Characterization of biomass PM emissions using thermophoretic sampling: Composition and morphological description of the carbonaceous residues

Abstract In this paper, a complete characterization of particulate matter (PM) emitted by a low-scale biomass combustor was performed. Samples were collected in three different zones of the installation (in-flame, boiler outlet and chimney outlet) using the thermophoretic sampling (TPS) method, and the different particle structures present in the biomass were studied from a chemical and a morphological point of view. Five types of particles were found: soot agglomerates, organic films, organic particles with imbibed fibrous structures, condensed tars and condensed inorganic salts. Transmission electron microscopy (TEM) was used for shape description, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) was used for determining elementary composition. Specifically, soot agglomerates were submitted to a deeper characterization in terms of fractal descriptors, obtaining values for primary particle diameter, d po , of 21.7 ± 8.4 nm, 21.4 ± 6.6 nm and 26.0 ± 5.9 nm for the three sampled zones, as well as values for fractal dimension, D f , between 1.40 and 2.60 and fractal prefactor, k f , between 2.20 and 2.40. The results were in agreement with other soot formation sources and showed an increasing tendency to cluster growth and compaction with the residence time inside the facility, being higher as they went further from the combustion zone. Fractal descriptors were not fairly influenced by the applied thermal treatment.