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SENSITIVITY OF RADIATION MODELING TO PROPERTY ESTIMATION TECHNIQUES IN THE FREEBOARD OF LIGNITE- FIRED BUBBLING FLUIDIZED BED COMBUSTORS ( BFBCs)

Predictive accuracy and computationally efficiency of method of lines (MOL) solution of the discrete ordinate method (DOM) coupled with different radiative property estimation techniques (GG, SLW, SNBCK) are assessed by applying them to the prediction of incident radiative fluxes along the freeboard walls of a 0.3 MWt atmospheric bubbling fluidized bed combustor (ABFBC) and comparing their predictions with measurements generated previously from two runs one without and the other with recycle. Freeboard is treated as a three-dimensional rectangular enclosure containing a gray/non-gray, absorbing-emitting-isotropically scattering medium. Radiative properties of particles are evaluated by using geometric optics approximation. A comparative study is also provided between the source term distributions predicted by MOL solution of DOM with gray gas (GG), spectral line-based weighted sum of gray gases (SLW), and statistical narrow-band correlated-k (SNBCK) along the centerline of the freeboard for both runs. Comparisons reveal that the MOL solution of DOM with SLW model and geometric optics approximation provides accurate and computationally efficient solutions for wall fluxes and source term distributions in the freeboard of fluidized bed combustors containing particle laden combustion gases.