Thermodynamic analysis of employing ejector and organic Rankine cycles for GT-MHR waste heat utilization: A comparative study

The waste heat from intercooler and pre-cooler of the gas turbine-modular helium reactor (GT-MHR) is utilized to drive organic Rankine and ejector refrigeration cycles for performance enhancement, in three different configurations. Meanwhile, a new 2D model is developed for the ejector to predict its performance more accurately. The cycles’ performances are analyzed from the viewpoints of both the first and second laws of thermodynamics. The results of optimization revealed that; one of the configurations is more efficient than the other ones from the viewpoint of first law of thermodynamics. In this configuration, at turbine inlet temperature of 850 oC the first law efficiency is 15.86% higher than the GT-MHR cycle and the fuel energy saving ratio (FESR) could be up to 20.06%. Another configuration is found to be the most effective (among the three) from the exergy utilization perspective. In this layout, the exergy efficiency is around 2.6% higher than that of the GT-MHR. Through parametric study, the effects of some important parameters such as turbine inlet temperature, pinch point temperature difference as well as the compressor pressure ratio, on the systems’ performances are investigated in detail. The results also showed that the compressor pressure ratio under optimized condition is higher for the configuration with the highest first law efficiency. This point can be accounted as an economic drawback for the configuration. Exergy analyses revealed that the compressor or recuperator (depending on the configuration) has the second highest exergy destruction after the reactor.

► Using ejector/organic Rankin cycles, three GT-MHR based combined cycles are proposed.
► Enhancements of 15.86% in first law efficiency and 5.66% in exergy efficiency are achieved.
► Two of the three layouts proved to be efficient from either the first or second law viewpoint.
► A new 2D model is developed for the ejector used in the combined cycles.