Measurement and numerical simulation of ultrafine particle size distribution in the early stage of high-sodium lignite combustion

Abstract

The formation of ultrafine particulate matter in the early stage of high-sodium lignite combustion was quantitatively investigated in a downward Hencken flat-flame burner under two ambiences of 1200K and 1500K. Spatially resolved measurement of the ultrafine particle size distributions (PSDs) was made by using a scanning mobility particle sizer with a high sensitivity in the 4.45–156.8nm size range. The experimental results indicate that, during the residence time of coal particles from ∼20 ms to ∼40 ms, the number PSDs under 1200K exhibit bi-modal while those under 1500K keep uni-modal. As time is evolved, the detected peak of ultrafine particles moves from 10.62nm to 80.54nm under 1200K, while that from 10.76nm to 38.46nm under 1500K. Then, a physico-chemical mechanism responsible for the incipient formation of ultrafine particles during high-sodium lignite combustion was developed and computed by solving a discrete-sectional population balance model. The number PSDs of ultrafine particles and the dynamic behavior of Na release measured in experiments are consistent with the simulation results. It is further divulged that the intrinsic cause of the PSD transition between different ambient temperatures is the high concentration of newly formed particles, instead of the enhanced collision frequency.