Research On Syngas Coaxial Jet Diffusion Flame Stability Under O₂/H₂O Condition

With environmental issues and global warming intensifying, countries focused on the development of advanced power generation technology with CO₂ capture and storage technologies（CCS）. Our research group proposed an Oxy-coal Combustion Steam System of Near-zero Emissions（OCCSS） based on the Clean Energy System（CES） technology, having a high power generation efficiency to achieve CO₂ capture sequestration and enhance oil recovery（EOR）. The OCCSS system used methane or syngas as fuel, oxygen and water vapor as oxidant. The combustion environment of OCCSS had a characteristic of high temperature, high pressure, high oxygen, high concentrations of water vapor concentration. According to the extream combustion condition, the paper experimentally studied the stability characteristics of syngas coaxial jet diffusion flame under O2/H₂ O atmosphere.The existing researches usually adopted air as oxidant, the paper mixed water vapor with oxygen as oxidant. The paper designed coaxial jet flame burner, verified the reliability and accuracy of the test bench. The burner can provide adequate and uniform O2/H₂ O oxidant atmosphere for the study of flame stability. On this basis, the paper studied the influences of syngas component 、 water vapor concentration 、 preheat temperature and diluent on the flame stability.Experiment results showed that the base of the CO flame existed quenching distance, and could not produce a stable lift-off flame, but blowoff directly from the nozzle. In all experimental conditions, CO/H₂ flame were unable to achieve stable lifting flame under O2/H₂ O atmosphere. With the increasing of hydrogen concentration, the syngas flame blow-out velocity grew more rapidly, the length of flame reduced and the flame propagation velocity increased. It attributed to the good reactivity, higher flame propagation velocity and high diffusion coefficient of hydrogen. Flame blow-out velocity decreased with the increasing concentration of water vapor（50%-90%）. When the water vapor concentration is greater than 70%, the flames blow-out velocity decreased very rapidly. This was due to the chemical and thermodynamic effects of water. High concentrations of water vapor absorbed much heat from reaction zone, changed the transport properties and involved in chemical reactions, but also had a high radiation characteristic. High preheat temperature changed the thermal physical property parameters and reactivity of fuel gas, created a favorable environment for combustion, greatly promoted the flame stability.CO₂ and N₂ were used to dilute the fuel respectively, compared to N₂, flame blowout limit decline more obvious when diluted with CO₂. There are different thermodynamic parameters and transport characteristics between CO₂ and N₂, meantime, CO₂ participated in the reaction and inhibited the positive reaction. After comparison and analysis the stabilization of CO/H₂ flame in O2/H₂ O 、 O2/N₂ 、 O2/CO₂ atomsphere respectively, the result showed that flame stability characteristics had big difference under the different CO/H₂ ratio. In the high CO concentrations（greater than 90%）, CO/H₂ mixed gas has highest blow-out limit in O2/H₂ O conditions. when CO concentration is less than 85%, the stability of the syngas in the O2/N₂ atmosphere is the best, O2/CO₂ atmosphere is the next, O2/H₂ O atmosphere is the worst. This is because H₂ O promoted to combustion in high concentrations of CO.Near the ultimate blow out velocity, The pulsation of flame base change the flow field, species concentration distribution、heat release、stretch,resulting in flame local quenching and aggravating the flame instability disturbance. When transition to turbulent flame, flame structure, combustion intensity, flame propagation velocity had a greater change, high intensity turbulence easily led to local flame extinguished, resulting in an unstable flame.