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A new concept of a system for Combined Heat and Power generation is presented. The concept is based on hybrid use of two renewable energy sources, direct solar (thermodynamic solar) and biomass (indirect solar energy). Biomass combustion is conducted using a fluidized bed combustor. A second source of energy, given by the direct irradiation of the bed with a concentrated solar radiation, is integrated in the same system, using the fluidized bed as solar receiver. A Stirling engine converts heat into mechanical power. A Scheffler type mirror is adopted to allow irradiation of the system in a fixed focal point. Advantages of the proposed solution are illustrated and some preliminary results on the performance of the system, obtained with a simple model, are presented. The principal improvements with respect to existing systems of similar size and primary energy source are illustrated. The most important are the enhanced heat transfer processes that are realized with the help of the fluidized bed, and the possibility of continuous cogeneration during the day. Different working conditions are considered to estimate the contribution given by the burning of fuel, in presence as well as in absence of sun irradiation (as during the night). The distribution of energy shares among the different flux contributes is reported versus the amount of biomass burned per unit time. The results clearly demonstrate the advantage of coupling, in the same system, two sources for heat generation, thus maintaining the option of producing electricity without the supply of biomass fuel.

Hot water heat stores with stratification are a common technology used in solar energy systems and reuse of waste heat. Adding a PCM module at the top of the water tank would give the system higher storage density, and compensate heat loss in the top layer. The work presented here includes experimental results and numerical simulation of the system using an explicit finite-difference method. Experiments and simulations were carried out using different cylindrical PCM modules. With only 1/16 of the volume of the store being PCM, 3/16 of water at the top of the store was held warm for 50% to 200% longer and the average energy density was increased by 20% to 45%. Furthermore, these 3/16 of water were reheated by the heat from the module after being cooled down in only 20 min.

In the last years, even more attention was paid to the alternative fuels that allow both reducing the fossil fuel consumption and the pollutant emissions. Gaseous fuels like methane and hydrogen are the most interesting in terms of engine application. This paper reports a comparison between methane and different methane/hydrogen mixtures in a single-cylinder Port Fuel/Direct Injection spark ignition (PFI/DI SI) engine operating under steady state conditions. It is representative of the gasoline engine for automotive application. Engine performance and exhaust emissions were evaluated. Moreover, 2D-digital cycle resolved imaging was performed with high spatial and temporal resolution in the combustion chamber. In particular, it allows characterizing the combustion by means of the flame propagation in terms of mean radius and velocity. Moreover, the interaction of turbulence with the local flame was evaluated. For both the engine configurations, it was observed that the addition of hydrogen results in a more efficient combustion, even though the engine configuration plays an important role. In PFI mode, the lower density of hydrogen causes a lower energy input. In DI mode, instead, the larger hydrogen diffusivity counteracts the charge stratification especially for larger hydrogen content. © 2016 Elsevier Ltd. All

Responses to recent climatic changes in the sediment of subarctic Lake Saanajärvi in northwestern Finnish Lapland are studied by comparison of various biological and sedimentological proxies with the 200-year long climate record, specifically reconstructed for the site using a data-set of European-wide meteorological data. The multi-proxy evidence of simultaneously changing diatom, Cladocera, and chrysophyte assemblages along with the increased rates of organic matter accumulation and pigment concentrations suggest that the lake has undergone a distinct typological change starting from the turn of the 20th century. This change, indicating an increase in lake productivity, parallels a pronounced rise in the meteorologically reconstructed mean annual and summer temperatures in the region between ca. 1850 and 1930's. We postulate that, during the Little Ice Age, the lake was not, or was only weakly, thermally stratified during summer, whereas the subsequent increase in air and hence epilimnetic water temperatures resulted in the development of the present summer stratification. The increased thermal stability of the lake created more suitable conditions for the growth of phyto- and zooplankton and changed the overall primary production from benthos to plankton. Mineral magnetic and carbonaceous particle records suggest long-distance pollution, particularly since the 1920's, yet the observed changes in lake biota and productivity can hardly be explained by this very minor background pollution; the 20th century species configurations are typical of neutral waters and do not indicate any response to pollution.

Chemical looping combustion allows a simple separation of CO2 during the combustion of fossil fuels, thanks to the use of regenerable oxygen carriers. In this work, novel materials containing manganese and iron/manganese oxides have been developed via geopolymerization, and characterized in thermogravimetric apparatus and fixed bed reactor. The materials demonstrated suitable characteristics for chemical looping combustion (CLC). The tests conducted in the temperature range 800-900 °C revealed the good performance of the developed oxygen carriers, which also exhibited the ability to release O2 in inert conditions. Efficiencies in CO conversion up to 99% were achieved, as well as some synergies between Fe and Mn oxides gave a beneficial effect toward the oxygen yield. X-ray diffraction analyses of the samples confirmed the effective reduction/oxidation behavior of the materials, as well as the morphological characterization did not reveal dramatic changes of the internal microstructure up to 900 °C

Capítulos en libros The importance of the natural gas sector in the electric power industry has increased substantially over the last decades, reaching 21% generation capacity in Europe in 2016. Generation companies that own gas fired units (GFUs), such us combined cycle gas turbines, have to take into account not only the fuel and the operation and maintenance costs, but also the costs related to the third-party access (TPA) tariffs to the gas network as any other gas consumer. This paper highlights the importance of modeling these TPA tariffs in a proper manner as they represent a significant share of the total operation cost of GFU. In addition, the fact that TPA final costs depend on the daily gas consumption for the whole month, makes traditional short-term unit-commitment (UC) models unable to capture the impact of the new complicating constraints. This paper presents the mathematical formulation of a UC model that models the TPA tariffs to the gas network in a more realistic manner where a joint assessment is formulated for all the units that withdraw gas from the same node of the gas network. The paper includes an example case that illustrates the impact on the optimal hourly scheduling of such detailed modeling, and it compares the results with the standard formulation based on individual cost functions of each thermal unit. info:eu-repo/semantics/publishedVersion

The most widely used process for hydrogen production is steam methane reforming. It can be carried out using a membrane reactor in which simultaneous hydrogen production and purification occur. Mathematical modeling of these reactors plays a key role in the selection of the design and operating parameters that yield high performance for the reactor. This review study discusses, synthesizes, and compares different mathematical modeling studies on the packed bed membrane reactors for hydrogen production from methane found in the literature. Different approaches used in these modeling studies for the hydrogen permeation steps, reaction kinetic expressions, phases involved (pseudo-homogeneous and heterogeneous), and spatial dimensions (one, two, and three dimensional) are given.

The reversible dissociation/carbonation of metal carbonates, performed in fluidized bed reactors, is one of the most promising technological solution for thermochemical energy storage (TCES) in concentrating solar power plants (CSP). In this framework, the SrCO3/SrO system is receiving increasing interest due to its high energy density (4 GJ/m3) and working temperatures (up to 1200 ?C). As the more investigated CaCO3/CaO couple, also SrO undergoes a dramatic drop of reactivity over multiple carbonation/calcina- tion cycles due to sintering. Even though the potentiality of this system has already been proved by thermo-gravimetric analyses, its actual reaction performances in a fluidized bed are strongly dependent on the gas-solid contact efficiency and heat/mass transfer between the gaseous and solid phase. In this work, the cyclic carbonation/calcination of the SrO/SrCO3 system for TCES-CSP has been investigated by thermo-gravimetric analysis and, for the first time, in a lab-scale fluidized bed rig, thus providing useful applicative insights. A new Al2O3-stabilized composite has been synthesized, i.e. Al2O3 has been added to SrO/SrCO3 system as both sintering inhibitor and flow conditioner. In particular, composite materials with different Al2O3/SrO composition have been synthesized to investigate the ef- fect of the inhibitor amount on both the fluidizability and energy storage performances.