A two-fluid hydrodynamic model for the transition between trickle and pulse flow in a cocurrent gas–liquid packed-bed reactor

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Three-phase catalytic reactors

A double-slit model developed can predict the frictional two-phase pressure drop, external liquid holdup, pellet-scale external wetting efficiency, and gas–liquid interfacial area in cocurrent downflow trickle-bed reactors operated under partially wetted conditions in the trickle flow regime. The model, an extension of the Holub et al. (1992, 1993) mechanistic pore-scale phenomenological approach, was designed to mimic the actual bed void by two inclined and interconnected slits: wet and dry slit. The external wetting efficiency is linked to both the pressure drop and external liquid holdup. The model also predicts gas–liquid interfacial areas in partially wetted conditions. An extensive trickle-flow regime database including over 1,200 measurements of two-phase pressure drop, liquid holdup, gas–liquid interfacial area and wetting efficiency, published in 1974–1998 on the partial-wetted conditions, was used to validate the modeling approach. Two new improved slip-factor functions were also developed using dimensional analysis and artificial neural networks. High-pressure and -temperature wetting efficiency, liquid holdup, pressure drop, and gas–liquid interfacial area data from the literature on the trickle-flow regime using conventional monosized beds and catalyst bed-dilution conditions were successfully forecasted by the model.

Double‐slit model for partially wetted trickle flow hydrodynamics

The original and extended Holub phenomenological models for pressure drop and liquid holdup in trickle flow regime systematically under-predicted frictional pressure drops at elevated pressure and at high gas throughputs. On the basis of an extensive historic trickle flow regime database and Ergun bed constants (over 4000 measurements from 34 references between 1959 and 1998), state-of-the-art correlations for shear and velocity slip factors and Ergun single-phase flow bed constants (Blake−Kozeny−Carman and Burke−Plummer bed parameters) were developed. The correlations involved combination of feed-forward neural networks and dimensional analysis. The shear and velocity slip factors were expressed as a function of the six most expressive dimensionless groups (ReL, ReG, FrL, WeL, XL, StL), whereas Blake−Kozeny−Carman and Burke−Plummer bed parameters were correlated to particle equivalent diameter, sphericity factor, bed porosity, and column diameter. These correlations fed into Holub's phenomenological mode...

Pressure Drop and Liquid Holdup in Trickle Flow Reactors: Improved Ergun Constants and Slip Correlations for the Slit Model

The scale-up of Taylor flow from a single capillary channel to a monolith is a critical step for the industrial application of microchannel reactors in general and monolith catalyst supports in particular. Characteristics of pressure drop in capillaries were used to identify the conditions under which all channels in a monolith behave essentially identically. This eliminated upflow as unstable and posed a criterion for the minimal stable gas and liquid velocity in downflow. The assumption that the pressure drop over all channels is the same allowed the transformation of feed maldistribution into a residence time distribution. The residence time of the bubble train was rather insentitive to feed maldistribution. Experiments confirmed the limited impact of maldistribution on the RTD for different distributors. The E curves in monoliths were described by a piston-dispersion-exchange (PDE) model, where the dispersion term quantified the maldistribution. Industrially relevant observations on distributor design...

Scaling-up Multiphase Monolith Reactors: Linking Residence Time Distribution and Feed Maldistribution

Hydrodynamic characteristics of two-phase flow through fixed beds: Air/Newtonian and non-Newtonian liquids

Residence time distribution of the liquid in gas-liquid cocurrent upflow fixed-bed reactors

New data on the liquid residence time distribution for two-phase downflow of air-Newtonian and non-Newtonian liquids through packed beds of porous and non-porous particles are presented. The piston-dispersion-exchange model is used to describe the liquid flow. With porous particles the dynamic evolution of the tracer concentration in the particles is described in terms of diffusion phenomena. The axial dispersion is very important in the case of two-phase downflow of air-water (trickle flow regime) and air-CMC systems through fixed beds with porous particles, and is negligible in the case of non-porous particles. With the porous particles, a key value is the effective diffusion coefficient of the tracer in the pores of the particles.

Residence time distribution of the liquid in two‐phase cocurrent downflow in packed beds: Air/newtonian and non‐newtonian liquid systems

The authors present the experimental investigation of the residence time distribution of the liquid in a gas-liquid downflow and upflow fixed-bed reactor with porous particles and air/Newtonian or non-Newtonian liquid systems. The influence of imposed gas phase distribution along the packing bed on the axial mixing of liquid was examined. A tracer injection technique was used and the dynamic responses were interpreted using the piston-dispersion-exchange model with Danckwerts' boundary conditions. The dynamic evolution of the tracer concentration in the particles was described in terms of diffusion phenomena. An imperfect pulse method was used to estimate the model parameters directly from the experimentally input nonideal response and output response.

O. Muntean

Papers

Hydrodynamic characteristics of two-phase flow through fixed beds: Air/Newtonian and non-Newtonian liquids

Residence time distribution of the liquid in gas-liquid cocurrent upflow fixed-bed reactors

Residence time distribution of the liquid in two‐phase cocurrent downflow in packed beds: Air/newtonian and non‐newtonian liquid systems

Axial dispersion of liquid in gas-liquid cocurrent downflow and upflow fixed-bed reactors with porous particles