Thermo-economic design, optimization, and evaluation of a novel zeotropic ORC with mixture composition adjustment during operation

Abstract

Abstract Organic Rankine cycle (ORC) is a proposing technology that converting low temperature (usually lower than 200\xa0°C) thermal energy into power. Mostly, the ORC is operated under off-design conditions and the operation performance is deteriorated remarkably from that achieved under rated condition. In the present study, a novel composition-adjustable zeotropic ORC is proposed. A liquid separation condenser-based unit, coupling the heat transfer intensification and mixture composition tuning, is conceptually designed, and integrated into the zeotropic ORC. A regulation strategy for working fluid composition is developed. A thermo-economic evaluation and optimization model and a mixture composition adjustment model are formulated to investigate the superiority of the proposed ORC. A sequential method and genetic algorithm (GA) are applied to conduct the thermodynamic optimization, component design, and thermo-economic optimization of the proposed ORC. A case study is conducted to validate the thermo-economic superiority of the proposed composition adjustable ORC driven by geothermal energy. Results show that the proposed ORC features 0.52% higher annual average net power output, 2.20% higher annual average thermal efficiency, and 21.43% lower average electricity production cost than conventional ORC. The fluid composition-regulating system can achieve the target composition within acceptable time.