Oxy-fuel combustion for carbon capture using computational fluid dynamics

The combustion of fossil fuels, in particular coal, meets the majority of energy demand worldwide, but produces carbon dioxide, which is believed to be the main cause of climate change. Since the majority of energy comes from coal-fired power stations, the deployment of carbon capture and storage (CCS) technologies, which remove the CO2 by either utilisation or storage, are necessary to mitigate climate change. Oxy-fuel combustion is one of the leading options for CCS. The fuel combusts in a mixture of oxygen and recycled ue gas, rather than in air and the change in the oxidiser environment poses questions relating to combustion characteristics such as heat transfer, emissions and burnout. To gain a further understanding of the process, the use of modelling and simulation techniques can be employed and in this thesis, Computational Fluid Dynamics (CFD) is used to model air and oxy-fuel environments using advanced combustion sub-models. An in-house Large Eddy Simulation (LES) CFD code has been updated to include models suitable for the prediction of NO. The model is verified and compared against available experimental data for three cases involving methane, coal and oxycoal combustion. Advanced simulations of a 250 kWth combustion test facility (CTF) are validated against experimental measurements of air-coal combustion. The geometry set-up and simplifications are discussed followed by a sensitivity study of grid refinement, turbulence models and approaches in modelling gaseous radiative properties. The validated CFD simulation of the facility were then numerically examined under a number of oxy-fuel environments. Finally, CFD simulations were performed on a full-scale utility boiler at 500MWe to examine the effects of firing coal and biomass under air and oxy-fuel environments. This included an assessment of the heat transfer as a method of addressing the performance of the boiler under these conditions.