Computational fluid dynamics for a non adiabatic flame fed with gas turbine flue gas, using the CFI reaction progress model
In a combined cycle, the gas turbine will produce an outlet stream, which contains approximately 15% oxygen . To decrease the amount of oxygen in the flue gases, a co-firing burner is necessary, which burns the 15% oxygen mixture. This second combustion step ensures that the oxygen level is reduced to 3% at the outlet of the combustor, without significantly increasing the NOx emissions.
For the application of a small steam boiler, a co-firing burner is designed with axial vanes for flame stabilization. The pressure drop of the co-firing burner is minimized.
The combustion performance of the axial swirler burner are explored using the CFI reaction progress model, which is developed at the University of Twente. The Flamelet-Generated Manifolds technique is used to calculate the flow properties in the 3D domain downstream the co-firing burner. Since the influence of heat loss on the production of NOx is significant, the model was extended with a transport equation for enthalpy. A source term for radiation is added to this transport equation, because the radiation strongly influences the temperature inside the combustor. The NOx emissions of the co-firing burner are estimated using the Zeldovich mechanism.
The performance of the CFI reaction progress model is compared with predictions of the Burning Velocity Model, as available in ANSYS CFX.