Modeling for thermal hydrolysis of microalgae slurry in tubular reactor: microalgae cell migration flow and heat transfer effects

Abstract

Thermal hydrolysis is an efficient technology to enhance biofuel production from microalgae biomass by fermentation, which is promising to realize industrialized application with tubular reactors. However, the physical fields (e.g. velocity, temperature, and cell concentration) in the tubular reactor are non-uniform, leading that the dissolution rate of organic matters cannot be directly predicted by the intrinsic kinetic model of hydrothermal hydrolysis. Herein, a computational fluid dynamics (CFD) model is proposed to simulate the mixture flow, heat transfer, and thermal hydrolysis of microalgae slurry in a tubular reactor. The radial migration of microalgae cells in tube flow can slightly increase the heat transfer coefficient. The variable effective thermal conductivity of microalgae slurries caused by the shear flow reduces Nu at the shear rate below 350 s−1, while keep constant over 350 s−1. The non-uniform distribution of temperature and microalgae cell concentration, influenced by microalgae cell migration flow and heat transfer, had effects on the dissolution rate of carbohydrates and proteins. The maximum dissolution rate of carbohydrates and proteins are appeared at the outlet temperature of 413 and 433 K, respectively. This CFD model provides the underlying insights needed to guide the design and optimization of tubular reactors for thermal hydrolysis of microalgae biomass.