Solid Oxide Fuel Cells (SOFCs) are considered fairly flexible in terms of employed fuel since the high operating temperature allows direct internal conversion of hydrocarbons to hydrogen. When fed with coal-derived syngas, significant fluctuations in the fuel composition are expected; hence, the study of the fuel cell response to sudden composition changes is a problem of interest. The fuel manifold is an essential component of a fuel cell system, since every change in the fuel upstream is delayed through the manifold before impacting the fuel cell performance. An accurate model of the manifold is extremely important to determine how the fuel cell can handle fuel composition variations.
In this work, a real-time model of a fuel manifold for a SOFC stack was developed. The model included a fuel valve, a pipe, and a distribution system of the fuel in the channels, and it was incorporated in a previously developed real-time, distributed model of a SOFC. Darcy equation for pressure losses and ideal gas law for the fuel properties were employed, ensuring the required computational time of 30 ms could be met. A parametric analysis was performed varying the geometry and the fuel conditions (composition, mass flow rate, temperature, and pressure) in order to ensure the validity of the assumptions in the operative range of interest.
The residence time in the manifold volume was evaluated with the model, and a composition change was applied to the inlet fuel in order to analyze the time delay. These aspects appeared to be very critical in a view of real-time control of the fuel cell dynamics.