Influence of Steam, Hydrogen Chloride, and Hydrogen Sulfide on the Release and Condensation of Cadmium in Gasification

The development of more efficient clean up techniques in coal power plants is essential in order to reduce trace metals emissions into the atmosphere. However, understanding of the behavior of the trace metals during the gasification process is necessary for the optimization of the hot gas cleaning systems. Thereby, in this work the influence of H₂O, HCl, and H₂S on the release and condensation behavior of Cd was experimentally investigated. The experiments were conducted in two different setups. The condensation behavior (temperature and speciation) of the trace metal vapors was investigated in a heated flow channel reactor housed in a furnace with a gas cooling zone. Experiments on the release of the inorganic vapors were carried out in a heated flow channel reactor coupled to a molecular beam mass spectrometer (MBMS) in order to analyze the gas in situ. The results of the experimental investigations were compared with Scheil–Gulliver cooling calculations performed by FactSage 6.3. Furthermore, thermodynamic pseudoequilibrium calculations were carried out to help in understanding the condensation mechanisms of the trace metal cadmium and the global kinetics in the experiments. The experimental results showed that the main chemical species detected in the condensation and release experiments were Cd, CdO, CdCl₂, and CdS. In general, the speciation as well as the temperatures at which the species condensed and were present in the gas phase in the release experiments had the same trend in the calculations and in the experimental results. Thus, the Scheil–Gulliver cooling model was proved to be an excellent tool for the prediction of the release and condensation of cadmium. With this work, a better comprehension of the behavior of cadmium under gasification conditions was obtained.