Distribution liquid holdup

Liquid Holdup The major factor influencing this property is the liquia flow rate, but the shape, size, and wetting characteristics of the particles and the gas rate and the initial distribution of liquid also enter in. One of the simpler correlations is that of Midoux et al. (J. 

Only a few investigations concerned with the measurement of gas holdup and residence-time distribution have been reported. The information regarding liquid holdup, which will be discussed in the following section, is considerably more abundant in some cases, values of gas holdup can be deduced from the reported data on liquid holdup and total voidage. 

Ross (R2) measured liquid-phase holdup and residence-time distribution by a tracer-pulse technique. Experiments were carried out for cocurrent flow in model columns of 2- and 4-in. diameter with air and water as fluid media, as well as in pilot-scale and industrial-scale reactors of 2-in. and 6.5-ft diameters used for the catalytic hydrogenation of petroleum fractions. The columns were packed with commercial cylindrical catalyst pellets of -in. diameter and length. The liquid holdup was from 40 to 50% of total bed volume for nominal liquid velocities from 8 to 200 ft/hr in the model reactors, from 26 to 32% of volume for nominal liquid velocities from 6 to 10.5 ft/hr in the pilot unit, and from 20 to 27 % for nominal liquid velocities from 27.9 to 68.6 ft/hr in the industrial unit. In that work, a few sets of results of residence-time distribution experiments are reported in graphical form, as tracer-response curves. 

Hoogendoorn and Lips (H10) carried out residence-time distribution experiments for countercurrent trickle flow in a column of 1.33-ft diameter and 5- and 10-ft height packed with -in. porcelain Raschig rings. The fluid media were air and water, and ammonium chloride was used as tracer. The total liquid holdup was calculated from the mean residence time as found... 

This brief discussion of some of the many effects and interrelations involved in changing only one of the operating variables points up quite clearly the reasons why no exact analysis of the dispersion of gases in a liquid phase has been possible. However, some of the interrelationships can be estimated by using mathematical models for example, the effects of bubble-size distribution, gas holdup, and contact times on the instantaneous and average mass-transfer fluxes have recently been reported elsewhere (G5, G9). 

The distribution of air and liquid in the pipe, and the proportion of the cross-section occupied by liquid (the holdup of the liquid) have an important beating on the flow of the two fluids, firstly because the hydrostatic pressure is affected by the liquid holdup, tind secondly because the nature of the flow affects the frictional pressure drop. Furthermore, the velocity of the air relative to the liquid is also dependent upon its pattern of distribution. 

The study of nonideal flow and liquid holdup can be done by residence time distribution (RTD) experiments (tracing techniques) or by use of correlations derived from literature. Dining this step, physical mechanisms that are sensitive to size are investigated separately from chemical (kinetic or equilibrium) studies (Trambouze, 1990). Here, the fixed bed is... 

Burghardt et al. (1995) studied, among others, the liquid distribution using needle-type distributors in trickle beds and found that the density of the liquid feed points does have an important effect on the value of the liquid holdup, and thus on the performance of the reactor. They concluded that for a density of more than 5000 feeding points per square meter, the liquid holdup was stabilized. 

Proper t.y Gas holdup Liquid holdup-Solid holdup Liquid distribution... 

F. Yin, A. Afacan, K. Nandakumar, K.T. Chuang, Liquid holdup distribution in packed columns gamma ray tomography and CFD simulation, Chem. Eng. Process. 41 (5) (2002) 473-483. 

The CFD simulations should be linked with the rate-based process simulator, providing important information on the process hydrodynamics in the form of correlations for mass transfer coefficients, specific contact area, liquid holdup, residence time distribution, and pressure drop. An ability to obtain these correlation via the purely theoretical way rather than by the traditional experimental one should be considered a significant advantage, because this brings a principal opportunity to virtually prototyping of new optimized internals for reactive separations. 

The bed void volume available for flow and for gas and liquid holdup is determined by the particle size distribution and shape, the particle porosity, and the packing effectiveness. The total voidage and the total liquid holdup can be divided into external and internal terms corresponding to interparticle (bed) and intraparticle (porosity) voidage. The external liquid holdup is further subdivided into static holdup eLs (holdup remaining after bed draining due to surface tension forces) and dynamic holdup eLrf. Additional expressions for the liquid holdup are the pore fillup Ft and the liquid saturation SL ... 

The first (distributed) layer of the control structure proposed in Section 5.4 was implemented as described in Equation (5.42), i.e., by stabilizing the holdups of the units within the recycle loop (the reactor and the vapor phase of the condenser) with proportional control laws. The liquid holdup in the condenser... 

Remark 5.2. Industrial implementations of the distributed layer of this control structure would depend on sensor availability. Thus, the holdup of the reactor and the gas phase in the condenser would be stabilized by controlling the pressure in these vessels, while the liquid-level measurements would be used to estimate and control the liquid holdup. A potential process and instrumentation diagram (P ID) for this process is presented in Figure 5.9. 

In concurrent downward-flow trickle beds of 1 meter in height and with diameters of respectively 5, 10 and 20 cm, filled with different types of packing material, gas-continuous as well as pulsing flow was realized. Residence time distribution measurements gave information about the liquid holdup, its two composing parts the dynamic and stagnant holdup and the mass transfer rate between the two. 

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