Effect Of CO₂ Addition On Natural Gas Combustion Process And NO_x Formation

Natural gas is a prominence clean energy.Compared with coal,oil and other fossil fuelsshi,natural gas is mainly composed of hydrocarbons and a small amount of nitrogen and sulfur compounds,which can effectively reduce the emission of pollutants,so it is widely used in power plants and other power machinery applications.With the end of the twelfth Five-Year Plan,and the beginning of thirteenth Five-Year Plan,the NOx emissions of natural gas cannot be ignored since the pollutant control policies are more stringent..Flue Gas recyculation technology?FGR?is one of the low nitrogen combustion technology,the main component of the Flue Gas is carbon dioxide.The technology is not only widely used in coal combustion technology,but also applied in landfill gas combustion,which is the main composition is methane.On the other hand,as the late period of the oil and gas field exploration,the carbon dioxide content in the gas increases gradually.The effect of carbon dioxide on the natural gas not only reduces the heat value but also change the flame structure and chemical kinetics mechanism.Therefore,the study of the influence of the carbon dioxide on the natural gas combustion has important significance.In this thesis,a laminar coaxial diffusion burner was designed,and an experimental rig conforming to the optical measurement standards was built based on the PLIF?Planar Laser Fluorescence?.OH-PLIF and CH-PLIF technique are used to measure the CH4/Air flame with different CO₂ concentration added in the fuel.The results show that:the equivalent ratio is 1,the mass flow of methane is constant;with the increase of CO₂,the flame is higher,and the fluorescence signal of OH in measured area increased;but the CH decreased.When the CO₂ content exceeds 20%,the CH is basically only distributed at the front of the flame,and the fluorescence intensity gradually decreases.Fluent software to simulate numerical calculation was carried out on the laminar diffusion flame,in order to verify the experimental results of laminar diffusion flame in the distribution of the qualitative accuracy,at the same time to study the effect of CO₂ on methane combustion NOx emission.To improve the calculation efficiency and satisfy the existing computing equipment conditions,the sensitivity analysis and direct relations detailed chemical reaction mechanism of methane?GRI-Mech 3.0?were simplified,and the skeleton mechanism is obtained,and the validity of the simplified mechanism was verified.Through comparison,it was found that the OH group increased gradually with the increase of CO₂,but the change was not very obvious,and the CH group decreased gradually with the increase of CO₂,which was consistent with the experimental results.The addition of CO₂,the emission of NO decreases gradually,which indicates that CO₂ has a certain inhibitory effect on the formation of NO.In this thesis,the method of bi-directional LIF of CH4/Air premixed flat flame has carried on the quantitative measurement.With the increase of equivalence ratio,the measurement results show that:the width of the flame gradually widened,and the equivalent ratio not greater than 1,the one-way OH fluorescence intensity can be approximately as a linear decreasing;while the equivalent ratio is greater than 1,one-way OH fluorescence intensity drop rapidly.With the increase of the equivalent ratio,the concentration of OH group increases first and then decreases,and reaches the peak when the equivalent ratio is 1.By comparing the results of literature,it is found that measure the absolute concentration of OH group is feasible by bidirectional LIF technique.Above measurement laies a foundation for the future development of two-dimensional measurement technology.Based on the flue gas recycling technology,the main components of CO₂ and H₂O were added to the oxidant in this study,and the effects of these two diluents on the flame characteristics in the air were studied by using Fluent in combination with the simplified mechanism.Both CO₂ and H₂O have a certain effect on inhibiting the generation of NO,but H₂O has a better effectsince H₂O has a large specific heat capacity.It is also found that H₂O promotes the transformation of NO and changes the transformation path of N.Turbulent flame is wildly used in some practical engineering applications.Therefore,we designed a turbulent burner with multi-nozzle,and has set up a test bench for the optical test standard,under different conditions,using PLIF to measure the flame,and measuring the flue gas by flue gas analyzer.The fluorescence intensity of OH increases with equivalent ratio increased.With the addition of carbon dioxide,the OH decreased firstly,then went up and fell down again.The concentration of NO and CO rose then fell.Therefore,the addition of an appropriate amount of CO₂ can inhibit the production of NO to a certain extent.