Abstract: A method for control of the air/fuel ratio of the burner(s) (excess air) of a thermal cracker includes three steps. The thermal cracker has three consecutive zones or portions through which combustion gases pass, a firebox portion, a bridge wall portion and a convection portion The first step is to direct a wavelength modulated beam of near infrared light from two different tunable diode lasers located in the bridge wall portion through combustion gas from the burner to a pair of near infrared light detectors, each positioned to receive the wavelength modulated beam of near infrared light from a different one of the two tunable diode lasers to generate a detector signal. The second step is to analyze the detector signals for spectroscopic absorption at wavelengths characteristic of oxygen and carbon monoxide to determine their respective concentrations in the combustion gas.

Abstract: A method for control of the air/fuel ratio of the burner(s) (excess air) of a thermal cracker includes three steps. The thermal cracker has three consecutive zones or portions through which combustion gases pass, a firebox portion, a bridge wall portion and a convection portion The first step is to direct a wavelength modulated beam of near infrared light from two different tunable diode lasers located in the bridge wall portion through combustion gas from the burner to a pair of near infrared light detectors, each positioned to receive the wavelength modulated beam of near infrared light from a different one of the two tunable diode lasers to generate a detector signal. The second step is to analyze the detector signals for spectroscopic absorption at wavelengths characteristic of oxygen and carbon monoxide to determine their respective concentrations in the combustion gas.

Abstract: A method for control of the air/fuel ratio of the burner(s) (excess air) of a thermal cracker which includes three steps. The first step is to direct a wavelength modulated beam of near infrared light from a tunable diode laser through combustion gas from the burner to a near infrared light detector to generate a detector signal. The second step is to analyze the detector signal for spectroscopic absorption at wavelengths characteristic for an analyte selected from the group consisting of oxygen, carbon monoxide and nitrogen oxide to determine the concentration of the analyte in the combustion gas. The third step is to adjust the air/fuel ratio of the burner(s) (excess air) in response to the concentration of the analyte of the second step.