1,721,195 research outputs found
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The water intensity of the transitional hydrogen economy
Full text linkThe water intensity of the transitional hydrogen economy is analyzed by quantifying the direct
and indirect water requirements to annually manufacture 60 billion kg of hydrogen partly by
thermoelectrically powered electrolysis. It is determined that up to 143 billion gallons of water
would be directly consumed as a feedstock, with a total consumption including evaporation of
cooling water at power plants of 0.5–1.7 trillion gallons annually. Total water withdrawals for
thermoelectric cooling (most of which is not consumed) are expected to increase by 27–97%
from 195 000 million gallons/day today, depending primarily on the aggregate efficiency of
electrolyzers that will be in place and the portion of hydrogen that is produced by
thermoelectrically powered electrolysis. On a per unit basis, thermoelectric power generation
for electrolysis will on average withdraw approximately 1100 gallons of cooling water and will
consume 27 gallons of water as a feedstock and coolant for every kilogram of hydrogen that is
produced using an electrolyzer that has an efficiency of 75%. Given that water withdrawals
have remained steady for decades, this increase in water use represents a significant potential
impact of the hydrogen economy on a critical resource, and is consequently relevant to water
resource planners. Thus, if minimizing the impact of water resources is a priority and
electrolysis becomes a widespread method of hydrogen production, hydrogen production would
need to be from hydrogen production pathways that do not use much water (such as wind or
solar), or effective water-free cooling methods (e.g. air cooling) will need to be developed and
widely deployed.Mechanical Engineerin
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Cow power: The energy and emissions benefits of converting manure to biogas
Full text linkThis report consists of a top-level aggregate analysis of the total potential for converting
livestock manure into a domestic renewable fuel source (biogas) that could be used to help
states meet renewable portfolio standard requirements and reduce greenhouse gas (GHG)
emissions. In the US, livestock agriculture produces over one billion tons of manure annually
on a renewable basis. Most of this manure is disposed of in lagoons or stored outdoors to
decompose. Such disposal methods emit methane and nitrous oxide, two important GHGs with
21 and 310 times the global warming potential of carbon dioxide, respectively. In total, GHG
emissions from the agricultural sector in the US amounted to 536 million metric tons (MMT) of
carbon dioxide equivalent, or 7% of the total US emissions in 2005. Of this agricultural
contribution, 51 to 118 MMT of carbon dioxide equivalent resulted from livestock manure
emissions alone, with trends showing this contribution increasing from 1990 to 2005. Thus,
limiting GHG emissions from manure represents a valuable starting point for mitigating
agricultural contributions to global climate change.
Anaerobic digestion, a process that converts manure to methane-rich biogas, can lower
GHG emissions from manure significantly. Using biogas as a substitute for other fossil fuels,
such as coal for electricity generation, replaces two GHG sources—manure and coal
combustion—with a less carbon-intensive source, namely biogas combustion.
The biogas energy potential was calculated using values for the amount of biogas energy
that can be produced per animal unit (defined as 1000 pounds of animal) per day and the
number of animal units in the US. The 95 million animal units in the country could produce
nearly 1 quad of renewable energy per year, amounting to approximately 1% of the US total
energy consumption. Converting the biogas into electricity using standard microturbines could
produce 88 ± 20 billion kWh, or 2.4 ± 0.6% of annual electricity consumption in the US.
Replacing coal and manure GHG emissions with the emissions from biogas would produce a
net potential GHG emissions reduction of 99 ± 59 million metric tons or 3.9 ± 2.3% of the
annual GHG emissions from electricity generation in the US.Mechanical Engineerin
Evaluation of power generation operations in response to changes in surface water reservoir storage
Full text linkWe used a customized, river basin-based model of surface water rights to evaluate the response
of power plants to drought via simulated changes in reservoir storage. Our methodology
models surface water rights in 11 river basins in Texas using five cases: (1) storage decrease of
existing capacity of 10%, (2) storage decrease of 50%, (3) complete elimination of storage,
(4) storage increase of 10% (all at existing locations), and (5) construction of new reservoirs
(at new locations) with a total increase in baseline reservoir capacity for power plant cooling
of 9%. Using the Brazos River basin as a sample, we evaluated power generation operations in
terms of reliability, resiliency, and vulnerability. As simulated water storage decreases,
reliability generally decreases and resiliency and vulnerability remain relatively constant. All
three metrics remain relatively constant with increasing reservoir storage, with the exception
of one power plant. As reservoir storage changes at power plants, other water users in the
basin are also affected. In general, decreasing water storage is beneficial to other water users
in the basin, and increasing storage is detrimental for many other users. Our analysis reveals
basin-wide and individual power plant-level impacts of changing reservoir storage,
demonstrating a methodology for evaluation of the sustainability and feasibility of
constructing new reservoir storage as a water and energy management approach.Mechanical Engineerin
Evaluating the energy consumed for water use in the United States
Full text linkThis letter consists of a first-order analysis of the primary energy embedded in water in the
United States. Using a combination of top-down sectoral assessments of energy use together
with a bottom-up allocation of energy-for-water on a component-wise and service-specific
level, our analysis concludes that energy use in the residential, commercial, industrial and
power sectors for direct water and steam services was approximately 12:3 0:3 quadrillion
BTUs or 12.6% of the 2010 annual primary energy consumption in the United States.
Additional energy was used to generate steam for indirect process heating, space heating and
electricity generation.Mechanical Engineerin
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Ammonia monitoring near 1.5µm with diode-laser absorption sensors
Full text linkWhen this research was performed, all the authors were with the
High Temperature Gasdynamics Laboratory, Department of Mechanical
Engineering, Stanford University. M. E. Webber is now
with Pranalytica, Inc. D. S. Baer is now with Informed Diagnostics.We investigated ammonia spectroscopy near 1.5 µm to select transitions appropriate for trace ammonia
detection in air-quality and combustion emissions-monitoring applications using diode lasers. Six ammonia
features were selected for these trace-gas detection applications based on their transition
strengths and isolation from interfering species. The strengths, positions, and lower-state energies for
the lines in each of these features were measured and compared with values published in the literature.
Ammonia slip was measured in the exhaust above an atmospheric pressure premixed ethylene–air
burner to demonstrate the feasibility of the in situ diode-laser sensor.Mechanical Engineerin
A temporal assessment of vehicle use patterns and their impact on the provision of vehicle-to-grid services
Full text linkWith the emerging nationwide availability of battery electric vehicles (BEVs) at prices
attainable for many consumers, electric utilities, system operators and researchers have been
investigating the impact of this new source of energy demand. The presence of BEVs on the
electric grid might offer benefits equivalent to dedicated utility-scale energy storage systems
by leveraging vehicles’ grid-connected energy storage through vehicle-to-grid (V2G) enabled
infrastructure. It is, however, unclear whether BEVs will be available to provide needed grid
services when those services are in highest demand. In this work, a set of GPS vehicle travel
data from the Puget Sound Regional Council (PSRC) is analyzed to assess temporal patterns
in vehicle use. These results show that vehicle use does not vary significantly across months,
but differs noticeably between weekdays and weekends, such that averaging the data together
could lead to erroneous V2G modeling results. Combination of these trends with wind
generation and electricity demand data from the Electric Reliability Council of Texas
(ERCOT) indicates that BEV availability does not align well with electricity demand and wind
generation during the summer months, limiting the quantity of ancillary services that could be
provided with V2G. Vehicle availability aligns best between the hours of 9 pm and 8 am
during cooler months of the year, when electricity demand is bimodal and brackets the hours
of highest vehicle use.Mechanical Engineerin
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Fiber-amplified-enhanced photoacoustic spectroscopy with near-infrared tunable diode lasers
Full text linkAt the time the research was completed all authors were with Pranalytica, Inc.A new approach to wavelength-modulation photoacoustic spectroscopy is reported, which incorporates
diode lasers in the near infrared and optical fiber amplifiers to enhance sensitivity. We demonstrate the
technique with ammonia detection, yielding a sensitivity limit less than 6 parts in 109, by interrogating
a transition near 1532 nm with 500 mW of output power from the fiber amplifier, an optical pathlength
of 18.4 cm, and an integration time constant of 10 s. This sensitivity is 15 times better than in prior
published results for detecting ammonia with near-infrared diode lasers. The normalized minimum
detectable fractional optical density,α min l, is 1.8 x 10-8; the minimum detectable absorption coefficient, α min, is 9.5 x 10-10 cm-1; and the minimum detectable absorption coefficient normalized by power and
bandwidth is 1.5 x 10-9 W cm-1/ √Hz. These measurements represent what we believe to be the first
use of fiber amplifiers to enhance photoacoustic spectroscopy, and this technique is applicable to all other
species that fall within the gain curves of optical fiber amplifiers.Mechanical Engineerin
FIGURES 23–24 in Two new species of Euscorpius (Scorpiones: Euscorpiidae) from Bulgaria, Serbia, and Greece
No full textFIGURES 23–24. Euscorpius solegladi sp. n., adult male, general habitus: 23 dorsal view, 24 ventral view.Published as part of Fet, Victor, Graham, Matthew R., Webber, Michael M. & Blagoev, Gergin, 2014, Two new species of Euscorpius (Scorpiones: Euscorpiidae) from Bulgaria, Serbia, and Greece, pp. 83-105 in Zootaxa 3894 (1) on page 94, DOI: 10.11646/zootaxa.3894.1.7, http://zenodo.org/record/25098
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Energy recovery from wastewater treatment plants in the United States: A case study of the energy-water nexus
Full text linkAshlynn Stillwell is with UT Austin, David Hoppock is with Duke University, and Michael Webber is with UT Austin.This manuscript uses data from the U.S. Environmental Protection Agency to analyze the potential for energy recovery from wastewater treatment plants via anaerobic digestion with biogas utilization and biosolids incineration with electricity generation. These energy recovery strategies could help offset the electricity consumption of the wastewater sector and represent possible areas for sustainable energy policy implementation. We estimate that anaerobic digestion could save 628 to 4,940 million kWh annually in the United States. In Texas, anaerobic digestion could save 40.2 to 460 million kWh annually and biosolids incineration could save 51.9 to 1,030 million kWh annually.Mechanical Engineerin
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In situ combustion measurements of CO2 by use of a distributed-feedback diode-laser sensor near 2.0µm
Full text linkM. E. Webber, S. Kim, S. T. Sanders,
D. S. Baer, and R. K. Hanson are with the High Temperature
Gasdynamics Laboratory, Department of Mechanical Engineering,
Stanford University. Ikeda is
with the Center for Instrumental Analysis, Department of Mechanical
Engineering, Kobe University.High-resolution absorption measurements of CO2 were made in a heated static cell and in the combustion
region above a flat-flame burner for the development of an in situ CO2 combustion diagnostic based on
a distributed-feedback diode laser operating near 2.0 um. Calculated absorption spectra of high temperature
H2O and CO2 were used to find candidate transitions for CO2 detection, and the R(50)
transition at 1.997 um (the v1 + 2v2 + v3 band) was selected on the basis of its line strength and its
isolation from interfering high-temperature water absorption. Measurements of spectroscopic parameters
such as the line strength, the self-broadening coefficient, and the line position were made for the
R(50) transition, and an improved value for the line strength is reported. The combustion-product
populations of CO2 in the combustion region above a flat-flame burner were determined in situ to verify
the measured spectroscopic parameters and to demonstrate the feasibility of the diode-laser sensor.Mechanical Engineerin
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