Simulation study and optimization of parameters for low temperature drying of sludge using waste heat

Aspen Plus process simulation software was used to model low-temperature waste heat drying process, focusing on the effects of drying parameters, i.e., sludge moisture content, recycling air flow rate and bypass ratio. Besides, energy consumption for the dying process was analyzed. The results indicated that the low-temperature drying of sludge was significantly influenced by the outlet temperatures of the heater and condenser. The optimal outlet temperature for the heater was 80℃, while the optimal outlet temperature for the condenser was 40℃. When the target moisture content was 30%, the minimum recycling air flow rate was 97598Nm3/h, and the maximum bypass ratio was 0.70. Increasing the recycling air flow rate and reducing the bypass ratio were beneficial for low-temperature sludge drying. The specific moisture extraction rate (SMER) exhibited an increasing-then-decreasing trend with the increase of recycling air flow rate and bypass ratio. When the target moisture content was 30%, the maximum SMER2 could reach to 24.7kg/kWh. Aspen Plus Simulation can be applied to guide the design of low-temperature sludge drying device and the optimization of corresponding parameters, and further provide theoretical supports for promoting large-scale application of low-temperature waste heat drying. © 2023 Chinese Society for Environmental Sciences. All rights reserved.