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BOF

2.3 Basic Oxygen Furnace Steelmaking

2.3.1 BOF Furnace

The predominant advantages of the BOF are very high production rates and low-residual-element, low-nitrogen liquid steel tapping. The BOF is fed liquid pig fron, almost always from blast furnaces, in amounts ranging from 65 to 90% of the total metallic charge. The average pig iron is approximately 74% of the charge; the balance is recycled scrap.

Efforts to improve BOF productivity and annual production capacity in recent years have included various automation technologies to optimize the blast furnace and the BOF relationship, better use of secondary refining processes (driven both by productivity and by new steel grades), and improved coordination with downstream facilities.

Trends and Drivers can be summarized as follows:

  • Advances in slag splashing that extend refractory life and use of post-combustion lances have improved furnace availability
  • Increasing demand for ultra-low-carbon (ULC) steels has made secondary processes more important.
  • Hot metal desulfurization is usually done in the BOF transfer ladle.
  • Meanwhile, steelmakers constantly experiment with BOF oxygen lance configurations, oxygen batching and flux additions practice.
  • Technological Challenges:

  • Life incompatibility of the lower hoods shorter than the furnace, and related maintenance issues.
  • Environmental standards are getting tougher.
  • Furnace vessel shell distortion and destruction dunng a long campaign must be overcome.
  • Refining of hot metal with a low manganese-silicon ratio impacts slag formation in the BOF vessel in addition to BOF operating issues.
  • New and Emerging Technologies:

    Work is being conducted to improve chemistry, temperature, and process control in the BOF.

  • The use of in-blow sensors with possible feedback control is being developed to improve carbon and temperature control to measure lance height and detect the advent of slopping; Improving techniques of adding alloys, usually with the aid of secondary processing; Upgrading computer and expert systems will also help operators achieve consistent process control.
  • Using inert gas bottom stiri-ing achieves better iron yields and alloy recovery through reduction of furnace slag iron oxide, but maintaining effective stirring continues to be a major inconvenience in many shops that have tried the technique.
  • Techniques that enable the aggressive use of post-combustion lances or supplemental fuels to extend the use of hot metal.
  • 2.3.2 Other Releted Technologies

    Those technologies that need further development include scrap preparation and handling, fluxes and methods of additions, recycling of waste oxides, and process sensors with feedback capability (for example, light meter, lasers, infrared temperature detectors).

    Trends and Drivers:

  • Scrap handling before recharging into the BOF; upward trend in scrap prices
  • Seme integrated plants are experimenting with lower-grade, higher-residual (and thus cheaper) scrap because it can be diluted by low-residual hot metal.
  • Higher importance of flux quality, size, and method of introduction
  • Increasing environmental pressures and opportunities for low-cost sources of iron and/or coolants in the furnaces.
  • Increased use of industrial gases
  • Technological Challenges:

  • Scrap systems. Scrap delivery and analysis systems are complicated, unreliable, and ineflicient. Without better systems, the amount of scrap used and effect an quality is limited.
  • Difficulty of maintaining reliable sensors and automated systems
  • Sslag analysis: A speedy, reliable slag oxide analysis teehnique is not available, particularly for fron oxides or for controlling lance height, making slag, and calculating alloy efficiencies.
  • In addition, slag analysis is expensive and slow and involves sampling separation problems related to the use of iron versus iron oxides.
  • New and Emerging Technologies:

  • Recent and developing BOF process improvements primarily affect scrap and process sensors. Additionally, development is ongoing in bumers and nozzles for the BOF process. This work could improve post-combustion performance.
  • Preheating techniques and quality improvements lead the emerging scrap technologies.
  • Light meters, lasers and infrared cameras and sensors are being studied to control carbon, temperature, slopping, waste gas composition, and lance height above the bath.
  • 2.3.3 BOF Steelmaking Research and Development Needs and Opportunities

    Despite all the ongoing research to improve BOF performance, numerous other research opportunities exist.

    Long-life refractories. Investigate ways to increase use of long-life refractories to improve stirring elements for furnaces or ladles and use in BOF tap holes. Also, the hood life should be extended to equal that of the refractory lining.

    Process sensors. Develop various user-friendly, robust process Sensors with feedback capability to detect bath carbon, temperature, and the advent of slopping, waste gas composition, dusty bin levels, and furnace shell temperatures. The temperature sensor should be able to measure continuously during the final minutes of the blow. Sensors for quick analysis of turndown manganese, sulfur, and other elements are also needed.

    Lances. Develop a reliable sensor to detect lanceto-steel bath distance to control the path of the process, particularly slag making and possibly slopping. Heat-to-heat feedback or real time feedback of lance height will improve the consistency of the process reaction path. Also, a clear understanding of the hydrodynamics of the oxygen lances and its effect an splash generation and decarburization kinetics needs to be developed.

     

    BOF Furnace

    • Robust process sensors for the BOF to measure process variables
    • Reliable sensors to detect lance-to-steel bath distance
    • Clear understanding of the hydrodynamics of the oxygen lances
    • Improved laser scanning system to characterize the condition of the furnace and ladles
    • Improved flux raw materials analysis and size, and reliable computer controlled bathing
    • Improved, easy-to-maintain hoods
    • Economical and environmental friendly methods of removing or controlling phosphorus
    • Inexpensive and fast slag sample preparation and composition analyzer
    • Longer-life, easily replaced stirring elements
    • Environmental method for primary and secondary control systems
    • Improved understanding of micro-alloying element recovery through the process

    Laser Scanning for refractories. A comprehensive Laser Scanning system is needed that is fast, robust, and userfriendly for characterizing the condition of the furnace and ladles. This technology Gould also provide refractory condition feedback and lance height control by integrating the volume of the furnace.

    Flux and Oxygen batching. Improved flux raw materials analysis and size and reliable Computer controlled batching are needed for better slag making consistency. This research also applies to developing better Oxygen batching methods for early slag making.

    BOF hoods. Improved, easy-to-maintain hoods, possibly in conjunction with protective coating techniques and/or constant temperature/pressure control techniques need to be researched.

    Dephosphorization. Economical and environmentally friendly methods of removing or controlling phosphorus need to be developed. Alternatively, find other viable uses for BOF slag rather than recycling to the Sinter plant. This will reduce the Input phosphorus load from the hot metal.

    Slag Oxide analysis. Inexpensive and faster slag-sample preparation and a composition analyzer would improve Slag analysis.

    Stirring elements. Longer lasting and more easily replaced stirring elements Gould make maintenance and bottom stirring Easier.

     

    Other BOF Steelmaking Needs

    • Method to use DC/EAF in a BOF vessel to preheat scrap
    • Comparison of process parameters vs. results of models for fluxing and oxygen blowing
    • Predictive maintenance procedures for drive bearings
    • Process to decrease the percentage of hot metal through the use of external energy units
    • Refining technology for low Mn/Si ratio metal
    • Submerged dust injection for recycling
    • Integrated melter guidance system
    • Scrap preheating techniques for stretching hot metal
    • Maintenance techniques to take advantage of increased BOF lining life from slag splashing
    • Model to optimize blast furnace and BOF operations
    • Charge control model for better end-point control

    Environmental controls. Primary and secondary environmental control systems need to be developed and upgraded to Best Available Technology (BAT) in all areas of emission concern. Constant technical review is necessary to meet environmental standards of the future.

    Other BOF steelmaking R&D needs include using models, maintenance procedures and new technologies to improve performance. One essential requirement is the development of scrap preheating techniques for stretching hot metal. Also needed is an integrated melter guidance system to take advantage of multiple sensors, instrumentation, and models. Production pacing models are needed for BOF's trying to supply steel for multiple casters. These models should consider steel ladle requirements and "what-if' production alternatives.

    Research into processes to remove residual elements, such as tin, copper, antimony, and others during the steelmaking process is needed. Maintenance techniques for mechanical and ancillary systems need to be developed to take advantage of increased BOF lining life from slag splashing. Regarding ULC steel production, better understanding of vacuum kinetics and precasting chemistry is required for improvement.

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