Modeling of Solid Oxide Heat Exchanger Integrated Stacks and Simulation at High Fuel Utilization

Abstract

This work provides an evaluation of the behavior of a planar circular solid oxide fuel cell stack with an integrated air preheater fed with hydrogen at the anode and air at the cathode under conditions of high fuel utilization. This evaluation is based on a simulation model, whose hypotheses and equations are presented and discussed, together with model validation. Indeed, it has been shown that the simulation results compare favorably with the experimental data of temperature distribution and I-V characteristics at low fuel utilization. Having ascertained the reliability of the model, the simulation results obtained at high fuel utilization are presented and discussed. I-V curves show an almost linear behavior up to fuel utilization factors above 80%. For higher utilizations, the slopes of the curves increase due to an increase of anodic polarization resistance, due to both activation effects and diffusion limitations in the electrode regions underneath the ribs of the gas distributor; on the contrary, diffusion limitations in the regions underneath the gas channels have been demonstrated to be negligible. The results for temperature distributions at high fuel utilization are discussed as well, indicating that the benefit of solid oxide fuel cells with an integrated air preheater, i.e., an almost even distribution of solid temperature on the cell plane, is still valid at high hydrogen utilization factors.

Simulation of a Tubular Solid Oxide Fuel Cell Stack Operating on Biomass Syngas Using Aspen Plus

“…This loss is low unless the current density is high and the fuel and air concentrations are low, caused by high utilizations. Costamagna and Honegger 40 have shown that at high fuel utilization anodic polarization increases due to both activation effects and diffusion limitations. Under these conditions, the limiting current may be reached reducing the fuel cell voltage to very low levels.…”

Electrochemical Impedance Spectroscopy Study of the Mass Transfer in an Anode-Supported Microtubular Solid Oxide Fuel Cell

“…To evaluate the impedance variation of each part of the cell under operation, gas feeding conditions for the anode and cathode were varied. In addition, very few experimental studies on current distributions in a cell that lead to temperature distributions have been reported to date, although a number of computational analyses have been reported (Campanari & Iora, 2004;Costamagna & Honegger, 1998;Kanamura & Takehara, 1993;Nishino et al, 2006;Suzuki et al, 2008). Thus the current distributions are estimated by using the overpotentials evaluated with EIS.…”

Integrated Planar Solid Oxide Fuel Cell: Steady-State Model of a Bundle and Validation through Single Tube Experimental Data

“…Concerning activation losses, they are expressed through the Butler-Volmer equation, which embeds, as an electrochemical parameter, the exchange current density i o . The complete mathematical formulation can be found in [18], and here, we wish to recall only the equation adopted for the anodic exchange current density, which is expressed as a function of the Arrhenius law and of the composition of the reacting gases [18,28]:…”

“…Several different expressions have been proposed in the literature for i o,a [28]; in particular, with some correlations, i o,a decreases when decreasing p H2O , while others display the opposite behaviour. Here, an expression with i o,a directly proportional to p H2O is chosen (Equation (4)), where the anodic exchange current density is small when either the H 2 partial pressure or the H 2 O partial pressure is low.…”

“…The main geometrical data of the simulated bundle are reported in Table 1 and include the dimensions of single cells and tubes of the simulated bundle. As far as the physical parameters of the model are concerned, they have been chosen on the basis of previously-published work [18,28] or literature values [31]. In particular, the data regarding the electrochemical kinetics and the electrical conductivities of the material are not reported here, as they are the same as used in a previous work on the electrochemical kinetics of IP-SOFCs [18], where they were also validated against experimental data.…”