Valorisation of recycled polymers as foaming and recarburising agents in EAF steelmaking

This innovative technique consists in the use of recycled polymers (or Secondary Reducing Agents, commercialised as BLUAIR®) in EAF steelmaking. They are used to substitute foaming/recarburising agents (e.g. anthracite). This approach enables the recycling in EAF steelmaking of a mixed plastics fraction (normally sent to incineration / landfills).
This technology was tested as part of the RFCS project OnlyPlastic in the period 2019 – 2023 at an EAF plant operated by Feralpi (Lonato, Italy).

TECHNICAL DESCRIPTION

Production of the Secondary Reducing Agent (SRA - BLUAIR® product):
The SRA production starts with the separation of high-value post-consumer plastic waste (e.g. PET and HDPE containers/bottles, rigid PP) which are sent for production of new plastic products. The remaining plastic waste stream, mainly composed of mixed and multilayer/ flexible packaging, which are not suitable for traditional recycling applications and have a low economic value on the market, is normally sent either to incineration or landfill. This is the case of mixed polyolefines (e.g. typically originating from food packaging). To avoid this scenario, this fraction is cleaned from undesired materials (e.g. small metal scraps, chlorine-bearing plastics, etc) and subject to mechanical treatment. In practise, a series of different pre-treatments (shredding, dry cleaning / optical sorting and/or flotation) are carried out, after which the material is densified and agglomerated to produce grains with a size of 2–6 mm, mainly made of polyethylene and polypropylene. This product, commercially identified under the name BLUAIR®, is used for injection in EAF steelmaking for substituting anthracite. The BLUAIR® product and its production process, was developed by I.Blu in Italy.

Use of the SRA (BLUAIR® product) in EAF steelmaking:
In EAF steelmaking, after the scrap has been completely melted, carbon- and hydrogen-bearing materials are injected during the refining stage in the molten metal bath to reduce the metal oxides present in the slag and perform important functions (e.g. foaming and recarburising). At this stage, recycled polymers can be used to substitute a portion of the injected anthracite and successfully perform the same functions in the process.

The recycled polymers are fed to the EAF through injection lances, they penetrate the slag above the steel bath thanks to their mechanical properties achieved through the agglomeration (e.g. density). Once they have reached the slag layer (> 1500°C), carbon and hydrogen combine with the oxygen deriving from both metal oxides of the slag layer and from the flow of supersonic oxygen injected through a dedicated lance. Part of the oxygen also derives from outside of the EAF, due to the negative pressure of the furnace. Once CO-H2 has formed, these elements contribute to the foaming and recarburising effects.

Recycled polymers injection is made possible by specific injection systems that have been developed by Tenova. This includes a specific twin injection system coupling a supersonic oxygen injector with coal injector in a single device that can be mounted on the furnace wall, designated as Tenova KT® Twin SRA. This injector can be used for revamping of existing installations. Also, a new injector enabling both the injection of recycled polymers and lime using the same device, designated as Tenova KT® Multi was also tested. In the OnlyPlastic project, both injectors showed good performance in terms of slag foaming with no solid material entrainment into the fume system.

Use of SRA in Blast furnaces (BF):
Although the use of SRA in EAF steelmaking constitutes a new development, it is important to mention that the use of SRA in blast furnaces was already included as BAT (BAT 70) in the current BREF document for iron and Steel production (2012). In BF, the use of recycled polymers can substitute virgin pulverised coal. According to the industrial experience and technical evidence gathered on the use of recycled polymers, it is necessary to use adequate waste streams as feedstock (post-consumer mixed polyolefin-based packaging) and to carry out specific recycling treatments of the waste in order to ensure high quality standard of the product and no negative impacts on the industrial emissions of steelworks.


BLUAIR product specifications:
A technical standard for SRA production was developed by the Italian Authorities (Standard UNI 10667-17), which defines several quality requirements that the BLUAIR® product needs to meet in order to be used for recycling in iron- or steelmaking applications. In particular, it contains specifications for the chlorine, sulphur, cadmium, lead and mercury content (See supporting information).


MATERIAL EFFICIENCY
Virgin fossil materials (coal / anthracite) are preserved and kept in the ground, as they are replaced by the recycled carbon and hydrogen contained in SRA. This reduces the impacts related to their extraction, long-distance transportation and refinement. In the current geo-political instability, raw material crisis and price volatility, the use of SRA in BF or EAF steelmaking could constitute a valid alternative to coal/anthracite which typically have to be imported from non-EU countries, especially at a time where other alternative decarbonisation techniques are not yet available on an industrial scale (e.g. hydrogen steelmaking).

DEGREE OF MATURITY

EAF steelmaking:
In the past 10 years, several European EAF steelworks have injected recycled polymeric reducing agents, ranging from experimental to consolidated industrial supplies. This technology is currently on TRL 9 (industrial scale), with industrial supply and/or trials running in about 20 EAF plants across Europe and with a total supply of about 60.000 ton in the past three years (I.Blu data on BLUAIR® product supply). According to the industrial experience gained over the years, the injected coal substitution rate normally ranges between 30% and 50%. In the framework of the RFSC Only-Plastic project, even 100% of the injected coal was substituted at Feralpi EAF plant. However, this is an exception as in most EAFs, it is not feasible to substitute 100% of the injected anthracite due to the lower fixed carbon content compared to coal (which is useful to boost the recarburising effect).

BF ironmaking:
The use of plastic waste as reducing agent in blast furnaces is a well-established industrial practice (BAT 70 of the Iron and Steel BREF - 2012). Example plants which have successfully implemented this technology include Voestalpine Stahl GmbH in Austria as well as Salzgitter in Germany. Over the past three years, more than 200.000 ton of treated plastics have been used in blast furnaces in the EU. For BF applications, typically the pulverised coal substitution rate with recycled polymers is maximum 20%.


CROSS-MEDIA EFFECTS:
The risk of higher contaminant concentration can be relevant if untreated plastic, which does not come from safe points of origin (e.g. mixed/multilayer polyolefin-based plastics from separate collection is a tried-and-tested safe source), is injected. To guarantee the compliance with specific criteria regarding the concentration of heavy metals and other relevant substances, the mixed plastic waste has to be adequately treated and recycled before supply and injection. The quality criteria for waste plastics specified in the technical standard UNI 10667-17 can be used as guideline to ensure quality of the SRA used in both EAF / BF applications.


BARRIERS TO IMPLEMENTATION:
The End-of-Waste status of the BLUAIR® product is an essential requirement, due to the significant legal, economic, and logistical constraints linked with the handling of waste materials that steelworks encounter otherwise, which in some cases can represents a barrier to the uptake of this technology. If the SRA is compliant with the Technical Standard UNI 10667-17, it can be considered as a secondary raw material, meaning that this material achieved the end-of-waste status according to Article 6 of the Waste Framework Directive. This aspect is very important since it allows to deliver to steel plants the SRA as a product instead of waste, with a strong simplification on the legislative side for the steel producer.

Basic information about the technique

Participant Companies