Effects of simultaneous acoustic and electric fields on removal of fine particles emitted from coal combustion

Abstract

Traditional electrostatic precipitation has a relatively low collection efficiency of fine particles emitted from coal combustion due to insufficient particle charging. This paper establishes an experimental system combining travelling sound waves with wire-duct electrostatic precipitation in order to measure the separated and simultaneous effects of an electric and acoustic field on fine particle penetration efficiency. The ranges of the main physical parameters are as follows: discharge voltage, V=8–12kV; acoustic frequency, ƒ=800–2400Hz; sound pressure level (SPL), SPL=130–148dB; residence time, t=2–6s; initial fine particle concentration, N0=6.5×105–4.99×106/cm3. The application of acoustic waves in an electric field is proven as an advisable method to remove fine particles with the lowest total penetration efficiency of 4.4%. Although the sound does not change the current–voltage curves of negative corona, it can distort the motion trajectory of the particles leading to a positive result for fine particle removal. The effectiveness of sound on the improvement of fine particle removal diminishes as the voltage increases. For a given discharge voltage, there exists an optimal frequency and SPL. The optimal frequency slightly increases, while the optimal SPL decreases as the applied voltage increases. The influence of residence time and initial fine particle concentration in combined fields are also studied.