Characterizing the Performance of kW-Scale Multi-Stack Solid Oxide Fuel Cell Modules through Modeling
Authors: Floerchinger Gus , Cadigan Chris , Sullivan Neal P. , Braun Rob J 
Published: September 2023

Commercial-scale SOFC systems are comprised of power modules that contain multiple SOFC stacks. In the last decade, there has been much work on individual SOFC stack development and SOFC systems at the commercial scale (100-1000 kWe). Development of these commercial systems often utilizes models of a single representative SOFC stack to simulate the system’s prime mover. In practice, however, these representative single-stack SOFC models fail to consider the effects that arise due to the reality of multi-stack power modules used to construct commercial scale systems. Effects such as flow maldistribution, inter-stack heat transfer, and area-specific resistance (ASR) variation between stack units within a single module will create deviations in performance from a single stack-based system simulation. In this presentation, we consider these thermofluidic effects and the associated performance deviations of a novel 30kWe SOFC multi-stack module using models in the gPROMS ModelBuilder environment and experimental test data. The model-predicted thermal and electrochemical performance of the multi-stack module is established from calibration and validation efforts that utilize full-scale test data from a unique pressurized test facility at Mines.

In this presentation, we consider the effect of reactant gas flow maldistribution on stack and module performance characteristics. A model for fluid flow in branching manifolds is presented. The parameters in the fluid flow model are calibrated from high-fidelity computational fluid dynamic simulation results for both inlet and outlet reactant gas manifolds. Anode and cathode inlet gases affect the fuel utilization, operating voltage, and temperature for an individual stack. Deviations in these operating parameters among stacks are investigated for a range of flow maldistributions (±10% of stack design flow) to quantify their effect on performance. Additionally, we simulate module performance over the expected load operating envelope for given supply fuel and air manifold geometries. Simulated performance deviations are presented and discussed over the module’s envelope to quantify changes in module performance that arise from changes in maldistribution at various flowrates. The manifold under study in this case shows a maximum anode gas fluid maldistribution of 1.5% at the design flowrate.

Stack performance characteristics such as voltage, ASR, power output, and degree of internal reforming, are highly dependent on operating temperature. Individual stack and module heat loss can affect performance. An inter-stack heat transfer model is presented and calibrated using single-stack experimental test results. The model is extended to multiple stack module configurations described above and is then exercised to evaluate the effect of insulation materials and inter-stack heat transfer on multi-stack module performance. This presentation will discuss modeling results and characterization of insulation properties. Simulation results indicate that deviations of up to 10°C in stack operating temperature can be reached which strongly affects the effective operating ASR of a given stack. The presentation concludes with a discussion of performance impacts due to combined thermofluidic deviations can have on module operation vs a single-stack modeling framework.