551 research outputs found
Molecular Dynamics simulation of sucrose coated and trehalose coated carboxy-myoglobin
No full textWe performed a room temperature
molecular dynamics (MD) simulation on a system
containing 1 carboxy-myoglobin (MbCO) molecule
in a sucrose–water matrix of identical composition
(89% [sucrose/(sucrose water)] w/w) as for a previous
trehalose–water–MbCO simulation (Cottone et
al., Biophys J 2001;80:931–938). Results show that, as
for trehalose, the amplitude of protein atomic meansquare
fluctuations, on the nanosecond timescale, is
reduced with respect to aqueous solutions also in
sucrose. A detailed comparison as a function of
residue number evidences mobility differences along
the protein backbone, which can be related to a
different efficacy in bioprotection. Different heme
pocket structures are observed in the 2 systems. The
joint distribution of the magnitude of the electric
field at the CO oxygen atom and of the angle between
the field and the CO unit vector shows a
secondary maximum in sucrose, absent in trehalose.
This can explain the CO stretching band profile (A
substates distribution) differences evidenced by infrared
spectroscopy in sucrose- and trehalose-coated
MbCO(Giuffrida et al., J Phys ChemB2004;108:15415–
15421), and in particular the appearance of a further
substate in sucrose. Analysis of hydrogen bonds at the
protein–solvent interface shows that the fraction of
water molecules shared between the protein and the
sugar is lower in sucrose than in trehalose, in spite of
a larger number of water molecules bound to the
protein in the former system, thus indicating a lower
protein–matrix coupling, as recently observed by Fourier
transform infrared (FTIR) experiments (Giuffrida
et al., J Phys Chem B 2004;108:15415–15421)
La certificazione di conformità del cd. “Halal Food”
No full textL’espressione Halal Food è frequentemente utilizzata nella prassi commerciale per indicare i prodotti del settore agroalimentare conformi alle prescrizioni islamiche. L’Autore offre
una disamina dei principali profili problematici connessi alla certificazione di qualità di tali
prodotti, anche in considerazione del crescente successo che il mercato dell’Halal Food riscuote nel mondo e, di recente, anche in Italia. La registrazione di marchi collettivi religiosi sembra attualmente il mezzo più affidabile di tutela dei consumatori circa l’effettiva conformità alle prescrizioni coraniche e, al contempo, il più rispettoso della libertà religiosa
dei fedeli nonché dell’autonomia dell’ordine confessionale
Etna CO2 Soil Flux during 2002-2010 (ECSF2002_2010)
No full textThe ETNAGAS network comprises 19 monitoring stations distributed across the flanks of Mount Etna, specifically designed for the continuous observation of soil-emitted carbon dioxide (CO₂). Each station is equipped with infrared (IR) sensors for the precise measurement of CO₂ concentrations, along with meteorological sensors that record key environmental parameters including air temperature, atmospheric pressure, wind speed and direction, and precipitation. These data enable the estimation of CO₂ soil fluxes through the application of the method proposed by Gurrieri and Valenza (1988) (see Methods for details). The ETNAGAS network represents a high-resolution geochemical surveillance system and constitutes an integral component of the national framework for monitoring volcanic gas emissions. Its primary objective is to contribute to the assessment of the volcanic activity state of Mount Etna through systematic and spatially distributed measurements of gaseous emissions.The monitoring stations of the ETNAGAS network were entirely developed by the Istituto Nazionale di Geofisica e Vulcanologia (INGV), Palermo section. These stations are capable of continuously measuring several environmental and geochemical parameters, including soil CO₂ concentration, atmospheric temperature, pressure, relative humidity, rainfall, wind speed, and wind direction. Data are acquired at hourly intervals and automatically transmitted to the monitoring center at INGV-Palermo. It should be noted that not all stations are equipped with the full suite of meteorological sensors.
CO₂ fluxes from the soil can be derived from the recorded data using the dynamic (or dilution) method described by Gurrieri and Valenza (1988). This method is based on measuring the CO₂ content in a mixture of soil gas and atmospheric air (Cd), obtained using a probe inserted approximately 50 cm into the ground. Soil gases enter the probe through its base and are mixed with ambient air; this mixture is then pumped into an infrared (IR) spectrophotometer, which measures the CO₂ concentration.
According to Gurrieri and Valenza, the measured diluted concentration (Cd) is empirically related to the actual soil CO₂ flux (ϕCO₂) through a relationship established under laboratory conditions, across a range of gas permeabilities (0.36–123 mm²) and pumping flow rates (0.4–4.0 L/min) [Camarda et al., 2006a, 2006b].
REFERENCE
• Camarda, M., S. Gurrieri, and M. Valenza (2006a), CO2 flux measurements in volcanic areas using the dynamic concentration method: Influence of soil permeability, J. Geophys. Res., 111, B05202, doi:10.1029/2005JB003898. Camarda, M., S. Gurrieri, and M. Valenza (2006b), In situ permeability measurements based on a radial gas advection model: Relationships between soil permeability and diffuse CO2 degassing in volcanic areas, Pure Appl. Geophys., 163(4), 897–914, doi:10.1007/s00024-006-0045-y.
• Gurrieri, S., and M. Valenza (1988), Gas transport in natural porous mediums: A method for measuring CO2 flows from the ground in volcanic and geothermal areas, Rend. Soc. Ital. Mineral. Petrol., 43, 1151–1158.
• Gurrieri, S., M. Liuzzo, and G. Giudice, (2008), Continuous monitoring of soil CO2 flux on Mt. Etna: The 2004–2005 eruption and the role of regional tectonics and volcano tectonics, J. Geophys. Res., 113, B09206, doi:10.1029/2007JB005003, 2008.
• Liuzzo M., Gurrieri S., Giudice G. & Giuffrida G. (2013) - Ten years of soil CO2 continuous monitoring on Mt. Etna: Exploring the relationship between processes of soil degassing and volcanic activity. Geochem. Geophys. Geosyst., 14, 2886-2899. https://doi. org/10.1002/ggge.2019
Thermodynamic assessment of IGCC power plants with hot fuel gas desulfurization
No full textIn IGCC power plants, hot gas desulfurization (HGD) represents an attractive solution to simplify syngas treatments and to improve the efficiency, potentially reducing the final cost of electricity. In the present study, the various consequences of the introduction of a HGD station in the power plant are discussed and evaluated, in comparison with conventional near-ambient temperature clean-up. Attention is paid to the potential improvements of the overall energy balance of the complete power station, along with the requirements of the sorbent regeneration process, to the influence of the desulfurization temperature and to the different solutions needed to control the NOx emissions (altered by the presence of HGD).
The net performance of complete IGCC power plants (with HGD or with conventional desulfurization) were predicted, with reference to status-of-the-art solutions based on an entrained flow, dry-feed, oxygen- blown gasifier and on an advanced, FB-class combined cycle. The net efficiency experiences about 2.5% point improvement with HGD, even if a small reduction in the power output was predicted, when using the same combustion turbine.
An exhaustive sensitivity analysis was carried out to evaluate the effects of different working conditions at the HGD station, e.g. desulfurization temperature and oxygen content in the gaseous stream for sorbent regeneration. According to the obtained results, these parameters have a weak influence on the efficiency. In particular, a very elevated desulfurization temperature (above 400–500 °C) does not provide decisive thermodynamic advantages. Therefore, the HGD unit optimization can be driven by technical and economical aspects and by emission abatement requirements. For instance, utilization of nitrogen for HGD sorbent regeneration (rather than for syngas dilution) and higher fuel temperature may improve the NO formation. Hence, different strategies to achieve acceptable NOx emissions (e.g. steam dilution) and their impact on the performance are investigated in the paper
A study of CO2 capture in advanced IGCC systems by ammonia scrubbing
No full textAbstractThis paper deals with post-combustion CO2 capture by aqueous ammonia in air-blown gasification-based combined cycles and follows previous authors’ investigations of CO2 capture by MEA scrubbing. Based on the calculations, CO2 capture seems to be more penalizing when realized by chilled ammonia instead of MEA. As a matter of fact, chilling down to 7°C both the exhaust gas and the ammonia solution results in significant power consumption of chillers, which is only partly balanced by the lower consumption for CO2 compression and lower steam extraction from the bottoming cycle compared to the MEA case. Cases with cooled instead of chilled ammonia are investigated as well. In particular, raising the process temperature up to 20°C seems to be an interesting solution, since temperature control in the absorber can be realized by passing the aqueous ammonia solution through an heat exchanger, using ambient-temperature water as refrigerant medium and removing the chillers from the system
Thermodynamic Performance of IGCC with Oxy-Combustion CO2 Capture
No full textThis paper discusses the relevant thermodynamic aspects of IGCC plants with CO2 capture, mainly focusing on oxy-combustion techniques. The following plant configurations were considered here, all based on a dry-feed oxygen-blown entrained-flow gasifier with syngas quench (Shell type) and a FB class gas turbine: (i) two reference cases, one without CO2 cap-ture and one with ‘conventional’ pre-combustion capture, (ii) three oxy-combustion cases, the first one with today’s technology and the other two with advanced technology, including CO2/SO2 co-sequestration or, alternatively, Hot Gas Desulfurization.
It is concluded that oxy-combustion techniques in IGCC cycles may deserve some attention in the near future, because they have the potential of achieving better thermodynamic and en-vironmental performance, in comparison with more conventional capture concepts: in the best case, 45% net efficiency and near-zero emissions were predicted. However, some tech-nological challenges are an obstacle to their development, especially as far as the re-design of the gas turbine is concerned
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