19 resultados para Airlift Suspension Reactor

em Doria (National Library of Finland DSpace Services) - National Library of Finland, Finland


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Työn teoriaosassa esitetään kirjallisuudessa esiintyviä teoreettisia ja kokeellisia yhtälöitä nesteen nopeuden, kaasun tilavuusosuuden, painehäviön ja lämmönsiirron laskemiseksi. Lisäksi käsitellään airlift-reaktoreiden toimintaa, rakennetta ja teollisia sovelluksia, sekä sekoitusta ja geometrian vaikutusta airlift-reaktoreiden hydrodynaamisiin ominaisuuksiin. Kokeellisessa osassa kuvataan käytetty koelaitteisto ja mittausmenetelmät sekä esitetään saadut koetulokset. Koelaitteisto on viidellä nousuputkella varustettu ulkoisen kierron airlift-reaktori. Kokeellisessa osassa pyritään ratkaisemaan tällaisessa reaktorissa mahdollisesti esiintyviä ongelmia, kuten "slug flown" muodostuminen nousuputkissa sekä fluidien epätasainen jakautuminen nousuputkiin. Lisäksi tutkitaan erilaisten muuttujien, kuten kaasun tilavuusvirran, nesteen viskositeetin, suutinkoon ja nesteen jakoputken rakenteen, vaikutusta kaasun tilavuusosuuteen ja nesteen nopeuteen nousuputkissa. Nesteen nopeudet mitataan merkkiainemenetelmällä ja kaasun tilavuusosuudet manometrimenetelmällä. Lämmönsiirtoa tutkitaan mittaamalla lämpötilaeroja nousuputkissa NiCr-Ni –termoelementeillä. Mittaustulosten perusteella muokataan korrelaatiot kaasun tilavuusosuudelle ja nesteen tyhjäputkinopeudelle. Korrelaatioista lasketut tulokset sopivat kohtuullisen hyvin yhteen mitattujen tulosten kanssa. "Slug flown" ei todettu muodostuvan ongelmaksi 2.5 mPa s pienemmillä viskositeetin arvoilla 2 metriä pitkissä ja 19 mm halkaisijaltaan olevissa putkissa. Lisäksi todettiin, että kaasu- ja nestefaasien jakautumisongelmat voidaan ratkaista rakenteellisesti.

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Airlift reactors are pneumatically agitated reactors that have been widely used in chemical, petrochemical, and bioprocess industries, such as fermentation and wastewater treatment. Computational Fluid Dynamics (CFD) has become more popular approach for design, scale-up and performance evaluation of such reactors. In the present work numerical simulations for internal-loop airlift reactors were performed using the transient Eulerian model with CFD package, ANSYS Fluent 12.1. The turbulence in the liquid phase is described using κ- ε the model. Global hydrodynamic parameters like gas holdup, gas velocity and liquid velocity have been investigated for a range of superficial gas velocities, both with 2D and 3D simulations. Moreover, the study of geometry and scale influence on the reactor have been considered. The results suggest that both, geometry and scale have significant effects on the hydrodynamic parameters, which may have substantial effects on the reactor performance. Grid refinement and time-step size effect have been discussed. Numerical calculations with gas-liquid-solid three-phase flow system have been carried out to investigate the effect of solid loading, solid particle size and solid density on the hydrodynamic characteristics of internal loop airlift reactor with different superficial gas velocities. It was observed that averaged gas holdup is significantly decreased with increasing slurry concentration. Simulations show that the riser gas holdup decreases with increase in solid particle diameter. In addition, it was found that the averaged solid holdup increases in the riser section with the increase of solid density. These produced results reveal that CFD have excellent potential to simulate two-phase and three-phase flow system.

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Diplomityö käsittelee kiehutusvesilaitosten transienttien ja onnettomuuksien analysointia APROS-ohjelmiston avulla. Työ on tehty Teollisuuden Voima Oy:n (TVO) Olkiluoto 1 ja 2 laitosyksiköiden mallin pohjalta. Raportissa esitetään ohjelmiston käyttämiä yhtälöitäja laskentamalleja yleisellä tasolla. Työssä esitellään laitoksen yleispiirteet turvallisuustoimintoineen ja kuvataan ohjelmaan suureksi osaksi aiemmin luotua laskentamallia. Työssä on luetteloitu voimassa olevatlisensiointianalyysit, joiden joukosta on valittu laskentatapauksia ohjelmiston suorituskyvyn arviointia varten. Lisäksi työhön on valittu laskentatapauksia muilla kuin lisensointiin käytetyillä ohjelmilla lasketuista analyyseistä. Lisäksi on suoritettu vertailulaskuja konservatiivisen ja realistisen mallin erojen esille saamiseksi. Laskentatapauksia ovat mm. ylipainetransientti, jäähdytteen menetysonnettomuus ja oletettavissa oleva käyttöhäiriö, jossa pikasulku ei toimi (ATWS). Diplomityön edetessä laitosmallia on kehitetty edelleen lisäämällä joitakin järjestelmiä ja tarkentamalla joidenkin komponenttien kuvausta. Työssä ilmeni, että APROS soveltuu jäähdytteenmenetysonnettomuuden ja suojarakennuksen yhtäaikaiseen analyysiin. APROS.n vaste nopeisiin transientteihin jäi kuitenkin vertailutasosta. Tämän työn perusteella APROS-mallia kehitys jatkuu edelleen siten, että se soveltuisi entistä paremmin myös nopeiden transienttien ja ATWS-tilanteiden kuvaamiseen. Työssä olevaa lisensointianalyysien kuvausta tullaan käyttämään hyväksi selvitettäessä laitoksen turvallisuuden väliarviossa tarvittavien analyysien määrää ja laatua. Nyt saatuja kokemuksia voidaan hyödyntää myös mahdollisen kolmiulotteisen sydänmallin hankinnassa APROS-ohjelmistoon. Tässä diplomityössä esitettyjä parannuksia voidaan käyttää hyväksi SAFIRtutkimusohjelman hankkeiden suunnittelussa.

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Gas-liquid mass transfer is an important issue in the design and operation of many chemical unit operations. Despite its importance, the evaluation of gas-liquid mass transfer is not straightforward due to the complex nature of the phenomena involved. In this thesis gas-liquid mass transfer was evaluated in three different gas-liquid reactors in a traditional way by measuring the volumetric mass transfer coefficient (kLa). The studied reactors were a bubble column with a T-junction two-phase nozzle for gas dispersion, an industrial scale bubble column reactor for the oxidation of tetrahydroanthrahydroquinone and a concurrent downflow structured bed.The main drawback of this approach is that the obtained correlations give only the average volumetric mass transfer coefficient, which is dependent on average conditions. Moreover, the obtained correlations are valid only for the studied geometry and for the chemical system used in the measurements. In principle, a more fundamental approach is to estimate the interfacial area available for mass transfer from bubble size distributions obtained by solution of population balance equations. This approach has been used in this thesis by developing a population balance model for a bubble column together with phenomenological models for bubble breakage and coalescence. The parameters of the bubble breakage rate and coalescence rate models were estimated by comparing the measured and calculated bubble sizes. The coalescence models always have at least one experimental parameter. This is because the bubble coalescence depends on liquid composition in a way which is difficult to evaluate using known physical properties. The coalescence properties of some model solutions were evaluated by measuring the time that a bubble rests at the free liquid-gas interface before coalescing (the so-calledpersistence time or rest time). The measured persistence times range from 10 msup to 15 s depending on the solution. The coalescence was never found to be instantaneous. The bubble oscillates up and down at the interface at least a coupleof times before coalescence takes place. The measured persistence times were compared to coalescence times obtained by parameter fitting using measured bubble size distributions in a bubble column and a bubble column population balance model. For short persistence times, the persistence and coalescence times are in good agreement. For longer persistence times, however, the persistence times are at least an order of magnitude longer than the corresponding coalescence times from parameter fitting. This discrepancy may be attributed to the uncertainties concerning the estimation of energy dissipation rates, collision rates and mechanisms and contact times of the bubbles.

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The purpose of this study was to investigate some important features of granular flows and suspension flows by computational simulation methods. Granular materials have been considered as an independent state ofmatter because of their complex behaviors. They sometimes behave like a solid, sometimes like a fluid, and sometimes can contain both phases in equilibrium. The computer simulation of dense shear granular flows of monodisperse, spherical particles shows that the collisional model of contacts yields the coexistence of solid and fluid phases while the frictional model represents a uniform flow of fluid phase. However, a comparison between the stress signals from the simulations and experiments revealed that the collisional model would result a proper match with the experimental evidences. Although the effect of gravity is found to beimportant in sedimentation of solid part, the stick-slip behavior associated with the collisional model looks more similar to that of experiments. The mathematical formulations based on the kinetic theory have been derived for the moderatesolid volume fractions with the assumption of the homogeneity of flow. In orderto make some simulations which can provide such an ideal flow, the simulation of unbounded granular shear flows was performed. Therefore, the homogeneous flow properties could be achieved in the moderate solid volume fractions. A new algorithm, namely the nonequilibrium approach was introduced to show the features of self-diffusion in the granular flows. Using this algorithm a one way flow can beextracted from the entire flow, which not only provides a straightforward calculation of self-diffusion coefficient but also can qualitatively determine the deviation of self-diffusion from the linear law at some regions nearby the wall inbounded flows. Anyhow, the average lateral self-diffusion coefficient, which was calculated by the aforementioned method, showed a desirable agreement with thepredictions of kinetic theory formulation. In the continuation of computer simulation of shear granular flows, some numerical and theoretical investigations were carried out on mass transfer and particle interactions in particulate flows. In this context, the boundary element method and its combination with the spectral method using the special capabilities of wavelets have been introduced as theefficient numerical methods to solve the governing equations of mass transfer in particulate flows. A theoretical formulation of fluid dispersivity in suspension flows revealed that the fluid dispersivity depends upon the fluid properties and particle parameters as well as the fluid-particle and particle-particle interactions.

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Paperin ja kartongin kierrätys lisääntyy taloudellisten intressien ja ympäristöhygieenisten tavoitteiden takia jatkuvasti. Lisääntyvän kierrätyksen myötä myös paperin ja kartongin epäpuhtauksien määrä kasvaa, mikä huonontaa kierrätysraaka-aineen laatua. Tämän työn tarkoituksena on antaa perustietoa eräästä kartongin päällystyksessä käytettävästä hydrofobisesta materiaalista, epäpuhtaan kartongin kierrätyksestä sekä ongelmista, joita epäpuhtaan kartongin kierrätyksestä syntyy. Kierrätyskuidun fraktiointi on yksinkertainen prosessi aallotuskartongin, testilainerin ja taivekartongin valmistuksessa. Kierrätysprosessin ensisijaisia tehtäviä ovat kuidutus ja epäpuhtauksien poisto sekä näiden epäpuhtauksien vaikutusten eliminointi, jotta kierrätysmassan laatuvaatimukset täyttyvät. Lisääntynyt epäpuhtauksien määrä raaka-aineessa asettaa vaatimuksia lajitteluprosessin kehittämiseksi. Nykyaikaisilla kierrätyslaitoksilla ei pystytä käsittelemään ylettömiä määriä epäpuhtauksia. Epäpuhtaudet aiheuttavat ongelmia ajettavuuteen ja heikentävät tuotteen laatua kierrätysprosessissa. Epäpuhtauksien poistoon on olemassa useita teknisiä ratkaisuja, mutta minkään niistä ei ole todettu täysin poistavan kaikkia ongelmia. Työn kokeellisessa osassa kartongin päällystykseen käytettävää hydrofobista materiaalia analysoitiin erilaisin menetelmin. Tutkittiin myös erilaisten olosuhteiden vaikutusta tämän materiaalin poistoon.

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The literature part of the work reviews overall Fischer-Tropsch process, Fischer-Tropsch reactors and catalysts. Fundamentals of Fischer-Tropsch modeling are also presented. The emphasis is on the reactor unit. Comparison of the reactors and the catalysts is carried out to choose the suitable reactor setup for the modeling work. The effects of the operation conditions are also investigated. Slurry bubble column reactor model operating with cobalt catalyst is developed by taking into account the mass transfer of the reacting components (CO and H2) and the consumption of the reactants in the liquid phase. The effect of hydrostatic pressure and the change in total mole flow rate in gas phase are taken into account in calculation of the solubilities. The hydrodynamics, reaction kinetics and product composition are determined according to literature. The cooling system and furthermore the required heat transfer area and number of cooling tubes are also determined. The model is implemented in Matlab software. Commercial scale reactor setup is modeled and the behavior of the model is investigated. The possible inaccuraries are evaluated and the suggestions for the future work are presented. The model is also integrated to Aspen Plus process simulation software, which enables the usage of the model in more extensive Fischer-Tropsch process simulations. Commercial scale reactor of diameter of 7 m and height of 30 m was modeled. The capacity of the reactor was calculated to be about 9 800 barrels/day with CO conversion of 75 %. The behavior of the model was realistic and results were in the right range. The highest uncertainty to model was estimated to be caused by the determination of the kinetic rate.

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This thesis gathers knowledge about ongoing high-temperature reactor projects around the world. Methods for calculating coolant flow and heat transfer inside a pebble-bed reactor core are also developed. The thesis begins with the introduction of high-temperature reactors including the current state of the technology. Process heat applications that could use the heat from a high-temperature reactor are also introduced. A suitable reactor design with data available in literature is selected for the calculation part of the thesis. Commercial computational fluid dynamics software Fluent is used for the calculations. The pebble-bed is approximated as a packed-bed, which causes sink terms to the momentum equations of the gas flowing through it. A position dependent value is used for the packing fraction. Two different models are used to calculate heat transfer. First a local thermal equilibrium is assumed between the gas and solid phases and a single energy equation is used. In the second approach, separate energy equations are used for the phases. Information about steady state flow behavior, pressure loss, and temperature distribution in the core is obtained as results of the calculations. The effect of inlet mass flow rate to pressure loss is also investigated. Data found in literature and the results correspond each other quite well, considered the amount of simplifications in the calculations. The models developed in this thesis can be used to solve coolant flow and heat transfer in a pebble-bed reactor, although additional development and model validation is needed for better accuracy and reliability.

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In this thesis concurrent communication event handling is implemented using thread pool approach. Concurrent events are handled with a Reactor design pattern and multithreading is implemented using a Leader/Followers design pattern. Main focus is to evaluate behaviour of implemented model by different numbers of concurrent connections and amount of used threads. Furthermore, model feasibility in a PeerHood middleware is evaluated. Implemented model is evaluated with created test environment which enables concurrent message sending from multiple connections to the system under test. Messages round trip times are measured in the tester application. In the evaluation processing delay into system is simulated and influence of delay to the average round trip time is analysed.

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In the theoretical part, the different polymerisation catalysts are introduced and the phenomena related to mixing in the stirred tank reactor are presented. Also the advantages and challenges related to scale-up are discussed. The aim of the applied part was to design and implement an intermediate-sized reactor useful for scale-up studies. The reactor setting was tested making one batch of Ziegler–Natta polypropylene catalyst. The catalyst preparation with a designed equipment setting succeeded and the catalyst was analysed. The analyses of the catalyst were done, because the properties of the catalyst were compared to the normal properties of Ziegler–Natta polypropylene catalyst. The total titanium content of the catalyst was slightly higher than in normal Ziegler–Natta polypropylene catalyst, but the magnesium and aluminium content of the catalyst were in the normal level. By adjusting the siphonation tube and adding one washing step the titanium content of the catalyst could be decreased. The particle size of the catalyst was small, but the activity was in a normal range. The size of the catalyst particles could be increased by decreasing the stirring speed. During the test run, it was noticed that some improvements for the designed equipment setting could be done. For example more valves for the chemical feed line need to be added to ensure inert conditions during the catalyst preparation. Also nitrogen for the reactor needs to separate from other nitrogen line. With this change the pressure in the reactor can be kept as desired during the catalyst preparation. The proposals for improvements are presented in the applied part. After these improvements are done, the equipment setting is ready for start-up. The computational fluid dynamics model for the designed reactor was provided by cooperation with Lappeenranta University of Technology. The experiments showed that for adequate mixing with one impeller, stirring speed of 600 rpm is needed. The computational fluid dynamics model with two impellers showed that there was no difference in the mixing efficiency if the upper impeller were pumping downwards or upwards.

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This Master´s thesis investigates the performance of the Olkiluoto 1 and 2 APROS model in case of fast transients. The thesis includes a general description of the Olkiluoto 1 and 2 nuclear power plants and of the most important safety systems. The theoretical background of the APROS code as well as the scope and the content of the Olkiluoto 1 and 2 APROS model are also described. The event sequences of the anticipated operation transients considered in the thesis are presented in detail as they will form the basis for the analysis of the APROS calculation results. The calculated fast operational transient situations comprise loss-of-load cases and two cases related to a inadvertent closure of one main steam isolation valve. As part of the thesis work, the inaccurate initial data values found in the original 1-D reactor core model were corrected. The input data needed for the creation of a more accurate 3-D core model were defined. The analysis of the APROS calculation results showed that while the main results were in good accordance with the measured plant data, also differences were detected. These differences were found to be caused by deficiencies and uncertainties related to the calculation model. According to the results the reactor core and the feedwater systems cause most of the differences between the calculated and measured values. Based on these findings, it will be possible to develop the APROS model further to make it a reliable and accurate tool for the analysis of the operational transients and possible plant modifications.

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Tutkimuksessa tarkasteltiin vuonna 2009 toimintansa käynnistävää kansainvälistä ilmakuljetusyhteistyöhankketta Strategic Airlift Capability (SAC) puolustusvoimien kolmen päätehtävän näkökulmasta. Strategic Airlift Capability on 10 Nato-maan sekä Ruotsin ja Suomen välinen yhteistyösopimus, jolla varmistetaan raskas ilmakuljetuskyky jäsenmaiden käyttöön seuraavaksi 26 vuodeksi. Raskas ilmakuljetuskyky tuotetaan kolmella SAC-järjestelyn jäsenmaiden yhteisesti omistamalla Boeing C-17 Globemaster III strategisella kuljetuslentokoneella. Tutkimuksen päätutkimuskysymys oli seuraava: Mitkä ovat keskeisimmät SAC-järjestelyn mahdollisuudet ja haasteet puolustusvoimien kolmen päätehtävän näkökulmasta ja mitä toimenpiteitä nämä edellyttävät puolustusvoimilta? Tutkimus oli luonteeltaan kvalitatiivinen. Tutkimusmenetelmänä käytettiin logistiikan tutkimukseen hyvin soveltuvaa abduktio-menetelmää, jossa teorian kehittäminen ja empiirisen tutkimusaineiston analysointi ja testaus vuorottelevat. Tutkimusasetelma oli hermeneuttinen. Tutkimusaineiston analysoinnissa käytettiin menetelmänä aineistopohjaista sisällönanalyysiä. Kahdella Delfoi-menetelmään perustuvalla kyselyllä selvitettiin puolustushallinnon sekä muiden hallinnonalojen ja siviilitoimijoiden näkemyksiä SAC-järjestelystä. Tutkimuksen yhtenä menetelmänä oli SWOT-analyysi.

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The thesis is related to the topic of image-based characterization of fibers in pulp suspension during the papermaking process. Papermaking industry is focusing on process control optimization and automatization, which makes it possible to manufacture highquality products in a resource-efficient way. Being a part of the process control, pulp suspension analysis allows to predict and modify properties of the end product. This work is a part of the tree species identification task and focuses on analysis of fiber parameters in the pulp suspension at the wet stage of paper production. The existing machine vision methods for pulp characterization were investigated, and a method exploiting direction sensitive filtering, non-maximum suppression, hysteresis thresholding, tensor voting, and curve extraction from tensor maps was developed. Application of the method to the microscopic grayscale pulp images made it possible to detect curves corresponding to fibers in the pulp image and to compute their morphological characteristics. Performance of the method was evaluated based on the manually produced ground truth data. An accuracy of fiber characteristics estimation, including length, width, and curvature, for the acacia pulp images was found to be 84, 85, and 60% correspondingly.

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Microreactors have proven to be versatile tools for process intensification. Over recent decades, they have increasingly been used for product and process development in chemical industries. Enhanced heat and mass transfer in the reactors due to the extremely high surfacearea- to-volume ratio and interfacial area allow chemical processes to be operated at extreme conditions. Safety is improved by the small holdup volume of the reactors and effective control of pressure and temperature. Hydrogen peroxide is a powerful green oxidant that is used in a wide range of industries. Reduction and auto-oxidation of anthraquinones is currently the main process for hydrogen peroxide production. Direct synthesis is a green alternative and has potential for on-site production. However, there are two limitations: safety concerns because of the explosive gas mixture produced and low selectivity of the process. The aim of this thesis was to develop a process for direct synthesis of hydrogen peroxide utilizing microreactor technology. Experimental and numerical approaches were applied for development of the microreactor. Development of a novel microreactor was commenced by studying the hydrodynamics and mass transfer in prototype microreactor plates. The prototypes were designed and fabricated with the assistance of CFD modeling to optimize the shape and size of the microstructure. Empirical correlations for the mass transfer coefficient were derived. The pressure drop in micro T-mixers was investigated experimentally and numerically. Correlations describing the friction factor for different flow regimes were developed and predicted values were in good agreement with experimental results. Experimental studies were conducted to develop a highly active and selective catalyst with a proper form for the microreactor. Pd catalysts supported on activated carbon cloths were prepared by different treatments during the catalyst preparation. A variety of characterization methods were used for catalyst investigation. The surface chemistry of the support and the oxidation state of the metallic phase in the catalyst play important roles in catalyst activity and selectivity for the direct synthesis. The direct synthesis of hydrogen peroxide was investigated in a bench-scale continuous process using the novel microreactor developed. The microreactor was fabricated based on the hydrodynamic and mass transfer studies and provided a high interfacial area and high mass transfer coefficient. The catalysts were prepared under optimum treatment conditions. The direct synthesis was conducted at various conditions. The thesis represents a step towards a commercially viable direct synthesis. The focus is on the two main challenges: mitigating the safety problem by utilization of microprocess technology and improving the selectivity by catalyst development.

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The direct synthesis from hydrogen and oxygen is a green alternative for production of hydrogen peroxide. However, this process suffers from two challenges. Firstly, mixtures of hydrogen and oxygen are explosive over a wide range of concentrations (4-94% H2 in O2). Secondly, the catalytic reaction of hydrogen and oxygen involves several reaction pathways, many of them resulting in water production and therfore decreasing selectivity. The present work deals with these two challenges. The safety problem was dealed by employing a novel microstructured reactor. Selectivity of the reaction was highly improved by development a set of new catalysts. The final goal was to develop an effective and safe continuous process for direct synthesis of hydrogen peroxide from H2 and O2. Activated carbon cloth and Sibunit were examined as the catalysts’ supports. Palladium and gold monometallic and palladium-gold bimetallic catalysts were thoroughly investigated by numerous kinetic experiments performed in a tailored batch reactor and several catalyst charachterization methods. A complete set of data for direct synthesis of H2O2 and its catalytic decomposition and hydrogenation was obtained. These data were used to assess factors influencing selectivity and activity of the catalysts in direct synthesis of H2O2 as well as its decomposition and hydrogenation. A novel microstructured reactor was developed based on hydrodynamics and mass transfer studies in prototype microstractural plates. The shape and the size of the structural elements in the microreactor plate were optimized in a way to get high gas-liquid interfacial area and gas-liquid mass transfer. Finally, empirical correlations for the volumetric mass transfer coefficient were derived. A bench-scale continuous process was developed by using the novel microstructral plate reactor. A series of kinetic experiments were performed to investigate the effects of the gas and the liquid feed rates and their ratio, the amount of the catalyst, the gas feed composition and pressure on the final rate of H2O2 production and selectivity.