SELECTIVE REDUCTION OF NITROGEN OXIDES BY GAS PHASE CHEMISTRY

IN THE "THERMAL DENOX" PROCESS, AMMONIA IS INJECTED INTO HOT FLUE GAS INSIDE A BOILER OR FURNACE, AND A GAS PHASE HOMOGENEOUS REACTION OCCURS, WHICH REDUCES THE NITROGEN OXIDES (NOX) TO MOLECULAR NITROGEN AND WATER. THE PROCESS IS THUS EXTREMELY SIMPLE, HIGHLY RELIABLE, AND FAR LESS EXPENSIVE THAN SELECTIVE CATALYTIC REDUCTION. IN LABORATORY EXPERIMENTS, THERMAL DENOX IS CAPABLE OF >90% NOX REDUCTION, BUT IN SUCH EXPERIMENTS THE TEMPERATURE OF FLUE GAS CAN BE ACCURATELY CONTROLLED. IN PRACTICAL APPLICATIONS, THE FLUE GAS HAS A DISTRIBUTION OF TEMPERATURES. BECAUSE THE RANGE OF TEMPERATURES IN WHICH THERMAL DENOX PROVIDES SATISFACTORY RESULTS IS NARROW, THE PRESENCE OF A TEMPERATURE DISTRIBUTION LIMITS NOX REDUCTION. THUS, IN PRACTICE THE THERMAL DENOX PROCESS IS LIMITED TO 50 TO 70% NOX REDUCTION. IN PHASE I, THIS PROJECT ANALYZES THE CHEMISTRY OF THE THERMAL DENOX PROCESS IN FUNDAMENTAL TERMS AND SUGGESTS WHY THE PROCESS WORKS IN A SATISFACTORY MANNER ONLY WITHIN A NARROW RANGE OF TEMPERATURES. BASED ON THIS ANALYSIS, A NEW PROCESS FOR NOX CONTROL IS PLANNED. COMPUTER MODELING EXPERIMENTS SUGGEST THAT THIS NEW PROCESS PROVIDES >90% NOX REDUCTION OVER A VERY WIDE RANGE OF TEMPERATURES (300 DEGREES TO 650 DEGREES CENTIGRADE). BECAUSE THIS RANGE OF TEMPERATURES IS CONSIDERABLY WIDER THAN IS ENCOUNTERED IN PRACTICAL COMBUSTION SYSTEMS, THE THERMAL DENOX PROCESS SHOULD BE EASILY ABLE TO PROVIDE >90% NOX REDUCTION. FURTHERMORE, BECAUSE THE NOX IS REDUCED BY HOMOGENEOUS GAS PHASE REACTIONS, THE SIMPLICITY AND RELIABILITY OF THE THERMAL DENOX PROCESS WILL BE RETAINED. IN PHASE I, THE KINETICS OF NOX REDUCTION BY VARIOUS CHEMICALS IS BEING MEASURED, AND COMPUTER MODELING EXPERIMENTS CARRIED OUT.