There are three principal methods for controlling gas turbine emissions: Injection of a diluent such as water or steam into the burning zone of a conventional (diffusion flame) combustor as seen in the earlier section of this chapter. Regulations increasingly require that emissions from land-based gas turbines be tightly controlled. Figure 2.17 shows the distribution of the air in the various regions of the diffusion type combustor. Another method is to deliberately dump air overboard prior to or directly from the combustion section of the engine. 2.27. The principal features of such a combustion system is the premixing of the fuel and air before the mixture enters the combustion chamber and leanness of the mixture strength in order to lower the flame temperature and reduce NOx emission. 2.22. Reliability was not sacrificed at the expense of cost, as the fuel system incorporates a high degree of redundancy. Figure 10-47. Flow measurement standards define the location for pressure measurement relative to the restriction. Proceedings of the IEEE, Vol. Figure 10-36. Burner staging is achieved, as shown in Figure 10-53, by splitting the premix gas fuel system into two groups: A rich main burner group, which is operated in a fuel-rich and stable mode. Fuel to the secondary nozzle only. Figure 21.8. This combustion system can operate in several different modes. Figure 10-28. The flame stability is inherently greater in conventional diffusion-type combustion over a wider range of fuel-to-air ratio. Figure 10-55. Further combustion control can be provided by means of an optional bypass system that allows the amount of dilution air to be varied. Generally, the addition of dilution air is so abrupt that if combustion is not complete at the end of the burning zone, chilling occurs which prevents completion. Figure 21.24. The design of the combustor provides sufficient mixing and residence time between the two burner groups to oxidize the fuel of the staged burners in the hot combustion gases of the main burner group. The pilot fuel is injected directly into the combustion chamber with little if any premixing. The staging of DLE combustor as the turbine is brought to full power. Boyce, in Combined Cycle Systems for Near-Zero Emission Power Generation, 2012. Source: Bell, David and Brian Towler. Design of the combustor to limit the formation of pollutants in the burning zone by utilizing “lean-premixed” combustion technology. Thus, making the assumption that b=a(1+ε) and ε≪1, it can be shown that λm,0 ∼ m/R and λm,n ∼ nπ/(b − a) for n ≥ 1, provided m∼ε−1 (Stow et al., 2002). A typical single can side combustor. Note the three concentric rings of swirlers and fuel nozzles, which are used in staging the combustion as indicated in the previous sections in this chapter. Figure 10-40 is a schematic of a typical cross section of a secondary single-fuel nozzle shown in Figure 10-37. 2.24. Use of water or steam admitted with the fuel for cooling the small zone downstream from the fuel nozzle. Figure 21.19. Flashback usually happens during unexpected engine transients, for example, compressor surge. 2010. Transverse oscillations: For increasing annular combustor radius, R, the cut-on frequency for spinning modes, ωc = mc/R, decreases. Steam from syngas processing is not shown. 2009. Schematic diagram of a circulating fluidized-bed boiler. Annular Type 4. Annular DLE combustor for an aero-engine. In its simplest and most common configuration, a fuel-staged combustor has two flame zone; each receives a constant fraction of the combustor airflow. The current rating is 30200 kW with a thermal efficiency of 39 per cent.