CHARACTERIZATION AND FORMATION OF SUB-MICRON PARTICLES IN COAL-FIRED PLANTS

Submicron particles resulting from pulverized coal combustion in coal-fired steam plants have been chemically characterized and the results interpreted in terms of various mechanisms for their formation. Elemental analyses using XRF, AA, and INAA techniques are reported for approximately 60 elements for flyash from two large coal-fired plants. The concentrations of elements volatilized during combustion are independent of particle size in the submicron size range, in contrast to the larger particle sizes where an inverse relationship with particle size applies. Scanning electron micrographs show the submicron particles are also much more homogeneous than larger flyash particles, while still showing evidence of some surface enrichment in ESCA studies. Various mechanisms for formation of submicron particles have been considered. The present results are most consistent with formation of submicron particles by the bursting of larger particles due to gas release during rapid heating, followed by coagulation and condensation of volatilized elements to form particles in the 0.1-1.0 μm size range. The importance of this mechanism in other coal-fired plants is probably dependent on both temperature and ash composition. © 1979.