Optimisation and exergy analysis of an organic Rankine cycle (ORC) used as a bottoming cycle in a cogeneration system producing steam and power

Abstract

In this study, the advantages of the ORC were used to improve overall performance of a simple gas turbine (GT) located in a wood production facility. In addition to ORC, a steam boiler (SB) is also coupled with the GT to improve overall performance and to produce needed steam. During study, benzene, cyclohexane, hexane, R11, R123, R600, R601 and toluene were used as working fluid. During parametric optimisation of ORC, entering pressure of turbine rose from 10 bar to 35 bar, while entering pressure of turbine rose from saturated steam temperature to fluid’s maximal temperature. The best performing working fluid was found as benzene for ORC turbine inlet pressure between 10 bar and 25 bar. Above 25 bar ORC-turbine inlet pressure, R123 showed the highest performance. The maximum ORC net power production, thermal and exergy efficiencies were found as 1076.76 kW, 21.14% and 47.00% for ORC used R123 at 230 °C and 35 bar. However, although ORC with R123 has the highest net power production, the payback periods of ORC with R11 is minimum (2.5 years). At this ORC turbine inlet parameters, performance parameters of the cogeneration system were found the highest as thermal efficiency 69.19% and exergy efficiency 75.51%.