THE DEVELOPMENT OF AN AMMONIA DETECTOR FOR PROCESS CONTROL OF ADVANCED NITROGEN OXIDE REMOVAL TECHNOLOGIES FOR COAL-FIRED GAS STREAMS

NITROGEN OXIDE POLLUTION (NO(X)) EMITTED FROM COMBUSTORS FIRING FOSSIL FUELS (GAS, OIL, OR COAL) IS A MAJOR CONTRIBUTOR TO THE ACID RAIN PROBLEM. THE MOST EFFECTIVE TECHNOLOGIES FOR REDUCING NO(X) INVOLVE THE INJECTION OF AMMONIA (NH(3)) INTO THE FLUE GAS TO REACT WITH NO(X), RESULTING IN THE FORMATION OF INERT MOLECULAR NITROGEN (N(2)) AND WATER. THESE PROCESSES INCLUDE THE USE OF BOTH CATALYSTS AND HIGH TEMPERATURES TO PROMOTE THE REACTION. IN ORDER TO OBTAIN HIGH NO(X) REMOVAL RATES IT IS NECESSARY TO INJECT LARGE QUANTITIES OF AMMONIA. HOWEVER, IF TOO MUCHAMMONIA IS INJECTED, SOME WILL PASS THROUGH THE SYSTEM UNREACTED. THIS AMMONIA SLIPPAGE IS HAZARDOUS BECAUSE IT CAUSES PLUGGING, CORROSION, FOULING OF THE ASH, AND INCREASED AMMONIA COSTS. TO OPTIMIZE THE NO(X) CONTROL PROCESS IT IS DESIRABLE TO CONTROL THE AMMONIA INJECTION RATE BY MEASURING THE AMMONIA SLIPPAGE AND MAINTAINING A LEVEL OF APPROXIMATELY 2 TO 5 PPM. THIS PROVIDES MAXIMUM NO(X) CONTROL WHILE MINIMIZING PROBLEMS RELATED TO THE EXCESS AMMONIA. HOWEVER, AFTER EVALUATING COMMERCIALLY AVAILABLE AMMONIA DETECTORS, THE ELECTRIC POWER RESEARCH INSTITUTE CONCLUDED THAT "NONE OF THE CURRENT MONITORS ARE JUDGED SUFFICIENTLY ACCURATE AND RELIABLE TO SERVE AS PROCESS CONTROL SYSTEMS". THE PURPOSE OF THE PRESENT RESEARCH AND DEVELOPMENT PROJECT IS TO DEVELOP AND TEST A RELIABLE INSTRUMENT THAT IS CAPABLE OF CONTINUOUSLY MONITORING PARTS-PER-MILLION LEVELS OF NH(3). THE INSTRUMENT WILL OPERATE ON THE PRINCIPLE OF ULTRAVIOLET ABSORPTION USING A PHOTODIODE ARRAY SPECTROMETER. THE SPECTROMETER IS CAPABLE OF IDENTIFYING AND ACCURATELY QUANTIFYING AMMONIA IN THE PRESENCE OF FLUE GAS INTERFERENCES.