Prediction of fuel gas pressure requirement for ALSTOM heavy duty gas turbines

Abstract: Within the ongoing development of Alstom's latest heavy-duty gas turbine, the motivation for this thesis is the need for a fuel gas pressure prediction software. The key challenge in the development of such a software is finding the model that predicts the pressure drop over the burner hardware. This model has to predict fuel pressure for over critical and under-critical flow over the entire load range with high accuracy. Old models are inadequate for predicting pressure drops at critical conditions. Four main fuel pressure prediction models are presented in this work. The Kv-model is a model where a pressure drop is attributable to a flow resistor and it contains one hardware parameter. By introducing a second hardware parameter the model is refined to work also for over-critical flow conditions. The outflow model is a model in which the fuel pressure drop can be calculated as being only due to the discharge through a nozzle. The two stage-model is a model, which combines the Kv-model, and the outflow model in order to offer a more sophisticated version. It contains the two hardware parameters from the models described above. Four variants of this model are herewith investigated, in which these parameters are considered either constant, Reynolds number-dependent or dependent of critical flow effects. Finally, by means of a nominalization of the variables, a polynomial fitting method, using the least squares procedure, provides the so-called polynomial model. Polynomials of second and fourth order are considered. In order to perform a structured and systematic selection between the different models, three design criteria were defined: accuracy, simplicity and physicality. It is shown that a modified version of the Kvmodel, in which the burner hardware is treated a pure flow resistor, is the best compromise between these design criteria. This model will predict fuel pressures with a high accuracy over the entire load range of the engine and also predict well for diluted gases. This thesis also contains an application of the finalised fuel pressure prediction software. Boundary limits of the operation of the burner hardware are found, based on defined fuel pressure limits.