Application of Acoustic Agglomeration to Reduce Fine Particle Emissions from Coal Combustion Plants
Removal of fine particles (smaller than 2.5 μm) from industrial flue gases is, at present, one of the most important problems in air pollution abatement. These particles, which are hazardous because of their ability to penetrate deeply into the lungs, are difficult to remove by conventional separation technology. Sonic energy offers a means to solve this problem. The application of a high-intensity acoustic field to an aerosol induces agglomeration processes which changes the size distribution in favor of larger particles, which are then easier to precipitate with a conventional separator. In this work, we present a semiindustrial pilot plant in which this process is applied for reduction of particle emissions in coal combustion fumes. This installation basically consists of an acoustic agglomeration chamber with a rectangular cross-section, driven by four high-power and highly directional acoustic transducers of 10 and/or 20 kHz, and an electrostatic precipitator (ESP). In the experiments, a fluidized be...
Experimental Study on Acoustic Agglomeration of Fine Particles from Coal Combustion
The removal of fine particles in coal-fired fumes was experimentally studied based on acoustic agglomeration. An experiment facility was designed and set up. In this facility, a fluidized bed coal combustor was used as fume generator, and an Electrical Low Pressure Impact or (ELPI) was used to measure the fine particle concentration and size distribution in the fumes. The results show that under the effect of high intensity sound waves, there is good performance to remove fine particles in coal-fired fumes, which with a number mean diameter of 0.07μm. Especially, under the conditions of the frequency of 1 000Hz and the sound intensity of 161.5dB, the number concentration of 0.0233~9.314μm particles decreased by 85.2%, and their mass concentration decreased by 92.5%.
A theoretical analysis of the effects of an electric field on the charging of fine particles
Recent measurements of charge imparted to fine particles by unipolar ions in a strong electric field have shown that this charge is appreciably higher than that predicted by previous theoretical analyses. The charge acquired by fine particles is due primarily to ions which strike the particle by virtue of their random heat motion. Previous analyses have assumed that the only field existing was that due to the charge on the particles, thus neglecting any external field which would be present in a corona discharge. Two effects of an external field which influence charging are critically examined: 1. Ions or electrons which travel in the direction of the external field toward the particle will acquire energy in addition to their heat energy. Their increase in energy will allow these elementary particles to overcome more readily the potential field of the charged particle. This effect is shown to be small for molecular ions at atmospheric pressure except for only the very smallest particles but, for charging by free electrons, which have a much longer mean free path, the effect could cause a large increase in charge. 2. The presence of an external field will alter the density distribution of ions around the charged particle since this field opposes the particle field on one side of the particle and aids it on the other side. The general equation for the ion density distribution was not able to be solved. However, approximate finite difference methods using computing machinery show that this effect is important and may almost completely account for the higher charge found with molecular ion charging.