An innovative techno-economic analysis for the selection of an integrated ejector system in the flare gas recovery of a refinery plant

The compression process in flare gas recovery, commonly carried by compressors, is the costliest. The use of an integrated gas-gas ejector system instead of a compressor is proposed and studied technically and economically in this paper. Thus, the flare gas recovery process modeling, including the gas sweetening unit, is performed for both compressor and ejector systems. Different arrangements of the integrated ejector system in the form of multi-stage ejectors (series) in parallel branches are also investigated. To find the geometry of ejectors for simulation of integrated ejector system in Aspen HYSYS, as well as the prediction of the ejector performance under different pressures and mass flow rates of inlet gas, a computer code was developed in MATLAB software. Results of the economic analysis demonstrated the compression method with a parallel three-branch arrangement (containing a three-stage ejector in each branch) were the most appropriate solution in the flare gas recovery of a typical oil refinery plant, with an investment cost of 4.84 $M and accepted payback period of 2 years and the recovery of approximately 90% flare gas volume during normal operation. •A gas-gas ejector system for the compression process in flare gas recovery is proposed.•A comparative study of the compressor and ejector compression process is performed.•Technically and economic analyses for both systems are performed.•A parallel three-branch arrangement is the most appropriate solution.•An investment cost of 4.84 $M and a payback period of 2 years are obtained for the optimum solution.