Combined thermodynamic and turbine design analysis of transcritical CO2 cycle for waste heat recovery

The utilization of low temperature waste heat has been under great interest in the recent times. One opportunity to utilize low-temperature waste heat sources is to convert the heat into electricity. For this purpose, organic Rankine cycles have been often considered. Another power system capable for converting low temperature heat to electricity is the transcritical CO2 power cycle. In this study, the utilization of exhaust gas heat at the temperature of 364 oC and the utilization of high temperature water at the temperature of 90 oC are investigated with transcritical CO2 cycles. The investigated waste heat temperature levels and the cycle cooling temperatures were selected based on typical values found in cruise ships using large-scale four stroke gas engines as their main power source. The transcritical CO2 cycle analysis and the design of radial inflow turbine for the cycle were combined, in order to investigate the cycle and turbine efficiency under different design power scales and conditions. The turbine geometry was designed based on the cycle operating conditions and mass flowrate, and the turbine efficiency was evaluated for each design case by using existing loss correlations for radial turbines. The investigated turbine losses are including stator loss, passage loss, tip clearance loss, disk friction loss and exit kinetic loss. Based on the results, heat can be utilized by the CO2 cycle and high efficiency radial turbines can be designed for the investigated transcritical CO2 cycles recovering waste heat. In addition, the use of CO2 as the working fluid would allow to have more compact systems, when compared to the use of ORC systems adopting high molecular weight fluids. The main drawbacks of using transcritical CO2 cycles for waste heat recovery, when compared to the ORC systems, are the high pressure level and high rotational speed of the turbomachinery required in the system.     «

The utilization of low temperature waste heat has been under great interest in the recent times. One opportunity to utilize low-temperature waste heat sources is to convert the heat into electricity. For this purpose, organic Rankine cycles have been often considered. Another power system capable for converting low temperature heat to electricity is the transcritical CO2 power cycle. In this study, the utilization of exhaust gas heat at the temperature of 364 oC and the utilization of high tempe...     »