Development of an FDM-TDLAS Sensor for Long-Term Online Monitoring of H2S and CO to Predict Water Wall Corrosion Trends

A laser sensor system was developed to be employed in power plants and specifically engineered for high-particulate and high-temperature environments to be applicable for the online monitoring of hydrogen sulfide (H2S) and carbon monoxide (CO) near the furnace water wall. The system was designed based on frequency division multiplexing (FDM) and tunable diode laser absorption spectroscopy (TDLAS). A corrosion-resistant Herriott multipass cell was designed to withstand temperatures of up to 120 °C while providing an 18 m optical path length. The sensor system exhibits measurement uncertainties below 1.5% and 2% under mechanical vibration testing and thermal cycling testing. Allan variance analysis revealed minimum detection limits of 111 ppb for H2S and 116 ppb for CO, achievable at integration times of 178 and 144 s, respectively. Long-term field validation in a coal-fired boiler included multipoint sampling to assess the sensor system performance, simultaneously analyzing water-wall combustion dynamics and evaluating corrosion propensity.