Impact de la composition du syngas sur la vitesse de flamme et la stabilité du front de flamme

Abstract

The integrated gasification combined cycle (IGCC) technology is considered by many electric power generation companies as a possible replacement for the current coal power plant technologies. The IGCC uses the synthetic gas (syngas) released during the gasification of coal or biomass to produce electricity through a gas turbine. Syngas is ideally a mixture of H2 and CO, but also often contains CO2 and CH4. Therefore, the objective of this thesis is to characterize the impact of the composition of the syngas on the laminar flame speed of the flame front and on the onset of cellular instabilities. To achieve this goal, experimental measurements were performed. It was found that laminar flame speed increases with increasing H2/CO ratio, while CO2 dilution or CH4 addition decreased it. The location of the maximum flame speed shifts to leaner mixtures with increasing H2/CO ratio or addition of CH4 because the flame speed of H2 and CH4 peak in leaner mixtures. The location of the maximum flame speed is also shifted towards leaner mixtures with the addition of CO2 due to the reduction of the adiabatic flame temperature. Comparison between experimental and numerical results shows a better agreement using a modified GRIMech 3.0, especially for H2/CO/CH4 mixtures containing between 1% and 40% CH4. A correlation, based on the experimental results, is proposed to calculate the laminar flame speed over a wide range of equivalence ratios, inlet temperatures, and fuel content. However, the onset of cellular instabilities causes the self-acceleration of the flame, which hence becomes faster than the laminar flame speed. One of the main parameters controlling the onset of cellular instabilities is the Lewis number. This thesis presents a three-step methodology for the calculation of the Lewis number of syngas. The methodology is validated by comparison with experimental results for H2/CO, H2/CH4, H2/CO/CH4 and H2/CO/CO2 fuels. Following the choice of the methodology for the calculation of the Lewis number, a study is performed to investigate the impact of the addition of CO2 or CH4 on the onset of instability in syngas. The addition of CO2 in syngas has no impact on the onset of cellularity since the promotion of instability through a decrease of Le is counterbalanced by the increase of the flame thickness. The addition of CH4, however, slows the onset, as the flame thickness is increased while Le remains stable. It was observed that the apparition of cells causes the self-acceleration of the flame, but does not lead to self-turbilization. This thesis shows that the self-acceleration coefficient of a flame can be used as a criterion for the identification of the nature of the instability. Finally, a correlation is proposed in order to predict the onset of cellular instabilities based on the hydrodynamic and thermodiffusive mechanisms.

Date	2 Jun 2017
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Patrice Seers (Supervisor)