Comparison between single-shaft and mutli-shaft gas fired 800 MWel combined cycle power plant

Multi-shaft and single-shaft configurations allow customization to optimize plant performance, capital investment, construction and maintenance access, operating convenience, and minimum space requirements. Technical comparison between both configurations at partial loads has not been published before. This paper will primarily address a comparison between the two configurations based on thermodynamic simulation results for a gross power capacity of approximately 800 MWel at ISO conditions. This capacity has been chosen based on power market requirements. The analysis approach for each configuration is divided into three components: (1) Performance, (2) Plant configuration, and (3) Environmental impact. The first component dealt with plant gross power output, plant gross efficiency, plant auxiliary power demand, plant generator losses and plant shaft power. The second component dealt with space limitations and extension capability. The third component dealt with specific emissions of NOx and specific emissions of CO2. The thermodynamic simulations have been carried out using Thermoflow® at base load and part load respectively. The results show that the single-shaft configuration is more suitable with regards to performance, NOx specific emissions, CO2 specific emissions, start-up and extension possibilities. The multi-shaft configuration is more suitable with regards to space limitations, steam turbine shaft power, availability, and reliability.