Abstract This paper aims to evaluate how condensational growth may be used to improve the performances of a Venturi scrubber in removing soot particles, which are among the most relevant air pollutants emitted in industrial and power plants exhaust gases. Former studies on this system, called Condensational Growth assisted Venturi scrubbers (CGVS), suggested that the most relevant step to address their efficiency is the assessment of the amount of water that condense on the soot particles, which determines the actual aerosol size distribution entering the Venturi. Unfortunately, a definite physical mathematical model to predict the actual condensational growth of an ensemble of non-spherical particles is not yet available and experimental investigation is better suited to assess this point. This study reports experimental data on the size distribution achieved by exposing model soot particles to a water supersaturated gas for different residence times. The obtained size distributions are used to estimate the efficiency of a Venturi scrubber in removing the water-soot aerosols, allowing a comparison with the removal of parent soot particles. The experiments were carried out at lab scale by using a laminar-flow growth tube, a simple device to perform a controlled condensational growth. The experiments indicated that, even for a hydrophobic material as soot, condensational growth is effective even at supersaturation levels as low as 1.02. Liquid-solid aerosols from nearly 2 to >3 times larger than the parent particles are produced with a supersaturation level lower than 1.15. Finally, the analysis of experimental data indicated that the fraction of particles subjected to condensational growth is relevant. Indeed, calling as ψ the fraction of particles that become larger than the 98% percentile of the original particle size distribution, we found that ψ can be as high as 78%. The analysis of data indicated that an appreciable linear correlation exits among ψ and the 95th percentile of the supersaturation level, S95, while not being dependent on the exposure time. The experimental evidences suggest that the adsorption of water molecules over the soot surface overcome the effects of hydrophobicity and of line tension effects, favouring condensation of water over the soot surface and leading to a higher nucleation rate even at low supersaturation. Application of the Venturi scrubber model to the water-soot aerosol leaving the growth tube indicate that the CGVS may remove particles with an efficiency far higher than that achieved by the stand alone Venturi. For a given Venturi's throat length and velocity and a given liquid-to-gas ratio, the CGVS efficiency depends almost linearly on ψ and, in turns on S95. Experimental and model results suggested that the CGVS can be a valuable and effective device to capture soot particles and that condensational growth can be used as a retrofit method for existing units.

中文翻译：

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冷凝增长辅助文丘里洗涤器，用于控制烟尘颗粒排放

摘要 本文旨在评估如何使用冷凝生长来提高文丘里洗涤器去除烟尘颗粒的性能，烟尘颗粒是工业和发电厂废气中排放的最相关的空气污染物之一。之前对该系统的研究称为冷凝生长辅助文丘里洗涤器 (CGVS)，表明解决其效率的最相关步骤是评估凝结在烟尘颗粒上的水量，这决定了进入过滤器的实际气溶胶尺寸分布。文丘里。不幸的是，还没有一个确定的物理数学模型来预测非球形粒子集合的实际凝聚增长，而实验研究更适合评估这一点。该研究报告了通过将模型烟灰颗粒暴露于水过饱和气体不同停留时间而获得的尺寸分布的实验数据。获得的尺寸分布用于估计文丘里洗涤器去除水-烟灰气溶胶的效率，允许与母烟灰颗粒的去除进行比较。这些实验是通过使用层流生长管在实验室规模进行的，层流生长管是一种进行受控冷凝生长的简单装置。实验表明，即使对于像烟灰这样的疏水材料，即使在过饱和度低至 1.02 的情况下，凝结生长也是有效的。产生的液固气溶胶比母体颗粒大近 2 到 >3 倍，过饱和度低于 1.15。最后，对实验数据的分析表明，受到凝结生长的颗粒的比例是相关的。实际上，将变得大于原始粒度分布的 98% 百分位数的粒子的分数称为 ψ，我们发现 ψ 可以高达 78%。数据分析表明，ψ 与过饱和水平的第 95 个百分位数 S95 之间存在明显的线性相关性，而不依赖于暴露时间。实验证据表明，水分子在烟尘表面的吸附克服了疏水性和线张力效应的影响，有利于水在烟尘表面凝结，即使在低过饱和度下也能产生更高的成核率。将文丘里洗涤器模型应用于离开生长管的水-烟灰气溶胶表明，CGVS 可以以远高于独立文丘里实现的效率去除颗粒。对于给定的文丘里管长度和速度以及给定的液气比，CGVS 效率几乎与 ψ 呈线性关系，进而与 S95 呈线性关系。实验和模型结果表明，CGVS 是一种有价值且有效的捕获烟尘颗粒的装置，并且冷凝生长可用作现有装置的改造方法。