Column liquid collector

Figure 11 shows a t pical liquid collector plate for a column that uses one side downcomer to withdraw the liquid. The maximum diameter for such a design is about 12 ft, which is limited by the hydraulic gradient necessary for such a liquid flow-path length, For larger diameter columns, two opposite side downcomers or a center downcomer normally is used unless the total amount of liquid collected is relatively small. 

We conducted cold flow model experiments in a air-water/glycerin system to investigate a cause of maldistribution in a catalyst bed. The apparatus used was a 30 cm I.D. acrylic column equipped with a liquid distributor at the top and a liquid collector with 33 compartments at the bottom. Bed depth can be varied by combining the pipes. Liquid distribution at a given depth of the bed was estimated by measuring the liquid flow from each compartment of the collector. We examined effects of gas and liquid velocity, liquid viscosity, particle shapes, and ways of catalyst loading on liquid distribution in the bed. An increase in liquid velocity or viscosity slightly improved liquid distribution. However, gas flow rate did not affect liquid distribution. 

VIO. Vestergaard, P., Witherell, C., and Piti, T., Magazine Fed Fraction Collector for multi-column liquid chromatography. J. Chromatog. 31, 337-344 (1967). 

At present, an off-line combination is in use in most instances. The mobile phase is collected batchwise and the fractions containing the substances of interest are then analysed by mass spectrometry. Huber et al. investigated the batchwise co]lection of eluent fractions with special reference to high-performance column liquid chromatography, and was able to elute components in a few seconds in a volume of less than 100 pi. The design of an automatic fraction collector ful-... 

Generally, redistributors for large-diameter (> 3-ft) columns are of the orifice or weir type. The orifice type is more popular because it does not require the addition of a liquid collector, which consumes vertical space and increases column cost and complexity. Other pros and cons of orifice and weir redistributors, as well as application guidelines for each type of redistributor, are identical to those described earlier for orifice and weir distributors. The general dos and don ts for distributors and for liquid inlets into distributors also extend to redistributors. Additional guidelines unique for selection, design, and operation of redistributors are presented below. 

In very large columns (>20 to 30 ft), a redistributor may not be sufficient to mix the liquid adequately. In such cases, mixing can be improved by adding a liquid collector, from which the liquid is fed to the redistributor. 

Chimney trays (Fig. 4.10a, 6) are used for withdrawing intermediate liquid streams from the column in a packed tower, they are also used as liquid collectors or vapor distributors. Alternative devices used for liquid withdrawal are downcomer trapouts in tray columns, chevron collectors, and some redistributors in packed columns. Compared to these alternative devices, chimney trays have the following advantages ... 

Chevron collectors are used in packed columns as liquid collectors for partial drawoff or for feeding to a redistributor which is not selfcollecting (e.g., a notched-trough redistributor). They are sometimes also used as total drawoffs, but are less suitable than chimney trays for this purpose. The chevron collector (Fig. 4.13) consists of evenly spaced chevron blades several inches high. Liquid collects at the bottom of the blades and runs into a draw pan. From there it can be taken out or fed to a redistributor. 

Liquid distributors are often used to correct liquid flow to a more uniform pattern and/or to add more liquid to the reactor. Liquid distributors are also often used to redistribute the liquid phase as well, but a simpler option, shown in Figure 9.9, would be a perforated plate with directional facing. Liquid collectors are used to channel the liquid into the liquid oudet in order to prevent converted/used liquid to stay in the column bottom. The hardest portion of designing a collector is to not interfere with gas distribution, and the available designs are quite wide and diverse. TBRs, on the other hand, tend to use liquid collectors, which are only used for collecting and extracting liquid. 

The multiple phase contact inside the column is promoted by internal mass transfer equipment. Three groups of mass transfer equipment are commonly differentiated, which are separation trays, random packings and structured packings. Besides mass transfer equipment, further column internals are required in rectification to ensure the proper operation of the mass transfer equipment. Such internals may include support and hold-down plates, liquid distributors and redistributors, vapour distributor devices, gas-liquid phase separators and liquid collectors that usually do not participate on mass transfer. 

A liquid collector plate must be of gasketed construction so that it can be sealed to the supporting ledge and will be liquid-tight. The sections could be seal-welded together however, future removal would be difficult. There must be sufficient liquid head available to cause the liquid to flow out the side nozzle in the column shell. The use of sumps pro-... 

Main features of a packed distillation column 1. mainways 2. liquid distributor 3. packing 4. liquid collector 5. support grid and 6. vapor from reboiler. 

Figure 8.4 draws attention to the principal internal components of a packed column. The parhcular packing shown is of the structural type displayed in Figure 5.5b. They allow the column diameter, which in distillahon is usually confined to 1 m or less, to exceed that limit many times. Liquid collectors and distributors, which are shown only twice, are usually used every 3 m to coxmteract channeling. This undesirable effect can be particularly severe at low liquid flow rates (vacuum operation).

A simple construction of liquid collector, used in some of the distillation columns constructed by the author s team and intended for columns with diametem not more than 1000 mm, is presented in Fig. 54. 

A small amount of collector (surfactant) or other appropriate additive in the liquid may greatly increase adsorption (Shah and Lemlich, op. cit.). Column performance can also be improved by skimming the surface of the liquid pool or, when possible, by removing adsorbed solute in even a tenuous foam overflow. Alternatively, an immiscible liquid can be floated on top. Then the concentration gradient in the tall pool of main hquid, plus the trapping action of the immiscible layer above it, will yield a combination of bubble fractionation and solvent sublation. 

For columns in which there is a substantial flash of the feed liquid, or in which the feed is a vapor of a different composition than the internal vapor, a collector plate can be installed above the feed point. The purpose of this plate is to provide mixing of the vapor phase in the gas risers so that a more uniform vapor composition enters the rectifying section of the column. 

The gas risers must have a sufficient flow area to avoid a high gas-phase pressure drop. In addition, these gas risers must be uniformly positioned to maintain proper gas distribution. The gas risers should be equipped w ith covers to deflect the liquid raining onto this collector plate and prevent it from entering the gas risers where the high gas velocity could cause entrainment. These gas riser covers must be kept a sufficient distance below the next packed bed to allow the gas phase to come to a uniform flow rate per square foot of column cross-sectional area before entering the next bed. 

Where only about 5% or less of the liquid dow iiflow is to be withdrawn from the column, a special collector box can be installed within the packed bed. This box can remove small quantities of intermediate boiling components that otherwise w ould accumulate in a sufficient quantity to interfere with the fractionation operation. Such a collector box must be designed very carefully to avoid interference with the vapor distribution above it or... 

Figure 4-1. Components of a simple liquid chromatography apparatus. R Reservoir of mobile phase liquid, delivered either by gravity or using a pump. C Glass or plastic column containing stationary phase. F Fraction collector for collecting portions, called fractions, of the eluant liquid in separate test tubes.

Figure 2, Block diagram of a liquid chromatograph. A, solvent reservoir B, filter C, pump D, pulse dampener (optional) E, pre-column (used only in liquid-liquid chromatography) F, pressure gauge G, infector H, column I, detector J, fraction collector K, recorder or oth readout device.

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