Simulation of a Novel Tubular Microalgae Photobioreactor with Aerated Tangent Inner Tubes: Improvements in Mixing Performance and Flashing-Light Effects.

Xuyang Cui,Yuanzheng Feng,Junhong Yang,Wenwen Zhang

doi:10.1155/2020/8815263

Abstract

At present, large-scale and high-efficiency microalgal cultivation is the key to realizing the technology for carbon capture and storage (CCS) and bioresource recovery. Meanwhile, tubular photobioreactors (PBRs) have great potential for microalgal cultivation due to their high productivity. To improve the mixing performance and flashing-light effect, a novel tube PBR with the inner tube tangential to the outer tube was developed, whose radial aeration pores are situated along the length of the inner tube. The direction of aeration, aeration rate, light/dark cycle period (L/D), light-time ratio, average turbulent kinetic energy (TKE), and degree of synergy between the velocity and direction of the light field in the PBR were optimized by a computational fluid dynamics (CFD) simulation and field synergy theory. The results show that a downwards aeration direction of 30° and an aeration rate of 0.7 vvm are the most conducive to reducing the dead zone and improving the light/dark cycle frequency. Compared to the concentric double-tube PBR, the light/dark cycle frequency and light time of the tangent double-tube PBR increased by 78.2% and 36.2% to 1.8 Hz and 47.8%, respectively, and the TKE was enhanced by 48.1% from 54 to 80 cm2·s−2. Meanwhile, field synergy theory can be extended and applied to the design of tubular microalgae PBRs, and the average synergy of the light and velocity gradients across the cross-section increased by 38% to 0.69. The tangential inner tube aeration structure generated symmetrical vertical vortices between the light and dark areas in the PBR, which significantly improved the mixing performance and flashing-light effect. This novel design can provide a more suitable microenvironment for microalgal cultivation and is promising for bioresource recovery applications and improving the yield of microalgae.

Highlights

Microalgae are considered to be one of the most promising technologies for carbon capture and storage (CCS) and have been identified as a superior feedstock for biodiesel production [1, 2]
We propose a novel tangent double tube with radial aeration pores along the length of the inner tube, in which the inner tube is tangential to the outer tube in order to strengthen the synergy between the light and velocity gradients
The simulation results show that, compared to the concentric double-tube PBR, the light/dark cycle frequency and light time of the tangent double-tube PBR increased by 78.2% and 36.2% to 1.8 Hz and 47.8%, respectively, and the turbulent kinetic energy (TKE) was enhanced by 48.1%, from 54 to 80 cm2·s−2

Summary

Introduction

Microalgae are considered to be one of the most promising technologies for carbon capture and storage (CCS) and have been identified as a superior feedstock for biodiesel production [1, 2]. The low biomass productivity of microalgal cultivation systems is a bottleneck in commercial production, which leads to the high cost of microalgae biofuels [3]. Before this situation can be reversed, a significant improvement in volumetric productivity is required [4]. Focusing on high efficiency and large-scale microalgal cultivation, tubular photobioreactors (PBRs) are considered one of the most suitable culture systems. Their weak mass transfer, wall growth, photoinhibition, and photolimitations have limited their development [7]. The development of computational fluid dynamics (CFD) has facilitated the study of hydrodynamic performance and the structural design of tubular PBRs [1]

Methods

Results

Conclusion