Study On Pulp Cooking Endpoint Soft Measurement In Displacement Digester Systems (DDS)

Owing to energy consumption, pollution and other issues, the development of paper pulp industry has been seriously hampered. Searching for a new environmental and energy-saving pulping technology is an important strategic issue placed in pulp and paper industry of china. Displacement digester systems, which was developed in 1980, is a high-efficiency and energy-conserving pulping technology. Because of its good environmental and economic benefits, displacement digester systems has gradually became an important development direction of pulp technology.Based on mechanism introduction of displacement digester systems, aiming at the difficulty of judging pulp cooking endpoint, the work in this paper was expanded from following aspects.Firstly, soft measurement method on cooking endpoint of displacement digester systems has been proposed in the article. The cooking endpoint, which is the basis for time, has a direct impact on pulp quality and energy consumption. At present, more scientific and reliable method for judging cooking endpoint is to rely on kappa number and other influencing factors. However, online direct detection of kappa number is very difficult as the complexity of the cooking process, a soft measurement scheme of kappa number was proposed based on artificial neural network to indirectly measure kappa number and determine the endpoint of cooking process. Kappa number was selected as the output variable of model and H factor, sulfidity and the effective concentration of alkali were selected as input variables of the model.Secondly, two approaches were used for soft measurement model by RBF neural network and BP neural network in this article. On the basis of the model, its application in the DCS control system was introduced. SIEMENS S7-400 PLC was chosen as hardware development platform and WinCC and Step7 software were selected as software development platform in DCS. In order to monitor and operate the entire production process, the host computer not only need to design WinCC development platform, but also achieve docking with the MATLAB software, which will embed soft sensor technology into DCS control system.Thirdly, based on the design of DCS control system, some control schemes of displacement digester systems were briefly presented, such as, H factor calculation, consistency of the upper and lower temperature of digester, the stability of digester pressure and so on.