The Midrex process produces metallurgical residues in the form of dust, sludge, and fines. As these have high iron content, herein, the aim is to recycle the residues and use them as an educt in the Midrex process, thus closing the material cycle and increasing raw material efficiency. Briquetting of these materials with binder is one possibility to prepare them for the use as an educt in the Midrex process. Experiments are conducted to test the suitability of the organic binders starch and cellulose for briquetting. Furthermore, tests with the inorganic bentonite are included for comparison. Briquettes are generally characterized by high strength. However, compared with iron oxide pellets, they have a low porosity and thus a higher apparent density, and consequently, a worse reducibility. The use of organic binders should improve the reducibility. The iron oxides are in close contact with the C‐carrier of the organic binder so that a solid–solid phase direct reduction can take place. Furthermore, the solid carbon reacts to CO, and thus, increases the presence of reducing gas in the enlarged pores of the briquettes, and should therefore increase the degree of reduction.

Hot briquetting tests with mixtures of direct reduced iron (DRI) pellets and residues of the Midrex direct reduction process are conducted on a hydraulic piston press with a closed die. The trials seek to test the feasibility of recycling these residues by introducing them directly into hot briquetted iron (HBI). The inclusion of residues is possible if a high pressure of 350 MPa and a high briquetting temperature of 800 °C are applied. It is ascertained that up to 20 wt% of the HBI can consist of residues and still meet the quality requirements for the safe transportation to the steel plant if the mixture contains sufficient HBI screened fines and HBI classifier dust. Under such conditions, the HBI briquettes have a compressive strength of >300 MPa, an abrasion resistance of >80%, and, most importantly, an apparent density of >5 g cm−3. It is further shown that the hot briquetting of Midrex residues is also possible without DRI pellets so that they can be reused as educt in the Midrex direct reduction process.

With the aim of achieving sufficient reducibility and thermal stability of briquettes for reuse as feedstock in the Midrex direct reduction process, a defined mixture of residues from the Midrex process is briquetted with an organic binder and bentonite. In the first step, briquetting tests are conducted to investigate the influence of water and binder content on the mechanical properties of the briquettes. Suitable briquettes are then used for reduction tests, where mechanical properties under Midrex‐relevant conditions are considered. The tests show that briquettes with an organic binder (with and without bentonite) are not stable under Midrex‐relevant conditions, whereas briquettes with a mixture composition with 5 wt% bentonite and 5 wt% water are. This can be justified on the basis of microscopic images. Bentonite favors the sintering mechanisms occurring between the particles. The organic binders decompose thermally and carbon remains, which prevents sintering. The reduction tests show that oxygen release from the briquettes occurs more slowly than for iron oxide pellets. However, the residual mixture already contains reduced material (Femet of briquettes with bentonite 28.1 wt%), so less oxygen has to be removed. Furthermore, a small briquette format (volume 10 cm3) shows better reduction behavior compared to bigger briquettes.

Auf der ACHEMA 2018 waren erneut zahlreiche Firmen vertreten, die im Bereich der Agglomerationstechnik tätig sind. Die Einsatzgebiete der vorgestellten Technologien reichten dabei von der Aufbauagglomeration über die Extrusion bis zur Pressagglomeration für mineralische, nachwachsende und biogene Rohstoffe sowie die pharmazeutische, chemische und Nahrungsmittelindustrie. Der Artikel gibt einen Überblick über die aktuellen Trends, wie Innovationen in der Messtechnik, Zusammenführung von Prozessschritten und Erweiterungen bestehender Apparate für neue Anwendungsbereiche.