Ludger Blum

- CO 2 sequestration from solid oxide fuel cells: Technical options and costs

Publisher Summary This chapter illustrates the vision of electricity generation from hydrocarbons by a tubular Solid Oxide Fuel Cell (SOFC) without carbon dioxide emission. It presents a conceptual design study involving the combination of a 20 MW SOFC with an electrochemical afterburner (ECAB) to reach the high CO2 concentration of about 90 mol-% in the exhaust gas that is required for efficient CO2 sequestration. A commercial simulation program (PRO/II) is used to quantify the influences of flow-sheet variations on plant efficiency and costs. Particularly the process variants involve different types of ECABs (oxygen pump, mixed oxide conductor, and second SOFC) and different possibilities of turbine integration into the cooling air system of the SOFC/ECAB generator. By comparison with a conventional reference system without CO2 capture CO2 abatement costs are calculated and economic break-even points on a scale of increasing CO2 tax values, expected for the future, are determined.

Recent Results of Stack Development at Forschungszentrum Jülich

Since the mid-nineties several generations of SOFC stacks have been designed and tested incorporating the anode substrate-type cells developed in Julich. The 6th generation, the so-called F-design stacks, with metallic interconnect has been the ‘work horse’ used for testing materials, cells and manufacturing processes in cell and stack development since its introduction in the year 2001. Stacks with up to 60 layers have been operated in recent years, delivering up to 13 kW of electric power. The ferritic parts are made of the commercial steel type CroFer22APU.

Experiences with a CFD Based Two Stage SOFC Stack Modeling Concept and Its Application

The parallel development of kW-range SOFC stacks and their systems at the Forschungszentrum Julich requires distinguished modeling capabilities by validated SOFC models targeting the three-dimensional stack structure itself as well as the entire system. For the full three-dimensional (3D) geometric resolution of a stack, Computational Fluid Dynamics (CFD) models are used whereas a one-dimensional (1D) behavior model based on ordinary differential equations (ODE) covers the system modeling requirements. The CFD model is using advanced data structures to reduce the computing time significantly. However, Computing times in the range of seconds or below required by system modeling are featured only by the 1D model. Both SOFC models are based on the same physical equations for electrochemical conversion and internal methane reforming. The application of these models is shown in practice, focusing on choosing the right model for an application, and how both models were validated against each other and against experiments.

Operation of Thin-Film Electrolyte Metal-Supported Solid Oxide Fuel Cells in Lightweight and Stationary Stacks: Material and Microstructural Aspects

In this study we report on the development and operational data of a metal-supported solid oxide fuel cell with a thin film electrolyte under varying conditions. The metal-ceramic structure was developed for a mobile auxiliary power unit and offers power densities of 1 W/cm2 at 800 °C, as well as robustness under mechanical, thermal and chemical stresses. A dense and thin yttria-doped zirconia layer was applied to a nanoporous nickel/zirconia anode using a scalable adapted gas-flow sputter process, which allowed the homogeneous coating of areas up to 100 cm2. The cell performance is presented for single cells and for stack operation, both in lightweight and stationary stack designs. The results from short-term operation indicate that this cell technology may be a very suitable alternative for mobile applications.

SOFC Worldwide — Technology Development Status and Early Applications

Solid Oxide Fuel Cells (SOFC) of various types and designs have been developed world wide through the last two decades. They offer interesting advantages over other fuel cell types, but also have inherent materials problems that have caused a slower development pace as, for instance, compared to the low temperature Polymer Electrolyte Fuel Cell (PEFC). Due to their high operating temperature in the range of 700 to 1000°C, SOFC can be used with a variety of fuels from hydrogen to hydrocarbons with a minimum of fuel processing, can be coupled with gas turbines for the highest electrical system efficiency known in power generation, deliver process heat in industrial applications or supply on-board electricity for vehicles, to name but some typical applications. This report summarizes the more prominent SOFC development strands and gives an overview of the achievements of the various R&D groups. The analysis includes a benchmark that attempts to compare cell and stack characteristics on a standardized basis.