The effect of boiler operating conditions on the composition, morphology, and microstructure of black liquor combustion aerosols

Black liquor is a waste sludge from the paper pulping process, that is burned in recovery boilers, where the pulping chemicals are recycled and the heat from burning organic matter is utilised. Black liquor consists of about 20% of sodium causing high inorganic concentration in flue gases. In this study particle formation in recovery boiler was studied via electron microscopy. Individual particles were collected from flue gases from the cold zone upstream of the ESP onto nuclepore filters and on impactor stages. Particles were collected by thermophoretic sampling on copper grids from the hot zone at about 800 degree C. Samples were studied with scanning electron microscope (SEM) and with high resolution transmission electron microscope (HRTEM). Particles for computer controlled scanning electron microscopy (CCSEM) were collected from the ESP. Ash samples collected from the ESP hoppers were also analysed by X-ray diffraction (XRD) for the composition of crystalline phases.