Combustion and emission characterization of upgraded biomass fast pyrolysis oil in a swirl burner

Fast pyrolysis oil (FPO, also called bio-oil) is a biofuel made from thermal decomposition of renewable or waste biomass. However, the physiochemical properties of FPO have limited its widespread use in combustion applications. In this study, the impacts of FPO upgrading with multi-stage condensation, catalytic pyrolysis with ZSM-5, and ethanol blending were studied through characterization of physiochemical properties and combustion in a swirl burner. A commercially available FPO sample (COMM) and diesel were used to benchmark the upgraded FPO samples. The non-catalytic FPO (NC) sample produced with multi-stage condensation had 9.0 wt% less oxygen and an HHV 2.2 MJ/kg higher than COMM. The FPO produced using ZSM-5 catalyst (CAT) had 19.0 wt% less oxygen, an HHV greater by 7.4 MJ/kg, and lower viscosity than COMM. The CAT sample also had fewer low-molecular-weight compounds, showing a peak mass loss rate 70 degrees C higher than NC. The NC and CAT samples were also blended with 10 vol% ethanol, which had minor effects on the measured physiochemical properties aside from improving volatility. Combustion was evaluated by measuring unburned hydrocarbon, CO, NOx, and particulate matter exhaust concentrations from a swirl burner as well as through flame visualization. Combustion of neat NC was stable, although compared to COMM, CO was -2-times higher and NOx was -2-times lower. In contrast, the CAT flame was unstable, resulting in the highest CO concentrations overall. Blending NC and CAT with 10 vol% ethanol resulted in lower CO concentrations (NC: 88% less, CAT: 96% less) and higher NOx (NC: 2-times, CAT: 1.4-times) compared to neat FPO. Although catalytic upgrading and multi-stage condensation improved HHV, oxygen content, and viscosity, changes to these properties did not improve combustion performance. Ethanol blending emphasized the outsize role of volatility in improving furnace combustion relative to other measured physiochemical properties as reflected by the improved flame stability and exhaust composition.