Chemical Process Engineering Institute, University of Alicante, 03690 San Vicente del Raspeig, Alicante, Spain.
Chemical Process Engineering Institute, University of Alicante, 03690 San Vicente del Raspeig, Alicante, Spain.
Waste Manag. 2023 Aug 1;168:116-125. doi: 10.1016/j.wasman.2023.05.054. Epub 2023 Jun 7.
The drying of flexible plastic waste is a current industrial problem in the plastic recycling sector. The thermal drying of plastic flakes is considered the most expensive and the most energy-consuming step in the recycling chain, which represents an environmental issue. This process is already present on the industrial scale but not well described in the literature. A better understanding of this process for this material will lead to the design of environmentally efficient dryers with an improved performance. The objective of this research was to investigate the behavior of flexible plastic in a convective drying process at a laboratory scale. The focus was to study the factors affecting this process such as velocity, moisture, size and thickness of the plastic flakes in both fixed and fluidized bed systems and to develop a mathematical model for predicting the drying rate considering heat and mass transfer of convective drying. Three models were investigated: the first one was based on a kinetic correlation of the drying, and the second and third models were based on heat and mass transfer mechanisms, respectively. It was found that heat transfer was the predominant mechanism of this process, and the prediction of the drying was possible. The mass transfer model, on the other hand, did not give good results. Amongst five semi-empirical drying kinetic equations, three equations (Wang and Singh, logarithmic and 3rd-degree polynomial) provided the best prediction for both fixed and fluidized bed systems.
柔性塑料废料的干燥是塑料回收行业目前面临的一个工业问题。在回收链中，塑料薄片的热干燥被认为是最昂贵和最耗能的步骤，这也是一个环境问题。该工艺已经在工业规模上得到应用，但在文献中描述得并不完善。更好地了解这种材料的干燥过程将有助于设计具有改进性能的环保型干燥机。本研究的目的是在实验室规模上研究柔性塑料在对流干燥过程中的行为。重点研究了影响该过程的因素，如固定床和流化床系统中塑料薄片的速度、湿度、尺寸和厚度，并开发了一个考虑对流干燥的传热和传质的干燥速率预测数学模型。研究了三种模型：第一种模型基于干燥的动力学相关性，第二种和第三种模型分别基于传热和传质机制。结果发现，传热是该过程的主要机制，干燥的预测是可行的。另一方面，质量传递模型没有给出很好的结果。在五个半经验干燥动力学方程中，有三个方程（Wang 和 Singh、对数和三次多项式）为固定床和流化床系统提供了最佳预测。
