Coupling Heat Pump and Vacuum Drying Technology for Urban Sludge Processing

Sludge vacuum drying equipment was developed to explore the feasibility of drying large amounts of sludge under vacuum. In this paper, we first describe the structure and working principles of the drying device, and then demonstrate drying of 30 kg sludge in three different temperature ranges: A (similar to 85 degrees C-87 degrees C), B (similar to 82 degrees C-84 degrees C) and C (similar to 76 degrees C-78 degrees C). All experiments were performed under vacuum at similar to 0.093-0.095MPa at absolute pressure equal to 6-8kPa. The results showed that the sludge drying process using our drying equipment occurs in the deceleration stage. The heat transfer efficiency of the device is about 30%. The average unit energy consumption during B and C stages is similar to that of hot air drying, but it is superior to the hot air drying during the initial drying stages. (C) 2019 The Authors. Published by Elsevier Ltd.