Dynamic Simulation of Distillation Sequences in Dew Pointing Unit of South Pars Gas Refinery

The understanding of the dynamic behavior of distillation columns has received considerable attention because distillation is one of the most widely used unit operations in chemical process industries. This paper reports a dynamic simulation study of the possible distillation columns sequences of Dew pointing unit in the second phase of South Pars Gas Refinery. In this unit, three columns are used for separating the feed of normal paraffin, from methane to n-Decane into the four mixtures of products; so five different simple columns sequences are possible. In this work, we made use of linking between Aspen dynamic and MATLAB Simulink software’s for achieving our purpose. At first, simulation and design of the distillation sequences were performed in steady state by using the process simulators Aspen Plus 2006.  After steady state simulation, the parameters required for the dynamic simulation were entered and the files were exported to ASPEN Dynamics. PI and PID controller as basic controllers were automatically added and were tuned by the conservative Tyreus–Luyben tuning method. Then the model which connects MATLAB to Aspen Dynamic was created in Simulink and the behavior of the five different sequences in dynamic regime was observed after changing the flow rate of the feed steam by. The results show that the steady state simulation is suitable for the start point, but it is better to use dynamic simulation to design and simulate the chemical process industries because in dynamic simulator there are nonlinear models for calculating the equations of state and simulating the chemical process. In addition, in dynamic simulation we are faced with real condition of process so the obtained results will be close to the real ones. After dynamic investigation, it were found that the sequences-2, sequences-4 and sequences-5 have suitable dynamic behavior for controlling because of auto-rejection of the disturbances, but the sequences-1 and sequences-3 have complex dynamic response and they are found to be hard to control.