Abstract

In this work the differences between and characteristics of water and high solids, heated black liquor sprays from air-assist atomizers are examined. Sprays were imaged with a high speed camera and the images analyzed with computer code to produce droplet size data and macroscopic spray characteristics such as mass distribution. Fluid flow rates were measured to allow relevant dimensionless groups for the spray to be calculated. A 1000 degree C tubular furnace was placed around the spray to determine the effect of industrially relevant temperatures on the droplet formation process, relative to room-temperature conditions. It was found that high solids black liquor forms long, thin ligaments rather than droplets. In high-temperature surroundings the size of these ligaments increases, which from a comparison with theory in the literature was attributed to enhanced skin-formation driven by heat transfer. The data suggest that this skin formation may prevent secondary breakup. All sprays for both fluids produced droplet size mass distributions that were well described by the square-root normal distribution. The normalized width (s*) of these distributions was similar for all sprays and consistent with literature data for other nozzle designs (0.24 < s* < 0.38). The image analysis method assumed droplets were spheres with the same projected area. When this assumption was changed for black liquor sprays to a cylindrical droplet assumption, the shape and normalized width of the resulting mass distributions remained the same, but the representative diameter (calculated from surface area to volume ratios) decreased. Based on the agreement between the normalized distribution width in this work and that in the black liquor spraying literature it was concluded that the addition of atomizing air cannot be considered a means to narrow a droplet size distribution independent of droplet size. The results also indicate the importance of including the effects of skin formation and temperature- and time-dependent fluid properties in spray modeling. It is intended that these results contribute to increased understanding of the black liquor atomization process and lead to improved computational modeling of the same.

Degree

College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering

Rights

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