Computational Investigation of Liquid Holdup and Wetting Efficiency Inside Trickle Bed Reactors with Different Catalyst Particle Shapes

Abstract

Liquid holdup and wetting efficiency are essential parameters for design of trickle bed reactors. Both parameters play an important role in reactor performance including pressure drop, conversion, and heat transfer. Empirical formulas are usually employed to calculate liquid holdup and wetting efficiency. However, factors such as particle shape and the wetting ability of liquid on the particle surface are not described clearly in traditional formulas. In this paper, actual random packing was built by DEM and CFD simulations were performed to investigate the factors affecting liquid holdup and wetting efficiency in trickle bed reactors, including particle shape, surface tension, contact angle, liquid viscosity, liquid density, liquid, and gas superficial velocity. Detailed fluid flow and liquid-solid interaction were described by VOF model. Four different particle shapes were investigated. It showed the particle shape has great effect and the 4-hole cylinder packing gained both highest liquid holdup and wetting efficiency. The overall simulations gave a detailed description of phase interactions and fluid flow in the voids between catalyst particles and these results could give further guidance for the design and operation of trickle bed reactors.

Effect of Particle Aspect Ratio and Shape on the Particle-Scale Dynamics of Gas–Liquid Flow through Packed Beds

“…The near-wall region, equivalent to 4 d p from the box wall in all directions, of the beds was trimmed to exclude the wall-influenced orientations of the cylindrical particles (see Figure b). In order to resolve the difficulties in the spatial discretization of the fluid domain, the particles were shrunk by 2% both in radial and axial directions to avoid sharp intersection angles formed in the region of particle–particle contacts (following the approch by Lopes and Quinta-ferreira, ,, Deng et al, and Qi et al). One such bed with h = 5 is shown in Figure b.…”

“…However, these studies consider oversimplified particle-resolved domains either in 2D (wherein the beds were represented by an array of circles) or in manually created 3D beds (wherein particles were arranged in a square or triangular pitch) with large interparticle distance. ,,,, Most of these 3D VOF simulations are performed with spherical particles due to challenges in the spatial discretization of complex void-topology of beds with shaped particles. Limited recent studies report the effect of particle shape on the aforementioned steady-state macroscopic parameters in small sections of realistic particle-resolved beds created using the discrete element method (DEM) and rigid body dynamic simulations (RBDS). ,, However, these studies do not report the particle-scale dynamics of liquid distribution as a function of particle shape which is crucial for improving the overall performance of packed beds. Further, these investigations were performed with a constant particle aspect ratio in the range of 1–2.67.…”

“…Limited recent studies report the effect of particle shape on the aforementioned steadystate macroscopic parameters in small sections of realistic particle-resolved beds created using the discrete element method (DEM) and rigid body dynamic simulations (RBDS). 16,18,19 However, these studies do not report the particle-scale dynamics of liquid distribution as a function of particle shape which is crucial for improving the overall performance of packed beds. Further, these investigations were performed with a constant particle aspect ratio in the range of 1−2.67.…”

Forces governing the dynamics of liquid spreading in packed beds

“…Lopes & Quinta-Ferreira 2009, 2010, wettability (e.g. Du et al 2015Du et al , 2017 and particle shape (Kang et al 2019;Deng et al 2020) on the steady-state liquid distribution. However, the effect of the aforementioned parameters on the contribution of different forces at different temporal stages of liquid spreading and their relationship with void-scale flow behaviour has not been explored.…”

Combined Two-Model CFD Simulation of Trickle Bed Reactors with Head-Sump Extension: Case Study on Hydrodynamics and Biological Methanation

“…To date, numerous studies have focused on modeling of trickle bed reactors. Applying computational fluid dynamics (CFD), particle-resolved models − and pseudocontinuous models − tackle the particle and reactor scale, respectively. Pseudocontinuous models are predominantly based on the Ergun equation and the Eulerian–Eulerian method.…”