Flashback analysis for hydrogen/methane mixtures for premixed swirl combustion

The flashback problem which occurs by using lean premixed combustion in gas turbines is considered. Flashback simulation studies using CFD modelling package are performed for a wide range of hydrogen/methane (H2/CH4) blends combusted by air using a swirl burner under premixed conditions. The laminar flame speed was calculated for H2/CH4 blends from pure methane up to pure hydrogen at various pressures, temperatures and equivalence ratios. This was done by using CHEMKIN-PRO software package with PREMIX code and an algebraic expression derived by asymptotic methods incorporated with Le Chatelier's Rule-like correlation. The feasibility of using a new approximation for laminar flame speed of H2/CH4 blends based on the gravimetric mixture ratio was checked and compared with the previous calculations. The new approximation gave a good prediction at various conditions. The numerical values for laminar flame speed calculated by CHEMKIN are then fed to FLUENT CFD model to create a PDF table for turbulent premixed combustion calculations and flashback studies. Flashback limits were defined and determined for H2/CH4 blends ranging from 0% (pure methane) up to 100% (pure hydrogen) based on the volumetric composition at atmospheric pressure and 300K for various equivalence ratios. The results show that the use of up to 50% blends of methane and hydrogen causes fewer problems with flame stability and flashback compared with the use of pure hydrogen. Also, the flashback limits depend on the values for both laminar and turbulent flame speed. What emerges is the need for more theoretical and experimental research work to obtain more accurate values for flame speeds