(118b) Modeling Water Injected Gas Turbines - Performance and Emissions

Natural gas-fired cogeneration systems are commonly used for large-scale industrial energy production – both electricity generation and heat recovery.  Industrial cogeneration currently represents about 8% of the U.S. total electricity generation capacity.  Plans call for cogeneration to increase to 20% of the generation capacity by the end of 2030 (ORNL/TM- 2008/224).  Industrial cogeneration systems attain both high thermal efficiency and low emissions. The attainment of low emissions from natural gas fired turbines, in particular low NO_xemissions, is of considerable environmental importance especially as coal becomes a less favorable fuel source.

Our current project addresses emissions and performance modeling of the 20 MW natural gas-fired cogeneration system located at Louisiana State University. Water injection is used to help lower emissions.  Data reconciliation and gross error detection are performed to adjust measured variables and determine efficiency.  A continuous emission monitoring system (CEMS) has been recently installed to measure both the O₂ and NO_x concentrations in the exhaust; CO is also measured.  These concentrations have been used to refine a kinetics model, based on GRI-Mech 3.0, in order to predict NO_x, CO and O₂ concentrations leaving the system. The kinetics model is used within a chemical reactor network consisting of PSRs and PFRs to represent the turbine combustion and dilution zones.  Changes in measured emission species combined with the reactor network simulation are used to help indicate the onset of mechanical problems in the combustion zone.