Study On The Effect Of Oxygen Dilution On The Process Of Non-catalytic Partial Oxidation Of Methane

The problems of strong exothermic reaction and flame instability in the non-catalytic partial oxidation reaction of natural gas affect the safe and steady operation of the reformer,the ablation of the burner and refractory caused by the high temperature flame also needs to be solved urgently.Based on this background,the experiment of flame characteristics in open space is carried out;the effect of oxygen dilution on the non-catalytic partial oxidation process of the methane is numerically investigated.The effects of different O2/CH4 mole ratio and CO2 dilution contents on the combustion flame shape,temperature and flame stability in CH4-O2 diffusion flame are investigated in open space.The results show that CO2 dilution has a notable influence on the flame shape,the yellow area at the root of the flame move up and the visible flame length decreases with the increase of CO2 dilution;the flame brightness and soot production decreased.When the CO2 dilution increases to 45%,the flame become unstable.The increase of O2/CH4 mole ratio increases the blue flame area near the flame front,and the width of the flame front decreases.The numerical model of a non-catalytic partial oxidation reformer of natural gas is established,and the effects of three diluents(N2,H2O,CO2)on the distribution of temperature and flame reaction zones in the reformer are investigated.The results show that the effects of N2 and H2O dilution on temperature and reaction zone profiles in the reformer are basically indistinguishable,and the effect of CO2 dilution is the most significant.And the increasing of CO2 content decreases the peak temperature by about 50K,also,the heat release rate is notably reduced,the reaction zone is wider and the flame brightness is reduced,compared with N2 and H2O dilution.Three effects of CO2 dilution on the temperature and radical distribution in the reformer are in the order of dilution effect>thermal effect>chemical effect.The effect of CO2 dilution and different oxygen jet velocity on the flame structure,temperature profile,combustion mode,and syngas composition in reformer are investigated.The results show that the peak flame temperature is reduced and decreasing of approximately 40 and 150 K are observed at 15%and 45%CO2 content of the oxidant at the same burner velocity of 100m/s,respectively;and the increasing of velocity decreases the peak temperature by about 40K compared with the same burner velocity case and CO2 content in oxidant.Meanwhile,based on the investigation of combustion modes in the core reaction zone of the furnace under different operating conditions,MILD combustion can be achieved when the CO2 content of the oxidant is 0-45%with the same burner velocity of 100m/s;however,the reaction is not in the MILD combustion zone as the CO2 content increases to 45%at a velocity of 182m/s.The syngas(H2/CO)ratio can be adjusted within the 1.35-1.96 range by increasing the concentration of CO2 in the oxidant from 0 to 45%.