Objective
The steel processing induces the production of 100 kilos of steel slags per ton of steel : that does represent more than 7000000 tons of slags per year within the European Union.
Nowadays, due to the iron-ore used coming from Mauritania or Brazil, the steel-slags have a lower content of nutritive elements, making them inadequate for the agricultural soil improvement : they are usually dumped into waste disposal sites.
the aim of the project was to realize an industrial unit able to process steel-slags for agricultural soil improvement. The innovative aspects of such a project are :
- to re-use a steel by-product usually dumped,
- to use new grinding and drying technologies innovative in terms of energy consumption allowing on economical process,
- to use blast furnace excess gas as the main energy source.
The environmental technical and financial advantages are :
- an energy economy due to :
* the substitution of this process to the pure lime processing, since steel slags contain approximately 50% lime.
* allowing to avoid the use of primary energy
* the use of blast furnaces gas, the use of low energy crushing and grinding equipment,
- a decrease of CO2 production due to the here-above facts
- an increase in the quantity of steel recovered within the slags, we are able to re-use.
ENRICHMENT : The product being a slag coming out of the production of steel out of iron plus additives, is heterogeneous. Depending on all the manufacturing parameters the Hardgrove Hardness index can vary between 28 and 86 coefficients, 28 = a virtually uncrushable product and 86 = fracturated limestone; the granulometry can also vary quite heavily : the biggest granulometry could be twice as big as the anticipated one i.e. more than 400 mm.
CRUSHING : taking into consideration these factors we took the initiative of taking a bigger size primary crusher. The size increase was at the origin of a financial negative impact on the investment side but it appears this change has been a key aspect of the success of the whole project since the way the product is prepared for going through the roller-press is essential.
GRINDING - DRYING : Looking after the samples given by SOLLAC it did appear also that the steel content could be much higher than the one anticipated; consequently we gave a particular attention to all the systems possible to neutralize it.
STOCKING - MIXING - DISPATCH : Taking into consideration the wishes of the customers, we redesigned completely this part of the installation. Today the system used which is completely automated is very versatile and allows the production of up to 30 different products in a quick delay.
Energy saving :
- through the saving of slags we suceeded in saving the lime content rich in energy since the traditional processing of lime needs approx. 360 thermies/ton produced.
- through the re-use of blast frunace gas we succeeded in not using almost any more primary energy, and we avoided the supplementary production of CO2 linked to the production of lime.
- through the set up of the RHODAX technology and the roller press concept, we succeeded in saving energy compared to ball mills technology(20.65 KWH/ton)
- Finally through the re-use of slags we are saving waste disposal dumping area.
The project has been located on the harbor of Dunkerque as near as possible to the blast-furnace gas tank to minimize the additional costs linked to the feeding pipeline.The installations can be split as follows :
ENRICHMENT PROCESS : crushed potassium is introduced within a tank at the same time as the molten slag is poured at very high temperature (16000C) coming out of the converters. These mixing tanks are then emptied into cooling pits of a 2000 tons capacity where the slag cools during approximately 6 to 8 hours.
CRUSHING : The second stage of the process consists in sorting out the bigger size elements, reducing the grain diameter and extracting all the iron possibly recoverable.
The preliminary grain size reduction is performed by a new type of crusher called Rhodax (TM) in which the material is compressed against itself : it is the attribution crushing concept. An additional advantage of this type of crusher is its relative low sensitivity to uncrushable objects as well as to the abrasiveness of the slags.
The extraction of steel is made just afterwards through magnetic belts, the steel extracted being recycled to the steel factory.
GRINDING - DRYING : The product with a grain size ranging from 0 to 50 mm, and a moisture content averaging 6%, must be transformed into a product whose physical characteristics should conform to French standard NF U 42001. The choice of the roller-press has been done at this stage to reach the required product fineness and at the same time to lower the energy consumption quite significantly compared to the use of ball-mills.
The material exiting from the roller press is highly compacted and the powder slabs issued are decompacted into a decompaction unit working under the centrifugal principle. The product is then conveyed to a dynamic classifier. STOCKING-MIXING-DISPATCH : the final crushed product is then stored in three 800 tons silos. This product can be mixed with additives (K,Magnesium oxide,...).
Fields of science (EuroSciVoc)
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
- engineering and technology environmental engineering waste management
- agricultural sciences agriculture, forestry, and fisheries agriculture grains and oilseeds
- natural sciences chemical sciences inorganic chemistry alkali metals
- natural sciences chemical sciences inorganic chemistry alkaline earth metals
- natural sciences earth and related environmental sciences soil sciences edaphology
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Coordinator
75016 Paris
France
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