Numerical modelling of oxy-coal combustion to access the influence of swirl strength, combustion environment and gasification reactions on the flow and combustion behaviour

Abstract

A simplified 2D axisymmetric computational fluid dynamics simulation of oxy-coal combustion is performed to address the influence of swirl strength and the combustion environment on the flow field and combustion characteristics. A quantitative analysis of the internal recirculation zone length and flame length under various operating conditions is studied by employing developed numerical models. The influence of char-CO2 and char-H2O gasification reactions on the species consumption and temperature profile is also studied through numerical modelling. The swirl strength considerably influences both the flow field and temperature profile inside the furnace. At higher swirl strength, radially dispersed shorter flames are obtained due to spreading of the secondary stream. Results showed that the flame shifted towards the burner at higher oxygen content due to rapid devolatilisation at higher flame temperature. The ignition of pulverised coal particles is enhanced at higher oxygen concentration due to increased stoichiometry near the burner. Oxy-35% O2 has 300 K higher flame temperature than oxy-21% O2. Endothermic gasification reactions significantly influence the temperature profile in the furnace. CO2-char gasification reaction has a more pronounced influence than the H2O-char gasification reaction. The consideration of gasification reactions has resulted in an approximately 5% reduction in peak temperature.