A METHOD FOR REMOVING NITROGEN OXIDES FROM A GAS USING AN IRON EXCHANGED ZEOLITE CATALYST
A method for removing nitrogen oxides NOx from a gaseous current, comprising the steps of: passing the gaseous current through a de-NOx catalytic bed with iron exchanged zeolite as a catalyst with the addition of ammonia as a reducing agent, wherein the molar ratio of NH3 over NOx is greater than 1.33.
1 - 11 . (canceled)
12 . A method for removing nitrogen oxides NOx from a gaseous current, the method comprising:
passing the gaseous current through a de-NOx catalytic bed including a catalyst that is an iron exchanged zeolite, with an addition of ammonia as a reducing agent;
wherein a molar ratio of NH3 over NOx in the gas admitted to said de-NOx catalytic bed is 1.4 to 2;
wherein said de-NOx catalytic bed is operated at a temperature in a range of 420° C. to 435° C.; and
wherein a space velocity in said de-NOx catalytic bed is 10000 h −1 to 14000 h −1 .
13 . The method according to claim 12 , wherein said molar ratio of NH3 over NOx is 1.4 to 1.6.
14 . The method according to claim 13 , wherein said molar ratio of NH3 over NOx is 1.5.
15 . The method according to claim 12 , wherein, after the passage though said de-NOx catalytic bed, a residual amount of NOx in the gas is not greater than 100 ppm.
16 . The method according to claim 12 , wherein, after the passage though said de-NOx catalytic bed, a residual amount of NOx in the gas is not greater than 50 ppm.
17 . The method according to claim 12 , wherein, after the passage though said de-NOx catalytic bed, a residual amount of NOx in the gas is not greater than 25 ppm.
18 . The method according to claim 12 , wherein the temperature at which said de-NOx catalytic bed is operated is 430° C.
19 . The method according to claim 12 , wherein the iron exchanged zeolite catalyst includes MFI, BEA, FER, MOR, FAU, MEL, or combinations thereof.
20 . The method according to claim 12 , wherein the iron exchanged zeolite includes an Fe-ZSM-5 type iron exchanged zeolite.
21 . The method according to claim 12 , wherein the space velocity in said de-NOx catalytic bed is 13000 h −1 .
22 . The method according to claim 12 , wherein the gas in said de-NOx catalytic bed exhibits an absolute pressure of greater than 1 bar.
23 . The method according to claim 22 , wherein the absolute pressure is 2 bar to 25 bar.
24 . The method according to claim 22 , wherein the absolute pressure is 5 bar to 15 bar.
25 . The method according to claim 12 wherein the gaseous current is a tail gas of a process for making nitric acid, withdrawn from an absorption column.
26 . The method according to claim 12 , further comprising:
passing the NOx-containing gas through a first de-NOx catalytic bed;
adding ammonia as a reducing agent to the effluent of said first-de-NOx catalytic bed until the molar ratio of NH3 over NOx in said effluent gas is 1.4 to 2; and
passing the effluent gas and ammonia directly through said de-NOx catalytic bed without a passage through a de-N2O catalytic bed.
27 . The method according to claim 26 wherein adding ammonia as a reducing agent to the effluent of said first-de-NOx catalytic bed until the molar ratio of NH3 over NOx in said effluent gas is 1.4 to 2 includes adding ammonia as the reducing agent to the effluent of said first-de-NOx catalytic bed until the molar ratio of NH3 over NOx in said effluent gas is 1.4 to 1.6.
28 . The method according to claim 12 , wherein the gaseous current is a flue gas of a combustion process, or a tail gas of a process for making nitric acid withdrawn from an absorption column; and
the method does not comprise passing the gas through a series of another de-NOx catalytic bed and a subsequent de-N2O catalytic bed, before the passage through said de-NOx catalytic bed.