IN-SITU GAS-ANALYSIS WITH INFRARED-LASERS

In the first part of the paper we present the experimental validation of models describing the NO(x) removal from flue gases through the SNC R process. The Selective Non-Catalytic NO, Reduction process was reali zed in a high temperature flow reactor, A lead salt diode laser system combined with second derivative spectroscopy monitored the concentrat ion of NO, NH3, N2O, NO2, HCN behind the reactor. After the injection of ethane at concentrations of up to 1000 ppm the shift (up to 220 K) of the temperature window of the SNCR process was measured. In the sec ond part a Laser In-Situ Ammonia-monitor (LISA) based on a (CO2)-C-13- wave guide laser is used to establish an on-line control of the SNCR i n an industrial environment by measuring in-situ the excess ammonia be hind the reduction zone. With differential absorption spectroscopy and a special referencing scheme sensitivities in the order of several pp m . m of NH3 at atmospheric pressure have been achieved even in heavil y dust laden flue gases. With a multi-channel LISA system the 2-dimens ional NH3 distribution in the flue gas channel of an experimental coal burner system could be measured and the persistence of spatial inhomo geneities, caused by incomplete mixing of NH3 and the flue gas could b e shown. In the third part we present first results aimed at the measu rement of the local O2-concentration in combustion systems. With a the rmally stabilized 5 mW NIR diode laser at 760 nm we detected oxygen at atmospheric pressure with a sensitivity of less than 500 ppm . m usin g two beam absorption spectroscopy.