Abstract:

Acoustic agglomeration is a potential aerosol preconditioning process，which shifts the particle size distribution towards a larger size and reduces the number of fine particles to enhance the performance of conventional filtering devices.This paper presents an experimental study on acoustic agglomeration of coal-fired fly ash at low frequencies.The particle size distribution of fly ash changed towards a larger size with sound application because lots of fine particles agglomerated.At a frequency of 1400 Hz and a sound pressure level of 147 dB，the total number concentration and PM_2.5 number concentration were reduced by 68.4% and 75.6%,respectively.Aggregates larger than 10 μm were observed in scanning electron microscopy photographs.The total number concentration of aerosol decreased exponentially with time in the acoustic agglomeration process.The results showed that the effect of sound waves was very sensitive to the frequency change，which meant that orthokinetic interaction governed the process.There existed an optimum frequency for a given particle size distribution，which decreased slightly as sound pressure level increased.Besides，the influences of sound pressure level，residence time and initial total number concentration on agglomeration were investigated.