Flare Gas-to-Power using Supercritical CO2 Power Cycle: Energy and Exergy Analyses

Abstract

Generating electricity from power cycle using supercritical carbon dioxide (sCO2) as a working fluid is a step towards efficiency improvement in power production field. The huge amount of studies on this topic shows promising results of utilization from low to medium grade heat of power generation. Several layouts, arrangements, and thermodynamical features were presented to improve the performance of the power cycle. The main property of such a power cycle is that it utilizes wasted heat to produce electricity. One source of wasted heat is flared gas in oil and gas industry. Flaring process is considered as an extensive economic loss due to its high heating value. This flare gas is burned in industry due to several purposes, mainly safety and process needs. Utilization of flare gas in producing electricity through sCO2 cycle is being proposed in this research, where two cycles were proposed to study the performance of the cycle using flare gas as fuel. First, the Flare-to-Power sCO2 (FTP1- sCO2) cycle utilizing the flare gas mixed with natural gas to heat the working fluid of the cycle which sCO2. The second cycle (FTP2- sCO2) flare gas is utilized in reheating process for the exhaust flow of a primary heating working fluid. The performance of the cycles is evaluated by implementing energetic and exegetic analysis. The results of the study showed that FTP 1 has higher thermal and overall exergy efficiencies compared to FTP 2. Furthermore, the analysis showed that as maximum pressure increases thermal efficiency increase, the same behavior was found also while increasing T_max. The maximum thermal efficiency was found to be 44.87% at T_max= 850 C, P_h= 25 MPa, P_l= 3.3 MPa, T_min= 32 C, and m_flare=0.18 kg/s, for a 50 MW power capacity.