Investigation of an Energy-Saving Strategy in a Rotating Paper Dryer Through Fundamental Research of Multiphase Flow Behavior

In the paper industry, the process of transforming pulp into finished paper involves several crucial stages that ensure paper quality. Among these stages, the paper drying stage is one of the most important stages. In this stage, multiple rotating cylinders are used in which superheated steam is ejected to heat wet paper web rolling over the cylinders. Steam relieves latent heat and condenses into water; this condensate accumulates and is extracted through stationary or rotary siphons. Due to rotation, the pool of condensate would go through different types of flow behaviors depending on the rotation speed, mainly appearing as puddling, cascading, rimming, and transitions between them, which predominantly affect heat transfer rates and rotating power consumptions. During rimming, the condensate would rotate with the inner cylinder forming a thin liquid layer, which behaves as an extra thermal resistance, resulting in reduction of effective transfer of heat. For that reason, the objective of this research is to conduct fundamental thermal-flow and heat transfer research in multiphase behavior in a Rotating Paper Dryer with a goal to achieve significant energy savings. This project has successfully completed the following tasks: (a) performing analytical study to establish a more accurate correlation for predicting rimming speed, (b) establishing a simplified 2D computational model by incorporating a source and sink sub model to simulate the steam-injection and condensate extraction behavior in 3D operation to improve understanding of condensate rimming behavior and heat transfer and power consumptions, (c) implementing steam condensation and condensate flashing sub-models in a comprehensive simulation of a complete 3-D rotating dryer, (d) developing an experimental test rig to study the flow movement of condensate, (e) exploring the innovative idea of applying hydrophobic coatings to the dryer inner surface to prevent the occurrence of condensate rimming via both computational and experimental approaches.