Higher Institute on Territorial Systems for Innovation
PORTO Publications Open Repository TOrinoNot a member yet
91193 research outputs found
Sort by
Carbon dioxide methanation for synthetic natural gas (SNG) production
No full textThis work deals with the coupling between high temperature steam electrolysis and carbon dioxide methanation (hydrogenation) to produce a synthetic gas directly injectable in the natural gas distribution grid. This system concept is one of the existing possibilities related to a pathway named Power-to-gas. According to this strategy, low-priced surplus electric energy coming from renewable energy sources (RES) or nuclear plants can be converted into chemical energy of a fuel in order to store it for a longer time. Another purpose is to compensate the unbalances of the electric grid due to the daily and seasonally fluctuations of electricity production from RES (especially wind and solar). The integration between solid oxide electrolysis cell (SOEC) technology and methanation seems to be promising due to the possible thermal integration between exothermal hydrogenation and thermal energy required within the water splitting unit. Hydrogen generated through steam electrolysis can react with carbon dioxide producing methane and water (4 H2 + CO2 ↔ CH4 + 2 H2O). A preliminary screening of nickel-based catalysts has been carried out at atmospheric pressure in order to identify the catalyst(s) with higher activity. During this experimental activity seven samples have been tested: a standard NiO on γ-Al2O3 catalyst (Ni/A); three Ni-based samples (Ni/C5, Ni/C10 and Ni/C15) with a composite support containing a mixture of γ-Al2O3 and other promoters (CeO2, ZrO2 and TiO2); two nickel-aluminum hydrotalcites (Ni-Al 8.7 and Ni-Al 12, prepared at a pH of 8.7 and 12, respectively) and a commercial NiO/γ-Al2O3 catalyst (CRG-F). Hydrotalcites and commercial catalyst present better performance than oxides-supported nickel samples and are more active especially at low temperature (below 300 °C). The different activity far from equilibrium can be put in relation with some physic and chemical properties. Hydrotalcites and commercial catalyst presented higher nickel content than the other samples. Moreover, also the metal dispersion seems to play a role in order to enhance the catalytic performance. Concerning oxide-supported Ni-based catalysts, the addition of promoters (CeO2, TiO2 and ZrO2) to γ-Al2O3 within the support showed a beneficial effect on the activity due to the increased catalyst reducibility. A new test rig has been designed and set up in order to perform an experimental activity at high pressure (up to 30 bar). Samples at both small (0.25-0.5 mm) and pellet (3 mm) size have been tested at different pressure, temperature and inlet gas composition. As a preliminary activity, a commercial catalyst at pellet size was tested at 300 °C and different residence times with two different inlet mixtures (in order to reproduce a series of two reactors with an inter-condensation of the produced water). This experimental activity enabled the production of synthetic gas with hydrogen content lower than 5%, which is the maximum acceptable H2 amount considered in this work for the direct injection of SNG into the natural gas distribution grid. Thus, the feasibility of the process in terms of overall conversion into methane was verified. Then, a test campaign has been carried out by varying several operating parameters in order to describe the methanation kinetics for a commercial catalyst (NiO/γ-Al2O3) at small particles size (250-500 μm). Total and reactants partial pressures and temperature were varied during the experimental activity. The obtained experimental points have been used into an ideal PFR model for the kinetic parameters estimation. Both power law and Langmuir-Hinshelwood (LHHW) rate equations were considered. Concerning LHHW-type equations, the one leading to the best fitting of experimental data is based on the dissociative chemisorption of both hydrogen and carbon dioxide as reaction mechanism. The obtained kinetics was used as a basis for a 1D plug flow reactor model applied to a series of two cooled multi-tube fixed bed reactors for methane synthesis: the main goal is to estimate temperature and conversion profiles along the axial coordinate. Evaporating water at 240 °C (i.e. at ≈ 33 bar) has been considered as a coolant: this strategy ensures a high heat transfer coefficient on the shell side. Both micro and macro kinetics equations are solved. Thus, transport phenomena between gas and solid catalyst have been taken into account. In addition, the evaluation of the effectiveness factor for isothermal particles enabled the estimation of the mass transfer inside the porous catalyst. In order to moderate the temperature increase (i.e. to prevent the hot spot risk) especially within the first reactor, part of the reacting CO2 is conveyed directly to the second reactor by-passing the first one. A carbon dioxide split ratio of 0.7 (meaning that the 30% of the total CO2 flow by-passes the first reactor) ensures that the maximum temperature reached within the solid catalyst is lower than 600 °C (this value has been fixed at the maximum acceptable temperature). The length of the second reactor was adjusted in order to ensure a methane fraction in the outlet gas equal to 95% (on dry basis), enabling the production of a synthetic gas with a H2 content lower than 5% (i.e. injectable in the NG pipeline). Inlet pressure has been set equal to 15 bar. The obtained results from the 1D model have been used for the design of the methanation unit consisting in a series of two cooled reactors with steam inter-condensation. Then, the process modeling of a plant coupling high temperature electrolysis and methanation is presented: the main goal of this analysis is the calculation of an overall plant efficiency (in terms of electricity-to-SNG chemical energy). The plant size has been set considering a 10 MWel SOEC-based electrolysis unit. It has been assumed that the heat produced from the exothermal methanation is entirely used for the water evaporation; the as generated steam is the key reactant of the electrolysis unit. Through the pinch analysis, a further thermal integration between hot and cold streams was performed. The external heat requirement obtained through the minimization of thermal needing was equal to 121 kW (≈1% of the electrolyser duty). However, such integration requires a too high number of heat exchangers, resulting in increasing costs and higher system complexity. Thus, the heat exchangers network has been re-designed in order to reduce the number of components. Hot and cold streams of electrolysis section have been coupled; a similar procedure has been applied to the methanation unit. Thus, the only integration between the two sections is represented by the reaction heat used for the water evaporation. The reduced complexity results in a higher external heat requirement (272 kW): this new value has been considered acceptable (≈3% of the electrolysis power). Efficiency was calculated as the ratio between the SNG chemical power and the overall electric input (including electrolysis power, compression duties and external heating). The SOEC-based power-to-gas system presented an HHV-based efficiency equal to ≈ 86 % (≈ 77 % on LHV basis)
Metal surfaces in medicine: Current knowledge of properties, modeling and biological response
No full textProcesso progettuale, vincoli e funzioni, mercato e valori, utenti e committenza: quale fattibilità?
No full textIdentification and Correction of Artifact in the Measurement of Pulsed Magnetic Fields
No full textAC magnetic flux density meters usually integrate a high-pass filter with a very low cutoff frequency (1-30 Hz) aiming at reducing the effect of slow oscillations. This can distort the actual time domain behavior of magnetic flux density waveforms detectable close to industrial or medical devices, even causing artifact high-amplitude oscillations. This paper proposes a procedure to identify the filter parameters that accurately reproduce its measured frequency behavior and suggests an algorithm to correct, in time domain, the field meter recorded waveform. Identification and correction procedures are extensively tested on magnetic flux density waveforms provided by a system for the generation of standard magnetic fields. Finally, the uncertainty associated with the identification and correction procedure is assessed by means of the Monte Carlo method (MCM). Assuming an overall standard uncertainty associated with the MCM model inputs of 0.3%, a standard uncertainty of 0.75% associated with the mean-square error between measured and reconstructed waveforms is obtained
Dimensionality reduction of the resilience model of a critical infrastructure network by means of elementary effects sensitivity analysis
No full text
Model predictive and reallocation problem for CubeSat fault recovery and attitude control
No full textDemolire le mura. Progettare la città
No full text"La demolizione delle mura segna in modo spettacolare il passaggio tra età moderna e età contemporanea, condizionando la legislazione, la simbologia e la toponomastica" . Uno dei primi atti, alle origini della città contemporanea, segna l'annullamento (costoso e complicato) della cinta difensiva che per secoli ha costituito il limite fiscale, politico, amministrativo del nucleo urbano. I cantieri di demolizione "assediano" la città per diversi decenni, lì dove qualche secolo prima altri uomini hanno costruito e costantemente potenziato le mura necessarie alla difesa, e quindi, alla sopravvivenza della comunità. L'attenzione per il proprio limite, per la difesa del "dentro" nei confronti del "fuori", da dove possono arrivare nemici e ostilità ha rappresentato un duro, ma necessario impegno per la città in età medievale e moderna. Attrezzarsi adeguatamente, conoscere le più moderne tecniche di guerra e, quindi, di difesa, assoldare il più bravo ingegnere militare, erano garanzie di sicurezza e inespugnabilità. La contemporaneità si apre con la cancellazione di quella che ormai pare una costrizione per le velleità di ampliamento, decoro e modernità
Noise characterization of analog to digital converters for amplitude and phase noise measurements
No full textImprovements on electronic technology in recent years have allowed the application of digital techniques in phase noise metrology, where low noise and high accuracy are required, yielding flexibility in system implementation and setup. This results in measurement systems with extended capabilities, additional functionalities, and ease of use. In most digital schemes, the Analog to Digital Converters (ADCs) set the ultimate performance of the system; therefore the proper selection of this component is a critical issue. Currently, the information available in the literature describes in depth the ADC features only at frequency offsets far from the carrier. However, the performance close to the carrier is a more important concern. As a consequence, the ADC noise is, in general, analyzed on the implemented phase measurement setup. We propose a noise model for ADCs and a method to estimate its parameters. The method retrieves the phase modulation and amplitude modulation noise by sampling around zero and maximum amplitude, a test sine-wave synchronous with the ADC clock. The model allows discriminating the ADC noise sources and obtaining the phase noise and amplitude noise power spectral densities from 10 Hz to one half of the sampling frequency. This approach reduces the data processing, allowing an efficient ADC evaluation in terms of hardware complexity and computational cost
Surface functionalization of chemically treated Ti6Al4V alloy with mentha piperita essential oil
No full textMentha piperita essential oil is a complex mixture of different natural biomolecules with proven antibacterial activity against Gram-positive and Gram-negative bacteria, fungi and viruses [1] and it has been widely used in folk medicine for various applications. Despite its increasing use in phytotherapy, application of peppermint essential oil in medicine is still quite scarce and almost no research work considers its application in combination with biomaterials. On the other hand, the possibility to employ the antibacterial properties of this essential oil together with its low resistance development risk and its low toxicity is a challenging approach for the development of smart biomaterials for prosthetic applications. The aim of the work is to combine the antibacterial properties of peppermint essential oil with those of bioactive titanium alloy for applications in which good osteointegrability and antimicrobial effects are required