Ultrasonic pretreatment on the influence of sludge convective drying and thermodynamic analysis
In order to investigate the drying effect of sludge after ultrasound pretreatment in convective drying,ultrasound with frequencies of 25 kHz and 40 kHz was used to pretreat the sludge for 2 and 4 h,respectively.The pretreated sludge was then subjected to convective drying at 70,90,110,and 130 ℃,and the experimental data was mathematically fitted.The results showed that ultrasound pretreatment can effectively increase the drying rate of the sludge.Within the entire drying temperature range,the sludge pretreated with 25 kHz ultrasound had a faster drying rate,with pretreatment times of 2 and 4 h reducing the drying time by 23.19％and 29.15％,respectively.This improvement was more significant at higher convective drying temperatures.Among the seven drying models,the Midilli model more accurately represented the behavior of the pretreated thin-layer drying.According to the Fourier transform of the Fick's second law,Deff exhibited exponential growth,and the increase in Deff for sludge treated with 25 kHz ultrasound was better than that for 40 kHz.The difference in apparent activation energy Ea of sludge pretreated with different ultrasound is small,but the 25 kHz ultrasound resulted in a higher D0 for the sludge,approximately 3.146×10-6 m2·s-1.In addition,the ultrasound pretreatment time should not be too long,as it may lead to an exacerbation of reabsorption phenomenon.
万方数据
维普
