To reduce carbon dioxide and hydrogen sulfide concentration in simulated biogas, experiments were performed on a laboratory scale. The main goal was to use calcium, lead and zinc from fly ash from waste combustion power plants to form carbonates and sulfides for biogas upgrading within a process water cycle. Thereby, the contact time between the simulated biogas and the ionized process water was limited to less than 1 s. The investigation focused on the influence of hydrogen sulfide partial pressure, reaction time, reaction temperature, and process water volume flows. The experiments were performed with two different ashes.

The results show that the kinetics for hydrogen sulfide reactions were better than for carbon dioxide where the mass transfer into the liquid phase slows down the upgrading process. This led to fast reactions for H2S in the initial volume and therefore to a bottleneck for further sequestration. For carbon dioxide the kinetics limit the process in the beginning until all reactants for carbonates and the process water volume flow limit the process also. For the process temperature, slightly better separation efficiencies were realized for carbon dioxide at 40 °C while the effect for hydrogen sulfide separation was contradictory for the used ashes. With higher process water volume flow, best results were achieved and the bottleneck of reactants ratios was compensated.