and a second solution outlet wherein said first endplate is adjacent said anode, said second endplate is adjacent said cathode and said separator is nonporous.

7. An apparatus for capturing CO.sub.2 from flue gas, comprising: an absorber including a flue gas inlet, a flue gas outlet, a CO.sub.2-lean amine absorbent inlet and a CO.sub.2-rich amine absorbent outlet; a stripper including a CO.sub.2-rich amine absorbent inlet, a CO.sub.2-lean amine absorbent outlet and a captured CO.sub.2 outlet; a heat exchanger adapted to receive (a) CO.sub.2-lean amine absorbent from said stripper being delivered to said CO.sub.2-lean absorbent inlet and (b) CO.sub.2-rich amine absorbent from said absorber being delivered to said CO.sub.2-rich amine absorbent inlet; an amine absorbent circulating through said absorber, said stripper and said heat exchanger; a water washing unit downstream from said flue gas outlet; and an electrochemical cell connected to said water washing unit and adapted to adsorb and decompose nitrosamine compounds present in liquid separated by said water washing unit.

8. The apparatus of claim 7, wherein said electrochemical cell includes: an anode including a first carbon xerogel electrode and a first current collector; a cathode including a second carbon xerogel electrode and a second current collector; a separator made from an insulating material; and a current source applying an electrical current to said anode and said cathode.

9. The apparatus of claim 8, including a first endplate including a solution inlet and a second endplate including a solution outlet.

10. The apparatus of claim 9, wherein said first current collector and said second current collector are made of titanium.

11. The apparatus of claim 10, wherein said anode is adjacent said first endplate, said cathode is adjacent said second endplate and said separator is porous.

12. The apparatus of claim 10, wherein said cathode is adjacent said first endplate, said anode is adjacent said second endplate and said separator is porous.

13. The apparatus of claim 8, including a first endplate having a first solution inlet and a first solution outlet and a second endplate having a second solution inlet and a second solution outlet wherein said first endplate is adjacent said anode, said second endplate is adjacent said cathode and said separator is nonporous.

14. A method, comprising; removing CO.sub.2 from a flue gas by contacting said flue gas with an amine absorbent in an absorber; separating water vapor and organics from flue gas discharged from said absorber; passing at least a portion of said separated liquid through an electrochemical cell; and decomposing nitrosamines in said liquid by applying an electrical current across an anode and a cathode of said electrochemical cell.

15. The method of claim 14, including returning said liquid to said absorber following decomposing of said nitrosamines.

16. The method of claim 15, including applying an electrical current of between 5.0 and 100.0 mA/cm.sup.2 across said anode and said cathode.

17. The method of claim 16, including continuously applying said electrical current of between 5.0 and 100.0 mA/cm.sup.2.

18. The method of claim 16, including delivering CO.sub.2-rich amine absorbent from said absorber to a stripper.

19. The method of claim 18, including stripping CO.sub.2 from said amine absorbent in said stripper.

20. The method of claim 19, including returning CO.sub.2-lean amine absorbent from said stripper to said absorber.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0020] The accompanying drawing figures incorporated herein and forming a part of the specification, illustrate several aspects of the electrochemical cell, the apparatus and the method and together with the description serve to explain certain principles thereof.

[0021] FIG. 1 is a schematic illustration of the apparatus for capturing CO.sub.2 from flue gas incorporating an electrochemical cell for nitrosamine decomposition.

[0022] FIG. 2 is a schematic illustration of one possible embodiment of that electrochemical cell illustrated in FIG. 1.

[0023] FIG. 3 is a schematic illustration of a second possible embodiment of the electrochemical cell illustrated in FIG. 1.

[0024] FIG. 4 is a schematic illustration of a third possible embodiment of the electrochemical cell illustrated in FIG. 1.

[0025] Reference will now be made in detail to the present preferred embodiments of the electrochemical cell, the apparatus and the method, examples of which are illustrated in the accompanying drawing figures.

DETAILED DESCRIPTION

[0026] An apparatus 10 adapted for thermal swing processing and capturing CO.sub.2 from flue gas is illustrated in FIG. 1. An aqueous amine absorbent is circulated between an absorber/absorption tower 12, a stripper 14, and a heat exchanger 16. The flue gas or acid gas, containing CO.sub.2, enters the bottom of the absorber 12 at the flue gas inlet 18. The amine absorbent enters the top of the absorber/absorber tower 12 at the CO.sub.2-lean absorbent inlet 19 in counter-current flow to the acid gas. As the acid gas and the amine absorbent come into contact in the absorber 12, amine absorbent removes the CO.sub.2 from the gas stream. The amine absorbent, now rich in CO.sub.2, is discharged from the bottom of the absorber/absorber tower 12 at the CO.sub.2-rich amine absorbent outlet 21 and passed, (note action arrow 20) through the heat exchanger 16 to improve efficiency before entering the top of the stripper 14 (note action arrow 22) at the CO.sub.2-rich amine absorbent inlet 23 where the amine absorbent is heated to a higher temperature. The stripper 14 removes the CO.sub.2 as a gas from the amine absorbent. The CO.sub.2 is passed through captured CO.sub.2 outlet 25 to the condenser 24 and separated from water at the separator 26. The CO.sub.2 is then subjected to downstream processing or storage while the water is returned to the stripper (note action arrow 28). The CO.sub.2 lean-amine solution exits the bottom of the stripper 14 through the CO.sub.2-lean amine absorbent outlet 27 (note action arrow 30) and is returned to the absorber 10 by way of the heat exchanger 16 and the chiller 32. The reboiler 34 functions to prevent amine absorbent from settling to the bottom of the stripper.

[0027] As should be appreciated, following removal of CO.sub.2 in the absorber, the acid gas or flue gas is discharged from the absorber 12 through the flue gas outlet 35 and delivered (note action arrow 36) to the water washing unit 38. Water washing unit 38 is a packed column adapted to recover water vapor, amine entrainment, aerosol and amine vapor and separate the flue gas from the liquid. As illustrated by action arrow 40, a portion or slipstream of the separated liquid is delivered to the electrochemical cell 42 where nitrosamines are absorbed and decomposed by oxidation and reduction before that liquid is returned from the electrochemical cell to the water washing unit 38 at action arrow 44. Treated liquid including recovered amine absorbent is returned from the water washing unit 38 to the absorber 12 at action arrow 46.

[0028] The electrochemical cell 42 illustrated in FIG. 1 is a flow-through cell that may comprise a number of different embodiments such as those illustrated in FIGS. 2, 3 and 4.

[0029] With reference to FIG. 2, the electrochemical cell 42 includes an anode 48 including a first carbon xerogel electrode 50 and a first current collector 52. The electrochemical cell 42 also includes a cathode 54 including a second carbon xerogel electrode 56 and a second current collector 58.

[0030] The carbon xerogel electrodes 50, 56 may be made in accordance with the method described in Example 1 below. The first and second current collectors 52, 58 may be made from titanium or other appropriate electrically conducting material.

[0031] The electrochemical cell 42 illustrated in FIG. 2 further includes a separator 60 made from any appropriate insulating material such as felt, porous membranes, ion exchange membranes, cloth-like or woven materials (such as filter paper or nylon woven mesh) or silicone rubber. In addition, the electrochemical cell 42 includes a current source 62 adapted for applying an electrical current across the anode 48 and the cathode 54.

[0032] As further illustrated in FIG. 2, the electrochemical cell 42 includes a first end plate 64 including a solution inlet 66 and a second end plate 68 including a solution outlet 70. Action arrow A illustrates the liquid or solution entering the electrochemical cell 42 from the water washing unit 38 while action arrow B illustrates the liquid or solution being returned from the electrochemical cell 42 to the water washing unit following decomposition of nitrosamines. The gaskets 72 between the first end plate 64 and the anode 48 and the second end plate 68 and the cathode 54 seal the electrochemical cell 42 when the illustrated components are compressed together.

[0033] Reference is now made to FIG. 3 illustrating an alternative embodiment of the electrochemical cell identified by reference numeral 42. The electrochemical cell 42 illustrated in FIG. 3 is identical to the electrochemical cell 42 illustrated in FIG. 2 except for the fact that the anode 48 and the cathode 54 are reversed in position so that the solution flowing through the electrochemical cell 42 contacts the cathode 54 before the anode 48 instead of the anode before the cathode as in the FIG. 1 embodiment. In both the electrochemical cell 42 illustrated in FIG. 2 and the electrochemical cell 42 illustrated in FIG. 3, the separator 60 is porous to allow the flow of liquid or solution through the electrochemical cell as illustrated by action arrows A and B.

[0034] Yet another alternative embodiment of the electrochemical cell 42 is illustrated in FIG. 4. Like structures are indicated by the same reference numbers: thus, FIG. 4 illustrates an anode 48 including a first carbon xerogel electrode 50 and a first current collector 52, a cathode 54 including a second carbon xerogel electrode 56 and a second current collector 58, a separator 60, a current source 62, a first end plate 64 and a second end plate 68.

[0035] The electrochemical cell 42 illustrated in FIG. 4 differs from the electrochemical cells 42 and 42 illustrated in FIGS. 2 and 3 in three primary respects. As shown, the first end plate 64 includes a first solution inlet 74 and a first solution outlet 76 and the second end plate 68 includes a second solution inlet 78 and a second solution outlet 80. In addition, the separator 60 in the embodiment of the electrochemical cell 42 illustrated in FIG. 4 is nonporous and does not allow liquid or solution entering and exiting the anode side of the cell through the first end plate 64 at the first solution inlet 74 and first solution outlet 76 to mix with solution or liquid entering and exiting the cathode side of the cell through the second solution inlet 78 and second solution outlet 80 in the second end plate 68.

[0036] Consistent with the above description, a method for capturing CO.sub.2 from flue gas and decomposing nitrosamines comprises the steps of removing CO.sub.2 from a flue gas by contacting the flue gas with an aqueous amine absorbent in the absorber/absorber tower 12, separating liquid from the flue gas discharged from the absorber at the water washing unit 38, passing at least a portion of the separated liquid through the electrochemical cell 42 and decomposing nitrosamines in the liquid by applying an electrical current across an anode 48 and a cathode 54 of the electrochemical cell.

[0037] The method may further include the step of returning the liquid to the absorber/absorber tower 12 (note action arrows 44 and 46) following the decomposing of the nitrosamines. Further, the method may include applying an electrical current of between 5.0 and 100.0 mA/cm.sup.2 across the anode 48 and the cathode 54. Further, the method may include continuously applying that electrical current.

[0038] Still further, the method may include the step of delivering CO.sub.2-rich amine absorbent from the absorber 12 to the stripper 14. Still further, the method may include the step of stripping CO.sub.2 from the amine absorbent in the stripper 14. Further, the method may include returning the CO.sub.2-lean absorbent from the stripper 14 to the absorber 12.

[0039] The following experimental example illustrates how to prepare a carbon xerogel electrode for the electrochemical cell and apparatus described above.

EXAMPLE 1

[0040] Carbon Xerogel PreparationWe first prepared a solution by adding 20.00 g resorcinol (C.sub.6H.sub.6O.sub.2, Sigma-Aldrich), 29.48 g formaldehyde (CH.sub.2O, 37 wt % in methanol, SigmaAldrich), 6.32 of 0.02 M Na.sub.2CO.sub.3 solution (SigmaAldrich), and 6.00 g of deionized H.sub.2O in a sealed glass bottle. The solution was stirred for 30 minutes. The resulting solution was used to infiltrate a dry carbon cloth. Subsequently, the wetted carbon cloth was immobilized between two glass slides, sealed with aluminum foil overnight, and heated at 85 C. for a period of 24 hours in air. A solvent-exchange process was performed for the polymerized sheets in which the sheets were subjected to soaking in deionized water, soaking in acetone, and air-drying. Time taken for each step was 2 hours. Finally, the dried sheets were carbonized using a quartz tube in a computer-controlled furnace at 900 C.

[0041] Oxidized Carbon XerogelThe pristine CX sheets were dipped once into the concentrated HNO.sub.3 for 30 minutes and heated at approximate 280 C. in air overnight.

[0042] Nitrogen Doped Carbon XerogelWe first prepared a solution by adding 20.00 g resorcinol (C.sub.6H.sub.6O.sub.2, Sigma-Aldrich), 29.48 g formaldehyde (CH.sub.2O, 37 wt % in methanol, SigmaAldrich), 6.32 of 0.02 M Na.sub.2CO.sub.3 solution (SigmaAldrich), 6.00 g of deionized H.sub.2O and 3 g of Diisopropylcarbodiimide in a sealed glass bottle. The solution was sonicated for 40 minutes. The resulting solution was used to infiltrate a dry carbon cloth. Subsequently, the wetted carbon cloth was immobilized between two glass slides, sealed with aluminum foil overnight, and heated at 85 C. for a period of 24 hours in air. A solvent-exchange process was performed for the polymerized sheets in which the sheets were subjected to soaking in deionized water, soaking in acetone, and air-drying. Time taken for each step was 2 hours. Finally, the dried sheets were carbonized using a quartz tube in a computer-controlled furnace at 700 C.

[0043] The foregoing has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Obvious modifications and variations are possible in light of the above teachings. All such modifications and variations are within the scope of the appended claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.