Process and apparatus for eliminating NOX and N2O

Patent metadata

Field	Value
Publication number	US-10022669-B2
Application number	US-201113700853-A
Country	US
Kind code	B2
Filing date	May 9, 2011
Priority date	Jun 4, 2010
Publication date	Jul 17, 2018
Grant date	Jul 17, 2018

Abstract

A process for removing N2O and NOx from offgases by catalytic decomposition of N2O by means of iron-containing zeolite catalysts and catalytic reduction of the NOx by means of reducing agents, the deNOx stage connected downstream of the deN2O stage being operated at inlet temperatures of T<=400° C., and the inlet gas for the deN2O stage comprising water and having a selected N2O/NOx ratio, and the operating parameters of temperature, pressure and space velocity of the deN2O stage being selected so as to result in an N2O degradation of 80 to 98%. Under these conditions, a degree of NOx oxidation of 30-70% is established at the outlet of the deN2O stage, which is defined as the ratio of the molar amounts of NO2 to the total molar amount of NOx. The result of this is that the downstream deNOx stage can be operated under optimal conditions. Also provided is an apparatus for carrying out the process.

First claim

The invention claimed is:

1. A process for reducing the NO x and N 2 O contents in gases comprising NO x and N 2 O, comprising the steps of
a) passing a gas stream comprising N 2 O, NO x and water into a deN 2 O stage comprising an iron-laden zeolite catalyst to reduce the N 2 O content by decomposing the N 2 O to nitrogen and oxygen, such that said gas stream entering the deN 2 O stage and a gas stream exiting the deN 2 O stage are characterized by compositional requirements selected from (i) or (ii):
(i) the gas stream entering the deN 2 O stage has a water content between 1.0 and 10% by volume and the ratio of the molar amount of N 2 O in the gas stream entering the deN 2 O stage to the molar amount of NO x in the gas stream exiting the deN 2 O stage (N 2 O/NO x ) is at least 1.0; or
(ii) the gas stream entering the deN 2 O stage has a water content between 0.1 and less than 1.0% by volume and the ratio of the molar amount of N 2 O in the gas stream entering the deN 2 O stage to the molar amount of NO x in the gas stream exiting the deN 2 O stage (N 2 O/NO x ) is at least 1.5;
wherein the temperature of the gas stream in the deN 2 O stage having been adjusted to a value between 400° C. and 650° C., the pressure in the deN 2 O stage having been adjusted to a value between 1 and 50 bar abs, and the space velocity in the deN 2 O stage having been adjusted to such a value as to result in an N 2 O degradation of 80% to 98% in the deN 2 O stage, with the additional proviso that the degree of NO x oxidation at the outlet of the deN 2 O stage is at least 30%,

b) supplying the gas stream leaving the deN 2 O stage to a cooling apparatus and cooling the gas stream, as it flows through this apparatus, to a temperature below 400° C., and
c) supplying the gas stream leaving the cooling apparatus to a deNO x stage for catalytic reduction of NO x with a reducing agent in the presence of a deNO x catalyst, with addition of such an amount of reducing agent which is sufficient to reduce the desired proportion of NO x to the gas stream, viewed in flow direction, after it leaves the deN 2 O stage and before it flows through the deNO x catalyst.

2. The process as claimed in claim 1 , wherein the ratio of the molar amount of N 2 O which enters the deN 2 O stage to the molar amount of NO x which leaves the deN 2 O stage is at least 1.5.

3. The process as claimed in claim 1 , wherein the molar ratio of N 2 O and NO x in the gas stream comprising NO x , N 2 O and water, even before it enters the deN 2 O stage, is at least 1.5, or wherein a reducing agent for NO x is added to the gas stream comprising NO x , N 2 O and water before or on entry thereof into the deN 2 O stage in such an amount that the NO x present in the gas stream is partly degraded, such that the molar ratio of N 2 O and NO x , immediately after the entry of the gas stream comprising NO x and N 2 O in the deN 2 O stage, is at least 1.5.

4. The process as claimed in claim 3 , wherein the water content of the gas stream comprising N 2 O, NO x and water, before it enters the deN 2 O stage, is adjusted by addition of water vapor and/or by addition of water in liquid form.

5. The process as claimed in claim 1 , wherein the water content of the gas stream comprising N 2 O, NO x and water before it enters the deN 2 O stage is adjusted by introducing an offgas stream from a combustion stage in which hydrogen and/or hydrogen-containing compounds are combusted, and/or wherein the water content of the gas stream comprising N 2 O, NO x and water is adjusted before it enters the deN 2 O stage by passing it through a water loading apparatus selected from a group comprising saturators and absorption towers.

6. The process as claimed in claim 1 , wherein the gas stream comprising N 2 O, NO x and water, before it enters the deN 2 O stage, is heated by means of a heating apparatus to a temperature between 400° C. and 650° C.

7. The process as claimed in claim 1 , wherein the resulting gas stream from the deN 2 O stage is supplied to a cooling apparatus which is a recuperator, the heat released being transferred to the gas stream comprising N 2 O, NO x and water before it enters the deN 2 O stage, thus heating it to a temperature between 400° C. and 650° C.

8. The process as claimed in claim 1 , wherein the gas stream comprising N 2 O, NO x and water, viewed in flow direction, is divided into two substreams upstream of a heating apparatus, a first substream, after bypassing the heating apparatus, being combined again with the second substream which has passed through the heating apparatus, or wherein the gas stream bypasses the heating apparatus, the amount of the sub streams being regulated by means of a valve.

9. The process as claimed in claim 1 , wherein the deN 2 O stage has an upstream guard bed which comprises random packings or structured packings of shaped bodies comprising alumina.

10. The process as claimed in claim 1 , wherein the deNO x stage comprises a deNO x catalyst based on V 2 O 5 —TiO 2 .

11. The process as claimed in claim 1 , wherein the process in the deN 2 O stage is performed at space velocities of 2000 to 50 000 h −1 .

12. The process as claimed in claim 1 , wherein the reducing agent for NO x is ammonia.

13. The process as claimed in claim 1 , wherein space velocity, temperature and pressure in the deNO x stage are adjusted such that NO x conversions between 80% and 100% are attained.

14. The process as claimed in claim 1 , wherein the ratio of the molar amount of N 2 O which enters the deN 2 O stage to the molar amount of NO x which leaves the deN 2 O stage is at least 2.

15. The process as claimed in claim 1 , wherein the ratio of the molar amount of N 2 O which enters the deN 2 O stage to the molar amount of NO x which leaves the deN 2 O stage is at least 5.

16. The process as claimed in claim 6 , wherein the heating apparatus is a heat exchanger.

17. The process as claimed in claim 1 , wherein the iron-laden zeolite catalyst of the deN 2 O stage is based on a BEA or WI type zeolite.

18. The process as claimed in claim 1 , wherein the iron-laden zeolite catalyst of the deN 2 O stage is based on a ZSM-5 zeolite.

19. The process as claimed in claim 1 , wherein the process in the deN 2 O stage is performed at space velocities of 2500 to 25 000 h −1 .

20. The process as claimed in claim 1 , wherein the process in the deN 2 O stage is performed at space velocities of 3000 to 20 000 h −1 .

21. The process as claimed in claim 1 , wherein space velocity, temperature and pressure in the deNO x stage are adjusted such that NO x conversions between 90% and 100% are attained.

22. The process as claimed in claim 1 , wherein the iron-laden zeolite catalyst of the deN 2 O stage is based on a zeolite type selected from the group consisting of MFI, BEA, FER, MOR, MEL, and mixtures thereof, and the deNO x stage comprises a transition metal-comprising SCR catalyst.

23. The process as claimed in claim 1 , wherein the N 2 O degradation in the deN 2 O stage is 90 to 95%.

Assignees

• Schwefer Meinhard
• Groves Michael
• Perbandt Christian
• Siefert Rolf
• Thyssenkrupp Ind Solutions Ag

Inventors

• Schwefer Meinhard
• Groves Michael
• Perbandt Christian
• Siefert Rolf

Classifications

• B01D2255/50

  Zeolites · CPC title

• B01J37/0009

  Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst · CPC title

• B01J29/46

  Iron group metals or copper · CPC title

• B01D2257/404

  Nitrogen oxides other than dinitrogen oxide · CPC title

• B01J29/072

  Iron group metals or copper · CPC title