Browsing by Subject "Greenhouse gas"
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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 Economics of biomass fuels for electricity production: a case study with crop residues(2009-05-15) Maung, Thein AyeIn the United Sates and around the world, electric power plants are among the biggest sources of greenhouse gas emissions which the Intergovernmental Panel on Climate Change argued was the main cause of climate change and global warming. This dissertation explores the factors which may induce electricity producers to use biomass fuels for power generation and thereby mitigate the impact of greenhouse gas emissions. Analyses in this dissertation suggest that there are two important factors which will play a major role in determining the future degree of bioelectricity production: the price of coal and the future price of carbon emissions. Using The Forest and Agricultural Sector Optimization Model?Green House Gas version (FASOMGHG) in a case study examining the competitiveness of crop residues, this dissertation finds that crop residues currently cost much more than coal as an electricity generation feedstock because they have lower heat content and higher production /hauling costs. For them to become cost competitive with coal, the combined costs of production and hauling must be cut by more than half or the coal price needs to rise. In particular, for crop residues to have any role in electricity generation either the price of coal has to increase to about $43 per ton or the carbon equivalent price must rise to about $15 per ton. The simulation results also show that crop residues with higher heat content such as wheat residues will have greater opportunities in bioelectricity production than the residues with lower heat content. In addition, the analysis shows that improvements in crop yield do not have much impact on bioelectricity production. However, the energy recovery efficiency does have significant positive impact on the bioelectricity desirability but again only if the carbon equivalent price rises substantially. The analysis also shows the desirability of cofiring biomass as opposed to 100% replacement because this reduces haling costs and increases the efficiency of heat recovery. In terms of policy implications, imposing carbon emission restrictions could be an important step in inducing electric power producers to include biofuels in their fuelmix power generation portfolios and achieve significant greenhouse gas emission reductions.Item Estimating emissions impacts to the bulk power system of increased electric vehicle and renewable energy usage(2013-12) Meehan, Colin Markey; Webber, Michael E., 1971-; Baldick, RossThe research presented in this thesis examines the use of electric vehicles and renewable energy to reduce emissions of CO₂, SO₂ and NO[subscript x], and within the state of Texas. The analysis examines the impact of increased renewable energy output and electric vehicle charging on the emissions of fossil fuel electric generators used to serve the bulk power system within Texas. The analysis then compares those impacts to alternative scenarios in which fossil fuel generation replaces some renewable energy generation, and Internal Combustion Engine (ICE) vehicles of varying efficiency are used instead of electric vehicles. This research uses temporally-resolved regression analysis combined with a unit commitment and dispatch model that incorporates several different scenarios for EV charging and fuel mixes to evaluate emissions outcomes based on a variety of conditions. Hourly historical generation and emission data for each fossil fuel generator, combined with hourly output data for non-fossil fuel units aggregated by fuel type (i.e. nuclear, wind, hydro-electric) within the Electric Reliability Council of Texas (ERCOT) footprint is regressed to assess the impact of wind generation output on fossil-fuel generation emissions. The regression analysis is used to assess potential increases in emissions resulting from the ramping of fossil-fuel Electric Generation Units (EGUs) to compensate for variability in wind generation output due to changing weather conditions. The unit commitment dispatch model is used to evaluate the impact of changes in customer demand due to increased usage and charging of electric vehicles on the ERCOT system and any resulting increase in emissions from generation used to meet this new demand. The model uses detailed cost, performance and emissions data for EGUs in the ERCOT footprint to simulate the impact of a variety of charging scenarios and fuel mixes on EGU dispatch patterns and any resulting change in system-wide emissions. The results of this model are combined with the results of the regression analysis to present a more complete analysis of the combined impacts of increase EV and renewable energy usage on the emissions of CO₂, SO₂ and NO[subscript x] within the ERCOT footprint. Based on these analyses the increases in renewable energy generation demonstrate clear benefits in terms of emission reductions when the impacts of increased emissions due to more frequent ramping of fossil-fuel units are taken into account. This analysis also finds that EV charging generally has emissions benefits across a range of charging patterns and bulk power system fuel mixes, although in certain circumstances EV charging might result in higher emissions than the use of ICE vehicles. This research finds when future ICE vehicles with reduced emissions are taken into account, approximately half of the modeled scenarios show net emissions benefits from EV charging, while half show net emissions costs when emissions impacts across pollutants are taken into account.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 A question of capacity assessing CO₂ sequestration potential in Texas offshore lands(2012-12) Miller, Erin Noel; Tinker, Scott W. (Scott Wheeler); Meckel, Timothy Ashworth; Flemings, PeterThe combustion of fossil fuels results in the release of carbon dioxide to the atmosphere, a known greenhouse gas. Evidence suggests that “most of the observed increase in global average temperatures…is very likely due to the observed increase in anthropogenic greenhouse gas concentrations” (IPCC, 2007). One solution currently being examined is carbon capture and storage (CCS). The advantage of CCS is that it does not require an actual reduction in the amount of carbon dioxide emissions created, but reduces emissions to the atmosphere by storing the greenhouse gases in the subsurface. Fundamentally, CCS works in the reverse of oil and gas production. Instead of extracting fluids from the subsurface, CCS injects carbon dioxide (CO2) into the pore spaces of developed oil and gas reservoirs, saline aquifers, or coal bed seams (Bachu, 2007), where it exists in a dense but low-viscosity phase (Supercritical state). The Gulf Coast Carbon Center, based at the University of Texas at Austin’s Bureau of Economic Geology, is currently evaluating the State of Texas Offshore Lands (STOL) in the Gulf of Mexico (GOM) in order to evaluate the carbon-storage capacity in the state owned lands. “Capacity is defined as the volume fraction of the subsurface within a stratigraphic interval available for [CO2] sequestration” (Hovorka, 2004). There are a variety of methods currently used to calculate capacity. With so many options, how does a project decide which method to employ in determining capacity? This paper discusses the methods, presents an analysis of the benefits and drawbacks of the various methods, and develops a process for future projects to utilize in determining which methodology to employ. Additionally, storage capacity is calculated using the various methods presented, in order to compare the methods and understand their various advantages and drawbacks. Reservoir specific simulations are expected to predict smaller capacities in comparison to more broad static methods. This will provide end member predictions of capacity, shedding light on what can be expected in best case and worst case scenarios. The lessons learned from this study can be applied to future endeavors and formations all over the world.Item Urban Form and Travel Patterns at the Regional Scale Considering Polycentric Urban Structure(2012-10-19) Yi, Young-JaeIncreasing concerns about climate change have attracted global interests in reducing auto travel. Regional average vehicle miles traveled (VMT) vary across the urbanized areas in the U.S., suggesting a potential influence of development patterns on greenhouse gas emission. To explore the contribution of development control to driving reduction at the regional scale, this dissertation estimated impacts of urban form on two travel outcomes at the metropolitan scale: daily vehicle miles traveled (DVMT) per capita and daily transit passenger miles (DPMT) per capita. To overcome major problems of previous studies, i.e., lack of generalizability and multicollinearity, a cross-sectional analysis of 203 U.S. urbanized areas was conducted, using directed acyclic graph and structural equation modeling. A literature review revealed gaps in the previous research: while individual-level behavioral studies have identified distance from the center as the most influential factor on VMT, regional-level studies have not reflected this relationship and failed to deliver effective implications for land use policies. A method to identify regional centers was evaluated to appropriately measure polycentric urban structure of contemporary metropolitan areas. The evaluation found that lower density cutoff, wider reference area, and equal treatment between central business district (CBD) and subcenters yielded better performance in McMillen's two-stage nonparametric method. Results also showed that for polycentric areas, the use of a polycentric model produced a better model fit than the monocentric model. Major findings of this dissertation include 1) higher regional concentration, greater local density and less road supply per capita lowered VMT, and 2) higher local density and more transit supply per capita increased PMT. These results imply that different approaches to development control are needed for different sustainable transportation goals - intensifying regional centers such as infill developments for VMT reduction, and compact neighborhood development approaches, such as transit oriented development for transit promotion. However, CBD has a limited capacity and indiscreet compact developments at the urban fringe can lead to decentralization from the regional perspective, and consequently result in increased VMT. This study suggests polycentricism as a potential solution for the contradictive development principle. By allowing dispersion and concentration at the same time, urban form control at the regional level will be more beneficial than conventional local-level control.