Auto-Thermal Reforming of Biodiesel-Ethanol-Diesel Blends for Solid Oxide Fuel Cell Applications

Solid Oxide Fuel Cell Applications

Jiefeng Lin⁺*, Thomas A. Trabold⁺*[1], Mark R. Walluk*, and Daniel F. Smith*

*Center for Sustainable Mobility, Rochester Institute of Technology

⁺Golisano Institute for Sustainability, Rochester Institute of Technology, 111 Lomb Memorial Drive

Rochester, New York 14623, United States

Solid oxide fuel cell-based auxiliary power units (SOFC-APUs) can be integrated in heavy duty trucks to supply auxiliary electricity for the drivers. Rather than keeping the full diesel engine running at rest, trucks utilizing the SOFC-APU systems achieve relatively high fuel efficiency and low environmental impacts. A hydrogen-rich reformate produced by hydrocarbon catalytic processes is fed into the SOFC-APU system. To avoid carrying an external tank, trucks with SOFC-based APUs would presumably use the same petro-diesel as the main fuel both for diesel engine combustion during traveling and hydrogen production at rest. However, rising concerns over volatile crude oil prices and adverse environmental impacts from using fossil fuels are accelerating the transition of fuel consumption from only diesel to diesel blended with biodiesel (e.g., B10). Thus, it is important to conduct studies on practical diesel blending recipes for truck transportation and evaluating the reformation performance of these diesel blends, which have not yet been widely reported in the open literature.

In this study, ethanol is added to the diesel blends to improve certain fuel properties and these mixtures are referred to as BED blends (biodiesel, ethanol, and diesel). Pertinent fuel mixing rules are extrapolated from previous work and applied to predict the fuel properties of BED blends. The compositions of viable blends are determined, based on ASTM fuel requirements for truck applications (viscosity, cetane number, cloud point, sulfur content, and lower heating value). The objective of this study is to assess the performance of auto-thermal reforming (ATR) of these practical BED blends and contribute to a fundamental understanding of blended hydrocarbons catalytic reforming processes. Ultra-low sulfur diesel (ULSD) ATR is also conducted to establish a baseline for this analysis. Solid carbon deposition during hydrocarbon ATR has been recognized as a primary degradation mode in SOFC-APU systems, but the dynamic carbon formation is difficult to detect and control. To overcome these challenges, this work applies a direct photo-acoustic soot meter to measure the onset of carbon production and quantify its formation in a single-tube reformer under various operating conditions (compositions of BED blends, temperature, steam/carbon ratio, oxygen/carbon ratio, and gas hourly space velocity). This work also reveals the fuel interactions of each component (ethanol, biodiesel, and diesel) during ATR and proposes possible oxygenates to suppress carbon formation. By integrating the carbon measurement with a mass spectrometer to determine the composition of effluent gases from the reformer, the optimum operating environment for BED blend ATR with carbon-free deposition and peak hydrogen yield can be identified. Thermodynamic analysis based on the method of total Gibbs free minimization is implemented as well to evaluate the equilibrium compositions of effluent products. The experimental investigation complimented with theoretical analysis of BED blend ATR enables effectively optimizing the onboard reforming conditions.