Xue Yongjie, Wang Chen, Hu Zhenhua, Zhou Yi, Liu Gang, Hou Haobo, Xiao Yue, Wang Teng, Li Jinping
State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070, China.
School of Resource and Environmental Science, Wuhan University, Wuhan 430070, China.
Waste Manag. 2018 Aug;78:917-928. doi: 10.1016/j.wasman.2018.07.009. Epub 2018 Jul 11.
Thermal drying of sewage sludge is not only an effective way to treat the waste, but also an essential step for further energy utilization. This work focused on drying property of sewage sludge by using electromagnetic induction heating. A novel drying method for sewage sludge was designed. The effects of different electromagnetic-induction media materials, working parameters and conditioning reagents on the efficiency of drying were investigated. Then, the kinetics was analyzed. The change of temperature and heat-transfer was analyzed during the drying process. Experimental results showed that sewage sludge combined with three kinds of induction medias can be efficiently dried by applying electromagnetic induction heating. Fast formation and development of cracks indicated that an increase of drying rates of sludge can be obtained. Considering the release of volatile organic compounds from sludge during drying process, estimated moisture content was used to evaluate the drying effect. A Higher working voltage leaded to a more weight reduction of sludge during a shorter drying time, but a lower voltage prolonged the drying time. It was noted that the estimated moisture rate was very close to the experimental moisture content. Sludge content, forming and induction media significantly affected the drying process. Plate and net media were fitted for thin layer and piled sludge, respectively. However, fiber media seemed to show lower drying rate due to no circuit for induction current. An addition of CaO and sawdust improved the drying process. As a result, few volatile organic compounds released from sludge. For kinetics, three periods (warm-up, constant rate and falling rate period) can be observed and the data fitted linear regression of Lewis drying model very well. The effective moisture diffusivity was influenced by the different induction media and the thickness of sludge. Infrared images showed that outside temperature was higher than central part temperature for all sludge samples. A higher evaporation rate and diffusion of moisture can be obtained from outside part of sludge due to the easy collapse of porous structure.
污水污泥的热干燥不仅是处理废弃物的有效方法，也是进一步能源利用的关键步骤。本研究聚焦于利用电磁感应加热处理污水污泥的干燥特性。设计了一种新型的污水污泥干燥方法。研究了不同电磁感应介质材料、工作参数和调质试剂对干燥效率的影响。然后，对干燥动力学进行了分析。分析了干燥过程中温度和热传递的变化。实验结果表明，通过施加电磁感应加热，污水污泥与三种感应介质结合可有效干燥。裂缝的快速形成和发展表明污泥干燥速率可以提高。考虑到干燥过程中污泥中挥发性有机化合物的释放，采用估计水分含量来评估干燥效果。较高的工作电压导致在较短干燥时间内污泥减重更多，但较低电压会延长干燥时间。值得注意的是，估计水分率与实验水分含量非常接近。污泥含量、形态和感应介质显著影响干燥过程。平板和网状介质分别适用于薄层和堆积的污泥。然而，纤维介质由于没有感应电流回路，干燥速率似乎较低。添加CaO和锯末改善了干燥过程。结果，污泥释放的挥发性有机化合物很少。对于动力学，可观察到三个阶段（预热、恒速和降速阶段），数据与Lewis干燥模型的线性回归拟合良好。有效水分扩散率受不同感应介质和污泥厚度的影响。红外图像显示，所有污泥样品外部温度均高于中心温度。由于多孔结构易于坍塌，污泥外部可获得更高的蒸发速率和水分扩散。
