Design and Economic Evaluation of a Hybrid Membrane Separation Process from Multiple Refinery Gases Using a Graphic Synthesis Method

Abstract

Petrochemical tail gases have various components and many separation methods, thus there are many possible design schemes, making it difficult to determine the optimal scheme. In this work, a graphic synthesis method was used to design a hybrid multi-input refinery gas separation process consisting of membranes, pressure swing adsorption (PSA), shallow condensation (SC), and distillation units for the production of valuable products which include H2, C2, LPG, and C5+. Ten refinery gases with different compositions were visualized and represented with vector couples in a triangular coordinate system. Firstly, according to the characteristics of the refinery gases, the feeds located in the same region of the triangular coordinate system were merged to simplify the number of input streams, then ten original input streams were combined into two mixed streams. Secondly, the optimal separation sequence was determined by using the unit selection rules of a graphic synthesis method. Thirdly, the process was simulated in UniSim Design and the process parameters were determined by sensitivity analysis. Finally, economic assessments were carried out, which led to an annual gross product profit of USD 38.62 × 106 and a payback period of less than 4 months.