Thermodynamic analysis of hydrogen production from decomposition of methane for different fuel cells

Abstract

This dissertation studies thermodynamic analysis of hydrogen production for different fuel cells including polymer electrolyte membrane fuel cell (PEMFC) and solid oxide fuel cell (SOFC). Firstly, hydrogen production from decomposition and steam reforming processes fed by different primary fuels; i.e. light hydrocarbons (methane, ethane, and propane) and alcohols (methanol, ethanol, and glycerol) was investigated and comparison of reaction performances between both processes under energy self-sustained operation by splitting feed or product gas stream to combust for heating the system was then carried out. From the study, it was found that the system with splitting feed can give higher hydrogen production, compared to that with splitting product stream, while the latter can provide higher carbon yield but lower CO₂ emission than the former. Although most of the steam reforming processes could gain higher hydrogen production than the decomposition processes, the decomposition ones were more interesting in term of the environmental concern. It was further revealed that the decomposition of light hydrocarbons at high temperature is suitable for PEMFC and SOFC. However, the decomposition of alcohols could be employed with SOFC. Among all processes, methane decomposition was an attractive choice under the environmental concern. In addition, biogas consisting of greenhouse gases i.e. methane and carbon dioxide was tested in the decomposition process. Considering biogas with the CO₂/CH₄ ratio of 40:60, it was necessary to separate carbon dioxide before supplying to the decomposition unit in order to achieve higher reaction performance. Nonetheless, the decomposition process fed by biogas with CO₂ capture under thermally self-sustained condition was not compatible with PEMFC due to the presence of carbon monoxide concentration higher than 10 ppm. For SOFC, the decomposition process fed by biogas with splitting feed was operated at 1275 K to obtain the highest hydrogen and carbon monoxide production, while that with splitting product stream was carried out at 1300 K to gain the highest carbon yield and the lowest CO₂ emission from the burner.