Investigation of Thin-Layer Drying Characteristics of Sludge as Affected by Temperature, Sludge Layer Thickness, and Flow Pressure Differential

To investigate the kinetic model of the thin-layer drying of the municipal sludge, establish the selection criteria for thin-layer drying models, and analyze the influence factor of model parameters and their roles in drying, this study constructs a sludge drying experimental test rig. Drying experiments are conducted on sludge under varying conditions: different drying temperatures (60, 70, 80°C), different flow pressure differences (0.61, 0.85, 1.0 kPa), and different sludge thicknesses (5, 10, 15 mm). The obtained drying characteristic curves are nonlinearly fitted with six different empirical models. The results demonstrate when the sludge thickness and the flow pressure difference were held constant, each 10°C increment in temperature induces approximately 20% decrease of drying time. When the temperature and flow pressure difference were set constant, each 5 mm reduction in thickness shortened the drying time by 30–45%. When the temperature and sludge thickness were maintained, and the flow pressure difference varies from 0.61 kPa to 1 kPa simultaneously, the drying time reduces by about 17%. The drying process of sludge is inclusively subjected to the Weibull distribution model, to furtherly improve the accuracy a pre-factor based on initial values is implemented. This research provides reliable parameter guidance which enhance the sludge drying performance and reduce energy consumption in drying processes.