BOF Cold Model: Mixing time study at multiphase conditions

Daniel Augusto Godinho de Carvalho

Research output: ThesisDoctoral Thesis

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Abstract

The BOF process was born in 1949 in Linz, Austria. Fast growth for the Basic Oxygen Processes (BOP) was observed in the 1960s. By 1971, Basic Oxygen Furnace (BOF) produced more than half of the world's steel. The LD process led worldwide steel production to increase from 0.2 to 1.8 billion metric tons of crude steel per year. The integrated steelmaking route based on the BF-BOF is directly responsible for 70% of total world steel production. At least up until 2050, primary steelmaking based on the BOF technology is assumed to continue the main process route. In an earlier work about lime dissolution and slag making for an industrial 330t BOF, the same process as presented in this thesis, several process parameters were studied. Nevertheless, the model's weak point was the efficiency factors that correlate the mixing energy related to top lance, bottom stirring, and decarburization reactions. A couple of different reports for the agitation of a top blowing jet to the bath and bottom stirring are available in the literature, and different expressions to calculate the agitation power have been proposed. Although experimental conditions are used, these empirical assumptions are not necessarily suitable for all BOF processes. Those parameters substantially impact the steel process productivity, costs, and quality, and the mixing time concept investigated through cold modelling is perfect for assessing the system performance. This thesis developed investigations through laboratory cold model to improve the mixing time and mass transfer rate due to a gradient of apparent density caused by different bottom stirring flow zone. The proposed setups were validated in the industrial environment, and more than 1750 trial heats were produced in a 330t BOF. This research introduced novel modified dimensionless numbers, the new parameters added in the equations delivered a unique solution to develop a complete BOF process similarity. For the first time, a similarity study employed and associated the effects of the multi-nozzle supersonic lance, slag-phase and the bottom stirring gas parameters to design a new BOF cold model. The methods applied in the laboratory measurements employed a mix of modified procedures available in the literature, and new techniques to evaluate the bath mixing time, mass transfer rate, jet penetration, decarburization area, sloping and projection rate for BOF cold modelling. The industrial-scale experiments were fundamental to validate the laboratory trials, the first phase of experiments delivered important laboratory and process data for seven different bottom stirring configurations. Despite the influence of many other parameters and variables faced in the industrial environment, the performed trials delivered essential process data for a statistical and machine learning analysis.
Translated title of the contributionSauerstoffkonverter Kaltmodell: Untersuchung der Vermischungszeit unter Multiphasenbedingungen
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Tavares, Roberto Parreiras, Co-Supervisor (external), External person
  • Schenk, Johannes, Supervisor (internal)
Publication statusPublished - 2021

Bibliographical note

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Keywords

  • BOF
  • Converter
  • LD
  • Cold Model
  • Mixing Time
  • Mass Transfer Rate
  • Mixing Energy
  • Industrial
  • Laboratory
  • Machine Learning
  • Decarburization Area
  • Jet Penetration
  • Bottom Stirring
  • Similarity
  • Dimensionless Numbers

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