Dear Mr. Achmad Zabir Ula,

I have come across a manufacturer of stone separating system. As described by the manufacturer, the system has stone sensor near conveyor head end. At the discharge end, there is a two-way chute with motorised quick action gate / grate.

The gate position gets automatically changed on sensing of stone. This results in, the stone along with its coal being discharged into a separate heap. Thus, coal without stone is obtained. The coal heap which is having sizeable proportion of stone is treated seperately.

The system can be located at any point in flow path.

Regards,

I G Mulani - Author - Book 'Engineering Science and Application Design for Belt Conveyors'.

parimul@pn2.vsnl.net.in ■

Dear Azabir

One method depends on the difference in strength between stone and coal, and on the stone size distribution. With stones of reasonable size (ie. pickable by hand), a rotary breaker will do it. The breaker, with a wall aperture set smaller than the desired stone size, will break the soft, low strength, coal and pass it through the wall, and transport the stronger stones to the waste end discharge.

Other means include separation by density difference between rock and coal. This is necessary with a very small stone size.

Look into the science of separators and tailor the device to your unspoken criterion.

Good Luck

Lawrence Nordell

Conveyor Dynamics, Inc.

website: www.conveyor-dynamics.com ■

Dear Mr. Achmad Zabir Ula,

As per the information and quotation available with me of 1994, the name of the company and its address are as below:

ANATEC GmbH, Gewerbepark Sud 1,

Gerhard-Hauptmann - Strase 15,

D-03044 Cottbus.

Tel.: 49-(0)355 79 52 66

Fax.: 49-(0) 355 79 52 19

Their Indian representative name and address is :

Ardee Business Service Pvt. Ltd.

9-30-4, Siripuram,

Vishakhapatnam - 530 003

India.

You may contact them for the required information. Only they will be able to say where they have supplied.

Regards,

I G Mulani - - Author - Book 'Engineering Science and Application Design for Belt Conveyors'.

parimul@pn2.vsnl.net.in ■

Achmad,

You might take a look at the following website:

www.imperial-technologies.com

They profess to differentially break coal and not rock by adjusting the impact speed of the "Accelerator" crusher impeller. Their website addresses the points you raise and that I have discussed wrt the Bradford Breaker. The big difference is the variable speed adjustment of the impeller to allow the operator to tune the breakage of coal and not stone. The friable coal then passes through a grate on the shell behind the tines.

Rob Christian is the president and seems to have the expertise you require.

I don't believe the sorter system, proposed by Mr. Mulani, can handle any reasonable tonnage. If you find it can, please advise the forum. We all have such need and have many applications in this profession.

Best Wishes

Lawrence Nordell

Conveyor dynamics, Inc. ■

Dear Mr. Achmad Zabir Ula,

Referring to the stone separating system mentioned by me, it functions as below; as informed to me by M/s ANATEC Germany (their representative). This is for general information of everyone concerned with the subject. I am not suggesting any particular system.

The stone detection is by Gamma Ray source (sensor) installed on belt conveyor. Stone detection is by difference in density of coal and stone (shale). The difference in density affects the rays reaching to receiver in the sensor, which is set for certain threshold limit of density. This enables to know the presence of stone (material denser than coal), and the system interprets this signal accordingly.

Now, suppose the sensor is 15 meters before the discharge pulley and if the belt speed is 3 mps, the sensor signal will activate stone removing system in discharge chute by 5 seconds delay. That is to say, the entire quantity of material on belt, for say one-two meter length, would get discharged separately, by quick action gate in discharge chute. As the manufacturer of this system says; it can be tuned for stone removal from very coarse to fine coal.

Thus the aforesaid system works on the principle of difference in density of coal & stone, to create stone removal by mechanised means. It will have small quantity of separated coal with very large proportion of stone.

The system / equipment referred by Mr. Lawrence Nordell works on the principle of difference in required crushing force.

Bradford breaker system will also have small quantity of separated heap i.e. reject containing unusually hard coal, wood & stones.

I cannot opine on forum as to which system would be better. It has to be analysed on theoretical considerations, nature of coal & stone, reliability, past reference, cost, feasibility of installation, safety etc.

Regards,

I G Mulani - Author - Book 'Engineering Science and Application Design for Belt Conveyors'.

parimul@pn2.vsnl.net.in ■

Dear Achmad

The separation by breaking or other process, involves knowledge of the refuse rock properties.

You state you have tried a Bradford Breaker and found it unsatisfactory due to the stone strength was very much like the coal strength. Can you give information on the Bradford breaker specifications? Have you tested the stone strength with conventional methods such as a JKMRC drop hammer test or drum test?

What is the type of stone - sandstone, shale ....? I will need information to characterize the material strength, size distribution, and other attributes, before I can be of help.

Lawrence Nordell

Conveyor Dynamics, Inc. ■

Dear Achmed

The Bradford breaker raises the product and drops it, using gravitational acceleration to produce a force sufficient to break the product (coal) but not the refuse rock. Size of the breaker diameter is choose to achieve this goal. To size the diameter you must first know the strength charateristics of coal and refuse. Either a self breakage (drop from various heights and sieve size fractions to quantify breaking strength - usually larger rock sizes) or drop hammer, as I suggested earlier, to raise the specific energy delivered to smaller size fractions. The plot of energy applied to surface area exposed yields the materials surface energy property that we use to charaterize crack tip propogation in all fracturable materials. The comminution process can then be modelled.

Your response does not include this information, and I see further dialog on the subject, in the forum,. to be too detailed for this type of correspondence. If you wich consultation to solve the problem, chose a reputable consultant or manufacturer who are known for solving the same.

As a side note, the Bradford breaker you are using may be to small a diameter, have improper lifters, run at the wrong speed, have the wrong grate openings, or is inappropriate for the class of material you are pdrocessing. Other euipment may be required.

Much Luck,



Lawrence Nordell

Conveyor Dynamics, Inc. ■

the best way is to use coal separation device such as jig, dense medium bath or heavy medium cyclone or dry separator. ■

Dear azabir

Most of the stones/slales can be seperated by Rotary breaker as sugested by Mr nordell however in case hard groove index of coal and shale is of the same range then it will be difficult to seperate stone by rotary breaker . Device as sugested by Mr Mulani is also possible.

To day photo sensors sensing different colour shades are available in the marcket in case stone colour is different than coal same can be sensed by photo sensor and stone can be spooled from conveyor as we do for sampling of coal .

Coloured photo sensor you can try with IFM, OMRON, Or Telemechanik

kindly let us know whether coal and stone colour are different so that equipment can be designed for this application

A R SINGH ■

zxm99 is perfectly correct. Coal washing used to be a South African forte, necessitated by the often poor coal quality. If you care to track down Chamber of Mines or South African Coal Owners Association papers you will find plenty of information therein. ■