Effects of Particle Hydrophilicity and Morphology on Aerosol Scavenging in a Wet Electrostatic Scrubber

Lipeng Su,Qisheng Ou,Qian Du,Min Tang,David Y.H Pui

doi:10.4209/aaqr.2019.04.0207

Abstract

ABSTRACT In this work, influences of particle hydrophilicity and morphology on its removal by electrically neutral and positively charged water droplets were investigated experimentally in a home-made chamber. Potassium chloride (KCl) and Di-Ethyl-Hexyl-Sebacate (DEHS) and agglomerated KCl aerosols were successively adopted as representative testing cases and each test was carried out batchwise. The results showed that minimal collection efficiency of DEHS particles (hydrophobic) could be improved from 38% to 82% due to droplet charging after spray for ten minutes, which is a significantly greater increment than that of KCl particles (hydrophilic) after same charging-spray time. Additionally, droplet charging enhances the operational stability of traditional spray to collect DEHS particles in tested sizes while contributes most to removal of KCl particles only in low concentration and intermediate size. As a comparison with nearly spherical particles (KCl), a higher collection efficiency by electrically neutral droplets corresponds to loose agglomerates in low particle concentration due to interception mechanism, but the difference could be weakened by an addition of electric field onto water spray.

Highlights

Over past few years, air pollution mainly caused by PM2.5 was commonly recognized as the one of most intractable issues in China to improve human settlement environment (Li et al, 2015; Zheng et al, 2016)
The results showed that minimal collection efficiency of DEHS particles could be improved from 38% to 82% due to droplet charging after spray for ten minutes, which is a significantly greater increment than that of KCl particles after same charging-spray time
As a comparison with nearly spherical particles (KCl), a higher collection efficiency by electrically neutral droplets corresponds to loose agglomerates in low particle concentration due to interception mechanism, but the difference could be weakened by an addition of electric field onto water spray

Summary

INTRODUCTION

Air pollution mainly caused by PM2.5 was commonly recognized as the one of most intractable issues in China to improve human settlement environment (Li et al, 2015; Zheng et al, 2016). In order to mitigate the PM2.5 pollution in China, a great deal of strategies and technologies emerged constantly, mainly involving high-efficient filters (Chang et al, 2016; Chen et al, 2016; Choi et al, 2017; Zhang et al, 2017), electrostatic precipitators (Park et al, 2017; Liao et al, 2018), wet removal (Jaworek et al, 2006a) and hybrid system. D’Addio et al (2013, 2014) designed a lab-scale WES (Wet electrostatic scrubbing) system to decouple the influences of droplet-particle interactions and study quantitatively the role of charged droplets in removing submicron particles. Jaworek et al (2002) numerically simulated and reviewed the scavenging rate of small particles by charged droplets, suggesting that smaller droplet size, lower Stokes number and higher Coulomb number have positive effects on collection efficiency. Experiment results showed that both particle hydrophilicity and morphology have significant influences on its removal by electrically neutral or positively charged droplets

METHODOLOGY

RESULTS AND DISCUSSION

CONCLUSIONS