Quality controls in the DRI process

17.01.2024 | Salzgitter Flachstahl GmbH

Photo of the DRI material — Figure 1: DRI pellets (left) and hot briquetted iron (right)

For the production of crude steel via the blast furnace route, established and reliable feedstock tests and product tests are carried out in the chemical laboratories of Salzgitter Flachstahl along the entire process route. With the conversion of the process for the production of CO2-reduced steel in our SALCOS project, the pig iron traditionally produced in the blast furnace will in future be replaced by the material reduced in the direct reduction process (DRI). So-called DRI pellets or pressed HBI material will be produced in the DRP plants required for this.

Of course, determining the chemical composition for process monitoring and further processing in the steelworks is also very important for these products. The challenge here is to introduce new, suitable and efficient analysis methods. The so-called degree of metallization of the DRI material is particularly important in this context. This is calculated from the percentage of metallic iron (Fe^±0) in the total iron (F_ges. = Fe²⁺ + Fe³⁺ + Fe^±0). Both values are currently measured using a manual dimensional analysis method to determine the degree of metallization. For this purpose, the material produced is sampled and prepared at regular intervals during production. Only a few grams of material are required for pure analysis. The sequence of these chemical analyses is shown below as an example:

Photo series of the sample analysis — Figure 2: Example of a titration procedure

The measured values are finally calculated and saved via a laboratory information and management system. The plant control system can access and retrieve them at any time. All tests used are already carried out in compliance with standards. The method used to determine the metallic iron content in accordance with ISO 16878 (2016-07) was included in the existing accreditation in accordance with DIN/EN ISO IEC 17025:2018. The corresponding expertise required for this has already been demonstrated by the accreditation of Salzgitter Flachstahl's laboratories in spring 2023. This also ensures quality assurance for the future hydrogen-based production route.