The mechanism of thermal accretion (mushroom) formation and the bubble and flow characteristics during cold gas injection

Abstract

The thermal accretion (or mushroom) which is formed around the tuyere in steelmaking plants was simulated by a cold model and its formation process was observed. Single- and multi-hole nozzles were used for gas injection. The multi-hole nozzle was an artificial mushroom-like nozzle. The bubble and flow characteristics were investigated using an electrical resistivity probe and the laser Doppler velocimeter system. The process of thermal accretion formation consists of the following three stages: (1) generation of a core; (2) separation of the core and regeneration of another core; and (3) steady growth of the accretion. The shape of the thermal accretion and the bubble characteristics changed with each stage, depending on the thermal conductivity of the material of the nozzle. The bubble and liquid flow characteristics for the multi-hole nozzle were examined in comparison with those for the single-hole nozzle. The following results were obtained: (1) the bubbling jet generated by the multi-hole nozzle spread more widely in the radial direction than that generated by the single-hole nozzle; and (2) the circulation flow rate for the former nozzle was 33% larger than that for the latter nozzle.