Grinding & Classification Circuits

Grinding & Classification Circuits

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How to define "specific power" in ball mill scale-up procedure? (4 replies and 4 comments)

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Peter.Li
6 years ago
Peter.Li 6 years ago

Herbst et al. proposed a procedure for ball mill scale-up. It is based on linear relationship between selection function S (1/min) and specific power P/H

S= SE×(P/H) 

Question 1:

"H is the mass of the charge in the mill excluding the media"

Does H represent mass of solid particles or mass of slurry?

Question 2:

I find 3 definitions of the net power P

1. "P is the net power drawn by the mill exclusive of the no-load power that is required to overcome mechanical and frictional losses in the mill" (R. P. King) . For convinience, name it as P1.

2. P=Pball where Pballs represents the contribution of the balls to the Net Mill Power Draw (Moly Cop Tools). Name it as P2, and P2=P1×Mball/(Mball+Mslurry).

3. P is the net power drawn by mill exclusive of the no-media power. Name it as P3. P3=power drawn by mill with media and slurry - power drawn by mill with only slurry. 

Which one is appropriate for the scale-up procedure?

 

Alex Doll
6 years ago
Alex Doll 6 years ago
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I'm not familiar with this equation.  Can you provide the reference to where you got it?

https://www.sagmilling.com/

Mike
6 years ago

Based on this: https://www.researchgate.net/publication/279770099_MATHEMATICAL_SIMULATION_OF_DRY_BALL_MILLING_USING_SPECIFIC_POWER_INFORMATION

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Peter.Li
6 years ago

This paper may give a good review of the procedure.
Population balance model Predictions of the Performance of Large-Diameter Mills
It can be download from OneMine.

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adrianh
6 years ago
adrianh 6 years ago
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1 like by Peter.Li

Question 1 - H is the mass hold-up of ore solids in the mill to be ground, which includes pebbles and rocks that could be construed as media. Steel media is excluded.

Question 2 - The net power is usually defined in terms of the gross electrical power [kW]  consumed by the drive motor with charge minus the no-load (mill empty) electrical power drawn by the mill. An alternative  definition is the mechanical power transmitted to the mill charge minus the mechanical power transmitted to the mill when its empty. This can be measured using a torque sensor at the pinion and a tachometer. During my time at Mintek, pilot AG/SAG tests involved both electrical and mechanical power measurments. Note that Bond's equations assume pinion power (mechanical).

 

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Peter.Li
6 years ago

Professional answer!
Just to make sure, does the "charge " you mentioned above mean (grinding media+ore solid+water) or (grinding media+ore solid) or (grinding media only)?
I know this question is silly, but I have to ask.

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adrianh
6 years ago
adrianh 6 years ago
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Hi Peter. The definition depends on the context. Charge is often defined in terms of the static (after a crash stop) total volume of the charge (steel balls, ore and water) expressed as a fraction of the internal volume of the mill. In the case of a SAG mill, this definition is given the symbol JT (T as a subscript). The fractional filling of the mill with balls only in the mill is given as JB (B as a subscript). In the case of a ball mill, the same definition applies. However, the definition gets a bit misleading when a slurry pool forms in the mill and the volume of the pulp exceeds the volume of the voids in the grinding media. 

millPower_Morrell1996b-2017_08_05-06_47_32-UTC.pdf
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Peter.Li
6 years ago

Get it, thanks a lot!

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emilyfreire
6 years ago
emilyfreire 6 years ago
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1 like by Peter.Li

Peter, to determinate the power in the ball mill or in the rod mill, we can use the Rowland's equation. 

The equation is attached.

Regards.

 

rowland's equation
https://www.911metallurgist.com/wp-content/uploads/2018/07/Rowlands-Equation.jpg

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