Influence of vapor generator design on thermodynamic and techno-economic performances of transcritical organic Rankine cycle

Abstract

Transcritical organic Rankine cycle is of great potential in converting low-grade heat into electricity. Due to sharp variations in fluid thermophysical properties, accurate design of vapor generator in transcritical cycle remains challenging. This work aims to investigate the influence of vapor generator design on both component and system levels. Vapor generator employing supercritical R134a or R1234yf was designed by two models. One is more accurate and the other is more commonly used but may be less accurate. A multi-factor evaluation method was developed to comprehensively analyze the system thermo-economic performance. Results show that two design models led to a difference up to 36% in the size of vapor generator Avapor, but only 1% change in system electricity production cost (EPC). The increase of turbine inlet temperature caused a 10% change in Avapor, while the change with operating pressure was only 1%. In the case of multi-objective optimization, two designs gave 16%∼36% deviation in Avapor and less than 2.5% changes in four performance indicators, but differences in their optimal operating conditions caused 2%∼8% deviations between design condition and the assumed real condition. Quite consistent results were obtained for two working fluids, and a linear correlation was found between uncertainties in Avapor and EPC.