Composition-based Non-gray Particle Radiative Property Model And Its Radiative Heat Transfer Law

For large power plant pulverized coal combustion system,the heat transfer process is dominated by radiation,accounting for more than 90% of the heat transfer in the furnace.Therefore,accurate prediction of radiative heat transfer is critical to the boiler design.In oxyfuel combustion,the volume of flue gas decreases,leading to the increase of particle concentration,and with the increase of optical thickness,the importance of particle radiation becomes more prominent.Therefore,it is necessary to carry out further research on particle radiative property model and radiative heat transfer characteristics in combustion system.In this study,based on the experimental data under different iron oxide content,a suitable complex index of refraction(CIR)model of fly ash particle was selected.Mie theory and the appropriate CIR model were used to calculate the spectral absorption and scattering efficiencies with iron oxide content increased from 5% to 30%.Introducing the rearrangement idea of full spectrum k-distribution(FSK)model and formula form of the weighted sum of the gray gas(WSGG)model,and use node optimization strategies to improve the model’s accuracy,a non-gray radiative property model(WSGP＿SK＿Fe)of fly ash particle considering the content of iron oxide is obtained.By using the LBL model as benchmark,the WSGP＿SK＿Fe model is validated in a one-dimensional plane-parallel slab system.In a nonisothermal and non-uniform particle medium,the mean relative errors of radiative heat flux and source term of WSGP＿SK＿Fe model and Planck mean model are less than 5%,13% and13%,22%.In order to explore the influence of gas and particle radiative models on heat transfer characteristics,the MILD combustion and swirling combustion in IFRF 0.88 MW pilot boiler were numerically studied.The influence of the non-gray property of the radiative model on the heat transfer and the law of the heat transfer efficiency under different characteristic length of the furnace were investigated.The radiation prediction in swirling combustion is more sensitive to the radiative property model.As the furnace size increases,the advantages of MILD combustion in heat transfer are highlighted.Since MILD combustion has a more uniform temperature and radiant participation medium distribution,MILD combustion has a higher heat transfer efficiency than swirl combustion.More precisely,when the characteristic length of the furnace increases from 1.55 m to 4.65 m,the relative difference in heat transfer between MILD combustion and swirling combustion increases from 3.6% to 5.0%.