1,720,954 research outputs found
Pressurized fluidized bed combustion
Get PDFTässä kandidaatintyönä tehdyssä kirjallisuuskatsauksessa aiheena on paineistettu leijukerrospoltto. Tavoitteena on selvittää, miksi paineistettu leijukerrospoltto ei ole edennyt kaupalliselle tasolle ja mitkä ovat paineistetun leijukerrospolton tulevaisuuden näkymät. Työ painottuu ensimmäisen sukupolven paineistettuun leijukerrospolttoon.
Erityisesti 1970-luvun öljykriisin jälkeen haluttiin kehittää uusia tuotantotapoja energian tuottamiseksi. Haluttiin kehittää tuotantolaitoksia, joissa voitaisiin hyödyntää monipuolisesti eri polttoaineita. Käytössä olleet tuotantolaitokset olivat vanhenemassa. Uutta kapasiteettia energian tuottamiseksi oli tarvetta rakentaa. Yksi tuolloin kehitettävistä uusista tuotantotavoista oli paineistettu leijukerrospoltto.
Suurin ero ilmanpaineessa toimivaan leijukerrospolttoon on, että paineistetussa leijukerrospoltossa (PFBC) polttokammio on painesäiliön sisällä ja prosessi toteutetaan ylipaineessa. Polttoaineena PFBC- laitoksissa käytetään kiinteitä polttoaineita. Paineistettua leijukerrospolttoa kehitettiin paljon, kunnes vuosituhannen vaihteessa kehitys romahti selvästi. Kilpailevat tuotantotavat, liian korkeat päästöt, korkea hinta sekä savukaasujen riittämättömästä puhdistuksesta johtuva kaasuturbiinin eroosio ja korroosio ovat syitä kaupallistumisen ongelmille.
Tällä hetkellä käytössä olevia PFBC- laitoksia on maailmalla kolme. Markkinanäkymät ovat huonot. Kehitystä on jatkettu tavoittelemalla korkeampaa hyötysuhdetta. Toisen sukupolven tekniikoilla pyritään nostamaan kaasuturbiinille menevien savukaasujen lämpötilaa. Prosessin tehostamiseksi on ehdotettu esimerkiksi Topping-cyclea, osittaiskaasutusta ja osittaiskaasutuksen sekä hiiltojäännöksen loppuunpolttoa ilmanpaineisessa kattilassa.The topic of this bachelor’s thesis, written as a literature review is pressurized fluidized bed combustion. The aim of the thesis is to find out why pressurized fluidized bed combustion has not progressed to a commercial level and what are the prospects of pressurized fluidized bed combustion. The thesis focuses on the first-generation technique of pressurized fluidized bed combustion.
There was a desire to develop new production methods to produce energy especially after the oil crisis of the 1970s. The goal was to develop production facilities where different fuels could be used versatilely. The production plants in use were becoming obsolete. There was a need for new capacity of producing energy. One of the new methods being developed at the time was pressurized fluidized bed combustion.
The biggest difference between pressurized fluidized bed combustion (PFBC) and fluidized bed combustion operating at atmospheric pressure is that in PFBC the combustion chamber is inside of a pressure tank and the process is carried out under excess pressure. Solid fuels are used as fuel in PFBC plants. Pressurized fluidized bed combustion was developed considerably until the turn of the millennium, when the development clearly collapsed. Competing production methods, too high emissions, high price as well as the erosion and corrosion of the gas turbine due to insufficient flue gas cleaning are considered the causes of the problems in commercialization.
There are only three PFBC plants in use in the world currently. The market outlook is bad. Development has been continued by aiming for a higher efficiency. The second-generation techniques are being used with the intent of raising the temperature of the flue gases going to the gas turbine. To make this process more efficient, there are ideas such as topping-cycle, partial gasification and combustion of the partial gasification and coal residue in an atmospheric boiler, that have been proposed
Kaksifaasisen virtauksen laskennallinen mallintaminen ja suotuisan kaasunpoistoreiän sijainnin löytäminen keskipakopumpuissa
No full textThis thesis studied the behaviour of a pulp–air mixture in centrifugal pump using computational fluid dynamics. The objective was to find suitable modelling methods for simulating gas accumulation and evaluating the favorable placement of degassing holes. Two simulation approaches were tested: the Lagrangian–Eulerian discrete phase model and a full Eulerian multiphase model. The discrete phase model was unable to predict the gas accumulation, as all injected gas exited through the pump outlet. The Eulerian model, on the other hand, was able to predict pump performance near the best efficiency point with reasonable accuracy.
The simulations showed that gas accumulation occurred mainly on the pressure side of the impeller blades, and the regions of highest gas concentration were identified as potential locations for degassing holes. It was also found that increasing the drag coefficient modification factor reduced gas separation but did not significantly affect the simulated pump head, efficiency, or power. However, the lack of experimental data on gas bubble size and inlet gas volume fraction limited the validation of the results. The study demonstrated that CFD can be a useful tool for modelling non-Newtonian two-phase flow in pumps and for supporting the design of degassing hole placement. The results offered practical insight for improving the performance of pumps handling gas–pulp suspensions.Tässä työssä tutkittiin sellumassasta ja ilmasta koostuvan kaksifaasiseoksen käyttäytymistä keskipakopumpussa käyttäen numeerista virtauslaskentaa (CFD). Työn tavoitteena oli löytää soveltuvia mallinnusmenetelmiä kaasun kertymisen simuloimiseksi sekä arvioida kaasunpoistoreikien sopivaa sijaintia. Työssä testattiin kahta simulaatiomenetelmää: Lagrangian–Eulerian diskreettiä faasimallia sekä täysin Eulerin menetelmään perustuvaa monifaasimallia. Diskreetti faasimalli ei onnistunut tuottamaan realistista kaasun erottumista, sillä kaikki syötetty kaasu poistui pumpun ulostulon kautta. Eulerian malli sen sijaan pystyi ennustamaan pumpun suorituskyvyn parhaan hyötysuhteen pisteen läheisyydessä kohtuullisen tarkasti.
Simulaatiot osoittivat, että kaasu kertyi pääasiassa juoksupyörän lapojen painepuolelle, ja suurimman kaasupitoisuuden alueet tunnistettiin mahdollisiksi kaasunpoistoreikien sijaintikohdiksi. Lisäksi havaittiin, että vastuskertoimen säätökertointa kasvattamalla kaasun erottuminen väheni, mutta vaikutus pumpun nostokorkeuteen, hyötysuhteeseen ja tehoon oli vähäinen. Tulosten validointia rajoitti kokeellisen tiedon puute kuplakokojakaumasta ja sisäänmenon kaasutilavuusosuudesta. Tutkimus osoitti, että CFD on käyttökelpoinen työkalu sellu-ilma virtauksen mallintamiseen pumpuissa ja kaasunpoistoreiän sijoittelun suunnittelun tukena. Tulokset tarjosivat käytännön näkökulmaa pumppujen suorituskyvyn parantamiseen kaasuja sisältävien kuitususpensioiden käsittelyssä
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
