Dynamic Characteristics Analysis of Metallurgical Waste Heat Radiative Drying of Thin Layers of Sewage Sludge

Abstract

The utilization of metallurgical waste heat for urban sludge drying and dewatering not only affects the subsequent cost of sludge treatment but also provides a pathway for the rational utilization of metallurgical waste heat. The influence of different experimental conditions on sludge drying characteristics, such as drying temperature and thickness, was analyzed based on metallurgical waste heat. Based on the analysis and evaluation of the drying kinetics parameters of commonly used drying mathematical models, a modified Midilli drying kinetic model is proposed. The kinetic parameters and effective diffusivity of sludge drying were analyzed in three stages of sludge drying: rising rate, constant rate, and falling rate. By utilizing the Arrhenius equation, the relationship between the effective diffusion coefficient and thermodynamic temperature is established, revealing the apparent activation energies for the three stages of urban sludge drying as 29.772 kJ·mol−1, 37.129 kJ·mol−1, and 39.202 kJ·mol−1, respectively. This is closely related to the migration, diffusion, and mass transfer resistance of sludge moisture, indicating that the thickness of sludge accumulation affects the drying time of sludge during the treatment of municipal sludge.

Microwave Drying of Sewage Sludge: Process Performance and Energy Consumption

“…The main reasons for the decrease in drying rate are as follows: (1) The bound water in the sludge is attached to the interior or the surface of the solid matrix via chemical or hydrogen bonds [10], requiring more energy to break than free water. (2) The dielectric constant of the matrix is much smaller than that of water [42,64]. Therefore, the overall dielectric constant of the sludge gradually decreases with decreasing moisture content, leading to a decrease in the absorbed microwave energy and water evaporation as the drying progresses.…”

“…Sewage sludge is dramatically increasing worldwide due to urbanization and industrialization [1,2]. Drying serves as a preliminary procedure for utilizing sewage sludge, such as pyrolysis [3], gasification [4], and combustion [5].…”