On site detection of hazardous and complex environmental index gases concentrations using aliasing laser absorption spectrum demodulation method

Abstract

Early detection of index gases such as carbon monoxide (CO) and ethylene (C₂H₄) is crucial for preventing incidents in many scenes. Laser absorption spectroscopy (LAS) has emerged as a powerful tool for this purpose, offering high sensitivity, selectivity, and real-time monitoring capabilities. This study takes coal spontaneous combustion prediction as an example to explore the application solution of LAS in online detection of CO and C₂H₄. Sub-ppm detection of CO and C₂H₄ is achieved by using tunable lasers with central wavelengths of 2326 nm and 1626 nm in combination with long optical path multi-pass cells. In view of the interference of high-concentration CH₄, a novel method named spectral adaptive transformation non-negative least squares (SAT-NNLS) for aliasing spectrum demodulation is proposed. Based on the above dual-gas sensor and spectral processing method, the detection performance of CO and C₂H₄ is experimentally verified and analyzed. Experimental results show that the detection limits of the sensor system for CO and C₂H₄ are 0.39 ppm and 0.34 ppm respectively. Even in the background of 10000 ppm CH₄, we have achieved for the first time that the impact on the detection of C₂H₄ does not exceed 0.61 ppm. In addition, an oxidation experiment is carried out on coal samples from Wulan coal mine to verify the feasibility and reliability of the system for the in-site detection of CO and C₂H₄. In summary, this sensor has demonstrated excellent performance and can provide reliable data guarantee for the timely warning of coal spontaneous combustion.