Scientific abstract:

The production of primary steel is characterized by a high emission intensity. Due to its high coal consumption, the steel industry is responsible for around 30 % of industrial greenhouse gas emissions and thus for 5 % of total German emissions. In North Rhine-Westphalia, steel production accounts for up to 30 million tonnes or even more than 10 % of the state's total emissions. The enormous coal consumption is not only due to the high energy demand, but also to the process-related coal dependency of the classic blast furnace process. For a far-reaching decarbonisation of the North Rhine-Westphalian industry, the introduction and rapid diffusion of new technologies and processes in steel production is essential. Two approaches are feasible: one is to maintain existing processes with retrofitted Carbon Capture and Usage or Storage, and the other is to avoid emissions through process changes (i.e. Carbon Direct Avoidance). Herein, direct reduction has emerged as a promising Carbon Direct Avoidance technique in the steel industry. All major German steel producers have announced specific steps to substitute coal-based feedstocks by switching to hydrogen-based direct reduction processes. If the hydrogen production and utilization of the steel producers are supplied by renewable energy sources, emissions can be largely avoided. However, this path is associated with far-reaching technical and procedural changes as well as a substantially increased demand for renewable electricity. Hence, this study presents a case study from Western Germany via quantifying the changes in the regional material and energy flows in the state of North Rhine-Westphalia until the planned decarbonisation in 2045. The quantitative analysis firstly presents a detailed material and energy flow model that depicts the existing supply chain of the regional industry and intersectoral relations. Thereafter, a detailed process simulation model of hydrogen-based steel production is developed according to the industry's detailed technological plans to track the regional impacts of such a transformation to achieve zero-emission steel. In combination with different assumptions on the availability of green hydrogen and complementary climate reduction measures, the results of the process simulation are integrated into the material and energy flow model to map possible stepwise transformation paths until 2045. Here, the analyses show that with a maximum focus on hydrogen, more than 47 TWh of electricity from renewable energies could be required per year for these structural changes. Consequently, our work quantifies different approaches by which the decarbonization of the steel industry can be achieved with lower amounts of renewable electricity. For example, partial reliance on natural gas as a reducing agent in combination with the use of CCUS technologies can significantly reduce electricity demand for the transformation, especially in the medium term.