An Experimental Study on the Collection of Inorganic Substances during Pyrolysis

Abstract

Combustible solid waste usually contains inorganic elements and compounds such as solid oxides (e.g., SiO₂, Al₂O₃, TiO₂, and Fe2O₃), alkali metals (e.g., Na, K, Mg, Ca, and Cs), and non-metals (e.g., S, P, and Se). When this waste is treated using thermal conversion processes such as combustion, gasification, or pyrolysis, the removal of inorganic substances depends on the process operating conditions. In this study, inorganic elements with a low melting temperature (S, Se, and Cs) were studied experimentally to analyze their evaporation process during thermal conversion and their cooling while passing through a gas-cleaning facility followed by collection in a filter. In the experiments, S, Se, or Cs (as a compound of CaNO₃) was mixed with combustible solid waste and fed into an electric heater with N₂. The proportion of these elements that were evaporated, condensed, or collected by filters installed in a post-cleaning system was then measured. It was found that the evaporation rate for S, Se, and Cs depends on the interaction between the vapor pressure and molecular weight. The amount of inorganic particles decreased linearly with the ratio of the wire temperature to the boiling temperature. In addition, the amount of Cs particles was higher than that of S and Se. This is because Cs has a much lower vapor pressure and thus condenses earlier on the reactor wall than S and Se at the same temperatures.