•A stochastic model for the optimal operation of virtual power plants is developed.•The scenario tree contains both market and renewable generation scenarios.•An ad-hoc decomposition method ...drastically reduces the computational time.•Despite optimal solution, PV generation is partially curtailed.•Cogeneration plant can effectively participate in more markets.
As more uncontrollable renewable energy sources are present in the power generation portfolio, the need of more detailed and reliable tools for the optimal operation of energy systems has increased in the last years. This work presents a multi-stage stochastic Mixed Integer Linear Program with binary recourse for optimizing the day-ahead unit commitment of power plants and virtual power plants operating in the day-ahead and ancillary services markets. Scenarios reproduce the uncertainty of the ancillary services market requests, and production of photovoltaic panels. A novel decomposition algorithm is proposed to tackle the challenging multistage stochastic program. The methodology is tested on three types of large power plants: a natural gas-fired combined cycle, a combined heat and power combined cycle with thermal storage, and a virtual power plant integrating a combined cycle with battery and photovoltaic fields. Compared to the typical deterministic unit commitment approach, the proposed stochastic optimization approach allows to increase the revenues of the conventional power plant up to 13.58% and, for the combined heat and power and virtual power plant case, it allows finding a feasible and efficient operational scheduling.
A relevant issue in the development of disaster risk reduction strategies is played by design of mitigation measures aimed at reducing risk to acceptable values. For rapid landslides, such as debris ...flows, sheltering structures are very common mitigation measures realized in exposed areas that allow to protect elements at risk and to stop flowing mass. For the design of these works, the debris flow–structure interaction mechanism is very important. The paper focuses on the evaluation of debris flow–structure interaction mechanism in earth reinforced embankments based on an uncoupled analysis of the interaction in two flow cases (dominant static and dynamic). In particular, a novel approach to evaluate the horizontal stress distribution at different time of the impact phenomenon along the upstream face height of deformable sheltering structures considering the dominant flow component has been proposed. First, impact force over the time against structure is calculated. Subsequently, assuming that debris flow is completely stopped by embankment according to a scheme of accumulation of material behind the obstacle, the deformative response of different geometrical types of embankment is obtained by FEM numerical analysis for considered flow cases. The results of numerical analyses are discussed in terms of horizontal displacements in different control points in sheltering structures. The analysis showed that the deformative response of two geometries of embankments depends on dominant static or dynamic components of impact force.
Supported metal hydrides are key reactive intermediates in various catalytic processes, such as hydrogenation and dehydrogenation, but are often challenging to characterize spectroscopically. Here, ...deuterium solid state nuclear magnetic resonance spectroscopy is used to understand the structure of the corresponding silica‐supported zirconium hydrides after H/D exchange as an illustrative example of supported metal hydrides, which have been shown to display notable reactivity towards small molecules (e. g., CO2 and N2O) and to activate both C−H and C−C bonds, hence their use in to the conversion of hydrocarbons (alkanes, polyolefins etc.)
Surface organometallic chemistry (SOMC) represents a unique synthetic platform for the preparation of model heterogeneous catalysts resembling those broadly applied in industry. SOMC techniques ...usually rely on the grafting of tailored molecular precursors onto the surface OH groups of oxide supports. The development of such precursors and the understanding of their reactivity with the supports are therefore crucial for the development of well‐defined surface species. While a large number of organometallic precursors of early transition metals are known, only few examples of group‐10 metal complexes are reported, in spite of the great interest for heterogeneous catalysts based on the Pt‐group elements. Herein, we report the reactivity of a family of group‐10 (Ni, Pd and Pt) alkyl complexes, towards partially dehydroxylated SiO2 yielding well‐defined supported species. We studied the effect of the metal, ligand, and support on the grafting mechanism of such precursors through a combined experimental and computational approach. Ultimately, we showed that at least two grafting pathways are possible for these compounds, namely the protonolysis of the M‐alkyl bond by surface OH groups and the opening of strained siloxane bridges: the proportion of the two depending on the nature of the metal and its ancillary ligand.
Waterproofing systems of tunnels is of crucial importance for the long-term effectiveness of the underground works and for the possible impact on the surrounding environment. In conventional ...tunnelling, polymeric geomembranes are nowadays used with fluid barrier function, while nonwoven geotextiles and geonets are commonly employed with mechanical protection and drainage functions. After some descriptions of the main requirements of the geosynthetics used in tunnels and underground structures, the durability aspects of the materials forming the waterproofing systems are briefly outlined.
Propane dehydrogenation is an important field of research due to an increasing world‐wide demand of propene while classical production routes through naphtha cracking are in decline. In that context, ...silica‐supported Ga(III) sites, synthesized from surface organometallic chemistry principles, show high selectivity and stability in the propane dehydrogenation reaction. This performance is in significant contrast to the reported fast deactivation and lower selectivity of most Ga2O3 and CrO3 based materials. The Ga‐catalyzed propane dehydrogenation reaction is proposed to proceed through the formation of Ga alkyl intermediates for which it would be desirable to have detailed structural and spectroscopic information. Here, we prepare a consistent series of Ga(III) molecular complexes with varying numbers of alkyl and siloxide ligands; they are characterized by single crystal X‐Ray diffraction and X‐Ray Absorption Near Edge Structure analysis, which is known to be highly sensitive to the Ga coordination environment. We report in particular the structure and the spectroscopic signatures of Ga(iPr)(OSi(OtBu)3)2(HOSi(OtBu)3), a molecular mimic of the key proposed reaction intermediates in the Ga‐catalyzed PDH reaction.
Techniques that can characterize the molecular structures of dilute surface species are required to facilitate the rational synthesis and improvement of Pt-based heterogeneous catalysts. 195Pt ...solid-state NMR spectroscopy could be an ideal tool for this task because 195Pt isotropic chemical shifts and chemical shift anisotropy (CSA) are highly sensitive probes of the local chemical environment and electronic structure. However, the characterization of Pt surface-sites is complicated by the typical low Pt loadings that are between 0.2 and 5 wt% and broadening of 195Pt solid-state NMR spectra by CSA. Here, we introduce a set of solid-state NMR methods that exploit fast MAS and indirect detection using a sensitive spy nucleus (1H or 31P) to enable the rapid acquisition of 195Pt MAS NMR spectra. We demonstrate that high-resolution wideline 195Pt MAS NMR spectra can be acquired in minutes to a few hours for a series of molecular and single-site Pt species grafted on silica with Pt loading of only 3-5 wt%. Low-power, long-duration, sideband-selective excitation, and saturation pulses are incorporated into t 1-noise eliminated dipolar heteronuclear multiple quantum coherence, perfect echo resonance echo saturation pulse double resonance, or J-resolved pulse sequences. The complete 195Pt MAS NMR spectrum is then reconstructed by recording a series of 1D NMR spectra where the offset of the 195Pt pulses is varied in increments of the MAS frequency. Analysis of the 195Pt MAS NMR spectra yields the 195Pt chemical shift tensor parameters. Zeroth order approximation density functional theory calculations accurately predict 195Pt CS tensor parameters. Simple and predictive orbital models relate the CS tensor parameters to the Pt electronic structure and coordination environment. The methodology developed here paves the way for the detailed structural and electronic analysis of dilute platinum surface-sites.
The main objective of this paper is to discuss the experimental and theoretical approaches developed by different researchers in order to understand and to evaluate the soil geosynthetic interaction ...under different loading conditions. In the paper, the soil-geosynthetic interaction in pullout, direct shear, and inclined plane tests under both static and cyclic loading is analyzed based on the different theoretical and experimental results carried out by the authors and also available in literature. For each type of test, the factors affecting test results and soil-geosynthetic interface behavior, the theoretical model developed to predict the interface resistance and mobilized friction, and the relevance of the interface parameters obtained through the different tests in the design and performance of geosynthetic reinforced earth structures are discussed in detail.
Construction of embankments on soft soil may be a challenge, owing to its low shear strength and high compressibility. Among the different methods of ground improvement, the geosynthetic encased ...columns (GEC) are often used to support embankments over soft soil. In order to evaluate the mechanical response of the geosynthetic encased columns, based on the soil and column properties, settlements and stresses can be determined by means of analytical solutions or numerical analyses.
The paper compares the results of these two approach by means of parametric analyses. The German regulation EBGEO proposed an analytical model for predicting the pressure-settlement response of an axisymmetric unit cell of clay with a GEC. The numerical simulation of the behavior of a GEC in soft clay loaded by an embankment has been carried out by means of a two-dimensional finite-element commercial code.
In Italy, since early times, the environmental aspects have always been a key issue on the design and the application. Consequently, the geosynthetic reinforced soil structures consist of vegetated ...face steep slopes. Furthermore, the use of vegetation has also been recognized and incorporated in engineering practice for
erosion
control and for stabilization of shallow slopes. Vegetation influences slope stability and erosion process by both mechanical effects and hydrological effects. In particular, in the paper, the mechanical effects of vegetation related to soil stabilization will be described. The purpose of this paper is to present the specific role of vegetation in soil reinforcement applications, by means of the analysis of the available literature on the (i) factors affecting root reinforcement of soil, (ii) experimental tests carried out on roots and on roots-soil system, and (iii) analytical and theoretical models. The erosion applications will not treated in this paper. The use of vegetation in civil engineering and landscape works has grown in importance, even if the specific design standard concerning the use of vegetation for slope stabilization is still under discussion. Therefore, design and management of stabilization systems by plants require an accurate knowledge about the quantitative reinforcing root effects on soil strength.
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