Carbo-thermal reduction of basic oxygen furnace slags with simultaneous removal of phosphorus via the gas phase

Christoph Ponak

Research output: ThesisDoctoral Thesis

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Abstract

Steel production is at an all-time high. Resource efficiency is a key factor for production in order to operate competitively in the steelmaking sector. In the course of the blast furnace-basic oxygen furnace steelmaking route, immense amounts of basic oxygen furnace slag are produced. Roughly a quarter of this co-product of steel production consists of valuable elements – namely iron, chromium, manganese and phosphorus – in the form of oxides and phosphates. If fully recovered by carbo-thermal reduction – one of the treatment approaches currently addressed by a number of research activities – phosphorus accumulates in the obtained metal product. Since phosphorus can only be removed from the mentioned process route in the basic oxygen furnace and its performance in this regard is limited, the internal recycling of the iron alloy produced by reduction is not feasible without negatively affecting the crude steel quality. In the course of this thesis, a novel reactor concept called InduRed is applied in order to remove phosphorus via the gas phase during reduction. Thereby, high phosphorus gasification rates of up to roughly 83% could be achieved after respective slag modification. The slag product contains virtually no iron, chromium or phosphorus. Additionally, the InduRed reactor concept is also applied as a step in an alternate process route. The initial slag reduction step described above can be conducted in a standard reduction unit so that the phosphorus is fully accumulated in the metal product. This alloy is subsequently treated in an additional refining step, so that mainly chromium and phosphorus are oxidised. The product slag obtained by this step can finally be reduced in the novel reactor in order to produce a low-phosphorus metal product. In the course of this thesis, such slags were produced synthetically and reduced by standard carbo-thermal reduction as well as in the InduRed reactor. The slag composition is based on theoretical assumptions and contains high manganese amounts as well. The gasification rates were much higher after reduction in the InduRed reactor compared to reduction according to the state of the art and the state of knowledge, reaching roughly 42%. An influence of high chromium and manganese amounts, however, was detected.
Translated title of the contributionCarbo-thermische Reduktion von LD-Konverterschlacken bei gleichzeitiger Entfernung von Phosphor über die Gasphase
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Antrekowitsch, Helmut, Co-Supervisor (internal)
  • Antrekowitsch, Jürgen, Assessor B (internal)
  • Raupenstrauch, Harald, Supervisor (internal)
  • Siebenhofer, Matthäus, Assessor A (external), External person
Publication statusPublished - 2019

Bibliographical note

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Keywords

  • basic oxygen furnace
  • slag
  • phosphorus
  • chromium
  • recycling
  • metallurgy
  • secondary raw material
  • reduction
  • induction

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