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Production and characterization of upgraded biomass fast pyrolysis oil for combustion in a swirl-stabilized burner

University of British Columbia

Biofuels have garnered attention because of their potential to displace conventional petroleum fuels with renewable feedstocks that lower greenhouse gas emissions. Bio-oil (fast pyrolysis oil) is a liquid made from thermal degradation of non-food-crop biomass and has been used as an alternative to heavy fuel oil on industrial scales. However, bio-oil is a complex mixture of biomass-derived compounds with different physical and chemical properties to petroleum fuels which affect the combustion performance. Bio-oil was produced from softwood pellets in a fast pyrolysis apparatus with a multi-stage condenser. Of the three bio-oil fractions collected, the sample from the third vessel had a viscosity of 30mPa-s and an HHV near 20 MJ/kg, thus was deemed appropriate for fuel testing. ZSM-5 was used as a catalyst in the fluidized bed reactor to produce bio-oil with 20wt% less oxygen and 5 MJ/kg higher in HHV. The two bio-oil samples produced, one with ZSM-5 catalyst (CAT) and the other without catalyst (NC), were compared to a commercially available bio-oil (COMM) and diesel. CAT had the highest HHV and lowest oxygen content but was the least volatile of the bio-oil samples, whereas COMM had the lowest energy density and highest volatility. The fuel samples were tested in a swirl-stabilized combustor to measure CO, NOx, particulate matter, and unburned hydrocarbon in the exhaust. COMM produced CO and NOx emissions near 95 and 97 ppm, respectively. The exhaust from NC had CO and NOx concentrations of approximately 185 and 50 ppm, respectively. Finally, the CAT flame was unstable, producing CO emissions around 300 ppm. Volatility appeared to have an outsize impact on emissions compared to properties like HHV or viscosity. Bio-oil/ethanol blends increased the volatile composition while having modest impacts on HHV or viscosity and produced CO and NOx concentrations of 18 and 105 ppm, respectively. Two-colour pyrometry measured flame temperature and soot concentration during combustion. The soot concentration in the flame was 56 times greater for diesel than bio-oil. In contrast, the average flame temperature for diesel and bio-oil were 1700 and 1900 K, respectively, although the bio-oil data may be uncertain due to flame heterogeneity.

Text

2020-10-22

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/76340

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/