Hybrid Modeling For Solvent Dehydratic Distillation Column In Pure Terephthalic Acid Industry

In the manufacturing process of pure terephthalic acid (PTA), the solvent dehydrate distillation column (SDDC) plays an important role in removing water, which is generated by p-xylene (PX) oxidation, maintaining water content in the process of PX oxidation and decreasing the consumption of acetic acid (HAc). Water content in the recycled HAc in the oxidation unit depends on the operation conditions of SDDC and water content affects the oxidation process of PX. At the same time, operation conditions of SDDC influence HAc content in the effluent from top of SDDC. The model for SDDC is the foundation for optimizing control of the unit.At present, modeling for industrial distillation column is mainly based on sole operation data with adjusting tray efficiency to minimize error of fitting. But key parameters will change as the operation condition of SDDC varies. So, the original model can't apply for the new operation condition one. Therefore, a hybrid model combining an intelligent model and mechanism model is developed in this paper. The intelligent model can imply tray efficiency and influence factors. So, the hybrid model has robust performance and prediction performance.The method of hybrid modeling for SDDC is as below:first, typical data of operation of SDDC is chosen for different mechanism models with adjusting tray efficiency to minimize the error of fitting. At the same time, tray efficiency and influencing factors are studied. Based on tray efficiency sample data developed by mechanism model and correlation analysis of input variables, it can be found feed flowrate has a strong relationship with pressure drop and reflux flowrate. Input variables of SDDC can be decreased. Considering tray efficiency and influencing factors has strong relationship, least square support vector machine (LS-SVM) and BP algorithm are used for developing model of tray efficiency respectively. Then a good intelligent model can be developed. Rigorous mechanism equilibrium model is employed to simulate SDDC. It refers to mass balance equation (M), phase equilibrium equation (E), tray efficiency equation (T), summation equation (S) and energy balance equation (H). In this paper, tray efficiency model is implanted into the rigorous mechanism of SDDC. So hybrid model can simulate different operation condition. Finally, performances of hybrid models are good according to field data. And performances of the two hybrid models are contrasted.