Experimental Research On Acoustic Inhalable Particles Agglomeration

Inhalable particle emissions, now widely recognized as a serious public health and air pollution concern, have become the focus of China government regulations. The problem comes in with the new standards as current conventional particle removal devices are ineffective in retaining inhalable particles (PM10 and PM2.5). This has triggered the search for alternative small-particle removal techniques.Among other innovative approaches for small-particle filtration, acoustic aerosol agglomeration has evolved as an efficient way of small particle emissions control[3]. Acoustic agglomeration is a pretreatment process of aerosol particles used to enhance the particles removal rate. An intense sound field produces relative motions and collisions between the initial small particles sequentially forming larger particles. Larger particles can be more easily caught by conventional filtering devices.An experiment facility was designed and set up to study the removal of inhalable fly ash particles emitted from coal fired plants in an acoustic field, and the influence of several factors, including frequency of the sound wave(f), sound pressure level(SPL) and mass concentrations(M) of gas aerosol, responsible for the acoustic particle agglomeration is analyzed. Results of the experiments showed that the optimum sound wave frequency varies with particle size. Low frequency (1-3kHz) acoustic wave is more efficient for fly ash inhalable particles agglomeration than high frequency wave. Higher intensity of sound field provides more acoustic agglomeration efficiency. However, it takes a risk of sound pollution and costs more energy consumption. Therefore, tech-economic problems have to be considered. The agglomeration of aerosol with higher initial mass concentration is more efficient because it increases particles collisions. The optimum operating conditions in our experiments are:acoustic frequency of 1000Hz, SPL of 140dB and the aerosol mass concentration of 20g/m3. The agglomeration efficiency of PMio and PM2.5 can reach 60.15% and 64.77%, respectively.The agglomeration rate is effected by several factors. Orthogonal experiments were operated using factorial analysis, in order to study the impact degree of f, SPL and M on agglomeration efficiency. The results showed that the SPLs have the largest influence on the agglomeration efficiency of PM10 and PM2.5, with a proportion of 51.6% and 42.7%. Followed by the acoustic frequency with a propotion of 28.2% and 32.7%, respectively. The contribution of initial aerosol mass concentration was small and only accounted for 7.02% and 8.21%.