Upgrading the Marib Gas Turbine Power Plant in Yemen with a Brayton–Organic Rankine Cycle for Higher Efficiency and Lower Emissions

The Marib gas turbine power plant in Yemen currently operates on a simple Brayton cycle, releasing high-temperature exhaust gases without recovery, resulting in substantial energy losses and elevated CO₂ emissions. This study proposes an integrated Brayton–Organic Rankine Cycle (BC–ORC) configured to capture and utilize this waste heat, improving performance and environmental sustainability. In the proposed system, the Brayton cycle serves as the topping cycle, while an organic Rankine cycle using toluene as the working fluid operates as the bottoming cycle, driven by the gas turbine exhaust gases. A steady-state thermodynamic model was developed using Engineering Equation Solver (EES) to evaluate the integrated system. Energy and exergy analyses were conducted for each component and the overall cycle. Parametric studies examined the effects of Brayton cycle pressure ratio (Pr), ORC turbine inlet temperature, and ORC turbine inlet pressure on net power output, efficiencies, and specific CO₂ emissions. Results show that integrating the ORC increases total net power output from 138.4 MW (BC only) to 195.9 MW, a 41.5% improvement. Thermal efficiency rises from 30.87% to 43.71%, and exergy efficiency from 29.81% to 42.21%, specific CO₂ emissions decrease by approximately 29%, from 639.1 to 451.3 kg/MWh. Parametric analysis indicates that moderate Pr values (6–10) provide the best balance between high net output and efficiency, higher ORC turbine inlet temperature enhances ORC contribution and slightly reduces emissions, while ORC turbine inlet pressure variation within 2000–3000 kPa has a negligible impact on performance. The findings demonstrate that implementing an integrated Brayton–ORC waste heat recovery system in the Marib power plant is a practical and cost-effective approach for enhancing Yemen’s electricity generation efficiency and reducing its environmental footprint. Keywords: Brayton Cycle, Organic Rankine Cycle, Waste Heat Recovery, CO₂ Emissions, Yemen, Marib Power Plant