Column diameter capacity

Where the liquid is likely to foam, these values should be halved. 

For vacuum distillations the maximum allowable pressure drop will be determined by the process requirements, but for satisfactory liquid distribution the pressure drop should not be less than 8 mm water per m. If very low bottom pressures are required special low pressure-drop gauze packings should be considered such as Hyperfil, Multifil or Dixon rings see Volume 2, Chapter 4. 

The ratio of liquid to gas flow will be fixed by the reflux ratio in distillation and in gas absorption will be selected to give the required separation with the most economic use of solvent. 

Sulphur dioxide produced by the combustion of sulphur in air is absorbed in water. Pure S02 is then recovered from the solution by steam stripping. Make a preliminary design for the absorption column. The feed will be 5000 kg/h of gas containing 8 per cent v/v S02. The gas will be cooled to 20°C. A 95 per cent recovery of the sulphur dioxide is required. 

As the solubility of S02 in water is high, operation at atmospheric pressure should be satisfactory. The feed-water temperature will be taken as 20°C, a reasonable design value. 

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Determine the column diameter (capacity), to handle the liquid and vapour flow... 

Calculation of column diameter (for packed columns, this is usually based on flooding conditions, and, for plate columns, on the optimum gas velocity or the liquid-handling capacity of the plate)... 

Once packing heights are determined in other sections from HETP (distillation) or Koa (absorption), the height allowances for the internals (from Figure 1) can be added to determine the overall column height. Column diameter is determined in sections on capacity and pressure drop for the selected packing (random dumped or structured). 

Many of the above factors that affect column operation are due to vapor flow conditions being either excessive or too low. Vapor flow velocity is dependent on column diameter. Weeping determines the minimum vapor flow required while flooding determines the maximum vapor flow allowed, hence column capacity. Thus, if the column diameter is not sized properly, the column will not perform well. Not only will operational problems occur, the desired separation duties may not be achieved. 

Capacity high for vapor and/or liquid as required. This yields the smallest column diameter for a given throughput. Flexibility or adaptability to high and low fluctuations in vapor and liquid rates. 

Column diameter for a particular service is a function of the physical properties of the vapor and liquid at the tray conditions, efficiency and capacity characteristics of the contacting mechanism (bubble trays, sieve trays, etc.) as represented by velocity effects including entrainment, and the pressure of the operation. Unfortunately the interrelationship of these is not clearly understood. Therefore, diameters are determined by relations correlated by empirical factors. The factors influencing bubble cap and similar devices, sieve tray and perforated plate columns are somewhat different. 

Increasing the speed of analysis has always been an important goal for GC separations. All other parameters being equal, the time of GC separations can be decreased in a number of ways (1) shorten the column (2) increase the carrier gas flow rate (3) reduce the column film thickness (4) reduce the carrier gas viscosity (5) increase the column diameter and/or (6) heat the column more quickly. The trade-off for increased speed, however, is reduced sample capacity, higher detection limits, and/or worse separation efficiency. 

Column Diameter Optimum (/tm) k > 1 Parameters at Different Capacity Factors(a) k - 5 ... 

Table 4.4 Relationship Between Column Diameter, Flow Rate and Sample Capacity...

Column Diameter (mm) Flow Rate (pl/min) Sample Capacity (pg)... 

Let us now compare columns of different lengths packed with different particle sizes as a function of the gradient run time. We also use a fixed column diameter, since we want to work with different flow rates. This allows us to see how the expansion and contraction of the gradient with different flow rates affects the peak capacity. In all the following studies, we will use a column diameter of 4.6mm. As seen above in our isocratic examples, the highest pressure will be 25 MPa (250 bar, 4000 psi). 

In RPC, as in all modes of chromatography, when a peptide is eluted under isocratic conditions, the retention can be expressed in either time, te, or volume, Ve, units. Expressions of the elution time or elution volume of a peptide, eluting with a peak width w (= 4ot=4ov), from a column packed with RPC particles of mean particle diameter dp, incorporate the physical aspects of the column (diameter dc, length L), the flow rate F (or linear flow velocity, v = LFIVm) and the phase ratio, mobile phase in the chromatographic column. Usually, retention dependencies for a peptide P, are represented in terms of a capacity factor k as follows ... 

The thickness required for the column-shell increases directly with the pressure and with the column diameter. For a given vapour-handling capacity, increasing the total... 

Use standard lengths (25 to 30 m). To avoid overloading the column, the capacity can be increased by using a thicker film thickness and a wider diameter. This will not alter the separation efficiency. Occasionally, very short columns (2 m) give better results. 

Flooding is by far the most common upper capacity limit of a distillation tray. Column diameter is set to ensure the column can achieve the required throughput without flooding. Towers are usually designed to operate at 80 to 90 percent of the flood limit. 

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