Development of LPP-Burner for Industrial Gas Turbine Application

Sammanfattning: This thesis reports the work done in the development of a modified Lean Premix Prevaporised (LPP) burner for the use in Alstom Power Sweden’s industrial gas turbines. Incentive for the development of the modified burner have been the need to increase the flame stability over the operating range for the burner, especially for the liquid fuel but also the gaseous fuel operation. Foundation for modifications to the baseline burner was placed by a theoretical analysis of the processes and demands, which directs the LPP burner operation. Numerical simulations were performed to establish the flow field of the existing burner and to evaluate principles for possible modifications. Based on the analysis proposal and the restrictions put by the existing hardware, a number of modifications were proposed. Modifications adapted to the burner included the introduction of a central body, a diffusion type gas pilot at the central lance tip, a quarl-diffuser burner outlet and the application of new main- and pilot liquid fuel injectors. To serve as a basis for the evaluation of the liquid fuel performance of the modified burner the liquid fuel injector’s isothermal spray characteristics were evaluated using PDA and water spray visualisation. The fuel injectors and the modifications flame stability and operation range for gaseous and liquid fuel operation at atmospheric conditions were evaluated in comparison to the existing baseline burner. Introduction of the geometrical changes to the baseline burner with the central body and quarl outlet has changed the internal aerodynamics of the burner so that at atmospheric operation the introduced modifications were able to suppress the pressure oscillations over the load range, and to decrease the Lean Blow Off limit (LBO) by a factor 1.5 for the gaseous fuel operation. By positioning the central body end at the beginning of the diffuser quarl the firm attachment of the forward stagnation point and the recirculation zone to the central body was achieved for the liquid fuel operation. This supplied a stable aerodynamics to the flame. Introduction of the liquid fuel spray inside the swirl generator, slightly downstream half the height of the swirl generator gave a good balance between the radial transport of the spray to provide an even distribution of the burner cross section, while reducing the risk of droplets impacting on the swirl generator vanes and burner wall. The liquid fuel operation with the new injection nozzle positioned in the central body have proven to be able to supply a stable main flame operation from a normalised flame temperature 30% below the design flame temperature. NOx emissions performance was found to be more or less solely dependent on the positioning of the spray within the swirl generator in contrast to the injection at the swirler/mixing tube transition