Quantification of the Improvement of Performance of Solid Oxide Fuel Cell Using Chiller-Based Fuel Recirculation

Abstract Solid oxide fuel cells operate at high temperature, typically in the range 650–850 °C, utilizing between 50% and 75% of fuel. The remaining fuel can be either burned in a post-combustor located downstream of the solid oxide fuel cells (SOFC) stack or partially recycled. Several of the SOFC-based power systems include recirculation which is used to supply the steam to the fuel processing unit based on steam reforming. In such a system, the recycled stream makes it possible to eliminate the supply of water from the external source. In the same time, recirculation aids in increasing the overall fuel utilization in the power system. As a result the efficiency increases by 5–12% points. The electrochemical reaction in SOFC generates a substantial amount of water by combining the hydrogen molecules with oxygen extracted from the air entering the cathodic compartments. The recycled stream contains water vapor which is circulated in the recycled loop. In the current analysis, the system for recirculation of the anodic off-gas with complete removal of water was proposed and studied. Performance of a planar cell operated with different rates of recycling was studied using the experimental setup with chiller-based recirculation. Quantification of the improvement of the efficiency was based on the analysis of the increase of voltage of cell operated at a given current density. The experimental study demonstrated that the performance of a stand-alone SOFC can be increased by 18–31%. Additionally, the numerical model was proposed to determine the performance in other operating conditions.

Download Full-text

An evaluation of thick-film silver die-attachment as micro solid oxide fuel cells (μ-SOFCs) interconnection packaging

Additional Conferences (Device Packaging HiTEC HiTEN & CICMT) ◽

10.4071/cicmt-2012-wa11 ◽

2012 ◽

Vol 2012 (CICMT) ◽

pp. 000269-000276

Author(s):

Bo Jiang ◽

Paul Muralt ◽

Thomas Maeder

Keyword(s):

Fuel Cells ◽

Fuel Cell ◽

Solid Oxide Fuel Cells ◽

Thick Film ◽

Operating Conditions ◽

Solid Oxide ◽

Processing Unit ◽

Oxide Fuel ◽

Thermal Mismatch ◽

Die Attach

Micro solid oxide fuel cells (μ-SOFCs) based on MEMS fabrication processes have become an increasingly attractive development for portable power generation applications, due to their high power density and their compatibility with hydrocarbon fuels. For system packaging, the silicon-based fuel cell membrane module needs to be integrated together with other functional elements such as the gas processing unit and the post-combustor. Silicon wafer bonding techniques can be utilized to avoid thermo-mechanical stresses, however, the complete integration in silicon technology is very challenging; ceramic carriers combined with thick film technology are much more practical for total integration, but exist other challenges. As ceramics may have a slight thermal mismatch with silicon, hermetic assembly by glass sealing can be problematic due to stress build-up. Moreover, the high necessary sealing temperatures are somewhat beyond the survival conditions of the current fuel cell modules. Therefore, a metallic thick-film silver die-attach approach is proposed as a potential bonding solution, due to its flexible fabrication requirements, the relatively low process temperatures and the high ductility and chemical stability of silver materials. Such a seal could potentially compensate the thermal mismatch between the silicon and the ceramic substrate as well as provide reasonable hermeticity under μ-SOFC operating conditions. In this work, we preliminarily evaluated several commercial thick-film silver products as interconnection materials in terms of mechanical strength, firing process and metallization approach, using shear testing and microstructure characterization. The failure mode of the die-attach was discussed in details and related to their bonding mechanism. The influence of firing temperature and additional prior metallization on those thick-film bonds were also studied.

Download Full-text

Mathematical model of a plate fin heat exchanger operating under solid oxide fuel cell working conditions

Archives of Thermodynamics ◽

10.2478/aoter-2013-0026 ◽

2013 ◽

Vol 34 (4) ◽

pp. 3-21 ◽

Cited By ~ 5

Author(s):

Jakub Kupecki ◽

Krzysztof Badyda

Keyword(s):

Mathematical Model ◽

Fuel Cells ◽

Heat Exchanger ◽

Power Systems ◽

Solid Oxide Fuel Cells ◽

Heat Exchangers ◽

Operating Conditions ◽

Solid Oxide ◽

System Level ◽

Oxide Fuel

Abstract Heat exchangers of different types find application in power systems based on solid oxide fuel cells (SOFC). Compact plate fin heat exchangers are typically found to perfectly fit systems with power output under 5 kWel. Micro-combined heat and power (micro-CHP) units with solid oxide fuel cells can exhibit high electrical and overall efficiencies, exceeding 85%, respectively. These values can be achieved only when high thermal integration of a system is assured. Selection and sizing of heat exchangers play a crucial role and should be done with caution. Moreover, performance of heat exchangers under variable operating conditions can strongly influence efficiency of the complete system. For that reason, it becomes important to develop high fidelity mathematical models allowing evaluation of heat exchangers under modified operating conditions, in high temperature regimes. Prediction of pressure and temperatures drops at the exit of cold and hot sides are important for system-level studies. Paper presents dedicated mathematical model used for evaluation of a plate fin heat exchanger, operating as a part of micro-CHP unit with solid oxide fuel cells.

Download Full-text

Modelling of Physical, Chemical, and Material Properties of Solid Oxide Fuel Cells

Journal of Chemistry ◽

10.1155/2015/414950 ◽

2015 ◽

Vol 2015 ◽

pp. 1-7 ◽

Cited By ~ 1

Author(s):

Jakub Kupecki

Keyword(s):

Fuel Cells ◽

Power Systems ◽

Solid Oxide Fuel Cells ◽

Material Properties ◽

3D Models ◽

Solid Oxide ◽

System Level ◽

Oxide Fuel ◽

Physical Chemical ◽

Modelling Techniques

This paper provides a review of modelling techniques applicable for system-level studies to account for physical, chemical, and material properties of solid oxide fuel cells. Functionality of 0D to 3D models is discussed and selected examples are given. Author provides information on typical length scales in evaluation of power systems with solid oxide fuel cells. In each section, proper examples of previous studies done in the field of 0D–3D modelling are recalled and discussed.

Download Full-text