Raceway Formation in a Moving Bed

Raceway is formed in the blast furnace when high velocity air is blown into a bed of coke particles. The blast furnace is treated as a moving bed as the burden descends to replace the coke particles consumed by the combustion in front of the tuyeres. In this study, an experimental setup is constructed using Perspex sheet to replicate the moving bed and a detailed study of raceway size is carried out with respect to different parameters such as gas velocity, bed height and particles flow rate. Compressed air is used as the gas phase and granules of Linear Low Density Polyethylene (LLDPE) are used as the packing particles. Results confirm the existence of the cavity hysteresis phenomenon in a stationary packed bed. For moving beds, it is found that the cavity hysteresis phenomenon is absent, except at a very low particles flow rate. It is also observed that raceway size in the moving bed is independent of the bed height and solid mass flow rate, except for a very low solid/particles flow rates. Results confirm the previous hypothesis that if there are no frictional forces then there would not be any raceway hysteresis in the system. The study also confirms that the raceway size obtained in a stationary packed bed for decreasing gas velocity condition is similar to that obtained in the moving beds.