Salzgitter Improves LD Converter (BOF) Process Optimization System

Salzgitter Flachstahl in Salzgitter, Germany, has upgraded the LD converter (BOF) process optimization system. The largest steel subsidiary in the Salzgitter Group, Salzgitter Flachstahl, employs 5,480 people and produced around 4.3 million tons of crude steel in 2021 while generating sales of 3.2 billion euros. The most important customers for flat products are vehicle manufacturers and their suppliers, tube and large-diameter pipe manufacturers, cold-rollers, the trading sector, and the construction industry.

The new Slag Expert model from Primetals Technologies has optimized the use of lime, improved the hitting rate—i.e., the number of successful heats in terms of carbon content and steel temperature—and reduced the number of reblows. Slag Expert is a new module for the process optimization system (Level 2) that calculates the target value for the required basicity of the slag at the end of the blowing process. Additionally, it provides the basis for determining the optimum amount of lime.

Expectations Exceeded

Slag Expert calculates the desired slag basicity at the end of the blowing process based on the amount of silicon in the feedstock, a pig iron analysis, and the targeted parameters of temperature, carbon, and phosphorus content in the crude steel composition. The availability of purging stones and the converter’s age are also considered. Furthermore, the Slag Expert module calculates lime saturation, phosphorus capacity, and slag viscosity values. The startup, fine-tuning, and the initial production process monitoring were largely accomplished remotely by the team from Primetals Technologies.

We were able to meet the identified improvements after just a few weeks, and we even exceeded them in some cases. The most important aspect for us is to optimize the input of lime in order to meet the required phosphorus levels.”

Christian Schlüter
Head of Metling Operations
Converter charging at Salzgitter Flachstahl. Primetals Technologies has recently implemented the Slag Expert module at two LD converters (BOFs) in Salzgitter, Germany.

Timely Production

The main objective of Slag Expert is to provide operators with exact data on the amount of feedstock and oxygen required to produce the desired steel quality on time. Combining Slag Expert with the Dynacon process model and an off-gas measurement system for LD converters (BOFs) ensures the optimal timing of the end of the blowing process. With the support of these systems, interruptions to the blowing process caused by the taking of measurements and samples are largely eliminated.

Long-term Partnership

The process optimization system from Primetals Technologies has already been in use at Salzgitter Flachstahl’s three 220-ton LD converters (BOFs) for 15 years, and the Slag Expert module is a result of many years of close collaboration between Salzgitter Flachstahl and Primetals Technologies. The process optimization systems have been maintained and improved for more than ten years as part of a services contract. In addition to the Level 2 systems at the LD converters (BOFs), this cooperation also focuses on automating the complete secondary metallurgical process and topics related to intralogistics and, for example, scrap management.

KEY FACTS: THE level 2 automation system

The system enables the production of a specific steel quality at a high productivity level while optimizing costs. The Level 2 automation system takes numerous factors into account, including:

  • Variations in feedstock
  • Steel grades produced
  • Condition of the converter vessel
  • Different blowing, purging, and material addition schemes for the process flow


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