196,053 research outputs found
Landscapes and landforms connected with anthropogenic processes over three millennia. The Servian Walls at the Esquiline Hill (Rome, Italy)
No full textUrban centers are characterized by scarcity of outcrops. At the urban-planning level, the examination of results from previous geological surveys and studies may provide sufficient data for an accurate subsurficial geologic modeling. In addition, in historical centers a GIS-based multitemporal analysis of historical and archaeological maps, and the examination of archive documents and reports, may be effective especially for the detection of geomorphic changes. The application of such a methodology at the Esquiline Hill allowed to detect the three-millennia-long landscape-modification main phases connected with the construction of the oldest city walls. They include a unique sequence of anthropogenic aggradational and erosional phases that shaped many anthropogenic landforms, presently visible and invisible, or vanished. Among them, the anthropogenic hill Monte della Giustizia, vanished since the end of the 19th century CE when it was erased, and the military moat, excavated in the 6th century BCE and enlarged in the 4th century BCE, finally backfilled in the 4th century CE, since then invisible. These geomorphic changes lastly output a flat leveled landscape similar to the previous volcanic plateau. Results suggest that the “geomorphological convergence,” that is, the resemblance between natural landforms created by different morphogenetic processes, also exists between natural and artificial landforms. Moreover, the study evidenced relationships between landforms and the damage status of historical masonry buildings, specifically connected with their foundation over thick layers of geotechnically-weak anthropogenic deposits. This advises that the multidisciplinary approach may also provide risk managers additional geological features to be evaluated as potential sources of natural hazard
Thermodynamic analysis of the humidification-dehumidification-adsorption (HDHA) desalination process
No full textThe process of Air Humidification-Dehumidification (HDH) for water desalination and purification can play an important role in the field of low-carbon water production from non-conventional sources. Our research group presented a novel process scheme consisting of a multiple extraction HDH with vapour adsorption (HDHA) and brine recirculation, able to approximate a closed-air closed-water loop with bottom temperature below the environmental one. This novel work presents the strategy of process optimization through the variance analysis and a mathematical algorithm of thermodynamic balancing adapted to this novel process. The results point out the optimization strategies and allow the literature comparison to show how HDHA can overcome the performances of conventional processes at similar conditions, also reaching acceptable values of second law efficiency. In fact, HDHA can overcome the GOR of similar “balanced” water heated HDH reaching GOR around 10 even at acceptable enthalpy pinch (around 15 kJ kg−1) with three air extractions.</p
Numerical Analysis of VPSA Technology Retrofitted to Steam Reforming Hydrogen Plants to Capture CO2 and Produce Blue H2
No full textThe increasing demand for energy and commodities has led to escalating greenhouse gas emissions, the chief of which is represented by carbon dioxide (CO2). Blue hydrogen (H2), a low-carbon hydrogen produced from natural gas with carbon capture technologies applied, has been suggested as a possible alternative to fossil fuels in processes with hard-to-abate emission sources, including refining, chemical, petrochemical and transport sectors. Due to the recent international directives aimed to combat climate change, even existing hydrogen plants should be retrofitted with carbon capture units. To optimize the process economics of such retrofit, it has been proposed to remove CO2 from the pressure swing adsorption (PSA) tail gas to exploit the relatively high CO2 concentration. This study aimed to design and numerically investigate a vacuum pressure swing adsorption (VPSA) process capable of capturing CO2 from the PSA tail gas of an industrial steam methane reforming (SMR)-based hydrogen plant using NaX zeolite adsorbent. The effect of operat-ing conditions, such as purge-to-feed ratio and desorption pressure, were evaluated in relation to CO2 purity, CO2 recovery, bed productivity and specific energy consumption. We found that conventional cycle configurations, namely a 2-bed, 4-step Skarstrom cycle and a 2-bed, 6-step modified Skarstrom cycle with pressure equalization, were able to concentrate CO2 to a purity greater than 95% with a CO2 recovery of around 77% and 90%, respectively. Therefore, the latter configuration could serve as an efficient process to decarbonize existing hydrogen plants and produce blue H2
Il Monte della Giustizia all'Esquilino (Roma)
No full textIl Monte della Giustizia rappresenta un interes- sante esempio di rilievo antropico, risultato di ripetuti e talora concorrenti episodi di scavo e deposito antropico in area ur- bana, succedutisi in oltre due millenni di storia. La sua presenza è stata tuttavia cancellata dalla demolizione pianificata per esi- genze urbanistiche e posta in atto nel giro di pochi decenni. Le testimonianze della sua esistenza provengono dalla cartografia storica e da fonti iconografiche, mentre minori sono le relazioni o gli articoli di valenza geologica, tenuto conto che la sua com- pleta demolizione è avvenuta ben prima che la geologia urbana e la conservazione dei siti di rilevanza storico-culturale assu- messero rilevanza. Tuttavia, alcuni contributi anche di tipo ar- cheologico sono risultati utili per gli scopi geologici. L’analisi multitemporale ed interdisciplinare dei suddetti dati ha per- messo di ricostruire le fasi salienti della sua costruzione e de- molizione, le dimensioni e caratteristiche del rilievo che nel suo complesso sembra corrispondere all’antico toponimo del Monte Superagio, poi denominato Monte della Giustizia
Geomorphology of the historic centre of the Urbs (Rome, Italy)
Full text linkBased on long-lasting multidisciplinary and multitemporal investigations, in 2016 the first geomorphological map of the central area of Rome was presented. It introduced innovative solutions for cartographic restitution of urban landforms. Under this work, the urban geomorphological analysis delved deeper, because the study focused on the smaller area of the Urbs, the ancient city centre that has been modified by human activities over millennia. The main goal of the new study was to verify if the 1:5000 scale survey could allow to improve the legend symbols, in order to better represent landforms from natural and anthropogenic processes in urban environment. Since the map scale was doubled compared with the previous and consequently the map area available was four times bigger, we were able to provide much more details. Moreover, results better highlighted the applicative significance of urban geomorphological maps as complementary tool for the assessment of natural hazards and risks
Design of a H2 pressure swing adsorption process at an advanced IGCC plant for cogenerating hydrogen and power with CO2 capture
Full text linkStrong dependency on fossil fuels and the associated price and supply chain
risk increase the need for more efficient utilisation of existing non-renewable energy
sources. Carbon capture and hydrogen purification technologies are expected to play
a key role in the future low-carbonised energy matrix. Integrated Gasification
Combined Cycles (IGCCs) are one of the emerging clean coal technologies which
pave the way for producing power from coal with a higher net power efficiency than
conventional PC-fired boiler power plants. It is also advantageous that in an IGCC
power plant a carbon capture unit can be applied to a stream having a very high CO2
partial pressure ahead of gas combustion that would not be available in case of a PC-fired
boiler power plant, leading to less energy penalty involved in carbon capture.
At the same time, the production of ultrapure hydrogen is both a sought target
and an appropriate environmental solution because it is commonly utilised as
feedstock in refineries’ hydrotreaters and hydrocrackers as well as energy carrier in
fuel cells. A high purity of hydrogen has been commercially produced out of raw
synthesis gas using a Hydrogen Pressure Swing Adsorption (H2 PSA) process. In this
thesis, it was aimed to design and optimise a bespoke H2 PSA system tailored for a
decarbonised syngas feed originating from a carbon capture unit. Therefore, a novel
H2 PSA has been studied that is applied to an advanced IGCC plant for cogenerating
power and ultrapure hydrogen (99.99+ mol%) with pre-combustion CO2 capture.
In designing the H2 PSA, it is essential to increase the recovery of ultrapure
hydrogen product to its maximum since the power consumption for compressing the
H2 PSA tail gas up to the gas turbine operating pressure should be minimised to save
the total auxiliary power consumption. Hydrogen recovery was raised by increasing
the complexity of the PSA step configuration that allows a PSA cycle to have a lower
feed flow to one column being used for adsorption and more pressure equalisation
steps. An in-depth economic analysis was carried out and discussed in detail. The
industrial advanced IGCC performances have also been improved by process
integration between the H2 PSA unit and other units in the plant
Post-combustion CO2 capture by RVPSA in a large-scale steam reforming plant
No full textSteam reforming (SR) of natural gas is the most widespread process to produce hydrogen. This paper presents a comprehensive simulation of an industrial plant for hydrogen production for the internal use in a refinery industrial complex based on the SR of different feedstocks. The reference plant is a 42,000 Nm3/h hydrogen production unit located in the South of Italy in the Refinery of Milazzo, Sicily. Hydrogen is produced from light gaseous hydrocarbons and purified by means of pressure swing adsorption technology. In the present work, a process simulation has been built on scientific basis and validated against field data at different feedstocks and operating conditions. The model correctly predicts the effect of relevant process parameters such as reformer feed pressure and temperature, steam to carbon ratio and plant load. In addition, the paper proposes the design of an industrial-scale rapid vacuum pressure swing adsorption (RVPSA) unit which was designed and simulated to capture carbon dioxide from the flue gas exiting the steam reformer. The RVPSA unit was integrated in the current plant enabling the concentration of CO2 with a purity of 96.64%, an overall recovery of 90.84% and a specific energy consumption of 628.93 kJ/kgCO2, thus meeting the requirements for transportation and geological storage. An energetic efficiency calculation was introduced to quantify the effectiveness of the hydrogen conversion process and to predict the effect of CO2 capture and some process parameters to the overall H2 production efficienc
Anthropogenic modifications to the drainage network of Rome (Italy). The case study of the Aqua Mariana
Full text linkRome is characterized by millennia of urbanization. Long lasting geomorphological investigations have allowed the geomorphological description of the city centre and the valorisation of its geomorphological heritage. In this paper the spatial change of the hydrographic network in historical times is illustrated, with some examples showing how deep has been, and still it is, the link between the historical-cultural development and the natural geomorphological and hydrological characteristics of the Roman territory. In particular, the most relevant human interventions on the drainage network, in the southern area of the city centre, have been investigated. Before the land-use modifications of Roman-age, this area was drained by the most important left tributary of the Tiber River within the city walls, the Nodicus River, more recently known as Aqua Mariana. This stream has undergone many anthropogenic modifications and diversions during the centuries, and its original path is known only downstream of the San Giovanni Basilica. According to geomorphological, archaeological and geological evidences, it is possible to hypothesize that the dimension of the pre-urbanization drainage basin, as known and reconstructed in the available literature, should have been until now underestimated
Kinetics of 4-nitrophenol biodegradation in a sequencing batch reactor
No full textIn this paper, the biodegradation process of 4-nitrophenol (4NP) in a sequencing batch reactor has been investigated. Kinetic tests have been carried out on biomass grown on mixed substrate (4NP plus biogenic substrate) both in the presence of a biogenic substrate fraction in the feed and with 4NP as the sole carbon source. Removal kinetics for all tests is well described by the typical substrate inhibition pattern as predicted by the Haldane equation. In both sets, estimated kinetic parameters are very similar: no beneficial effect of the biogenic fraction is observed on the 4NP removal while increasing trend of 4NP maximum removal rate with the 4NP/CODTOT ratio in the feed has been observed. This finding has been modelled by estimating the fraction of the total biomass involved in 4NP biodegradation as a function of 4NP concentration in the feed. High removal rates, short acclimation times and good settling characteristics of produced sludge (observed during the whole working period) confirm the suitability of periodic systems in enhancing the bacterial potentialities for biodegradation of xenobiotic compounds. (C) 2003 Elsevier Science Ltd. All rights reserved
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
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