Effect of sweeping gas flow rates on temperature-controlled multistage condensation of pyrolysis vapors in an auger intermediate pyrolysis system

•Sweeping gas did not change bio-oil yield but increased yield of organic compounds.•Sweeping gas fractionated bio-oils through temperature-controlled condensers.•Higher flow rates reduced water content in higher temperature-controlled condensers.•Large amount of organic compounds was collected from high temperature-condensers.

The vapors produced from pine wood using an intermediate auger pyrolysis process under various sweeping gas flow rates were condensed by three temperature-controlled condensers and analyzed. Increasing sweeping gas flow rate from 20 to 40 L/min did not change the yield of the pyrolysis products, however, noticeable changes were found in the bio-oil composition, such as a decrease in water content and an increase of amount of organic compounds. Increasing sweeping gas flow rate influenced the bio-oil fractionation in each temperature-controlled condenser with a reduction in bio-oil yield in the first condenser controlled between 85 and 90 °C and outgoing vapor temperature of 121 °C. There were no changes in the second condenser maintained at 45–50 °C and outgoing vapor temperature of 107 °C, and an increase in the third condenser regulated at 10–15 °C and outgoing vapor temperature of 25 °C. Higher sweeping gas flow rates also resulted in changing the bio-oil composition in the first and second condensers including a reduction in water content and an increase in viscosity and density, suggesting that refining this fraction as an intermediate source would be a more efficiency way to produce fuels and chemicals than treating the whole bio-oil. The bio-oil from the third condenser contained elevated water content, acidity and light oxygenated compounds with increasing sweeping gas flow rate, suggesting that this fraction would be more suitable as an energy source for hydrogen production via microbial electrolysis processes. In summary, the sweeping gas flow rate used for pyrolysis with an intermediate auger reactor is an important factor to change bio-oil properties in temperature-controlled multistage condensation processes.