Convective enhancement of microalgae slurry in continuous tubular reactors for biocrude production during hydrothermal liquefaction

Continuous hydrothermal liquefaction (HTL) reactor is promising in the large-scale production of biocrude from microalgae biomass. To optimize the temperature distribution and biocrude yield of microalgae slurry, the convection of microalgae slurry is enhanced through adjusting flow rate (1 – 24 mL/min) and inserting twist tapes (twist ratio: 3 – 10) in the flow channel, respectively. A computational fluid dynamics (CFD) model integrated HTL kinetics of microalgae biomass is proposed to simulate the contour plots of temperature and biocrude yields at the heating temperature from 523 to 623 K. Comparing to increasing flow rate, the swirl flow induced by the twist tape can significantly increase the convective heat transfer coefficient from 669 to 1707 W·m−2·K−1, while the conversion rate of biocrude from 0.188 to 0.298 g·L-1·s−1 at 8 mL/min and 623 K. As the enhancement factor of convective heat transfer coefficient h /h0 is higher than 2, the biocrude yield YBC of microalgae slurry appears obvious increasing by the enhancing convective heat transfer. This investigation provides the insights to optimize the flow channel of tubular reactors for the optimization of HTL conversion of microalgae biomass.