Effect of Fume on Radiative Heat Transfer in Kraft Recovery Boilers, 1998 International Chemical Recovery Conference Proceedings

Recent measurements of optical and radiative properties of recovery boiler ash were used in a three-dimensional numerical model to evaluate the effect of fume on heat transfer in a kraft recovery boiler. Absorption and scattering efficiency of fume particles were calculated from measurements of the complex refractive index of ash. Radiative properties of black liquor, char and smelt particles were calculated based on correlations for emissivity as a function of temperature. Radiative properties of molten smelt and fume deposits on the furnace walls were approximated by emissivity correlations as a function of deposit surface temperature, incident radiation and ash melting characteristics.

Predicted furnace heat transfer results are presented for test conditions on a single-drum recovery boiler, including gas flow patterns, gas temperature, dust concentration, and radiative properties. Conditions on the furnace wall are also presented for deposit surface temperature, radiation properties, and absorption heat flux. The effect of deposit thermal conductance, fume particle size and concentration are evaluated. These results demonstrate that measurements of optical and radiative properties of ash have improved our understanding of, and ability to predict furnace heat transfer.