Exergy analysis of the compression systems and its prime movers for a FPSO unit

The Brazilian production of oil and gas from offshore platforms tends to increase due to the exploration and production of reservoirs in the so-called pre-salt basin. The associated gas is a mixture of hydrocarbons, water and inert gases that requires robust gas treatment and compression systems. Once treated, the stream of hydrocarbon gas and the CO2-rich stream need to be exported by pipelines and/or reinjected into reservoirs. The electric motors of the hydrocarbon gas compressors are the largest energy consumers and are attached to the main power generation system. In turn, the CO2 compressors are driven mechanically by independent gas turbines. This paper aims to assess the performance of the compression systems and its prime movers, considering the off design operation of turbines, compressors, pumps and heat exchangers. Three conditions of well fluid composition and mass flow were modeled, illustrating the maturity of the oil field. The methodology adopted in this assessment was the second law of thermodynamics. Identifying the major sources of irreversibility in each process can offer opportunities for improved energy use, exergy efficiencies and possibilities for waste heat recovery.