Search

Coupling the San Diego gas phase reaction mechanism and the Moss Brookes soot model using FLUENT14.0 software, the effect of adding H2/CO on the fuel side on soot formation in an ethylene/air laminar diffusion flame was studied. A specific analysis was conducted on the effects of H2, CO and its chemical effects on flame temperature, soot volume fraction, mole fractions of important intermediate products OH, H, and C2H2, as well as rate of soot mass nucleation, surface growth, and oxidation. In the numerical calculation, the virtual substances FH2 and FCO are set to separate the chemical effect of H2 and CO and to analyze the chemical effect of adding H2 and CO on soot formation. The results show that the flame temperature increases slightly, and the soot volume fraction decreases monotonically with adding H2 and CO. The chemical effect of H2 increases the temperature, the mole fraction of C2H2 and H, the soot nucleation rate, and the surface growth rate, and finally, it promotes soot formation. The chemical effect of CO increases the temperature and H mole fraction, reduces the OH mole fraction, and then increases the soot surface growth rate and reduces the soot oxidation rate. The higher soot nucleation, surface growth rate, and lower oxidation rate jointly promote soot formation. [ABSTRACT FROM AUTHOR]

Hydrogen mixed natural gas for combustion can improve combustion characteristics and reduce carbon emission, which has important engineering application value. A casing swirl burner model is adopted to numerically simulate and research the natural gas hydrogen mixing technology for combustion in gas boilers in this paper. Under the condition of conventional air atmosphere and constant air excess coefficient, the six working conditions for hydrogen mixing proportion into natural gas are designed to explore the combustion characteristics and the laws of pollution emissions. The temperature distributions, composition, and emission of combustion flue gas under various working conditions are analyzed and compared. Further investigation is also conducted for the variation laws of NOx and soot generation. The results show that when the boiler heating power is constant, hydrogen mixing will increase the combustion temperature, accelerate the combustion rate, reduce flue gas and CO2 emission, increase the generation of water vapor, and inhibit the generation of NOx and soot. Under the premise of meeting the fuel interchangeability, it is concluded that the optimal hydrogen mixing volume fraction of gas boilers is 24.7%. [ABSTRACT FROM AUTHOR]

Oxy-combustion is an effective carbon capture technology. Many oxy-combustion technologies utilize recycled flue gas (RFG) for dilution to control temperature and heat flux. As the concentration of dilution gas on the fuel and oxidant side changes, stoichiometric mixture fraction (Z st) and flame temperature will change and significantly impact the flame structure and soot formation characteristics. In this work, the effects of stoichiometric mixture fraction and flame temperature on soot formation characteristics in laminar diffusion flames are studied by diluting the fuel and changing the oxygen concentration. CO 2 is used as a dilution gas to simulate the RFG in oxy-combustion. The numerical calculation combines gas reaction kinetics with a soot formation model. Soot nucleation, surface growth, oxidation processes are considered, as well as the distributions of temperature, soot concentration, and key substances. The experimental flame appearances and spectral radiation data are imaged by a hyperspectral imager, and the temperature and soot concentration are reconstructed. The results of experimental measurement and numerical calculation are compared to evaluate the applicability of the soot formation mechanism to oxy-combustion with elevated Z st and using CO 2 as diluent. As the Z st increases, the flame changes into a blue flame, soot concentration and temperature in flames decrease, because nucleation and surface growth are both inhibited and oxidation is enhanced. As the flame temperature increases, the flame becomes brighter, numerical results indicate that soot formation and oxidation are both enhanced, while the promoting effect of temperature increase on surface growth is stronger than that of oxidation, resulting in an increase in soot concentration. This study provides a fundamental understanding of the effects of RFG utilization (fuel dilution and oxygen enhancement) on flame structure, temperature distribution, soot concentration and formation characteristics in non-premixed oxy-combustion systems. [ABSTRACT FROM AUTHOR]