Effects Of Tar Model Compound Toluene On Flameless Combustion Of Biomass Gasification Gas

Flameless combustion is a new type of combustion technology with uniform temperature distribution,low NO_X emission and without visible combustion flame.It can be applied to gas,liquid,and solid fuels,and pollutant emissions are far lower than traditional combustion.Biomass gasification gas（BGG）has complex composition,mixed with tar,has low calorific value,and unstable combustion.Flameless combustion can solve the problems of traditional combustion of BGG.Research on the flameless combustion of BGG is of great significance for the use of low-calorific gas and the development of flameless combustion.In this paper,the flameless combustion of tar-free BGG and tar-containing（toluene）BGG are studied by numerical simulation.Taking the burner of the test system as the research object,a numerical model based on ANASYS-FLUENT software was established.The numerical model simplifies the composition of BGG,which is called model gasification gas composed of CO₂,CO,H₂,CH₄ and N₂.The non-premixed laminar small flame surface model,and the multi-component multi-step reaction mechanism is introduced in the combustion model,and radiation effects and NO_X generation are considered.The verification results of the numerical model show that the numerical simulation results are in good agreement with the experimental results.The effects of factors such as air preheating temperature,combustion equivalence ratio,and CO₂ concentration in the combustion gas on the temperature distribution,oxygen concentration distribution,and NO_X emissions of the combustion chamber during the flameless combustion of BGG are studied.The orthogonal experiment method is used to analyze the comprehensive influence of each factor.The results show that the air preheating temperature has the greatest effect on the temperature in the combustion chamber,followed by the equivalence ratio and the ratio of non-combustible CO₂ and N₂ in the gas.With the increasing of the air preheating temperature and equivalence ratio can increase the combustion reaction rate and increase the combustion chamber temperature.It results in the increase of NO emission too.Under low-temperature combustion conditions of flameless combustion,CO burnout depends more on the mixing of fuel gas and oxygen.Increasing the equivalence ratio from 0.45 to 0.9 can increase the CO emissions.Changing from 5%CO₂+60%N₂ to 20%CO₂+45%N₂ of composition of non-combustible gas of the composition in the gas can drop the temperature in the combustion chamber by 10K.Toluene was added as a tar model compound to the BGG.Toluene-containing BGG was numerically simulated,and the toluene concentration and operating parameters were analyzed.Temperature distribution,oxygen concentration distribution,and CO and NO emissions in the flameless combustion chamber were analyzed.The results show that toluene has a significant effect on the flameless combustion of BGG.The addition of toluene reduces the temperature level in the combustion chamber and significantly reduces the emissions of CO and NO compare with BGG without toluene.Increasing the toluene concentration from5 g/m³ to 20g/m³,CO emissions were less than 5 ppm and NO emissions were less than 3mg/m³ in the combustion exhaust gas.Increasing the air preheat temperature from 400K to700K or the equivalence ratio from 0.45 to 0.9 can increase the NO emissions at the toluene concentration is 15 g/m³,but the increase is not obvious still less than 5 mg/m³.The CO emissions are less affected by the air preheating temperature,but the CO emissions increase rapidly at the equivalence ratio is 0.9.