13 research outputs found

    Relaxation, Incubation, and Dissociation in CO 2

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    Kinetics mechanism of asphaltenes liquid-phase pyrolysis

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    The world energy demand is continuously increasing while the energy supply is still strongly related to fossil fuel, and likely to say so in the near future. However, the availability of high-quality crude oil feedstocks is constantly depleting. Heavy Fuel Oils (HFOs) are expected to play a vital role in the future of the energy supply as fuels for power generation and marine shipping. This work presents the first step in the formulation of a kinetics model aimed to reconstruct the HFOs pyrolytic behavior as the weighted sum of their SARA (Saturates, Aromatics, Resins, Asphaltenes) fractions contribution. In this work, details of the model to describe the asphaltenes pyrolysis is reported. The development of the model followed two main steps. The first one concerned the formulation of a suitable characterization framework being HFOs and asphaltenes complex mixtures made by thousands of different compounds. The characterization framework is based on the design of five pseudo components which are used to generate surrogate mixtures to mimic actual asphaltenes samples. The surrogate mixture is generated as the linear combination of pseudo components to reproduce the sample’s elemental composition. The pseudo components structure was designed taking advantage of experimental information from literature and in-house experiments performed at King Abdullah University of Science and Technology (KAUST). The second step was the development of the pyrolysis kinetics scheme. The formulation of the kinetic model proceeded through chemistry-related considerations intending to reproduce the all-significant pyrolysis products. A reaction pathway is assigned to each pseudo component with the task to approximate the overall kinetics. Model parameters such as activation energy, pre-exponential factors, and stoichiometric coefficients of each reaction were tuned following a data fitting approach to match experimental evidence. The model obtained is predictive and versatile being able to reproduce the pyrolytic behavior of different asphaltenes samples just knowing their elemental composition. The mechanism of asphaltenes represents a first step in the formulation of a comprehensive kinetics scheme for HFOs, which can be adopted for design, tuning, and optimization of combustion modeling processes

    Sonoprocessing of oil: Asphaltene declustering behind fine ultrasonic emulsions

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    Despite the transition toward carbon-free energy carriers, liquid fossil fuels are expected to occupy an important market share in the future. Therefore, it is crucial to develop innovative technology for better combustion reducing the emissions of pollutants associated with their utilization. Water in oil (w/o) emulsions contribute to greener combustion, increasing carbon efficiency and reducing emissions. Water content, emulsions stability, and droplet size distributions are key parameters in targeting the efficient use of emulsions as combustibles. In particular, for fixed water content, the finer the emulsion, the better its beneficial effect on combustion. In this work, two emulsions, mechanically and ultrasonically generated, were compared. Cryogenic scanning electron microscopy (cryo-SEM) allowed the visualization of water droplets inside the oily matrix. No surfactants were added to the oil, due to its high asphaltenic content. Asphaltene molecular aggregates, namely clusters, act as natural surfactants stabilizing the emulsions by arranging at w/o interface and forming a rigid film. The asphaltenic rigid film is clearly visualized in this work and compared for the two emulsions. The results showed finer water droplets in the ultrasonically generated emulsion, together with a reduction in the thickness of the asphaltenic film. Ultrasonically induced cavitation favored the de-clustering (breakage of intermolecular forces) of asphaltene molecules. Thus, smaller clusters allowed to stabilize smaller water droplets resulting in an ultra-fine emulsion, which improves the combustion performances of the fuel

    Numerical model of an ultrasonically induced cavitation reactor and application to heavy oil processing

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    This study describes a numerical approach to model ultrasonically induced cavitation (UIC) reactors. UIC forms vapour-filled cavities in a liquid medium due to an applied acoustic field and their eventual collapse. UIC reactors are characterized by the presence of a vibrating probe that generates pressure waves by high-frequency oscillations (>20 kHz), which control the formation, dynamics, and eventual collapse of the vapour cavities. Those vapour cavities eventually enhance mixing and favour the occurrence of gas-liquid reactions. The zones of high mixing and reactivity coincide with the presence of the bubble cloud, which depends on the shape of the vessel and sonotrode. The development of advanced computational fluid dynamics (CFD) models is crucial to optimizing UIC processes’ geometry and operation parameters. A new algorithm for modelling UIC has been implemented within the OpenFOAM framework in the present study. The volume-of-fluid (VoF) method employs a diffuse interface approach for the volume fraction transport equation. The bubble dynamics are solved with sub-grid models, and the coupling between the main flow field and the sub-grid scales is performed through source terms in the transport equations. The source terms are de-coupled from convective and diffusive components of the volume fraction equation. The history of the bubbles is considered to consist of nucleation, oscillations, and collapse. The oscillations are resolved via the Rayleigh–Plesset equation. The concluding part of the work demonstrates the application of the algorithm to simulate the operation of an UIC reactor, which was designed to desulfurize fuels using the oxidative (ODS) process

    The Indian consensus guidance on stroke prevention in atrial fibrillation: An emphasis on practical use of nonvitamin K oral anticoagulants

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    The last ten years have seen rapid strides in the evolution of nonvitamin K oral anticoagulants (NOACs) for stroke prevention in patients with atrial fibrillation (AF). For the preparation of this consensus, a comprehensive literature search was performed and data on available trials, subpopulation analyses, and case reports were analyzed. This Indian consensus document intends to provide guidance on selecting the right NOAC for the right patients by formulating expert opinions based on the available trials and Asian/Indian subpopulation analyses of these trials. A section has been dedicated to the current evidence of NOACs in the Asian population. Practical suggestions have been formulated in the following clinical situations: (i) Dose recommendations of the NOACs in different clinical scenarios; (ii) NOACs in patients with rheumatic heart disease (RHD); (iii) Monitoring anticoagulant effect of the NOACs; (iv) Overdose of NOACs; (v) Antidotes to NOACs; (vi) Treatment of hypertrophic cardiomyopathy (HCM) with AF using NOACs; (vii) NOACs dose in elderly, (viii) Switching between NOACs and vitamin K antagonists (VKA); (ix) Cardioversion or ablation in NOAC-treated patients; (x) Planned/emergency surgical interventions in patients currently on NOACs; (xi) Management of bleeding complications of NOACs; (xii) Management of acute coronary syndrome (ACS) in AF with NOACs; (xiii) Management of acute ischemic stroke while on NOACs
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