Graduation date: 1995

Black liquor gasification is one of the promising alternatives to eliminate the drawbacks of the conventional recovery unit of the kraft process. A numerical model has been developed to simulate an industrial pilot scale entrained-flow gasifier currently operating at Tampere, Finland. The objective of the model is to investigate the effect of the key operating parameters on the efficiency of sulfate reduction during black liquor gasification. The results of the sensitivity analysis indicates that reduction is dependent of the ratio of the amount of carbon in black liquor to the amount of air being fed into the system, the reactor temperature and the initial particle size. Decreasing the air ratio can improve the efficiency of reduction. The rates of both reduction and carbon gasification increase with increasing in temperature. Higher reduction can be obtained by increasing the initial particle size. However, the values of those parameters need to be optimized based on the desired degree of sulfate reduction and the completion of carbon conversion. Economic considerations such as the length of the gasifier needed to achieve both high reduction efficiency and carbon conversion also need to be considered when selecting operating conditions. / Graduation date: 1994

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

Graduation date: 2004

Graduation date: 1995

No description available.

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

No description available.

No description available.