Revalorization of black steel slags as thermal storage material

AZTERLAN participates in the LIFE HI4S project, targeted at the revalorization of this relevant industrial waste. The project includes as well the construction of a prototype plant for heat regeneration and electricity production.

The recently started European project HI4S (Heat It yourself For Sustainability) is aimed at reusing black steel slag for heat regeneration and production of electricity by reusing waste heat from the electric arc furnaces of ArcelorMittal steel manufacturing plant in Sestao (Bizkaia). The project will measure “in situ” the environmental benefits of this pilot plant to foster its replicability. In the words of the research team, “the possibility of building and installing a full-scale prototype in a steel plant working at full capacity offers the best possible scenario for the validation of the new developments”.

This prototype will have a thermal storage system based on the black slags generated in the steel manufacturing process. In relation to this type of granular bed storage, one of the most important challenges is to ensure the durability of this solid material to mechanical and thermal wear. In this area, AZTERLAN Metallurgy Research Centre will evaluate the long-term mechanical stability of the steel slags, by performing a preparation and advanced characterization of this waste. Among others, variable axial load cycles and heating/cooling cycles will be evaluated on slags to validate their performance as thermal storage material. The research team is convinced that “not only will we be able to improve the energy management of the steel industry, but will contribute as well to its efficiency and competitiveness by means of the valorization of this solid secondary product (black slag)”.

Complementarily, the HI4S project aims to build and validate a high temperature filtering system that will avoid the usual obstruction problems associated to heat exchangers and that will reduce the costs of the associated emissions. Also a flexible, cost-effective and sustainable waste heat reuse system that allows several modes of operation will be developed. This system will save about 37.5 GWh/year in the steelworks.

In this line, the HI4S project foresees the generation of substantial environmental impacts such as the reduction of CO2 emissions from steel mills by 9 Tm/year (which would represent 6% of the total emissions of the steel industry) and the reduction of waste (black slag) by 560,000 t/year (10-15% of the total generated in the EU). As a result, the reduction in energy consumption would mean 200 million€/year of emission savings and the energy recovered (37.5 GWh/year) could mean saving 4.9% of the electricity consumption from the electric arc furnace.

The HI4S (Heat It yourself For Sustainability) project has a funding of 1.5 million euros from the European Union through its LIFE Environment and Climate Action programme. The project is led by the CIC Energigune and in addition to the AZTERLAN Metallurgy Research Centre it counts the participation of 5 additional important partners: the companies ArcelorMittal, Fivemasa, Enerbasque, Life Cycle Engineering-LCE and SDEA Solutions.

Variable axial fatigue testing at AZTERLAN facilities (left) and black steel slags (right).
AZTERLAN team will prepare and evaluate the mechanical stability of siderurgical waste to validate its performance as a long-term thermal storage material.