Studies On Fly Ash Agglomeration In High Frequency Sound Field And Normal Temperature

Coal is the main energy resources of our country. Coal combustion makes serious pollution to the environment. The exhausted gas from coal combustion is the important source of the Inhalable Particle (PM₁₀) emission to the atmosphere. PM₁₀, especially PM2.5 has become the most important atmosphere pollutant in our country. 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 the PM₁₀.Acoustic agglomeration is an effective method in removing PM₁₀. By subjected to the intense sound, the fine particles can collide with 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. By this way, it is easy to remove these bigger particles from the exhausted gas and the control of the fine particle release can be obtained.In this article, the acoustic agglomeration experimental platform was designed and established, 20 KHz high-power sound wave was used as sound resource. The powder-feeding system was specially designed and studied.A screw powder-feeder was specially designed for the experimental platform, because steady and continuous micro-feeding was needed in this platform. Experiments were done on the quantity of the powder given by the screw powder-feeder. The relationships between the feed rate with the pitch of screws, the speed of the screw rod were obtained. The flow process of the powder in the storehouse was analyzed, and the reason of arch-made was given. By adding an agitation-equipment, the arch-made problem in the storehouse was solved.The acoustic agglomeration experimental studies were conducted on the fly ash from the coal combustion power plant. Agglomerations were obtained after treated by the sound wave. Particles with smaller size decreased and the bigger ones increased, the concentration of particles decreased. Agglomerations mainly occurred in the fine fraction of fly ash, because the frequency of the sound wave was so high. After the experiment, the relationship between the effect of the acoustic agglomeration and sound power, initially particle concentration and residence time was obtained. The results show that increase of sound power, particle concentration and residence time all led to increase of acoustic agglomeration. The relationship between the effect of the acoustic agglomeration and the humidity of atmosphere in the agglomeration room was studied.Based on the orthokinetic and hydrodynamic interaction as main mechanisms, acoustic agglomeration simulation was established , the kernel for acoustic agglomeration was obtained. The method of numerical simulation was used to solve the aerosol dynamics equation of the acoustic agglomeration. The results of the numerical simulation were compared with the experiment result and a good agreement was obtained.