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

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.

本研究提出了一种基于计算流体动力学（Computational Fluid Dynamics, CFD）的生物过滤模型，用于探究生物过滤器内的气流分布特性，以及床层流动不均匀性（Bed Flow Unevenness, BFU）对挥发性有机物（Volatile Organic Compounds, VOCs）去除效果的影响。该生物过滤模型包含气流子模型与VOCs去除子模型，并通过中试实验完成了模型验证。
研究利用该模型分析了生物过滤器反应器尺寸参数——包括填料床宽高比与空床停留时间（Empty Bed Residence Time, EBRT）、BFU与VOCs生物过滤性能之间的定量关联。
仿真结果表明，随着反应器尺寸参数的变化，填料层的流动不均匀性指数（Flow Unevenness Index, FUI）取值区间为0.06至0.48 m²·s⁻¹。在空床停留时间固定的条件下，随着填料床宽高比的提升，FUI升高，BFU发生变化，截面流速波动幅度增大，最终导致VOCs去除效率下降约10%，且VOCs浓度在水平方向上的分布趋于不均匀。
在填料床宽高比固定的条件下，空床停留时间的延长会使FUI升高，进而降低VOCs去除效率。当填料床宽高比为0.5时，填料床截面的流速波动较小，VOCs浓度沿填料床层均匀降低，且FUI处于较低水平（0.06–0.11 m²·s⁻¹）。
研究意义：本研究首次构建并验证了基于CFD的VOCs生物过滤器生物过滤模型，并首次阐明了反应器尺寸、床层流动不均匀性与VOCs生物过滤性能之间的定量关联。本研究可为实际工程应用中提升VOCs去除效率、优化生物过滤器整体性能提供理论支撑。