Progress in Understanding ISP Particle Characteristics and Sources in Recovery Boilers, 2004 Paper Summit, Spring Technical & International Environmental Conference, (including Papermakers; Process Control, Electrical & Information; Product & Product Qual

A combined experiment and modeling program has increased the understanding of the importance of intermediate size particles (ISP) in recovery boiler ash deposition and has also provided new information on the sources of ISP in recovery boilers. Laboratory experiments on suspended-drop combustion of black liquor and on black liquor char bed combustion have demonstrated that both processes generate ISP particles, generally on the order of 1-2% of the black liquor dry solids mass. Boiler measurements on a northwest U.S. and a southeast U.S. recovery boiler show similar, highly variable loadings of ISP particles in the upper furnace, averaging between 1-2 g/Nm3, or 10-20% of the mass loading of fume particles. The measurements show that the ISP mass size distribution generally increases with size from 5-100 µm, meaning that a substantial amount of ISP inertially deposits on steam tubes. Larger ISP particles are depleted in potassium, chlorine, and sulfur relative to the fuel composition. Comprehensive boiler modeling for these same two boilers demonstrates accurate temperature, velocity, and fume concentration predictions, once anomalies in the boiler operation data are rectified. ISP concentrations are substantially overpredicted when using a previously developed algorithm for modeling ISP generation.