Due to the transition to hydrogen-based steel production, based on the direct reduction, current internal recycling ways for iron containing materials occurring during the iron and steel production via sinter plant and blast furnace will be cut off. In the project TransZeroWaste, BFI is focussing on the preparation of iron containing materials, as low-quality irons ores, oily scale and further materials as mandatory step before a metallurgical reuse in direct reduction plants. Three different approaches as the hot pelletisation with microwaves, cold pelletisation and briquetting and the hydrometallurgical treatment for the removal as disturbing impurities as oil and grease will be investigated as low carbon treatment methods.
Microwave heating offers an efficient alternative to the energy-intensive conventional heating techniques that are still common in many industrial manufacturing processes. In contrast to conventional heating, microwave heating is based on the conversion of electromagnetic energy into heat at the molecular level. The microwaves couple directly to the electrons in the atoms, molecules, crystals or cluster structures of the materials, and the energy can be used almost completely for material heating and activation energy, so that only residual heat is released into the system (cool kiln). This was successfully tested in the predecessor project DESTINY. To ensure proper conversion, TransZeroWaste will include new validated concepts for microwave kiln configuration, material preparation and control to industrialise microwave heating as a solution for highly energy-efficient processes, Figure 1.
Figure 1: Comparison of current and planned microwave application
In the investigations of the agglomeration of selected iron and iron oxide-containing residues from the steelworks in laboratory tests, the agglomerates are produced using a binder with a tablet press (press agglomeration or briquetting) and with a pelletizing plate (build-up agglomeration), Figure 2. The focus of the investigation is on the development of agglomerates for reuse, particularly in new processes in the smelter, such as direct reduction. Various cements, molasses, water glass, cellulose and polymers were used as binders. Above all, the agglomerates must have sufficient compressive strength for the respective process. To date, it has already been possible to produce pellet-sized agglomerates during briquetting with some binders that meet the compressive strength requirements for a direct reduction process.
Figure 2: Agglomeration with tablet press
In the case of oil and grease containing material as oily mill scale, currently the impurities avoid or hinder a metallurgical reuse, while the thermal treatment leads to high CO2 emissions. The hydrometallurgical treatment is based on the magnetic separation of iron containing particles, followed by de-oiling by spraying cleaning agent on the removed oily material. Main subject of the work is the determination of suitable cleaning agents (e.g. tenside, solvents) and cleaning conditions considering technical, environmental and economical aspects. Considering a holistic approach, the recovery of the cleaning agent by ceramic flat sheet membranes and suitable recovery conditions are investigated as well.
