Effects Of Diluents On Combustion Characteristics Of Syngas Laminar Premixed Flames At Elevated Temperatures And Pressures

Currently, coal gasification technology and Integrated Gasification Combined Cycle (IGCC) play an very important role in developing clean coal combustion technology. The main components of synthesis gas (syngas) from coal gasification are H2 and CO, and dilutions such as N2, CO2 and H2O etc. However, subject to the different gasification sources and procedures, the syngas composition changes significantly, which brings the trouble for the combustor design of syngas gas turbine and impedes the wide usage of syngas. Therefore, it is essential to study the syngas combustion characteristics at different conditions, especially at high pressure and temperature conditions which near operating conditions of gas turbine combustor. The main content of the present work is to study the effect of dilutions (CO2, H2O) on the syngas combustion characteristics at elevated pressures and temperatures.The experiments of the present work were conducted by a developed dual-chambered, pressure-release type spherical flame apparatus. First, the sealing washer, ignition electrode, heating method and pressure reliever of the experimental apparatus were modified and improved for the accurate measurement of syngas laminar flame speeds and Markstein lengths at elevated pressures and temperatures. Then the laminar flame speeds and Markstein lengths of H2/CO/CO2/air(O2/He) mixtures were measured at normal and elevated pressures and initial preheat temperatures for different CO2 dilution ratio; the laminar flame speeds and Markstein lengths of H2/CO/O2/CO2 mixtures were measured at normal and elevated initial preheat temperatures for different CO2 dilution ratio. It was found that the laminar flames speed was significantly reduced by CO2 dilution, and the laminar flame speeds of H2/CO/CO2/air(O2/He) mixtures decreased linearly with increasing CO2 dilution ratio. The Markstein lengths decreased with increasing CO2 dilution ratio and pressure. At low or high CO2 dilution ratio, the Markstein lengths decreased or increased with elevating temperature separately. Experimental results were simulated by PREMIX code using three kinetic mechanisms (Davis, Li and Keromnes mechanisms) for syngas oxidation in the literature. It was found that the Davis mechanism predicted experimental results well at normal and elevated temperatures, while the Keromnes mechanism showed a better agreement with experimental results at elevated pressures. However, differences of experimental results and numerical results were amplified with increasing preheat temperature, such as the 450 K cases in the present work, which indicated the further modification of kinetic mechanisms at high temperature.The numerical simulations of the present work were conducted to discussed the radiation re-absorption effect of CO2 dilution on syngas combustion characteristics. The variation of the chemical effect of CO2 dilution was analyzed at different conditions. Furthermore, the effect of H2O dilution on syngas laminar flame speeds at elevated pressures was discussed. Numerical results showed that the radiation re-absorption effect of CO2 dilution could preheat the preheat zone, thus relieving the radiation lose and increasing the laminar flame speed, and should be considered in numerical simulation at high CO2 dilution ratio. The chemical effect of CO2 dilution increased with increasing CO2 dilution ratio and pressure, and decreased or increased with elevated temperature at low or high CO2 dilution ratio. The chemical promotion effect of H2O dilution was reduced with elevating pressure, and the peak vale of the non-monotonic variation in syngas laminar flame speeds turned to low H2O dilution direction at high pressure.