Evaluation of Solid-State Electrochemical Sensors for Real Time Monitoring of NO and O₂ in the Exhaust of a Commercial 60kW Gas Turbine

This study examines the viability of electrochemical solid-state nitric oxide sensors as an alternative to CEM (Continuous Emission Monitoring) instruments for use in monitoring the emissions of a 60 kW gas turbine. While CEM equipment is used regularly at large scale centralized power plants, it is not cost effective for small generators used for distributed power generation. Yet in areas with poor air quality, assessment of the emissions generated by such generators is an important question. A commercial and inexpensive potential alternative to the complex CEM systems used in power plants comes from the automotive industry, which employs solid-state sensors to monitor and control emissions in diesel vehicles. In the present study, two models of commercial solid-state sensors (UniNOx^® and NTK) were evaluated in the exhaust stream of the Capstone C-60 gas turbine engine. A referee instrument (Horiba PG-350) using the EPA approved NO measurement method, chemiluminescence, was used in the study as a reference point. Over 8 months of testing, it was found that both solid state sensors followed the general NO trends measured by Horiba PG-350 analyzer. Both solid-state sensors responded to small incremental changes in engine load with high-resolution changes in NO ppm. It was determined that the NTK sensor had more favorable performance over test period than the UniNOx^® sensor with regards to Accuracy, Lower Detectable Limit (LDL), and Rise Time and Fall Time. The UniNOx^® sensor was found to have higher precision than the NTK sensor.