CFD-PBM Approach with Different Inlet Locations for the Gas-Liquid Flow in a Laboratory-Scale Bubble Column with Activated Sludge/Water

Le Wang,Jie Chen,Qiang Pan,Shunsheng Yang

doi:10.3390/computation5030038

Le Wang, Jie Chen + Show 2 more

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https://doi.org/10.3390/computation5030038

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Abstract

A novel computational fluid dynamics-population balance model (CFD-PBM) for the simulation of gas mixing in activated sludge (i.e., an opaque non-Newtonian liquid) in a bubble column is developed and described to solve the problem of measuring the hydrodynamic behavior of opaque non-Newtonian liquid-gas two-phase flow. We study the effects of the inlet position and liquid-phase properties (water/activated sludge) on various characteristics, such as liquid flow field, gas hold-up, liquid dynamic viscosity, and volume-averaged bubble diameter. As the inlet position changed, two symmetric vortices gradually became a single main vortex in the flow field in the bubble column. In the simulations, when water was in the liquid phase, the global gas hold-up was higher than when activated sludge was in the liquid phase in the bubble column, and a flow field that was dynamic with time was observed in the bubble column. Additionally, when activated sludge was used as the liquid phase, no periodic velocity changes were found. When the inlet position was varied, the non-Newtonian liquid phase had different peak values and distributions of (dynamic) liquid viscosity in the bubble column, which were related to the gas hold-up. The high gas hold-up zone corresponded to the low dynamic viscosity zone. Finally, when activated sludge was in the liquid phase, the volume-averaged bubble diameter was much larger than when water was in the liquid phase.

Highlights

The bubble column, which is a reactor that is widely applied in chemical engineering and biochemical industrial processes, can be used in the activated sludge process to treat industrial sewage and municipal wastewater
The models used for numerical simulations of the gas-liquid two-phase flow in bubble columns mainly include the Euler-Euler two-fluid model [5], Euler-Euler two-fluid model coupled with a population balance model (PBM) [6,7,8] and discrete particle model (DPM) [4]
When thewas inlet was located in the middle of the bottom of the column, bubble column, two symmetric were formed in the bubble column, and their centers were located in the lower part of the vortices were formed in the bubble column, and their centers were located in the lower partbubble of the column, as shown

Summary

Introduction

The bubble column, which is a reactor that is widely applied in chemical engineering and biochemical industrial processes, can be used in the activated sludge process to treat industrial sewage and municipal wastewater. Due to the complex nature of two-phase flow in bubble columns, researchers have studied two-phase hydrodynamic behavior experimentally [1,2,3] and using numerical simulations [4]. The fundamental properties of two-phase hydrodynamics, such as the liquid-gas two-phase flow with a non-Newtonian liquid, remain incompletely understood. Because of its cost-effective nature and ability to conveniently predict behavior, such as liquid-phase velocities and gas hold-up values, at different positions in a bubble column, numerical simulation has been extensively applied. The models used for numerical simulations of the gas-liquid two-phase flow in bubble columns mainly include the Euler-Euler two-fluid model [5], Euler-Euler two-fluid model coupled with a population balance model (PBM) [6,7,8] and discrete particle model (DPM) [4].

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