Optimization and 4E assessment of a modified Rankine cycle utilizing cement plant waste heat for freshwater via reverse osmosis

With recent advances in thermodynamic modeling and optimization, integrating modified Rankine cycles with industrial waste heat sources has become increasingly viable. This study presents a novel small-scale cogeneration system that utilizes waste heat from the clinker cooling section of a cement plant to simultaneously produce electricity and freshwater via reverse osmosis. The system incorporates a modified Rankine cycle enhanced by an ejector for improved energy recovery. A comprehensive 4E analysis – encompassing energy, exergy, economic, and environmental aspects – was carried out. Thermodynamic modeling was based on conservation laws of mass, energy, and momentum, while exergy analysis was conducted using the first and second laws of thermodynamics. Key parameters affecting performance, such as turbine inlet/outlet flow rates and boiler heat input, were optimized using a genetic algorithm developed in Python 3.10. The base case showed energy and exergy efficiencies of 29.13% and 23.08%, respectively. After optimization, these improved to 37.87% (energy) and 31.55% (exergy), alongside an 18.5% cost reduction. The results also showed that the Pressure ratio had the most significant influence on the overall system performance. Sensitivity analysis identified inlet pressure, temperature, and mass flow rate as the most critical variables affecting system performance.