Radex recently installed six massive magnets for its 9,000-mtph coal processing plant in Russia.

Magnetic Separation is a key stage of any screening, crushing and sorting plant, and MK Vega-Po LLC (Radex) of St. Petersburg, Russia, recently purchased six Electro Overband Magnets for its coastal coal processing complex in Nakhodka on the Trudny Peninsula, approximately 85 km east of Vladivostok.

Radex started work on the Nakhodka project in early 2013, and the task was to integrate new equipment into an existing coal processing plant specifically for the screening, crushing and removal of magnetic tramp metal prior to feeding the loading vessels. The end specification of the coal dictated that all the output product needed to be below 50 mm with a maximum ferromagnetic content of 0.5 kg per 10,000 metric tons (mt) or 0.000005%, which also could be no more than 50 mm in size in any one dimension. Magnetic separation, to remove the tramp metal and protect the screens, crushers and conveyors and guarantee the high output specification of the coal, formed two important stages within each of the three process lines.

The plant receives around 9,000 mtph of coal, which is then split into three lines each handling 3,000 mtph. At the first stage of the process, material can either be fed directly onto the output conveyor feeding the loading vessel or into the screening and crushing plant. The material that is fed through the screening and crushing plant immediately passes under the first Electro Overband Magnet. This is installed to remove large tramp iron such as excavator teeth, bits, blasting caps, etc., to protect the roller screen. After the screening stage, minus 50-mm material (approximately 95% of the main infeed) in size is fed straight to the main output conveyor feeding the loading vessel, while between 150 and 250 mtph of the 50-to 300-mm coal (between 5% and 8% of the main infeed) is conveyed to an impact crusher. After crushing, the material is returned to the original screening stage, but not before passing under a second Electro Overband Magnet, which removes any metal that has been liberated or introduced during the crushing process.

The Electro Overband Magnet is the most powerful overband separator from the Mastermag range and is designed to operate and separate at increased suspension heights where the operating gap (the distance between the magnet and the conveyed material) will also be higher. Higher strength magnetic power enables the extraction of ferrous metals even from material conveyed along deep troughed conveyors. The magnets consists of a coil, wound of aluminum wire, centrally located inside a mild steel fabricated box and mounted around a solid steel core. When powered, the coil produces a magnetic field that is focused and projected downward by the steel core and a thick steel back plate. All the units supplied to the Nakhodka project are oil cooled, where the coil is efficiently maintained at an optimum working temperature by recirculating oil inside the stainless steel box. Oil-cooled magnets produce higher magnetic fields than air-cooled magnets.

The oil-cooled magnets operate at increased suspension heights where the operating gap (the distance between the magnet and the conveyed material) is high.
The oil-cooled magnets operate at increased suspension heights where the operating gap (the distance between the magnet and the conveyed material) is high.

Prior to installation, a computer model was used to assess applications where there are set separation objectives, and this enables the size, type and design of the magnet to be considered in detail. Other parameters, such as operating at potentially low temperatures, around -20°C, had to be considered when finalizing the design. The high-strength magnetic field meant that ferrous metal would be attracted and propelled up onto the magnet at speed with a high impact force, so the entire base plate is wear-resistant manganese steel.

Radex ordered the Electro Overband Magnets in two stages, with an initial order for two units placed in May 2013 and a second order for four further units placed in February 2014. All the equipment was designed and built by Master Magnets at their U.K. manufacturing and test facility in Redditch, near Birmingham.

The initial order in May 2013, for the first line processing 3,000 mtph, was for one model 200 OCW 45-in. and one model 105 OCW 45-in. Electro Overband Magnet and it was supplied in July 2013. Both were supplied with transformers. The 200 OCW was positioned over the 2-m-wide main infeed conveyor running at 3 m/sec prior to the roller screen, with the 105 OCW situated on the 1.2-m-wide return conveyor post crushing of the oversize fraction. Both units are positioned in line with the conveyor over the head pulley, with separated ferro-magnet material being lifted and then discharged away from and out of the natural trajectory of the coal.

Electro Overband Magnets used in the in-line orientation generally achieve a better separation performance than when positioned across the conveyor belt as the conveyor belt flattens as it passes over the head pulley, breaking the surface of and opening the conveyed material and enabling the more effective removal of tramp metal, especially when located at the bottom of the burden.

The 200 OCW is currently the largest Electro Overband Magnet manufactured by Master Magnets, weighing approximately 10 mt and drawing up to 15.6 kW from the 17.5-kW transformer rectifier set. The overall dimensions, including the running gear, are 4.3 m long by 2.67 m wide and 2.07 m high, which presented several manufacturing challenges. The manufacturing facility is equipped with heavy cranes to handle and manufacture equipment of this size and greater, and there was a heavy reliance on the skills and experience of the engineering and production teams. Subtle changes to the standard design were required as the size and weight of the magnet increased and this knowledge is already being used for future projects where larger Electro Overband Magnets are required. The smaller Model 105 OCW posed no such manufacturing challenges, weighing approximately 5.6 mt with overall dimensions of 3.275 m long by 2 m wide and 1.49 m high and drawing up to 8.7 kW from a 9-kW transformer rectifier.

Following the successful installation of the first two units, Radex placed a second order in February 2014 that was collected for shipment to Russia on June 2014 for the second and third screening and crushing lines, replicating the equipment purchased for the first line. The plant is now fully operational, processing more than 9,000 mtph of coal and maintaining the high quality specification of the final coal product.

This article was written and submitted by Master Magnets, based in Redditch in the U.K.