Blasenbildung in Flüssigmetallreaktoren: Experimentelle und theoretische Grundlagen zur Optimierung der Methanpyrolyse

Anthropogenic climate change currently poses one of the biggest societal challenges. Decarbonization measures and the associated use of hydrogen as an energy source play a significant role in mitigating the effects of global warming. Currently, 99 % of global hydrogen is produced through CO2-intensive processes, such as steam methane reforming. As the projected electrolyser capacity will not be able to meet the expected H2 demand by 2030, alternative processes for hydrogen production, such as methane pyrolysis, are required. In the methane pyrolysis process, CH4 is split into hydrogen and solid carbon at high temperatures. The use of catalysts to enhance reaction kinetics is possible, for example, in a liquid metal reactor, where the melt serves as both a catalyst and a heat transfer medium. The dynamics of the bubbles play a crucial role here, as the size of the bubbles formed significantly influences the process efficiency. Critical parameters that affect bubble dynamics include the surface tension and the viscosity of the liquid, as well as the type of gas injection and the flow behaviour. This work examines the factors influencing bubble dynamics. The calculation of these factors, along with the gas flow in the lance and the reactor, is the subject of the theoretical section. In the experimental section, pressure measurements and image recordings are carried out to determine the primary bubble size in the fluids. Experiments with water, silicon oil, and liquid tin demonstrate that the indirect measurement method is highly effective for the lance type with a large opening. The bubble size increases with the flow rate, with the smallest bubbles forming in tin and the largest in oil. In the tin melt, a transition to turbulent flow is suspected at a specific volume flow rate. The results show that the fluid characteristics heavily affect the size of the resulting bubbles. The nozzle design also influences the bubble dynamics. However, evaluating these parameters is challenging because the interaction of liquid properties yields results that are difficult to predict. Additional experiments in different liquids are necessary to better understand the dynamics and flow behaviour of bubbles. Further research is required with a special focus on gas injection, particularly purging stones, and their effects on bubble dynamics. Furthermore, it is crucial to investigate how the bubble size affects the conversion rate during methane pyrolysis and how this can be improved by optimizing the gas injection or alloy design.