An explicit dynamic model for direct reforming carbonate fuel cell stack

A nonlinear, lumped-parameter mathematical model of direct reforming carbon ate fuel cell stack is extended by deriving an explicit set of differential equations for computer simulation. The equilibrium assumption used for the water-gas shift reaction results in an implicit equation set, previously s olved using numerical techniques. An explicit equation set is derived by el iminating a key variable associated with the water-gas shift reaction. In a ddition, results are improved by incorporating a fuel cell performance mode l to account for reversible cell potential and polarization losses. This re quires determination of intermediate gas composition at the cell anode inle t, resulting in additional computations. All results and physical data used are specific to a lumped 16-stack 2-MW system design, a precursor to a dem onstration plant that had been operated at the City of Santa Clara, CA. Ste ady state results are validated for several load points over the upper regi on of operation and transient results are provided for sudden load change.