Deploying Small Scale Biodiesel Facilities Throughout California

Author : Tyler Hatch
Publisher :
ISBN 13 : 9781303153563
Total Pages : pages
Book Rating : 4.1/5 (535 download)

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Download or read book The California Multimedia Risk Assessment Protocol for Alternative Fuels written by Tyler Hatch and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The need to understand and to minimize negative impacts of chemicals to human health and the environment calls for comprehensive assessment of risks associated with impacts in multiple environmental media. In California, multimedia risk assessment (MMRA) has been developed to assist in the process of approving and regulating alternative fuels in the state based on the relative risk of different fuels over their life cycle. As part of this process guidelines for conducting a multimedia risk assessment have been created by researchers at the University of California, Berkeley and the University of California, Davis. The guidelines specify a three-tier process for: determining the state of knowledge about a proposed fuel and its reference fuel; evaluating gaps in knowledge regarding possible impacts to the environment and human health from releases to water, air, and soil; and making recommendations to the Environmental Policy Council (EPC) for conditions for allowing use in the state of California. Emphasis in the California Multimedia Guidelines is on a relative assessment, meaning that a proposed alternative fuel needs to not exceed the risk associated with the reference fuel.Biodiesel is an alternative fuel made from plant- or animal-derived oils and has a growing market. As a popular alternative to petroleum-derived diesel, it requires specifications be developed by the state regulators and as part of this process the State sought to perform a multimedia risk assessment for biodiesel. In California, the current standard diesel is Ultra Low Sulfur Diesel #2 (ULSD) so this was used as the reference fuel for the relative risk assessment of biodiesel. The research reported in this dissertation describes both the overall MMRA for biodiesel, of which my role was as lead junior researcher, and the particular experimental testing for risk of mobility of the fuels in the subsurface, for which I was the primary researcher and hold primary responsibility.The MMRA is performed in three tiers, as detailed in the following chapters. The Tier I multimedia risk assessment identified key knowledge gaps regarding aquatic toxicity, biodegradation, and subsurface fate and transport. Other knowledge gaps were noted, but only the higher priority knowledge gaps were pursued. Tier II experiments were designed and executed to address the knowledge and emphasized Soy and Animal Fat Biodiesel relative to ULSD. Additional studies for air quality were pursued using newer diesel engines and comparing ULSD emissions to those of biodiesel. The biodegradation experiments were performed using aerobic respirometry in microcosms. The aquatic toxicity experiments were performed for 6 species (three estuarine and three freshwater). The subsurface transport experiments were performed using 2D infiltration columns for determining lens formation and redistribution. My contributions were the overall multimedia assessment with emphasis on the subsurface transport experiments in Tier II. Details of each are found in the following chapters.The results of the Tier II experiments suggested that both soy and animal fat biodiesel were more readily biodegradable than ULSD under aerobic conditions. The experimental results for toxicity exhibited somewhat increased toxicity to several tested species compared to ULSD. The antioxidant-additized blends increased toxicity for a smaller group of tested species compared to unadditized blends. The subsurface infiltration and redistribution experiments showed that overall soy and animal fat 20% blends resulted in very similar fuel fate and transport in the subsurface, including similar formation of fuel "lens"es on the water table. The neat soy biodiesel also showed very similar lens distribution to ULSD. The neat animal fat biodiesel showed increased residual in the vadose zone and smaller lens geometry than ULSD. Due to the complexity of laboratory experiments and the qualitative nature of the (photographic) data, simplified numerical simulations of multiphase flow were coded in TMVOC to replicate the conditions seen in the laboratory experiments using physical properties for biodiesel and biodiesel components taken from the literature. Single species, pure biodiesel infiltration experiments were simulated for each soy and animal fat biodiesel and compared to behavior of a simplified ULSD using literature composite properties and other data found with similar carbon chain length, density, and viscosity. The numerical experiments were conducted with homogeneous permeability, and a capillary pressure-saturation relationship for the porous media (medium sand) that was the same for all cases, and I effectively neglected differences in the infiltration due to interfacial tension differences between the biodiesels and ULSD. Where data was not available approximate values were calculated from relationships found in chemical engineering textbooks.The results of the numerical simulations showed a very similar infiltration time to lens formation to the laboratory experiments. The laboratory experiments showed more pore to pore effects not able to be resolved in the macroscale averaged numerical solution. The extent of spreading and thickness of the lenses appear to be consistent between the laboratory simulations and the numerical simulations of the same scale. Due to lower viscosity in the ULSD, it was able to spread slightly further and to make a slightly larger lens in a similar amount of time. In addition, ULSD has a slightly lower density, but it was not low enough to counteract the effects of the lower viscosity. Based on these numerical model simulations, very similar results can be visualized with the use of literature data when comparing laboratory and numerical simulations. The benefit of the numerical simulations is the ability to control the conditions for consistency between trials. On the other hand, the benefit of the laboratory experiments allows for visualization of small scale effects not able to be seen in the numerical model due to macroscale averaging and to small scale heterogeneities in the pore space. From a multimedia risk perspective, numerical models do provide a way to evaluate the mobility of fuels or other chemicals in the subsurface environment in order to make recommendations regarding relative risk. Additional laboratory data would be very helpful in fine tuning the experiments using the properties of the exact fuels used rather than literature values that may be slightly different.