Hybrid Separation Process of Refinery Off-gas toward Near-Zero Hydrogen Emission: Conceptual Design and Techno-economic Analysis

This article presents a conceptual design of hybrid separation processes of refinery off-gas on the refinery scale, aiming at the recovery of high-value-added components toward near-zero hydrogen emission to the fuel system. The whole design consists of three interrelated subsystems, namely, hydrogen production, hydrogenation, and nonhydrogenation. In each subsystem, we propose appropriate hybrid separation methods based on the compositions of the feed streams and the available industrial applied separation techniques. In the system scope, the hydrogen production subsystem receives the hydrogen-rich streams from the other two subsystems and produces and supplies high-purity hydrogen to the hydrogen pipeline for the demand of the hydrogenation subsystem. On the other hand, the light distillate recovered by the hydrogenation subsystem is further processed by the nonhydrogenation subsystem to promote the yield of C2 and C3 products. The entire process is captured by a detailed process simulation model incorporating a user-customized module for better representing the industrial data. Design specifications and sensitivity analysis are carried out for optimizing critical operating parameters in this system. The hydrogen emission ratios under single-, double-, and triple-stage membrane separation are calculated to be 2.58, 1.65, and 1.35%, respectively, which are considered as near-zero hydrogen emission. These three cases are further evaluated based on the economic analysis. The enhanced recovery of components with high net present value gives adequate profit, showing the techno-economic feasibility of the design.