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Simulation of flow conditions in nuclear power plant reactor pressure vessel lower plenum experimental facility
Blaž Kamenik, 2019, magistrsko delo

Opis: The flow conditions during the experiment LIVE2D on reactor core melt behaviour in the lower plenum of a reactor pressure vessel, performed at the Karlsruhe Institute of Technology (Germany), were simulated with a Computational Fluid Dynamics computer code. In this hypothetical severe accident scenario in a pressurized water reactor nuclear power plant, the melt is divided into an oxidic layer and a metallic layer on top of it, and the oxidic layer is volumetrically heated due to decay heat. In the experiment, oil and salt were used as simulant materials for metallic and oxidic melt, respectively. The main goal of performed simulations was to investigate the so-called “focusing effect”, where a thin layer of the reactor vessel steel wall is exposed to high heat flux. Due to the length of experiment, which exceeds 100 hours, only intervals of the melt behaviour were simulated. Four cases were simulated. The first case investigated different boundary conditions for the oil layer behaviour for layer thickness 35 mm. The second case investigated the same conditions with added modelling of the reactor vessel steel wall and salt crust from the lower layer. The third case used similar modelling as the second case to investigate the oil layer behaviour for layer thickness 75 mm. The fourth case investigated both salt and oil layers for oil layer thickness 75 mm. Different analytical and numerical calculations were performed to determine heat losses from simulant liquids to the surroundings, which played an important part in the experiment.
Ključne besede: nuclear power plant, severe accident, reactor core melt, lower plenum, heat flux focusing effect
Objavljeno: 17.09.2019; Ogledov: 361; Prenosov: 62
.pdf Celotno besedilo (6,83 MB)

Scale-up research in a dual fluidized bed gasification process
Miha Narobe, Janvit Golob, Jernej Mele, Mihael Sekavčnik, Andrej Senegačnik, Dušan Klinar, 2015, izvirni znanstveni članek

Opis: A successful co-gasification of plastics and biomass was achieved in the 100 kW dual fluidized bed (DFB) gasification pilot plant. The results of a pilot plant experiment were used as a sound basis for scale-up prediction to 750 kW semiindustrial DFB plant. By an eightfold increase of mass and heat flows a rather simplified co-gasification process was predicted. Namely, the losses occurring in gasification plants are expected to be relatively smaller in larger plants. The effect of decreased losses was studied with an equilibrium model. Three different situations were simulated with the following fixed values of losses: 70 kW, 115 kW and 160 kW. The model showed an increase in fuel conversion when losses were reduced.
Ključne besede: gasification, simulation, dual fluidized bed reactor, scale up
Objavljeno: 25.08.2017; Ogledov: 487; Prenosov: 235
.pdf Celotno besedilo (1,09 MB)
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Pressure stability of lipases and their use in different systems
Maja Leitgeb, Željko Knez, 2001, izvirni znanstveni članek

Opis: For the investigation of the solvent impact on the enzymes, lipases from different sources (Pseudomonas fluorescences, Rhizopus javanicus, Rhizopus niveus, Candida rugose and Porcine pancreas) were used. Stability and activity of these lipases in aqueous medium in supercritical $CO_2$ and liquid propane at 100 bar and 40°C were studied. On the basis of previous results lipases were used for their application in two different systems. The application of the polysulphone membrane in the continuous stirred tank membrane reactor was studied on the model system of the hydrolysis of oleyl oleate in propane at high pressure. As a catalyst the Candida rugosa lipase was used. The next utilization of lipases was the use of on silica arerogel self-immobilized lipase from Porcine pancreas as catalyst for esterification reaction in near-critical propane at 40°C and 100 bar.
Ključne besede: chemical processing, supercritical fluids, lipases, enzyme stability, high pressure membrane reactor
Objavljeno: 10.07.2015; Ogledov: 783; Prenosov: 92
.pdf Celotno besedilo (608,04 KB)
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Optimal reactor systems for Van de Vusse reaction scheme with multicomponent feed
Duško Bikić, Branko Butinar, Peter Glavič, 2002, izvirni znanstveni članek

Opis: In the present paper, product yield in the Van de Vusse reaction scheme with multicomponent feed has been studied. The optimal reactor structures have been found by investigating optimality conditions. The optimum product yield and criteria for selecting an appropriate reaction system have been obtained as functions of kinetic parameters. On the basis of optimization results the parameter space has been classified into regions indicating optimum reactor structure.
Ključne besede: optimal reactor structure, optimum product yield, multicomponent feed, parameter space, Van der Vusse reaction
Objavljeno: 01.06.2012; Ogledov: 1725; Prenosov: 92
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An integrated strategy for the hierarchical multilevel MINLP synthesis of overall process flowsheets using the combined synthesis/analysis approach
Nataša Iršič Bedenik, Bojan Pahor, Zdravko Kravanja, 2004, izvirni znanstveni članek

Opis: This paper describes an integrated strategy for a hierarchical multilevel mixed-integer nonlinear programming (MINLP) synthesis of overall process schemes using a combined synthesis/analysis approach. The synthesis is carried out by multilevel-hierarchical MINLP optimization of the flexible superstructure, whilst the analysis is performed in the economic attainable region (EAR). The role of the MINLP synthesis step is to obtain a feasible and optimal solution of the multi-D process problem, and the role of the subsequent EAR analysis step is to verify the MINLP solution and in the feedback loop to propose any profitable superstructure modifications for the next MINLP. The main objective of the integrated synthesis is to exploit the interactions between the reactor network, separator network and the remaining part of the heat/energy integrated process scheme.
Ključne besede: multilevel MINLP, MINLP synthesis, attainable region, economic attainable region, concentration attainable region, continous stirred tank reactor, plug flow reactor, recycle reactor, nonlinear programming, mixed integer nonlinear programme
Objavljeno: 01.06.2012; Ogledov: 2001; Prenosov: 87
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Microcrack initiation and growth in heat-risistant 15Kh2MFA steel under cyclic loading
P. Yasniy, V.B. Hlado, V. Hutsaylyuk, Tomaž Vuherer, 2005, izvirni znanstveni članek

Opis: This paper presents the results of investigation of a nuclear reactor pressurevessel steel 15Kh2MFA of two strength levels under cyclic loading. Themechanism of microcrack formation on the surface and in the bulk of 15Kh2MFA steel under cyclic deformation was investigated. Analysis of the specimen surfaces has shown that microcracks are caused by cyclic sliding in grains most favourably oriented with respect to the direction of the maximum shear stresses. Transmission electron microscope investigations show that microcracks in the material inside the grains are formed mainly along the band-type dislocation structure parallel to the dislocation subboundary. During cyclic deformation, the dislocation density on the subboundaries increases, in the local areas the dislocation density becomes limiting and it reaches the plasticity limit and causes microcrack formation. The interrelation of the average length of microcracks and their surface density with the energy density of inelastic deformation has been found.
Ključne besede: material testing, nuclear reactor, pressure vessel, cyclic loading, cyclic deformation, dislocation structure, fatigue crack growth, TEM, fracture mechanics
Objavljeno: 01.06.2012; Ogledov: 1194; Prenosov: 27
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Development of a mathematical model for the dynamic optimization of batch reactors, and MINLP synthesis of plug-flow reactors in complex networks
Marcel Ropotar, Zdravko Kravanja, 2007, izvirni znanstveni članek

Opis: This paper describes the development of a robust and efficient reactor model suitable for representing batch and plugflow reactors (PFRs) in different applications. These would range from the nonlinear (NLP) dynamic optimization of a stand-alone batch reactor up to the mixed-integer nonlinear (MINLP) synthesis of a complex reactor network in overall process schemes. Different schemes for the Orthogonal Collocation on Finite Element (OCFE) and various model formulations, in the case of MINLP model, were studied in order to increase the robustness and efficiency of the model. A deterministic model for known kinetics was obtained for batch and PFR reactors and extended for uncertainties in process parameters and reaction kinetics when the kinetics is unknown. Different variations of the developed model were applied to certain problems, as examples. The first motivating example was the dynamic optimization of batch reactor and the second the MINLP synthesis of a process scheme for the production of allyl chloride. The NLP version of the model with moving finite elements was found to be the most efficient for representing a batch reactor in the dynamic optimization example, and PFR trains in the process synthesis example.
Ključne besede: batch reactor, orthogonal collocation, off-line optimization, on-line optimization, flexibility, uncertainty
Objavljeno: 31.05.2012; Ogledov: 1625; Prenosov: 48
.pdf Celotno besedilo (520,87 KB)
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Enzyme-catalyzed reactions in different types of high-pressure enzymatic reactors
Mateja Primožič, Maja Leitgeb, Muzafera Paljevac, Željko Knez, 2006, izvirni znanstveni članek

Opis: The enzyme-catalyzed hydrolysis of carboxy-methyl cellulose (CMC) was performed in three different types of reactors; in a batch stirred-tank reactor (BSTR) operating at atmospheric pressure, in a high-pressure batch stirred-tank reactor (HP BSTR) and in a high-pressure continuous tubular-membrane reactor (HP CTMR). In the high-pressure reactors aqueous SC C02 was used as the reaction medium. The aim of our research was optimization of the reaction parameters for reaction performance. All the reactions were catalyzed by cellulase from Humicola insolens. Glucose production in the high-pressure batch stirred-tank reactor was faster than in the BSTR at atmospheric pressure. The optimal temperature for the reaction performed in the BSTR at atmospheric pressure was 30°C, while the optimal temperature for the reaction performed in SC C02 was 32°C. The influence of the application of tubular ceramic membranes in the high-pressure reaction system was studied on the model reaction of CMC hydrolysis at atmospheric pressure and in SC C02. The reaction was catalyzed by cellulase from Humicola insolens covalently linked to the surface of the ceramic membrane. The hydrolysis of CMC in SC C02 and at atmospheric pressure was performed for a long time period. The reaction carried out in SC C02 was more productive than the reaction performed at atmospheric pressure.
Ključne besede: chemical processing, enzymatic reaction, cellulase, supercritical carbon dioxide, high-pressure batch reactor, high-pressure membrane reactor
Objavljeno: 31.05.2012; Ogledov: 1415; Prenosov: 252
.pdf Celotno besedilo (454,51 KB)
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