Powder Hold-up Research Articles

充填層内ガス-粉体2相流れの1次元流動特性

Gas-powder two phase flow in packed beds were investigated by using a one-dimensional cold model and a mathematical model for clarifying the behavior of powders in a blast furnace. Following results were obtained;(1) Two phase flow showed higher pressure drop compared to clean gas flow. The increase in the pressure loss was mainly caused by the increase in the hold-up of powders in the region of low gas velocity and by the interaction force between powders and packed particles in the region of high gas velocity.(2) A mathematical model of gas-powder two phase flow in packed beds was developed considering an interaction force between gas and powders expressed by the drag force and the Richardson-Zaki's voidage function.(3)An interaction coefficient between powders and packed particles which was defined on the basis of the momentum balance equation of powders in packed beds was obtained from the experimental data.(4) Blockade occured at the certain gas velocity where the hydraulic diameter of packed bed including powders was below 6 times as long as powder diameter.

Analysis of mill capacity using a theoretically derived selection function applied to ball and Hardgrove mills

The grinding capacity of a mill depends upon the grinding mechanism and the operational conditions. The absolute rate of breakage or the mill capacity is conventionally given as the product of the selection function and a powder hold-up (or a fractional volume of powder filling). The present study assumes that the grinding mechanism is dominated by impacts of balls falling onto the bed surface. The derived selection function is then used to estimate the mill capacity for ball mills, as a function of operational parameters such as powder and ball fillings. The results are in reasonable agreement with experimental data. Further, application to Hardgrove mills is also studied in terms of the mill capacity in relation to some operational parameters concerned.