Improving acoustic agglomeration efficiency by addition of sprayed liquid droplets

Acoustic agglomeration is a potential pretreatment technology for industrial flue gas to efficiently reduce particulate matter emission. However, the process requires a huge amount of energy input, which restricts its commercial industry application. In order to reduce the energy requirement, the spraying of liquid droplets into the aerosol is proposed in this study. It is thought that the droplets sprayed would improve the acoustic agglomeration process through two mechanisms: 1) increasing the adhesion factor due to the formation of liquid bridge forces between particles; and 2) as seed particles, which enhance the relative movement between particles and then increase the collision probability. The experimental results in this study show that the acoustic agglomeration efficiency can be greatly improved by up to 55% with the assistance of water spray droplets. It is also found that the influence of acoustic frequency on agglomeration efficiency basically remains unchanged regardless of the existence of spray droplets, and an optimum frequency corresponding to the highest agglomeration efficiencies exists. The only difference is that when frequency deviates from the optimum value, the agglomeration efficiency drops less sharply with the presence of the water spray than that without it. The agglomeration efficiency increases significantly with the increase of the liquid-gas ratio, up to 80% at liquid-gas ratios above 0.13. For pure acoustic agglomeration, the sound pressure level required for a 50% agglomeration efficiency is 146 dB, while the efficiency could achieve 55%-73% with water sprayed at only 140 dB, saving approximately three-quarters of energy consumption. The performance of two wetting agencies (SDS and TX100) in acoustic agglomeration is also tested, which could make a further increase of agglomeration efficiency by 5%-20% comparing to that using pure water. The results show that the optimum concentrations of SDS and TX100 solutions are 0.2% and 0.05%, respectively, corresponding to the minimum surface tension and contact angle. (C) 2017 Elsevier B.V. All rights reserved.