Biochar in the Höganäs sponge iron process – techno-economic analysis of integrated production

Sammanfattning: Biomass-based reducing agents have a potential to substitute fossil reducing agents in the steel industry. However, the industrial use of biomass-based reducing agents is currently in an early stage of development and has not yet been considered as a means to reduce fossil CO2 emissions, even though the use of fossil-based reducing agents for the iron and steel making cause the highest share of CO2 emissions. This master thesis presents a techno-economic analysis of a 10 MW biochar production plant integrated with sponge iron production in Höganäs. In this study, a steady-state process model was developed, where state-of-the-art research and development in biochar production for increased biochar yield was applied and adapted, using the principle of bio-oil recycle. The developed process model was used to evaluate the biochar production plant, in terms of conversion efficiency, production costs and CO2 emissions, for different process configurations. The results show that bio-oil recycle with 20 wt.% bio-oil increases the energy yield of biochar with 14%. However, it was found that bio-oil recycle increases the required heat input of pyrolysis which led to reduced plant efficiency with 4%-units and increased biochar production costs of 500-1000 SEK/ton biochar. It was found that system integration with Höganäs can reduce the production cost of biochar from over 5000 SEK/ton to under 2000 SEK/ton, where the most significant integration aspect was flue gas integration. The sensitivity analysis showed that the cost of biomass feedstock and total capital investment were the most sensitive input parameters. It was found that system integration with Höganäs was essential to achieve production costs of biochar below the price of fossil reducing agents. It was also found that co-produced bio-oil becomes a main product, essential for the economic performance of the biochar plant, even though the intended main product was the biochar.