Flare gas-to-power by direct intercooled oxy-combustion supercritical CO2 power cycles

Abstract

With more than 150 billion m3 of gases annually flared around the world, gas flaring is a major source of greenhouse gas emissions that contaminates the environment with more than 400 Mt CO2/year. Therefore, utilizing the flared gases efficiently becomes inescapable and one of the most promising utilization technologies is using Gas-to-Power (GTP). However, most of the available GTP technologies are still using conventional power cycles that have limited efficiencies and produce high-level of emissions. Herein, we use direct oxy-combustion (DOC) supercritical CO2 (sCO2) power cycle, instead, to realize the desired no flaring-no emissions solution. Two innovative flared-intercooled sCO2 power cycles that utilize flare gases and natural gas as fuel are introduced. In the first flared power cycle (FPC1), the flare gases are mixed with the natural gas before being combusted in the DOC. While in the second cycle (FPC2), the flare gases are used to perform a reheating process for the exhaust flow of the primary heater (DOC) after being partially expanded in a high-pressure turbine. Comprehensive energetic, exergetic, exergoeconomic, levelized cost of electricity (LCOE), and multi-objective optimization analyses are conducted for each configuration over practical ranges of operating conditions for six flare gas samples that significantly differ in their composition and specifications. A minimum LCOE of 5.02¢/kWh is achieved by sweet flare gas sample in FPC1 at Tmax of 731 °C, Pmax of 300 bar, Pmin of 40 bar, Tmin of 32 °C, and Ẇnet of 50 MW with energy efficiency of 45.10%. At the optimized conditions, FPC1 and FPC2 show superior energetic and economic performances compared to indirect-combustion power cycles, however, indirect combustion of flare gases may perform better than FPC2 at low capacities and therefore recommended for future work.