Technical evaluation and optimization of a flare gas recovery system for improving energy efficiency and reducing emissions

Gas flaring is a significant cause of air contamination and a source of energy losses in the oil and gas industry. A liquid ring compressor is a cost-effective and appropriate technology, which can be used to recover flare gas from various sources. In this paper, a novel flare gas recovery process based on liquid ring compressors is proposed, in which flare gases are compressed and treated simultaneously using methyl diethanolamine. This process is simulated here through some custom models in Aspen HYSYS and MATLAB software, and the effects of operating and design parameters on the performance of the proposed flare gas recovery system are examined. Results demonstrate that the H2S absorption efficiency can be improved by reducing amine temperature or raising the flow rate of the recycling amine. However, the energy consumption of the process increases in these conditions. It is also demonstrated that there is an optimum value for the lean amine solvent concentration to minimize the H2S concentration of the outlet gas. The process analysis shows that by integrating the proposed flare gas recovery system with a refinery plant generating 0.5 MMSCFD of flare gas, it is possible to recover 87% of the available heating value in the flare gas. Also, the environmental aspects of the plant is considerably improved by preventing the release of 28 mtCO2 equivalent per day to the atmosphere. Due to the overlapping effects of system operating parameters, a multi-objective optimization is conducted to optimize the process, and the Pareto solutions set consists of the best possible trade-offs between process energy consumption, H2S concentration of outlet gas, and lean amine solvent consumption are generated.