Effect of multi-tube injector geometry on flame stability and NOx emission in a high pressure gas turbine combustor

Future generation gas turbine combustors for power production are expected to have the capability of operating on high hydrogen content fuels. To ensure the implementation of high hydrogen content (HHC) fuel in a power generation unit without negotiating with operational or emission advantages, the study of the flame stability regime and behavior of (HHC) fuel under gas turbine condition leads to the necessity of the development of an optically accessible high-pressure combustor. This dissertation first presents the design of an optically high-pressure combustor facility based on 500 kW power and 1.5 MPa pressure which is the representative pressure of a real gas turbine. The combustion chamber is designed to accommodate multiple geometrical configurations including a non-swirl stabilized and center-body stabilized swirl flow. The combustor is made of stainless steel 410. It has four primary modular parts: outer stainless steel chamber, inner quartz chamber, front cap and end cap. It has three optically accessible windows and three instrumentation ports for a broad range of investigation techniques. Finite element analysis has performed to get the wall thickness. The test chamber is also fitted with a variable area flow restrictor to control the desired pressure across the combustion chamber. Cooling system is also included in the design to extract heat and avoid structural failure. The outer stainless steel chamber will be equipped with copper coiling using cooling water as a driving fluid and inner quartz chamber will be convectively cooled using nitrogen. The use of a variable throat area restrictor, multiple cooling systems, as well as removable modular sections and optical access will allow the combustor to be compatible to work in a wide range of operations and have the flexibility operating with variable syngas compositions. This will allow analysis of the flame stability, flow field characterization, pollutant emissions in high hydrogen content fuel under realistic gas turbine conditions. The ignition and control systems of this high pressure combustor have also been developed in the present work. LabVIEW was used as the controlling interface that controls the proportional valves, and solenoiod valves. A modified spark plug was used as an ignition source. In order to ignite the main fuel-air stream, a diffusion flame was used. Functional test of the equipment, leak test and pressure testing were carried out prior to conducting the ignition experiments. The system has the capability to withstand the maximum pressure allowed by the air compressor which is 758 kPa. The high-pressure combustion chamber design allows for testing in realistic gas turbine conditions. Fuels that show promise as an energy source are high-hydrogen content fuels derived from coal which have a much higher specific heat, higher diffusivity, flammability limits and higher laminar flame speed compared to other hydrocarbons. These properties induce flame flashback especially when the hydrogen content in the fuels is high. A multi-tube injector has been designed to mitigate the flashback of high hydrogen content fuel. The present work studies the blowout characteristics of syngas mixtures emitted from a novel multi-tube injector. Compositions are varied for syngas from 10% to 30% hydrogen concentration by volume in carbon monoxide (CO). Three different conditions were tested for these compositions: 1) where jet velocity was greater than the laminar flame speed 2) where the jet velocity was equal to the flame speed and 3) where jet velocity was less than the laminar flame speed. Results were used to model the blowout behavior of the designed injector. The critical velocity gradient gB which was defined as the ratio of laminar burning velocity to blow-off distance was used to make a correlation between blowout behavior of different syngas compositions. A dimensionless parameter, Peclet number, was used to capture the blowout characteristics of the injector. Results showed that the degree of blowout tendencies decreased with increasing hydrogen concentration for this multi-tube injector. The Peclet model showed a good agreement yielding approximately similar correlation constants for different syngas compositions at different conditions. A cold flow numerical simulation of the designed multi-tube injector was also done to characterize the fluid flow behavior of the injector and assist in the present and future design of similar injector systems. Also presented in this paper is a numerical simulation of NOx emission. The models used for syngas fuel combustion consist of the k-&egr; model for turbulent flow, mixture fractions/PDF model for partially premixed premixed gas combustion, and P-1 radiation model. Numerical results revealed the flame location and maximum NOx emission values of 4, 42 and 52 ppm were measured at an equivalence ratio of 0.5, 0.75 and 1 respectively