As Roland says using magnet separators is your best bet. Then still maintain a metal detector downstream of the separator that will alarm and trip the belt if detected.

With a suspended Eriez Magnet placed correctly over the conveyor we successfully pulled tramp metal out from the stream of primary crushed salt at 2500 TPH and a belt width of 48" running at 650 FPM. We always placed the magnet just downstream of the primary crusher which was the main source of the tramp metal. The efficiency of this set-up is dependent on the size/weight of the tramp metal and the capacity of the magnet. But if it gets by the magnet you would definitely want the belt to stop and prevent any damage to the system just as Roland describes.

Eriez Magnets is one company that has what you need and there are many others. http://www.eriez.com/Products/Index/...neticseparator ■

Hello,

The coal being conveyed gets mixed up with very tiny proportion of metal pieces (tramp metals), during mining and subsequent handling. The tramp metal can have bolts, nuts, nails, crow-bars, screw drivers, spanners, liner pieces, etc. The mining and handling machines are mainly of iron / steel and therefore the major proportion of tramp metal is tramp iron which is magnetic. Very small proportion will be non-magnetic tramp metal.

So practice is that the coal flow first passes under magnetic separator which separates out tramp iron, without any disturbance to conveying system. Then the coal flow passes under metal detector, which can only detect but cannot remove non-magnetic metal. The metal detector stops the conveyor (and thereby entire system feeding to this conveyor) for physical removal of non-magnetic metal.

The installation of magnetic separator being first and then metal detector, it will reduce the frequent disturbance to working of the system by metal detector (which is dealing with very less number of non-magnetic tramp metals). This is well known by concerned people and generally the installation will be as per this sequence.

Adjust the metal detector sensitivity such that it would not disturb the working of the system unnecessarily by harmless size of non-magnetic metal items. Generally plant engineers and operators make safe compromise decision suitable to their plant and resolve the issue.

Mostly, there is system to separate out stone pieces from coal being conveyed by conveyor, without stopping conveyor. But it seems non has applied such system in conjunction with metal detector.

Ishwar G. Mulani

Author of Book : Engineering Science And Application Design For Belt Conveyors (new print November, 2012)

Author of Book : Belt Feeder Design And Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India.

Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

Hi,

A belt magnet is critical in a materials handling operation where conveyors are used. Contaminant tramp iron can cause serious damage to the conveyor belts and to other process equipment downstream. The capital cost of a magnet is usually easily justified by the replacement cost of damaged conveyor belting and crushing equipment.

A Magquip type self air cooled belt magnet would be perfect for your application. Magquip belt magnets are self air cooled and require no cooling oil (environmentally friendly), they use almost half the kW power consumption of a equivalent oil cooled type magnet with the exact same magnetic performance and flux density figures (energy efficient).

You should ensure that the magnet is adequately sized to handle the the expected range of tramp iron from either ROM / underground sources.

For a video of a Magquip magnet in operation see this link - http://www.youtube.com/watch?v=DOKDfHYFWEY

The video shows a large belt magnet being tested for a wide overland conveyor belt, the expected coal material burden depth was 550mm, the belt was traveling at over 3.5m/s.

Rory Flanagan

MAGQUIP ■

The other way instead of using magnet separator is Two-way chute.

Whenever the metal detector find any metal it sends a signal that run the motor of two way chute. So a part of material which include tramp such as metal rejected.

However in this way you will lose some of your process material with metal. ■

Hi,

Removing tramp ferrous metal and non-ferrous metal are easy if done properly. Only metal detector is not good enough to remove such material, it will effect your down steam production on repeated tripping of material conveyor. Both Metal Detector and Magnetic Separator to be used for 100% tramp metal removal. We have executed several project and had been successful in this. Volume or quantity or frequency of tramp metal is not any issue, but separation is meant for different equipment.

For a vivid introduction let inform you metal detector can detect any metal ferrous or non-ferrous, but tripping the convey every time is not ideal. Magnetic separator has to be installed before this metal detector, which will remove the tramp iron / ferrous metal first, now for the left-over non-ferrous metal keep it for metal detector to detect. In this way the chances of tripping the main conveyor is reduced hugely. You might find that presence of non-ferrous metal among tramp metal is comparatively less.

Magnetic Separator will automatically remove the tramp material, but remember metal detector must have marking device to locate the tramp metal in conveyor. Point to be noted SS / Stainless Steel of grade 304 & 306 is neither separated by magnet nor detected by metal detector. Metal Detector Strength to be selected wisely of what size of metal you want to be detected and for magnetic separator the strength / lifting capacity in weighted to be selected wisely.

Please note for effective selection of magnetic separator few parameters to be affirmed. For which i have attached two pdf that will help you how to select the magnetic separator and metal detector.

NOTE: not all magnetic separator can remove tramp metal effectively but selection of actual gauss (magnetic field) required to lift the tramp metal from conveyor is important. Magnetic strength to be decided in hot steady condition of magnet.

For example: For 1200mm belt width, magnet surface shall be not less than 1400mm, strength 1000gauss in hot steady state at operating height of 400mm, minimum 10KW magnet rating i.e. 60Amp DC at 165VDC; will effective to remove 30KG of tramp iron piece. motor to drive the magnetic separator belt shall be not less than 11KW with gear ratio i=7.5 to remove the 30kg tramp iron from magnet surface.

Fell free to contact for any help!

With Regards

Bitesh Biswas

Ph: 09432014017

email: bitesh@electrozavod.com

Originally Posted by mechdesign

Magnetic Separator in Coal Conveyor (Alarm / Tripping) ?

Dear Sirs,

In our power plant, metal detectors are provided in the conveyors. The metal detector gives an alarm when metal pieces are detected and signals to trip the conveyor drive is not provided. The contractor says that alarm is sufficient and if tripping of the conveyor is provided, then it will stop all the upstream conveyors (totally 7 Nos.) and restarting the same would take 15-20 minutes. (Please note the conveyors are 1800 TPH capacity and many drive motors are HT).

I would like to know the general practice in the power plant industry regarding tripping of conveyor when metal pieces are detected by metal detector.

Attachments

electro zavod magnetic separator presentation (PDF)

md mounting (PDF)

■

Hello,

This stone removing system mentioned by me earlier, is principally working in a manner similar to the information mentioned by Mohandes. The plant manufacturers can think of using such system in conjunction with metal detection (after removal of tramp irons by magnetic separator).

The sensor (X-ray, metal detection, radioactive and so on) senses the objectionable item (object, material) in material flow and positions the flap gate in 'divert position' at right moment, so that particular patch of material along with objectionable (or acceptable) goes into right path.

Proper design analysis along with high quality automation and quick reaction flap gate will minimise the size of material patch going into particular path.

Ishwar G. Mulani

Author of Book : Engineering Science And Application Design For Belt Conveyors (new print November, 2012)

Author of Book : Belt Feeder Design And Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India.

Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

Dear all,

There are "metal separators" work both for ferrous as well as non-ferrous materials , based on eddy current principle? I had gone through such article, though I do not have experience with them.

Regards, ■