Dynamic Simulator-Based APC Design for a Naphtha Redistillation Column

Abstract

In this simulation study the operation of a naphtha redistillation column (a column with two feeds and three products) was analyzed with the application of Aspen HYSYS ® software. The simulator, structure of local con-trollers and the product-quality estimators were based on the data of an industrial column in the Danube Refin-ery. The aim of the analysis was to identify the dynamic and steady-state effects of heating and cooling as well as the sidestream of product qualities. The relationship between the tray temperatures and the quality of the products was also identified and inferential calculations were made. Based on the identified relationships, a two-level hierarchical control structure was developed. On the lowest level of the hierarchy are the local controllers of flowrates, liquid levels, pressure and duty. The inferential calculations are important components of the controller which serve as the controlled variables at the coordination level. The inputs of the estimators are the process data of the column, e.g. temperature, pressure and flowrate. On the top level of the control hierarchical structure the quality of the products are controlled by manipulating the setpoint of the local controllers. Based on the analysis of the Controlled Variable – Manipulated Variable relationship, closed-loop quality control was achieved with PID controllers. The result of the analysis may form the basis of Advanced Process Controller implementation.