Waste Heat Recovery from Gas Turbine Exhaust using Multiple Configurations of Rankine Cycles

Gas turbines, widely used for power generation and industrial applications, release significant thermal energy as exhaust. Recovering this waste heat is essential for enhancing energy efficiency and sustainability. This study evaluates waste heat recovery systems through thermodynamic and exergy analyses to maximize energy recovery and parametric study on evaporating temperature and thermal efficiency. The analysis was conducted using the DWSIM program, which simulated various configurations: the standalone Steam Rankine Cycle (SRC), standalone Organic Rankine Cycle (ORC), combined SRC with Cascade ORC (SRC + C-ORC), and combined SRC with Series ORC (SRC + S-ORC). Exhaust gas, with a high-temperature heat source of 508.99°C, served as the energy input for all configurations. Thermodynamic analysis showed that the SRC + S-ORC configuration achieved the highest net power output of 3,159.67 kW and a cycle thermal efficiency of 19.14%. The S-ORC reached a peak thermal efficiency of 20.125% at an evaporating temperature of 180°C, emphasizing the importance of optimal operating conditions in minimizing irreversibilities. In contrast, the C-ORC's thermal efficiency declined slightly from 8.75% to 8.7% with increasing evaporating temperatures due to a reduced temperature differential and ineffective superheating, which increased heat input without a proportional rise in turbine work output. Exergy analysis revealed that the standalone ORC configuration exhibited the highest cycle exergy efficiency at 50.37%, demonstrating how it’s close to ideal performance. However, the SRC + S-ORC configuration, despite its superior power output, showed significant exergy destruction of 3,340.20 kW. Across all configurations, the evaporator was identified as the component with the highest exergy destruction, making it the most critical area for improvement.