Source: http://www.google.com/patents/US4126529?dq=7,603,356
Timestamp: 2017-06-29 12:40:11
Document Index: 269599517

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Patent US4126529 - Ferrous ion scrubbing of flue gas - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsAn apparatus and method for removing oxides of nitrogen and sulfur from flue gases. The apparatus comprises an enclosure wherein the flue gases are washed with a scrubbing solution, preferably containing ferrous chelates and sulfite ions, and an electrochemical cell for regenerating the spent scrubbing...http://www.google.com/patents/US4126529?utm_source=gb-gplus-sharePatent US4126529 - Ferrous ion scrubbing of flue gasAdvanced Patent SearchTry the new Google Patents, with machine-classified Google Scholar results, and Japanese and South Korean patents.Publication numberUS4126529 APublication typeGrantApplication numberUS 05/822,212Publication dateNov 21, 1978Filing dateAug 5, 1977Priority dateAug 5, 1977Publication number05822212, 822212, US 4126529 A, US 4126529A, US-A-4126529, US4126529 A, US4126529AInventorsDavid W. DeBerryOriginal AssigneeSouthern California Edison CompanyExport CitationBiBTeX, EndNote, RefManPatent Citations (7), Referenced by (25), Classifications (9) External Links: USPTO, USPTO Assignment, EspacenetFerrous ion scrubbing of flue gas
US 4126529 AAbstract
An apparatus and method for removing oxides of nitrogen and sulfur from flue gases. The apparatus comprises an enclosure wherein the flue gases are washed with a scrubbing solution, preferably containing ferrous chelates and sulfite ions, and an electrochemical cell for regenerating the spent scrubbing solution. The electrochemical cell preferably comprises a plurality of cathode and anode compartments separated by ion transfer membranes. The spent scrubbing solution is regenerated by passing the solution through the cathode compartments of the electrochemical cell. The regeneration process involves the removal of the sulfate ions from the scrubbing solutions through the ion transfer membranes and the reduction of the nonreactive ferric chelate to the reactive ferrous chelate.
1. A method for regenerating a spent gas scrubbing solution to remove ferric chelates and sulfate ions therefrom comprising the steps of:introducing said solution into the cathode compartment of an electrochemical cell, said cell having an anode compartment separated from said cathode compartment by an ion transfer membrane; circulating water through said anode compartment; passing a current from said cathode compartment to said anode compartment to cause the reduction of the ferric chelates to ferrous chelates and the oxidation of water in the anode compartment to form hydrogen ion, said current causing the transportation of sulfate ions in said cathode compartment through said ion transfer membrane into said anode compartment, said sulfate ions reacting with said hydrogen ions to form sulfuric acid. 2. The method of claim 1 wherein said chelates are selected from the group consisting of acetyl-acetone, pyrogallol, ethylenediaminetetraacetate, nitrilotriacetate, triethylenetetramino, N,N'-disalicylidene-1,2-propylenediamine, diethylenetriaminepentaacetate, pyrocatechol and hydroxyethylethylene diamine triacetate.
9. The method of claim 6 wherein the pH of said scrubbing solution is maintained at about 4.8 to about 8.0.
The present invention relates to an apparatus and method for scrubbing flue gases to remove oxides of nitrogen and sulfur and, in particular, the present invention relates to an apparatus and method for regenerating the gas scrubbing solution.
It is therefore an object of the present invention to provide an improved apparatus and method for removing oxides of nitrogen and sulfur from flue gases.
A more thorough disclosure of the objects and advantages of the present invention is presented in the detailed description which follows and from the accompanying drawing which is an illustration of a suitable regenerative electrochemical cell for the practice of the present invention.
The present invention relates to an apparatus and method for scrubbing flue gases to remove oxides of nitrogen and sulfur. The apparatus comprises generally an enclosure for wet scrubbing of the flue gases and an electrochemical cell for regenerating the spent scrubbing solution. A suitable enclosure for use in the practice of the present invention is enclosed in the Weir U.S. Pat. No. 3,948,608 issued on Apr. 6, 1976, the disclosure of which is incorporated herein by reference. However, it will be obvious to one skilled in the art that other suitable types of enclosures may also be utilized in the practice of the present invention.
In solution, the ferrous ion complexes with the chelate. The ferrous-chelate complex concentration is preferably maintained at about 0.05 molar to about 0.4 molar and most preferably at about 0.25 molar to about 0.4 molar. The sulfite ion concentration is maintained at about at least 0.03 molar to about 0.2 molar. The pH of the scrubbing solution is maintained at about 4.8 to about 8.0 and preferably at about 6.0-7.0. At a more alkaline pH, ferric hydroxide begins to precipitate out from the scrubbing solution.
I. SO2 Reaction:
SO2 + 2OH- &#8594; SO3 =  + H2 O
ii. no absorption Reaction:
Fe+2 - EDTA + NO &#8594; NO - Fe+2 - EDTA
iii. subsequent Reactions:
2NO - Fe+2 - EDTA + SO3.sup.× + H2 O &#8594; N2 + SO4 = + Fe+3 - EDTA + 2OH-  2Fe+2 - EDTA + 1/2O2 + H2 O &#8594; 2Fe+3 - EDTA + 2OH- No - fe2+ - EDTA + SO3 = + H2 O → 1/2N2 + 1/2 S2 O6 = + Fe3+ - EDTA + 2OH- also during the scrubbing process, the nitrogen dioxide in the flue gas reacts with the sulfite ions in solution to form nitrogen. Further, minor amounts of dithionate ion are formed during the process. It is believed that during the scrubbing process the nitric oxide complexes with the ferrous chelate to enhance its reduction to non-polluting nitrogen gas.
The following example is given primarily by way of illustration and not of limitation. An apparatus according to the present invention was tested at the Mohave Generating station. The flue gas which was washed during the test comprised about 320 to 350 ppm NOx and 350 to 450 ppm SO2. The flue gas flow rate was 2200 scfm. The regeneration system comprised four electrochemical cell modules arranges in parallel. Each cell module comprises 16 cathode plates and 15 anode plates having dimensions of about 42 inches by 18 inches. Two cell modules also comprised 30 anion transfer membranes each and two comprised 30 cation transfer membranes each sold by Ionics, Inc. as 103 PZL 183 and 61 CZL 183, respectively. Each cell module was equipped with independent AC/DC power supply and the electrodes were connected in parallel to the power supply. Each power supply required 480 volts (three phases) and delivered up to 3,000 amperes DC at 5 volts with less than five percent AC ripple during the test which corresponded to 28 amperes per square foot of cathode area. The cell voltage at full load was approximately 3 volts. Each module was internally manifolded to supply scrubber solution to the cathode compartments and aqueous sulfuric acid to the anode compartments.
______________________________________Test No.         D-1     D-2     D-3   D-4______________________________________Test Duration (Hours)            9.0     9.0     9.0   9.0Cell Amperes (per cell)            2780    2840    2750  2373Reagent Flow rate(gpm/cell)       15      15      15    15Acid Flow Rate(gpm/cell)       11      15      14    13Reagent Concentrations(gram mole/liter)Fe+2Start        0.286   0.269   0.240 0.268Finish           0.252   0.222   0.231 0.228Fe+3Start        0.027   0.093   0.105 0.103Finish           0.096   0.094   0.063 0.102EDTAStart        0.205   0.295   0.410 0.370Finish           0.305   0.255   0.262 0.284SO3 = Start            0.057   0.049   0.063 0.050Finish           0.077   0.077   0.082 0.074Reagent pH Start 5.9     7.1     7.3   7.1Finish           7.1     7.8     7.7   8.0Circulating H2 SO4(gram moles/liter)Start            0.220   0.265   0.355 0.417Finish           0.967   0.698   0.784 0.797Fe+2 Regenerated(%)            97      95      99    90SO4 = transferred toanode as % of SO2removed from fluegas (%)          67      66      69    83______________________________________
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