An optimized economic-environmental model for a proposed flare gas recovery system

Iran is the second largest oil and gas producer among the Persian Gulf states, with 13.26 billion m3 gas flaring in 2020, approximately 9.34% of the global gas flaring. To reduce pollutants emissions and energy loss, an accurate feasibility study of flare gas recovery technologies is needed as the first step. Multi-objective optimization of process structure for the development of a comprehensive flare gas recovery system based on process simulation has not attracted much attention in the literature. In this study, a process structure for a flare gas recovery system was proposed using a multi-objective optimization approach to decrease associated gas flaring in southern Iran with a current flaring capacity of 279.7 MMSCFD. In the proposed structure, associated gas goes through sweetening and Natural Gas Liquids (NGL) units. After separating the liquid and vapor products, the NGL outlet gas is allocated to different units, including reinjection of gas to oil wells, gas pipelines, Liquefied Natural Gas, Compressed Natural Gas, Gas to Liquid, Gas to Power, and Desalination units. These units were simulated in Aspen HYSYS, providing an accurate economic and environmental analysis. Afterward, the shares of NGL outlet gas allocated to downstream units were considered optimization variables. The process structure was optimized by maximizing the economic (net present value) and environmental (greenhouse gas emission) objective functions. Results show that in the optimized process structure, 93.4% of the NGL outlet gas is allocated to gas injection and 6.6% to the power generation unit, resulting in a reduction of 6.22 million tons of CO2 emissions per year in this oilfield. The net present value of the flare gas recovery system is approximately 1.504 billion dollars, with a payback period of 1.60 years, suggesting the feasibility of the process.