Design And Performance Analysis Of A Gas Turbine Dry Low NO_X Combustor

DLN(Dry low NO_X) combustion technologies are used in gas turbine to meet the even more strict criteria for pollutant emission, and the DLN combustors of heavy-duty gas turbine widely adopt lean premixed multi-nozzle combustion to realize fuel staged, stable combustion, load adjustment and pollutant emission control. This paper analyzed the different design requirements of DLN combustor and diffusion combustor. Based on the typical characteristics used in the advanced DLN combustors, the design principles of fuel staged, premixing uniformity, combustion stability and cooling technology used in the advanced DLN combustors were studied from angle of structure. Then according to the inlet and outlet parameters and the overall design requirements of the combustor, the overall scheme and the components of swirler, nozzle, combustor liner and transition piece are designed by using lean premixed multi-nozzle combustion. The combustion system of the unit is composed of 20 can-type combustors, each combustor contains 6 identical nozzle assemblies. The function of diffusion combustion, partial premixed combustion and fully premixed combustion can be realized by a single nozzle. Also the plan of fuel staged was proposed based on the requirements of load adjustment and pollutant emission.Numerical simulation was applied to study the performance of the designed combustor at rated load, and the velocity distribution, temperature distribution, component distribution and multiple-swirls interaction in the combustion chamber were analyzed. Results showed that maximum non-uniformity ROTDF=0.034, NO_X and CO emission was 5.26×10-6(15%O2) and 2.12×10-6(15%O2), combustion efficiency η =99.62%, total pressure recovery coefficient σ=0.968. All parameters reached to the design requirements.The numerical simulation of designed combustor in the diffusion combustion mode at 95% speed and in the pilot premixed combustion model at 25% load were carried out. Compared with the premixed combustion mode under rated load, NO_X emissions of the two combustion modes at low operating condition increased. And maximum non-uniformity of outlet temperature in the pilot premixed combustion model became large due to the uneven distribution of flame. The combustion efficiency of all combustion modes were all above 99%. The total pressure recovery coefficient increased with the increase of load.Finally, the effects of the outlet angle of swirler blade, the fuel injection holes diameter and arrangement of the fuel injection holes on the premixing uniformity and NO_X emission were discussed: The increase of outlet angle could intensify premixing, reduce NO_X emission and maximum non-uniformity of outlet temperature, but flashback would occur if outlet angle was too large; Decrease of the fuel injection holes diameter, using big-small holes and dislocation arrangement could effectively improve the premixing uniformity and lower NO_X emission. Research work above could offer some reference for preliminary design and optimizing of the heavy-duty gas turbine DLN combustor.