SIMULTANEOUS DIODE-LASER-BASED IN SITU DETECTION OF MULTIPLE SPECIES AND TEMPERATURE IN A GAS-FIRED POWER PLANT

We have developed a diode-laser (DL)-based spectrometer and demonstrated, to our knowledge, the first simultaneous in situ detection of all major combustion species and the temperature in the same measurement volume for active combustion control purposes and to ensure a safe ignition procedure of large-scale multi-burner gas-fired combustion systems. Two distributed-feedback DLs at 760 nm and 1.65 μ m were used to detect O 2 , CH 4 , and CO 2 , while a Fabry-Perot DL at 812 nm served to extract absolute H 2 O concentrations and the temperature from multiline water spectra. Permanent alignment of the laser beams could be ensured, despite strong wall deformation, with a new active alignment control loop. We analyzed the instationary ignition procedure of a full-scale gas-fired power plant with a 10 m furnace diameter using the spectrometer. A time resolution of 1.6 s and a minimum detectable absorption better than 10 −3 OD could be achieved. CH 4 could be detected with a dynamic range of more than two orders of magnitude and a detectivity in the 100 ppm range. A strong dependence of the CH 4 signal on the burner height was found. This spectrometer is well suited to enable an on-line control of the furnace atmosphere and a rapid detection of ignition delays by unburned CH 4 .