(570p) Rigorous Dynamic Simulation Study on the Ethylene Refinement Process within the Bio-Ethanol to Ethylene Section

Yingzhe Yu, Lu Kong, Zhongfeng Geng, Xiuqin Dong, Minhua Zhang^*

Key Laboratory for Green Chemical Technology of Ministry of Education, R&D Center for Petrochemical Technology, Tianjin University, Tianjin 300072, P. R. China

*Corresponding author   Tel. & fax: +86-22-27406119,  E-mail address: mhzhang@tju.edu.cn

 In this work, two types of ethylene rectification simulation process are developed to refine the raw ethylene flow (ethylene content > 98 wt %). The normal simulation method is that two Radfrac columns with the condenser and reboiler inside the model. The more rigorous one is a two-rectification columns process with a propylene refrigerant cycle, which provides the heat and cooling energy. This Aspen simulation utilizes explicit heat-exchanger for the condensers and the reboilers, which means the column itself is a Radfrac model without any reboiler or condenser. These are added externally as Aspen HeatX models, as are separate reflux drums and circulation from the columns through the reboilers. Design and control of the processes are investigated using Aspen Plus and Aspen Dynamics.

When the steady-state simulation is completed and proper geometric parameters of the equipment are added, it is just the time to do the dynamic works. As the feed flow consists of high concentration ethylene, it is quite difficult to choose a sensitive plate when it comes to lay out a temperature control structure on the column. However, a combination of the traditional method in steady simulation and the dynamic simulation could provide an effective way to deal with this situation. Then with the control structures for the two processes, the dynamic simulation results are achieved using Aspen Dynamics. The feed flow rate and feed composition disturbances are taken using dynamic simulation to evaluate the control structure. With the proper complete process in Aspen Dynamics, the safety analysis, such as condenser failure and heat-input surge, is explored. It is indicated that the traditional distillation simulation with a Radfraccolumn alone could not accurately predict the process variables changes during the disturbances.

Keywords: Dynamic simulation, ethylene distillation, rigorous distillation process, sensitive plate selection, safety analysis