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VALUTAZIONE DI PTEN E Nm23 QUALI FATTORI PROGNOSTICI ED INDICATORI DI REMISSIONE NEL CANCRO DELLA MAMMELLA STADIO T1
No full textSimulation of a Natural Gas Steam Reforming Reactor at Different Scales
No full textThe concept of sustainable energy is often associated to the so-called hydrogen
economy. However, hydrogen cannot be regarded as an energy source, since it is not
present in nature as free H2. Therefore, it must be produced using chemical processes.
Among them, natural gas steam reforming (NGSR) is the most widespread and economically
feasible process. Natural gas (NG) is a mixture with no well-defined and
constant composition. However, methane is the prevailing component (around 85-
90%), but also higher hydrocarbons (i.e. ethane, propane, butane...) can be found.
NGSR involves the proper endothermic reaction of reforming which produces syngas
(a mixture of H2, CO and CO2). Then, the slight exothermic reaction of water gas
shift, further converts CO in CO2 producing more hydrogen. The overall process is
highly endothermic, so requires a large amount of heat. Therefore, the reactors are
tubes placed in a furnace which provides direct heat to the tubes. Even though this
process implements a well-established technology, it still presents some issues, such
as carbon formation and deposition. Usually, a high steam to carbon (S/C) ratio allows
to reduce carbon formation and its deposition: a value of S/C higher than 2.5
is generally believed to be safe for coke-free operation, nevertheless the problem of
carbon formation and deposition is still not solved.
The aim of the first part, is the development of an accurate model for these reactors.
The mathematical model underlying the chemical and physical system is made
of the mass and energy balances. The constitutive equations are then coupled with
the kinetic equations for all the reaction involved in the process. The kinetic equations
for the NGSR process are retrieved from the literature (i.e. Xu and Froment) but, with
a simplified approach, they are adapted to our specific case. The overall set constitutes
a partial differential and algebraic equation (PDAE) system which and requires
boundary conditions which generally are chosen to be flowrate and composition of
the feeding mixture. The resolution of the PDAE system needs the implementation
of a numerical method through a finite element method (FEM), implemented through
COMSOL Multiphysics®. The major problem which has shown up is the numerical
method convergence. However, at the end of the simulation it is possible to obtain
plots and maps of the main physical and chemical quantities of interest.
Furthermore, an experimental analysis of end-of-life commercial catalyst coming
from a full-scale industrial SMR reactor is carried out. This experimental analysis
provides interesting results regarding catalyst structure and the eventual carbon deposition.
Therefore, a possible qualitative explanation for the carbon formation can be
given
FDI oriented simulation of an MSR reactor for application in SOFC systems
No full textWe propose a modelling approach, applied to an experimental methane steam reforming reactor, aiming at investigating carbon deposition by embedding the kinetics of the methane decomposition reaction. The results show that for a steam/methane feeding mixture with a steam-to-carbon ratio equal to 3, carbon deposition is predicted to occur in the first 0.001 m of the reactor, and this is expected to build-up during time, causing catalyst deactivation and progressive shift of the methane steam reforming and water gas shifting reactions downwards the reactor. The modelling tool is designed to be the basis of a fault detection and isolation tool, aiming at early detection and possible remediation of the coke deposition fault in methane steam reforming reactors for application in SOFC plants
Model of H2S catalytic oxidation in an IAC-PBR
No full textWe focus our attention on hydrogen sulphide (H2S), which originates from various sources and is one of the major air pollutants. Concentrations above 140 mg m-3are immediately harmful for human health. Below that threshold, H2S is an odorous compound, which can be detected by human beings in concentration higher than 5 μg m-3. Its removal is conventionally performed through scrubbing with amine or NaOH aqueous solutions. Adsorption on activated carbons is an alternative technique, particularly suitable for application in the low H2S concentration range, being a typical example of odour removal technique. In this work, we propose a model of packed bed reactor (PBR) embedding impregnated activated carbons (IACs), where the H2S adsorption involves a catalytic partial oxidation step causing the deposition of elemental sulphur on the catalyst, with consequent gradual deactivation. The model equations are integrated numerically through the software COMSOL Multiphysics 5.3a. Simulation results are validated through comparison with literature experimental data. Furthermore, application to an industrial case study is presented and discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Diagnostics and Prognostics-Oriented Modeling of an NGSR Fuel Processor for Application in SOFC Systems
No full textDiagnostics and prognostics of natural gas steam reforming (NGSR) reactors are of utmost importance for solid oxide fuel cell (SOFC) systems, where a fuel processor fault can cause damage to the SOFC stack. Most common faults are due to carbon deposition. We investigate this phenomenon through a model based on microscopic mass, energy and momentum balances of a tubular NGSR reactor. The model includes a detailed local reaction kinetics specific for Ni-based catalysts, and is integrated numerically using a finite element method (FEM) implemented through COMSOL Multiphysics 5.2. Results obtained from the simulation of a laboratory scale reactor are validated on the basis of literature data. Furthermore, the model is applied to an NGSR fuel processor designed for an 1.1 kW SOFC system. The model allows to identify the area where carbon deposition is expected to occur, which is a key feature in view of developing specific diagnostic and prognostic tools. The simulation results demonstrate that safety criteria based on the feedstock steam to carbon (S/C) ratio can be misleading in a number of operating conditions
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