239 posts
TimePosted 08/11/2010 04:58:41
xxxx says

### MATERIAL RETENTION TIME IN A BALL MILL & VRM

DEAR ALL CAN ANYBODY SUGGEST ME HOW TO CALCULATE THE MATERIAL RETENTION TIME IN A CLOSED CIRCUIT BALL MILL IN EACH COMPARTMENT? SIMILARLY FOR A VERTICAL MILL . WHAT IS THE USE TO CALCULATE THE SAME? IS IT HELPFUL FOR OPTIMISATION LIKE IN KILN ? PLEASE DO REPLY RAJ

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138 posts
TimePosted 08/11/2010 06:35:46
lalbatros says

### Re: MATERIAL RETENTION TIME IN A BALL MILL & VRM

You could do that by measuring the material flowrate Q[tons/h] through the mill as well as the quantity M[tons] of material that accumulates within the mill. The retention time, also called residence time, is the ratio (M/Q) [h] .

The flowrate Q could be measured from the production P[tons/h]  and the circulating load C and given by Q[tons/h] = C P[tons/h] . The circulating load could be obtained by measuring the particle size distribution of the feed, the product and the reject, and by then using the Koulen method. (see this post)

The material M accumulated within the mill could be observed by measuring the level of the material within the mill, deducting the volume occupied by the balls and assuming a reasonable value for the material density. Alternatively, you might empty the mill and weight what comes out.

Another method uses fluorescein injection.

See also page 33 §3 in this Mapei document .

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28 posts
TimePosted 08/11/2010 21:38:19
Saddam Hu says

### Re: MATERIAL RETENTION TIME IN A BALL MILL & VRM

Hi

I do not think that retention time is critical parameter for grinding optimization. Focus on the ball charge distribution, filling degree, aeration and separator performance.

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