Energy and Exergy Analysis of Waste Heat Recovery Closed-Cycle Gas Turbine System while Operating with Different Medium

Abstract

In this paper is performed energy and exergy analysis of waste heat recovery closed-cycle gas turbine system. Analyzed system can use waste heat from various main propulsors (gas turbines or internal combustion engines). Basically, the observed system operates by using CO2, what was the baseline for the analysis. It is investigated did the observed system, while retaining the same configuration, can operate with different operating mediums instead of CO2. Other observed operating mediums were Air and Helium. During the change in operating medium, pressures and temperatures in some system operating points cannot remain the same as in the process with CO2, but the intention was to perform only the necessary changes (to ensure proper operation of each system component). Obtained results show that the system, while retaining the same configuration, can operate by using different operating mediums. Energy analysis of the system shows that the whole configuration is composed to operate with CO2, because the whole system energy efficiency is much higher than in operation with Air or Helium. The energy efficiency of the whole system during operation with CO2 is 87.68%, with Air is 58.39% and operation with Helium gives energy efficiency of 49.25%. Exergy analysis of the observed system shows that the system has a good potential to operate with other mediums, because in any observed situation exergy efficiency of the whole system was higher than 50%. In this analysis the highest exergy efficiency of the whole system was obtained during operation with Air (57.76%). In the observed system, low-temperature regenerator and main turbo-compressor are detected as components which are highly influenced by the change of operating medium. Therefore, these two components should be a baseline for further improvements and system optimization.