Retrofit design of an industrial natural gas liquids recovery process based on the pinch technology concept

Energy consumption is increasing very rapidly, especially in the high-energy consuming industries such as oil, gas, and Natural Gas Liquids refineries. Pinch analysis as a well-established and successful technique is used to improve the energy efficiency of the above-mentioned plants. However, the limitations on ΔTmin and those related to the technical and economic aspects result in the lack of capability by the pinch analysis in reducing the utility beyond a specific amount. Also, this analysis only uses the existing process streams and cannot identify and develop high potential streams reducing the external utility consumption. Opportunities for saving energy consumption would increase through the self-refrigeration methods, and they further decrease the utility consumption. Moreover, for minimizing the process changes, the Heat Exchanging Network should be optimized by pinch analysis and then, the opportunities for self-refrigeration of the process should also be challenged. Thus, the present study was conducted to consider the opportunities for reducing the energy consumption and the required utility in a real-life case study of a Natural Gas Liquids plant. Finally, the heat exchanging network redesigned by the grass root plant was revamped with side streaming from the demethanizer column by changing the ΔTmin to 3 °C resulting in the provision of an additional refrigeration stream for inlet feed instead of external utility. This scheme resulted in saving 3671 kW of refrigeration compressors shaft work and saving 6100 kW of the needed energy for the reboiler and condenser. As the result, 546 kW (53 %) of the plant's total energy consumption will be saved by the pinch and self-refrigeration scheme. The total savings in the purchased equipment costs and operating costs saving of the NGL plant are equal to 3,891,560 (USD) and 3,757,451 (USD/year), with 378 days' payback period.