Laminar entrained flow reactor (LEFR) was used to determine the effect of temperature and residence time on the distribution of carbon, sulfur and nitrogen between gaseous and condensed phase products from low temperature pyrolysis of kraft black liquor. The operating furnace temperatures were between 400��C-600��C where the effect of condensable organic and organic sulfur compounds may be important. The residence times ranged from 0.3 to 2.0 seconds. In the evolution of carbon as gases, an oxidizer was used to convert all oxidizable components in LEFR effluent gas to carbon dioxide which was detected by an infrared carbon dioxide meter. With this, measurement of total carbon in the gas phase, the fine particles, and the char residue were made. The carbon yield in the gas phase increased as residence time increased. The higher the temperature, the higher the carbon yield as gases phase at each residence time. The carbon yield in the fine particles differed very little with temperature at residence time below 1.1 seconds. At higher temperature, the carbon yield in the fine particles is about the same at 500��C and 600��C, but lower at 400��C. The carbon yield in the char residue decreased as residence time increased. The carbon yield in the char residue at 500��C and residence time above 1.1 seconds was a little lower than at temperature 600��C, due to an apparent loss of char at 500��C. The char yield at 500��C was lower than expected based on the 400��C and 600��C data because of accumulation of larger, more highly swollen char particles at the tip of collector at this temperature. The average of the sum of carbon recovered as char residue, gases, and fine particles was 96.2% at 600��C, 88.1% at 500��C, and 95.7% at 400��C. The main reason for the poorer carbon recovery at 500��C was the loss of char particles which accumulated on the tip of the collector. When the char yield at 500��C is increased so that the carbon balance closed to 96%, the char yield, carbon yield, and sulfur yield at 500��C fell between the values at 400��C and 600��C. The sulfur yield in the char residue decreased as residence time increased. The higher the temperature, the lower the sulfur yield in the char residue. The nitrogen yield in the char residue also decreased as residence time increased. / Graduation date: 1997

Graduation date: 1995

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. / Graduation date: 2002

Black liquor recovery boilers experience significant fire-side fouling problems due to the deposition of entrained particulate matter. Increased understanding of the mechanisms by which particles deposit on these surfaces will lead to more effective management of the resultant problems. There is some evidence which suggests that the sub-micron fraction of this particulate matter deposits by thermophoresis. In an effort to determine conclusively if this is the case, a facility (the Multifuel Combustor at Sandia National Laboratories) was used which could generate and deposit fly ash under conditions that mimic those found in full scale recovery boilers, and dynamically monitor deposit growth rates. Experiments where both the deposit thickness and surface temperature were monitored in situ resulted in linear deposit growth rates despite highly non-linear surface temperature increases. This rules out thermophoresis as the dominant deposition mechanism since it is dependent on the changing thermal driving force. The morphology of the windward side deposit indicates an inertially-dependent mechanism is at work in spite of the size of the particles, which are considerably smaller than what would be commonly considered inertially impacting particles. Leeward side deposits also grow linearly, indicating that thermophoresis, although possibly contributing to deposition, is not the rate-controlling mechanism. Deposition efficiencies fell in the range of 5-15%. The morphology of the sub-micron deposits is highly structured and dendritic in appearance, with over 90% voidage. The particles form long strings or filaments which grow in parallel, indicating that the particles have a high sticking efficiency and do not roll or settle subsequent to impacting. There is minimal contact between adjacent filaments. Recently published research confirms the presence of particles in the 1-50 micron range in recovery boilers. Deposition experiments were performed on this size range as well. Termed Intermediate-size, these particles deposit many times more efficiently, and produce linear deposit growth rates just as the sub-micron particles. They also deposited in clusters of filaments which grew rapidly upward and slowly outward until the adjacent clusters merged. However in this size range the clusters tended to branch out more rapidly than the sub-micron deposits. Deposition efficiencies fell in the range of 40-65%. / Graduation date: 1999

The importance of two sources of NO formation, nitrogen in combustion air and nitrogen in the fuel, during black liquor combustion was studied using a laminar entrained flow reactor. Pyrolysis and combustion experiments were conducted in nitrogen atmosphere and in a mixture of argon and helium in the composition 99% argon, 1% helium. The experiments were performed at three different temperatures: 700, 900, and 1100��C and at two residence times: 0.6 and 1.6 seconds. The results indicated that there was NO formation from the combustion air which was found to be prompt NO. There was NO formation from combustion air at all temperatures, and it decreased as temperature increased. Depending on conditions, prompt NO formation accounted for 6-80% of the total NO formation. NO reduction experiments were conducted to investigate the effect of molten sodium carbonate on NO reduction. The experiments were performed at two different temperatures, 800��C which is lower than the melting point of sodium carbonate and 900��C which is higher than the melting point of sodium carbonate. The rate constant for NO reduction was calculated and was found to agree well with that obtained in a previous study. The effect of the molten sodium carbonate on NO reduction was found to be negligible during black liquor pyrolysis. The rate in absence of any reducing gas components could explain NO reduction during black liquor combustion only to a limited extent. Models for nitrogen evolution during pyrolysis and combustion were developed by using data from previous studies. A model for nitrogen release during pyrolysis was developed as a function of residence time and temperature. Nitrogen release during pyrolysis was also found to be directly proportional to carbon release and the rate of nitrogen evolution with respect to the rate of carbon evolution decreased as temperature increased. / Graduation date: 1997

Graduation date: 1995