Development of a CFD model indicating the quantitative relationship among reactor dimension, bed flow unevenness, and performance for VOCs biofilters

ABSTRACT

This study presents a Computational Fluid Dynamics (CFD) based biofiltration model to investigate the airflow distribution and the impact of bed flow unevenness (BFU) on the removal of Volatile Organic Compounds (VOCs) in biofilters. The biofiltration model consists of a gas flow sub-model and a VOCs removal sub-model, which were validated by pilot-scale experiments. The model was used to examine the quantitative relationship among reactor dimensions, including the width to height ratio of the filter bed and empty bed residence time (EBRT), BFU, and performance for VOCs biofilters. Simulation results demonstrate that the flow unevenness index (FUI) of the packing layer changes from 0.06 to 0.48 m²‧s⁻¹ with reactor dimension changes. With an increase in the width to height ratio at a constant EBRT, FUI increases, BFU changes, and flow velocity fluctuation on the cross-section becomes larger, leading to a reduction of about 10% in VOCs removal efficiency. Concentration distribution of VOCs becomes uneven in the horizontal direction. At a constant width to height ratio of the filter bed, an increase in EBRT causes an increase in FUI, leading to a decrease in VOCs removal efficiency. When the width to height ratio is 0.5, velocity fluctuation of filter bed cross-section is small, the concentration of VOCs decreases evenly across the filter bed layer, and FUI is at a low level (0.06–0.11 m²‧s⁻¹).

Implication: In this manuscript, a biofiltration model of VOCs biofilter based on CFD has constructed and validated. And the manuscript gave the quantitative relationship among reactor dimension, bed flow unevenness and performance for VOCs biofilters for the first time. This study can lead to enhanced VOCs removal efficiency and improved overall performance of biofilters in practical engineering applications.

Nomenclature

VOCs	=	Volatile Organic Compounds
CFD	=	Computational fluid dynamics
EBRT	=	Empty bed residence time
BFU	=	Bed flow unevenness
FUI	=	Flow unevenness index, m2∙s−1
Re	=	Reynolds number, a dimensionless parameter
V	=	Characteristic velocity, m∙s−1
ρ	=	Gas density, kg∙m−3
L	=	characteristic length, m
μ	=	Gas viscosity, Pa∙s
u	=	Gas velocity, m∙s−1
P	=	Gas pressure, Pa
g	=	Gravitational acceleration, m∙s−2
F	=	Other forces of fluid elements, N∙m−3
Yi	=	Local mass fraction of component I, a dimensionless parameter
Ji	=	Diffusive flux of i, kg·m−2·s−1
Ri	=	The net spawn rate of component i, kg·m−3·s−1
Si	=	The generation rate of i of other sources, kg·m−3·s−1
rb	=	The VOC biodegradation rate，mg∙m−3∙h−1
k1	=	The first-order reaction rate constant, h−1
Cf, VOC	=	The VOC concentration in the biofilm, kg·m−3
Cg, VOC	=	The VOC concentration in the airflow, kg·m−3
H	=	Henry coefficient, a dimensionless parameter
kg	=	The VOCs reaction rate constant, h−1
Δh	=	The distance between cross sections, m

Acknowledgment

The authors express their gratitude to the National Natural Science Foundation of China (Grant No. 52070113) for their support, as well as to LetPub (www.letpub.com) for their linguistic assistance during the preparation of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data available on request from the authors.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/10962247.2023.2267010.

Additional information

Funding

The work was supported by the National Natural Science Foundation of China [Grant No. 52070113].

Notes on contributors

Ziyu Liu

Ziyu Liu is a Ph.D. student in School of Environment, Tsinghua University.

Dong Dong

Dong Dong is an engineer in International Consulting Office, China Urban Construction Design & Research Institute Co. Ltd, Beijing, P.R. China.

Jinying Xi

Jinying Xi is an associate professor in School of Environment in Tsinghua University.