Chemical Engineering Journal, Vol.334, 891-899, 2018
Improving acoustic agglomeration efficiency of coal-fired fly-ash particles by addition of liquid binders
Acoustic agglomeration is an efficient pretreatment technology for industrial flue gases, which can significantly improve their removal efficiency of conventional dust filters that follow. However, its two main shortcomings, i.e. high energy consumption and the breakage of aggregates, restrict its commercial application. In this paper, a novel method is proposed to overcome these shortcomings by addition of liquid binders. The mechanisms of acoustic agglomeration efficiency improvement by the addition of liquid binders are thought to be: 1) The binder droplets, acting as coarse seed particles, raise the agglomeration kernels based on both orthokinetic interaction and hydrodynamic interactions, thus increase the collision frequency of aerosol particles; 2) Liquid bridges and solid bridges between particles are formed in the presence of binder droplets, which are much stronger than van der Waals force to increase the adhesion factors and avoid the breakage of aggregates. The performance of three polymer binders: Xanthan Gum (XTG), Kappa Carrageenan (KC) and Polyferric Sulfate (PFS), is experimentally investigated. With addition of binders, the agglomeration efficiency reaches as high as 75-85% at an acoustic power of 2.5 W. In contrast, the agglomeration efficiency is only 60% under the same conditions with addition of water. The promotion effect of binders on agglomeration is found to be in the order of: XTG > KC > PFS. It is therefore concluded that the longer polymer chains and the higher viscosity of binders are more favorable for aerosol acoustic agglomeration. It is also found that the agglomeration efficiency becomes much less sensitive to the acoustic frequency change with addition of binders, comparing with the case without the addition of binders.