Coal Size Reduction

Posted in: , on 1. Jul. 2003 - 14:43

We have a RUN of MINE Sampler system. The sampler system is designed to handle coal of -150mm. Some oversize coal is present which is taken out by means of a grizzly. (So much for a representative sample).

The customer wants a way to break to oversize coal to go through the grizzly. There is no space for a crusher. The idea is to make use of a hydraulic ram.

What is the hardness of typical coal?

What size of hydraulics can be used?

What is the best shape of the ram?

Quantity is about 3tons per day.

Stone on the grizzly will trip the sampler system.

Hugo Lombaard [email][/email] Johannesburg South Africa

Re: Coal Size Reduction

Posted on 1. Jul. 2003 - 08:11

Please clarify whether you are referring to breaking of coal discharged by primary sampler, or at some other place. Is the grizzly mentioned by you, fed by primary sampler?


Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyor.

Email :

Tel.: 0091 (0)20 5882916

Coal Breaking

Posted on 2. Jul. 2003 - 07:52

The coal is taken from the main belt by the primary cross-travel hammer sampler. This coal fall onto the grizzly. The fines go through the grizzly onto a conveyor feeding the sampler tower.

It is the big stuff that remains on the grizzly that need to be break to smaller pieces to pass through the grizzly as well.

Hugo Lombaard [email][/email] Johannesburg South Africa

Re: Coal Size Reduction

Posted on 2. Jul. 2003 - 08:31

The basic rule for the sampling system is that the sample should be taken and processed without any prejudice / selection. Therefore, the entire quantity of primary sampled coal should go into crusher, and then portion of this crusher output without any prejudice, should go towards secondary sample.

Accordingly, the presence of grizzly after primary sampler is not conforming to this basic rule. You need to use bigger crusher of appropriate type, to deal with the entire lot from primary sampler. You have three options:

1) If the system arrangement permits; then remove the grizzly and put a crusher which can deal with the primary sampled coal, in the condition as it is.

2) If the serial no. 1 is not feasible due to space restrictions, put small cross-conveyor of required belt width to receive discharge from primary sample and to feed into right type / size of crusher at suitable distance. Bring back the coal from this crusher output, into the existing sampling system.

3) If you cannot opt for serial no. 1 and 2, then think of putting the sampling system at some onward location in conveying system after secondary crushing. Here it will be dealing with smaller size coal. This will avoid big lump and thereby big crusher in sampling system.

I suggest you to contact reputed manufacturers of sampling systems also, to seek their advice.


Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyor.

Email :

Tel.: 0091 (0)20 5882916

Re: Coal Size Reduction

Posted on 5. Jul. 2003 - 04:14

Yes, you may be able to ram the coal through the grizzly and you and determine the ram size from the following procedure:

Break representative samples individually in a drop hammer test, by size, to get the Population Balance Model (PBM - such as JKTech process circuit simulator or other equivalent) Breakage Function (B). This gives you the surface energy liberated for the known lump volume/mass. From this data, a surface energy differential equation is determined that extends over a range of particle sizes that encompasses your product size distribution.

This gives you the scale up factor you need to find the energy to break pieces of any size. There is a little stretch, which can be worked out with our (CDI) rock/coal fracture mechanics model. The shape of the grizzly and administration of the ram need some definition. Pick them, model rock sizes and placements, with the selected ram kinematics, and the model will return all your points of interest.

As you noted, so much for sampling statistics. However, this can be addressed to a reasonable degree by more than one method.

Need more information contact us:

see our website: for breakage sim.

I will be in South Africa for Beltcon 12 July 23-24. If you would like to get together give me your coordinates and timing.

Lawrence Nordell

Conveyor Dynamcis, Inc.

Bellingham, Washington

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: phone: USA 360-671-2200 fax: USA 360-671-8450
(not verified)

Hydraulic Impact Ram

Posted on 6. Jul. 2003 - 09:05

Have you space above the grizzly? Pls. provide dimensions and details of the grizzly (specifically % open area)and verify the type of coal. Can possibly provide an articulating arm & pedestal base. Need envelope dimensions available above grizzly grade & what electrical service, if any, is available?