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Utilizing solar thermal energy for post-combustion CO2 capture
Full text linkPost-combustion amine absorption and stripping can remove 90% of the CO2 from power plant flue gas, but systems can
reduce electrical output by approximately 30% due to energy requirements for stripping CO2 from solvent and CO2 compression. The
CO2 capture energy penalty can be reduced while developing renewable energy technologies by meeting CO2 capture energy
requirements with a solar thermal energy system, particularly when electricity demand and prices are the highest. This study presents an
initial review of solar thermal technologies for supplying CO2 capture energy, with a focus on high temperature systems. Parabolic
troughs and central receivers are technically able to provide energy for CO2 capture. However, the solar system’s capital costs would be
roughly half that of the base coal-fired plant with CO2 capture, and high electricity prices are required to offset the costs of operating the
solar thermal system. For high temperature solar thermal systems, direct electricity generation is likely a more efficient way to use solar
energy to replace output lost to CO2 capture energy. However, low temperature solar thermal systems might integrate better with
solvent stripping equipment, and more rigorous analysis is required to definitively assess the feasibility of using solar energy for CO2
capture.Mechanical Engineerin
Textile Dry Cleaning Using Carbon Dioxide: Process, Apparatus and Mechanical Action
No full textFabrics that are sensitive to water, may wrinkle or shrink when washed in regular washing machines and are usually cleaned by professional dry cleaners. Dry cleaning is a process of removing soils from substrate, in this case textile, using a non-aqueous solvent. The most common solvent in conventional dry cleaning is perchloroethylene (PER). Despite its satisfactory cleaning performance, PER has several drawbacks. One approach is to develop an alternative solvent for PER. CO2 is chosen in this study because it has several advantages compared to the other alternative solvents. The main objective of this study is to improve the cleaning performance of CO2 dry cleaning for particulate soils, firstly by studying and solving the redeposition problem, secondly by enhancing the amount of mechanical action applied to the fabric. Another objective of this thesis is to achieve more insight in the cleaning process since little information is available regarding the textile movement inside the rotating drum in the CO2 medium. This has been studied with an endoscopic camera in the 25 L CO2 dry cleaning machine. Experiments with an observation cell equipped with a mechanical actuator were performed to apply well defined forces on the textile, and use these results to perform a quantitative analysis of the mechanical forces. Based on the results of the above, an ideal CO2 dry cleaning machine and process has been designed. This is a combination of best practices, new insights obtained from the results of this study and the best available technologies. The performance and the investment costs of CO2 dry cleaning are not yet comparable with the conventional solvents or the other alternative solvents. However, we believe that CO2 is the only real green solvent for textile dry cleaning and our studies have shown that it has a high potential to replace PER in the future. The economy evaluation also showed that the operating costs for dry-cleaning using CO2 are comparable to the costs using PER.BiotechnologyApplied Science
Comparing post-combustion CO2 capture operation at retrofitted coal-fired power plants in the Texas and Great Britain electric grids
Full text linkStuart Cohen is with UT Austin, Hannah Chalmers is with University of Edinburgh, Michael Webber is with UT Austin, and Carey King is with UT AustinThis work analyses the carbon dioxide (CO2) capture system operation within the Electric Reliability
Council of Texas (ERCOT) and Great Britain (GB) electric grids using a previously developed
first-order hourly electricity dispatch and pricing model. The grids are compared in their 2006
configuration with the addition of coal-based CO2 capture retrofits and emissions penalties from 0 to
100 US dollars per metric ton of CO2 (USD/tCO2). CO2 capture flexibility is investigated by
comparing inflexible CO2 capture systems to flexible ones that can choose between full- and zero-load
CO2 capture depending on which operating mode has lower costs or higher profits. Comparing these
two grids is interesting because they have similar installed capacity and peak demand, and both are
isolated electricity systems with competitive wholesale electricity markets. However, differences in
capacity mix, demand patterns, and fuel markets produce diverging behaviours of CO2 capture at
coal-fired power plants. Coal-fired facilities are primarily base load in ERCOT for a large range of CO2
prices but are comparably later in the dispatch order in GB and consequently often supply intermediate
load. As a result, the ability to capture CO2 is more important for ensuring dispatch of coal-fired
facilities in GB than in ERCOT when CO2 prices are high. In GB, higher overall coal prices mean that
CO2 prices must be slightly higher than in ERCOT before the emissions savings of CO2 capture offset
capture energy costs. However, once CO2 capture is economical, operating CO2 capture on half the
coal fleet in each grid achieves greater emissions reductions in GB because the total coal-based
capacity is 6 GW greater than in ERCOT. The market characteristics studied suggest greater
opportunity for flexible CO2 capture to improve operating profits in ERCOT, but profit improvements
can be offset by a flexibility cost penalty.Mechanical Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Turning CO2 capture on and off in response to electric grid demand: A baseline analysis of emissions and economics
Full text linkCoal consumption accounted for 36% of America’s CO2 emissions in 2005, yet because
coal is a relatively inexpensive, widely available, and politically secure fuel, its use is
projected to grow in the coming decades (USEIA, 2007, “World Carbon Dioxide Emissions
From the Use of Fossil Fuels,” International Energy Annual 2005, http://
www.eia.doe.gov/emeu/iea/carbon.html). In order for coal to contribute to the U.S. energy
mix without detriment to an environmentally acceptable future, implementation of
carbon capture and sequestration (CCS) technology is critical. Techno-economic studies
establish the large expense of CCS due to substantial energy requirements and capital
costs. However, such analyses typically ignore operating dynamics in response to diurnal
and seasonal variations in electricity demand and pricing, and they assume that CO2
capture systems operate continuously at high CO2 removal and permanently consume a
large portion of gross plant generation capacity. In contrast, this study uses an electric
grid-level dynamic framework to consider the possibility of turning CO2 capture systems
off during peak electricity demands to regain generation capacity lost to CO2 capture
energy requirements. This practice eliminates the need to build additional generation
capacity to make up for CO2 capture energy requirements, and it might allow plant
operators to benefit from selling more electricity during high price time periods. Postcombustion
CO2 absorption and stripping is a leading capture technology that, unlike
many other capture methods, is particularly suited for flexible or on/off operation. This
study presents a case study on the Electric Reliability Council of Texas (ERCOT) electric
grid that estimates CO2 capture utilization, system-level costs, and CO2 emissions associated
with different strategies of using on/off CO2 capture on all coal-fired plants in the
ERCOT grid in order to satisfy peak electricity demand. It compares base cases of no
CO2 capture and “always on” capture with scenarios where capture is turned off during:
(1) peak demand hours every day of the year, (2) the entire season of peak system
demand, and (3) system peak demand hours only on seasonal peak demand days. By
eliminating the need for new capacity to replace output lost to CO2 capture energy
requirements, flexible CO2 capture could save billions of dollars in capital costs. Since
capture systems remain on for most of the year, flexible capture still achieves substantial
CO2 emissions reductions.Mechanical Engineerin
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