Exhaust-gas purification device and method for the reduction of nitrogen oxides from an exhaust gas of a fossil-fired power plant

Patent metadata

Field	Value
Publication number	US-9387436-B2
Application number	US-201314410210-A
Country	US
Kind code	B2
Filing date	May 21, 2013
Priority date	Jun 27, 2012
Publication date	Jul 12, 2016
Grant date	Jul 12, 2016

Abstract

A catalytic exhaust gas purification device and method for the reduction of nitrogen oxides from an exhaust gas of a fossil-fired power plant, having a heating gas duct along a flow direction and having a reactor chamber which is arranged in the heating gas duct is provided. In the reactor chamber there are arranged a first reduction reactor for the reduction of nitrogen oxides NOx to form water H 2 O and nitrogen N 2 , an oxidation reactor, which is connected downstream of the first reduction reactor in the flow direction, for the oxidation of nitrogen monoxide NO to form nitrogen dioxide NO2, and a second reduction reactor, which is connected downstream of the oxidation reactor in the flow direction, for the reduction of nitrogen oxides NOx to form water H 2 O and nitrogen N 2 . A reduction of nitrogen oxides NOx from an exhaust gas of a fossil-fired power plant is achieved.

First claim

The invention claimed is:

1. A process for the reduction of nitrogen oxides NO x in a nitrogen oxide-containing exhaust gas (AG 1 ) from a combustion process, wherein
a) the exhaust gas (AG 1 ) and a reducing agent (R 1 ) are fed into a first reaction process (K 1 ), where part of the nitrogen oxides NO x present in the exhaust gas is reduced to water H 2 O and nitrogen N 2 by selective catalytic reduction at a first reaction temperature (T 1 ) to form an exhaust gas (AG 2 ) which has a reduced nitrogen oxide content NO x ,
b) part of the nitrogen monoxide NO present in the exhaust gas (AG 2 ) having a reduced nitrogen oxide content NO x is oxidized to nitrogen dioxide NO 2 by means of oxygen O 2 at a reaction temperature (T 2 ) in a second reaction process (K 2 ) to form an exhaust gas (AG 3 ) having a ratio (V) of nitrogen monoxide NO to nitrogen dioxide NO 2 ,
c) the exhaust gas (AG 3 ) and a reducing agent (R 2 ) are fed into a third reaction process (K 3 ), where nitrogen monoxide NO and nitrogen dioxide NO 2 are reduced to water H 2 O and nitrogen N 2 by means of the reducing agent (R 2 ) at a reaction temperature (T 3 ) by means of fast selective catalytic reduction to form an exhaust gas (AG 4 ) which has been essentially freed of nitrogen oxides NO x .

2. The process as claimed in claim 1 , wherein the reaction temperature (T 1 ) is set in the range from 250° C. to 450° C., the reaction temperature (T 3 ) is set in the range from 80° C. to 250° C. and the reaction temperature (T 2 ) is set to a value between (T 1 ) and (T 2 ).

3. The process as claimed in claim 1 , wherein the reducing agent (R 1 ) introduced into the exhaust gas (AG 1 ) is introduced via a first regulating process so that, on average over time, complete conversion of the reducing agent (R 1 ) is achieved in the first catalysis process (K 1 ).

4. The process as claimed in claim 3 , wherein, in the first regulating process,
a) the exhaust gas mass flow (Q Ag1 ), the nitrogen monoxide NO concentration (C 1 ) and the exhaust gas temperature (T 4 ) are measured in a first measurement procedure (P 1 ) upstream of the first catalysis process (K 1 ) and an expected concentration (C 2 ) of nitrogen monoxide NO after the first catalysis process (K 1 ) is determined as a function of temperature, loading of ammonia NH 3 in the first catalysis process (K 1 ) and the nitrogen monoxide NO concentration (C 1 ) in a first evaluation and control process with the aid of characteristic data for the nitrogen monoxide reduction,
b) the nitrogen monoxide NO concentration (C 3 ) is measured in a second measurement procedure (P 2 ) between the first catalysis process (K 1 ) and the second catalysis process (K 2 ),
c) the calculated concentration (C 2 ) is compared with the measured concentration (C 3 ) and the amount of the first reducing agent (R 1 ) introduced is reduced by means of a first control process as soon as the calculated concentration (C 2 ) becomes lower than the measured concentration (C 3 ).

5. The process as claimed in claim 1 , wherein the second catalysis process (K 2 ) is controlled in such a way that a largely balanced ratio V of nitrogen monoxide NO to nitrogen dioxide NO 2 of about 1 is achieved.

6. The process as claimed in claim 1 , wherein the second reducing agent (R 2 ) which is introduced into the exhaust gas (AG 3 ) is introduced via a second regulating process so that, on average over time, complete conversion of the reducing agent R 2 is achieved in the third catalysis process (K 3 ).

7. The process as claimed in claim 6 , wherein, in the second regulating process
a) the exhaust gas temperature (T 5 ) and the exhaust gas mass flow (Q Ag2 ) are measured in the second measurement procedure (P 2 ) before the second catalysis process (K 2 ) and the concentration (C 4 ) of nitrogen dioxide NO 2 and a degree of reduction (G) which can be achieved in the catalysis process (K 3 ) is determined in a second evaluation and regulating process on the basis of characteristic data for the catalysis process (K 2 ),
b) the exhaust gas temperature (T 5 ) and the nitrogen dioxide NO 2 concentration (C 5 ) is measured in a third measurement procedure (P 3 ) after the third catalysis process (K 3 ),
c) the calculated concentration (C 4 ) is compared with the measured concentration (C 5 ) and the amount of the second reducing agent (R 2 ) introduced is set by means of a second control process on the basis of the achievable degree of reduction (G) and is reduced as soon as the calculated concentration (C 2 ) becomes smaller than the measured concentration (C 5 ).

8. The process as claimed in claim 1 , wherein ammonia NH 3 or an ammonia-releasing substance is used as reducing agent (R 1 , R 2 ).

9. The process as claimed in claim 1 , characterized by use in a fossil fuel-fired power station.

10. A catalytic exhaust gas purification apparatus for the reduction of nitrogen oxides in an exhaust gas from a fossil fuel-fired power station, having a heating gas channel extending along a flow direction and a reactor space arranged in the heating gas channel, wherein the reactor space comprises a first reduction reactor for the reduction of nitrogen oxides NO x to water H 2 O and nitrogen N 2 , where a first injection device is arranged upstream of the first reduction reactor, an oxidation reactor for the oxidation of nitrogen monoxide NO to nitrogen dioxide NO 2 located downstream of the first reduction reactor and a second reduction reactor for the reduction of nitrogen oxides NO x to water H 2 O and nitrogen N 2 located downstream of the oxidation reactor, wherein a second injection device is arranged upstream of the second reduction reactor.

11. The catalytic exhaust gas purification apparatus as claimed in claim 10 , wherein the first reduction reactor comprises heating surfaces which on at least part of them have a first catalytic coating, where the first catalytic coating is selective for nitrogen oxides NO x and is stable up to a temperature of 500° C.

12. The catalytic exhaust gas purification apparatus as claimed in claim 11 , wherein the first catalytic coating and the third catalytic coating are SCR catalyst layers which have thicknesses of greater than 10 μm and less than 50 μm so that a reduction reaction of nitrogen oxides NO x with ammonia NH 3 to form water H 2 O and nitrogen N 2 can be carried out.

13. The catalytic exhaust gas purification apparatus as claimed in claim 11 , wherein the heating surfaces are superheater heating surfaces, vaporizer heating surfaces or economizer heating surfaces.

14. The catalytic exhaust gas purification apparatus as claimed in claim 10 , wherein the oxidation reactor comprises heating surfaces ( 10 ) which on at least part of them have a second catalytic coating, where the second catalytic coating is selective for nitrogen oxides NO x and is stable up to a temperature of 300° C.

15. The catalytic exhaust gas purification apparatus as claimed in claim 14 , wherein the second catalytic coating is a noble metal-containing coating which has a thickness of greater than 10 μm and less than 50 μm and whose geometric surface area is less than 30% of the geometric surface area of the first catalytic coating so that an oxidation reaction of nitrogen monoxide NO with oxygen O 2 to form nitrogen dioxide NO 2 can be carried out.

16. The catalytic exhaust gas purification apparatus as claimed in claim 10 , wherein the second reduction reactor comprises heating surfaces which on at least part of them have a third catalytic coating, where the third catalytic coating is selective for nitrogen ox

Assignees

• Siemens Ag

Inventors

• Brückner Jan
• Hammer Thomas

Classifications

• B01D2258/0283

  Flue gases · CPC title

• B01D2255/504

  ZSM 5 zeolites · CPC title

• B01D2255/1021

  Platinum · CPC title

• B01D53/864

  Removing carbon monoxide or hydrocarbons · CPC title

• Y02T10/12

  Improving ICE efficiencies · CPC title