Dynamic Simulation and Evaluation of NGL Recovery Process

Abstract

Because NGL (Natural Gas Liquid) recovery process separating methane gas from NGL is operated at high pressure and low temperature than other natural gas process, it is especially important to determine the control scheme and evaluate the dynamic response and safety before construction. Therefore, we conducted a study to determine the appropriate control scheme of the HY-NGL recovery process, one of the NGL recovery processes using turbo expander. To do this, we first suggested theoretically-possible control schemes of this process, just considering paring a single controlled variable with a manipulated one, and then selected a few promising cases through intuition judgment. Then, dynamic state modeling for remained control schemes was simulated by Unisim®, one of commercial process simulators. Dynamic response and safety of each control scheme was evaluated by changing the feed conditions (i.e. mass flowrates, composition of components) and the most appropriate control scheme was determined. In addition, to deal with malfunction of reboiler control valve, which can lead to poor process performance, another variable highly-sensitive with process performance is introduced as an additional manipulated variable. Through a case study, it was confirmed that safety of process is considerably improved when using multiple manipulated variables suggested in this study.