Analyses of Solid Oxide Fuel Cell and Gas Turbine Hybrid Power Plants Accounting for Long-term Degradation Effects

Abstract

Electricity generation from fossil fuels such as coal and natural gas (NG) contributes more than half of the global electricity production and is anticipated to still account for a major share in the medium term till 2050. To reduce the environmental impacts such as global warming potential of global electricity generation, it is vital to improve the current conventional power production technology that utilizes fossil fuels. Solid oxide fuel cells (SOFC) are a promising alternative power generation technology to conventional fossil fuel-based power production due to their higher efficiency and lower greenhouse gas emissions. However, the large-scale commercialization of SOFCs is limited due to their fast degradation under constant power operation which results in a short lifetime. In a SOFC and gas turbine (GT) hybrid design, the SOFC can be operated in constant voltage mode with decreasing power output over time such that the stack lifetime can be largely extended due to much slower degradation. This constant voltage mode of SOFC operation results in increasing heating value of the exhaust stream over time which can be utilized by the GT for power production, allowing this hybrid plant to keep an overall baseload power production. This thesis focuses on the designs, eco-technoeconomic analyses, and life cycle analyses of coal-based and NG-based SOFC/GT hybrid plants (with and without a steam cycle) accounting for long-term degradation effects, in comparison with standalone SOFC plants (with and without a steam cycle). A pseudo-steady-state model simulation approach was employed to integrate real-time dynamic 1D SOFC models with steady-state balance-of-plant models, in order to capture dynamic behaviours caused by degradation. Model simulations, eco-technoeconomic analyses, and life cycle analyses were conducted over a 30-year plant lifetime using Matlab Simulink, Aspen Plus, Python, and SimaPro. The results reveal that the main factors affecting the eco-technoeconomic and life cycle environmental results are the plant efficiency and total SOFC manufacturing over the plant’s lifetime, which are both strongly connected to SOFC long-term degradation effects. Compared to a standalone SOFC plant with a steam cycle, the design of SOFC/GT hybrid plant with a steam cycle sacrifices the plant efficiency (4.1 percentage point in coal-based cases and 12 percentage point in NG-based cases), but greatly increase the SOFC stack lifetime (around 16 times longer) which results in much lower cost (reduces levelized cost of electricity by 68% in coal-based cases and 82% in NG-based cases) and lower life cycle environmental impacts (reduces around 6% ReCiPe endpoint).