Analysis, Modeling And Optimization Of Multicylinder Paper Machine Dryer Section Energy System

The papermaking industry is a big consumer of energy. As the world's energy problems become more and more serious, energy consumption reduction in industries is very important. It is a new challenge for the papermaking workers. So improvement of the efficiency without adversely affecting the product quality is very important to the pulp and paper industry.Papermaking is essentially a massive dehydration operation. Although drying removes the least amount of paper in absolute terms, it still remains the most costly and energy intensive step in the papermaking process. The type of dryers used in the paper industry can be classified by the basic means of transferring heat to the paper. An estimate of the distribution of dryer types shows that the conventional steam-heated cylinder dryers are still dominant in paper industry, which reaches a proportion of 85~90%. The energy system of multicylinder dryer section is becoming focus of study. A systematic study on paper machine dryer section has great significance for papermaking industry.The research is beginning from the total plant energy system. The three-link model is used to analyze the energy flow of a typical paper plant. Paper machine dryer section is found to be the most energy consumer. The structure of the dryer section is introduced in details. And it is divided into three subsystems. Energy and exergy balance and Sankey diagram are used together to analyze a newsprint paper machine in this paper. Data from the dry section of the machine is collected to find out the factors affect the energy using efficiency. The result shows that the paper machine needs lots of air to take out the vapor from the wet web. The energy in exhaust air is very high, reaches 62.05%, and the process exergy lose reaches 36.51%. Humidity of hood air has a significant impact on the process energy consumption. When higher hood humidity increasing, lower energy consumption is achieved. According to these characters of the dryer section, the process mathematical model is established. The characteristic function which reflects the relationship between steam consumption and evaporated water is made. By the help of the online data collection system, the model is verified. And the simulation results is in good agreement with the test resultsBased on the mathematical model, by analyzing the characteristics of the energy system of the dryer section in paper machines, a nonlinear programming (NLP) model of the system energy is established, and the corresponding optimization method is proposed. In the method, the dryer section is divided into several functional modules, and the process model of each module is set up based on material and energy balance. By using the operation parameter ranges as the constraints and taking the minimum energy consumption per unit product as the objective, the operation parameters corresponding to the minimum energy consumption are determined with the help of the algorithm presented in Matlab. It is found that the proposed NLP model is well adaptive and convenient for the energy optimization at different operation parameters, concretely. Applied on a linerboard machine which has surface sizing, the method can reduce the energy consumption by 5.6%. For newsprint machines; the energy consumption in the dryer section reduces by about 6%.The heat recovery system of online coating paper machine is a complex heat exchange network. Applied the pinch technology to diagnoses and optimization analysis of heat exchange networks in the drying-section of coated paper machine producing1500 t/d, The result showed that there is a biggish energy-saving potential in the existing heat exchange networks and the quantity of heat-saving in new heat exchange networks after optimizational reforming increased from 4821.6 kJ/s to 9973.1kJ/s, save2.3% fresh steam of drying-section. The energy-saving effect is evident. An object-oriented computer-assisted program is developed for the convenience of the users. The program increases the efficiency and accelerates the application of pinch technology.