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The present study concerns with an optimization method of Solid Oxide Fuel Cell (SOFC) systems for electricity generation, directly fed by CH4 (methane) or C2H5OH (ethanol). By considering a detailed thermodynamic analysis, an innovative simulation model, namely THERMAS (THERmodynamic MAthematical Simulation), was designed and implemented. A specific SOFC-based system was selected to be the reference simulation, which is assumed to be equipped with heat exchangers (preheaters), a reformer, a SOFC-stack system and an afterburner. THERMAS allows for an extended parametric analysis in terms of energy and exergy and offers the opportunity to investigate all the operational characteristics that affect system's efficiency. The optimization process relies on the difference between the energy and exergy efficiency, where an OPF (OPtimization Factor) has been introduced and particularly estimated for each simulated scenario, based on several operational parameters, such as fuel composition, extension of chemical reactions and temperatures. The introduction of this OPF is actually an innovative improvement towards an easy-to-use optimization of SOFC systems. It is found that the design of a SOFC-based power plant fueled by pure hydrocarbons, has to be carefully simulated before its, otherwise the purification of fuels sounds meaningless.

This work simulates electricity production in a Solid Oxide Fuel Cell (SOFC)-based power plant, fed by biogas of various compositions. Steam reforming of the gas feed stream is used to produce the required supply for the SOFC. Given the constraints of the feed stream compositions, resulting from the origin of biogas, i.e., by the biomass from which the biogas has been produced as well as by the operating conditions selected for its production, the overall plant performance is modelled in terms of energy and exergy. The model provides results on the efficiency, power output and thermal behavior of the system, thus presenting the potential to offer great advantages in generating electricity from biogas and reducing the environmental impact. This research study presents the efficiency of such a system in terms of energy and exergy, by considering several values of the operational parameters (extensions of reactions that take place in the apparatus, temperatures, feed stream compositions, etc.). It is found that moving towards a methane richer fuel, the energy and exergy efficiency can remain almost constant at high levels (around 70%), while in absolute value the electric energy can increase up to 35% according to the system’s needs. Therefore, under this prospect, the present research study reveals the usefulness of low content methane fuels, which through the optimization process can succeed identical energy management compared to high content methane fuels.

Greece has to recycle 70% of Construction and Demolition Waste (CDW) by 2020, in the context of the enforcement of Waste Framework Directive (WFD) 2008/98/EC. CDW recycling has started only recently to a small extent and is restricted to road works. The reuse of CDW in new concrete production could contribute to the construction sector sustainability through minimizing landfill and the need for new raw materials. Literature data are found regarding the performance of recycled concrete, but limited knowledge is available regarding the chemical and mineralogical properties of recycled aggregates (RA) and how these affect concrete. Moreover, Greek aggregates are not siliceous aggregates as are most of the aggregates investigated in literature. Against this background, this study aims to evaluate for the first time mechanical and durability performance of concrete made with RA from different Greek recycling plants. All recycled materials used were characterized in terms of chemical and mineralogical composition and certain chemical and physical properties have been determined. It was found that all RA are enriched in Si, Al, and alkali oxides, which was mineralogically verified by the identification of quartz and minor quantities of mica and feldspars. They proved though innocuous to alkali aggregate reaction. Higher water absorption of coarse RA is their most negative physical characteristic. Fine fractions of RA have low Sand Equivalent and significantly high water absorption values, which make them unsuitable to replace natural sand. Water soluble ions are at the same level to that of natural aggregates. Furthermore, concrete mixtures were prepared using an RA percentage ranging from 0% to 75%. Results indicate that the compressive strength of recycled concrete ranges from significantly lower (37% reduction) to equal, compared to conventional concrete, depending on the composition of RA. The majority of literature data relate the inferior quality of RA to their high water absorption, the findings of the present research though indicate that the presence of clay minerals has a more pronounced adverse effect to concrete's strength. As for the durability properties examined, i.e. water absorption, sorptivity, frost and carbonation resistance, the recycled concrete mixtures exhibited somewhat lower performance than reference concrete.

Aim: The aim of this project was to identify the characteristic flavor and off-flavor compounds that could be used as potential oxidation markers to establish the quality of the stored wines and to predict the wines’ shelf life employing a mathematical model.Materials and methods: Six mono-varietal Greek white wines (produced by three varieties) were bottled using two types of corks having different oxygen permeability properties. Volatile compounds, resistance to oxidative degradation and total and free-sulfur dioxide content were recorded in all samples. Results were processed using the root cause analysis versus packaging and storage conditions. Additionally, a predictive model has been constructed to estimate the shelf life of the bottled wine.Results: Physicochemical analysis indicated the absence of significant oxidative degradations during the first 7 months. Furthermore, 12-month stored samples showed a significant alteration in their flavor profile. Based on the concentration of the selected oxidation marker (isoamyl-alcohol), the possibility of the bottled product not reaching the end of its shelf life, has been used to quantify the product’s quality. A very successful fit was achieved between mathematical and experimentally obtained data concerning shelf life predictions.Significance and impact of the study: The modeling of the results indicated the importance of cork selection due to the Oxygen Transmission Rate (OTR) values that potentially impact the quality of the wines in time, according to the evolution of the isoamyl-alcohol concentration. For the wine industry, the selection of the appropriate cork according to the wine type is an important consideration.

Olive oil has gained much appreciation among consumers worldwide leading to increased markets as well as greater consumer expectation and thus more challenges for the relevant food sector. By understanding the product, its interactions with the environment, and the protective role of the package, decisions can be made on the barrier properties required of the packaging materials to achieve the desired shelf life. To this end, the shelf life of packaged olive oil under various storage and distribution environments can be predicted by mathematical modeling. This review examines the basic factors affecting the shelf life of olive oil in different packaging systems and describes the main oxidative degradation mechanisms for them. Since an experimental investigation to correlate the basic quality factors and the shelf life of a product is time- and effort-consuming, the use of mathematical modeling for the prediction of packaged olive oil shelf life is also discussed. In the presented works, shelf life predict...

A descriptive model was applied to study the shelf life of packaged olive oil, based on 24 month simulations and for various combinations of storage conditions close to the “real-life” situations. The major factors influencing oxidation (namely light, oxygen permeability of packaging materials and temperature of storage), were combined in various case studies otherwise requiring time-consuming experiments. The time evolution of the possibility for packaged olive oil not to reach the end of its shelf life and the month, after bottling, at which this possibility becomes 70%, 50% and 30%, were presented. It was found that exposure of packaged olive oil to light in continuous or alternating patterns should be avoided since, even for a short time, it could significantly stimulate the oxidative degradation caused only by elevated temperatures and presence of oxygen. In general, all the packaging materials tested could be considered adequate for preserving the quality of olive oil under a variety of storage conditions. Plastic containers had a particularly stronger protective role when oil was stored light, while glass was the most protective material when oil was stored in the dark.

The experimentally defined oxidative alterations taking place in packaged olive oil stored in various packaging materials and storage conditions, were used as basic evidence in order to develop and support a descriptive mathematically expressed theory, and eventually to conclude on a predictive model. Hexanal was experimentally quantified for extra virgin olive oil packaged in 0.5 L glass, PET, and PVC bottles, and stored at 15 °C, 30 °C and 40 °C under fluorescent light or dark conditions for 12 months. A set of mass transport equations describing the chemical reactions occurring in the oil phase as well as the diffusion of oxygen in the oil phase and through the packaging material, was numerically solved for various combinations of temperatures, light conditions and packaging materials. In addition, the probability of the packaged olive oil not to reach the end of its shelf life during a certain time period, was estimated and proposed as a quality reduction indicator. The suggested model could be used as a tool for an accurate forecast of the quality issues for packaged olive oil.

In the present study, the probability of packaged olive oil not reaching the end of its shelf life, P safe, was used as a quality factor to evaluate the time taken for olive oils stored at various conditions to reach the end of their shelf lives. P safe was used to comment on the activation energy required during the degradation process per actual or simulated case, and hexanal was used as the main quality-related indicator. Based on the month after bottling at which P safe reached 70%, the activation energy of an “equivalent” chemical reaction, representative of overall quality degradation, was calculated for several storage conditions. Using the differences between activation energies estimated using the above method, we found the most important factors influencing the shelf life of the packaged olive oil to be the initial storage period in the dark, the role of elevated temperatures, and the presence of light, either continuous or in alternating patterns, in association with the packaging materials used in this study. These results were in qualitative agreement with previously reported experimental observations and simulations, indicating the validity of using P safe, and of activation energies calculated from it, to predict the shelf life of packaged olive oil.

Based on a thermodynamic and economic analysis presented in the first part of this paper, ethanol is considered as an alternative fuel with suitable characteristics for electricity generation in SOFCs. Ethanol fed steam reformer-SOFC systems attain high theoretical efficiencies in the range of 83.7–93.4% operating at carbon-free conditions between 800 and 1200 K . These efficiencies classify ethanol as the second most valuable fuel option for SOFCs after natural gas, higher than important other fuel candidates such as gasoline and methanol. A discussion is made upon the benefits obtainable from the utilization of ethanol for generation of electricity in SOFCs and a complete “ethanol scenario” is proposed as a competitive energy policy and a step forward to the target of sustainable development. The analysis reveals the cost relations between each fuel scenario and focuses upon the measures required so as the “ethanol scenario” to break through the threshold of economic viability.

The method of exergy analysis is presented for a SOFC power plant involving external steam reforming and fueled by ethanol and methane. The optimal operation parameters of the integrated SOFC plant are specified after minimizing the existing energy and exergy losses. A comparison of methane and ethanol as appropriate fuels for a SOFC-based power plant is provided in terms of exergetic efficiency assuming the minimum allowable (for carbon-free operation) reforming factors for both cases. Then, a parametric analysis provides guidelines for practical design. It is concluded that the exergy calculations pinpoint the losses accurately and that the exergy analysis gives a better insight of the system's process.

In the present work, energy and exergy system analysis are used to estimate the thermodynamic performance of a SOFC system fuelled by methane. More precisely, the present work examines in detail the influence of the presence or absence of the reformer within the whole apparatus and the consequent energy and exergy losses due to the reforming process. It was found that the exergetic efficiency for the Direct-Methane-SOFC-PP is very high (92.5%) compared with that obtained by assuming Reforming-SOFC-PP (66.9%). Finally, it was stressed that the influence of the fuel utilisation on the cell output is positive in the direction of the maximisation of the energetic and exergetic efficiency.