Highly Sensitive CO/O₂ Sensor for In Situ Measurement in Industrial Heating Furnace Based on Calibration-Free Wavelength Modulation Spectroscopy

The continuous catalytic reforming heating furnace is a large-scale system that provides consistent and stable heat support for catalytic reactions. Real-time, in situ and simultaneous measurement of carbon monoxide (CO) and oxygen (O2) is essential for optimizing its performance. Here, we present a highly sensitive CO/O2 sensor based on calibration-free wavelength modulation spectroscopy (WMS) for application in a 10-m-long large-scale continuous reforming heating furnace. The first harmonic-normalized second harmonic WMS (WMS-2f/1f) technique and a time-division-multiplexed strategy were employed to address the challenges of harsh industrial environments. A single-ended configuration with a retroreflector and a through-hole parabolic mirror effectively doubled the optical path while simplifying the sensor setup, providing a novel solution for monitoring large-scale heating furnaces. The sensor demonstrated detection limits of 0.3 ppm and 0.04% for CO and O2, respectively, achieving high sensitivity at high temperature around 850 K. Long-term in situ monitoring confirmed the sensor’s reliability in detecting CO and O2 concentrations. Observational data further revealed several instances of incomplete combustion process lasting for 1–2 h, caused by fluctuations in fuel supply. These findings highlight the significant potential of the proposed laser absorption-based gas sensor to enhance heating furnace control, contributing to improved economic efficiency, environmental protection, and operational safety.