Influence of fly ash composition on non-gray particle radiation in combusting systems

Abstract

In this study, chemical composition dependency of both radiative properties of ash particles and radiative heat exchange are investigated for conditions typically encountered in industrial coal-fired furnaces. For that purpose, chemical composition dependent / independent complex index of refraction models are utilized to evaluate (i) spectral particle absorption efficiencies, scattering efficiencies and asymmetry factors, (ii) particle cloud properties representing pulverized coal fired furnaces (PC-Fired), bubbling fluidized bed combustors (BFBC), circulating fluidized bed combustors (CFBC) and (iii) radiative heat flux and source term predictions for five different ash compositions. Results show that spectral particle radiation is of significant importance for accurate calculation of radiative heat transfer in combusting systems and it is originated from the spectral nature of the complex index of refraction rather than spectral nature of the incident radiation. It is also seen that chemical composition has a significant effect on particle absorption properties as well as heat flux/source term predictions. Hence complex index of refraction models used in radiative property estimations must take into consideration this composition dependency. Accordingly, one spectral and one gray complex index of refraction models are recommended for the evaluation of ash particle properties.