Acoustic Agglomeration Of Coal Combustion Inhalable Particles

Inhalable particles (Ips) from coal combustion are the important sources of atmosphere pollution in cities. These particles are very fine, numerous, and contain many harmful materials. They have adverse impact on environment and human health. But the efficiencies of the current conventional particle removers like ESP and cyclone are very low for these Ips. Acoustic agglomeration (AA) is an effective method in removing Ips. By subjected to the intense sound, the fine particles can collide each other and agglomerate together in a short period of time. The PSD of particles will evolve from small sizes to big ones. The mean diameters of agglomerated particles or agglomerates will increase and the total number will decrease.So by this way it is easy to remove these bigger particles from the exhausted gases and goal of fine particle release control can be obtained.According to theoretical analysis of standing sound field, two experimental platforms under adscititious standing wave sound field were designed and established which are the microcosmic platform for dynamic characteristics of Ips and the macroscopical platform for AA efficiencies. Experiments were done to study the motion details and overall removal effect of Ips.On the microcosmic platform, first the forces acted on single particle was analyzed,and the characteristics and rules of particle motion in standing sound field were studied. By microscopy High speed CCD observation technology, the real entrainment and drift motion of fine particles in the sound field was successfully recorded and it verified the correctness of the particle's entrainment and drift theory. By theoretical and experimental method, it is verified that the viscous force acted on particle is the major force in the sound field. Under the viscous and gravitational force, particle undergoes sedimentation, entrainment and drift motions simultaneously, and the drifting direction pointss to the nearest node of standing sound. The characteristic was proved by the recorded pictures. In addition, a new fine particle diameter measurement method based on the independence of entrainment and sedimentation movement was proposed to calculate the stokes diameter of particle.The macroscopical platform aimed the industrial fine particle removal as the goal. The effects of different parameters such as sound intensities, retention times, initial particle concentrations and sound frequencies on the PSD change after the AA were studied. The experimental and numerical results were also compared and they fit well. The results showed the increase of sound intensities, retention times and initial particle concentrations favor the removal effect, but there existed an optimal frequency for AA. In addition to the overall removal effect, the experimental removal effect of each individual diameters size were studied and the parametric influences were further forecasted for the industrial application.