Method for reducing the nitrogen oxide concentration in gases
The method comprises passing an N 2 O- and NO x -containing gas over a sequence of two catalyst beds, adding reducing agents for NO x and for N 2 O between the catalyst beds in such an amount that not only NO x but also a predetermined proportion of N 2 O is reduced. The reaction conditions are set so that the N 2 O content of the gas is reduced by not more than 95%, based on the N 2 O content at the entrance of the first catalyst bed, by decomposition to nitrogen and oxygen in the first catalyst bed and that not only chemical reduction of NO x but also chemical reduction of N 2 O occurs in the second catalyst bed so that the N 2 O content of the gas is reduced by at least 50%, based on the N 2 O content at the entrance of the second catalyst bed.
1. A method for reducing the content of N 2 O and NO x in gases, comprising:
a) passing the N 2 O- and NO x -containing gas over two catalyst beds, wherein the first catalyst bed contains a catalyst for decomposing N 2 O into nitrogen and oxygen and the second catalyst bed contains a catalyst for chemically reacting N 2 O and NO x with a reducing agent;
b) selecting temperature, pressure, and space velocity in said first catalyst bed so that the decrease of N 2 O content of the gas is not more than 95%, based on the N 2 O content of the gas at the entrance of said first catalyst bed, and
c) adding a reducing agent for N 2 O and a reducing agent for NO x between the first and second catalyst beds in an amount sufficient to chemically remove all of the NO x and at least 50% of the N 2 O, based on the N 2 O content of the gas at the entrance of said second catalyst bed.
2. The method of claim 1 , wherein temperatures of less than 500° C. are set in the first and second catalyst beds.
3. The method of claim 1 , wherein gas pressures of at least 2 bar are set in the first and second catalyst beds.
4. The method of claim 1 , wherein the N 2 O- and NO x -containing gas is passed over said catalyst beds at a space velocity of from 5000 to 50 000 h −1 , based on the summed catalyst volume of the two catalyst beds.
5. The method of claim 1 , wherein at least one metal-laden zeolite catalyst is used in at least one of said catalyst beds.
6. The method of claim 5 , wherein said at least one metal-laden zeolite catalyst is of the MFI, BEA, FER, MOR, FAU, and/or MEL type.
7. The method of claim 6 , wherein said at least one metal-laden zeolite catalyst in the first catalyst bed is an iron-laden zeolite of the MFI and/or FER type.
8. The method of claim 6 , wherein said at least one metal-laden zeolite catalyst in the second catalyst bed is an iron-laden zeolite of the MFI and/or BEA type.
9. The method of claim 6 , wherein said at least one metal-laden zeolite catalyst in the first and second catalyst beds are an iron-laden zeolite of the MFI type.
10. The method of claim 1 , wherein iron-laden zeolites which have been treated with steam are used in at least one catalyst bed.
11. The method of claim 1 , wherein iron-laden zeolites in which the ratio of extra-lattice aluminium to lattice aluminium is at least 0.5 are used as catalysts in at least one catalyst bed.
12. The method of claim 11 , wherein ammonia is used as reducing agent for NO x and hydrocarbons are used as reducing agent for N 2 O.
13. The method of claim 12 , wherein the hydrocarbons are used as reducing agents for N 2 O in an amount of 0.2 to 1.0 mol per mol of N 2 O to be removed.
14. The method of claim 1 , wherein nitrogen-containing reducing agents, hydrocarbons, carbon monoxide, hydrogen, or mixtures containing at least two of these components are used as reducing agents for NO x and as reducing agents for N 2 O.
15. The method of claim 1 , wherein ammonia is used as reducing agent for NO x and as reducing agent for N 2 O.
16. The method of claim 15 , wherein ammonia is used as reducing agent for NO x in an amount of from 0.9 to 2.5 mol per mol of NO x to be removed and ammonia is used as reducing agent for N 2 O in an amount of from 0.5 to 2.0 mol per mol of N 2 O to be removed.
17. The method of claim 1 , wherein it is integrated into the process for nitric acid production.
18. The method of claim 1 , wherein it is integrated into the process of operating a gas turbine.
19. The method of claim 1 , wherein it is integrated into the process of operating a power station.