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Different flow regimes are known to occur in the interaction of multiphase gas–liquid flows over packed beds of solid particles, such as those observed in trickle bed reactors (TBRs). There are four major flow regimes that are known to occur in downward cocurrent flow in TBRs, namely: trickle, pulse, bubble, and mist flow regimes. In this work, the focus is on macro-scale experimental visualizations and investigations of the flow regimes in a two-dimensional TBR. Experimental observations are made to investigate the development and transition of these flow regimes over a wide range of liquid and gas velocities. Cylindrical particles are placed between two glass plates that are sealed on the sides, and water and air are injected over them using an injection manifold to simulate multiphase flow in a TBR. A diffused light emitting device (LED) light table is used to illuminate the experimental window, while real time images are obtained using a high-speed camera. Flow maps are reported depicting all four regimes and the transition regions between them. Transition regions occur where the characteristics of more than one flow regime coexist. The 2D experimental results are then compared with the existing literature data of three dimensional results and found to be in good agreement. Emphasis is placed on the transition between the trickle and pulse regimes, since that is the most important mode of operation in industrial TBRs. It is observed that the change in diameters of the cylindrical particles in a two-dimensional TBR has little effect on the transition between the flow regimes when the porosity of the bed is kept constant. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) used to investigate pressure drop and liquid holdup in high- and low-pressure trickle-bed reactors (TBRs). CFD results compared with experimental data from literature and found that CFD is a useful tool for hydrodynamics investigation of high-pressure TBRs. It is shown that by increasing pressure in TBRs, pressure drop increased and liquid holdup decreased. Finally, it is observed that pressure drop is more sensitive to velocity changes than to the reactor pressure changes. This result is the same as several findings by experiments in the literature. [ABSTRACT FROM PUBLISHER]

Performance of a two-stage biofiltration system was investigated for removal of styrene-acetone mixtures. High steady-state acetone loadings (above CinAc= 0.5 g.m−3corresponding to the loadings > 34.5 g.m−3.h−1) resulted in a significant inhibition of the system's performance in both acetone and styrene removal. This inhibition was shown to result from the acetone accumulation within the upstream trickle-bed bioreactor (TBR) circulating mineral medium, which was observed by direct chromatographic measurements. Placing a biofilter (BF) downstream to this TBR overcomes the inhibition as long as the biofilter has a sufficient bed height. A different kind of inhibition of styrene biodegradation was observed within the biofilter at very high acetone loadings (above CinAc= 1.1 g.m−3or 76 g.m−3.h−1loading). In addition to steady-state measurements, dynamic tests confirmed that the reactor overloading can be readily overcome, once the accumulated acetone in the TBR fluids is degraded. No sizable metabolite accumulation in the medium was observed for either TBR or BF. Analyses of the biodegradation activities of microbial isolates from the biofilm corroborated the trends observed for the two-stage biofiltration system, particularly the occurrence of an inhibition threshold by excess acetone. [ABSTRACT FROM AUTHOR]

A set of hydro treating experiments are carried out on vacuum gas oil in a trickle bed reactor to study the hydrodesulfurization and hydrodenitrogenation based on two model compounds, carbazole (non-basic nitrogen compound) and acridine (basic nitrogen compound), which are added at 0–200 ppm to the tested oil, and dibenzotiophene is used as a sulfur model compound at 3,000 ppm over commercial CoMo/Al2O3and prepared PtMo/Al2O3. The impregnation method is used to prepare (0.5% Pt) PtMo/Al2O3. The basic sites are found to be very small, and the two catalysts exhibit good metal support interaction. In the absence of nitrogen compounds over the tested catalysts in the trickle bed reactor at temperatures of 523 to 573 K, liquid hourly space velocity 1 to 3 hr−1, and a pressure range of 16 to 20 bar, the results show an increase in conversion from 0.2214 to 0.6748 and 0.2920 to 0.7341 for CoMo and PtMo, respectively, with the increase of temperature, a little positive effect on conversions when pressure increases, and a significant decrease in conversion: 0.6748 to 0.3284 and 0.7341 to 0.3734 for CoMo and PtMo, respectively, when liquid hourly space velocity increases. The results showed a first-order kinetic of Dibenzothiphene (DBT) hydrodesulphurization. The activation energies are 75.399 and 67.983 kJ/mol for hydrodesulphurization of DBT over CoMo and PtMo, respectively. [ABSTRACT FROM AUTHOR]

Steady-state performances of a trickle bed reactor (TBR) and a biofilter (BF) in loading experiments with increasing inlet concentrations of polar solvents, acetone, methyl ethyl ketone, methyl isobutyl ketone and n-butyl acetate, were investigated, along with the system's dynamic responses. Throughout the entire experimentation time, a constant loading rate of aromatic components of 4 gc·m−3·h−1 was maintained to observe the interactions between the polar substrates and aromatic hydrocarbons. Under low combined substrate loadings, the BF outperformed TBR not only in the removal of aromatic hydrocarbons but also in the removal of polar substrates. However, increasing the loading rate of polar components above the threshold value of 31–36 gc·m−3·h−1 resulted in a steep and significant drop in the removal efficiencies of both polar (except for butyl acetate) and hydrophobic components, which was more pronounced in the BF; so the relative TBR/BF efficiency became reversed under such overloading conditions. A step-drop of the overall OLPOLAR (combined loading by polar air pollutants) from overloading values to 7 gc·m−3·h−1 resulted in an increase of all pollutant removal efficiencies, although in TBR the recovery was preceded by lag periods lasting between 5 min (methyl ethyl ketone) to 3.7 h (acetone). The occurrence of lag periods in the TBR recovery was, in part, due to the saturation of mineral medium with water-soluble polar solvents, particularly, acetone. The observed bioreactor behavior was consistent with the biological steps being rate-limiting. [ABSTRACT FROM PUBLISHER]

Axial dispersion has been measured in a laboratory-scale model trickle bed reactor at different liquid and gas flow rates under co-current down-flow condition. Air was used as gas phase and water or aqueous polyethylene glycol solution was used as liquid phase, covering the Reynolds number range of 0-164 for gas phase and 4-86 for liquid phase. Liquid phase residence time distribution was measured using a 1 M KCl pulse tracer. The axial dispersion model was used to simulate the observed RTD, and liquid phase PeL and BoL were estimated as model parameters. Based on the results, it was observed that under low interaction flow regime (trickle flow), liquid phase Bodenstein number, BoL, increased gradually with liquid phase Reynolds number, ReL, and was found to be nearly independent of gas phase Reynolds number, ReG. Near the flow transition point, BoL or PeL decreased, and in the high interaction regime it showed an oscillatory response. In the trickle flow regime [image omitted]. [ABSTRACT FROM AUTHOR]

Many published studies show the benefits of forced pulsation of the liquid flow rate in a trickle bed reactor, especially when mass transfer phenomena are rate controlling. Two types of periodic liquid pulsation, the slow and fast mode, are examined in the literature, depending on the period of the pulsation. The aim of this work is to show that, when slow mode pulsation occurs, the quasi steady-state model can be applied. The model assumes that the mean conversion rate in pulsed mode is the weighted mean of the two steady conversion rates at the minimum and maximum liquid flow rates. In fact, the period of the liquid pulsation is long enough to allow the reactor to reach the quasi steady-state conditions at every level of the liquid flow rate. The validity of the model is checked with experimental data concerning a-methylstyrene hydrogenation to cumene. [ABSTRACT FROM AUTHOR]

In this work, a comparative study on the combined effects of hydrodynamics and kinetics on the hydrodesulfurization (HDS) of a straight-run gas oil (SRGO) using a trickle-bed reactor with and without diluent (SiC) and different catalyst volume (0.1, 0.07, and 0.050 × 10−3 m3, respectively) was carried out. The tests were conducted in a pilot plant under conditions close to those used in industrial-scale units (5492 kPa, 445.4 m3(STP)/m3 H2/oil ratio, 623–643K, 0.9 and 2.5 h−1 LHSV values). The catalyst used was a commercial CoMoP/Al2O3 formulation shaped as tri-lobed extrudates (1/20 in, nominal size) or as crushed particles (dp = 1.2 × 10−3 m). Contrarily to that usually claimed, the undiluted systems showed better performance than those comprising small diluent (SiC) particles (dp ˜ 5 × 10−5 m). Calculations to evaluate hydrodynamic variables (plug-flow behavior, wall effects, wetting, and back-mixing) were carried out in order to explain the observed facts. The possible influences of the size of the diluent particles used are discussed. [ABSTRACT FROM AUTHOR]

The stability of the hydrodynamic states corresponding to the operation on two branches of the hysteresis loop of pressure drop was examined for a trickle bed. The effect of nonsteady operation on the pressure drop and the gas-liquid mass transfer rate was investigated with several types of periodical perturbation on gas flow rate. It is found that the pressure drop and mass transfer coefficient obtained during operation under the conditions of the lower branch can be increased up to or even beyond those obtained by following the upper branch of the loop without necessarily traversing along the loop to pass through the pulsing point. These results shed light on the mechanism of performance enhancement by periodical operation of trickle beds and might provide a possible way to improve the operation of trickle bed reactors. [ABSTRACT FROM AUTHOR]

A three phase heterogeneous model was used to analyse the performance of a pilot plant trickle bed reactor employed for hydrodesulphurisation of atmospheric gas oil fraction. have presented a three phase heterogeneous model for hydrodesulphurisation of vacuum gas oil in a trickle bed reactor and showed that it can be used to include the inhibiting effect of hydrogen sulphide on sulphur conversion. This model was based on two film theory and incorporated mass transfer phenomena at the gas–liquid and liquid–solid interface. The chemical reaction rates were described using Langmuir-Hinshelwood mechanism. Though heterogeneous models are assumed to be more rigorous than the pseudo homogeneous models, the validation data using different reactors and reaction systems is scarce. The present study aims to validate the model with particular attention to show the influence of hydrodynamic parameters and intrinsic rates of reaction on reactor performance. The model predictions were compared with experimental observation under wide range of operating conditions. The data generated on hydrodesulphurisation of an atmospheric gas oil fraction over commercially available CoO–MoO3/A12O3 catalyst was used to test the model. The simulation showed good agreement with the experiments carried out in a wide range of operating conditions. [ABSTRACT FROM AUTHOR]

Attempts to employ a trickle-bed air biofilter for treating acetone (AT) and methylacetate (MA) mixtures under different influent carbon loadings. Description of the biofilter process; Higher removal efficiencies of MA than those of AT; Efficiency of TBAB for treating ATMA emission with low to medium carbon loadings.