Negative Emission from Electric Arc Furnace using a Combination of Carbon capture and Bio-coal

Abstract: Steel is one of the most essential metals in the world, and it plays a vital role in various industries. The growing demand for steel has resulted in increased CO2 emissions, with the steel industry contributing to approximately 7% of global emissions of carbon dioxide. Among the different production methods, the electric arc furnace (EAF) has emerged as a promising option, and its market share is expected to double in the future. While the EAF exhibits high efficiency and a reduced carbon footprint in comparison to alternative production routes, there is still considerable room for improvement. In the EAF, a significant amount of input energy, ranging from 15% to 30%, is wasted through off-gas, along with a substantial amount of CO2. To better understand the current state and ongoing research in off-gas handling, a literature review and a preliminary analysis were conducted which revealed that the waste heat from the off-gas can be effectively recovered using an evaporative cooling system, yielding approximately 105 kg of steam per ton of liquid steel. This emphasizes the importance of waste heat recovery in conjunction with CO2 capture. Calcium looping stands out as a promising carbon capture technology among the available options, primarily because of its lower environmental impacts and energy penalty. Furthermore, with its operation at elevated temperatures and dependence on limestone, calcium looping presents a potential solution to reduce the emissions from steel industry. Therefore, this study focuses on the analysis of a waste heat recovery system integrated with calcium looping technology, aiming to capture CO2 and utilize waste heat from the EAF off-gas. Additionally, the potential of coal substitution with bio-coal in the EAF for achieving negative emissions is also investigated. Through a steady state analysis and by employing semi-empirical mass and energy balance equations, it was determined that capturing 90% of the CO2 emissions from a 145-ton EAF requires 12 MW of heat and 16 kg of fresh limestone per ton of liquid steel. Although the average off-gas temperature is high, it cannot be considered as a reliable heat source. Therefore, the heat demand is met by burning biomass inside the calciner. Despite the increased heat demand, the waste heat recovery system integrated with calcium looping has the potential to generate approximately 11 MW of electricity using a supercritical steam cycle. This significant output can be attributed to the elevated temperature of the off-gas and the exothermic carbonation process. The economic analysis reveals that the levelized cost for capturing and storing CO2 is 1165 SEK per ton of CO2 with a negative Net Present Value (NPV). It was noted that, a higher carbon tax could significantly enhance the economic viability of the system. Moreover, the study found that by introducing bio-coal in the EAF with a fossil coal share below 69%, it has the potential to achieve negative emissions. Furthermore, recent studies have shown an increase in the CO2 content in the off-gas when introducing bio-coal into the EAF which further enhances the efficiency and economic feasibility of carbon capture.