Flash drying of slurry-liquid sewage sludge based on avoidance of latent heat of phase change: Laboratory to pilot-scale evolution

Abstract

Industrial slurry, municipal sewage, and other slurry-liquid sludges pose a formidable challenge for quick and comprehensive drying in a single step due to their large volume, and high water content. Conventional slurry sludge drying methods, driven by the necessity to overcome the latent heat associated with phase change, entail notable drawbacks, including high energy consumption, and suboptimal efficiency. In this study, we introduce a cyclone-based non-phase change drying process, specifically designed to achieve efficient, one-step drying of slurry-liquid sludge, all while operating at temperatures below the phase change of water. Our study focuses on the use of the industrial titanium gypsum slurry (TiGs) as the primary research subject, exploring the factors influencing the efficiency of cyclone non-phase change drying at both laboratory and pilot scales. Our results underscore the significant impact of temperature, gas velocity, and gas–solid ratio on the drying process of TiGs. Notably, in our pilot-scale experiments, employing an air volume of 1300 m3/h, a temperature of 90℃, and a gas–solid ratio of 16 m3/kg, we achieved an impressive reduction in water content in the TiGs, dropping from 72 % to 15 % in mere 30 s. Mechanistic investigations elucidated that the overall drying process includes several important processes, encompassing slurry hot air crushing, rotary granulation, and spin dewatering. Furthermore, our thermogravimetric and elemental analyses unveiled that the augmented expansion of pores facilitated low-temperature dehydration, thereby preserving the stability of the dried material's composition. Additionally, we ascertained that this technology also delivers highly effective drying for municipal wastewater.