In this paper we design an observer for online estimation of species concentrations in a steam reformer based Solid Oxide Fuel Cell (SOFC) system with anode recirculation and with methane as fuel. Since in SOFCs steam reforming occurs both in the reformer and in the fuel cell, a large number of concentration sensors are necessary for accurate control of critical performance variables such as utilization and steam-to-carbon-ratio. The purpose of the observer is to reduce the number of sensors required for control. In contrast to existing observers which are either designed for chemical reactors or for fuel cells exclusively, our design considers the coupled dynamics of the reformer and the fuel cell. We design an adaptive observer where the rates of reforming reactions are treated as slowly varying unknown parameters. Using a few concentration sensors we show that all other species concentrations, molar flow rates, and reaction rates in the fuel path can be dynamically estimated. Simulation results are provided in support of the proposed design.

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