Formation and Emission of Submicron Particles in Pulverized Olive Residue (Orujillo) Combustion

The particle formation and emission in the combustion of pulverized olive residue (orujillo) is studied in this work. The fuel has been burned in controlled combustion conditions in an entrained flow reactor. A bimodal distribution with mode peaks at 155 nm and 110 μm is found for fly ashes. Coarse particles have been characterized by laser diffractometry and SEM, while fines have been analyzed by low-pressure impaction, DMA, SEM, and X-ray diffraction. Particles with Dp < 1 μm are composed of only K₂SO₄ and KCl in the same mass proportion, and possibly K₃PO₄ (less than 7% in mass). The use of a new particle sampling probe and a TEM allowed a detailed study of the formation of these particles when flue gases cool down. K₂SO₄ is experimentally found to start nucleation over 900°C, while KCl is not observed at this temperature. Condensation of KCl on these nuclei is observed in a sample taken at 560°C. These “formation steps” are in good agreement with both theoretical calculations by other authors and a simple equilibrium schema shown here.