Blast Furnace and Steel Making

Blast Furnace Operation

• Approximately 800 tons of pig iron are produced in a blast furnace around five times per day
• The blast furnace operates continuously for 7 days a week, 8 months a year.
• Around 1400 tons of ore, 500 tons of coke, 320 tons of limestone, and 3200 tons of hot air, are used to produce 800 tons of pig iron

Steel Making Process

• Steel is created by oxidizing carbon, silicon, manganese, sulfur, phosphorus, and other impurities from molten blast furnace pig iron inside a converter furnace.
• Refining pig iron involves air or oxygen to burn away impurities, which transform into oxides
• These oxides are less dense than the molten steel and form a liquid slag that can be separated.
• Converter furnaces also process recycled scrap steel in addition to pig iron
• Steel mills use converter furnaces as an initial processing step, due to the ability to process scrap

Bessemer Converter

• In the 1850s, the Bessemer converter was developed and became integral to the Industrial Revolution during the late 1800s.
• Oxidized carbon in pig iron turns into carbon monoxide, further combusting at the converter's mouth into carbon dioxide
• Air blasts oxidize other impurities, forming floating slag, and lime can enhance slag separation from molten steel
• Impurity oxidation is exothermic, raising the molten metal's temperature
• However, the Bessemer process has a drawback, nitrogen absorption from the air blast embrittles the steel

Basic Oxygen Converter (BOC) Process Steps

• Charging scrap
• Adding pig iron
• Blowing
• Tapping molten steel
• Pouring off slag

Electric Arc Furnaces

• Electric arc furnaces utilize electric arcs to generate the heat needed for steelmaking
• These furnaces contain carbon electrodes that extend through the roof
• A three-phase potential of roughly 40 V is applied with a high current between 12,000 to 40,000 A
• A charge of typically up to 200 tons, contains a large amount of steel scrap
• During melting, oxygen is injected into the molten bath to oxidize carbon, which turns into CO
• The addition of fluxes helps remove other impurities, forming slag that floats atop the molten steel

Advantages of Electric Arc Furnaces

• The ability to control the chemistry of the slag allows for the production of a wide variety of steels
• Electric arc furnaces commonly process steel from scrap, eliminating the need for pig iron or blast furnaces
• These operations are typically composed of several components:
• Electric arc furnaces melting primarily 100% scrap charges
• Continuous casting machines to produce plates, bars, or rods
• Downstream bulk deformation processes