Investigation on the Combustion of Silicon as a Carbon‐free Energy Carrier

Renewable metallic and metalloid particles are currently being discussed as a renewable energy source for combustion with air and water, which could supplement and expand the possible applications of hydrogen or synthetic biofuels. In literature, silicon is identified as one of such elements. Silicon is a proven fuel in many pyrotechnic applications with a high energy density, especially in relation to volume. Silicon reacts strongly exothermically with oxygen, air, and water. When water is used, a large amount of hydrogen is formed. The energy required to produce silicon particles from mineral silica can be provided by environmentally friendly or regenerative methods, which are currently worldwide under development. The transport and operational safety of silicon particles is not critical. As the most abundant element in the Earth’s crust after oxygen, it is ubiquitous as rock. Like hydrogen, coal, and fossil fuels, it is the only metallic energy carrier with the distinct option to be used as a one-way energy source whose reaction products do not need to be recycled. However, the combustion process does produce silica, a stable, harmless mineral that cannot be released into the atmosphere as a gas but can be a useful raw material, for example, for the construction and packaging industries. One drawback of the application is that silicon is difficult to ignite. Therefore, its combustion properties with gaseous oxidants have not yet been investigated, in contrast to iron, aluminum, or magnesium particles. However, this is essential for assessing it as a fuel. This is the focus of this paper. Combustion could be realized with oxygen, air, and steam. There exist active and passive combustion regimes, which must be considered. The flame structure and combustion temperature are measured, and the resulting combustion products are also being characterized. Quasi-stationary combustion of silicon dust stabilized with a hydrogen-oxygen flame was demonstrated. The combustion products consist to a significant extent of aggregated silica nanoparticles. The products consisting of amorphous SiO2 have the potential to be used as valuable building materials. The investigations provide preliminary parameters for the design of combustion chambers and exhaust gas cleaning as temperatures and products