Influence of Gas Turbine Combustor Design and Operating Parameters on Effectiveness of NO_x Suppression by Injected Steam or Water

Steam or water injection has become the state-of-the-art abatement technique for NO_x, with steam strongly preferred for combined-cycle application. In combined-cycle plants, the degradation of the plant efficiency due to steam injection into the gas turbine combustor provides a powerful incentive for minimizing this flow over the entire plant operating map. This paper presents the results of extensive tests carried out on a variety of gas turbine combustor designs. Both test stand and field test data are presented. The usual fuel in the tests is methane; however, some data are presented for combustion of No. 2 distillate oil and intermediate Btu gas fuel. Similarly, the usual inert injected is steam, but some water injection data are included for comparison. The results support the conclusions: 1. Steam and water injection suppress NO_x exclusively through thermal mechanisms, i.e., by lowering the peak flame temperature. 2. Design changes have little effect on NO_x suppression effectiveness of steam or water in jet-stirred or swirl-mixed combustors. 3. Primary zone injection of steam in methane-fueled, jet-stirred combustors is equally effective whether the steam enters with an air stream or with the fuel stream. 4. Water-to-fuel ratio corrected to equivalent energy content correlates NO_x suppression effectiveness for turbulent diffusion flame combustors.