Full-scale 3D-modelling of the radiative heat transfer in rotary kilns with a present bed material

Artikel i vetenskaplig tidskrift, 2020

This work discusses the development and use of a detailed 3D radiative heat transfer model of a rotary kiln with a present bed material, used for iron ore pelletizing. A discrete ordinates method is used to solve the radiative heat transfer equation with radiative properties calculated using a weighted-sum-of-grey-gases (WSGG) model for gases and Mie and Rayleigh theory for particles including fuel, ash and soot. Measurement data gathered from a pilot-scale test furnace, comprising temperature, gas composition and particle concentration, is used in combination with temperature data and operation parameters gathered from a conventional rotary kiln to model a full-scale rotary kiln with a present bed material. The modelled cases have a thermal input of about 37 MWth and in addition to radiative heat transfer, conductive heat transfer within, as well as between, the bed and wall material are included in the model along with convective heat transfer from the gas and heat release from exothermic reactions in the bed. The model also considers the rotational wall and includes a simplified mixing model of the bed material as well as heat losses from the outside wall of the rotary kiln due to radiation and convection. For two different flames, one coal and one oil flame, surface temperatures are calculated on the inside and outside of the rotary kiln and compared to measurements. The model appears to predict the inner wall and bed surface temperatures well with errors less than 11%. The total heat transfer to the present bed material was also studied revealing that more than 80% originated from the radiative heat transfer within the furnace.