It is well established that the metallurgical sector generates a lot of wastes, whose treatment is not easy to carry out and can also be dangerous. So, slag coming from electric-arc furnaces has been always intended for dumping. The typical process for this technical waste treatment involves a discontinuous discharge of slag from the furnace, and room temperature refrigeration (although sometimes solidification can be accelerated by water sprinkles). Nowadays, EAF slag is simply poured on the ground, or is gathered in large pots for being discharged on the ground in separated areas, and water is used for avoiding an excessive foaming. As a consequence, slags solidification is not controlled and can last a long time, and manipulation of slag is highly dangerous (as slag is extremely hot, and water sprinkles can lead to explosions. Moreover, in order to reuse this by-product some additional mechanical separating processes like crushing and milling need to be applied. The direct obtainment of a readily usable slag as in the case of blast furnace slags is not possible as water granulation, i.e. pouring the slag into a large mass of water, cannot be applied due to the large variation of EAF slag parameters.
The project undertakes to develop a machine for obtaining a reusable material directly from EAF slags. It was funded by the CIP programme, a grant funding programme, under the coordination of ASO Siderurgica Srl, a metallurgical company based in Ospitaletto (Italy). For developing this equipment, the company was supported by an Italian engineering company (Cabra Engineering) and an equipment manufacturer from Austria (Maschinenfabrik Liezen und Giesserei GmbH).
The new developed system uses two contra rotating cylinders for granulating and vitrifying slag thanks to its quick cooling, which is performed by air sprays below the cylinders. Two heading refractory plates assure the lateral containment of the liquid slag. Additionally, the continuity of the process is assured by a continuous evacuation system of the granulated slag using a series of oscillating tanks or a belt conveyor. The inter-axe distance of cylinders can be adjusted to adapt the rolling width responding to different needs (slag temperature, viscosity, foaming state, etc.). By using this device, slag from Electric Arc Furnaces can be used for several applications like bituminous mixtures, concrete and prefabricated structures, substituting other renewable resources like sand or gravel. As a result, making use of this device in normal conditions to steelmaking processes a huge amount of EAF slag could be reused (in Europe 12 million tons/year are actually dumped).
Within the framework of the project a prototype machine has been developed, which has been tested properly and exhibited to more than 60 steel companies. Furthermore, the device was presented in the 7th Global Slag Conference 2011 and was awarded with the prize of innovation of the year. Steel Shops from several countries (Turkey, Finland, Japan, etc.) are interested in the device. However, ASO needs major investments to develop a full-scale prototype in order to obtain the EC mark and to start its commercialization. This auto-funding cannot be assumed by the coordinator alone. Thus, the project reaches a level 8 in the TRL scale, according to the scope of CIP, which provides public grant funding for demonstration.