Acoustic agglomeration to lower the particulate matter

Acoustic agglomeration is a potential pretreatment for reducing fine particulate matter (PM) emissions from industrial flue gas. This experimental study examined biomass-derived fly ash particles exposed to standing high-intensity sound waves, addressing an aerosol type that has received less attention than coal-derived fly ash. The effects of acoustic frequency (16–36 kHz), sound pressure level (SPL; 110–135 dB), chamber residence time (τr; 2–8 s), and initial particle number concentration (2 × 104–13 × 104 cm−3) were investigated. Under the specified laboratory conditions, PM2.5 number concentration decreased by 72.5% and 87.6% at 16 and 32 kHz, respectively, at an SPL of 135 dB, τr= 4 s, and an initial PM mass concentration of 175 mg m−3. Agglomeration efficiency increased with τr and SPL across the tested ranges, tending toward saturation at the highest exposures.