Graduate Thesis Or Dissertation
 

Liquor to liquor differences and the effects of liquor feed rate on the distribution of condensed phase combustion products of kraft black liquor solids burned in a laminar entrained-flow reactor

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  • Combustion properties of kraft black liquor solids were studied using a laminar entrained flow reactor. The tendency of black liquors to release fume (compounds containing Na⁺, K⁺, Cl⁻, SO₄²⁻, SO₃²⁻, S₂0₃²⁻ and C0₃²⁻) during combustion were observed at 1000°C. Black liquor solids with a size fraction of 63 to 100 μm were burned in a mixture of 4% 0₂ and 96% N₂ at a residence time of 0.67 seconds. Combustion properties of one black liquor (liquor #3) were studied by varying the solids feed rate from 0.47 to 1.08 g/min (liquor feed rate study). Combustion properties of five North American and Finnish black liquors were studied at a target solids feed rate of 0.73 g/min (liquor to liquor study). Black liquor fuming was observed to be a decreasing function of solids feed rate and an increasing function of excess oxygen. The appearance of char residues varied from black and porous at high solids feed rates to white and dense at low solids feed rates. Combustion may have been enhanced at low solids feed rates by liquor swelling due to a combination of heat and mass transfer effects and limited at high solids feed rates by inter-particle and bulk gas mass transfer limitations. For the liquor to liquor study, black liquors were observed to release fume differently. Chars produced during this study varied in appearance, indicating that the black liquors had unique combustion properties. Variations in temperature and mass transfer effects resulting from liquor swelling properties were likely responsible for the variability in liquor fuming behavior. The liquors that contained the most NaCl and had the highest anionic equivalents as C0₃²⁻ (or other chemical species) produced the most fume. Sodium vaporization varied from 25.2% to 33.7%: Liquors #2 and #5 vaporized the most sodium and also had the lowest concentrations of measured anions in their char residues. Potassium and chloride enrichment factors for the five liquors were slightly lower than those of common industrial boilers. Liquor #3 had a concentration of Cl⁻ that was (roughly) an order of magnitude higher than the other liquors studied; however, it also had the lowest chloride enrichment factor.
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