Differences between rod mills and ball mills
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Previously, ball mills were used, but now rod mills have been adopted. I’m not sure what the differences between the two are, nor what their advantages and disadvantages are. Everyone is welcome to discuss this.
Water-coal slurry is generally ground fine using rod mills or ball mills. In other words, ball milling results in a too uniform particle size distribution, whereas rod milling allows the particle size to be kept within a certain range – for example, a minimum of 14 mesh, with 98-100% at 20 mesh ； 40 mesh 90-98% ； 120 mesh 50-70% ； 325 mesh 25-40%.
The rod mill has a high load, saves electricity, produces uniform coal particles, and the wear rate of the steel rods is slower than that of steel balls； Adding grinding media to a ball mill is more convenient than using a rod mill, but due to the uneven size of coal particles, over-grinding may occur, resulting in overly fine particles.
During a recent investigation at a TEXACO facility, I encountered this issue: the coal powder produced by the ball mill had particles that were too fine, with 50% of them being finer than 325 mesh. As a result, the viscosity of the coal slurry became too high, preventing an increase in its concentration, which could only be maintained at around 58%. As for the ball mill itself, as mentioned upstairs, it has a high energy consumption, and the steel balls tend to wear out easily. Furthermore, based on past experience, foreign design institutes prefer ball mills, while domestic design institutes tend to favor rod mills.
For the reasons mentioned by those upstairs, let me add one more point: in fluidized bed boilers, ball mills are used. For the preparation of water-coal slurry, since specific requirements exist regarding the particle size distribution, open-type rod mills with no return flow and overflow design are generally chosen!