Control System Design And Analysis Of TE Process Based On Two-time Scale

There are many devices of gas-liquid coexistence in practical chemical process,and physical properties of gas-liquid phase are of great differences.However,dynamic equations associated with the gas phase material are ignored and treated as quasi-stable state which results in process variables of gas-liquid phase changing in the same time scale,and the real dynamic characteristics of process can not be reflected.When control system design is implemented based on quasi-stable state model,the design of material balance and energy balance will simultaneously to be done to ensure system stability and product quality due to the pressure completely depending on temperature,rather than separate design.TE(Tennessee Eastman)process is proposed according to an actual chemical plant of Eastman chemical company,it is composed of several chemical devices which contain gas-liquid phase.It is not only a multivariable large system with recycle streams,but also is a typical two-time scale system.Therefore,it is of great significance to do the two-time scale characteristics analysis and control system research based on TE process.In this paper,TE process is chosen for the study based on the above analysis.Full dynamical model of TE process is built by increasing the independent dynamic characteristic equations of pressure and gas temperature based on mechanism modeling and two-time scale modeling principle,and quasi-stable state model is obtained by dealing with the full dynamical model.Next,simulation platform of TE process is built with gPROMS software.Dynamic characteristic of each device is compared with quasi-stable state model and full dynamical model,the results indicate that the full dynamic model of each device reflects the fast change of pressure and gas temperature,and the fast change is relevant to characteristics of gas material;and then dynamic characteristic of whole TE process is compared with quasi-stable state model and full dynamical model,the results manifest that the full dynamical model of whole TE process recovers the fast change of pressure and gas temperature,and the true dynamic characteristics of TE process is obtained.Finally,control system of TE process is designed based on quasi-steady-state model and full dynamical model.Though the comparative analysis of material balance control,it is shown that pressure control can improve material balance of system and has an impact on the system temperature afterfast change of pressure recovered;Through the comparative analysis of energy balance control,the results show that system performance can be further improved by energy balance control;By contrast of the material balance control affecting energy balance,the results indicate that temperature drift can be reduced and system performance is enhanced by pressure control.