A Static Energy Model of Conventional Paper Drying for Multicylinder Paper Machines

A static energy model was developed to describe the conventional paper drying process for a multicylinder paper machine. The model is based on the mass and energy balance relationships written for fiber, steam, air, and water. With the purpose of developing a clear understanding of the paper drying process and evaluating its drying performance, the model developed was made up of seven basic blocks according to the technical art of paper drying. In this work, a multicylinder newsprint machine was chosen to illustrate the energy model. The module schematic and instructions are presented first, followed by mathematical descriptions for each block. In addition, paper drying models are reviewed. The specific drying rate, specific heat consumption, and energy efficiency are introduced to evaluate the drying performance. Experiments were conducted to measure the operating parameters and the newsprint drying process was simulated based on the model. A Sankey diagram is also presented. The results are compared with a typical newsprint machine to identify more energy-saving opportunities. The calculations indicate that the consistency of the energy model with experimental results and experience is reasonable. A series of simulations was performed to examine the effects of supply air temperature and exhaust air humidity on specific heat consumption. The results show that the specific heat consumption was decreased by 3.3% when the supply air temperature decreased from 112 to 100 degrees C by adjusting the steam flow into the air heaters. Correspondingly, increasing the exhaust air humidity to 0.14 kg water/kg dry air from 0.10 kg water/kg dry air by adjusting the fan speed led to a 4.6% reduction in specific heat consumption and a 32% power savings for the fans.