Online Measurement of the Size Distribution of Pneumatically Conveyed Particles through Acoustic Emission Detection and Triboelectric Sensing

In a thermal power plant, online measurement of the size distribution of pneumatically conveyed pulverized fuel is essential for the improvement of combustion efficiency and the reduction of pollutant emissions. In this article, an innovative instrumentation system based on acoustic emission (AE) detection and triboelectric sensing is proposed for the on-line continuous measurement of particle size distribution. With a waveguide protruding into the flow, the AE signal is generated from the impacts of particles with the waveguide. The peak voltage of the AE signal is related to the particle size and impact velocity. For the first time, two triboelectric sensor arrays each with three arc-shaped electrodes near to the waveguide are used to measure the impact velocity. Meanwhile, a novel particle sizing algorithm with Gaussian prediction is proposed to reduce the effect of overlapping impacts and environmental noise on the peak distribution. With the known impact velocity measured from the triboelectric sensor arrays and the modified peak distribution, the measurement of particle size distribution is achieved. Experimental tests were conducted on a gas-solids two-phase flow rig to assess the performance of the developed measurement system. Silica sands in three size ranges of 116-750, 61-395, and 10- 246~\mu \text{m} , respectively, were used as test particles. The experimental results demonstrate that Spearman's rank correlation coefficients between the measured and reference size distributions for all test particles are all greater than 0.8, while the discrepancy for each particle size segment is within ±4.8%.