GAS MONITORING IN THE PROCESS INDUSTRY USING DIODE-LASER SPECTROSCOPY

Gas monitors for industrial applications must have high reliability an d require little maintenance. Monitors for in-situ measurements using tuneable diode laser absorption spectroscopy in the near infrared, can meet these requirements. A brief description of monitors using high-f requency wavelength modulation spectroscopy with second-harmonic detec tion is presented. Some problems related to industrial applications ar e discussed, in particular line broadening effects, and frequency drif t of diode lasers. Typical applications for monitoring of O-2, CO, NH3 , HCl and HF are described together with measurements from several ins tallations. The monitors show continuous measurements with fast respon se and good sensitivity, all of which is difficult to obtain with conv entional techniques such as wet chemical analysis.