A simulation study of laboratory scale ball and vertical stirred mills

The aim of this study was to investigate the grindability of solid fossil fuels from a thermal power plant by using a vertical stirred mill and conventional ball mill. The solid fossil fuel sample was obtained from the Zonguldak Catalagzi thermal power plant in Turkey. The sample below 3350µm (d80 = 2100µm) was ground in the laboratory scale stirred mill and ball mill. The d80 sizes of the products at the end of grinding periods of 0.25, 0.50, 1 and 4 min in the stirred mill were determined as 190, 102, 78 and 28µm, respectively. For this purpose, the stirred mill was used at a stirring speed of 360 rpm and with a 6 mm diameter ball. In the ball mill, the d80 sizes of product after 1, 4, 8, 12 and 24 min of grinding were determined as 1802, 1130, 324, 167 and 81µm, respectively. The results indicated that grinding by means of a stirred mill was much more efficient than grinding with a ball mill in terms of size distribution of the products. The energy consumption of the product with d80 = 78µm was obtained as 10.53 kWh/t after 1 min of grinding time in the laboratory scale stirred mill. In the same manner, the energy consumption of product with d80 = 81µm by using the laboratory scale ball mill was 72.73 kWh/t after 24 min of grinding. It can be clearly seen that the d80 size of the fossil fuel reduced from 2100µm to 1130µm after a 4 min grinding period in the ball mill grinding tests. However, the d80 size of the solid fossil fuel reduced to 28µm after the same grinding time in the stirred mill and it was also possible to efficiently obtain size reduction below 100µm. However, the ball mill grinding process cannot provide this efficient size reduction for longer grinding times. The ball mill grinding experimental results and simulation results showed that they were fairly consistent with each other. The simulation of higher speed mills such as pin type stirrers has been extensively investigated for relatively small-scale applications by JKSimMet. In this study, the JKSimMet software package was adapted for a stirred mill with the help of the base model of ball milling. The aim of this study was to investigate the grindability of solid fossil fuels from a thermal power plant by using a vertical stirred mill and conventional ball mill. The time evolution of particle size and the related energy consumption have been determined. Furthermore, a simulation tool was used to describe the observed behavior. Copyright © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim