Numerical study on the NOx formation in an incinerator

Abstract

Numerical analysis has been carried out to investigate the combustion characteristics in the three-dimensional incinerator. The applied mathematical models for prediction of velocities, turbulence quantities, enthalpy and chemical species involved have been described and discussed in detail. Turbulence combustion has been modeled by using the eddy dissipation model, while in modeling the radiative heat transfer finite volume method for radiation have been followed. Also, multi-block method is adopted to simulate the complex geometry easily using structured grids. Introducing Beta PDF (Probability Density Function) method to see the effect of turbulence on NOx chemistry, formation, distribution, and emission of NOx have been studied numerically. Considering only thermal NOx, parametric studies in terms of excess air ratio, secondary air injection, and radiation have been undertaken. Increase of primary air supply in other words, higher excess air ratio lowers the temperature inside the incinerator. Thereafter, the amount of NOx formation is lessened. Also, its average emission reduces. When another factor or secondary air injection is considered, it is hard to mention that more secondary air injection reduces NOx formation because of co-effective factor of equivalence ratio. Additionally, in order to simulate the incinerator similar with the real case, non-gray gas (WSGGM) radiation is necessary. It is apparent that including the radiation effect results in lower NOx formation because of radiative heat loss.