Column section generalized

The pulsed-plate column is typically fitted with hori2ontal perforated plates or sieve plates which occupy the entire cross section of the column. The total free area of the plate is about 20—25%. The columns ate generally operated at frequencies of 1.5 to 4 H2 with ampHtudes 0.63 to 2.5 cm. The energy dissipated by the pulsations increases both the turbulence and the interfacial areas and greatly improves the mass-transfer efficiency compared to that of an unpulsed column. Pulsed-plate columns in diameters of up to 1.0 m or mote ate widely used in the nuclear industry (139,140). 

Fig. 7a-c also illustrates the liquid saturation distribution along the length of the column. In general, it is observed that as the liquid moves downward, liquid saturation increases. At all conditions studied, the uniformity factor shows that the liquid distribution improves at the bottom section of the bed (i.e. 3.5D). This could be due to the... 

The results described in the above sections were obtained in batch studies, which generally run for less than one day. Long-term effects of water quality on catalyst activity are better observed through continuous flow columns which can operate for months or years. These column experiments generally use packed bed reactors (as in the field) and provide better simulations of field conditions. However, because the Pd technology is relatively new, few column studies have been conducted thus far results of published studies are discussed in the following section in more detail. Note that for both the column and field studies, the most relevant parameters are residence time, conversion data and pore volumes treated. The residence... 

An extractor column is generally a tall, vertical packed tower that has two or more bed sections. Each packed bed section is typically limited to no more than 8 ft tall, making the overall tower height about 40 to 80 ft. Tower diameter depends fully upon liquid rates, but is usually in the range of 2 to 6 ft. Liquid-liquid extractors may also have tray-type column internals, usually composed of sieve-type trays without downcomers. These tray-type columns are similar to duoflow-type vapor-liquid separation, but here serve as contact surface area for two separate liquid phases. The packed-type internals are more common by far and are the type of extractor medium considered the standard. Any deviation from packed-type columns is compared to packing. 

Rigorous testing of a plant column is generally the most reliable method of obtaining tray efficiency. Test procedures are outside the scope of this book and are addressed in a companion book(l) and elsewhere (130). Alternative methods of obtaining tray efficiency are calculation and scaleup (or scale-down). Calculation is addressed in this section scaleup in Sec. 7.3. 

In contrast to the eluent pH value, the column temperature is seldom relevant for optimizing the separation. Retention can be somewhat reduced by raising the column temperature. Generally speaking, the viscosity of the mobile phase will be reduced and the chromatographic efficiency will be increased when the column temperature is raised. For mechanistic investigations, however, a variation in column temperature offers the possibility to determine the temperature dependence of the retention and to derive important thermodynamic quantities such as the sorption enthalpies (see also Section 3.2). 

This assumption is more restrictive than the assumption of constant relative volatilities, or relative X-values, that is used in the Fenske and Underwood methods. The payback for this assumption is the ability to generalize the model to different degrees of column complexity. The success of the method is dependent on proper evaluation of effective /C-values or other model parameters that would represent actual behavior of the column section. The equilibrium coefficient is commonly lumped with the vapor and liquid molar flows in the column to define the stripping factor. 

Excessive column pressure drop. In general, a pressure drop per tray greater than 50 to 60 percent of the tray spacing in the relevant column section indicates flooding (2, 186, 231). In packed columns, the following rules of thumb are useful. 

When the "free stream in an MB control system (Sec. 16.2) is the boilup rate, it is sometimes manipulated by the differential pressure across a column section or across the entire column (Fig. 19.12a). Column pressure drop is primarily a measure of column vapor load, although it is also influenced by the liquid load. Therefore, controlling differential pressure generally maintains a uniform vapor load in the column. 

Scaling up of bubble columns is generally based on the requirement of keeping kiA constant. Since A is proportional to, this imphes keeping the superflcial gas velocity constant. Some design aspects of bubble reactors will be illustrated in an example following the section on stirred vessel reactors. 

FIGURE 9.2 A generalized membrane column section (MCS). Material moves through the membrane from the Yd pressure (ttr) retentate (R) side to the low pressure (np) permeate (P) side [1]. 

Airlift bioreactors can be viewed from two different perspectives. One is that the airlift bioreactors are variations of the bubble column. The bubble-bubble interactions, forces, construction, and bioreactor applications are very similar to those of the bubble column. On the other hand, airlift bioreactor hydrodynamics are strongly biased on the interactions between the riser and downcomer gas holdup. The gas separator, in conjunction with gas injection in the riser section, generally leads to the gas holdup in the riser section being larger than in the downcomer. This effect creates a hydrodynamic pressure difference, which leads to the liquid-gas mixture circulating in a fairly controlled manner. This mechanism is a source of many advantages unique to the airlift bioreactor. 

For each additional column section there will be another set of equations for constant flow rates. Note that in general L T and Y V, Equations 14-81 and 14-91 will be valid if every time a mole of vapor is condensed a mole of liquid is vaporized. This will occur if ... 

In a more general case, when there are several distributed components, it is necessary to obtain from Eq. (5.3) the common roots for two sections. After the substitution of each of these roots into Eq. (5.1) or (5.2), we obtain the system of hnear equations relatively to di and or bi and the solution of which determines separation product compositions and internal vapor and liquid flows in the column sections. In addition, one can find the compositions of equilibrium phases in the cross-sections of constant concentration zones (i.e., stationary points of sections trajectories bundles). 

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