Steelworks

As the composition of tyres includes a large quantity of carbon, it is thus possible to replace the anthracite that EAF plants use to reduce the rust in the end-of-life scrap.

This use of tyre shred is an effective, economical and ecological process that has been validated since 2004. Every year, 7,000 tonnes are thus recycled in France and 1,500 tonnes in Belgium. The quality of the steel remains identical, and both the gas and dust emissions are equivalent.

How to replace anthracite with end-of-life tyres in steelworks

Since 2004, ALIAPUR and the steelworks LME have successfully used a new recycling technology for end-of-life tyres in an EAF plant. This technology was developed by Arcelor Research at the request of Arcelor and Michelin, and supported by the ADEME.

The manufacture of steel in an electric arc furnace is based on the fusion of scrap metal at a high temperature (1,650°C) for around 45 minutes until it is molten. An electric arc at a temperature of more than 15,000°C ensures that the temperature rises progressively.

Usually, in an electric arc furnace, around 3,300 kg of lime and 1,150 kg of carbon in the form of anthracite are added to 100 tonnes of scrap metal. The anthracite provides the carbon, which dissolves in the liquid metal, where it plays the role of reducing the iron oxides: rust.

The process

First of all, oxygen and methane lances are used as burners. These burners heat the scrap metal situated in cold spots of the furnace that the electrode does not reach effectively. Once the scrap metal has melted, the lances inject pure oxygen, thus generating the “decarbonisation” and “post-combustion” of the excess carbon anthracite, added to the scrap metal, and creating additional energy by means of exothermal reactions.

A tyre is composed of carbon and iron. The possibility of replacing all or part of the anthracite placed in the electric arc furnaces with end-of-life tyres opens the way for new technology for recycling tyres. Arcelor, via its research pole Arcelor Research, has been working since 1997 with a range of partners (ADEME, Michelin) on this research theme.

The tests

The initial on-site tests were carried out in two steelworks in the Lorraine region of France.

The technique was first tested, then refined, in the EAF plant of Ascométal in Hagondange.

Finally, in order to validate the principle, regular and prolonged industrial use was tested in the furnace of SAM Neuves-Maisons. Once it had been verified that it was possible to function without incident, different means of introduction were tested: from whole tyres to powder, all whilst monitoring the material and thermal reviews, as well as the emissions of the furnace.

It was possible to identify several good practices:

• Controlling with precision the quantity of tyres added
• Adding tyres at the right place in the load, neither on top, nor at the foot of the bath
• Adapting the use of burners and the implementation of post-combustion.

The results of the tests

5 to 12 kg of tyres are added per tonne of steel, that is to say, a quantity similar to that of coal. If the tyres have been cut into pieces measuring around 10 cm and are added to the load in bulk, the thermal balance of the furnace revealed no distinction between the carbon obtained from anthracite and that from tyres. The substitution rate calculated was 1.7 kg of tyres for 1 kg of anthracite. The metallurgy results, particularly with regard to sulphur, were not affected.

A positive environmental review

• Measurements in capturing: no incidence (VOC, SO₂),
• Stack emissions: no incidence on the concentrations measured in HAP, BTEX and PCDD/F (PolyChloroDibenzoDioxines and Furanes) in the gaseous phase and in C, S, Cd, Zn, Pb, TMS (concentrations of soluble materials) and HAP in the dust,
• Heart of the furnace: no notable modifications.
• An industrial success, and an environmental success

Following these conclusive tests, the project to use end-of-life tyres was developed industrially at the LME site in Trith-Saint-Léger (59), in partnership with Aliapur. During the first year of industrial operations (2004-2005), LME and Aliapur wanted to confirm the feasibility and good practices identified during the on-site test phase.

Roughly 1 tonne of tyres in the torn form is incorporated into the scrap metal by casting as a replacement for the anthracite, or approximately 1% of tyres per cast.

The observation carried out jointly by Aliapur and LME focused on the environmental evaluation of this type of substitution: impact on dust (LRCCP) and impact on gaseous effluent (Air Liquide). The review of these analyses made it possible to highlight the fact that all the operations took place in a normal manner and that the dust samples did not reveal any significant differences when either tyres or anthracite were used.

These tests confirm that the use of tyres requires the adaptation of the post-combustion parameters (oxidation of the CO into CO₂), so that the combustion of the CO takes place in the furnace and not partially in the capture circuit, which would result in a loss of energy in the smoke as well as excessive thermal solicitation of the installation.

Since 2005, the LME site in Trith-Saint-Léger (59), which is capable of processing 7,000 tonnes of tyres per year, shows the viability of the recycling of end-of-life tyres in an electric arc furnace.

Other industrialists are renewing the experience

In view of the initial results from LME, and encouraged by the Wallone Region, Industeel Belgium (Arcelor) in turn developed the process, from 2004, in order to attain a heat pattern of 1,500 t per year. This second industrial experience confirmed the results from LME, both in terms of specific tyre consumption and anthracite savings. Both these industrial experiences now open the way for technology that is favourable to the environment, for the recycling of end-of-life tyres, all whilst producing savings in raw materials for steelworks.

Further information

A video explains the use of shreds in steelworks (Aliapur).