Operational analysis of natural gas combined cycle CHP plants: energy performance and pollutant emissions

The natural gas-fired combined cycle (NGCC) plants are among the best technologies for power production, especially when operating in combined heat and power (CHP) generation feeding a district heating (DH) network. Even if usually designed to operate with very high utilization factors, thus satisfying mainly the base load, nowadays these plants are often used also as backup power. This is due mainly to the necessity to compensate the nonprogrammable renewable energy sources (RES) production, and it can be done, thanks to the good flexibility of these plants. However, in off-design conditions, the energy performance and the pollutant emissions may not be as good as the expected nominal ones. In this paper, the real operation of three NGCC units has been analysed in detail by considering mean hourly data over several years. A gas turbine efficiency curve at partial loads has been obtained, showing a decrease of conversion efficiency at lower unit loads. The CO emissions during the start-up and shut-down procedures of the plant reached values that are some orders of magnitude higher than in normal operation. This criticality should not be forgotten when using these units for frequent on-off operations

Data Analysis of the Energy Performance of Large Scale Solar Collectors for District Heating

District Heating systems are an interesting opportunity for the increase of renewable energy share in the heating and cooling sector. The possibility of a centralized heat production allows the integration of multiple sources, including RES such as biomass, heat pumps and solar energy. This paper provides an operation analysis of the energy performance of large scale solar collectors supplying heat to DH systems in Denmark. Thanks to the availability of hourly data it has been possible to track the evolution of the collectors’ performance throughout the year, and compare it with the available radiation. The results show the good reliability of such systems, which are generally able to convert 40% to 60% of the available radiation, with annual production yields higher than 400 kWh/m2/y. The conversion efficiency shows some seasonal variations, being the winter months the less favorable, probably because of a lower direct radiation. The DH systems considered in the study show a similar performance but with some differences: other parameters such as slope, azimuth and operating temperatures could be the causes of these variations

Opportunities for heat pumps adoption in existing buildings: real-data analysis and numerical simulation

The space heating of buildings represents one of the most important causes of energy consumption in Europe. The necessity to increase the share of renewable energy within the sector is hindered by the difficulty to renew and refurbish the existing building stock. In this context, heat pumps can have an important role in helping increase the renewable share of thermal energy production for the civil sector, in particular in those countries in which the electricity generation mix has large contributions from renewable energy sources. The paper presents a real-data analysis and a numerical simulation to evaluate the opportunity to substitute traditional heat generation systems (natural gas boilers) with air-source heat pumps or hybrid solutions. Three buildings located in Turin (Italy) are taken as case-study, and the hourly profiles of outdoor temperature, water supply temperature and absorbed thermal power are used to simulate four heat generation scenarios, that are compared in terms of primary energy consumption. Results show that (1) the substitution of the traditional natural gas boiler with a heat pump (with backup electric resistance) is always favorable (18% to 32% of primary energy reduction); (2) the influence of water supply temperature of each building on the overall primary energy saving is very high; (3) the adoption of a hybrid system (heat pump and natural gas boiler working alternatively) provides advantages in terms of reduced primary energy consumption only if the required supply water temperature is high. Further studies will investigate the economic aspects and will introduce comparisons with condensation natural gas boilers

Planning and operation of two small SDH plants as test site: Comparison between flat plate and vacuum collectors

A small solar district heating plant has been built to provide heat to an existing district heating system supplied by natural gas CHP units. This test site, located at 1,600 m a.s.l., allows comparing the performances of evacuated solar collectors (ETC) with flat plate double glazed ones (FPC) in a mountain environment. The preliminary results of the first months of operation show a better performance of ETC than FPC. The daily heat production shows a good correlation with available radiation, with the FPC having a slightly larger variability. Moreover, while ETC system efficiency is comparable with the theoretic curve, the FPC system efficiency show lower values. The monitoring of the SDH is still ongoing, and some control logics of the system are being performed in order to optimize the heat production from FPC. The specific electricity consumption for pumping is in the range 5 – 20 kWhel/MWhth, in accordance with usual literature values. The specific pumping consumption decreases with increasing daily heat production, and no significant difference arises from the trends of the two systems

Antibacterial activity of different root canal sealers against Enterococcus faecalis

The aim of the present study was to compare in vitro the antimicrobial activity of different root canal sealers against Enterococcus faecalis, prior and subsequent to setting. Agar diffusion test (ADT) was used for evaluating the antibacterial activity of non-set sealer while the direct contact test (DCT) was used for after setting. ADT: Except for TotalFill BC Sealer all the others sealers tested showed antibacterial activity. BioRoot?RCS, MTA Fillapex and Sealapex Root Canal Sealer showed the lowest antibacterial activity, a significant increase in antibacterial effect for both Pulp Canal Sealer? and AH plus sealers were found. Significantly higher were the mean diameters of the bacterial inhibition zone by both EasySeal or N2 sealers. DCT: AH plus and Sealapex Root Canal Sealer doesn?t show any bactericidal effect after 6 min of contact. After 15 and 60 min of contact a significant increment for AH plus and for Sealapex Root Canal Sealer of the bactericidal effect was found. Significantly much higher was the antibacterial effect of Sealapex Root Canal Sealer compare to that observed for AH plus. BioRootTMRCS, MTA Fillapex, Pulp Canal Sealer? and N2 showed at least means of the number of colonies formed in milliliter after 6 min of contact. Except for N2, a significant increase in bactericidal effect after 15 and 60 min for the other compared sealers (BioRootTMRCS, MTA Fillapex and Pulp Canal Sealer?). For every contact times considered, both TotalFill BC Sealer and EasySeal were bactericidal against E. faecalis and killed all bacteria

Resin infiltrant for non-cavitated caries lesions: evaluation of color stability

The objective of this in vitro study was to evaluate the over time color stability of one resin infiltrant (Icon) upon exposure to staining solutions (coffee and wine) compared with one nano-hybrid sealant (Grandio Seal), one transparent fissure sealant with fluoride (Control Seal) and one nanofilled composite (Filtek Supreme XTE). All materials were polymerized according to manufacturers’ instructions into silicon rings (height 1 mm; internal diameter 6 mm; external diameter 8 mm) to obtain specimens identical in size. The specimens were immersed in staining solutions at room temperature over a 28-day test period. The control samples have not been subjected to the staining process. A colorimetric evaluation according to the CIE L*a*b* system was performed by a blind trained operator at 7, 14, 21, 28 days of the staining process. Shapiro Wilk test and Kruskal Wallis ANOVA were applied to assess significant differences among different materials. Means were compared with Scheffe’s multiple-comparison test at the 0.05 level of significance. In the case of all materials, immersion in solutions resulted in clinically perceivable color changes after 1 week (∆E 0.05). Color coordinate CIE b* varied similarly for all materials tested (P > 0.05). Immersion in coffee or red wine resulted in clinically perceivable color changes for all materials tested. Icon showed the highest color variations both after 1 week and 1 month. Icon can fix the initial esthetic problem associated with white spot lesions, but the resin may become more discolored than other materials over time

Evaluation of the antibacterial activity of a new ozonized olive oil against oral and periodontal pathogens

In the present study, the antimicrobial properties of a new ozonized olive oil (O-zone gel) against oral and periodontal pathogens will be evaluated and compared with that of common CHX-based agents. O-zone gel was compared with two agents based on chlorhexidine digluconate (CHX): Corsodyl Dental Gel and Plak Gel. A. actinomycetemcomitans, P. intermedia and S. mutans, were selected and the antibacterial capability of the compounds was tested by using direct contact agar diffusion test (DCT) and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) evaluations. Differences between specific means were analyzed by a one-way analysis of variance (ANOVA). Group means were compared using a one-way ANOVA and Tukey?s test (P<0.05). O-zone gel reported inhibition zones which correspond to 33% and 43% of that achieved by the CHX agents. No inhibition of bacterial growth (MIC) on the Gram-positive strain by using O-zone gel was found and no antimicrobial effect (MBC) was observed by using O-zone gel on both Gram-negative and -positive strains. The new ozonated oil was a relatively moderate antiseptic. Gram-negative bacteria proved to be more sensitive to ozonized olive oil than Gram-positive ones. The ozonized olive oil demonstrated a lower antibacterial activity if compared to the CHX-based agents tested

In vitro antibacterial activity of different pulp capping materials

Background: Direct pulp capping involves the application of a dental material to seal communications between the exposed pulp and the oral cavity (mechanical and carious pulp exposures) in an attempt to act as a barrier, protect the dental pulp complex and preserve its vitality. The aim of this study was to evaluate and compare, by the agar disc diffusion test, the antimicrobial activity of six different pulp-capping materials: Dycal (Dentsply), Calcicur (Voco), Calcimol LC (Voco), TheraCal LC (Bisco), MTA Angelus (Angelus), Biodentine (Septodont). Material and Methods: Streptococcus salivarius , Streptococcus sanguis and Streptococcus mutans strains were selected to evaluate the antimicrobial activity by the agar disc diffusion test of different pulp capping materials. Paper disks were impregnated whit each pulp capping materials and placed onto culture agar-plates pre-adsorbed with bacterial cells and further incubated for 24 h at 37°C. The growth inhibition zones around each pulp capping materials were recorded and compared for each bacterial strain. Results: For the investigation of the antibacterial properties the ANOVA showed the presence of significant differences among the various materials. Tukey test showed that MTA-based materials induced lower growth inhibition zones. Conclusions: MTA-based products show a discrete antibacterial activity varying from calcium hydroxide-based materials which present an higher antibacterial activity

Fluoride release and uptake abilities of different fissure sealants

Background: The long-term capability of resin sealants and glass ionomer cements to release fluoride is associated to a reduction in pit and fissure caries. The regular use of fluoride varnishes/toothpastes can result in the absorption of fluoride into the sealant. The objective of the present study was to assess the fluoride release/uptake capacities of different fissure sealants. Material and Methods: Three different fissure sealants (Fuji Triage/GC, Fissurit FX/Voco and Grandio Seal/Voco) were examined. Ten discs of each material were prepared. Each disc was incubated with distilled water and then the solution analyzed for diluted for fluoride concentration, using a combination of fluoride electrode (OrionGP 1 S/N 13824, Orion Research Inc, Boston, MA, USA) connected to an expandable ion analyzer (Orion 720A, Orion Research Inc, Boston, MA, USA). Standard curves between 1 and 100 ppm F- were used to calibrate the electrode. Cumulative fluoride release was measured on days 1, 2, 3, 5, 7, 21, 35 and 49, then two different fluoride varnishes/ pastes (Profluorid Varnish/Voco, MI Paste Plus/GC), were applied to the sealants tested, and fluoride release (after reuptake) was measured on days 56, 70 and 84. Results: Kruskal Wallis test confirmed significant differences in fluoride release between Fuji Triage/GC and Fissurit FX/Voco and Grandio Seal/Voco from day 1 ( P < 0.001). The application of fluoride varnish Profluorid Varnish enhanced the fluoride release for all sealants ( P < 0.05). MI Paste Plus enhanced the fluoride release for all sealants except for Fuji Triage/GC ( P > 0.05). Conclusions: The GIC-based sealant (Fuji Triage/GC) released significantly more fluoride than the resin sealants tested. The exposure to the fluoridated varnish (Profluorid Varnish) significantly recharged the sealants tested more than the CPP-ACPF toothpaste (MI Paste Plus)

Biological and antibacterial properties of a new silver fiber post : in vitro evaluation

The incorporation of nano silver particles (AgNPs) to improve antibacterial properties of dental materials has become increasingly common. The aim of the present study was to compare the antibacterial activity and cytotoxicity effects of different fiber posts: glass fiber post, quartz fiber post, nano fiber post and silver fiber post. The antibacterial activity against S. mutans, S. salivarius and S. sanguis was evaluated by using the agar disc diffusion test (ADT). Four wells of 3x2 mm (one for each material) were made with a punch by removing the agar and filled with the materials to be evaluated. The size of the inhibition zone was calculated. An extract was made eluting the posts in cell culture medium using the surface area-to-volume ratio of approximately 1.25cm²/ml between the surface of the samples and the volume of medium. Cell cultures were then exposed to 100 ?L of the extracts medium. After 24 h, cell viability was determined using the MTT assay. Silver fiber post was the only material showing a fair antibacterial effect against all the three streptococcal strains. The level of cytotoxicity of all the fiber posts tested was higher than 90% and therefore they were considered not cytotoxic. The new silver fiber post reported a fair antibacterial activity. On the other hand all the fiber posts tested (including the post with incorporated AgNPs) proved to be biocompatible, suggesting that their application does not represent a threat to human health