The stainless steel industry has grown substantially in the past decade, with an increase in global melt shop production of nearly 40 per cent. Within the industry, there is now a strong commitment to transforming stainless steel manufacturing into more environmentally friendly production processes. The transformation generally includes changing to fossil-free electricity and developing robust supply chains for high-quality recycled scrap, thereby contributing to the circular green economy.
However, seen from a life cycle perspective, there are still challenges to overcome on the journey towards truly sustainable stainless steel manufacturing and net-zero emissions. A life cycle assessment (LCA) of the melt shop processes reveals both direct and indirect CO2 emissions. Direct CO2 emissions arise mainly from the decarburisation of the steel and will depend on incoming carbon levels and the desired steel grade. The indirect emissions stem primarily from electricity consumption and the amount and source of additives and alloying materials used in the processes.
Assessment of the current situation
To reach an efficient and sustainable stainless steel production, the producer must therefore implement a system for control and optimisation of the resources used in the melt shop and follow up the environmental performance of implemented changes and optimisations. The first step should be to assess the current situation and collect data on emissions associated with the production. The assessment should include both direct and indirect emissions and map the resources used in normal practice. Apart from electricity, the indirect emissions in the EAF mostly arise from electrode consumption and carbon injection. The indirect emissions in VOD and AOD converter refining are mainly connected to the process gases, alloys, reduction agents, and lining used during processing.
Process design optimisation
The second step is to optimise the processes to find the most sustainable route. This step requires some form of a process design system that allows the process metallurgists to design and simulate the most efficient and sustainable practice based on actual production data and reliable thermodynamic models. The system must be able to consider indirect emission factors such as refractory wear, gas-blowing mixes, and the use of additives. The pre-designed practice should then be the basis for the operative process control. Ideally, the two modules – process design and operative process control – should be integrated in the same system to assist the operator in making informed decisions based on actual conditions and pre-designed measures.
Process evaluation and continuous improvement
The third step is to review the measures taken to lower the total emissions from the processes. With collected data from several different heats and campaigns, the production management team is then able to evaluate the environmental performance of the melt shop. The evaluation should preferably be made in a built-in module in the steel production management system to avoid any time-consuming manual data extraction. Once the evaluation is ready, the data can be used for new optimisations and contribute to the continuous environmental improvement of stainless steel production can evaluate the melt shop’s environmental performance.
Following these three steps, the stainless steel producer will take control of direct and indirect emissions and lower the steel plant’s overall carbon footprint. If the power of steelmaking digitalisation is seamlessly integrated with the producer’s environmental and sustainability objectives, actual continuous process improvements and optimised resource usage can be achieved.