Electrification is seen as a promising solution to the transition towards sustainable energy. However, the operation of the electricity network, is disrupted by intermittency of these sustainable energy sources. Therefore stockpiled fuels are needed to deal with supply disruptions and variability of these clean sources. One of these storable energy sources is metal, that can be used as a recyclable dense energy carrier of green energy. Metals like iron can be burnt with air or react with water to release its chemical energy even up to industrial scale with a high power output. The thermal energy which is released during this process provides heat to high energy- and emission- intense industries. After combustion the generated metal oxides are captured and reduced back to metal. It is also possible to export the metal over long distances, or store it indefinitely with minimal loss.
The main issue is that our scientific knowledge to support the metal fuel combustion/regeneration cycle is largely missing and needs to be developed. While the oxidation element of the cycle is a widely studied part of the metal fuel cycle, the regeneration of the energy carrier is still in a starting point of development. Study of the reduction process is essential for the future success of the metal fuel cycle. One application which can be used for reduction is the fluidized bed. The fluidization of particles depends on the type of gas, gas density, as well as solids characteristics, such as bed porosity, particle size and particle density.
In this experimental study, we aimed to investigate and understand factors contributing to the sticking phenomenon and its impact on the reduction process within a fluidized bed. Pressure drop measurements were monitored throughout the reduction process, and it was observed that after a certain amount of time, there was a significant decrease in fluidization due to partial defluidization of the bed. To further comprehend the sticking behavior and its underlying causes, the reduction reduction reaction was stopped for different time intervals. This to analyze the powder composition with X-ray diffraction (XRD) and the size distribution of the powder using a Particle size Analyser (PSA). Next to this, the particle morphology is analyzed using Scanning Electron Microscopy (SEM).
Initial findings from the powder composition analysis revealed the presence of metallic iron and various iron oxides in the iron ore feedstock. Over time, as the reduction process progressed, the abundance of metallic iron increased, while the iron oxide phases diminished. These changes in the powder composition could be linked to the sticking behavior observed during the reduction process. The analysis of powder composition and size distribution provided valuable information on the changes occurring within the particles, highlighting the potential causes of sticking. Understanding and mitigating the sticking behavior can contribute to the improved efficiency and effectiveness of the iron ore reduction process, facilitating the advancement of the metal fuel cycle for sustainable energy production.