Column Sizing Example

Example 9.2 For the depropanizer in Examples 2.4 (Sec. 2.3.1), 3.4 (Sec. 3.2.5). and 6.1 (Sec. 6.5.2), would a packed tower be better than a tray tower Praoeas loads and physical properties are the same as those in Table 6.10. The service is nonfouling, the streams have a negligible solid content, the corrosive tendency is low, and pressure surges are unlikely. 

Flood paint by GPDCintapolation G.lh/hft 12U84/4J. 129,112Mr TaUeftlO 

Both calculations eure in good agreement. Since data interpolation is more accurate than correlation, the values calculated by interpolation will be used in the design. 

To calculate a column diameter, the column will be designed for 75 percent of flood as per the criterion in Sec. S.2.12. In addition, a derating factor of 0.9 will be applied for the calculation as per discus sion on foaming in Sec. 9.4.2, 

Diameter caleulaHon using the maximum pressure drop criterion. The maximum pressure drop criterion is used jointly with the flood-point criterion, and the column diameter is set so that it satisfies the more conservative of the two criteria (Sec. 8.2.12). Table 8.4 gives the maximum pressure drop criteria. These are used in the calculation below. 

---

Column sizing example design and performance summary... 

Column sizing example speculation on suppliers modifications to the preliminary deatgn... 

H type resins are available in different pore sizes. Examples of calibration curves for polystyrene standards are shown in Figs. 4.38 and 4.39. Other series of H type columns have similar calibration curves. Exclusion limits are listed in Tables 4.12-4.16. 

In order to reduce the time-consuming open-column chromatographic processes, conventional methods of hydrocarbon-group-type separation have been replaced by MPLC and HPLC. Flash column chromatography is a technique less commonly applied than open-column version, but several applications have been described [2,24—27]. The common technique version is to use a silica-gel-filled column for example, 230 to 400 mesh 20 X 1 cm column size with a back pressure of 1.5 X 10 Pa of an ambient gas such as nitrogen. Solvents are similar to the ones apphed in the case of open-column chromatography fractionations. 

Thus, the column diameters chosen for the two dimensions are determined by the amount of sample available and will dictate the flow rate ranges available to use. In split-flow systems, where only a portion of the first-dimension effluent is injected into the second dimension, the choice of column size is unlimited and the two methods can be developed independently. In comprehensive systems where the entire sample from the first dimension is injected into the second dimension, the flow rates are generally lower in the first dimension to accommodate the lower injection volumes into the second dimension. For example, for a 1-mm ID column in the first dimension with a flow rate of 50 (tL/min and a sampling rate of 1 min, 50 pL could be injected onto the second dimension. A 50-(lL injection onto a4.6-mm ID column flowing at 1 mL/min should be accommodated fairly well based upon its composition. In Chapter 6, the first dimension column diameters are estimated based upon the injection volume and sampling rate into the second dimension. 

The previous sections have pointed out that mathematical models of the processes must be proved by experiments, or adapted to experimental results with the aid of pilot extractors. For economic reasons, pilot extractors are usually much smaller than large-scale industrial apparatus. Pulsed pilot columns, for example, have a diameter between 30 and 250 mm, whereas industrial-size columns are up to 2500 mm and more in size. Thus, the question arises of whether or not the calculations or pilot experiments may be used for the dimensions of large-scale apparatus. This is a general problem for engineers. 

Chromatography is a well-known analytical method, but is also a validated industrial purification tool. However, the preparahve or produchon approach is very different from the analytical one. In analyhcal chromatography, the focus is on analyzing a mixture in order to separate the peaks of each component. The injected amount is small and peak resolution tends to be maximized. Column size is generally small in order to minimize analyhcal costs. An example of an analytical chromatogram is presented in Figure 12.1. 

As stated in the introduction to Chapter 6, detailed tray layout is performed in the sscondary phase of tray design. A preliminary layout, however, is needed at the primary phase, because the layout influences column size. In the present example, the preliminary layout will be based on tray layout guidelines detailed in a companion book (1). 

The output of a computer program (DISTIL 2.0) is shown in the chart within this example. Two column sizes have been used, in order to bracket the 80% flood case. The results are summarized as ... 

The data on column size, number of trays, reboiler, and condenser duty can then be extracted from the simulation and put into a cost model or spreadsheet to carry out optimization of the total annual cost of production. The results of the optimization are described in Example 1.1. 

---