Fall in raw mill tph after addition of clay

Dear Sir,

We have airswept ball mill Dia 2.8 x 7.32m length for raw material grinding, before it was giving 48 to 50 tph comfortably, when we increased the clay addition from 3% to 12% in the raw mix, the mill output has drop down from 50 to 40 tph, moisture % in clay is 10 to 20%, we are taking hot gas from kiln, and maintaining outlet temp around 85 Deg C, what is the way to increase mill output since clay is easily grindable material, please suggest.

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re Fall in raw mill tph after addition of clay

Hello Ramesh,

Higher clay levels tend to coat the balls and reduce grinding efficiency, especially if the clay is moist. Therefore higher clay usage may require a higher temperature to drive off inherent moisture locked within the clay mineral structure. Normal outlet temperatures may not be enough to dry out the clays within the mill residence time. Check your raw meal moisture levels at different clay usage rates. If the moisture level in the raw meal increases with clay usage rate, this is confirmation that the mill outlet temperature needs to be increased.

To find the optimum temperature at a certain clay usage rate, increase the outlet temperature in say 5degC steps and see if the rate improves, waiting until the mill rate stabilises after each temperature increase. Test the raw meal moisture content at each temperature increase and continue until the optimum mill rate and raw meal moisture level is achieved. (Hopefully this can be reached before you run out of hot gas capacity from the kiln.)

Hope this helps...

Regards,

Ted.

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