Energy and exergy costings of organic Rankine cycle integrated with absorption system

Abstract

This paper presents enhancement efficiency of an organic Rankine cycle (ORC) by using an absorption system, which the 3 ORC-absorption models are considerably investigated. R-245fa is used to generate power of the ORC system. The 2 absorption types of an ammonia-water (NH3-H2O) solution and a water-lithium bromide (H2O-LiBr) solution are chosen as the absorption working fluids. The optimal systematical model is evaluated by using the energy efficiency, exergy efficiency, levelized electricity cost (LEC) and exergy cost (EC) indicators. From the simulation results, the conventional ORC unit showed the average energy and exergy efficiencies as approximately 6.98% and 11.51%, respectively. The suitable absorption type was the H2O-LiBr absorption unit at the higher energy and exergy coefficient of performances compared with that of the NH3-H2O absorption unit at approximately 37.23% and 22.69%, respectively. The model 1 (absorption unit replaced the ORC condenser) could simultaneously generate power and cooling energies at the average energy and exergy efficiencies of 20.61% and 21.54%, respectively, which was similarly with the model 2 (absorption unit combined with the ORC condenser to extract heat) at approximately 15.89% and 17.15%. The model 3 (absorption unit was used to produce cooled water for reducing heat at the ORC condenser) showed the highest energy and exergy efficiencies for only generating power as 7.21% and 12.16%. The suitable integrated model was the ORC-absorption model 1 because of the highest exergy efficiency, which was particularly supported by the lowest economics results of the LEC and EC values of 0.074 USD/kWh and 0.080 USD/kWh, respectively.