On the aero-thermal characteristics of gasifier-fuelled gas turbine combustors with complex geometries

Abstract

This paper describes the application of a mathematical model to predict the aerodynamics, combustion,and NO emission performances of a gas turbine combustor. The numerical basis of the model is a specially constructed code that uses a generalised nonorthogonal and boundary conforming coordinate system. The gas turbine is a component of the British Coal “Topping Cycle,” a coal-fired fluidised-bed-based combined-cycle technology. A distinctive feature of this study is therefore that the fuel for the gas turbine is produced from the partial gasification of coal. Since this fuel contains nitrogenous species derived from the fuel-bound nitrogen of the parent coal, there is concern that these species might give rise to high NO emissions from the combustor. In addition to the fuel NO, the prompt and thermal NO are modelled. The aerodynamic and combustion performances of the combustor, a Frame-9 unit, for this rather unusual fuel are found to be generally good, with no indication of flame stabilisation difficulties and only a relatively small temperature nonuniformity over the exit plane. This nonuniformity can be traced to products that manage to “skirt round” the dilution jet flows. The predicted level of NO emission corresponds remarkably well with that measured. Most importantly, a significant reduction of NO to N 2 by NH 3 occurs within the primary zone, with the result that the NO emission from the gas turbine component of the Topping Cycle is considerably diminished.