The Study On The Adhesion Force Of Fine Particles And Spray Agglomeration Based On The Calciumbased Liquid Bridge

Emissions of fine particulates(PM_2.5) are the main reason for the frequent fog haze weather in China currently, which is the important source from the power plants’ coal combustion. The dust removal device is difficult to contr ol fine particles due to the small size. Agglomeration is the technology that makes the fine particles in the smoke grow up, and the bigger the size of the particles are, the easier to be removed. Agglomeration technique can not only reduce the concentration of mass of fine particulates, but also has a good effect on the decrease of the number concentration of fine particles. Chemical agglomeration has the most application prospect, which can connect the particles together by the liquid bridge and prevent the separation again. However, the theoretical study of chemical agglomeration is very little, which leads to the lack of theoretical guidance for application. In addition, Limestone-gypsum Wet Flue-gas Desulfurization（WFGD） device can remove some fine particulates coming from the fly ash, meanwhile, fine particles also can be produced due to the gypsum. Therefore, it is more practical to study the fine particle aggregation in WFGD.In this paper, the experimental study of the adhesion force between the atomic force microscope（AFM） probe and the fly ash is carried out. In order to study th e law of the change of adhesion force with distance, the saturated solution of calcium based material, the surfactant and polymer binder are used as the components of the liquid bridge. Research results show that, the surface active agents can reduce the adhesion force and the rupture distance of liquid bridge, and the maximum adhesion force value decreases and then increases, with the increase of surfactant concentration. The trend of changes in greater contrast when different surface active agents and polymer binders are used in coordinated service.Secondly, the adhesion force under the action of the liquid bridge, between the AFM tip and the fly ash is studied theoretically. According to the existing form of liquid bridge, two volume liquid bridge models convexly and concavely are established. Four formulas based on the existing research for calculating the capillary forces of the two models are proposed, meanwhile, the adhesion forces such as Van der Waals forces and dynamic viscous force are analyze d. Research results show that,adhesion force is attractive for the two convex and concave models, and among that the capillary force accounted for dominance, van der Waals force works only at the nanoscale effect distance. Moreover; dynamic viscosity force and electrostatic force can be neglected. Furthermore, the theoretical calculation has the same law as the experiment.Then, the capillary force between the micron-sized fly ash particles possessing poor wettability is studied. Under the action of the liquid bridge, two types of volume models are established. The effect of capillary force and dynamic viscous force are analyzed theoretically, when calcium based solution and wetting agents as the composition of the liquid bridge. Results show that the capillary force between the particles is repulsive, and the capillary force between particles is decreased. Moreover, PM_2.5 is more likely to form an effective continuous liquid bridge with large particles. At the same time, based on the principle of minimum energy, the numerical simulation of the liquid bridge between fly ash and fly ash is carried out. The theoretical calculation is in good agreement with the numerical simulation results, when the volume of the liquid bridge is relatively small, while the shape of the bridge becomes more complex, when the liquid bridge volume is relatively large, and the principle of the circular arc is no longer applicable. Besides, the surface active agent can delay the rupture distance of the liquid bridge, and increase the range of the aggregation of the particles.Finally, an experimental system to study the effect of agglomeration on the removal efficiency of fine particles is designed and constructed. Experimental results show that saturated calcium base material solution has better removal effect, when the proportion of PM_2.5 in flue gas is higher than 95%, and the effect is improved, with the addition of surfactants. It should be pointed out that the increasing value of removaling efficiency of fine particles, concentrates in the range of the particle diameter 0.48 to 2 μm, when the use of Compound No.3 and PG simultaneously, and the efficiency exceeds 13%. Furthermore, the removal efficiency of PM_2.5 increases, as the spray liquid, and the concentration of agglomeration agents and the ratio of liquid to gas increase. Moreover, the removal efficiency of fine particles can improve significantly, as temperature increases, during the temperature range from 25 to 75 degrees.