OPTICAL BASED EMISSION MONITORING SYSTEMS FOR COMBUSTION TURBINE SCR PROCESS CONTROL AND CEM APPLICATIONS

In parallel with the trend of increasing gas generation, regulatory scrutiny of utility gas turbine emissions is projected to increase as utilities operate their gas turbine fleets dynamically in response to the variability of wind and solar generation resources. While SCR systems have historically provided significant incremental NOx control capability beyond dry low NOx combustor emission levels, associated ammonia injection process control systems are still reliant on extractive based sampling approaches, with up to several minute response time delays. These response time delays in ammonia injection control can lead to time periods of over, or under injection of SCR ammonia during load cycling. In-situ, optical based monitoring systems have the potential to improve SCR process control time response, while also reducing lifecycle operating and maintenance costs associated with NOx/diluent monitoring systems used for SCR process control. The current paper assesses the accuracy associated with several in-situ optical monitors applied on the stack of a gas turbine combined cycle unit. Moreover, the demonstration explores novel optical monitor configurations for multi-specie measurements that could ultimately reduce the number of measurement paths required for typical continuous emission monitoring (CEM) purposes (e.g., NO, NO2, CO, NH3, CO2, O-2 and H2O). In regard to potential CEM applications, the current paper also examines in-situ optical monitor calibration approaches required under the current CEM regulatory framework, associated issues and measurement configurations that could potentially comply with current CEM quality assurance requirements.