• Biodegradation Of Petroleum And Alternative Fuel Hydrocarbons In Moderate To Cold Climate

      Horel, Agota Anna (2009)
      Microbial degradation of hydrocarbon fuels contaminating soil in the Arctic and subarctic environment is a relatively slow process. Nevertheless, due to transportation and logistical limitations in rural Alaska, biodegradation might be the best and cheapest contaminant removal option. The aim of this thesis was to investigate the environmental effects on biodegradation by naturally occurring microorganisms for some innovative hydrocarbon fuels and to determine the overall fate of hydrocarbons in soil, including degradation by fungi and bacteria, volatilization, and transport in the soil. Three major types of fuels were investigated in small scale microcosms and larger soil columns: conventional diesel as a control substance, synthetic diesel (arctic grade Syntroleum) and different types of fish oil based biodiesel. The environmental conditions investigated included different soil types (sand and gravel), different temperatures (constant 6�C, 20�C, and fluctuating between 6 and 20�C), moisture levels (from 2% to 12% GWC), fuel concentrations (from 500 to 20,000 mg fuel/kg soil) and nutrient dosages (0 or 300 mg N/kg soil). Microbial response times and growth phases were also investigated for different inoculum types. Conditions of 20�C, 300 mg N/kg soil, sand, ?4000 mg of fuel/kg soil and ?4% GWC were favorable for bioremediation, with a short lag phase lasting from one day to less than a week, and pronounced peaks of daily CO 2 production between week 2 and 3. At suboptimal conditions, all phases were extended and slow, however at low temperatures steady metabolization continued over a longer time. The relative importance of fungal and bacterial remediation varied between fuel types. Diesel fuel degradation was mainly due to bacterial activities while fish biodiesel degradation occurred largely by mycoremediation. For Syntroleum both bacterial and fungal remediation played key roles. Volatilization contributed up to 13% to overall contaminant removal. In soil columns, degradation was slower than in microcosms, due to an uneven concentration profile of contaminants, nutrients and oxygen with depth. In general, biodegradation showed promising results for soil remediation and the alternate fuel types were more biodegradable compared with conventional diesel fuel.
    • Modeling Of A Novel Triple Turbine Solid Oxide Fuel Cell Gas Turbine Hybrid Engine With A 5:1 Turndown Ratio

      Burbank, Winston Starr, Jr.; Witmer, Dennis E. (2009)
      Electrical production using solid oxide fuel cell gas turbine (SOFC-GT) hybrid systems has received much attention due to high-predicted efficiencies, low pollution and the availability of natural gas. Solid oxide fuel cell (SOFC) systems and hybrid variants designed to date have had narrow operating ranges due largely to the lack of control variables available to control the thermal requirements within the SOFC. Due to the higher value of peak power, a system able to meet fluctuating power demands while retaining high efficiencies is strongly preferable to only base load operation. This thesis presents results of a novel SOFC-GT hybrid configuration designed to operate over a 5:1 turndown ratio. The proposed system utilizes two control variables that allow the hybrid to maintain the SOFC stack exit temperature at a constant 1000�C throughout the turndown. The first control variable is the setting of a variable-geometry inlet nozzle turbine, which most directly influences the system airflow. The second control variable is an auxiliary combustor, which allows control of the thermal and power needs of the turbomachinery independently from that of the SOFC. At low turndown the proposed hybrid operates similarly to previous hybrids, in that roughly 80% of the power is delivered from the SOFC. However, the newly proposed hybrid uses the unique turbomachinery to drastically increase the delivered power at higher power demands. A unique aspect of the proposed hybrid is the contribution of half the rated power being supplied by the inexpensive turbomachinery with the expensive SOFC contributing the other half. This will significantly lower system capital costs compared to previous hybrid designs. The proposed hybrid has high efficiencies throughout turndown with peak efficiencies occurring at low turndown levels.