Silicon - an established pyrotechnic fuel as zero-carbon, high-density energy carrier

Silicon is a proven fuel in many pyrotechnic applications as e.g., delay compositions or thermite-based incendiaries. In the form of micro-porous particles, it is even discussed as additive in high explosives. Silicon reacts strongly exothermically with oxygen, air, and water. When water is used, additionally a large amount of hydrogen is formed. This predestines silicon as a carbon-free energy carrier and hydrogen storage. The energy required to produce silicon particles can be provided by environmentally friendly or regenerative methods. The transport and operational safety of silicon particles is not critical. Silicon is the most abundant element in the earth's crust after oxygen and is ubiquitous as stone. Like carbon or hydrogen, it has the distinct advantage that the products of combustion do not have to be collected and transported back to the reprocessing site. It is quite conceivable that in powder form silicon could be used in a combustion process like coal to generate electricity in a power plant. The diffusion-controlled combustion process may be realized in classical particle burners as it is shown in this paper. It seems feasible that the existing power plants, or at least large parts of them, will continue to be used. The most important difference to coal is that mainly condensed combustion products are formed. The characteristics of the combustion of silicon with respect to the burning behaviour, the combustion temperature and the particle size-dependent combustion time of silicon particles are currently being investigated at the Fraunhofer ICT and described. Combustion could be realized with oxygen, air, and steam. 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 in SiO2 have the potential to be used as valuable building materials and construction sand. The investigations provide first parameters for the design of combustion chambers and exhaust gas cleaning as temperatures and products. The experimental studies are supported by thermodynamic and reaction kinetic studies on the formation of NOx, hydrogen, and silica particles. Initial approaches to simulating the burning of silicon particles are discussed. Both active and passive combustion regimes must be considered.