Numerical Simulation of Combustion in the Ironmaking Blast Furnace Raceway
As almost all conversion of raw iron ore to pig iron at the start of the ironmaking process currently takes place in a blast furnace, these furnaces remain a critical component in the iron and steelmaking industry. Enhancements in the efficiency of blast furnace operation have a significant effect on industrial energy consumption, as the process represents nearly 70% of the total energy consumption of the iron and steelmaking process. Over the past several decades, auxiliary fuel injection has been adopted as a method of reducing the total amount of coke necessary for furnace operation. Coke making is both energy intensive and environmentally unfriendly, and as such, any reduction in coke usage by the blast furnace is positive for the iron and steelmaking industry. However, the intricate variations in blast furnace raceway conditions and injected fuel combustion characteristics due to the method and conditions at which auxiliary fuels are injected into the furnace are still not fully understood. The goal of this research is to utilize computational fluid dynamics (CFD) modeling to provide a deeper level of understanding of the complex relationships between blast furnace injection system designs and operating conditions on the combustion processes and phenomena within the raceway. In this vein, a multi-stage 3-D CFD model has been developed and applied to simulate combustion phenomena within several industrial blast furnace raceway regions. The three primary components of focus in this research are the tuyere and injection apparatus, raceway formation, and raceway combustion. A comprehensive CFD methodology for simulation operating conditions and combustion within the blast furnace raceway has been developed. This methodology utilizes CFD modeling to simulate conditions within the raceway region. A revised raceway formation model has been developed to better correspond to industrial observations, and new methodology for analysis and presentation of simulation results from these models have been developed. The models have been validated against industrial observation and measurements from three currently operating industrial blast furnaces. The models have also been utilized to examine varied operating conditions in the aforementioned furnaces. Two new methods of exploring raceway gas temperature using simulation modeling were developed in this research, namely a Topographical Flame Temperature (TOFT) and a Raceway Adiabatic Flame Temperature (RAFT) analogue. These methods allow for both better validation of computational modeling results against industrial observation and measurement, as well as providing a new path to explore raceway gas temperature distribution under unique conditions, including extremely high natural gas injection rates, which may present potential for significantly improving the economic and operational efficiency of the furnace. The analyses of industry blast furnaces provide significant insight into the effects of injection conditions and apparatus designs upon combustion characteristics and reaction phenomena within the raceway. Previously unexplored novel fuel injection techniques were explored within this research, and simulations have indicated that injected fuel burnout rates could be improved by as much as 23% in specific scenarios and production could be increased by roughly 2.5%. While a switch to these injection techniques may pose some difficulties in practice, industrial project partners have already begun trials for implementation on a full-scale furnace. Finally, this modeling revealed significant potential benefits to blast furnace operation through modification of natural gas and pulverized coal injection locations, pulverized coal carrier gas type, injection lance tip design, and other parameters. While these exact parameters cannot be implemented identically across all plant furnaces, they provide a baseline of fundamental understanding from which furnace operators and engineers can draw in their ongoing attempts to optimize combustion efficiency and reduce operational expenditures.
Zhou, Purdue University.
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