The Fate of Flame Volatized Sodium During the Combustion of Pulverized Coal in Reaction With Silica and Sulfur (Studied with the Aid of a Synthetic Coal)
Date of Award
Master of Science (MS)
The interaction of flame volatilized sodium with sulfur and silica (quartz) was studied under coal fired boiler conditions in a laminar flow reactor. Measured compositions of sodium, sulfur and quartz were bound together in a synthetic coal matrix and subject to various temperature profiles ranging from 900-1500°C and residence times ranging from 0.1 to 1.4 seconds. As well as studying the inorganic reactions, a detailed look was also spent on the actual combustion characteristics of the synthetic coal. These results are serendipitous in nature but deserve attention as well.
The addition of a carbon matrix to a model mixture alters the formation of the resulting fly ash largely due to the exothermic reaction of the carbon which increases the temperature of the immediate combustion environment. The combustion of the carbon may raise the temperature of the immediate environment as much as 1000°C.
The formation of sodium silicates during coal combustion is favored by longer residence times and higher temperatures. The formation of sodium sulfates does not interfere to any large degree with the formation of sodium silicates. Theoretical calculations (SOLGAS mix) supports this also demonstrating the dominance of sodium silicates in the presence of a burning carbon atmosphere. The higher temperatures formed a much more homogenous particle than at lower temperatures. At higher temperatures the formed sodium silicate is either an amorphous glass or a sodium silicate formed while highly molten.
Short residence time studies show evidence of fragmentation of coal early in combustion and the formation of cenospheres during the later stages of combustion. The degree of coalescence depends on the degree of fragmentation.
Particle size analysis of the resulting fly ash indicate that at lower temperatures (900-1100°C) fly ash particles form through coalescence in which one ash particle is formed for each coal particle. At higher temperatures there are multiple fly ash particles formed for each coal particle implying that fragmentation is taking place during combustion. All temperatures produce sodium silicate spheres with small sodium sulfate particles condensed on the outside surface. The sodium sulfate is much more abundant at the lower temperatures. Thermochemical calculations predicted similar conditions. The lower temperature particles were not homogeneous while at higher temperatures they achieved homogeneity.
Erickson, Thomas A., "The Fate of Flame Volatized Sodium During the Combustion of Pulverized Coal in Reaction With Silica and Sulfur (Studied with the Aid of a Synthetic Coal)" (1990). Theses and Dissertations. 837.