Investigation on the condensation behavior of the trace element zinc in (Ar/H2O/HCl/H2S) gas mixtures and its practical implications in gasification-based processes for energy and power generation

Abstract Fuels used in combustion and gasification, such as coal, biomass and wastes, yield large amounts of trace elements, which can cause both technological and environmental concerns. This work provides an in-depth insight into the condensation behavior of the trace element zinc under gasification-like conditions in atmospheres containing the HCl and H2S trace gases. A lab-scale quartz reactor with a multi-stage cooling zone was used to determine the condensation content and species distribution of the zinc deposition in different gasification atmospheres. The Scheil-Gulliver cooling model was used to simulate the zinc condensation process, since it provides a good reference to analyze the degree of supercooling during the condensation process. Competition of the gaseous species HCl and H2S with respect to the ZnO condensation behavior has been observed. HCl leads to significant supercooling of the ZnO condensation. It is shown that this can be compensated by ZnS acting as nucleation sites for ZnO if significant amounts of H2S are present. It is further shown that there is a significant bypass effect, i.e. even after nucleation has started there is a significant amount of Zn remaining in the gas phase which significantly extends the condensation regime to lower temperatures. To visualize both effects, a H2S-temperature-transition diagram is proposed. The potential applications including the prevention of problematic depositions (slagging and fouling) and sorbent selection as well as design for removal of trace element zinc from the syngas in IGCC power plants are proposed and discussed in the light of developing clean power technologies.