Effects of Diluent Gases on Combustion of Coal Gasification Gas: Comparison Between N₂ and CO₂ Dilutions

Combustion properties of coal gasification gas with CO₂ dilution were investigated for a newly proposed IGCC power generation system with CO₂ capture. In this system, the gasification gas was burned under high CO₂ concentration atmosphere. In order to clarify the properties of the flames under such atmosphere, the laminar and turbulent burning velocities were investigated for outwardly propagating stoichiometric H₂/O₂/CO₂ and H₂/O₂/N₂ flames under the two conditions, 1: the same amount of diluent of CO₂ or N₂, 2: the constant flame temperature irrespective of diluents. Under the condition1 of the same amount of diluents, the unstretched laminar burning velocities, u_l of CO₂ diluted flames were smaller than those of N₂ diluted flames. The ratios of the turbulent burning velocity at the flame radius 30mm, u_tn(30mm) to u_l of the CO₂ diluted flames were found to be larger than those of N₂ diluted flames. Under the condition2 of the constant flame temperature, it was set to 1300, 1500, 1700, and 2135 degrees Celsius. At the flame temperatures except for 2135 degrees Celsius, u_l of CO₂ diluted flames were slightly smaller than those of N₂ diluted flames. The ratios, u_tn(30mm) / u_l of CO₂ diluted flames were larger than those of N₂ diluted flames. Increase in the turbulence Karlovitz number and decrease in the Markstein number by the CO₂ dilution might cause the increase in u_tn(30mm) / u_l of CO₂ diluted flames in both conditions.