Packed column hydraulics

Wad flow (66,67,140,141-149). The tendency of liquid to flow toward the walls of packed columns is a fundamental phenomenon associated with packed-column hydraulics. The development of wall flow is illustrated in Fig. 9.4 using typical measurements by Hoek (140) in a pilot-scale column. The column diameter was 20 in, and the outer distributor nozzle was located about 1.5 in from the wall. In these experiments, wall flow was defined as the flow in the outer ring of the column (with an area of 16 percent of the column cross section). 

These regimes appear to be an approximate function of the dimensionless flow parameter, introduced earlier in connection with tray and packed column hydraulics ... 

Strigle [82, 94] describes the hydraulics and HETP performance of a packed column by referring to Figure 9-22. As noted, the HETP values are essentially constant over a wide range of Cg alues shown as B-C on the figure. Note that Cg can be expressed ... 

Figures 9-63A and -63B illustrate for a specific packing the hydraulic flood and mass-transfer efficiency limitations. The differences in crimp height can influence the results. Figure 9-63B shows the effect of a higher flow parameter taken using larger columns the system apparendy was approaching its critical, but the cause of the performance is not yet known.

With decreasing packing size in SEC columns, the probability of physical entrapment of macromolecules increases. To estimate the molecular weight limit above which ultrafiltration will occur, we must first calculate an average radius of the interstices formed in a packed bed. This is done by assuming that the packed column consists of a bundle of capillaries in which the capillary radius can be estimated from the bed hydraulic radius ... 

C. Mozenski and E. Kucharski, Hydraulics of packed columns under elevated pressure, Inzyniera Chemiczna I Procesowa, 3 (1986) 373-384. 

Anderson et al. (1963) have described a more comprehensive system for nucleotide analysis. Their system has been recommended for adaptations of some amino acid analysers. A single column 0.9 X 160 cm of Dowex-1 ( x8, 200- 00 hydraulically fractionated to about 60 p particle diameter) washed in acid and alkali was packed in sections in 0.15 M sodium acetate pH 4.4. The sample, vol 0.5-1.5 ml in buffer, was eluted by a 1.4-1 linear gradient from 0.15-3 M sodium acetate at a constant pH (4.4), flow-rate (1 ml/min) and temperature (40°C). The first few peaks were extremely sharp and a lower flow rate could be used here. Good separations of quite complex mixtures were obtained in 28 hr. The triphosphates, UTP, ATP, GTP could be separated more quickly (in 6 hr) on a 0.9 x 50 cm column of the same resin eluted with a 1 1 linear gradient from 0.5 M sodium acetate, 0.25 M NaCl to 1.0 M sodium acetate, 0.5 M NaCl pH 3.6 at 1.7 ml/min at room temperature. A freshly packed column was used for each determination in both cases. 

Ozmihci, S. and Kargi, F. (2008). Ethanol production from cheese whey powder solution in a packed column bioreactor at different hydraulic residence times. Biochem. Eng. ]. 42, 180-185. 

The tray hydraulics model may be extended to include mass and heat transfer rates for calculating the liquid and vapor flow rates and compositions in trayed columns on the basis of a rate-based model. The objective is to more realistically represent the actual performance of the column by providing a basis for estimating a tray. For this approach to be practical, methods should be available for reliably predicting the mass and heat transfer rates. General rate-based models are also discussed in Chapter 15 for solving packed columns. 

Another parameter in the design of a packed column is the column diameter, which is determined on the basis of hydraulic considerations, such as pressure drop and flooding conditions. The hydraulic behavior of the column depends on the packing type and operating conditions. Correlations based on experimental data are available for calculating column packing hydraulics, and are discussed in this chapter. 

An understanding of column hydraulics in both trayed and packed columns is essential for a complete performance analysis and design of such devices. The reader will find instructional coverage of these topics, as well as rate-based methods and tray efficiency, in subsequent chapters. 

To utilize the available potential of narrow-bore packed columns, the liquid chromatograph Including Injector, hydraulic pumping system, and detectors must have a matching level of performance. 

The design of hydraulic systems for narrow-bore packed column HPLC Is particularly challenging because of the low flow rate used In narrow-bore packed columns. The potential performance of narrow-bore packed columns Is greatly reduced by the constraint of operable constant low flow rates and the operable pressure limit. 

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