Efficiency In Trickle-bed Reactors Research Articles

Comparative study on packing materials for improved biological methanation in trickle Bed reactors

Packing materials improve biological methanation efficiency in Trickle Bed Reactors. The present study, which lies in the field of energy production and biotechnology, entailed the evaluation of commercial pelletized activated carbon and Raschig rings as packing materials. The evaluation focused on monitoring process indicators and examining the composition of the microbial community. Activated carbon resulted in enhanced methane purity, achieving a two-fold higher methane percentage than Raschig rings, maintaining a stable pH level within a range of 7–8 and reducing gas retention time from 6 h to 90 min. Additionally, the digestate derived from biogas plant was found to be a sufficient nutrient source for the process. Fermentative species with genes for β-oxidation, such as Amaricoccus sp. and Caloramator australicus could explain the production of hexanoic and valerate acids during reactor operation. Based on the physical properties of packing materials, the efficiency of biological methanation could be maximized.

Computational Investigation of Liquid Holdup and Wetting Efficiency Inside Trickle Bed Reactors with Different Catalyst Particle Shapes

Liquid holdup and wetting efficiency are essential parameters for design of trickle bed reactors. Both parameters play an important role in reactor performance including pressure drop, conversion, and heat transfer. Empirical formulas are usually employed to calculate liquid holdup and wetting efficiency. However, factors such as particle shape and the wetting ability of liquid on the particle surface are not described clearly in traditional formulas. In this paper, actual random packing was built by DEM and CFD simulations were performed to investigate the factors affecting liquid holdup and wetting efficiency in trickle bed reactors, including particle shape, surface tension, contact angle, liquid viscosity, liquid density, liquid, and gas superficial velocity. Detailed fluid flow and liquid-solid interaction were described by VOF model. Four different particle shapes were investigated. It showed the particle shape has great effect and the 4-hole cylinder packing gained both highest liquid holdup and wetting efficiency. The overall simulations gave a detailed description of phase interactions and fluid flow in the voids between catalyst particles and these results could give further guidance for the design and operation of trickle bed reactors.

Analysis of catalyst wetting efficiency influence on performances of industrial TBR for hydro desulfurization and hydro de aromatization reactions

Many industrial scale trickle bed reactors (TBR) operate at lower liquid superficial velocities (<0.5 cm/s) at which the catalyst particle are not completely wetted. This phenomenon of incomplete wetting has therefore received significant attention and numerous studies have addressed the influence of wetting on the overall rate, conversion/selectivity behavior, and heat effects in TBR. The incomplete wetting conditions correspond to stagnant liquid pockets due to lower liquid superficial velocity which could cause significant influence on reactor performances. In this paper, several models for wetting efficiency in TBR on industrial level are examined and influence on reaction rate and reactor performance is discussed.

Measurements and Modeling of Wetting Efficiency in Trickle-Bed Reactors: Liquid Viscosity and Bed Packing Effects

An experimental parametric study on wetting efficiency is reported which evaluates the influence of liquid viscosity, as well as the effect of particle size(/shape) and bed porosity (εB), separately. A 10-fold increase of liquid viscosity improves slightly catalyst wetting (by about 10%), while an increase of either bed porosity or particle size has the opposite effect. Wetting efficiency is reduced by about 0.1 for an increase of εB from 0.38 and 0.40 due to a change of particle size from 1.8 to 7 × 10−3 m while the decrease is only 0.05 for a similar variation of εB (0.38−0.41) with the same particles. The effect of particle shape (cylindrical/trilobe extrudates or spheres) appears very small in the investigated conditions. A new correlation for wetting efficiency is proposed, using a bounded function and only three dimensionless groups (liquid Froude and Morton numbers and bed porosity). This correlation is able to predict wetting efficiency with a very good precision on a large database, provided wetting liquids are used. Adding fines in the fixed bed is also examined, and its positive effect can be correlated with the size ratio between catalyst particles and fines.

Magnetic resonance imaging as a quantitative probe of gas–liquid distribution and wetting efficiency in trickle-bed reactors

The potential of magnetic resonance imaging (MRI) measurements to investigate gas and liquid distributions within a fixed-bed reactor operating in co-current downflow in the trickle-flow regime is demonstrated. Liquid holdup and wetting efficiency are studied for a range of gas (66– 356 mm/ s ) and liquid (0.5– 5.8 mm/ s ) superficial velocities. Two-dimensional and three-dimensional (3-D) magnetic resonance images have been acquired for flow within a packing of 5 mm diameter glass ballotini contained in a cylindrical column of internal diameter 40 mm . The images are of sufficiently high resolution to be able to characterise liquid rivulets within the bed and to detect the presence of thin water films on the surfaces of the packing elements. As expected, liquid holdup and wetting efficiency increase with increase in liquid flow rate, at a fixed gas flow rate. A transition in the holdup and wetting characteristics is observed at a liquid superficial velocity of 1.5– 2 mm/ s . The number of liquid rivulets increased rapidly as the liquid superficial velocity was increased from 0.5 to 2.0 mm/ s and then reached a plateau; the increase in liquid flow as the liquid flow rate was further increased was taken up in the increasing size of existing rivulets. Differences in the nature of the liquid distribution within the bed are also reported for different conditions of prewetting of the packing. Gas flow rate affected the onset of flow instabilities but not the liquid distribution. 3-D MRI data enabled the visualisation of the extent of liquid filling of individual ‘pores’ within the inter-particle space as a function of liquid flow rate, and how this depended on the ‘pore’ size. For each packing element, the fraction of the surface area that was wetted was found to correlate with the number of contact points that packing element made to other packing elements within the bed.

Multiple-Zone Model for Partially Wetted Trickle Flow Hydrodynamics

This paper describes an implicit 1-D two-fluid hydrodynamic trickle-bed model designed to approximate the actual two-phase flow and bed void using four inclined slits consisting of a dry, a gas-(static)liquid, a (dynamic)liquid-(static)liquid and a gas-(dynamic)liquid slits. Based on the Holub et al.1 mono-slit phenomenological approach, the model can be used to predict the frictional two-phase pressure drop, the external, dynamic and static liquid hold-ups, the pellet-scale external, dynamic and static wetting efficiency in trickle-bed reactors operated under trickle flow regime and partially wetted pellet conditions. In this context, a collection of data relative to the wetting efficiency, liquid hold-up and pressure drop measured under high pressure/high temperature has been compiled from the literature concerning the trickle flow regime in undiluted and diluted beds of catalysts and fines. This useful data provided sufficient and pertinent information to practically implement and successfully validate the model.

Determination of Wetting Efficiency in Trickle-Bed Reactors by a Reaction Method

External wetting efficiencies were determined in a trickle-bed reactor by employing conversion data from the hydrogenation of the anthracene contained in an anthracene oil. Reactions were carried out at 573 K and 9.8 MPa on a sulfided Ni-Mo/{gamma}-Al{sub 2}O{sub 3} catalyst. The results were compared with the total wetted area determined from the correlations based on the tracer method and developed by other authors. The discrepancy between both sets of data was attributed to the existence of a certain surface wetted by stagnant fluid whose fraction, f{sub s}, was estimated from the comparison between tracer and reaction data. The correlations of Ring and Missen (1991) and Al-Dahhan and Dudukovic (1995), developed for high pressure trickle-beds, were employed to estimate f{sub s}. A geometrical model has been employed to relate the static holdup with the fraction of surface covered by stagnant liquid which yielded an estimation of the mean distance between particles. The product of effectiveness factor and intrinsic rate constant were obtained for liquid- and gas-covered surfaces. Individual and overall effectiveness factors were estimated from a liquid phase intrinsic kinetic constant obtained in a previous work, showing that reaction tool place preferably on the wetted surface.

Catalyst wetting efficiency in trickle-bed reactors at high pressure

Trickle-bed reactors are widely used in industrial high pressure operations (up to 30 MPa). The knowledge of catalyst wetting efficiency as a function of operating conditions is needed for relating laboratory and pilot scale reactor data to large scale reactor operation. The available predictions of the wetting efficiency rest on data collected at atmospheric pressure. In this study a phenomenological analysis has been developed to relate the wetting efficiency with operating conditions such as reactor pressure, gas and liquid flow rate. Experimental data for the wetting efficiency at high pressure have been obtained via a tracer technique. The data support the developed model which can be expressed by the following correlation: ƞ CE = 1.104 RE L 1/3 1 + [( ΔP Z )/p Lg] Ga L 1/9 This correlation is also in good agreement with the data correlated previously at atmospheric pressure and provides the means for assessing liquid-catalyst contacting at all operating pressures.

Experimental studies of liquid—solid wetting efficiency in trickle-bed cocurrent reactors

The literature concerning liquid—solid contacting efficiency in trickle-bed reactors is reviewed. A mathematical description of the dynamic tracer method employed in experiments is formulated. The assumptions of the mathematical model are given together with the basic differential equations and the resulting model equations. The experimental set-up and procedure are described. The results are presented using diagrams and appropriate correlating formulae.

Wetting efficiency in trickle-bed reactors: its effect on the reactor performance

A new model of a trickle-bed reactor in which the catalyst particles may be partially wetted is developed. Analytical solutions are derived for the outlet concentrations of reactants involved in a first-order reaction. They are a function of the Thiele modulus, the mass transfer coefficients, including the gas—solid mass transfer coefficient, and the wetting efficiency. Computations indicate that the effect of the wetting efficiency on the performance of a trickle-bed reactor may be significant.

Wetting efficiency in trickle-bed reactors. The overall effectiveness factor of partially wetted catalyst particles

Expressions of the overall effectiveness factor as a function of the wetting efficiency, the Biot numbers for the gas liquid covered parts of the catalyst and the Thiele modulus have been developed for a slab, a cylinder and a sphere. The effect of particle shape on the overall effectiveness factor is discussed. Its significance over a wide range of wetting efficiencies, Biot numbers and Thiele moduli is pointed out.

Liquid-solid contacting efficiency in trickle-bed reactors.

Liquid-solid contacting efficiency in trickle-bed reactors.