A theoretical method is presented to investigate the combustion and the NOx formation behaviors of fuel-staged combustor currently adopted in gas turbine power systems. In the present analysis method, the combustor is considered to comprise the swirler zone, the primary zone, the recirculation zone, the secondary zone and the dilution zone are approximated by well-stirred or plug-flow reactor models. Combustion and NOx formation in each reaction zone are analyzed by incorporating the reactor model with methane gas chemical kinetics and Zel'dovich thermal NOx mechanism. The amount of recirculation flow to swirler zone is estimated through empirical correlation expressed in terms of the temperature at the primary reaction zone, the temperature and injection angle of cold air entrained into secondary zone.Based on the present analysis method, parametric studies have been attempted to achieve low NOx gas turbine combustor design by varying the fuel split ratio at each reaction zone. The present analysis method reveals that the fuel split ratio at each zone significantly affects combustion mode transition which, in turn, leading to the variation of NOx emission level in the combustor. Optimal fuel distribution scheme can be found to minimize the NOx formation of the combustor with fixed total fuel consumption. In additions, effects of changing stream injection location on Nox reduction are examined quantitatively when stream is injected into the combustor to reduce NOx level.
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