Advanced Control System Development And Application Of The Ethylene Rectification Tower

Ethylene distillation column is one of the finished products of ethylene plant, which has important significance to improve the stable operation of ethylene plant and the economic benefit of the enterprise. Ethylene distillation process is very complex and requires a high product quality. The ethane concentration in top of the column and ethylene concentration in bottom of the column are the two important indicators, which play an important role for the column. The ethane concentration and ethylene concentration can be obtained by online analysis instrument, but the measurement has a big time-delay. It cannot meet the real-time requirements of automatic control. So the operator need to manually adjust the reflux and reboiler heating. In order to ensure that the technical indicators to meet the requirements, the operator often take the over-distillation method to control. Thus, the tower's adjustment flexibility is reduced, the stable operation of the ethylene distillation column is affected.In order to stabilize the operation of ethylene distillation column, improve the quality of products and solve the problem of measuring time-delay and over-distillation, an advanced control scheme based on key components of soft sensor is proposed. Through analyzing of key factors influencing the ethylene distillation tower, the instrumental variables of key components of soft measurement model are selected. Comparing the prediction accuracy of PLS, the PLS method, and RPLS method with forgetting factor by the simulation method, so the concentration of ethane and ethylene can be predicted. The soft measurement values and the adjusting valves constitute an automatic control loop, and the quality of the products can be controlled.Based on the proposed advanced control scheme of ethylene distillation tower, the soft sensing program and automatic correction of the key components are developed, and the realized process on DCS and the implementation method of the advanced control system are presented. Through analysis of operation results of the new control system, the effect of the proposed scheme is verified. The critical operation of the ethane and ethylene concentration is achieved. It ensures the stable operation of the column and the qualified quality of the products.