The suspended electromagnet is a vital part of the quality assurance process in coal mining. As the mined coal travels along conveyors to storage areas it passes under suspended electromagnets that remove process debris. Eriez Magnetics Europe, based in Caerphilly Wales, is a specialist magnet manufacturer, having designed and manufactured the world’s largest electromagnet. Now; the company has designed and built the world’s first suspended superconducting electromagnet (SSE magnet), which is also by far the strongest suspended magnet ever built.

The SSE magnet has been purchased by China National Coal Industry Importing and Exporting Group, for installation at the Qingdao Port in the Huangdao district of Qingdao City, China. The SSE magnet will be suspended over a conveyor to attract and remove small ferrous metal contamination present in the coal. Specifically, the SSE magnet will be used for the removal of detonating caps. These present not only a fire and explosion hazard but could also damage valuable coal processing and transporting equipment, as well as degrade the value of the coal being exported.

Esther Apoussidis, spokeswoman for Eriez, explains further. ‘For locations where there are high capacities and a need for the best level of separation, the SSE is the only solution,’ she says. ‘In this case, the extraction of smaller tramp iron, upwards, through thick burdens of coal, is always difficult. This unit gives a totally new level of extraction.’

The SSE magnet system incorporates a cryogenic superconducting magnet, made of steel, placed in a sealed vacuum enclosure incorporating two cryo-cooler heads and a recycling liquid helium reservoir. This results in the coil temperature being maintained below 4K and so in a superconducting state. Once ramped up, the magnet only requires a trickle of power to maintain its very high magnetic field, which, according to Apoussidis, is nine times stronger than a conventional unit and four time stronger than the company’s best water-cooled unit.

The new magnet provides a field intensity of 4,000 Gauss at a suspension height of 550mm. This results in an extremely high force density, leading in turn to a significant improvement on the separation performance previously attainable. Conventional suspended electromagnets have up to now been limited in the separation levels obtainable over high capacity conveyors, especially with regard to ferrous tramp metals and detonating caps.

The commercial benefits of superior separation performance include improved end-product value and increased productivity, both attributes that could see SSE magnets used in other industries, such as waste recycling, or any situation where there is a need to remove problematic contamination from conveyed materials.

So, is this the ultimate magnet? ‘For today yes.’ says Apoussidis. ‘But Eriez is always looking towards the next development.’