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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Kinetics of reduction of titaniferous ores with lignite coal

Sucre-García, Gustavo A. January 1979 (has links)
An inductively heated rotary reactor has been used to study the reduction kinetics of Westport and Florida ilmenites, and Glenbrook iron-sands with Saskatchewan lignite coal. The effect of speed of rotation, char to ore ratio, temperature, and pre-oxidation on the reduction behaviour was examined, and the reaction rate followed by gas analysis and flow measurement. Independent activation energies have been determined; for the reduction of Westport and Florida ilmenites the values were 25 and 7.5 Kcal/mole respectively, while Glenbrook ironsands and pre-oxidized West-port ore showed a change from 25 to 7.5 Kcal/mole due to a change in the rate controlling step. For the Boudouard reaction the activation energy was 55 Kcal/mole. Ore reducibilities (in cm³/g.s) have been calculated to be 4 x 10⁵ for Westport ore; 4 x 10³ for Florida ilmenite; 2 x 10⁶ and 2 x 10³ for pre-oxidized ore; and 9 x 10⁴ and 8 x 10¹ for Glenbrook ironsands; in the last two cases the two values given correspond to the two activation energies specified above. Char reactivity has been found to be 2 x 10¹¹ cm³/g.s. The reduction mechanism has been shown to be very sensitive to the ore type and temperature. In general, a mixed control between the reduction and gasification reactions was observed below 1000°C. Mixed control also existed during the reduction of pre-oxidized and Florida ores at 1050°C until 75% reduction; above this reduction level the reduction reaction limited the process which was also the case of Westport and Glenbrook ores at this temperature. The Boudouard reaction was found to govern the overall rate only during the reduction of Florida ilmenite at 950°C below 45% reduction. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate
12

La réduction d'effectifs est-elle une mesure souhaitable? : Essai de réponse à cette question grâce au concept de valeur ajoutée / Reduction of workforce is a measure desirable ? : Test answer to this question through the concept of added value

Dzreke, Komla Agbessinyalé 09 November 2012 (has links)
« Il n'apparaît pas nettement que les réductions d'effectifs profitent aux actionnaires, ni même qu'elles améliorent la santé financière de l'entreprise ».Telle est la conclusion de l‟étude de Patrick SENTIS3. En effet, en examinant le mode de répartition de la valeur ajoutée dans les entreprises, cet auteur trouve que la réduction des effectifs est le fait des entreprises en difficulté4. Il considère que lorsque les entreprises sont confrontées aux difficultés, la valeur ajoutée, concept estimateur de la richesse de l‟entreprise, diminue. Cette diminution se répercute mécaniquement sur le résultat disponible pour les actionnaires. « Afin de maintenir la répartition initiale, les dirigeants devront abaisser les rétributions des autres parties prenantes pour maintenir celles des actionnaires » (Patrick SENTIS, 1998). Cet auteur précise que cette condition conduit les dirigeants à être confrontés à un choix politique. «En présence d’actionnaires, de créanciers et d’employés, il est aisé de constater que le choix des dirigeants est fortement contraint. Il n’est pas possible de modifier la richesse allouée aux créanciers dans la mesure où celle–ci est fixée contractuellement. Il est délicat de répercuter totalement les difficultés de l’entreprise sur la rétribution des actionnaires dans la mesure où ces derniers décident de la nomination, de la révocation et de la rémunération des dirigeants via les assemblées générales. La modification de la richesse attribuée aux employés semble être le levier d’action le plus approprié dans une telle situation. En France, les réductions de salaires décidées unilatéralement n'étant pas légalement possibles, la réduction de la richesse du personnel passera par une réduction des effectifs. Un transfert de richesse est alors susceptible de se produire entre les salariés et les actionnaires, car le risque économique est répercuté sur les premiers» (Patrick SENTIS, 1998).Notre étude s‟est inscrite dans le prolongement de celle de Patrick SENTIS. Nous avons examiné de façon approfondie et appliqué sa méthodologie. Bien que nous ayons utilisé un autre échantillon, composé des entreprises en difficulté lors de l‟opération, nous sommes parvenus au même constat que Patrick SENTIS : Les réductions d’effectifs ne profiteraient pas aux actionnaires. A ce titre cette politique semble être une mesure financièrement condamnable.Cependant, en appliquant la valeur ajoutée à la réduction d‟effectifs, cet auteur semble n‟avoir pas examiné le cas des entreprises qui étaient en bonne santé économique et financière lors de l‟opération. Rappelons que de nos jours bon nombre sont des entreprises prospères qui réduisent leurs effectifs. Alors, pour compléter les travaux de cet auteur, à l‟aide du même outil, nous avons examiné le cas des entreprises qui n„étaient pas en difficulté. Selon les résultats obtenus, il apparaît que, pour la majorité des entreprises de notre échantillon qui étaient en bonne santé financière et économique lors de la réduction d‟effectifs, les parts de la valeur ajoutée aux actionnaires ont augmenté après. La réduction d’effectifs semble être une mesure bénéfique pour les actionnaires de ces entreprises prospères lors de l’opération. Nous avons aussi constaté que, c‟est à peine pour 4% des entreprises de l‟échantillon global que les parts des cinq parties prenantes ont augmenté après la réduction d‟effectifs alors que dans 34% des cas, seules les parts de la valeur ajoutée pour les actionnaires et pour l‟entreprise ont augmenté simultanément. La réduction d’effectifs ne semble donc pas être une mesure prise pour augmenter la rémunération de toutes les parties prenantes.Il apparaît nettement que la réduction d’effectifs ne profite pas aux actionnaires dans les entreprises en difficulté lors de l’opération. Par contre elle semble leur être bénéfique dans les entreprises déjà florissantes. / Pas de résumé en anglais
13

Thermal reduction of beryllium chloride with metallic magnesium

Strunk, Mailand Rainey. January 1947 (has links) (PDF)
Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1947. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed June 17, 2010) Includes bibliographical references (p. 32-33) and index (p. 35-36).
14

Performance Evaluation of a Power Generation Unit-Organic Rankine Cycle System with Electric Energy Storage

Warren, Edward Harrison Randall 06 May 2017 (has links)
This research proposes the use of electric energy storage (EES) in conjunction with a power generation unit organic Rankine cycle system (PGU-ORC). The EES is used when available so that continuous operation of the PGU is not required. The potential of the PGU-ORC-EES system’s performance is evaluated in terms of operational cost, primary energy consumption (PEC), and carbon dioxide emissions (CDE) from simulations of a restaurant building in twelve U.S. locations with different climate conditions. The performance of the proposed system is compared to a conventional system. Results indicate that the EES addition to the PGU-ORC system is beneficial for most locations. Ratios between electricity and fuel cost, CDE conversion factors, and PEC conversion factors are used to estimate potential performance benefits. The effect of the EES size and the capital cost available are also analyzed.
15

Fundamental Studies Related to Gaseous Reduction of Iron Oxide

Kazemi, Mania January 2016 (has links)
The demands for increasing the efficiency and lowering the environmental effects in iron and steelmaking industries have given rise to interests in application of direct reduction (DR) processes for production of iron by different gases. These advancements require comprehensive models for better control of the process conditions and the product properties. In the present thesis fundamental aspects in reduction of iron oxide were investigated. The experimental studies on reduction of iron oxide pellets were performed under well-controlled conditions in a setup designed for thermogravimetric investigations. The results indicated that the reaction rates by the applied procedure are higher compared to the procedure similar to conventional thermogravimetric analysis (TGA). This difference was caused by the time required for replacing the inert gas by the reaction gases. Reduction by H2-CO mixtures was accompanied by deposition of carbon and formation of cementite. The variations of cementite contents in the industrial iron ore pellets reduced isothermally for different durations, showed that cementite formation starts from the initial stages of reduction. The experimental conditions such as reaction temperature, carbon activity in the reaction gas and reaction time have a large impact on carbide content of the reduced samples. The kinetics of reduction of iron ore powder by H2 and CO gas mixtures with different compositions were studied using a commercial TGA setup. The results showed that the apparent rates of reaction vary linearly with the H2 and CO contents of the gas. Larger amount of H2 resulted in higher reaction rates. The data were employed in the developed reduction model for pellets. The model was based on the mechanism observed in the commercial iron ore pellets reduced by pure hydrogen. The microstructure of reacted pellets showed that reduction of the examined industrial samples is controlled by both chemical reaction and gaseous diffusion. The reduction model was developed by combining computations for the flow and mass transfer in the gas phase, diffusion of gases in the solid phase and chemical reaction at the reaction sites. The modelling and experimental results were in reasonably good agreement. The present model provides a good foundation for a dynamic multi-particle process model. The results highlighted the importance of considering the reduction mechanisms in different types of pellets prior to modelling. Experiments were undertaken to investigate the selective reduction of iron oxide in zinc ferrite. It was observed that gaseous reduction by hydrogen at temperatures up to 873 K is a potential method for reduction of iron oxide to metallic iron, while the zinc oxide remains in the product and losses of metallic zinc are negligible. Using this primary step in the hydrometallurgical processing of EAFD can overcome the difficulties for leaching of zinc ferrite. / <p>QC 20160823</p>
16

Electron-transfer processes : the electrochemical reduction of N,N-dimethyl- and p-cyanobenzenesulfonamide

Santelices, Carlos G January 2011 (has links)
Digitized by Kansas Correctional Industries
17

Reductive Dehalogenation of Gas-phase Trichloroethylene using Heterogeneous Catalytic and Electrochemical Methods

Ju, Xiumin January 2005 (has links)
REDUCTIVE DEHALOGENATION OF GAS-PHASE TRICHLOROETHYLENE USING HETEROGENEOUS CATALYTIC AND ELECTROCHEMICAL METHODSXiumin Ju, Ph.D.The University of Arizona, 2005Director: Dr. Robert G. ArnoldThe first part of this work investigates catalytic hydrodechlorination (HDC) of gas-phase trichloroethylene (TCE) using 0.5 wt.% Pt/g-Al2O3 and 0.0025 wt.% Pt/SiO2 in packed-bed reactors. TCE was efficiently transformed on the platinum surface using H2 as reducing agent. The main products of the reaction were ethane and chloroethane. In the case of Pt/Al2O3, more than 94% TCE conversion efficiency was maintained for over 700 hours of operation at 100ºC at a residence time of 0.37 seconds. At 22ºC, severe catalyst deactivation was observed. Catalyst deactivation was attributed to coking and chlorine poisoning. A series of treatments including (i) hydrogen gas addition at high temperature (oxygen free) to remove chlorine and (ii) oxygen addition at 500ºC to remove coke were attempted to regenerate the deactivated catalyst. Only hydrogen treatment partially restored catalyst activity. When using Pt/SiO2, catalyst deactivation was severe even at 100ºC, probably due to low surface area of Pt and the silica support. Adding KOH to the packed Pt/SiO2 catalyst during (otherwise) normal operation slowed catalyst deactivation. Adding O2 to the influent improved catalyst activity and slowed deactivation.The second part of this research involves the destruction of gas-phase TCE using an electrochemical reactor similar in design of a polymer electrolyte membrane (PEM) fuel cell. With a proton-conducting membrane in the middle, the anode and cathode comprised of carbon cloth and carbon-black-supported Pt were hotpressed together to form a membrane electrode assembly (MEA). TCE contaminated gas streams were fed to the cathode side of the fuel cell, where TCE was reduced to ethane and hydrochloric acid. The results suggest that TCE reduction occurs via a catalytic reaction with atomic hydrogen that is reformed on the cathode's surface rather than an electrochemical reduction via direct electron transfer. Substantial conversion of TCE was obtained, even in the presence of molecular oxygen in the cathode chamber. The process was modeled successfully by conceptualizing the cathode chamber as a plug flow reactor with a continuous source of H2(g) emanating from the boundary.
18

A methodology for evaluating fleet implications of mission specification changes

Brett, Paul S. 12 January 2015 (has links)
Civil aviation has matured to become a vital piece of the global economy, providing the rapid movement of goods and people to all regions. This has already led to significant growth and expectations of further growth are on the rate of 5% per year. Given the high projected rate of growth, environmental consequences of commercial aviation are expected to rise. To mitigate the increase of noise and emissions, governing bodies such as ICAO and the FAA have established and are considering additional regulation of noise, NOₓ, and CO₂ while the European Union has integrated aviation into their Environmental Trading Scheme. The traditional response to new regulation is to integrate technologies into the aircraft to reduce environmental footprint. While these benefits are positive on the aircraft level, fleet growth is projected to outpace benefits provided by technology alone. To further reduce environmental footprint, a number of mitigation strategies are being explored to determine the impact. One of those strategies involves changing the mission specifications of today's aircraft by reducing range, speed, or payload in an effort to reduce fuel consumption and has been predominantly focused at the vehicle level. This research proposes an approach that evaluates mission specification changes from the aircraft design level up to the fleet level, forecasted into the future, to assess the impact over a number of metrics to fully understand the implications of mission specification changes. The methodology Mission Specifications and Fleet Implications Technique (MS-FIT) identifies stakeholder requirements that will be tracked at either the vehicle or fleet level and leverages them to build an environment that will allow joint evaluation to facilitate increased knowledge about the full implications of mission specification adoption. Additionally laid out is an approach on how to select prospective routes for intermediate stops based on fuel burn and operating cost considerations. Guidance is provided on how to filter down a list of candidate airports to those most viable as well as regions of the world most likely to benefit from intermediate stops. Three sample problems were used to demonstrate the viability of MS-FIT: cruise speed reduction, design mission range reduction, and the combination of speed and range reduction. Each problem was able to demonstrate different implications from the implementation of the different specification changes. Speed reduction can negatively impacts cost while range reduction has consequences to noise at the intermediate airports. The combination of the two draws in negative implications from both even though the environmental benefits are better. Finally, an analysis of some of the assumptions was conducted to examine the sensitivity to the results of speed and range reduction. These include variation in costs, reductions in annual utilization of aircraft, and variation in intermediate stop adoption. Speed reduction is strongly sensitive to increases in crew and maintenance rates while landing fees significantly eat into the benefits of range reduction and intermediate stops. Minor utilization reductions can significantly reduce the viability of speed reduction as the increase in capital costs offset all the savings from fuel reduction while range reduction is a little less sensitive. Intermediate stop variation does not eliminate the benefits of range reduction and even can provide cost savings depending on the design range of the reduced variant but it can have consequences to airport noise to higher traffic airports. With the proposed framework, additional information is available to fully understand the implications with respect to fuel burn, NOₓ emissions, operating cost, capital cost, noise, and safety. This can then inform decision makers on whether pursuing a particular mission specification strategy is advantageous or not.
19

The hydrogen reduction of silver, copper, nickel, cobolt and iron sulfides and the formation of filamentary metal

Cech, Robert Edward, January 1967 (has links)
Thesis (Ph. D.)--University of Wisconsin, 1967. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.
20

MIT International Motor Vehicle Programme Modularization and Outsourcing Project Preliminary Report of European Research Team

Warburton, Max, Sako, Mari 06 October 1999 (has links)
No Abstract Provided

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