Numerical Investigation On Combustion Flows And Pollutions Of Dual-Fuel Combustor In Gas Turbine

Chemical recuperated technology is an advanced cycle technology of gas turbine. It can turn the mixture of oil and high temperature steam into pyrolysis gas which is rich of H₂, CO, CH₄ etc. by making use of the exhaust heat to heat the oil and water. This method requires that the liquid-oil fuel should be used in the first stage of combustion, and the gas fuel should be used after liquid-oil has been changed into pyrolysis gas. Then the key of the method is that the combustor should be able to burn the two different fuels respectively or together. It has been a focus for higher combustion efficiency, lower NOx emission and widely flexibility of fuel etc. So it is important for popularizing the chemically recuperated technology and directing the design of combustor to research duel-fuel combustion of gas turbine deeply.In this dissertation, the present situation about designing methods of combustors, experimental analytic means and numerical simulation of combustion flows were introduced. And the properties of pyrolysis gas were analyzed. And reaction models, math-physical methods and numerical simulation technologies were described in details. The RNG k ?εmodel for turbulence, Mean Mixture Fraction/PDF model and finite-rate Eddy-Dissipation-Concept model for reaction, spray model for atomization of liquid and the SIMPLEC algorithm were applied to predict the different combustion flows with different load. At the same time, the flows in the prototype combustor and the duel-fuel combustor with single fuel, and the mixed combustion flows with duel fuels in duel-fuel combustor under an experimental condition including NOx emission were calculated respectively.According to different results, the relationship of performances of combustors between different load and different fuels, and the distributions of air in the flame chamber, and the relationship between performances of combustors and different diameters of primary holes and dilution holes were studied. Under the condition of experimental parameters, the characters of combustion with mixed fuel were analyzed with different ratios of fuels. The research was supported by the following conclusions: 1) multi-point distributed duel-fuel nozzle was designed, and it could suffice for the combustor of the Chemical Recuperated Gas Turbine; 2) energy saving target was beyond 26.7% when pyrolysis gas was used under different designing standards of mass flow rate with the same exit temperature and the same fuel inlet enthalpy of duel-fuel combustor; 3) the combustion efficiency was elevated with the increasing load; 4) the flame temperature, NO_x emissions and the uniformity export temperature would be decreased with steam-inject and pyrolysis gas, but the combustion efficiency of pyrolysis gas would decrease slightly because of lower flame temperature than that of oil as well. However the combustion efficiency could increase when some oil fuel was added in pyrolysis gas as mixed combustion; 5) reducing the diameter of primary and dilution holes would enhance the resistance loss. Reducing the diameter of primary holes would reduce the uniformity of temperature in outlet, and reducing the diameter of dilution holes would reduce the emission of NOx when pyrolysis gas was burned; 6) there was an off-center phenomenon in flame zone of the original duel-fuel combustor, and it could be amended with reducing diameters of 6 holes of combustor. So the structure with 6 smaller holes was recommended for duel-fuel combustor of CRGT.Innovations of this dissertation were: 1) it was first time to study mixed combustion flows with the duel fuels in the gas turbine with numerical simulation method and EDC reaction model. And disciplinarians between components of pyrolysis gas and performances of combustor were gained; 2) the mass flow rate of pyrolysis gas was gained under different conditions of combustor. It provided a reference for fuel system of CRGT; 3) the structure of duel-fuel combustor was designed through optimizing the combustion flows. The series of research work provided a reference to further develop the structure design, experiment, optimization, and combustion mechanism of dual-fuel combustor.