1,721,161 research outputs found
Micro gas turbine combustor performances in CO2/O2 oxidizer atmosphere
No full textIn fossil fuel energy power plants the oxy-combustion technique, is one of the possible approaches to the problem of greenhouse gases emissions, through the CO2 capture and subsequent storage. It is realized using recirculated flue gas enriched with oxygen as oxidizer and it is suitable more than other techniques to retrofit existing plants. The commercial gas turbine combustors currently available are however designed and optimized for air combustion. In this work, through a series of CFD simulations, a typical commercial micro turbine burner has been tested in oxy-combustion conditions, in order to verify the performances. Through this study it has been shown how these class of combustors cannot be used in an optimal way in terms of efficiency, pollutant emissions and oxygen consumption. Some possible solutions have been also proposed
Nuove e antiche schiavitù. Atti del convegno internazionale Chieti università "G.D'Annunzio", 4-6 marzo 2008
No full textModeling and simulation of an oxygen-blown bubbling fluidized bed gasifier using the Computational Particle- Fluid Dynamics (CPFD) approach
No full textFluidized beds are conventional components of many industrial processes, such as coal gasification for energy generation and syngas production. Numerical simulations help to properly design and understand the complex multiphase flows occurring in these reactors. Two modeling approaches are usually adopted to simulate multiphase flows: the two fluids Eulerian-Eulerian model and the continuous/discrete Eulerian-Lagrangian model. Since fluidized beds account for an extremely large number of particles, tracking each of them could not assure to get results within a reasonable computational time. The Computational Particle-Fluid Dynamics (CPFD) approach, which belongs to the Eulerian-Lagrangian models class, groups together particles with similar key parameters (e.g. composition, size) into computational units (parcels). Parcel collisions are modeled by an isotropic solid stress function, depending on solid volume fraction. In this paper, the bubbling fluidized bed (BFB) upstream gasifier of the EU research infrastructure ZECOMIX (Zero Emissions of Carbon with Mixed technologies) has been simulated using a CPFD approach via Barracuda® software. The effect of different fluidizing agent injection strategies on bed bubbling and mixing, for non-reacting cases, has been studied. The numerical results for a reacting case have been compared to the available experimental data, gathered during the coal gasification campaign. The model has proved to be very useful in the choice of the more efficient injection configuration that assures a more effective contact of the gas with the solid bed and a good bubbling fluidization regime, together with a satisfactory prediction of the outlet gas composition. The numerical approach has turned out to be robust and time-saving and allowed to dramatically reduce the computational cost with respect the classical two fluids Eulerian-Eulerian models. © 2018, Isfahan University of Technology
Approfondimenti sul bruciatore trapped-vortex. Analisi di sensibilità e scalatura del prototipo
Full text linkNel report in oggetto viene approfondito lo studio sul nuovo bruciatore trapped-vortex alimentato a syngas. È importante infatti valutare sia gli effetti della variazione dei principali parametri operativi, nonché indagare su quali sono gli effetti di scala sul prototipo. Altrettanto interessante è studiarne il comportamento in regime dinamico attraverso una Large Eddy Simulation (LES), allo scopo di verificare la stabilità del vortice intrappolato. Nelle pagine seguenti viene innanzitutto ripreso e descritto il principio di funzionamento del prototipo, passando poi alla vera e propria analisi di sensibilità alle grandezze operative del sistema. Successivamente vengono descritti i diversi criteri di scalabilità e riportati i risultati nel caso di un bruciatore di potenza sia raddoppiata che dimezzata. Vengono infine riportati i risultati dell’analisi LES
Analysis of a Fuel Flexible Micro Gas Turbine Combustor Through Numerical Simulations
No full textThe work in this paper investigates on how a fuel flexible microgas turbine (MGT) combustion chamber, developed by ANSALDO ENERGIA and installed in a Turbec T100 P MGT, can operate when transferring from natural gas (NG) to a hydrogen-rich syngas. A syngas composition, which satisfies the fuel supply system specifications, is identified. Such syngas contains (by volume) 45% of hydrogen, 50% of carbon dioxide, and 5% of methane. The transfer procedure from NG to syngas is defined and modeled. A series of nonreactive and reactive Reynolds-averaged numerical simulations (RANS) on a fullscale three-dimensional (3D) model of the combustion chamber is then performed. The thermo-fluid dynamics inside its casing, the combustion regimes, the heat transfer across the liner walls as well as NOx emissions are evaluated. Results provide useful information on the operational problems associated with the fuel change and on how to define a successful fuel transfer procedure. Copyright © 2018 by ASME
About the use of compact schemes approach for the modelling of fuel pulverization phenomenon
No full textIn recent times the studies related to the analysis about industrial combustion processes has known a rapid growth, moreover due to the energy demand for productive activities worldwide. Therefore, to reduce contaminants emissions and to improve the gains in the related processes oriented to the energy production, the sectorial studies on combustion are knowing enormous progress with the auxilium of new survey instruments. Actually the computational fluid dynamics (CFD) is a valuable tool for technical support in carrying out the experimental studies on combustion and related methods of process, in fact even the flame stability issue or the mixing and diffusion questions with reacting flows need to have been submitted by accurate numerical problem solving approach. In this particular case, where the fuel is present in liquid state, according with the point of view to make feasible a combustion process, it needs that the fluid has to be previously reduced in sufficiently little part (droplets) which are able to be easily combined with the air in same mixing ratio to determine ignition conditions. Since in the practice there are effected several operations to increase the contact surface among combustible and combustive gas in order to optimise both the mass exchange process, both energy one among these two phases, these operations are very difficult to realize completely because the fluid is initially in forms compacts due to a resistance of viscous nature. It's well known that this phenomenology is strongly influenced by some disturbs, like the pressure fluctuations, conferred to the liquid jet and conditioned by the local turbulence and the gaseous properties within the flow is injected. The introduced work has focused its effort in the development of an ad hoc adopted numerical procedure to the particular fluid dynamic situation in examination by the recourse to numerical tools with spectral-like characteristics those provide to guarantee the validity of the NS equations and, meanwhile, don't modify the physical-chemical ownership of the mixture
Closure to "Head-Drop Method for the Modeling of Pressure Reducing Valves and Variable Speed Pumps in Water Distribution Networks"
No full textImpact of COVID-19 emergency on residential water end-use consumption measured with a high-resolution IoT system
No full textIn the era of Smart Cities, in which the paradigms of smart water and smart grid are keywords of technological progress, advancements in metering systems allow for water consumption data collection at the end-use level, which is necessary to profile users' behaviors and to promote sustainable use of water resources. In this paper, a real case study of residential water end-use consumption monitoring shows how data collected at a high-resolution rate allow for the evaluation of consumption profiles. The analysis was carried out by calculating consumption statistics, hourly consumption patterns, daily use frequency, and weekly use frequency. Then, the comparison of two consumption profiles, computed before and after the COVID-19 lockdown, allows us to understand how a change in social and economic factors can affect users' behavior. Finally, new perspectives for water demand modeling and management, based on data with high temporal frequency, are presented
Kinetic parameter estimation for methanol dehydration to dimethyl ether over sulfonic and polymeric acid catalysts
No full textBACKGROUND: The methanol dehydration to dimethyl ether (DME) has received considerable attention in the literature, because of its potential use as a multipurpose fuel. A wide literature of kinetic studies is available for γ-Al2O3, reference commercial catalyst but only a few authors report a kinetic analysis of attractive and alternative catalysts to γ-Al2O3 in DME production. The aim of this work was to contribute in this direction, by performing a catalytic test focused on the determination of kinetic parameters for methanol dehydration over sulfonic acid catalysts and polymeric materials. RESULTS: The catalytic and kinetic behavior of these materials for the methanol to DME dehydration reaction has been investigated using a fixed bed reactor at total pressure of 1 bar within a temperature range of 50 to 450 °C. The sulfonated fluoropolymer (Aquivion) exhibited the highest activity and stability for the dehydration reaction at relatively low temperatures at which the γ-Al2O3 did not display any dehydration activity. The tested catalysts showed good time stability when both methanol and methanol/water mixtures were used as feed reactants. Good agreement was achieved between experimental data and the proposed model. CONCLUSION: The -SO3H groups enhanced the surface acidity and the catalytic performances. The sulfonated perfluorinated polymer (Aquivion) was able to catalyze the methanol/DME conversion at temperatures as low as 90 °C. The selectivity to DME at lower temperatures was 100%. Apparent activation energy for this reaction was experimentally evaluated to 110 KJ/mol and theoretical calculated to 96 KJ/mol: there was a comparable and good agreement with the experimental data. © 2020 Society of Chemical Industry
CO2 methanation in a shell and tube reactor CFD simulations: high temperatures mitigation analysis
No full textCO2 methanation is gaining increasing interest in the last years as a way of storage of the energy surplus produced by renewable energy sources. Shell and tube reactors are among the most widespread type of methanation reactors. One-dimensional pseudo-homogenous/heterogeneous models and CFD (Computational Fluid Dynamics) models using some simplifications, as imposed heat exchange coefficients and constant coolant temperatures, have been applied up to now to study the problem. In this article those simplifications have been removed and the CO2 methanation in a cooled multi-tubular catalyst reactor has been investigated through 3D CFD simulations, using a commercial software and a porous model. Nitrogen and oil cooling have been studied and the results have been compared. The goal is to identify suitable solutions that allow the use of gas cooling, while maintaining low temperature levels and high conversions. The oil cooling case has been also analyzed for comparison and in the perspective of a future system upgrade. After a validation of the model using the available experimental data, a sensitivity analysis has been conducted for what concerns coolant and reactants temperatures and flow rates, catalyst load and operating pressure in the tubes. Strategies for the high temperatures mitigation in the reactive zones have been evaluated and discussed. In particular the proposed technique of catalyst uneven distribution has revealed to be very effective. The model has proved to be very useful for a detailed analysis of the phenomenon and for obtaining essential data that resulted difficult to measure by experimentation
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