Scientific African (Nov 2021)
Thermo-economic analysis of solid oxide fuel cell using human waste as a source of fuel
Abstract
The production of fuel cell technology for commercial purposes is hindered by limited durability and cost. Hence, we focused on the thermo-economic analysis of solid oxide fuel cell (SOFC) that is fuelled with hydrogen produced from human waste to generate 200 kW power. This was achieved through computer simulation using Thermolib 5.4 version (a MATLAB/Simulink's software). Two configurations were adopted for biomass production and are based on gasification and slow pyrolysis. The results obtained revealed that producer gas from gasification and slow pyrolysis have a thermal efficiency of 82.2 % and 34.69 respectively. Lower heating value (LHV) of 113.14 kJ/mole and 466.37 kJ/mole accounted for the variation. Additional energy requirements of 571.50 kW for gasification and 353.04 kW for slow pyrolysis would be needed to achieve the set power output. Exergy analysis further showed that producer gas (slow pyrolysis) had the highest exergy input of 11848.86 kW and corresponding output of 11160.91 kW which was far higher than that of producer gas (gasification) with exergy input as 5,992.17 kW, and exergy output of 5698.44 kW. The difference was due to the presence of ethane which had the highest standard exergy of 1437.2 kJ/mole in addition to the methane content of the gas. The exergy efficiency indicated that auto-thermal reformer (ATR) had an efficiency of 99.71% and 99.6% for gasification and slow pyrolysis respectively. The SOFC from producer gas gasification had an efficiency of 57.59 % with the reformate stream having a mole fraction of 0.3543 and 0.0028 for hydrogen and carbon monoxide respectively whereas producer gas from slow pyrolysis had 72.50% exergy efficiency with mole fractions of 0.5194 of hydrogen and 0.1288 of carbon monoxide in the reformate. The cost analysis indicated that the total annual cost for producer gas from slow pyrolysis configuration was $190,380.70, which is higher than that of producer gas from gasification configuration by 52.66%. Exergy and economic performance favoured the choice of gasification configuration as the preferred route to produce hydrogen gas for Solid Oxide Fuel Cell configuration. We concluded that fuelling of Solid Oxide Fuel Cell with producer gas from human waste is viable, efficient, and highly economical.
