Vertical shaft kilns – Electrofused magnesia production

During the 1980s, the benefits of using electrofused magnesia in steelmaking refractories became widely recognised. QMAG’s electrofusion plant consists of three 4.5-megawatt Higgins-type electrofusion furnaces.

Our furnaces use high purity QMAG calcined magnesia as process feed material. In each of the three furnaces, large amounts of electricity pass through three high-quality, large diameter graphite electrodes. This effectively and rapidly heats up the calcined magnesia from room temperature to around 3000 °C. The material in the centre of the ingot becomes molten liquid MgO. Additional calcined magnesia is fed into each ingot during the fusion process until the optimum ingot size is reached.

The ingots have water-cooled shrouds to stop the molten MgO from escaping. This is where the properties of magnesia come into play, with the calcined MgO on the outside of the ingot acting as a heat-resistant insulation layer to contain heat within the ingot.

The fusion process takes around 8 hours and is followed by a controlled cooling process. This is critical to ensure we obtain the correct physical properties from the solidified electrofused magnesia (EFM).

Once the ingots have been allowed to cool, they are broken apart using hydraulic excavators and sorted into their respective grades. The feed material’s chemistry defines the final product’s chemical properties, which is vital to achieving the highest performance EFM products. The overall amount and ratio of impurities are also important to produce high melting-point secondary phases. These chemical properties, combined with the high density and very large periclase crystal size, ensures that QMAG’s EFM products are considered to be among the best in the world. As a result, QMAG has superior performance in steelmaking refractories when compared to competitor magnesia carbon brick products.