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Patent US4026992A successfully refreshed from Google Patents.
US4026992A
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US
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Method for removing nitrogen oxides from combustion exhaust gases
Assignee: Sumitomo Chemical Co Ltd
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Filing: 1975-10-31
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Granted: 1977-05-31
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Expires: 1995-10-31
Abstract
Abstract A method for removing nitrogen oxides from combustion exhaust gases obtained after removing sulfur oxides by a wet process, which is characterized in that the gases obtained after removing sulfur oxides from the combustion exhaust gases by a wet process are introduced into a wet electrostatic precipitator to remove most of the impurities such as dusts, fumes and mists, passed through a dummy catalyst layer in the form of a fixed bed or a moving bed to remove the remaining impurities which is set before or after heating the gases to a temperature suitable for the reaction of reducing nitrogen oxides, and passed through a metal oxides catalyst layer in the form of a fixed bed in the presence of ammonia which is used at least in the stoichiometric amount required for reducing nitrogen oxides to nitrogen gas by which the gases containing nitrogen oxides are reduced to harmless gases.
Inventors
- 👤 Shujiro Shiga
- 👤 Takeshi Katsumata
- 👤 Eiji Inaba
- 👤 Yasushi Okamoto
- 👤 Atsushi Inmaru
- 👤 Tsugio Nishioka
- 👤 Takashi Nakata
- 👤 Seiji Takaki
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 10:26
CPC Classifications
B; B01; B01D; B01D53/00; B01D53/34; B01D53/92; B01D53/94; B01D53/9404; B01D53/9409; B01D53/46; B01D53/60; B03; B03C; B03C3/00; B03C3/017; Y; Y02; Y02A; Y02A50/00; Y02A50/20
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
140 words
A method for removing nitrogen oxides from a combustion gas which comprises first removing sulfur oxides by a wet process comprising absorption in an aqueous or slurry of an effective absorbent for said sulfur oxides and secondly removing nitrogen oxides by a dry catalytic reduction, wherein the gas obtained after removing the sulfur oxides by said wet process is passed through a wet electrostatic precipitator to remove most of the impurities therefrom, passed through a dummy catalyst layer which is not catalytically active for reducing the nitrogen oxides with ammonia and which comprises carrier particles made of the same carrier as is employed in the second catalyst layer to remove the remaining impurities therefrom, and then passed through a second catalyst layer comprising a metal oxide effective for reducing the nitrogen oxides to nitrogen gas in the presence of ammonia.
Claim 2
Independent Claim
140 words
A method for removing nitrogen oxides from a combustion gas which comprises first removing sulfur oxides by a wet process comprising absorption in an aqueous or slurry of an effective absorbent for said sulfur oxides and secondly removing nitrogen oxides by a dry catalytic reduction, wherein the gas obtained after removing the sulfur oxides by said wet process is passed through a wet electrostatic precipitator to remove most of the impurities therefrom, passed through a dummy catalyst layer which is not catalytically active for reducing the nitrogen oxides with ammonia and which comprises carrier particles made of the same carrier as is employed in the second catalyst layer to remove the remaining impurities therefrom, and then passed through a second catalyst layer comprising a metal oxide effective for reducing the nitrogen oxides to nitrogen gas in the presence of ammonia.
Claim 3
Dependent Claim
37 words
The method according to claim 1, wherein the gas is passed through the said second catalyst layer at a temperature of 250° to 450° C. and at a space velocity of 1,000 to 20,000 hr.sup. -1 (STP).
Claim 4
Dependent Claim
29 words
The method according to claim 1, wherein the ammonia is used in an amount of 1.0 to 2.0 times of the stoichiometric amount with respect to the nitrogen oxides.
Claim 5
Dependent Claim
51 words
The method according to claim 1, wherein the wet electrostatic precipitator is operated under the following conditions; the electric field strength: 2,500 to 6,000 V/cm, the current density of the collecting electrodes: 0.2 to 0.8 mA/m 2 and the retention time of the gas between the electrodes: 1 to 30 seconds.
Claim 6
Dependent Claim
36 words
The method according to claim 1, wherein the dummy catalyst layer is in the form of a fixed bed or a moving bed and said second catalyst layer is in the form of a fixed bed.
Claim 7
Dependent Claim
36 words
The method according to claim 1, wherein the dummy catalyst layer in the form of a fixed bed and the second catalyst layer in the form of a fixed bed are disposed in the same vessel.
Claim 8
Dependent Claim
28 words
The method according to claim 1, wherein the absorbent for the sulfur oxides is an aqueous solution or a slurry of sodium sulfite, potassium sulfite or calcium hydroxide.
Claim 9
Dependent Claim
23 words
The method according to claim 1, wherein the carrier for the catalyst is alumina, silica, aluminosilicate, diatomaceous earth, silicon carbide or titanium oxide.
Claim 10
Dependent Claim
26 words
The method according to claim 1, wherein said metal oxide is an oxide of vanadium, molybdenum or tungsten, or a mixture thereof, on a suitable carrier.
Claim 11
Dependent Claim
180 words
In a method for removing sulfur oxides and nitrogen oxides from a combustion exhaust gas by first recovering the sulfur oxides by a wet process comprising absorption in an aqueous solution or slurry of an effective absorbent for said sulfur oxides to remove the sulfur oxides therefrom and then by reducing the nitrogen oxides contained in said gas with ammonia to nitrogen gas in contact with a metal oxide catalyst effective for reducing the nitrogen oxides to nitrogen gas in the presence of ammonia, the improvement for prolonging the life of said metal oxide catalyst which comprises passing the wet gas obtained after removing said sulfur oxides therefrom through a wet electrostatic precipitator and then through a dummy catalyst layer which is not catalytically active for reducing the nitrogen oxides with ammonia and which comprises carrier particles made of the same carrier as is employed in the metal oxide catalyst in order to remove dusts and condensable gas components therefrom, and introducing the resulting gas into said metal oxide catalyst to reduce the nitrogen oxides to nitrogen gas with ammonia.
Claim 12
Dependent Claim
180 words
In a method for removing sulfur oxides and nitrogen oxides from a combustion exhaust gas by first recovering the sulfur oxides by a wet process comprising absorption in an aqueous solution or slurry of an effective absorbent for said sulfur oxides to remove the sulfur oxides therefrom and then by reducing the nitrogen oxides contained in said gas with ammonia to nitrogen gas in contact with a metal oxide catalyst effective for reducing the nitrogen oxides to nitrogen gas in the presence of ammonia, the improvement for prolonging the life of said metal oxide catalyst which comprises passing the wet gas obtained after removing said sulfur oxides therefrom through a wet electrostatic precipitator and then through a dummy catalyst layer which is not catalytically active for reducing the nitrogen oxides with ammonia and which comprises carrier particles made of the same carrier as is employed in the metal oxide catalyst in order to remove dusts and condensable gas components therefrom, and introducing the resulting gas into said metal oxide catalyst to reduce the nitrogen oxides to nitrogen gas with ammonia.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1980-05-30 | 1980-11-29 | 1981-05-31 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1984-05-30 | 1984-11-29 | 1985-05-31 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1988-05-30 | 1988-11-29 | 1989-05-31 | $7700.00 | Window Closed / Lapsed |