Numerical and experimental study of methane and propane flames in relation to gas flaring.

This research is concerned with the application of experimental and numerical methods to the investigation of gas flares. Gas flares are ubiquitous in the oil and gas industry and knowledge of the emissions from flares are of vital importance. Also, flares subjected to a cross-wind behave differently from flares in quiescent atmosphere and the stability of flares are important due to the possibility of blow offs in strong cross-winds. Natural gas flares are common on oil and gas production fields and given that natural gas is predominantly methane, many researchers have carried out numerical studies on methane cross-flow flames. In the present study, a propane cross-flow flame has been numerically investigated in addition to the investigations on methane and the predicted results have been compared against experimental data. The first chapter presents an introduction to the topic of gas flares and also outlines the objectives of the project. The second chapter presents a review of the literature on related topics. The third chapter presents the methods of investigation employed in this thesis. The fourth, fifth and sixth chapters present the results of the investigations carried out while the final chapter gives the general conclusions and suggestions for future investigations. The numerical aspect of the work investigates the capability of the existing codes in the ANSYS Fluent software to predict propane flares both with and without cross-flows. Comparisons have been made between the non-premixed and the partially premixed combustion models in their capability to predict wake-stabilized cross-flow flames. Also, the results obtained using the Reynolds stress turbulence model was compared against the Large Eddy Simulation technique with the latter showing better predictions for the temperature and species. The reaction mechanism of Ranzi et al. (2012) was used to model the kinetics of the propane reactions while the GRI 3.0 was used to model the kinetics of the methane reactions. Soot in the propane flame was modelled with the Moss-Brooke-Hall model. The experimental aspect of the work involved comparing the lift-off behaviour of the methane and the propane flames given the effect of lift-off on the emission from the flames.