Internal and surface temperature profiles of spherical biosolids particles during convective drying
Journal Publication ResearchOnline@JCUAbstract
The convective drying of spherical biosolids particles from two wastewater treatment plants (Type 1: anaerobic/anoxic treatment with belt filter press dewatering; Type 2: aerobic/anoxic treatment with centrifuge dewatering) was studied under 10 conditions across 44 trials. A wide spectrum of conditions including three drying temperatures (88, 109, and 138�C), two gas velocities (1.6 and 2 m s−1), and particle sizes of 2 cm and 4 cm were investigated. Measured variables included particle mass, center/internal temperature, surface temperature, shrinkage, and qualitative observations of morphological changes. Most samples showed two drying periods, a constant rate period followed by a falling rate period. Additionally, it was found that drying rates and morphological changes depended significantly on particle size and drying intensity (i.e., drying gas temperature and gas velocity) with higher intensities resulting in larger, more porous particles. Internal temperature profiles displayed a consistent pattern, an initial heating phase where internal temperatures quickly rose to approximately the wet bulb temperature of the drying gas, a quasi-constant temperature phase at that temperature, and a final sharp increase/spike to reach equilibrium with the drying gas temperature. Moreover, IR images showed that sub-surface temperatures (between the core and surface) were significantly lower than surface temperatures. Surface temperatures showed a more linear increase throughout drying until equilibrium with the drying gas temperature. The consistent temperature difference between the center and surface, as well as the internal temperature profile, suggests the existence of a drying front, moving radially inward as the particle dries. This research contributes to a better understanding of biosolids drying dynamics, offering insights to improve thermal treatment strategies thereby contributing to the broader field of waste management.
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Drying Technology
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DOI
10.1080/07373937.2024.2407959