Size Distribution Functions of Ultrafine Ashes From Pulverized Coal Combustion

Abstract

The major drawbacks of coal combustion are connected with the large emission of particulate matter. This paper deals with the experimental investigation of ultrafine (D < 100 nm) and nano (D < 10 nm) ashes formed during conventional high temperature pulverized coal combustion on a laboratory-scale reactor. The reactor consists of an atmospheric pressure laminar premixed flame homogeneously doped with pulverized coal particles, monodisperse in size. It allows the investigation of the early stage of ash formation. Generated aerosols, sampled using high dilution probes, are conveyed into high resolution Differential Mobility Analyzers (DMA) to perform on-line measurements of the size distribution function of ultrafine ashes. Two DMA systems are used: the first is equipped with a Faraday cup electrometer detector and identifies particles as small as 1 nm, and the second is equipped with a condensation nucleus counter and exhibits 3 nm lower detection limit. Measurements have been performed at several dilution ratios to understand the nature and behavior of detected particles. Results indicate that nanosized coal ashes are formed during pulverized coal combustion. They are the most abundant in number and also a significant fraction of ultrafine ash mass, implying they should be detected at the exhaust of pulverized coal furnaces.

Keywords:

• Nanoparticles
• Particle size distribution functions
• Ultrafine coal fly-ash

ACKNOWLEDGMENTS

The work was partially supported by Ministry of Economical Development (MSE, Italy) under the Accordo di Programma CNR–MSE “Carbone Pulito.” The authors thank R. Pagliara, F. Montagnaro, and M. Urciuolo for their contribution to experiments and the undergraduate students R. La Gala and P. Capasso for their assistance.