The study presented hereby investigates experimentally and with CFD simulations the gas distribution effect on the hydrodynamic of a Geldart Group A turbulent fluidized bed. Experiments were carried out on a cold flow fluidized bed column with an even and uneven gas distribution. Local solid volume fraction profiles were measured using optical probes at different bed heights and along two radial directions. Optical probe measurements allow catching a clear hydrodynamic difference between both even and uneven gas distributions. These results were then used to assess CFD simulations with the code Barracuda™ (MP-PIC approach). It is noteworthy that the choice of drag correlation and boundary conditions strongly influences the agreement between the experimental and CFD results. Once the correct parameters are chosen, CFD simulations captured the effect of gas distribution changes.

Many of the probes used to understand hydrodynamics in circulating fluidized bed risers intrude into the environment they are measuring, although assumptions are typically asserted that the intrusive probes do not affect the data collected. This could be a poor assumption in some cases and conditions. We found that intrusive fiber‐optic probe measurements consistently mis‐predicted the solids concentration compared to the nonintrusive pressure drop measurements outside the fully developed flow region of a riser containing fluid catalytic cracking catalyst or glass bead particles. The discrepancy was sensitive to superficial gas velocity, solid circulation rate, probe position, and flow direction. Barracuda VR™ computational fluid dynamics simulations confirmed this, and indicated that particle momentum was lost at the leading edge of the probe and particles were spilling over to the probe tip. Accordingly, new probe designs were proposed to mitigate the intrusiveness of a fiber‐optic probe for more accurate characterization. © 2017 American Institute of Chemical Engineers AIChE J , 63: 5361–5374, 2017

In fluidised bed processes, the solids are in vigorous motion and thus inevitably subjected to mechanical stresses due to inter-particle and particle-wall impacts. These stresses lead to a gradual degradation of the particles by surface wear, abrasion and body fragmentation commonly termed attrition. One significant contribution of attrition comes from the air jets of the fluidised bed distributor. Particles are entrained into the air jet, where they get accelerated and impacted onto the fluidised bed particles. The jet induced attrition only affects the part of the bed which is limited by the jet length, where the mode of attrition is largely collisional. The overall jet attrition rate is therefore the result of the combination of the single particle damage and the flux of particles entering into that region. The attrition behaviour of particles in the jet region is analysed by evaluating their propensity of breakage experimentally and by simulating an air-jet in a bed of particles by CFD-DEM. The frequency of collisions and impact velocities are estimated from which the attrition due to a single air-jet is predicted.

Particles attrition is an important phenomenon to account for when developing and scaling up new fluidized bed processes. Most of the time, little amount of particles is available at the early development stage and only lab scale experiments can be carried out. Most of the available tools and methodologies to investigate attrition at small scale were developed for the FCC process on group A particles. However, attrition also needs to be evaluated for new applications such as Chemical Looping Combustion (CLC) with different particle properties. In this work, we propose a method using a jet cup apparatus that aims to compare attrition rate of solids having different properties. Materials studied in this paper are a Group A FCC catalyst (Dp(50) of 70 mu m, grain density of 1450 kg/m(3)) and a Group B CLC oxygen carrier (Dp(50) of 180 mu m, grain density of 3600 kg/m(3)). Based on experimental data and CFD modeling, comparative testing conditions could be defined in order to apply the same mechanical stress for all solids tested. Classical attrition indexes usually quantify the generation of fine particles below 40 mu m which does not describe fully attrition of Group B powders. Therefore, a new attrition index was defined to calculate the total amount of particles generated by attrition over the entire size range of all solids tested. Finally, the attrition rates of both materials were compared applying the methodology developed. It was found that attrition rate is less important for the oxygen carrier. It is important to notice that attrition due to thermal or chemical stresses is not investigated in this study and needs separate evaluation. (C) 2015 Elsevier B.V. All rights reserved.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Combustion en boucle chimique (CLC) Thierry Gauthier

Hydroconversion reactivity of an Athabasca vacuum residue (VR) has been studied in a batch autoclave reactor, as part of a work dedicated to the study of detailed hydroconversion mechanisms. In this work, as a first step, a detailed analytical study was performed on several vacuum residues. Saturates, Aromatics, Resins and Asphaltenes (SARA) composition strongly varies for different feeds, but SAR fractions analyses show strong similarities (C-13 NMR distribution and molecular weight). Therefore, SARA compositions may explain feed hydroconversion differences.The reactivity of the whole Athabasca vacuum residue has been studied under deep hydroconversion conditions in a batch autoclave. Process severity was adjusted varying by temperature from 395 up to 420 degrees C. Catalytic effect was also evaluated. As expected, results show that VR conversion increases with temperature. Product yields were obtained and depend mostly on residue conversion. The results also confirm that cracking reaction mechanisms are initiated thermally and that radicals formed are stabilized by catalytic hydrogenation.In order to better understand feedstock effects on reactivity, we have also conducted a dedicated study in order to separate the Athabasca vacuum residue in different families, each of them containing mainly asphaltenes, resins or an aromatics/saturates mixture. The reactivity of those cuts will be studied in a next step to highlight feed composition effects. (C) 2009 Elsevier B.V. All rights reserved.

Rapid, effective separation of phases is an essential step in many hydrocarbon conversion gas-solid processes. In heavy oil upgrading, fluid catalytic cracking (FCC) and biomass pyrolysis, for example, very fast separation of reacting gases from catalytic or heat-bearing solids is required to inhibit further reaction. The primary functions of a rapid separator in the context of a gas-solid flow are, first, to terminate contact between the reacting gases and the catalytic or hot solid particles and, second, to recover the isolated product vapors. Uninterrupted vapor-solid contact results in degraded, overcracked and generally less valuable products. Increasing interest in rapid separation has led in the past 25 years to a wide variety of proposed separator designs in the literature.Centrifugal separation is the fundamental principle underlying cyclone operation and most rapid gas-solid separation processes. Traditional cyclones rely on centrifugal separation and are very widely applicable. They are used for the removal of solid particulate matter from gas or liquid streams, for gas demisting, and in hydrocyclones. Most FCC processes employ traditional cyclone configurations for secondary and tertiary separation. The review briefly summarizes important topics studied in reverse flow cyclone operation. For initial separation, however, most fast gas-solid separators in the literature feature only partial cyclone layouts. Separation typically occurs more quickly in these devices relative to traditional cyclones, likely at the expense of separation efficiency.The current review places emphasis on experimental results and novel separation techniques in the context of fast gas-solid separation. Several recent methods of rapid gas-solid separation employ co-current or "uniflow" centrifugal arrangements. Hence, particular attention is directed to co-current centrifugal separators. These devices have been studied much less intensively than their reverse flow counterparts. Fast co-current separators, with their novel, partial cyclone layouts, are interesting for their performance characteristics in relation to popular commercial designs.

The compositional analysis (speciation) of heavy oil products is a key step to improve our understanding of hydrotreatment processes and reaction mechanisms. Thus, detailed characterization of polar fractions, such as asphaltenes, should be considered. Here, we employ atmospheric pressure photoionization Fourier transform ion cyclotron mass spectrometry to monitor the evolution of the asphaltene hydrocarbon and sulfur families in deep hydrotreatment processes (fixed and ebullated beds). The results suggest that the complexity of the asphaltenic fractions (in terms of chemical polydispersity) is drastically lowered with increased process severity. In either fixed or ebullated beds, the evolution of the sulfur species is quite similar in class composition, aromaticity (DBE/carbon number ratio), and polycondensation (DBE). The compositional changes are marked by a drastic increase in aromaticity to highly polycondensed dealkylated aromatic structures. Asphaltene disaggregation followed by a dealkylation of the remaining species could be suggested. The proposed scheme would converge toward those previously proposed.

Fluidized bed processes are widely used in the refining industry, mostly for conversion applications (e.g. fluid catalytic cracking, fluid coking, residue hydroconversion, Fischer-Tropsch Synthesis, etc.). These are large scale processes operating under severe conditions. Fluidized bed processes involve many complex phenomena that need to be considered in order to ensure proper design, operation and reliability. There have been thousands of publications over many years in the field of fluidization, but some of the fundamentals of fluid-particle flows still remain to be clarified. As a consequence, scale-up and industrialization of new technologies or processes remain a difficult, challenging and risky task.IFP is deeply involved with fluidized bed processes used in the refining industry. Over the last twenty years, industrial developments and PhD studies were conducted to explore new concepts, to develop new technologies, to scale-up hydrodynamics, to understand and quantify key phenomena. This paper discusses R&D practices in the field and current challenges encountered, mostly based on IFP experience. It does not intend, however, to provide an extensive literature review of all topics addressed in this paper.Interactions between particles, multiphase flow and reactor geometries are complex issues in fluidized beds. Therefore, experimentation is required to study new concepts such as downflow systems, complex phenomena such as vaporization of droplets in contact with gas-particle systems. The design of the experiment and the development of appropriate instrumentation are never simple and in the absence of simple similarities, anticipation of the main flow features is unavoidable. Modeling of results is then mandatory in order to translate results to industrial perspectives. Over the last 15 years, CFD has appeared as a promising tool to describe multiphase flow phenomena in complex geometries. Unfortunately, the lack of theoretical models to describe gas particle flow, at least for Group A powders, still leads researchers to conduct experiments to validate simulations or to adjust the gas-particle closure equations to validate results. Furthermore, observation in industrial units, during start-up or under steady conditions, when possible, greatly aids in validating research efforts and methodology.Despite its maturity, our industry is moving forward. There are ongoing developments in the energy and fuels market as well as in environmental fields, but also in the scientific background available to describe multiphase flow. Therefore, evolutionary R&D in the field is still needed to progress in the description of complex phenomena in order to optimize reactors and technologies and to face the changes of our industry.