A New Angular Light Scattering Measurement of Particulate Matter Mass Concentration for Homogeneous Spherical Particles.

Under the condition of ultra-low emission for power plants, the particulate matter concentration is significantly lower than that of typical power plants a decade ago, which posed new challenges for the particulate matter monitoring of stationary emission. The monitoring of particulate matter mass concentration based on ensemble light scattering has been found affected by particle size. Thus, this study develops a method of using the scattering angular distribution to obtain the real-time particle size, and then correct the particulate matter concentration with the real-time measured particle size. In this study, a real-time aerosol concentration and particle size measurement setup is constructed with a fixed detector at the forward direction and a rotating detector. The mass concentration is measured by the fixed detector, and the particle size is measured from the intensity ratio of the two detectors. The simulations show that the particle size has power law functionality with the angular spacing of the ripple structure according to Mie theory. Four quartz aerosols with different particle size are tested during the experiment, and the particle size measured from the ripple width is compared with the mass median size measured by an electrical low pressure impactor (ELPI). Both techniques have the same measurement tendency, and the measurement deviation by the ripple width method compared with ELPI is less than 15%. Finally, the measurement error of the real-time mass concentration is reduced from 38% to 18% with correction of the simultaneously measured particle size when particle size has changed.

Influences of In-Furnace Kaolin Addition on the Formation and Emission Characteristics of PM2.5 in a 1000 MW Coal-Fired Power Station.

The impacts of in-furnace kaolin addition on the formation and emission characteristics of PM2.5 from a 1000 MW coal-fired utility boiler equipped with electrostatic precipitators (ESPs) are investigated for the first time ever in this contribution. Detailed characterization of the chemical composition, micromorphology, melting characteristics of the fine PM, total fly ash, and/or bottom ash samples were carried out using the X-ray fluorescence probe, the field emission scanning electron microscope coupled with an energy dispersive X-ray detector, the ash fusion analyzer, and the dust specific resistivity analyzer. The results showed that the formation of fine PM was reduced when kaolin was added, and the mass concentrations of the particulate matter with the aerodynamic diameters of ≤0.3 and 2.5 µm (PM0.3 and PM2.5) were reduced by 55.97% and 5.48%, respectively. As expected, kaolin reacted with the volatile mineral vapors (e.g., Ca, Na) and inhibited their partitioning into ultrafine PM. It was interesting to find that the added kaolin modified the ash melting behavior, and promoted the capture of the ultrafine PM onto the coarse particles. What is more, the added kaolin reduced the specific resistivity of the fly ash and improved their capture efficiency in the ESPs. Finally, the above combined effects brought about the emission reductions of 41.27% and 36.72% for PM0.3 and PM2.5 after the ESPs. These results provided a direct confirmation on the feasibility of in-furnace kaolin addition on the PM reduction in the realistic combustion conditions.

A novel light scattering method with size analysis and correction for on-line measurement of particulate matter concentration.

Based on the difference in particle size sensitivity between forward and backscattering during the measurement of particulate matter (PM) mass concentration using laser angular scattering, a method was proposed to improve its on-line measurement accuracy using three fixed detectors. Experimental and theoretical calculations indicate that the PM mass concentration sensitivity (PMCS) of the particles at the 22.5° detection angle and the asymmetry factor (I45°/I135°) are linearly related to the average particle size, and both decrease as the particle size increases. The average particle size obtained from the asymmetry factor was used to correct the PMCS. Compared with the unmodified light scattering method, when the PM mass concentration varies in the range of 1-8 mg⋅m-3, the average deviation between the light scattering method with particle size correction and the reference is reduced from 191.11 % ± 9.12 % to 8.90 % ± 3.20 %, and the maximum deviation is reduced from 227.04 % to 21.54 %. The effect of particle size on the measurement is reduced by size analysis and correction, and the accuracy of the light scattering method is much improved. Finally, laboratory measurements of the fly ash from coal-fired and biomass-fired power plants were performed.