Fixed-bed reactor

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The use of TiO2 as catalyst in thin film fixed bed reactor for the treatment of landfill water

The use of TiO2 as catalyst in thin film fixed bed reactor for the treatment of landfill water

2 Ecole Nationale Polytechnique, Unité URIE, 10 Avenue Pasteur, El Harrach, Algiers, Algeria Abstract: The main purpose of this study is the use of TiO 2 as catalyst in thin film fixed bed reactor (TFBR) for the treatment of landfill water with the high initial concentration of recalcitrant organic matter. The effectiveness treatment process was determined by the evaluation of the influence of the experimental

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Oxidative pyrolysis of wood chips and of wood pellets in a downdraft continuous fixed bed reactor

Oxidative pyrolysis of wood chips and of wood pellets in a downdraft continuous fixed bed reactor

a b s t r a c t In air staged gasification and advanced carbonization processes, oxidative pyrolysis occurs in downdraft continuous fixed bed reactors. An oxidation zone separates the virgin fuel from the resulting char and propagates upward. Here, the oxidation zone was stabilized at a fixed elevation in a 20 cm I.D. fixed bed reactor using wood chips or wood pellets. In controlled continuous operating mode, we investigated the impact of air flux and bed bulk density on the behavior of the oxidation zone in terms of wood con- sumption, and yields of char, gas and tars. An air:wood mass ratio of 0.7 was measured and in our oper- ating conditions, and was not sensitive to air mass flux and bed density. With oxidative pyrolysis, yields of organic condensates were lower than with allothermal pyrolysis, whereas the production of pyrolysis water and permanent gases increased. Finally, the oxidation zone was shown to be flat and horizontal in a wood pellet bed but inclined in a wood chip bed.
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A new experimental continuous fixed bed reactor to characterise wood char gasification

A new experimental continuous fixed bed reactor to characterise wood char gasification

a b s t r a c t Two-stage fixed bed gasification is one of the most promising technologies for low and medium energy production from biomass. In industrial processes, control and optimisation is often based on constructor know-how rather than on an understanding of the mechanisms involved. We present a new original tool, the Continuous Fixed Bed Reactor (CFiBR), which was specifically designed and built to enable a fine understanding of the limiting stage of a gasifier: the char bed gasification zone. The reactor, the instru- mentation, the operating procedure and set-up tests are described in detail. The potential of the reactor is demonstrated through the characterisation of the gasification of a continuous wood char bed. Tempera- ture profiles and gas concentrations along the 65 cm bed were established and showed that the most reactive zone was the first 10 cm of the char bed. Accurate energy and mass balances provided relevant information regarding the contributions of the main reactions involved in the fixed char bed gasification process.
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Dynamic modeling of three-phase upflow fixed-bed reactor including pore diffusion

Dynamic modeling of three-phase upflow fixed-bed reactor including pore diffusion

b Homogeneous Catalysis Division, National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411 008, India Abstract The dynamics of a three-phase upflow fixed-bed reactor are investigated using a non-isothermal heterogeneous model including gas-liquid and liquid-solid mass transfer and diffusion / reaction phenomena inside the catalyst. The partial differential and algebraic equations (PDAE) involving three integration variables (time and two space coordinates) are solved via discretization of the spatial coordinates coupled with the Gear method. For a multistep hydrogenation on a shell catalyst the model exhibits significant effects of the external and above all internal resistance to hydrogen transfer but also non trivial internal hydrocarbons concentration profiles. A simplified model is compared to the extended one and to experimental data in transient regime. In the investigated conditions – hydrocarbons in large excess – the diffusion of hydrocarbons appears to be actually not limiting, so that the simplest model predicts accurately the transient reactor behavior.
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Dynamic modeling of three-phase upflow fixed-bed reactor including pore diffusion

Dynamic modeling of three-phase upflow fixed-bed reactor including pore diffusion

Homogeneous Catalysis Division, National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411 008, India Abstract The dynamics of a three-phase upflow fixed-bed reactor are investigated using a non-isothermal heterogeneous model including gas-liquid and liquid-solid mass transfer and diffusion / reaction phenomena inside the catalyst. The partial differential and algebraic equations (PDAE) involving three integration variables (time and two space coordinates) are solved via discretization of the spatial coordinates coupled with the Gear method. For a multistep hydrogenation on a shell catalyst the model exhibits significant effects of the external and above all internal resistance to hydrogen transfer but also non trivial internal hydrocarbons concentration profiles. A simplified model is compared to the extended one and to experimental data in transient regime. In the investigated conditions – hydrocarbons in large excess – the diffusion of hydrocarbons appears to be actually not limiting, so that the simplest model predicts accurately the transient reactor behavior.
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A mathematical modeling of catalytic milli-fixed bed reactor for Fischer–Tropsch synthesis: Influence of tube diameter on Fischer Tropsch selectivity and thermal behavior

A mathematical modeling of catalytic milli-fixed bed reactor for Fischer–Tropsch synthesis: Influence of tube diameter on Fischer Tropsch selectivity and thermal behavior

6. Conclusions Simulation results based on the described two dimensional model have shown a high dependency of the thermal behavior with respect to the thermal conductivity of the gas mixture, which is linked to the hydrogen consumption, exhibiting a high thermal conductivity compared with other compounds, along the reactor. Although the viscosity and the heat capacity slightly change during synthesis, this variation does not cause the same variation of temperature within the bed. The simulations of different tube diameters of the fixed-bed reactor allowed to highlight the high performance of millimeter-scale for FT synthesis. No exact con- vergence was achieved for diameter tube higher than 3.11 mm due to the thermal runaway affecting the other variables strongly coupled. Therefore, in the work reported here using a kinetic associated with a highly active catalyst, the critical diameter involving a hot spot lower than 10 K is found to be lower 2.50 mm. No significant temperature rise occurs below this dia- meter range preventing the increase of light hydrocarbons selec- tivity. Millichannel catalytic reactor provides effective heat removal for this exothermic synthesis, leading to an isothermal temperature profile which induces low methane selectivity and production of long chain hydrocarbons. The campaign of simula- tions also allowed to find out an optimal space velocity to maximize the production rate of C 5 þ . Results obtained from
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A mathematical modeling of catalytic milli-fixed bed reactor for Fischer–Tropsch synthesis: Influence of tube diameter on Fischer Tropsch selectivity and thermal behavior

A mathematical modeling of catalytic milli-fixed bed reactor for Fischer–Tropsch synthesis: Influence of tube diameter on Fischer Tropsch selectivity and thermal behavior

Although several drawbacks are identified, MFBR are widely used in FT process. These reactors are indeed capable of being easily scaled-up when going from a single tube to multitubular reactor to the extent that a good inlet distribution can be ensured. Moreover, many preliminary studies are carried out in packed-bed reactors at lab-scale such as catalysts developments, kinetic mea- surements and deactivation studies. Nevertheless, within years of development and improvement, some of these drawbacks have been reduced especially those regarding heat removal concerns. However, one of the main limitations of MFBR lies in high pressure drops that can arise when decreasing the catalyst particles dia- meter. No such limitation occurs in slurry phase reactors allowing consequently the use of particles as small as possible and higher effectiveness factors of the catalyst. Actually, particles diameters range from about 100 μ m when using a slurry reactor to about the millimeter for a MFBR. The use of smaller catalyst pellets in MFBR can obviously increase the effectiveness factor by reducing the diffusion limitations but the catalyst activity rises thereby and heat removal might be difficult to process using conventional reactors. Alternatively, the catalyst and/or the inlet reactor feed need to be highly diluted to prevent hot spot formation. On the other hand, process intensification that has emerged for the recent years has demonstrated the ability of new heat-exchanger reactors to operate in a new way with enhanced mass and heat transfers mainly due to a large surface to volume ratio. Actually, channel size mostly leads to laminar flow but the reduction of the diameter to millimeter allows avoiding unexpected transfer limitations. Milli-structured reactors allow for a strong increase of heat transport in radial direction and thus isothermal operation, even for highly exothermic reactions, becomes feasible.
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Dynamics of a three-phase upflow fixed bed catalytic reactor

Dynamics of a three-phase upflow fixed bed catalytic reactor

Keywords: fixed bed reactor; cocurrent upflow; dynamic modeling INTRODUCTION Reactor control and reactor safety are important features in the design and operation of industrial processes that carry out complex reactions with constraints of thermal stability or/and selectivity as for example exothermic hydrogenation reactions. In this light, a dynamic model of the reactor is very useful to study both the start-up period and the effects of a sudden (accidental) change in the operating conditions, particularly on the thermal reactor stability. So far steady state models of multiphase fixed bed reactors have been extensively developed in several reviews (Herskowitz and Smith, 1983; Zhukova et al., 1990; Gianetto and Specchia, 1992), while only a few papers have investigated their transient behavior. Feick et al. (1970), Visser et al. (1994) compared models of various complexities to describe the dynamic behavior of packed bed reactors. Wärna et al. (1996) performed dynamic models for slurry and fixed bed reactors operating in non-isothermal conditions. The dynamic model of the fixed bed reactor was applied to describe the start-up of a fixed bed reactor during the hydrogenation of toluene on a Ni/Al 2 O 3 catalyst.
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Dynamics of a three-phase upflow fixed bed catalytic reactor

Dynamics of a three-phase upflow fixed bed catalytic reactor

Keywords: fixed bed reactor; cocurrent upflow; dynamic modeling INTRODUCTION Reactor control and reactor safety are important features in the design and operation of industrial processes that carry out complex reactions with constraints of thermal stability or/and selectivity as for example exothermic hydrogenation reactions. In this light, a dynamic model of the reactor is very useful to study both the start-up period and the effects of a sudden (accidental) change in the operating conditions, particularly on the thermal reactor stability. So far steady state models of multiphase fixed bed reactors have been extensively developed in several reviews (Herskowitz and Smith, 1983; Zhukova et al., 1990; Gianetto and Specchia, 1992), while only a few papers have investigated their transient behavior. Feick et al. (1970), Visser et al. (1994) compared models of various complexities to describe the dynamic behavior of packed bed reactors. Wärna et al. (1996) performed dynamic models for slurry and fixed bed reactors operating in non-isothermal conditions. The dynamic model of the fixed bed reactor was applied to describe the start-up of a fixed bed reactor during the hydrogenation of toluene on a Ni/Al 2 O 3 catalyst.
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X-ray micro-tomography and pore network modeling of single-phase fixed-bed reactors

X-ray micro-tomography and pore network modeling of single-phase fixed-bed reactors

a b s t r a c t A three-dimensional (3D) irregular and unstructured pore network was built using local topological and geometrical properties of an isometric bead pack imaged by means of a high-resolution X-ray computed micro-tomography technique. A pore network model was developed to analyze the 3D laminar/inertial (non-Darcy) flows at the mesoscopic (pore level) and macroscopic (after ensemble-averaging) levels. The non-linear laminar flow signatures were captured at the mesoscale on the basis of analogies with contraction and expansion friction losses. The model provided remarkably good predictions of macro- scopic frictional loss gradient in Darcy and non-Darcy regimes with clear-cut demarcation using chan- nel-based Reynolds number statistics. It was also able to differentiate contributions due to pore and channel linear losses, and contraction/expansion quadratic losses. Macroscopic mechanical dispersion was analyzed in terms of retroflow channels, and transverse and longitudinal Péclet numbers. The model qualitatively retrieved the Péclet-Reynolds scaling law expected for heterogeneous networks with pre- dominance of mechanical dispersion. Advocated in watermark is the potential of pore network modeling to build a posteriori constitutive relations for the closures of the more conventional macroscopic Euler approaches to capture more realistically single-phase flow phenomena in fixed-bed reactor applications in chemical engineering.
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Fluidized bed as a solid precursor delivery system in a chemical vapor deposition reactor

Fluidized bed as a solid precursor delivery system in a chemical vapor deposition reactor

3 Chemistry Department, University of Minnesota 207 Pleasant St., SE, Minneapolis, MN 55455 United States Chemical vapor deposition (CVD) using precursors that are solids at operating temperatures and pressures, presents challenges due to their relatively low vapor pressures. In addition, the sublimation rates of solid state precursors in fixed bed reactors vary with particle and bed morphology. In a recent patent application, the use of fluidized bed (FB) technology has been proposed to provide high, reliable, and reproducible flux of such precursors in CVD processes. In the present contribution, we first focus on the reactor design which must satisfy fluidization, sublimation and CVD reactor feeding constraints. Then, we report mass transport results on the sublimation of aluminium acetylacetonate, a common precursor for the CVD of alumina films. Finally, we discuss the efficiency of the precursor feeding rate, we address advantages and drawbacks of the invention and we propose design modifications in order to meet the process requirements.
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Kinetic study of biomass char combustion in a low temperature fluidized bed reactor

Kinetic study of biomass char combustion in a low temperature fluidized bed reactor

A B S T R A C T The purpose of this work is the kinetic study of biomass char combustion in a low temperature fluidized bed reactor. This char was obtained from fast pyrolysis of beech stick in an annex batch fluidized bed reactor at 923 K and atmospheric pressure. Operating conditions of the combustion were thoroughly characterized so that the reaction takes place in isothermal conditions and a constant oxygen partial pressure. The kinetic study was performed for temperatures up to 643 K, oxygen partial pressures ranging from 5065 to 21273 Pa and cylindrical char particles (D = 4 mm and L = 9 mm). The Volumetric Model was found to be in very good agreement with experimental data. Values of activation energy and reaction order with respect to oxygen are respectively equal to 144 kJ/mol and 0.59. The reaction scheme during char combustion showed that char first reacts with oxygen to form CO which is further oxidized either at the particle surface or in the gas phase to produce CO 2 . Besides, it
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Accelerating Palladium-Catalyzed C-F Bond Formation: Use of a Microflow Packed-Bed Reactor

Accelerating Palladium-Catalyzed C-F Bond Formation: Use of a Microflow Packed-Bed Reactor

conversion within 20 minutes, however unsatisfactory results were obtained at 1.25 mol % Pd loading (Figure 3a). It is worth noting that the infusion of stainless steel spheres into the reactor matrix was also investigated, due to presumed increases in heat transfer, [13] but gave no advantage over a pure CsF packing in terms of residence times or product yield. As stated, one of the major advantages of flow chemistry is the ability to ‘superheat’ solvents above their boiling point in a safe and controlled manner by employing a backpressure regulator (BPR). [14] Figure 3b depicts the temperature dependence of the Pd-catalyzed
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Experimental study of torrefied wood fixed bed: thermal analysis and source term identification

Experimental study of torrefied wood fixed bed: thermal analysis and source term identification

A B S T R A C T In this paper, self-heating scenarii were experimented on torrefied wood chips under atmospheres containing oxygen. These tests were carried out in a packed bed reactor. The experimental device was equipped with numerous thermocouples at different levels in the wood bed reactor ensuring temperature monitoring. The impact of oxygen supply was investigated at low-temperature (150 °C) both regarding oxygen content and at- mosphere gas flow rate. The related results pointed out the propensity of the wood bed to self-heating parti- cularly under a growing oxygen content or a low flow rate of oxidizing gas causing thus a spontaneous com- bustion. Furthermore, during self-heating, the source term was assessed relying on the local energy balance equation based on the experimental temperature fields. To summarize all results, source term values were fitted to a basic heat generation term of an oxidation reaction expressed as follows: Π ∆ = H × ∊ × A exp ( ) − Ea × ρ
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3D Numerical simulation of natural gas combustion in a fluidized bed reactor

3D Numerical simulation of natural gas combustion in a fluidized bed reactor

3 Numerical simulations Unsteady three dimensional numerical simulations of the fluidized-bed reactor have been carried out using a Eulerian n-fluid modeling approach for gas-solid turbulent polydisperse flows developed and implemented by IMFT (Institut de Mécanique des Fluides de Toulouse) in the NEPTUNE CFD V1.08@Tlse version. NEPTUNE CFD is a multiphase flow software developed in the framework of the NEPTUNE project, financially supported by CEA (Commissariat à l´Energie Atomique), EDF (Electricité de France), IRSN (Institut de Radioprotection et de Sûreté Nucléaire) and AREVA-NP. The numerical solver has been developed for High Performance Computing (Neau et al., 2013). The Eulerian modeling used in this work was described in Section (2). One class of particle was simulated, with a particle diameter The latter represents the average sample size used in the experiments (the particle diameter in the sample ranges between and (Dounit et al., 2001b)). Other quantities of interest for the numerical simulation are the particle mass density the particle emissivity and the particle restitution coefficient, which accounts for particle energy exchanges in (partially elastic) collisions. The fluidizing gas is a mixture composed of methane and air injected at the following operating conditions: pressure , total flow rate= air factor= and fluidizing velocity= at In the experiments, a distributer
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Convective Drying of Mixtures of Sewage Sludge and Sawdust in a Fixed Bed

Convective Drying of Mixtures of Sewage Sludge and Sawdust in a Fixed Bed

Liège, Belgium jie.li@ulg.ac.be ABSTRACT. This work is part of a project aiming at developing a renewable fuel for gasification purposes, through the convective drying of sludge/wood mixtures. The first step consists in characterizing the drying behaviour of sludge/sawdust mixtures, in a convective fixed bed dryer. In particular, the influence of the mixing step (no mixing against 30 s at 40 rpm) and the sawdust/sludge ratio (1/9, 2/8, 3/7 and 4/6 on a dry basis) have been investigated, as well as the drying temperature (50 °C, 80 °C and 110 °C). As showed in a previous work, the addition of dry matter into sludge has an impact on the initial 3D structure of the bed of extrudates to be dried. Moreover, it is well known that the volume shrinkage occurring during sludge drying will affect the drying velocity. In this study, X-ray tomography, a non-invasive imaging technique, is used to assess changes in volume, porosity and exchange surface between the beginning and the end of the drying process. Results first confirm the importance of the mixing step on the drying behaviour: the drying rate of the mixed sludge is slower than the one of original sludge. Nevertheless the addition of sawdust is shown to have a positive impact on the drying process from mass ratio of 2/8, with observed drying rates higher than for the original sludge. During the whole drying process, the volume and exchange surface of the sample increase and the porosity decreases as the mass ratio increases. These results indicate that the air and the sample contact more fully with more sawdust addition, resulting from bed expansion and exchange surface increase. Hence, the heat and mass transfer efficiency between the air and the material increases and consequently the drying rate. Further work will be done in order to assess the impact of the drying temperature and to characterize the behaviour of these samples during pyrolysis using thermo gravimetric analysis.
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Kinetic study of biomass char combustion in a low temperature fluidized bed reactor

Kinetic study of biomass char combustion in a low temperature fluidized bed reactor

2.2.2. Sampling method and gas analysis The sampling of gases is carried out by a stainless steel mobile probe (inner diameter 4 mm) located at the fluidized bed surface. A thermo couple is placed inside the mobile probe to measure the precise tem perature at the entrance of the probe. The gas sample is sucked by a vacuum pump connected to a flowmeter (volume flow rate of 100 mL.min −1 at STP). At the mobile probe outlet, the pumped gas passes through a cyclone and a filter to separate gas from particles and through a wash bottle cooled at 0 °C to remove any traces of water. To prevent any condensations of steam, all of the lines from the reactor to the entrance of the condensation system are heated to a temperature of 150 °C.
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Novel fluidized-bed biofilm reactor for concomitant removal of microcystin-LR and organics.

Novel fluidized-bed biofilm reactor for concomitant removal of microcystin-LR and organics.

16 quantified for Sphingomonas sp. (RS) depicts low biofilm formation ability inside the biocarriers. The reason could be the poor attachment property of this strain on the biocarrier surface. Azeredo et al., (2000) [23] shown that exopolymers have a determinant role for the Sphingomonas sp. to form biofilm and thus low biofilm formation in RS could be attributed to the low exopolymer formation marked by weak cell-to-cell adhesion property which led to detachment of biocells before much colonization has occurred. On the other hand, other stains hold long-term (50-70 days) promise in terms of biofilm attachment and thus the possible secretion of MC-degrading enzymes viz. mlrA, mlrB and mlrC encoded by mlr gene cluster (which is often responsible for the effective breakdown of the complex MCs structure), may have been effectively processed in the EPS matrix (Dziga et al. 2016) [24]. Hence, on this pretext, the RS reactor was rejected and not studied further. However, reactor RC was continued, as it was the negative control to study for the removal of MC-LR and other organics (COD removal, nitrate, nitrite, and ammonia removal) without the involvement of MC-LR degraders.
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Oxidative pyrolysis of pine wood, wheat straw and miscanthus pellets in a fixed bed

Oxidative pyrolysis of pine wood, wheat straw and miscanthus pellets in a fixed bed

duction decreased at higher temperatures. Some remarks need to be made before positioning the present work. First, we need to emphasise that almost all the research related to forced counter-current smouldering has been performed with high air flux compared to studies of oxidative pyrolysis. Indeed, in those studies, air flux varied from stoichiometry conditions (equivalence ratio equal to 1) to fit combustion applications, down to gasification ones with equivalence ratio close to 0.25. Several authors [ 10 , 11 , 13 ] investigated a lower air flux but none as low as the level in the present study. Thus, information is missing on the propagation rate, geometry, and con- version during counter-current smouldering in packed bed in very low air flux conditions. Moreover, it has also been reported that with such a small air mass flux, steady state regime is difficult to reach [ 10 ]. Sec- ondly, very little information is available on the influence of the nature of the biomass on the features of the oxidation zone; quantitative results in particular, would advance our understanding of the process. And finally, in counter-current smouldering in a downdraft reactor, com- paction occurs in the oxidation zone and thus needs to be taken into consideration for a global understanding and potential applications.
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Experiments support simulations by the NEPTUNE_CFD code in an Upflow Bubbling Fluidized Bed reactor

Experiments support simulations by the NEPTUNE_CFD code in an Upflow Bubbling Fluidized Bed reactor

A B S T R A C T Long tubes with small internal diameter find increasing applications in indirect concentrated solar receivers using an Upflow Bubbling Fluidized Bed of Geldart-A powders as heat carrier. Although successfully demon- strated for tubes of 0.5 to 1 m length, longer tubes are required to increase the solar energy capture efficiency and capacity. The fluidization phenomena differ with the tube length, and freely bubbling fluidization will be transformed into slugging, thus hampering the heat transfer. The behavior of Geldart-A powders in tall tubes of small I.D. has not been extensively studied. The research experimentally investigated the different fluidization modes in a 4 m long tube, and demonstrated the occurrence of freely bubbling at the bottom section of the bed, and slugging from a bed depth in excess of about 1.25 m. Slug characteristics (frequency, length, velocity) were measured and correlated. The results were used to validate 3D numerical simulations based on an Euler-Euler approach in the NEPTUNE_CFD code applied to a fine mesh of 15,000,000 cells. A positive match between experimental and simulation results concerning frequency and velocity of large bubble structures was obtained. The effect of mesh refinement on the slugging behavior prediction was discussed.
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