Grate and its specification can significantly affect the performance of ball mills, semi-autogenous grinding (SAG) and fully autogenous grinding (FAG) mills equipped with this type of discharge mechanism. The grate design, open area and grate aperture size affect grinding throughput. In SAG and FAG mills, the inadequate design of discharge grate can lead to inefficiency of comminution device and creation of a slurry pool which practically stops particles' breakage. In optimization projects, investigation on discharge grate and its effect on grinding process is critical due to particle size classification at mill exit, which necessitate the effect of grate to be considered in process modeling and simulation. In this project, discharge grates of Esfordi and Gol-e-Gohar plant ball mills and their effect on mill performance were investigated in details to make sure that the modeling and simulation and subsequent optimization studies are accurate as much as possible. To study and determine the effect of the discharge grate, samples were collected from mill feed and discharge streams when the circuits were under steady-state operation. After mass balancing, the discharge streams were simulated by BMCS®. Then the observed and simulated PSD of output were compared. The obtained results showed that the grate inside Esfordi ball mill does not affect the particle size distribution of mil output. In Gol-e-Gohar pilot plant ball mill the grate behaves like a fine screen which should be considered in mill mathematical modeling and simulation.
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