Energy and exergy analyses of a cogeneration unit in an oil refinery: a case study

This case study performed energy and exergy analyses of a cogeneration plant in an oil refinery, generating 97.8 MW of electrical power and 885 t/h of steam at 485 degrees C and 91 bar to identify strategies for real-time decision-making. The exergy efficiencies of the gas turbine and steam turbine were 31.6% and 66.3%, respectively; however, the former should be privileged for load allocation because the condensation route in the steam turbine (3.88 kW/kW) is more irreversible per unit of electric power than the gas turbine (3.16 kW/kW). Exergy efficiency was higher in gas turbine heat-recovery boilers (50.65% and 42.84%) than in conventional boilers (39.51%), and a higher mass of steam should be obtained from the former, given their lower consumption of exergy per unit of mass of steam. Exergy analysis and industrial exergy indicators can well predict marginal efficiency and can be used in decision making.