118,502 research outputs found
Techno-Economic Analysis for Biogas Reforming using PSWA: Case Study on Methanol Synthesis
No full textThe production of biogas, a mixture of methane and carbon dioxide, from anaerobic digestion from different biowaste sources has been interesting for its application in chemical processes. Currently, it is invested in the production of thermal and electrical energy, but it has also been investigated for the production of syngas, which is usually derived from fossil fuels. A fundamental step for this application is the conditioning of biogas to produce valuable syngas, this can be achieved through a water absorption column among other technologies. This study aimed at the optimal configuration of a pressure swing water absorption (PSWA) tower for the optimal operation of a biogas reforming process. Results show how the placement of the water column has an impact on capital and operating costs, and how the level of conditioning can be useful for chemical synthesis
The Vajont disaster: SPH modelling of the post-event 2D Experiments
No full textThe Vajont disaster occurred on October 9, 1963, when an extremely large landslide fell into the Erto hydroelectric reservoir and generated a wave which overtopped the Vajont dam, sweeping away the downstream village of Longarone and causing about 2000 casualties. Several experiments were carried out after the disaster to assess why previous technical estimates had underestimated the real wave height; among them a series of 2D experiments were performed at the Hydraulics laboratory of Padua University: their results, made available only recently, have been considered to perform numerical experiments with the Smoothed Particle Hydrodynamics (SPH).
SPH is a well-established lagrangian mesfree particle method initially developed for astrophysical applications (Lucy, 1977; Gingold & Monaghan, 1977) and subsequently successfully extended to free-surface flows (Monaghan 1994).
SPH proved to be effective even in the simulation of coupled soil-water dynamics in the rapidly varied scouring of non-cohesive sediment at the bottom of an artificial reservoir owing to a flushing manoeuvre (Manenti et al., 2012; Manenti 2011).
In this work is analysed the motion of a volume of non-cohesive material (reproducing the part of Vajont landslide close to the dam) induced by a moving piston in a 2D laboratory basin.
The adopted model treats the water and non-cohesive sediment as weakly compressible fluids with small density fluctuations, responding to a linear state equation; both water and sediment are divided into a set of material particles responding to the Newton’s equations of the classical physics; the i-th particles’ motion results from the numerical solution of the discretized mass and momentum conservation equations according to classic SPH approach adopting a staggered first-order explicit time integration scheme.
Boundary conditions are simulated by ghost-particles: this method appears to be one of the most rigorous and can be easily implemented in a 2D geometry with straight boundary sides (Randles & Libersky, 1996).
In order to keep control of ordinary numerical noises affecting the pressure field, a periodical density smoothing is carried out (Di Monaco et al., 2011).
The rheological model adopted for the landslide is derived from Chambon et al. (2011) and consists in introducing a threshold t for the apparent viscosityapp above which the material behaves like a Newtonian fluid.
The research, apart from the comparison of the maximum wave run-up on the mountain side with the 2D laboratory experiments, aimed at using the numerical tool to give a theoretical interpretation of the relative importance between the different physical mechanisms which concurred in generating the catastrophe
Life Cycle Assessment (LCA) of Dimethyl Ether (DME) Production: Fossil Fuels vs. Biogas
No full textThis study conducts a comprehensive Life Cycle Assessment (LCA) to compare the environmental impacts of two alternative pathways for producing dimethyl ether (DME): one utilizing conventional fossil fuel-based processes and the other relying on biogas feedstocks. LCA is employed as a robust tool for evaluating the sustainability of these fuel production methods. The authors meticulously quantify resource inputs and outputs for both production routes in the inventory analysis phase. For conventional fossil fuel-based production, the value of the impact categories is retrieved from SimaPRO database. On the other hand, for biogas-based production, Aspen HYSYS is utilised to perform process simulations. The results of these are used as input for LCA analysis. Our findings reveal significant disparities between the two production pathways. Biogas-derived DME exhibit lower greenhouse gas emissions and reduced dependence on finite fossil resources. The biogas route also provides valuable co-benefits, such as organic waste valorization and potential improvements in soil quality through feedstock cultivation. However, it is essential to recognize that biogas-based production requires more land and water resources than fossil fuel-based. Therefore, trade-offs between reduced carbon emissions and increased resource use should be carefully considered, particularly in regions with limited land and water availability
Economic Optimization of the Synthesis Section of a Small-Scale Biogas-to-Methanol Plant
No full textAs global concerns about carbon emissions and the sustainability of energy sources grow, the utilization of biogas has gained significant attention for reducing greenhouse gas emissions and moving away from fossil-based chemicals. Biogas, predominantly composed of methane and carbon dioxide, is generated through the anaerobic digestion of organic materials, such as agricultural residues, municipal waste, and wastewater sludge. To exploit the full potential of biogas and increase its energy density, the conversion of biogas into valuable chemical products seems to be a viable and feasible solution. Specifically, the production of methanol and the development of small-scale biogas-to-methanol plants has received notable recognition. This study focuses on the economic optimization of the synthesis section within such plants. The optimization of this section plays a crucial role in ensuring both the economic viability and the sustainability of the process. The synthesis section is modeled with two reactors arranged in series, where liquefaction of the methanol and water produced takes place after each reactor. To maximize methanol production, unreacted gases are recycled back to the first reactor. This article presents the economic optimization perspective on the reactor's design and operating conditions, finding a compromise between maximizing methanol yield and minimizing reactor costs. This study highlights the potential for biogas-based methanol in the transition between greener energy alternatives. Moreover, it offers a systematic procedure for optimizing the design of the synthesis sections, which is applied to a typical case study. By addressing the complex factors involved in this process, this research actively contributes to the progress of sustainable energy solutions and provides a valuable baseline for future development
Surrogate-Based Optimization of the OPEX of a Modular Plant for Biogas Conversion to Methanol Using the MADS Algorithm
No full textThe present work studies the potential of surrogate models for the global optimization of complex chemical processes. In particular, a modular plant for the conversion of biogas to methanol is considered. The Aspen HYSYS simulation of this plant was run 480 times, which ensured the even distribution of points in the input space. The evenness of this design of experiments was evaluated using a discrepancy measurement called the Mixture Discrepancy. With the simulation data, some of the most widely used surrogate models such as regression models and the Kriging Gaussian process were trained. The most accurate model for the prediction of each output variable was selected and used for the optimization of the OPEX. The optimization complemented the trained surrogate models with the Mesh Adaptive Direct Search (MADS) algorithm. For this purpose, the openaccess computational implementation of the MADS algorithm called NOMAD was used. With the surrogate-based optimization, the computational times were reduced an 88% with respect to the simulation-based optimization. In addition, the accuracy of the surrogate model was paramount, as an average 0.75% prediction error was found. Consequently, the models proved sufficient for optimizing the studied process, resulting in a 22.2% reduction in the OPEX
Crystallization
No full textCrystallization is the non-conventional operation allowing to obtain crystals with high purity from a liquor. Taking advantage of different components solubilities, more than one pure species can be obtained from the same solution. Nucleation and growth phases can be described by dedicated models. The delta-L law derivation for the crystal growth process is explained in detail and the relationship between linear growth and growth ratio is discussed by mean of a case study
Assessing Thermodynamic Flexibility Boundaries via Residue Curve Maps
No full textResidue curve maps (RCMs) are a widely exploited tool to assess whether a multicomponent mixture separation by distillation results to be feasible or not. They usually refer to a given feed composition and to the products purities as specifications; sometimes the whole distillation regions can be discussed in order to evaluate all the mixture possible splits (Petlyuk&Danilov (2001), Petlyuk (2004)). All these considerations are nevertheless related to nominal operating conditions, that is for a given and constant feed composition. If feed perturbations are likely to occur (e.g. separation downstream a fermentation process) a flexibility analysis is required to assess the operation feasibility boundaries under uncertain conditions (Swaney& Grossmann (1985)). Moreover, product recovery is often a more appealing specification from an industrial point of view since it is directly related to the process productivity. For all these reasons, this study deals with the use of RCMs to assess the thermodynamic flexibility limits of a simple distillation case study for a given bottom product recovery and purity under uncertain operating conditions. The starting binary mixture is water and n-butanol, a common and well-known mixture whose separation by simple distillation shows an heterogeneous azeotrope. One component at a time is then added up to obtain an ABE/W (acetone, butanol, ethanol and water) mixture. Due to the high nonideality of the mixture, the addition of an organic component substantially affects the equilibria. A thermodynamic flexibility analysis methodology was outlined for both the binary and ternary cases as well as for the quaternary one. After that, the separation feasibility of the binary mixture was compared to the others (Di Pretoro et al. (2019)). Beside illustrating the procedure for thermodynamic flexibility assessment via RCMs, this analysis aims to show how to enhance the separation from a flexibility point of view taking advantage of the mixture nonideality
SPH Modelling of the 3D laboratory experiments on the Vajont landslide
No full textThe Vajont disaster occurred on October 9, 1963: a huge landslide fell into the Erto hydroelectric reservoir and generated a wave which overtopped the Vajont dam, sweeping away the downstream village of Longarone and causing about 2000 casualties. Before the catastrophic event, some experiments were performed at the Research Centre of Nove (Treviso, Italy) on a 3D physical model of the Vajont reservoir. Owing to the uncertainties on the complex physical mechanism (i.e. volume of the landslide and its kinematic), the energy of the generated wave was underestimated. These experimental data, which were made available recently, have been considered to perform numerical experiments of the Vajont landslide with the Smoothed Particle Hydrodynamics (SPH).
SPH is a well-established Lagrangian mesh-free particle method initially developed for astrophysical applications (Lucy, 1977; Gingold & Monaghan, 1977) and subsequently successfully extended to free-surface flows (Monaghan 1994). SPH proved to be effective in a number of different applications, e.g. for simulating coupled soil-water dynamics in a flushing manoeuvre (Manenti et al., 2012a) and for analyzing the 3D dynamics of a tsunami wave propagating on a beach (Guandalini et al., 2013).
The study has been carried out using the code SPHERA (Agate et al., 2010), developed at RSE in the frame of the SPH project funded by Energy Research System. The main code features include the continuum discretization by means of a finite number of material particles carrying physical properties and moving according to Newton’s equations of the classical physics, as the traditional SPH. Spatial derivatives of a variable at a point are approximated by using the information on the neighboring particles based on the kernel approximation. Other basics of the code concern innovative developments of many modelling aspects as the boundary treatment (Di Monaco et al., 2011), the time integration scheme and the interactions among particles with different material properties (Manenti et al., 2012b).
The geometrical complexity of the 3D model provided to SPHERA, required the development of a proper pre-processing methodology including digitalization and rendering of the terrain maps before and after the disaster, the generation of corresponding contour lined surfaces and the generation of final 3D geometry, using GIS tools and properly developed software.
The research, apart from the evaluation of the maximum wave run-up on the mountain side, aimed at using the numerical tool to give a theoretical interpretation of the relative importance between the different physical mechanisms which concurred in generating the catastrophe
Impact of Methanol Synthesis Kinetics on Bulk Production Prediction: an In-Silico Assessment
No full textKinetic modelling covers a key role in process simulation and design. Recently the methanol sector is assisting a remarkable enhancement due to its applications as fuel, solvent, and precursor as shown in Bozzano and Manenti (2016). The increasing number of patents, the market prospects, and recent research witness this renewed interest. However, despite this rate in developing and improving technologies, the kinetics modelling does not follow these trends. The methanol synthesis chemical paths, the intermediates, and the real role of the active sites are nowadays still unclear. However, process engineering requires reliable models to estimate the methanol synthesis rate, hence, to design and size the reactor and downstream equipment. Currently, the most used kinetics are Graaf and Vanden Bussche - Froment’s models which in any case show some shortcomings and weaknesses. Starting from these premises, the need for updated kinetics is clear. This work aims at comparing and highlighting the impact of different kinetic models (1) original Graaf (or-GR), (2) Vanden Bussche - Froment (VBF), and (3) refitted Graaf (ref-GR) on the methanol synthesis configuration for different feedstocks through an in-silico assessment. The general simulation flowsheet includes the single-stage PFR for the methanol synthesis, the condensation step, and recycle loop for the unreacted syngas. The comparison with industrial data proves that the ref-GR model predicts better than the original Graaf model as in Graaf et al. (1988), while the VBF, Vanden Bussche and Froment (1997), tends to overestimate methanol production. The validation exploits industrial data published in the literature
The dental hygienist in Europe and in Italy: survey on future expectations of the profession
No full textThe dental hygienist in Europe and in Italy: survey on future expectations of the profession
I. Casula, C. Manenti, L. Bonfanti, A. Ganda, E. Marchesini, T. Anzaldi, M. Bianchi
Department of Medical and Surgical Specialties, Radiological Sciences, and Public Health (DSMC) – University of Brescia
Aim The purpose of this study is to learn about training, skills and regulation of the dental hygienist profession in the European Union/ European Economic Area (EU/EEA) countries and at the same time to highlight the skills that the Italian dental hygienists believe can improve their professional practice.
Materials This work is split into two parts: the first one consists of a review of literature and legislation regarding the current status of dental hygienist in the EU/EEA countries; information was also found on the main dental hygienist institutions websites (IFDH, EDHF, CECDO) and on the official websites of training schools in Europe. The second part consists of a questionnaire, which was provided to graduated Italian dental hygienists to evaluate their professional status. The questionnaire is divided into three parts: biographical data, current skills, desirable skills.
Results The dental hygienist profession is regulated in two thirds of EU/EEA countries. In Austria, Belgium and Germany is not yet recognized, but the situation seems to be evolving. Northern Europe has the highest level of dental hygiene education. The harmonization of dental hygiene profession has not been achieved yet. At the same time, the range of professional responsibilities today is not the same for each country.
Instead, the survey included a total of 601 participants, 77% females and 23% males. 52% of the sample is between 20 and 30 years old and 31% comes from Lombardy.
According to the questionnaire results, 71% of dental hygienists are satisfied with their current skills, but the main competencies that they consider to improve are the ability to take X-rays (62%), to make diagnosis (56%) and to administer topical anesthetic under the dentist supervision (41%) or autonomously (39%). These skills would be able to put him in better professional conditions, improving his cultural and professional autonomy. The need is to expand the range of professional skills.
Conclusion The dental hygienist has made a lot of progress since birth, but today is not recognized and educated in the same way in all countries. The goal is to reach a more common identity at European level. Even if the Italian dental hygienist performs less skills than the European one, his training is often better. So the profession needs to expand beyond traditional roles. The invitation is to prosper and grow to face future challenges with competence and professionalism
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