Regenerative Energie
About 300 kg of molten slag are the by-product from one ton hot metal produced at integrated iron and steel mills. This slag has of about 1500 °C and a sensible heat of approximately 1.5 GJ/ton. In Europe rapid cooling with closed water granulation plants is state of the art, because the result of fast freezing is an amorphous granulate, called slag sand. The milled slag sand can be sold to the cement industry because of its latent hydraulic properties. The disadvantage of this method is on one hand, the need of a proper water management and on the other hand the necessary drying of the slag sand. So, not only the sensible heat of the molten slag will be lost, but it is also necessary to have an upstream sand drying for using this product in the cement industry.
Therefore a dry slag granulation lab rig (short DSG) has been developed by Siemens VAI in cooperation with Montanuniversitaet Leoben to avoid the negative aspects of wet systems. The main objectives for the new lab rig, which has been built up at the hall of the Chair of Thermal Processing, are the production of slag sand for the cement industry with nearly same properties (> 95 % glassy) like the wet method on one hand and getting hot air from slag cooling for heat recovery on the other hand.
This pilot plant is based on the "Rotating Cup" or also called Davy-principle, where the molten slag will be atomised by a cup, which can be rotated at variable speed. The molten particles are freezing during their flight towards the granulator wall before falling into a developed fluidized bed made by solidified particles before. Different tests will be done with 300 kg slag per batch which will be molten by the flash reactor situated nearby the DSG.
In the 1990's first tests with dry slag granulation were performed at British Steel (today Tata Steel) at Redcar (United Kingdom). The distance from the atomising cup to the chamber wall was about 10 m to prevent molten slag sticking. Slag particles with the same quality and amorphous structure like slag sand made by wet systems could be found, so it seemed that the dry method is suitable in future. But upscaling wasn't necessary due to the absence of political and economical pressure on the steel industry.
In the years 2002 to 2004 a smaller designed granulator was used in Vitkovice in the Czech Republic. These tests were also successful. This granulator was designed for a mass flow of 20 kg/minute of molten slag and without heat recovery too.
| Copyright: | © Lehrstuhl für Abfallverwertungstechnik und Abfallwirtschaft der Montanuniversität Leoben |
| Quelle: | Depotech 2012 (November 2012) |
| Seiten: | 4 |
| Preis: | € 2,00 |
| Autor: | Markus Kofler Klaus Doschek Univ. Prof. Dipl.-Ing. Dr.techn. Harald Raupenstrauch |
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