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.