CFD Assessment of a Wet, Low-NOx Combustion System for a 3MW-Class Industrial Gas Turbine

Abstract

A wet low-NOx combustion system being developed for the AlliedSignal ASE40 industrial gas turbine is assessed using advanced 3-D CFD analysis. A PDF combustion-turbulence interaction model was modified to allow analysis of simultaneous injection of water with gaseous or liquid fuel. To the authors’ knowledge, such a CFD analysis is unique in the open literature. Analyses of the wet low-NOx combustion system were performed with and without water injection at full power engine conditions. Good qualitative agreement between engine emission data and predictions was seen. NOx reductions of 58% and 77% were measured for water-to-natural gas mass ratios of 0.5 and 1.0, respectively, compared to 75% and 93% for CFD calculations. Corresponding CO levels were measured to increase by factors of 3 and 9, compared to CFD predictions of 4 and 7. Similar trends were predicted for water injection with DF-2 diesel fuel. Predicted overall flow patterns were not significantly changed with water injection. NOx reductions were caused by a reduction in maximum flame temperatures in the primary and intermediate zones when water was injected. CO increases were caused by a reduction of CO oxidation downstream of the dilution zone (in the turn-around duct) due to lower gas temperatures with water injection.