Utilization of molten chloride salt derived from MSWI fly ash washing as energy storage material: thermophysical properties and corrosion behavior

Abstract

Fly ash, as a byproduct of municipal solid waste incineration, contains several kinds of pollutants, especially dissolvable salts that cause a severe challenge for fly ash disposal. Washing combined with cement kiln co-processing for fly ash disposal has been applied in China. After washing, the wastewater was evaporated to produce fly ash salt (FAS). In this study, FAS was mixed the KCl and LiCl to be used as molten chloride salt for energy storage material. Twenty-three types of molten salts with various ratios of FAS-KCl-LiCl were evaluated. Thermophysical properties (melting point and latent heat) and thermal stability of these salts were characterized. The increase in FAS fraction decreased the latent heat of molten salts. Among the tested samples, the best compatibility ratio of FAS:KCl:LiCl was 10:50:40 (%, in weight), with latent heat of 108.7 J/g and melting point of 333 °C. This molten salt also showed good thermal stability after 1–13 h of thermal experiments, and the mass loss was less than 2% after 5 heating cycles at 600 °C. By corrosion test, FAS-KCl-LiCl (10:50:40, % in weight) could be more safely used in vessels made of nickel-based alloy, but it might cause corrosion risk for stainless steel.