Supercritical Carbon Dioxide Power Cycles for Waste Heat Recovery of Gas Turbine

Abstract

For developing a sustainable power system, the key is to maximize the use of available resources with minimal impact on the environment. One technique of achieving this is waste heat recovery. In this study, the combined cycles are proposed based on the concept of gas turbine waste heat recovery which comprise of two parts: topping gas turbine and bottoming sCO2 Brayton power cycles. The combined cycle configurations selected for thermodynamic analysis are the combined gas turbine simple regenerative sCO2 cycle (CGTSRC), the combined gas turbine recompression sCO2 cycle (CGTREC) and the combined gas turbine preheating sCO2 cycle (CGTPHC). The energy and exergy analysis are conducted to investigate the power production, exhaust heat recovery, energetic and exergetic efficiencies of selected cycles for variation in mass flow rate, mass split percentage and compression ratio. Using Engineering Equation Solver (EES) software, the thermodynamic calculations and optimization are carried out to find the design point which provide maximum exergetic efficiency. In addition to determination of design point, the comparison of selected combined cycles is performed with simple gas turbine cycle (SGT) and conventional air bottoming combined cycle (ABC) to highlight the thermodynamic and environmental significance of sCO2 bottoming power cycles. For comparison, heat recovery, power output of combined and bottoming cycles, mass flow rate, energetic efficiency, exergetic efficiency and environmental impact are considered as the key performance parameters. The results and comparison indicate that optimum cycle configuration is CGTPHC which provide energy efficiency of 46.8%, exergy efficiency of 64.8% and 47.3 MW combined power output. Moreover, the energetic and exergetic performance of combined supercritical CO2 cycles are better than ABC cycle and SGT cycle. The turbomachinery (compressor and turbine) of optimum bottoming sCO2 power cycle are designed which include the determination of accurate geometry and efficiency using preliminary and 1D mean line design methods. A robust design code is developed in MATLABr coupled with REFPROP property library for retrieval ix of sCO2 properties. The compressor design code is validated with experimental results taken from literature. The efficiency of compressor and turbine calculated from the turbomachinery design code are 81.2% and 86.17%, respectively.