Numerical and experimental study of natural gas preheating effects on the soot formation, flame luminosity and NO emission

In this paper, the effect of inlet gas temperature on the soot content, flame temperature and overall efficiency of a 120 kW boiler have been investigated. For modeling the impact of inlet gas temperature on combustion and soot production, a non-premixed turbulent model was employed. Besides, using the Reynolds turbulent stress model, stress terms in momentum equations were solved. Also, Moss-Brooks model and a beta probability density function (β-PDF) is used to describe the effect of turbulencies on soot formation. Moreover, experiments were conducted on a boiler which its inlet gas temperature is preheated with a Chrome-Nickel electric heater. The results demonstrate that the preheating of natural gas up to about 510 K has no considerable effect on the flame luminosity. Otherwise, preheating the inlet fuel up to 700 K increases the flame soot content up to 3 times resulting in a serious luminosity rise. This increase causes a reduction in flame temperature (150K) and NO emission. It is seen that the predicted results have good agreement with measurements.