Process of removing nitrogen oxides from gas streams of varying composition

Claim 1

A PROCESS FO REMOVING SMALL AMOUNTS OF NITROGEN OXIDES FROM A NITRIC ACID PLANT TAIL GAS STREAM WHICH CONSISTS OF NITROGEN, NITROGEN OXIDES, OXYGEN AND WATER VAPOR, THE AGGREGATE TOTAL VOLUME OF SAID CONSTITUENTS OTHER THAN NITROGEN BEING NORMALLY LESS THAN 5%, BUT SAID STREAM BEING SUBJECTED FROM THE TIME TO TIME TO SHARP INCREASES IN OXYGEN CONTENT TO VALUES APPROACHING 20%, SAID PROCESS COMPRISING CONTINUOUSLY ADMIXING WITH THE TAIL GAS STREAM SUFFICIENT AMOUNTS OF A REDUCING GAS SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, CARBON MONOXIDE AND HYDROCARBONS WHICH ARE VAPORS AT ATMOSPHERIC CONDITIONS TO RENDER THE NORMAL GAS STREAM SLIGHTLY REDUCING, CONTINUOUSLY CONDUCTING THE RESULTING GAS STREAM THROUGH A FIXED BED OF A CATALYST CONSISTING ESSENTIALLY OF FROM 1 TO 5% BY WEIGHT OF A METAL SELECTED FROM THE GROUP CONSISTING OF IRON, COBALT NICKEL AND COPPER SUPPORTED UPON AN INERT REFRACTORY CARRIER, SAID STREAM PASSING THROUGH SAID BED AT A SPACE VELOCITY OF LESS THAN 40,000 VOLUMES OF GAS PER VOLUME OF CATALYST PER HOUR THE INLET TEMPERATURE OF THE GAS STREAM ENTERING SAID BED BEING SO ASJUSTED THAT THE TEMPERATURE OF THE EFFLUENT GASSES BETWEEN ABOUT 1500* F. AND ABOUT 1900* F., AND SAID NITROGEN OXIDES BEING REDUCED BY THE REDUCING GAS TO ELEMENTAL NITROGEN, AND FROM TIME TO TIME ALLOWING THE COMPOSITION OF THE TAIL GAS STREAM TO VARY FROM THE AFORSAID MORMAL COMPOSITION BY SHARPLY INCREASING THE OXYGEN CONTENT THEREOF.