The Laminar Premixed And Non-premixed Combustion Characteristics Of N₂ Diluted Syngas Flames Investigated By PLIF And CHEMKIN Simulation

Accompany with the rapid development of the world economy,the issue of environment pollution and energy lacking grown serious day by day,as a result,the demand for a clean and sustainable energy is increasing gradually.Recently,the development of IGCC technology call tremendous attentions,thus the syngas which produced by gasification process of coal and biomass has more broad application prospects.However,the various row materials for gasification process contribute to complex components of the syngas,which adds the difficulty for its industry application.So,It is necessary to study the combustion characteristics of the syngas,in order to have a better use of the syngas.As a fact,both premixed and non-premixed combustion are significant combustion method in the gas turbine of IGCC plants.Thus this context is mainly about the combustion characteristics of the syngas with these two methods.As to premixed combustion,the flame structure and the distributions of OH radicals were both studied.And a new method which called slope averaging method was proposed to calculate the burning velocity of the syngas.For further studying the influence of the Nitrogen in the combustion process,various proportion of N2 were adding to the syngas.Simulations were conducted with CHEMKIN to study the rate of production of OH radicals and analyze the chemical dynamics.As for non-premixed combustion,a typical Medium-Btu syngas was adopted in this research.And different fractions of N2 were adding to the Air-side and Fuel-side separately,to study the effect of dilution gas in the non-premixed combustion.Simulations were also conducted with CHEMKIN to study the formation of OH radicals and pollutant of NOX.The results concluded from premixed combustion can be:(1)When the equivalence ratio keeps constant,the height of the inner flame and the superficial area of the flame front are increasing with the increase proportion of the N2,but the flame height and width will go shrink.(2)The results calculated by three methods fits well,but the slope averaging method performs the same accuracy as the flame surface area method and superior to the cone angle method.(3)The slope averaging method has its unique advantages to consider the speed attenuation by correcting U0.Thus,the results in speed attenuation area are more precise.(4)It is known from the chemical dynamic analysis that the dominant reactions on the formation and consumption of OH radicals are R38(H+O2=O+OH)and R84(OH+H2=H+H2O),and these two reactions are most sensitive to addition of the N2.The results concluded from non-premixed combustion can be:(1)With the increase ratio of N2 dilution,the whole height of the flame turns to shrink.And N2 dilution is effective to inhibit the formation of the Local High-Temperature Region.(2)It is known from the OH-PLIF images,the concentrations of OH radicals increase firstly and then decrease with the increase of excess air coefficient when the XN2 keeps constant,and the effects of OH radical concentration decline are more obvious in the way of fuel-side dilution at the same excess air coefficient.(3)The chemical kinetic analysis indicate that the OH radicals play an important role on the formation of NOX.Comparing with two dilution methods,the fuel-side dilution is superior to air-side dilution on reduction of NOX emission in syngas non-premixed flame.