Identification of the Combustion Degree of Oil in the Blast Furnace Tuyeres

In spite of its ancient origin the blast furnace has remained competitive against other alternative processes for production of iron for primary steelmaking. A reason for this is that several inherent bottlenecks have been removed gradually through ingenious modifications of the process, e.g., by introducing metallurgical coke in the 18th century, pre-heating of the blast in hot stoves in the 19th century, and burden agglomeration in the 20th century. Another change during the last century was the introduction of auxiliary reductants, mainly pulverized coal, oil and natural gas, injected along with the blast, often in combination with oxygen enrichment. Today, when alternative processes for production of iron for steelmaking emerge, an economic operation of the blast furnace under high productivity and low fuel rate often requires that a considerable part of the charged coke be replaced by injected fuels. However, at high injection rates, and particularly for the case of injection of heavy (and viscous) oil, the extent of combustion may be a limiting factor. The combustion can be enhanced by raised temperature, turbulence, and simultaneous injection of oxygen, or by appropriate design of the injection equipment, e.g., using co-axial oxy-oil lances. Because of the deficiency of oxygen in the raceways the conversion of oil droplets may still be incomplete. A possible remedy is to allow the combustion to take place partly within the tuyeres by supplying the oil (and oxygen) at some distance from the tuyere tip. Some authors have discussed the implications of gasification and combustion of supplementary fuels (mainly coal) in the tuyeres, but the conditions at partial combustion of heavy oil in the region have not attracted much attention; this is the topic of the present short note. By a simplified model of the conditions in combination with measurements from experiments at an operating industrial blast furnace it is demonstrated that about half of the injected oil may be burned in the tuyeres before entering the raceways.