Abstract：An acoustic method was proposed and investigated based on the sound scattering theory, taking the influence on the acoustic attenuation caused by the irregularity of the coal powder into account. Meanwhile, numerical simulations of the acoustic attenuation were conducted to analyze the influence of different physical parameters' variation and establish the relationship between ultrasonic attenuation and coal volume fraction, size.Two one-piece ultrasonic probes with center frequencies of 40, 200 kHz were developed, where superimposed wave was adopted as a probe excitation source reduced the complexity of the experimental setup. The on-line coal parameter experiments were then conducted in a coal-fired power plant. The in-line measurements were carried out at zones with different depths from the pipe wall, and a one-hour continuous monitoring was also conducted, yielding a mean volume fraction of 0.11% and size of around 35 μm. Therefore the proposed method can real-time online measure coal powder volume fraction and size in power plant pipelines, improve the coal pulverizers' working condition and increase the boiler's combustion efficiency.

Keywords: dual-frequency; ultrasound method; pulverized coal; superposition wave