Improve acoustic agglomeration of fine particles by droplet spray

doi:10.11949/j.issn.0438-1157.20161586

Abstract

Abstract:

Acoustic agglomeration is a potential pretreatment technology for efficient reduction of particulate matter emission in flue gas. However, high energy consumption restricts its commercial application. To improve acoustic agglomeration efficiency, droplet spray was added to aerosol. The influences of operating parameters on agglomeration efficiency were studied to explore compounding effect of acoustic field and droplet spray. The results showed that acoustic agglomeration efficiency was increased by 25% to 40% with addition of droplet spray. Whether the droplet spray existed or not, similar influence of sound frequency on agglomeration was observed with optimum frequency at 1400 Hz. The agglomeration efficiency rose with the increase of sound power, liquid-gas ratio or aerosol residence time, which reached to maximum when liquid-gas ratio was over 0.10 or aerosol residence time exceeded 4.2 s. Two main mechanisms were proposed for the improvement of agglomeration efficiency with presence of droplet spray. One was that droplet spray created liquid bridge forces between particles, which were much stronger than van der Waals forces, and increased collision efficiency greatly. The other was that liquid droplets acted as particle seeds for agglomeration, which had significantly different entrainment factors compared to surrounding small particles. Consequently, relative movement among aerosol particles was enhanced so agglomeration efficiency was promoted. The results suggest that energy consumption of acoustic agglomeration process can be reduced dramatically with addition of droplet spray.

Key words: aerosol, spray, acoustic, agglomeration, particle size distribution

摘要：

以燃煤烟气为对象，实验研究了各参数对喷雾促进声波团聚的影响。结果表明，添加喷雾后，声波团聚效率提高了25%~40%。无论有无喷雾，声波团聚均存在相同的最佳频率，为1400 Hz左右。较低液气比时，团聚效率随液气比的增加而明显增大，但超过0.10后，团聚效率趋于稳定。添加喷雾时，团聚效率随停留时间的增加而提高，但达到4.2 s时基本达到最大值。分析了喷雾提高团聚效率的机理，在喷雾作用下，颗粒之间形成比范德华力更强的液桥力，增大了有效碰撞系数；同时，雾化液滴的加入为气溶胶团聚提供了种子颗粒，周围的细颗粒易与之发生碰撞团聚，使团聚效率提高。研究表明，喷雾方法可以大幅降低声波团聚工艺的操作能耗。

关键词: 气溶胶, 喷雾, 声波, 团聚, 粒度分布

CLC Number:

X513

ZHANG Guangxue, ZHU Yingjie, ZHOU Taotao, WANG Jinqing, XU Hong, CHI Zuohe. Improve acoustic agglomeration of fine particles by droplet spray[J]. CIESC Journal, 2017, 68(3): 864-869.

张光学, 朱颖杰, 周涛涛, 王进卿, 徐鸿, 池作和. 喷雾对促进细颗粒物声波团聚的影响[J]. 化工学报, 2017, 68(3): 864-869.

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