Grinding & Classification Circuits

Grinding & Classification Circuits

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Calling on all Fine and Ultra-fine Grinding Experts... (2 replies and 1 comment)

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babygenius76
7 years ago
babygenius76 7 years ago

I have a West African project where we use a pendulum roller mill along with classifier to dry-grind high purity (95% to 98%) calcite to d50 10 micron with a relatively steep PSD curve.  The top feed size into the mill is 5000 microns (5 mm) because of sieving prior to the grinding in roller mill.

From what I understand of the grinding mechanism of the roller mill, it is mostly abrasion against the roller media. Very little of the breaking comes from inter particle contact. It seems to me that theoretically, a smaller feed size should produce faster mill throughput, all other factors being constant. Then, why is it that the roller mill's output does not vary significantly between a top feed of 5000 micron and a feed size of d50 74 micron? Is it a classifier inefficiency? It bothers me. Any suggestions or thoughts would be helpful. Thank you.

S
saguero
7 years ago
saguero 7 years ago
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air classifier is a key element in dry grinding!...and that is why it is happening you!...in cement industries  were they have a 30 microms P80 they are shifting to high efficiency separators!.You must have nwo a high fines circulating load!....feeding again the system!. Are you using a Trump curve to plot a graph?...or Rossin Ramler?

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Robert
7 years ago
Robert 7 years ago
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1 like by David

The energy consumed in size reduction from 5 mm to 10 um is highly nonlinear, e.g., consider feed size reduction from 5000 to 2500 um, the influence could be less than increasing product size from 10 to 20 um.

Consider the IsaMill signature plot and description shown:  

https://www.911metallurgist.com/blog/ultrafine-grinding-test-report-isamill-signature-plot

The classifier inefficiency is of course another concern on top of this.

There is possibility to add a classification aid to mill which may improve classifier separation efficiency.

Have you completed any process audits of this grinding system?

 

 

B
babygenius76
7 years ago

Robert,
Yes, the grinding from 5000 to 10 microns is highly energy intensive. As you see above, I have even tried a 2 stage grinding where in the first stage, I reduced it from 5000 to 74 micron. In the second stage of grinding, the 74 micron did not have any significantly higher throughput than the 5000 micron.
I really think that what you and others are pointing out is the lack of classifier efficiency. What are the types of classification aids? I am not familiar with these.

Thank you, and best regards

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