Thermodynamic and economic analysis of a revised Graz cycle using pure oxygen and hydrogen fuel

Abstract

In order to improve the energy efficiency of hydrogen storage for power generation, in this work, an improved Graz cycle (R-Graz cycle) was proposed, which can realize more efficient hydrogen to electricity conversion. The modeling and optimization program of the cycle was developed based on MATLAB, and the thermodynamic properties of the working fluid were obtained by REFPROP. The results show that the R-Graz cycle can reach a net efficiency of 70.98% at the design point, which is about 0.5% higher than that of the Graz cycle with the same input parameters, and much higher than that of the modern gas-steam combined cycle. With the same amount of hydrogen input, the R-Graz cycle can produce 0.34% more electricity than the Graz cycle. At the design point, the levelized cost of electricity (LCOE) of the R-Graz cycle is 156.23 $/MWh, which is 0.22% lower than that of the Graz cycle, and the net present value is also higher. Analysis on the influence of key parameters shows that increasing the inlet temperature and pressure of the high-temperature gas turbine and the inlet temperature of the high-pressure steam turbine as well as reducing the condenser pressure are conducive to improving the R-Graz cycle efficiency, among which the influence of the inlet pressure of the high-temperature gas turbine and condenser pressure is particularly significant. This study also presents the impact of these key parameters on the LCOE. This research can effectively increase the conversion efficiency of electricity-hydrogen-electricity mode, and provides a new path for hydrogen utilization.