Numerical Investigation of Char Reactivity in Oxy-Coal Combustion in Carbon Capture and Sequestration Technologies

Oxy-coal combustion with CO2 capture from flue gas is an emerging technology that can be adapted to both new and existing coal-fired power stations leading to substantial reduction in carbon emission from the power generation industry. However, switching to oxy-coal brings a number of uncertainties to the combustion process and there is a significant knowledge gap in this new technology. Computational Fluid Dynamic (CFD) studies can be used as one of the tool to identify the extent of the modifications required due to changes in the process. One of the possible challenges is related to the the changes in char combustion and char reactivity which may have an impact on unburned carbon in the furnace. In this study, two approaches have been undertaken to investigate the impact of oxy-coal combustion on char reactivity: simple equilibrium calculations and numerical 3-D simulations. As the focus of this study, the influence of CO2 -O2 combustion environment on char reactivity and particularly carbon in ash has been investigated. It has been found that the effect of C-CO2 and C-H2 O reactions on overall char reactivity cannot be disregarded. In addition, in this study, it is suggested that using the Langmuir-Hinshelwood mechanism can provide a more accurate prediction for the effect of gasification reactions on unburnt carbon and char reactivity. The accuracy of the CFD modeling has been investigated using experimental data from a one MWth combustion test facility. In order to improve the validity of the CFD code for design purposes, further modeling improvements for accurate predictions are addressed.