Blast Furnace and Basic Oxygen Furnace. (BF/BOF): this is a two-step process, in which the Blast Furnace begins by smelting the iron ore into pig iron. This is done by tipping the ore, coke and limestone into a tall cylindrical furnace in which various hot ‘reducing gases’ are moving upward, removing oxygen content from the iron ore feedstock as it moves downward. Coke – a metallurgical- grade, carbon-rich form of coal – is required because it provides enough carbon to remove the oxygen from the ore, as well as the heat to melt the iron. (APP, 2007) The second step then takes place. The molten pig iron is taken to the Basic Oxygen Furnace, where it is injected with oxygen. This progressively combines with the carbon in the pig iron, exiting the molten iron as CO2. Once the carbon content of the iron has been reduced from about 4% to less than 2%, the iron has become steel. The process is largely used for the creation of virgin steel – although a percentage of scrap can be recycled in the Basic Oxygen Furnace, this is relatively low, at around 10-30% of the volume being processed. When a Blast Furnace and a Basic Oxygen Furnace exist on the same site, a steel plant is referred to as an ‘integrated steel mill’. (Xxxxxxx, 2009; IEA, 2009; APP, 2007) The IEA note that the Blast Furnace is the most CO2 intensive part of the BF/BOF process, emitting 1.5–2.0 tonnes of CO2 per tonne of iron produced (IEA, 2009). Wooders (2009) reports that the largest and most advanced plant is able to operate at 1.5 tonnes of CO2 per tonne of steel produced. Assuming similar tonnage of pig iron and primary steel, this is roughly equal to 60-80% of the total CO2 produced per tonne of steel.
