Trickle flow characteristics

Dimensions The numerical constants in Equation (15) are dimensional, with length in feet, mass in pounds, and time in hours. This unfortunate bit of untidiness does not detract from the utility of Equation (15), however. A proper dimensional analysis must wait until we have a better physical understanding of the mechanics of trickle flow. Presumably the characteristic length needed to make "10 3 " dimensionless would be the diameter of a disturbance that spontaneously forms in the upper part of the bed. The characteristic drag force for "3 X 105 " would presumably involve liquid-solid capillary effects. 

Despite the experience with batch reactors it may be worthwhile to operate continuous reactors also for fine chemicals. Continuously operated reactors only demand for one start-up and one shut-down during the production series for one product. This increases the operating time efficiency and prevents the deactivation of dry catalysts this implies that the reactor volume can be much smaller than for batch reactors. As to the reactor type for three phase systems an agitated slurry tank reactor [5,6] is not advisable, because of the good mixing characteristics. Specially for consecutive reaction systems the yields to desired products and selectivities will be considerably lower than in plug flow type reactor. The cocurrent down flow trickle flow reactor... 

RTD models for trickle-bed reactors are quite numerous. They are reviewed in part 2 in order to evidence the main fluid flow characteristics that have been considered by the authors developing these models. The fluid mechanics description is based on percolation concepts. The main implications of these concepts are analyzed in part 3 whereas part 4 is devoted to the development of a percolation model describing the liquid flow distribution in a trickle-bed reactor. This model is then applied to derive correlations for the wetting efficiency and the dynamic liquid holdup (part 5) and, finally, for the axial dispersion coefficient (part 6) a classical example... 

Some contrasting characteristics of the main lands of three-phase reactors are summarized in Table 23-15. In trickle bed reactors both phases usually flow down, the liquid as a film over the packing. In flooded reactors, the gas and hquid flow upward through a fixed oed. Slurry reactors keep the solids in suspension mechanically the overflow may be a clear liquid or a slurry, and the gas disengages from the... 

In this paper correlations presented by Sato et al. for liquid holdup and pressure drop in trickle bed reactors were used to examine the characteristics of large-scale columns. The trickling-pulsing transition relationship given by Ng was also employed to determine the flow regime present. Some interesting phenomena were observed, specifically ... 

Tubular fluidized and fixed bed fermenters are deviations from the simple bubble column fermenter. Often utilized in producing beer and ciders, these fermenters contain immobilized microorganisms or microbial films on support surfaces. Microbes lost with the product are continuously replenished by adding fresh microorganisms into the packed bed fermenters. In the fixed bed case, slow downward flow of the medium significantly reduces the shear removal (mobilization) of the microbes from the support materials and increases the residence time in the packed column. This is a typical characteristic of the trickle bed fermenter for continuous operation. Readers are referred to the packed bed reactor entry in this volume for a more... 

It will be worthwhile to compare the efficiency of the pulsed trickle bed reactor with that of a trickle bed reactor in the gas continuous flow mode and with a monolith reactor. Based on its good heat and mass transfer characteristics the suggestion is that for reaction with a relatively small adiabatic temperature rise and a low reaction rate the trickle bed reactor in the gas continuous mode can be used. For high reaction rates and low thermal effects the monolith reactor is promising. In between the two a trickle bed reactor with shell-catalyst establishes itself... 

The configuration of the reactor for the supercritical-phase reaction was similar to that of a conventional pressurized fixed-bed flow reactor system. The only difference was that a vaporizer and an ice-cooled high pressure trap were set upstream and downstream of the reactor, respectively, as shown in Figure 4.8-1. To compare characteristic features of the gas-phase, liquid-phase and supercritical-phase reactions, all three kinds of reactions were conducted in the fixed bed reactor. The liquid-phase reaction was operated in a downflow-type trickle bed. The balance materials were nitrogen for the gas-phase reaction, and n-hexadecane and nitrogen for the liquid-phase reaction [15-17]. 

In addition to the flow regimes characteristic of trickle-bed reactors, there are also the usual controlling regimes, as described previously for MASRs. We summarize in Table 17.7 the effects of different variables on trickle-bed reactor performance in these regimes. 

The discrete distribution described by Eq. 7 is characterized by a minimum non zero value of the density of connection - it equals 1. The actual velocity distribution observed in a trickle-bed reactor has a similar characteristic. There exist a minimum liquid velocity u below which the liquid film trickling over a solid surface becomes unstable. The smaller this minimum liquid velocity, the better the ability to spread over the packing surface. This parameter gives a physical meaning to the concept of packing accessibility. Accounting for the proportionality between the liquid flow velocity and the density of connection, Eq. 7 may be transformed in an actual liquid velocity distribution (Eq. 8). is proportional... 

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