Study on microwave-induced thin-layer drying of municipal sludge for fuel reclamation

Since the adverse factors such as deficient penetration and long reaction time have restricted the complete microwave-used drying of municipal sludge, the microwave-induced drying is considered, which has advantages in such aspects. The investigation of the microwave-induced drying to uncover the mechanism bears great meaning for its development and utilization. The effects of temperature and microwave cracking in municipal sewage sludge drying characteristics are studied through municipal sewage sludge drying experiment. Experiments shows that higher drying temperature would lead to a more acutely changing drying rate (D _R). The D _R had increased from 0.005 g/(g·min) to 0.060 g/(g·min), which was 12 times enlarged, while the temperature rose from 70 °C to 160 °C. The higher the temperature was, the earlier the peak value of D _R appeared. The experiments indicated that the temperature was the decisive factor affecting the D _R. The microwave-induced sludge reached the highest D _R at the moisture rate (M _R) of 40%, with a 20% grade promotion compared with that of the original one. The molecular fracture caused by microwave radiation had obviously accelerated the drying process and the DR was rising in proportion to the microwave radiation dose. The diffusion coefficient had been calculated according to Fick??s law. In comparison to that of the original one, the diffusion coefficient of microwave-induced sludge was obviously enlarged more than two times. By fit examinations, Model Weibull was proven to be the most fit one for thermal thin-layer drying of municipal sludge. By means of Arrhenius equation, the obtained average activation energy of municipal sludge was 37.1 kJ/(mol·K).