Study On Modeling And Simulation-Optimization For Energy Efficiency In Paper Drying Process

This study presents an overview of the current research status related to modeling, simulation and optimization for energy efficiency in paper drying process. Considering the shortcomings of previous studies and actual requirements in production of Paper-Making enterprises, the purpose of the study is to solve two practical operating problems during paper drying, process monitoring and energy efficiency optimization, focusing on the study of systematic method about mathematical model establishment, simulation development and Operating parameters optimization in paper drying process.A specific field test was occurred on the in-depth investigation of energy system of dryer section, a mathematical model was established for describe energy efficiency quantitatively based on field test data, which has improved the existing methods of energy system diagnosis in paper drying process. A preliminary experimental study on drying mechanism of pulp materials was also done in the current study. Utilizing low field nuclear magnetic resonance(LF-NMR), it was validated that there are three different forms of water in pulp materials, free water, capillary water and bond water, and their variations during drying were measured and used to analysis the drying mechanism of pulp materials in different drying stages. A new method was designed to quantitatively describe energy consumption of water evaporation in different stages. The method was based on drying curve, which was simple, fast, and low requirements for testing environment.Mathematical models of paper drying simulation system was established using sequence modular approach based on the principle of mass and energy conservation. According to the actual characteristics of dryer section, the whole simulation system model was divided into 4 key subsystem models and 15 key function modules including DAS. In the modeling process, the easily acquired variables were selected as input data of mathematical models, in addition, the mathematic models can been solved by combining the heat and mass transfer models of steam, paper and air, in purpose of solving the problem on determination of some mathematic models’ boundary conditions.The simulation model was converted to a executable program and the paper drying simulator PDS.Lab was developed in MATLAB software platform. The simulator PDS.Lab meet the following requirements:(1) can solve all mathematic models of simulation system;(2) can simulate a specific paper drying process easily and accurately after configuring the actual operating conditions with convenient operations;(3) can assess energy performance of paper drying process;(4) can display key parameters of paper drying process by visualization. The application research of simulator PDS.Lab showed that it could monitor paper drying process well, which remedied the defects of the existing monitoring system. And the its assessment system provided a convenient tool to analysis drying capacity, energy efficiency and operating efficiency during paper drying. Avoiding the complex mechanism analysis, this tool made the analysis procedure simple and helped operators monitor and control the paper drying process scientifically.Applicating SQP optimization algorithm,A study on simulation-optimization of operating parameters in paper drying process was done based on the simulator PDS.Lab. An optimization model was established in which the objective was energy cost and the decision variables were steam pressure in main section, different pressure between sections, power load of air blowers and temperature of supply air. Correspondingly the constraint conditions of energy efficiency optimization model were also analyzed, including dryness of paper web leaving the dryer section, dew point of moisture air, hood balance, humidity of hood exhaust air, capacity of equipment and so on. The case study showed that the optimized operating papameters can reduce energy costs during paper drying including steam costs and power costs. Applicating the optimization model, a study was done on how did the optimal operating condtions of paper drying process change when machine speed, basis weight, temperature and humidity of environment changed. It was found that the changes of optimal condition present a certain regularity due to the changes of evaporation load influenced by machine speed and basis weight, steam pressure generally increased as evaporation load increased, and vice versa. However, when the environment conditions(temperature and humidity) changed, the optimal operating conditions changed complexly due to the influence of dew point constraint. It is difficult to make the best decision, and need a scientific optimization.The simulator PDS.Lab developed in this study can be used only for offline or ―not-real time‖ process simulation and optimization. The simulation results can reflect the changing trend of the process variables, but there is still a certain deviation between simulation results and measured results. The following study can work at the method of improving the accuracy of simulator PDS.Lab and development of ―real-time‖ process simulator.