Numerical analysis of the combustion behaviour of coal gases in a gas turbine model combustor

In this thesis, combustion and emission characteristics of coal gases are numerically investigated in a model gas turbine combustor. In addition, Energy and exergy analyses of the existing gas turbine were performed in this study. Gas turbines are generally operated using natural gas and the major component of natural gas is methane. Within the scope of this study, the pure methane as baseline fuel was firstly modelled. Then, coal gases, which are called coke oven gas, town gas I, town gas II, water gas and generator gas, were modelled under the same operating conditions. These operating conditions were two different heat powers (40 kW and 60 kW) and excess air ratios (?=1,1, ?=1,3 ve ?=1,5) and two type model combustors were performed for numerical simulations. The combustor was modelled firstly as 3-dimensional and then 2-dimensional and axisymmetrical. Modelling has been performed by using ANSYS Fluent CFD code. Mathematical models used in this study include the k-? model of turbulent flow, the PDF/Mixture Fraction model of non-premixed combustion (turbulent diffusion flame) and P-1 of radiation model. Predictions were evaluated in terms of combustion and emission characteristics. In comparision with methane, the best predicted temperature levels were for coke oven gas, town gas I and town gas II. The other fuels comprise lower heating value. For this reason, the predicted temperature levels were also lower. When emissions were evaluated for coke oven gas, town gas I and town gas II, the combustion characteristics were not satisfactorily good in that excessive NOX in accordance with methane was emitted. But, this problem was achieved supplying by dilution air to the combustor. After this process, the combustion performances of these coal gases were better than the combustion performance of methane in terms of NOX formation at ?=1,5 combustion conditions anymore. Moreover, CO and CO2 were evaluated for all gases. CO including in coal gases were burned throughout the combustor and it was not predicted at the combustor exit. CO2 formations for all coal gases generally was near the metane at the combustor exit.