Investigation Of Pressure Effects On Combustion And Emission Characteristics Of Syngas Turbine Combustors

Integrated Gasification Combined Cycle (IGCC) power generation is an important clean coal technology, and the syngas fueled heavy duty gas turbine is its core equipment. Syngas characteristics of hydrogen-rich and component variation will bring problems in flame stability, high emissions and liner temperature controlling. Meanwhile, to improve efficiency by continuous increases of the compressor pressure ratio and the combustor outlet temperature is an important direction of gas turbine development. Therefore, the combustor working in the environment of high temperature and high pressure is the key technology of IGCC system that needs to break through. The operating pressure affects the flame structures, heat transfer and chemical reactions, resulting in that the combustor characteristics such as wall temperature and emissions change with pressure. In this thesis, the numerical simulation method is established and validated for high-pressure syngas combustor based on the combustion and flow characteristics. Using experimental and numerical methods, the pressure effects on the flame structure, wall temperature, heat transfer, and pollutant emissions are studied deeply from three different levels of the concept burner, the model combustor, and the full-size combustor. The main work is drawn as follows:(1) A CFD numerical method for syngas combustor is developed and validated based on model combustor verification experiments and open literature data. Based on the governing equations, the models, solving methods, and property fitting formulas suitable for high pressure combustors are chosen. Public data of experiments which have similar flow pattern as in our combustors are used for comparison, and the turbulence models are screened and modified. The combustion model and the chemical kinetic scheme are validated at high pressure through a series of open and experimental data. Thus complete CFD method is established. And then, the performance of the CFD method is validated by combustor verification experiments.(2) Pressure effects on flow field, mixing, species and temperature distribution in the combustors are numerically and experimentally studied. The variations of the reaction heat release and the adiabatic flame temperature of syngas with pressure are investigated by the reactor model. The non-reacting flow field and OH* are measured on the transparent combustor, and the pressure effects are numerically studied on the transparent combustor, the model combustor and the R0110 combustor. It shows that the position of peak flame temperature moves towards downstream as the operating pressure increases. When Re is higher than 105, the flame shape is similar under different pressures. The peak flame temperature increases with pressure and keeps relation with pressure as Tpeak～p0.04. The peak flame temperature could be considered independent on pressure when the operating pressure is high than 0.5 MPa.(3) The pressure effects on liner temperature of the model combustor and the R0110 combustor are numerically and experimentally studied. The computational data are further analyzed to reveal the variation of heat flux, convection and radiation with pressure. It shows that, when pressure increases, the liner area near air holes cools down but the diffusion liner area heats up due to lack of cooling holes. The relationship of the peak liner temperature with pressure keeps approximately Tmax～p0.06. When Re is higher than 105, the convection is nearly independent on pressure. When pressure is higher than 0.5 MPa, liner radiation tends steady.(4) CRN models are established and validated for the model combustor and the R0110 combustor. Pressure effects on emissions are studied through the CRN modeling and the transparent combustor experiments. It shows that NOx emissions keep a power-law with pressure in the full pressure range up to 2.0 MPa when Tad,full is higher than 1800 K. However, when Tad,fuli is lower than 1800 K, NOx emission shows parabolic profiles with pressure. It is mainly because thermal NOX dominates the emissions at former condition, but the N2O type NOx contributes the most under latter condition. CO emissions also keep a power-law with pressure in general. Reducing the NOx contribution ratio of thermal/N2O could be helpful to control the emissions at high pressure. Therefore, premixed and mild combustion is suggested for NOx emissions controlling at elevated pressure. Converting rate of NH3 is suppressed at high pressure, and NH3 can obviously shift the emission behaviors at elevated pressure.Above all, the flow and thermodynamics requirements should be satisfied to meet the scaling criterion of the flame structure to high pressure. For fluid mechanics, when Re is higher than 105, the flame shape is similar under different pressures. As for thermodynamics, the peak flame temperature could be considered independent on pressure when pressure is high than 0.5 MPa, since less than 1% of the temperature is increased by per 0.1 MPa pressure rise.