Simulation of a Tubular Solid Oxide Fuel Cell Stack Operating on Biomass Syn-gas using Aspen Plus

Abstract

A tubular solid oxide fuel cell (SOFC) stack is modelled and its operation on biomass syn-gas is investigated. The objective of this work is to develop a computer simulation model of a biomass gasification-SOFC (BG-SOFC) system capable of predicting performance under various operating conditions and using diverse fuels. The stack is modelled using Aspen Plus and considers ohmic, activation and concentration losses. It is validated against published data for operation on natural gas. Operating parameters such as fuel and air utilisation factor (Uf and Ua), current density (j) and steam to carbon ratio (STCR) are varied and have significant influence. The model is run on wood and miscanthus syn-gas. The results indicate that there must be a trade-off between voltage, efficiency and power with respect to j and the stack should be operated at low STCR and high Uf. High efficiencies are predicted making these systems very promising.

High Efficient Combined Heat and Power SOFC System for Residential Power Applications: Lifetime-Efficiency-Simulations Using AspenPlusTM

“…The dry composition was analyzed because the model from Zhang et al was intended to simulate overall SOFC based power generation with CO 2 capture (3). With increasing U f the CO 2 -and the N 2 -concentration in the dry gas increase while the H 2 and CO-concentration decrease because of hydrogen consumption based on reactions [4][5][6]. The same system behavior is predicted by the here proposed model as can be seen in Figure 3 and Figure 4 on the right side.…”

“…In the Rgibbs ANODE block the electrochemical reaction of hydrogen [4], the methane steam reforming reaction [5] and the water-gas shift reaction [6] are considered. All of them are specified to reach thermodynamic equilibrium at a given temperature (910 °C within the model).…”

“…⇔ + [16] are implemented with a fuel utilization coefficient that can be varied by using an AspenPlus TM SensivityAnalysis block. In common system analysis hydrogen is assumed to be the only fuel that is electrochemically oxidized and by methane steam reforming (equation [5]) and water gas shift reaction (equation [6]) as implemented by Zhang et al additionally hydrogen is produced that can be oxidized electrochemically (14). Nevertheless keeping Hess's law of constant heat summation in mind at the end CO and CH 4 are oxidized and the intermediate steps are not important for the heat balance.…”

“…All these components except the SOFC can be effectively modeled using commercial available process simulation software tools like AspenPlus TM or HYSYS. Regarding the SOFC commercial process simulation software tools including AspenPlus TM offer no built in model for a SOFC (3), (5). For this reason a common approach published by different authors is to develop a SOFC model using a programming language like Fortran, Visual Basic or C++ and link it to the simulation software as a subroutine (5).…”

“…Calculations of ohmic losses based on equations reported by Song et al (10), activation losses based on Achenbach's semi-empirical correlations (11) and concentration losses based on equations from Chan et al (12) were implemented. TM for modeling the SOFC stack of a biomass gasification-solid oxide fuel cell power plant (5). Also this model was implemented using a Fortran subroutine.…”