Flowfield Effects on Distributed Combustion for Clean Gas Turbines

Abstract

Swirling distributed combustion has been shown to offer substantial performance improvement of gas turbine combustors with uniform thermal field in the entire combustion chamber (improved pattern factor), ultra-low emission of NO x and CO, low noise, enhanced stability, fuel flexibility and higher efficiency. Critical factors in achieving distributed combustion are controlled mixture preparation and flame anchoring prevention. Controlled mixing between the injected air, fuel and hot reactive gases from within the combustor prior to mixture ignition is vital. The mixing process impacts spontaneous ignition of the mixture to effect improved distributed combustion reactions. Near Zero emissions of NO and CO have been demonstrated using methane under distributed combustion conditions at heat release intensities of 22-36 MW/m 3 -atm, that are commensurable to current stationary gas turbine applications. In this paper, distributed combustion is further investigated to achieve distributed reaction conditions through variation of air injection velocities with emphasis on pollutants emission and combustor performance. The isothermal flow field is examined using Particle Image Velocimetry (PIV) to determine key features associated with the flowfield that emanate from change in injection velocity. The obtained flow field characteristics are coupled with combustor performance in terms of pollutants emission and stability. Results obtained from isothermal PIV experiments showed that higher injection velocity offered higher recirculation ratio inside the combustor with overall higher turbulence. Measured pollutants emission demonstrated that increase in injection velocity decreased NO emissions by some 20%-48% with minimal impact on CO emission. Near distributed combustion conditions with less than 4 PPM NO was demonstrated with an injection velocity of 46 m/s at a heat release intensity of 31.5 MW/m 3 -atm at rather high equivalence ratio of 0.7 using standard inlet air temperature. NO emission was decreased by 20% to 3.2 PPM at high injection velocity under the same operating conditions. Up to 48% reduction in NO emission was also demonstrated under preheated inlet air conditions where the injection velocity was further increased to result in 2 PPM NO at an equivalence ratio of 0.5. Further reduction of NO x is expected with improved distributed combustion condition.