Nitric acid plant and control system

Claim 1

IN A PLANT FOR PRODUCING NITRIC ACID INCLUDING A CATALYTIC CONVERTER, A LINE SUPPLYING AMMONIA TO SAID CONVERTER, A LINE SUPPLYING AIR TO SAID CONVERTER, A CONDENSER, AND ABSORPTION COLUMN, AN EFFLUENT LINE EXTENDING FROM SAID CONVERTER TO SAID CONDENSER TO SUPPLY AN EFFLUENT COMPRISING NITROGEN OXIDES, WATER AND UNREACTED OXYGEN TO SAID CONDENSER, MEANS FOR TRANSFERRING CONDENSATE AND UNCONDENSED VAPORS FROM SAID CONDENSER TO SAID ABSORPTION COLUMN WHEREIN NITROGEN OXIDES ARE CONVERTED TO NITRIC ACID, A GASEOUS EFFLUENT CONDUIT EXTENDING FROM THE TOP OF SAID COLUMN, AND MEANS FOR WITHDRAWING NITRIC ACID FROM THE BOTTOM OF SAID COLUMN, A CONTROL SYSTEM WHICH COMPRISES, IN COMBINATION A RATIO CONTROLLER HAVING SENSING ELEMENTS IN SAID AMMONIA LINE AND SAID AIR LINE AND OPERATIVELY CONNECTED TO A CONTROL VALVE IN ONE OF SAID LINES SO AS TO CONTROL THE AMMONIA-AIR RATIO IN SAID CONVERTER, AN OXYGEN RECORDER CONTROLLER HAVING A SENSING ELEMENT IN SAID GASEOUS EFFLUENT CONDUIT, SAID RATIO CONTROLLER BEING OPERATIVELY CONNECTED TO SAID OXYGEN RECORDER CONTROLLER SO AS TO MAINTAIN A PREDETERMINED EFFLUENT OXYGEN CONTENT THROUGH CONTROL OF SAID AMMONIA-AIR RATIO.