Bed cooling effects in solid particulate matter emissions during biomass combustion. A morphological insight

• Published in: Energy (Oxford) 2020-08, Vol.205, p.118088, Article 118088
• Main Authors: Pérez-Orozco, Raquel, Patiño, David, Porteiro, Jacobo, Míguez, José Luis
• Format: Article
• Language: English
• Subjects: Agglomerates; Air staging; Air supplies; Biodegradation; Biomass; Biomass burning; Biomass combustion; Cases (containers); Combustion; Cooled bed; Cooling; Cooling effects; Emission analysis; Environmental regulations; Low-temperature combustion; Morphology; Operating temperature; Particulate emissions; Particulate matter; Particulate matter emissions; Soot; Temperature gradients; Thermophoretic sampling; Typology
• ISSN: 0360-5442; 1873-6785
• DOI: 10.1016/j.energy.2020.118088

Considering recent environmental regulations, the need to adapt domestic biomass combustion systems to models that generate less emissions has gained relative importance. The present research proposes an analysis of the bed cooling effects on emission patterns, specifically focusing on the concentration, typology and morphological aspects of the released particles. The study was carried out by comparing the behaviour of a small-scale pilot plant with air stratification, with and without bed cooling. The results revealed an optimal behaviour of the facility with distributions of 30% primary-70% secondary air, accompanied by a significant decrease in emissions due to the reduction in the operating temperatures. More than 75% of the particles were retained in the bed on the cooled surfaces due to the effect of the prominent temperature gradient that was produced. Among the types of emitted particles (mostly with sizes below 0.1 μm), the presence of partial biomass degradation remnants was observed, representing three-quarters of the total collected matter. To a lesser extent, the presence of carbonaceous agglomerates was detected and usually in very compact clusters; however, in cases of high primary air supply, large amounts of immature soot were observed. •Optimal results involved air staging distributions of 30% primary – 70% secondary.•CB tests notably reduced bed temperatures, with a lesser effect on gas phase values.•Bed cooling appears to be a promising strategy, reducing PM emissions more than 75%.•The PM size distribution showed 80% of particles were smaller than 0.1 μm.•75% of particles were char and thin layers, 15% were agglomerates and 10% were tars.