Reduction of the flue gas recirculation rate in oxycoal processes by means of non-stoichiometric burner operation

Non-stoichiometric burner operation in oxycoal processes has been proposed as a means to control flame temperature and heat exchange on admissible levels similar to air combustion when reducing the recirculation rate i.e. increasing the oxygen concentration in the oxidizer. Thus, the additional energetic and tangible expenditure of oxyfuel operation compared to conventional air firing can be lowered. Non-stoichiometic burner operation leads to gradual release of combustion enthalpy. On this way lower (adiabatic) flame temperatures are achievable compared to stoichiometric combustion. By combining two or more burners in over- and sub-stoichiometric operation global stoichiometries between λ = 1.10-1.15 and low oxygen concentrations at the combustion chamber outlet are adjustable.In this work the theoretical foundation of staged combustion is presented. Results from measurements on a single flame are given which indicate the controllability of the flame temperature by varying stoichiometry. Gas species concentration profiles normal to the flame axis have been taken. Images obtained from an optical flame surveillance system allow for the visual interpretation of flame stability and shape.