| Carbon emissions is increasingly concerned by countries as the critical factor of climate warming,zero emission power generation systems play a very important role for controlling carbon emissions.Oxy-coal combustion steam system of near-zero emissions(OCCSS)can realize efficient utilization of energy and low cost of CO2 capture.As the important source of fuel,this paper experimentally studied the stability characteristics of coflow CO/H2 diffusion flame under O2/H2 O atmosphere.Compared with other oxidizing atmosphere,analysising the effect of H2 O and H2 content on the combustion system,studying the relationship between the flame structure and stability,exploring the impact of pressure on the stability limit.This paper compares diameter blowoff velocities under the different nozzles(1mm、2mm),and analyzes the blowoff velocities changing with the H2 content.Under 1mm nozzle,the stability limits of CO/H2 were studied with various H2 content under O2/H2 O,O2/CO2,O2/N2,O2/(CO2+N2)atmospheres.Results show that the effect of H2 O on combustion stability is more sensitive,H2 O has a promoting effect on the combustion stability of the CO/H2 with the low H2 content(5%),and a inhibiting effect with the high H2 content(10%、20%),but the other three kinds of atmosphere is not sensitive to the change of the H2 content.As a result,the stability of flame can’t be judged by thermal effect、chemical effect and dilution effect for the dilute gas as the main antioxidant components of combustion systemcombustion system.The results of normalization show that,with the increase of dilution ratio,blowoff limits decrease slowly in oxygen-enriched combustion region,but blowoff limits fall rapidly in lean oxygen combustion region,flame reaction area is elongated.Therefore,lean oxygen combustion environment would worsen flame stability quickly.The flame roots in the O2/H2 O atmosphere always maintain the thick ring structure in favour of flame stability,but flame roots appear as tapered structure in others atmospheres.So,the presence of H2 O is an important reason of the thick ring structure.Blowoff changing with the dilution rate and H2 content are studied under O2/H2 O and elevated pressures condition.The experiment results show that,blowoff velocities decrease with increasing the dilution rate,and increase with increasing H2 content,The blowoff velocities are almost completely turbulent.when the pressure reach 4atm,the effects of pressure to blowoff velocities are impaired,but the flame structures are significantly different.So,blowoff limits should consider the effects of combustion system,as well as turbulence intensity,furthemore,the higher the pressure,the more obvious the influence of turbulence intensity.So,it’s more reasonable that the flame stability is analysised by Reynolds number at elevated pressures.Thick ring structure of flame roots is existent and more obvious at elevated pressures when the dilution rate reaches 0.79.As pressure is incresaed,mass burning rate and flame luminosity rise,however,from the point of the regularity of blowoff velocity,mass burning rate is not the determinants of flame stability. |
