Plantwide control and dynamic assessment of a novel NGL/LNG integrated scheme

The integrated natural gas liquids (NGL)/liquefied natural gas (LNG) processes take precedence over standalone NGL and LNG units due to the lower investment and operating costs. Several studies have been conducted to improve the performance of integrated schemes, but few have looked into the controllability of these configurations. For the first time, a plantwide control structure based on proportional-integral-derivative (PID) controllers is proposed in this study for a novel NGL/LNG scheme. In this regard, after the determination of the control objectives, 47 dynamic manipulated variables are recognized. Then, according to Luyben's method, the appropriate controlled variables and their setpoints are determined, and the tuning parameters of the PID controllers are adjusted. The performance of the proposed decentralized control structure is assessed in rejecting the effects of disturbances in temperature, composition, and flow rate of the feed gas. This structure is capable of successfully handling the aforementioned disturbances and ensuring the smooth operation of the co-production scheme. The analysis of the dynamic responses indicates that the largest fluctuations occur during the feed flow disturbances. This research presents a potentially useful application, and the findings can be utilized to improve the control structures of integrated configurations in the future.