The fuel ratio in small blast furnaces exceeds that of large blast furnaces, a phenomenon determined by fundamental principles in metallurgical physics and chemistry. Small blast furnaces, characterized by their squat design, have shorter material columns compared to large blast furnaces. Consequently, the gas heating of the charge is insufficient, and the reaction time is shorter, leading to reduced indirect reduction of iron ore within the blast furnace.
Indirect reduction of iron ore involves exothermic reactions, while direct reduction is an endothermic process. Due to the lower degree of indirect reduction, smelting in small blast furnaces requires higher energy consumption. Additionally, the top pressure in small blast furnaces is approximately 200–250 kPa lower than that in large blast furnaces, resulting in a fuel ratio that is 6%–10% higher.
Small blast furnaces employ large fans, ensuring high smelting intensity with substantial air volume. Typically, wind consumption per ton of iron ranges from 1200 to 1300 m³. For every 1 m³ of air produced by the blower, approximately 0.085 kg of standard coal equivalent (ce) is consumed.
Compared to large blast furnaces, small blast furnaces consume an additional 17.0–42.5 kg of standard coal per ton of iron due to their higher fuel ratio and larger air volume. Consequently, blower energy consumption increases. Under normal conditions, blast furnace fans account for 10% of the total energy consumption in ironmaking. Furthermore, small blast furnace gas contains approximately 5% less CO₂ than that of large blast furnaces. A 1.0% reduction in CO₂ content leads to a 4–5 kg/t increase in the blast furnace’s fuel ratio.
A reduction in iron grade within the furnace results in a 1.5% increase in the fuel ratio, a 2.5% decrease in pig iron production, a 30 kg/t rise in iron slag output, and a 15 kg/t reduction in the coal injection ratio.
Blast furnace ironmaking is based on concentrate, so the quality of raw materials and fuel, production conditions, the level of technical equipment, and the level of blast furnace operation all affect the production efficiency of small blast furnaces.
