Numerical prediction on minimum fluidization velocity of a supercritical water fluidized bed reactor: Effect of particle shape

Abstract

Supercritical water fluidized bed reactor (SCWFBR) is a novel gasification reactor for hydrogen production. Compared with traditional hydrogen production technique, the SCW-based gasification has outstanding advantages such as high hydrogen production efficiency, no emission of gaseous pollutants, low water consumption and strong material adaptability. In this paper, based on Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulations, numerical investigation is conducted on the effect of particle aspect ratio (α) on the minimum fluidization velocity (Umf) of a SCWFBR containing cylindrical biomass particles. The coupled CFD-DEM model is firstly validated against previously published experimental data. Then, the Umf for six types of particle shapes are calculated under different working conditions of temperature ranging from 633 to 693 K, pressure ranging from 25 to 27 MPa and α ranging from 1 to 6. Numerical results show that Umf increases with the temperature, but decreases with the pressure. Moreover, Umf is increasing with α. The underlying mechanisms are revealed by investigating the micro-structure of different shaped particles. It is shown that the increase of Umf with α is caused by the weakened fluid-solid interaction force and enhanced inter-particle locking. And the weakened fluid-solid interaction force is mainly due to the increase of the voidage. Finally, a predictive correlation of Umf for the SCWFBR is proposed considering α which demonstrates strong predictive capability for cylindrical particles.