Introduction
Blast furnaces are essential components of steelmaking. A blast furnace is a large, tall structure that produces molten iron from coke, lump ore and flux. Bottom-blown blast furnaces are of the most common type today. In these blast furnaces, air enters through a series of tuyeres (nozzles) located near the bottom of the furnace. The air enters the furnace and is mixed with fuel and reactants at high temperatures, forming an intense heat zone. This intense heat zone is used to achieve the chemical and physical changes necessary for the reduction of the furnaces feed materials and the production of molten iron.
The availability of a reliable source of gas for bottom-blown blast furnaces is critical for proper operation. The type of fuel and air supply needed is dependent upon the type of blast furnace and its intended use. This paper presents an overview of the different sources of gas available for bottom-blown blast furnaces, their characteristics and limitations.
Characteristics of Gas Sources for Bottom-Blown Blast Furnaces
The choice of a gas source for bottom-blown blast furnaces is an important consideration. The most common fuel and air sources include furnace gas, coke oven gas, blast furnace coke and coal, natural gas, and oil. Each of these gases has unique characteristics that are important to understand and consider when selecting a gas source.
Furnace gas is the gas produced by the combustion of the burdening material in the blast furnace. It is a combustible gas composed mainly of carbon monoxide and hydrogen, with smaller amounts of hydrocarbons and carbon dioxide. Furnace gas is generated in the zones of the furnace where the coke and iron ore are burned. It is a readily available source of fuel and air, but it is relatively low in calorific value and has limited energy content.
Coke oven gas is a by-product of the carbonization of coal in ovens. It contains a substantial quantity of methane and ethane, with lesser amounts of hydrogen, carbon monoxide and nitrogen. Coke oven gas can be used as a gas source for some blast furnace operations, but its calorific value is lower than other sources of fuel and air, and it can provide limited energy content.
Blast furnace coke and coal is a combustible solid fuel composed primarily of carbon and hydrocarbons. Blast furnace coke is produced by burning a blend of coals in an oxygen-starved environment and is generally used as a source of heat for iron production. It has a higher energy content than furnace gas, but is not suitable for prolonged use as a source of fuel and air due to its physical characteristics, which can lead to clogged tuyeres.
Natural gas is the most commonly used fuel and air source for bottom-blown blast furnaces. It is a clean burning gas composed mainly of methane, with lesser amounts of other hydrocarbons, nitrogen and carbon dioxide. Natural gas is non-toxic and has a high calorific value and energy content.
Oil is a combustible liquid composed of hydrocarbons and other organic compounds. Oil is used as a fuel and air source for blast furnaces and is highly efficient, but is not suitable for prolonged use due to safety issues.
Conclusion
Bottom-blown blast furnaces require a reliable source of fuel and air for proper operation. Various sources of gas can be used to meet this requirement, each of which has unique characteristics that must be considered when selecting a gas source. Furnace gas, coke oven gas, blast furnace coke and coal, natural gas and oil are all potential sources of fuel and air for bottom-blown blast furnaces. Each of these gases has definite advantages and limitations that must be factored into the decision making process when selecting the best source of fuel and air.
