The use of charcoal as a fuel and reductant in ironmaking and steelmaking in place of fossil fuel-based carbon sources has been assessed from both an environmental and economic point of view. Life cycle assessment methodology has been used to indicate potential reductions in greenhouse gas emissions resulting from charcoal substitution rates up to 100 % in the integrated, direct smelting and mini-mill routes for steelmaking. The results indicated that based on typical costs of charcoal and coal, charcoal is not competitive with coal in the steelmaking applications considered. However, the introduction of a carbon trading scheme or carbon taxes can be expected to improve the competitiveness of charcoal compared to coal. Based on a long-term price of $US90/t for metallurgical coal, a carbon tax in the order of US$30-35/t CO 2 would be required with the direct smelting and integrated routes for the overall charcoal and coal costs to be roughly equal, including a charcoal electricity co-product credit. However, if the recent increase in price of metallurgical coal is sustained for an extended period of time, the required carbon tax rate would fall to about US$18/t CO 2 .KEY WORDS: charcoal; steelmaking; life cycle assessment; greenhouse gases; costs; carbon taxes. © 2009 ISIJ Steelmaking and Opportunities for Charcoal UseThe integrated steelmaking route begins with iron ore extracted from the earth. After crushing and screening, the iron ore fines are either sintered or pelletised and then fed into the blast furnace along with iron ore lump. Coke, produced from coal in the coke ovens, is used as a fuel and reductant in the blast furnace together with fluxes to produce pig iron. Natural gas is also commonly used as a supplementary fuel in the blast furnace. The pig iron is transferred to the basic oxygen furnace (BOF) along with steel scrap, where oxygen is used to refine the pig iron into steel by reducing the carbon content.In direct smelting processes, smelting takes place in a single reactor where ore and coal are both charged into the same melt or bath (hence the name "bath smelting"). The processes utilise post combustion of the process offgases, the heat released being transferred back to the bath to compensate for the endothermic smelting reactions. The HIsmelt process produces molten iron utilising fine iron ores (and other iron-bearing fines) and non-coking coals. The iron oxides are rapidly reduced by the bath whilst carbon from the coal dissolves in the bath. The primary product from the HIsmelt process is hot metal (iron). This iron is tapped continuously through an open forehearth and is slagfree. It can be used as direct feed to steelmaking processes or cast into pig iron.The main opportunities for the use of biomass in the integrated route for steelmaking would appear to be:• replacement of coke as a reductant and fuel in the blast furnace; • replacement of coal and natural gas as a fuel in the blast furnace; • replacement of coke as a fuel in sintering and pelletising. However, it has been suggested ...

The behaviour of lar ge gas bubbles in a liquid bath and the mechanisms of splash generation due to gas bubble rupture in high-intensity bath smelting furnaces were investigated by means of physical and mathematical (CFD) modelling techniques. In the physical modelling work, a two-dimensional Perspex model of the pilot plant furnace at CSIRO Process Science and Engineering was established in the laboratory. An aqueous glycerol solution was used to simulate liquid slag. Air was injected via a submerged lance into the liquid bath and the bubble behaviour and the resultant splashing phenomena were observed and recorded with a high-speed video camera. In the mathematical modelling work, a two-dimensional CFD model was developed to simulate the free surface flows due to motion and deformation of lar ge gas bubbles in the liquid bath and rupture of the bubbles at the bath free surface. It was concluded from these modelling investigations that the splashes generated in high-intensity bath smelting furnaces are mainly caused by the rupture of fast rising large gas bubbles. The acceleration of the bubbles into the preceding bubbles and the rupture of the coalescent bubbles at the bath surface contribute significantly to splash generation.

Top Submerged Lance (TSL) furnaces used for non-ferrous smelting have high heat and mass transfer rates due to the intensive stirring and splashing generated by the lance. While splashing can cause accretion build-up in the upper cooler regions of the furnace, it plays an important role in heat and mass transfer and needs to be controlled to minimise accretion formations while maximising furnace productivity. In this work, splashing was studied by measuring the splash flux from a molten slag bath in a 300 kg pilot-scale TSL furnace and also from an ambient temperature aqueous-glycerol solution bath in a physical model. In both systems, total injection gas flowrate, lance immersion depth and splash height were examined to determine their effects on the splash flux. An empirical correlation was developed based on the results of the aqueous-glycerol physical model using the methodology of dimensional analysis. This correlation was then used to predict the splash for high temperature smelting conditions. Comparison of the predictions with both hot and cold experimental measurements showed the same variation trends and the predicted values were within an acceptable range, particularly in splash heights within 1 m above the bath surface and at medium to high gas flowrates with lance immersion depths being 1/6-1/3 of the bath height. It is concluded that the correlation can be potentially applied to predict splashing behaviour in TSL furnaces.