Intermediate-Sized Particle (ISP) Formation During Black Liquor Droplet Combustion, 2004 International Chemical Recovery Conference

Single-droplet black liquor combustion experiments were conducted to provide definitive evidence and quantity of intermediate-sized particle (ISP) formation. ISP, with a size range of 1-100 µm, is one of the three types of particles found in the recovery boiler. Five different liquors, two softwood liquors and three softwood/hardwood mixed liquors, at two initial solids contents (50% and 70%), were examined for this investigation. Small explosions on the droplet surface occur during drying, and this might represent a small contribution to ISP. Devolatilization produced insignificant amounts of ISP, relatively to other stages. ISP formation occurred mainly during late char burning and smelt oxidation. The amount of ISP generated increases with increasing initial solids loading and varies additionally from liquor to liquor. Total ISP formed from varied from were 0.2% to 0.8 % of black liquor solids for liquors with 50% solids loading and from 0.4% to 1.8% for liquors with 70% initial solids loading. Initial droplet mass (size) affected ISP amount proportionally. SEM analyses indicate five different particles. Large particles (>50 µm) were spherical with cracked surfaces. Particles with about 20 µm diameter were nearly spherical and had agglomerates on the surface. Smaller particles (~10 µm) had irregular shapes, and particles less than 5 µm may be agglomerated from fume particles. Small amount of fume were also collected. These particles appeared to be consistently formed from all liquors.