Particulate emissions from the co-combustion of forest biomass and sewage sludge in a bubbling fluidised bed reactor

In the present study, particulate emissions from the co-combustion of forest biomass residues with sewage sludge in a pilot-scale bubbling fluidised bed combustor were characterised. The combustion flue gas was exhausted to the atmosphere after passing through a cyclone separator. Physical-chemical characteristics of the particles were studied: i) morphology and aerosol size, surface and volume distributions before the cyclone and ii) chemical composition (carbonates, water soluble-inorganic ions, organic and elemental carbon) before and after the cyclone. Chemical composition data were used to calculate aerosol density and refractive index. Aerosols showed a unimodal size distribution with a geometric mean diameter of 2.25 ± 0.02 μm and a geometric standard deviation of 1.27 ± 0.01. The surface and volume mean diameters were 2.64 ± 0.02 μm and 2.91 ± 0.05 μm, respectively. Water-soluble inorganic ions were predominant in the fine particle fraction (PM2.5). The filters were loaded of crystallised mineral particles. The analysis revealed a dominance of calcium carbonate/oxide and halide (NaCl or KCl), sulphate and aluminosilicate nanocrystals forming larger mixed aggregates.This work was supported by Portuguese Science Foundation (FCT) through the projects PTDC/AAC-AMB/098112/2008 Bias-to-soil — Biomass ashes: Characteristics in relation to its origin, treatment and application on soil and PTDC/AMB/65706/2006 (BIOEMI). The electron microscopy analyses were conducted at CNME-UCM through the AEROCLIMA project (Fundación Ramón Areces). Ana I. Calvo acknowledges the pos-doc grant SFRH/BPD/64810/2009 from the FCT. We would also like to thank Diana Patoilo (University of Aveiro, Portugal) for supporting the chromatographic analyses, and Véronique Pont (University of Toulouse, France) and Darrel Baumgardner (Droplet Measurement Technologies, Boulder) for their valuable comments.publishe