Chemical Kinetic Models for Enhancing Gas Turbine Flexibility: Model Validation and Application

Abstract

In recent years, market trends towards higher power generation flexibility are driving gas turbine requirements of operation at stable conditions and below environmental emission guarantees over a wide range of operating conditions, such as load, and for changing fuels. In order to achieve these targets, engine components and operation concept need to be optimized to minimise emissions (e.g. CO, NOx) and combustion instabilities, as well as to maximize component lifetime. Therefore the combination of field experience, experimental studies and theoretical modelling of flames with state of the art tools play a key role in enabling the development of such solutions. For many applications the relative changes of reactivity due to changes in operation conditions are important thus in this report a few examples are shown, where chemical kinetics simulations are used to determine the reactivity and to predict engine behaviour. The predicted trends are validated by correlating them to validation data from high pressure test rigs and real gas turbine operational data. With this approach the full operational range from highest reactivity (flashback) to lowest reactivity (blow out or CO emission increase) are covered. The study is focused on the sequential combustor (SEV) of reheat engines and addresses both the safety margins with respect to highly reactive fuels and achievable load flexibility with respect to part load CO emissions. The analysis shows that it is necessary to utilize updated kinetic mechanisms since older schemes have proved to be inaccurate. A version of the mechanism developed at NUI Galway in cooperation with Alstom and Texas A&M was used and the results are encouraging, since they are well in line with experimental test data and can be matched to GT conditions to determine, predict, and optimize their operational range. This example demonstrates nicely how a development over several years starting from fundamental basic research over experimental validation finally delivers a product for power plants. This report therefore validates the kinetic model in combination with the approach to use modelling for guidance of the GT development and extending it fuel capabilities. The GT24 / GT26 can not only be operated with H2 containing fuels, but also at very low part load conditions and with the integration of H2 from electrolysis (∼power to gas ∼PTG) the turndown capability can even be further improved. In this way the energy converted at low electricity prices can be stored and utilised at later times when it is advantageous to run the GT at lower loads increasing the overall flexibility. This development is well suited to integrate renewable energy at highly fluctuating availability and price to the energy provisioning by co-firing with conventional fuels.