Performance Evaluation of Two Medium-Grade Power Generation Systems with CO2 Based Transcritical Rankine Cycle (CTRC)

As CO2 is emerging as an environment friendly working fluid its application in high temperature engine’s waste heat recovery systems is found to be more suitable than other hydrocarbons. This paper presents a performance comparison of two systems based on transcritical Rankine cycle using CO2 as working fluid. A heavy-duty truck is opted for analysis in which coolant is used to preheat CO2 and further the engine exhaust is used to transfer the heat to main heater. The System-1 and System-2 having single and dual loop based transcritical Rankine cycle are analysed. The independent parameters taken for the investigative analysis are turbine inlet temperature (TIT), pressure ratio and effectiveness of heat exchangers. Comparison results show that System-2 is producing 11.8 kW more power than system-1 at 12 MPa pressure ratio and at 489°C TIT. However, under same conditions, system-1 is having 16.88% of thermal efficiency which is higher than system-2 by around 3%. Further, the Engine coolant utilization rates when compared are nearly same in both the systems, the exhaust gas utilization rate came out higher for System-2. In respect of exergy destruction, system-1 shows maximum destruction in regenerator and System-2 in heater-2.

Thermodynamic Analysis of the Air-Cooled Transcritical Rankine Cycle Using CO2/R161 Mixture Based on Natural Draft Dry Cooling Towers

Heat rejection in the hot-arid area is of concern to power cycles, especially for the transcritical Rankine cycle using CO2 as the working fluid in harvesting the low-grade energy. Usually, water is employed as the cooling substance in Rankine cycles. In this paper, the transcritical Rankine cycle with CO2/R161 mixture and dry air cooling systems had been proposed to be used in arid areas with water shortage. A design and rating model for mixture-air cooling process were developed based on small-scale natural draft dry cooling towers. The influence of key parameters on the system’s thermodynamic performance was tested. The results suggested that the thermal efficiency of the proposed system was decreased with the increases in the turbine inlet pressure and the ambient temperature, with the given thermal power as the heat source. Additionally, the cooling performance of natural draft dry cooling tower was found to be affected by the ambient temperature and the turbine exhaust temperature.