Hydrogen vs. methane: A comparative study of modern combined cycle power plants

Abstract

This article compared modern hydrogen power plants over a wide range of total compression ratios while maintaining constant system output. In addition, the conventional modern new combined cycle power plant fueled by 100 % methane serves as a reference (comparative) variant representing the currently constructed generating units. Simulations were done using Ebsilon Professional software in the total compression ratio range of 20–50. Previous literature has mainly been based on comparing only the efficiency of GRAZ systems with a combined cycle power plant. The paper discusses a number of performance characteristics. Attention was drawn to the limitations of the currently used COT temperature and the temperature of the compressed medium. For the gas-steam power plant, hydrogen was traditionally burned in air, and in the Graz system, hydrogen was burned in pure oxygen. The structures of the analysed systems were presented and characterised, and their main computational assumptions were standardised in order to compare the systems. A common turbine cooling model was used for both systems. The methodologies for evaluating the performance of energy systems were discussed. Efficiencies, and levels of CO2 emissions per unit were compared for the studied systems. The calculations showed that for the currently used combustion outlet temperature (COT) of 1600 °C, the Graz system achived the best results. The system achieved a COT of 1600 °C for a total compression ratio of 82, which is much higher than that of the main analyses. It operated without CO2 emissions and had an efficiency of 56.21 %, considering the energy consumption of the air separation unit (ASU). For the modern new combined cycle power plant fueled by 100 % methane and for a hydrogen-fueled variant systems, the efficiencies were 53.86 % and 51.39 %, respectively. The modern gas-steam power plant had a high emission rate compared to other systems, reaching 325.17 kgCO2/MWh.