Browsing by Subject "GHG"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item Analysis of a novel thermoelectric generator in the built environment(2011-08) Lozano, Adolfo; Webber, Michael E., 1971-; Schmidt, Philip S.This study centered on a novel thermoelectric generator (TEG) integrated into the built environment. Designed by Watts Thermoelectric LLC, the TEG is essentially a novel assembly of thermoelectric modules whose required temperature differential is supplied by hot and cold streams of water flowing through the TEG. Per its recommended operating conditions, the TEG nominally generates 83 Watts of electrical power. In its default configuration in the built environment, solar-thermal energy serves as the TEG’s hot stream source and geothermal energy serves as its cold stream source. Two systems-level, thermodynamic analyses were performed, which were based on the TEG’s upcoming characterization testing, scheduled to occur later in 2011 in Detroit, Michigan. The first analysis considered the TEG coupled with a solar collector system. A numerical model of the coupled system was constructed in order to estimate the system’s annual energetic performance. It was determined numerically that over the course of a sample year, the solar collector system could deliver 39.73 megawatt-hours (MWh) of thermal energy to the TEG. The TEG converted that thermal energy into a net of 266.5 kilowatt-hours of electricity in that year. The second analysis focused on the TEG itself during operation with the purpose of providing a preliminary thermodynamic characterization of the TEG. Using experimental data, this analysis found the TEG’s operating efficiency to be 1.72%. Next, the annual emissions that would be avoided by implementing the zero-emission TEG were considered. The emission factor of Michigan’s electric grid, RFCM, was calculated to be 0.830 tons of carbon dioxide-equivalent (CO2e) per MWh, and with the TEG’s annual energy output, it was concluded that 0.221 tons CO2e would be avoided each year with the TEG. It is important to note that the TEG can be linearly scaled up by including additional modules. Thus, these benefits can be multiplied through the incorporation of more TEG units. Finally, the levelized cost of electricity (LCOE) of the TEG integrated into the built environment with the solar-thermal hot source and passive ground-based cold source was considered. The LCOE of the system was estimated to be approximately $8,404/MWh, which is substantially greater than current generation technologies. Note that this calculation was based on one particular configuration with a particular and narrow set of assumptions, and is not intended to be a general conclusion about TEG systems overall. It was concluded that while solar-thermal energy systems can sustain the TEG, they are capital-intensive and therefore not economically suitable for the TEG given the assumptions of this analysis. In the end, because of the large costs associated with the solar-thermal system, waste heat recovery is proposed as a potentially more cost-effective provider of the TEG’s hot stream source.Item Atmospheric emissions and air quality impacts of natural gas production from shale formations(2014-08) Zavala Araiza, Daniel; Allen, David T.; Webber, Michael; McDonald-Buller, Elena; Hildebrandt Ruiz, Lea; Edgar, ThomasNatural gas is at the core of the energy supply and security debates; new extraction technologies, such as horizontal drilling and hydraulic fracturing, have expanded natural gas production. As with any energy system, however, natural gas has an environmental footprint and this thesis examines the air quality impacts of natural gas production. Greenhouse gas (GHG), criteria pollutant, and toxic emissions from natural gas production have been subject to a great amount of uncertainty, largely due to limited measurements of emission rates from key sources. This thesis reports direct and indirect measurements of emissions, assessing the spatial and temporal distributions of emissions, as well as the role of very high emitting wells and high emitting sources in determining national emissions. Direct measurements are used to identify, characterize and classify the most important sources of continuous and episodic emissions, and to analyze mitigation opportunities. Methods are proposed and demonstrated for reconciling these direct measurements of emissions from sources with measurements of ambient concentrations. Collectively, the direct source measurements, and analyses of ambient air pollutant measurements in natural gas production regions reported in this work improve the estimation, characterization, and methods for monitoring air quality implications of shale gas production.Item An enviro-economic assessment of waste vegetable oil to biodiesel conversion : an analysis of cost and GHG emissions for the University of Texas at Austin(2014-08) Ernst, Kendall Robert; Blackhurst, Michael F.With its multiple dining halls, close proximity to restaurants, and diesel vehicle fleet, the University of Texas at Austin (UT) has both the supply of raw materials to implement a waste vegetable oil to biodiesel recycling program and the capacity to use it. At face value, implementing a large-scale recycling program provides a source of cheap, low emissions fuel. However, the feasibility of such a program is contingent on its economic cost and environmental impact relative to alternative fuel sources. Thus, this research estimated the greenhouse gas (GHG) inventories and the unit cost associated with 1 megajoule worth of recycled biodiesel derived from three production processes –Alkali Catalyzed, Acid Catalyzed, and Supercritical Methanol–using environmental life cycle assessment and life cycle costing. These GHG inventories and unit costs were then compared to the conventional diesel and oilseed biodiesel sources that make up UT’s current fuel portfolio. This analysis suggested that implementing a recycling program using a Supercritical Methanol biodiesel conversion process would have the lowest combined GHG impact and unit cost, although as an emerging technology, it poses a high investment risk. In general, these findings are encouraging to the success and impact of a large-scale recycling program.Item Life cycle global warming emissions for natural gas(2012-08) Randel, Tony Lynn; Allen, David T.; Crawford, RichardClimate change is a topic of social and political commentary and controversy, and is a topic that will continue to be addressed by future scientists and laypersons alike. This report contains information and laboratory exercises for use in a greenhouse gas (GHG) and global warming potential (GWP) learning module, to be employed in secondary or entry level university engineering and environmental science curricula. Exercises include a hands-on experience with the greenhouse effect and calculations of GWP for 20-year and 100-year timeframes.Item Sustainable energy systems : the environmental footprints of electricity generation systems : mechanisms for managing electricity, water resources and air quality(2012-08) Alhajeri, Nawaf Salem; Allen, David T.; McDonald-Buller, Elena; Corsi, Richard; Webster, Mort; Webber, MichaelThis thesis examines the response of air pollutant emissions, water use and carbon emissions from electric power supply systems (electrical grids) to market forces and natural and human disruptions. Specifically, the response of electrical grid operation decisions to emissions pricing and other factors, such as drought restrictions, is examined. The grid of the Electricity Reliability Council of Texas (ERCOT) is used as a source of data, and as a spatial and temporal test-bed. Price signals for NOx emissions have the potential to reduce NOx emissions from the ERCOT grid by up to 50%. In addition to lowering NOx, there are co-benefits to introducing NOx prices, including reductions in the emissions of SOx (24.9% to 70.9%), Hg (16.8% to 81.3%) and CO2 (8.7% to 21.1%). Water consumption was also decreased by 4.3% to 8.2%. The costs of redispatching electricity generation to reduce NOx emissions are, in many scenarios, comparable to conventional control costs. Higher CO2 prices produce many of the same changes in electricity generation as increases in NOx prices, but the simultaneous application of NOx and CO2 pricing produces complex effects. Under stress, such as drought induced water scarcity, dispatching decisions have the potential to increase water availability in regions in which drought is a concern. This dispatching had relatively small impacts on total water consumption summed over all regions of the ERCOT grid. However, the dispatching scenarios resulted in net increases in NOx, SOx, and CO2 emissions rates summed over all regions of the grid, particularly in regions that were absorbing the electricity generation that was exported out of the drought impacted regions. The costs of electricity dispatching, per volume of water consumption reduced in the drought impacted region, was generally greater than the cost of implementing dry cooling in the same facilities at high electricity demand levels, but comparable to dry cooling at low to moderate demand levels. Finally, while changes in total emissions can be used as a surrogate for air quality impacts, actual changes in air pollutant concentrations, such as ozone, exhibit complex spatial and temporal patterns in response to redispatching, including the creation of hot spots of elevated concentrations.