Browsing by Author "Kapadia, Bhavin K."

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Open Access
Experimental study of oxyfuel combustion for stationary gas turbine applications
(Stuttgart : Deutsches Zentrum für Luft- und Raumfahrt, Institut für Verbrennungstechnik, 2017) Kapadia, Bhavin K.; Aigner, Manfred (Prof. Dr.-Ing.)
Oxyfuel combustion is a concept proposed for the implementation of carbon capture and storage (CCS) technologies in coal and gas turbines power plants to prevent emission of carbon dioxide into the atmopshere. In order to apply the concept to gas turbines power plants, they have to be modified or alternatively new cycles need to be developed for using this concept. Amongst the different cycles proposed those involving oxygen and carbon dioxide as working fluid offer simplicity of design together with promising carbon capture and cycle efficiencies. New burners need to be designed for use in such oxyfuel gas turbines. The combustion characteristics of such burners would strongly depend on the proportion of oxygen and carbon dioxide in the oxidizer. In this work oxyfuel combustion with a mixture of oxygen and carbon dioxide as oxidizer has been studied experimentally using a well-researched methane-air swirl burner with an optically accessible combustion chamber. Partially premixed swirl stabilized oxyfuel flames have been investigated using optical measurement techniques at atmospheric and elevated pressure conditions. The effect of changing parameters such as carbon dioxide dilution, flow velocity, equivalence ratio, and thermal power on flame stabilization, flow field and flame chemistry has been studied. The investigations were performed under conditions of comparable thermal power and inlet flow velocity for different carbon dioxide dilutions. A strong dependence of the flame shape and stability on carbon dioxide dilution was observed at similar thermal powers and inlet flow velocities. Flames containing less than 26 % oxygen in the oxidizer could not be stabilized, while 26 % oxygen flames showed poor stabilization over a wide operating range. Flames with 30 % oxygen were predominantly stable over a large range of operation and had a typical conical swirl flame shape. Flames with an oxygen concentration higher than 30 % showed a flat flame shape and excited thermo-acoustic oscillations. A comparison to air flame behavior showed similarity between the influences of carbon dioxide dilution in oxyfuel flames to a change in equivalence ratio for air flames. Laser Raman Spectroscopy measurements revealed that despite similar conical flame shape of 30 % oxygen oxyfuel and lean air flames, the stabilization of the oxyfuel flame was poorer due to the lower reactivity. The 30 % oxygen flame and air flames were investigated under elevated pressure conditions with a modified version of the atmospheric burner with optical access to the combustion chamber. At conditions of increased oxidizer preheat and elevated pressure an unconventional flame shape was observed, where the flame burned at close proximity to the burner plate and chamber windows. A change in burner aerodynamics at elevated pressure was identified as the cause for the unconventional flame shape. The burner design for oxyfuel gas turbines is dependent on the carbon dioxide dilution intended to be used. The investigations showed unsuitability of using partially premixed combustion for low oxygen concentrations. The high oxygen concentration flames are thought to be suitable for a staged combustion concept where the higher reactivity of such flames would be useful for pilot flame stabilization and keeping overall temperatures in an acceptable region for the gas turbine. At the end of the work the differences between air and oxyfuel combustion are summarized and an overview is presented of burner configurations favorable for use in real oxyfuel gas turbines.