Towards Zero CO 2 Continuous Steelmaking Directly from Ore
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CONTINUED emergence and consolidation of shale gas resources have immense implications for the iron and steel industry worldwide. Also, recognition of the beneficial attributes of zero gas emission steelmaking must be taken into account urgently in the interests of climate change and the well being health and safety of the general public. The challenges of global climate change and energy conservation demand a paradigm shift in iron and steel technology in the longer term. The disruption caused by sub-surface nucleation and growth of CO bubbles in previous attempts to implement continuous steelmaking must be addressed. Primary attention should be focused on iron melts containing effectively no dissolved carbon.[1,2] To the author’s knowledge, no attempt has ever been made to effect continuous steelmaking directly from iron ore employing an essentially carbon-free iron melt with small carbon addition at the very end of the continuous steelmaking process, if this is deemed necessary to meet steel product specification. To make real progress, it is imperative that the iron melt being continuously processed is similar to any other normal liquid phase. Once this essential requirement is satisfied, rigorous process engineering can then be applied in conceptual designs to meet the challenge. For gaseous reductants, carbon pick-up into the iron
NOEL A. WARNER, Emeritus Professor, is with the University of Birmingham, Birmingham, U.K. Contact e-mail: warnerna@ btopenworld.com Article published online August 9, 2014. 2080—VOLUME 45B, DECEMBER 2014
melt can be precluded in approaches employing generic melt circulation technology.[3] The techno-economic feasibility of direct continuous steelmaking based on natural gas employing melt circulation within a singleclosed loop reactor has already been assessed.[2] A proposed melt circulation arrangement with hydrogen is to be seen as the ultimate solution to zero gas emission continuous steelmaking. According to the internet the world’s fourth-largest steelmaker, which accounts for 10 pct of South Korea’s carbon emissions, plans to switch to a hydrogen-based steelmaking process from 2021. Their plan is to produce hot-compacted direct reduced iron (DRI) using established technology, employing a sequence of high-pressure fluidized beds and feed DRI into an EAF. However, even with only minor contamination with carbon, violent sub-surface gas bubble evolution is not precluded. Accordingly, disruption of truly continuous steelmaking, if attempted in-line, is almost inevitable with the strategy involving DRI. The technology envisaged typically employs input pressures of about 12 to 13 bar for hydrogen reduction of beneficiated iron ore fines to produce hot briquetted iron (HBI) at a Process Fuel Equivalent (PFE) of about 16.8 GJ/t HBI. The carbon content of the HBI can be adjusted to between 1.0 and 2.5 pct. By comparison, the hydrogen continuous steelmaking process under discussion in this paper is anticipated to have a PFE of around 12 to 13 GJ per tonne of refined clean steel ready for c
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