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US 8,409,534 B2Granted
Control of emissions
AssigneeThe United States of America as represented by the Administrator of the National Aeronautics and Space Administration
InventorsClyde F. Parrish, Landy Chung
Life of this patent
Estimating the term…
Abstract
Methods and apparatus utilizing chlorine dioxide and hydrogen peroxide are useful to reduce emissions of NOx, SOx, and heavy metals, e.g., mercury, emissions from combustion flue gas streams.
Claims27
A method of treating a combustion gas stream including at least sulfur oxides, nitric oxide, and heavy metal selected from the group consisting of heavy metal oxides, heavy metal hydroxides, and elemental heavy metal, comprising:
- a) scrubbing the gas stream in a first scrubber tower including:
- i) reacting sulfur oxides with a first hydrogen peroxide solution to convert the sulfur oxides to sulfuric acid, thereby producing a first scrubber liquor;
- ii) recycling at least a portion of the first scrubber liquor with the first hydrogen peroxide solution, thereby producing a scrubbing mixture for further scrubbing the gas stream;
- iii) measuring a hydrogen peroxide concentration in the first scrubber liquor;
- iv) maintaining a desired hydrogen peroxide concentration in the first scrubbing mixture by regulating a flow of the first hydrogen peroxide solution in response to the measured hydrogen peroxide concentration of the first scrubber liquor;
- v) converting at least a portion of any heavy metal oxides or heavy metal hydroxides in said gas stream to metal sulfates by contact with the sulfuric acid generated in said first scrubber tower;
- vi) removing a first by-product stream containing sulfuric acid and metal sulfates from said first scrubber tower after attaining a desired sulfuric acid concentration in the first scrubber liquor;
- b) after scrubbing the gas stream with the first hydrogen peroxide solution, oxidizing the nitric oxide and at least a portion of the elemental heavy metal in the gas stream in an oxidation tower including:
- i) contacting the gas stream with gaseous chlorine dioxide in the oxidation tower to oxidize the elemental heavy metals to metal oxide and oxidize nitric oxide to nitrogen dioxide;
- c) after oxidizing the gas stream with the gaseous chlorine dioxide, scrubbing the gas stream with a second hydrogen peroxide solution in a second scrubber including:
- i) reacting the gas stream with the second hydrogen peroxide solution to convert nitrogen dioxide to nitric acid and convert metal oxides to nitrates of heavy metal upon contact with the nitric acid, thereby producing a second scrubber liquor;
- ii) maintaining a desired hydrogen peroxide concentration in the second scrubber liquor by regulating a flow of the second hydrogen peroxide solution;
- and
- iii) removing a second by-product stream containing nitric acid and nitrates of heavy metal from said second scrubber.
11 more elements
A method of treating a combustion gas stream containing at least sulfur oxides, nitric oxide, and mercury selected from the group consisting of mercury oxides, mercury hydroxides, and elemental mercury, the method comprising:
- a) scrubbing the gas stream in a first scrubber tower including:
- i) reacting sulfur oxides with a first hydrogen peroxide solution to convert sulfur oxides to sulfuric acid, thereby producing a first scrubber liquor;
- ii) recycling at least a portion of the first scrubber liquor with the first hydrogen peroxide solution, thereby producing a scrubbing mixture for further scrubbing the gas stream;
- iii) measuring a hydrogen peroxide concentration in the first scrubber liquor;
- iv) maintaining a desired hydrogen peroxide concentration in the scrubbing mixture by regulating a flow of the first hydrogen peroxide solution in response to the measured hydrogen peroxide concentration of the first scrubber liquor;
- v) converting at least a portion of any mercury oxides or mercury hydroxides to mercury sulfates by contact with the sulfuric acid generated in said first scrubber tower;
- vi) removing a first by-product stream containing sulfuric acid and mercury sulfates from said first scrubber tower after attaining a desired sulfuric acid concentration in the first scrubber liquor;
- b) after scrubbing the gas stream with the first hydrogen peroxide solution, oxidizing the nitric oxide and at least a portion of the elemental mercury in the gas stream in an oxidation tower including:
- i) contacting the gas stream with a gaseous chlorine dioxide mixture in the oxidation tower to oxidize the elemental mercury to mercury oxide and oxidize nitric oxide to nitrogen dioxide;
- c) after oxidizing the gas stream, scrubbing the gas stream with a second hydrogen peroxide solution in a second scrubber tower including:
- i) reacting the gas stream with the second hydrogen peroxide solution to convert nitrogen dioxide to nitric acid and convert mercury oxide to nitrates of mercury upon contact with the nitric acid, thereby producing a second scrubber liquor;
- and
- ii) removing a second by-product stream containing nitric acid and nitrates of mercury from the second scrubber liquor.
10 more elements
Dependencies are inferred from the claim text.