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Half a century of DRI/HBI electric arc furnace (EAF) use, coupled with low-cost American natural gas (NG) suggests a needed review of trends and controversial issues surrounding this alternative iron source (AIS). Aspects such as iron ore quality and operational influence; DRI stockpiling and transportation auto-ignition; optimum charge design, temperature and mechanism; compositional impact on EAF operation and performance; oxygen/carbon balance; and chemical energy need to be addressed.
DRI/HBI production has grown "exponentially" since its inception in the seventies (Fig 1)[1]. Mexican, Trinidadian and Argentinean steel mills use captive DRI. Venezuela produces captive DRI and exported (merchant) HBI. Recent significant Venezuelan production curtailment has created a worldwide AIS shortage.
This dearth (and dependence) has renewed interest in USA DRI/HBI production where Natural Gas (NG) availability and price evolution now make low-cost AIS production possible.
Aspects of DRI/HBI production and use, such as iron ore quality, stockpiling, transportation, optimum charge design, method; temperature and chemistry; and its influence on EAF operation, energy balance and performance, are reviewed in this article.
NOTE: Unless otherwise stated, DRI is used for both DRI and HBI.
Iron ore quality
Most gas-based DRI production uses pellets since DRI quality lump ore is rarely available. Quality iron ore production usually includes concentration steps which, while influencing gangue and phosphorus content, isn't enough to compensate for decreasing DRI pellet feed quality arising from over-exploitation of resources during the first eight years of the last century[2].
Besides gangue and phosphorus, sulfur released during the pellet reduction process is important for modules using process gas in the reformer. During the pelletising operation, DRI gangue content (SiO2 and Al2O3) can increase (from the binder) as can sulphur (from the induration fuel). Many DRI pellet producers use organic binders[3] (Peridur for example[4]) instead of bentonite to lower gangue content[7], improve metallurgical and chemical qualities, and thereby improve EAF operations and lower overall steel production costs.
To counteract lower ore quality, miners are changing concentration schemes [5, 6] and using new approaches to better define the relationship between mineralogy, pelletising and reduction behaviour [7].
Auto-combustion risk
Despite the known auto-ignition risks involved in stockpiling and transporting DRI, more DRI than HBI has been shipped annually since 2006: in 2013, 8.56 MTe DRI vs. 5.65 MTe HBI (Venezuelan...