Non-catalytic conversion of glycerol to syngas at intermediate temperatures: Numerical methods with detailed chemistry

•Non-catalytic glycerol reforming is studied numerically with detailed chemistry.•Various numerical models are presented, verified and validated by experiments.•The optimum model is applied for extensive simulations of glycerol reforming.•Impacts of temperature, mixture stoichiometry and methanol impurity are studied.•Ideal operating conditions for glycerol conversion to quality syngas are proposed.

Glycerol is available in high volumes and at low costs as a byproduct of bio-diesel production. While combustion characteristics are poor, it is appealing to investigate potential reforming processes to recover its hydrogen and carbon in the form of synthesis gas, i.e. a combustible mixture of hydrogen, carbon monoxide, methane and other small hydrocarbon species. This study pursues a non-catalytic approach, where reactions occur in the gas-phase at elevated temperatures favored by chemical kinetics. Detailed glycerol reaction chemistry involves many species and reactions, which makes a careful selection of numerical approaches critical. In this work, Eulerian and Lagrangian viewpoints for numerical calculations of a non-catalytic reforming process at intermediate temperatures are studied. All approaches are validated by propane partial oxidation, where non-catalytic experimental results are available in literature. Testing the numerical approaches for a wide range of operating conditions, it is illustrated that the Lagrangian approach outperforms other models in terms of efficiency. Using a transient zero-D Lagrangian technique, glycerol reforming characteristics are discussed at various wall temperatures and mixture conditions. The impact of fuel stoichiometry is investigated based on the oxygen ratio, which is a metric for mixture stoichiometry that accounts for the amount of oxygen bound in the fuel molecules. Results clearly indicate that wall temperatures higher than 1173 K and oxygen ratios in the range of 0.3-0.45 represent conditions that are favorable for glycerol reforming. It is further shown that excess methanol - a commonly found contaminant in crude glycerol - does not affect the reforming performance. As there is a lack of information on non-catalytic glycerol reforming in literature, qualitative comparisons between non-catalytic (from this work) and catalytic (from literature) glycerol reforming are discussed.