Optimization of biomass materials for use in the Sponge Iron Process

Sammanfattning: This master thesis was a project in cooperation with Höganäs AB. The aim was to increase the apparent density (AD) of two biomass chars, by three different agglomeration methods. The reason for the investigation is that biomass char could be used as a reducing agent in the sponge iron process at Höganäs AB. The goal was to exchange anthracite in the reduction mixture to agglomerated biomass char. Biomass char is a more environmentally friendly alternative to anthracite. The fact that the price of anthracite of good quality is also increasing, which makes it necessary to find an alternative material. A characterization of the biomass chars was performed at first, where the specific surface area, higher heating value and composition of the biomass chars were determined. Extrusion, tumble agglomeration and granulation in a planetary mixer were performed in order to increase the AD of the biomass chars. A binder was necessary in all agglomeration methods, which is why a preliminary binder investigation took place. Four different organic polymers and one inorganic binder have tested in this investigation. In order to see if the AD had increased and what properties that might have an effect on the AD, an evaluation of the agglomerates was performed. The evaluation included measuring the AD, determining the particle size distribution, moisture content and the reactivity of the agglomerates. The final experiments were made in a pilot scale process, which is similar to the sponge iron process, in order to see how an increase in AD could affect the reduction. The agglomerates made in the extruder resulted in the highest AD. The result was expected since extrusion is a high-pressure method compared to the other methods. A surprising result was, however, the increase in reactivity of the agglomerates made in the extruder. The agglomerates made by tumble agglomeration and granulation decreased in reactivity.