Analytical study for the comparison between hygroscopic and Rankine cycle. An exergy approach

The Hygroscopic Cycle Technology (HCT) is a proprietary technology that allows producing energy with better performance and more sustainable than traditional Rankine Cycle (RC). The aim of this study is to implement analytical models for comparing the performance of HCT and RC operating at industrial scale conditions. The study focuses on energy and exergy analysis in order to compare the cycles and determine the equipment with the higher irreversibilities for providing a base to improve them. A base case of each cycle has been defined and compared. Also, a sensitivity analysis of the main parameters of the cycles has been done. Grassman diagrams of the base cases have been studied to quantify the exergy distribution and destruction. According to the results obtained exergy efficiency of the HCT can be 2.52% greater than that of the regenerative RC for high cooling temperatures. For cooling, dry coolers can be used with ambient temperatures of up to 46 degrees C for HCT while for the RC it is limited to 38 degrees C. The variables with the greatest influence on the exergy efficiency are the condensing pressure and the boiler air-fuel ratio. In the HCT, due to the excess of air required for complete combustion, the exergy destruction rate in the boiler can be increased by 1% and the exergy efficiency of the HCT can be 1.3% lower than the value for the stoichiometric air-fuel ratio. For a 10 MW power plant the exergy of the fuel in absolute terms was lower for the HCT (37.08 MW) than for the RC (37.92 MW).