Staged columns diameter calculation

Figure 6.7 gives flowsheet conditions and equipment sizes. Based on a feed flowrate of 2000 kmol/h and a feed composition of 6 mol% THF, the column diameters calculated by Aspen s Tray Sizing lae 1.36 and 1.43 m. The total number of stages in each column is set at 17 since the separations are fairly easy. Feed tray locations are shown in the figure. The economizers are sized using minimum approach temperatures of 10-15°C and overall... 

After the theoretical or actual stage requirements have been calculated, the fionl step is diet of specifying the optimum distiliaiion column (fractionator) that is, the proper combination of columa height, column diameter, and contacting internals must be chosen. 

Gas absorption can be carried out in a column equipped with sieve trays or other types of plates normally used for distillation. A column with trays is sometimes chosen instead of a packed column to avoid the problem of liquid distribution in a large diameter tower and to decrease the uncertainty in scaleup. The number of theoretical stages is determined by stepping off plates on a y-x diagram, and the number of actual stages is then calculated using an average plate efficiency. The plate and local efficiencies are defined in the same way as for distillation [Eqs. 

For example, the cost of a distillation column can be assembled from the cost of elements vertical cylindrical vessel, plus internals (trays or packing), reboiler, condenser, and reflux drum. The height of the shell can be determined from the number of trays and inter-stage height. The column diameter can be found by hydraulic calculations based on the flooding point. In this way, the volume of the cylindrical part can be easily evaluated. The volume of auxiliary vessels, as drum and reboiler, can be estimated from the residence time, typically of 10 minutes. 

The question of the distillation pressure will be fully discussed in section 5.4. The number of stages and the minimum reflux ratio are calculated as described in 4.7.2 the temperature of the feedstock is usually kept as near as possible to its boiling point. The dimensions of the column and the heat requirements can be found as detailed in sections 4.11 and 4.12, respectively. When calculating the column diameter one should remember that the lower half-column is loaded with an amount of reflux... 

In a simulation problem the column has already been built, and we want to know how much separation can be obtained. As noted in Tables 3-1 and 3-3. the real number of stages, the real feed location, the column diameter, and the types and sizes of reboiler and condenser are known. The engineer does the detailed stage-by-stage calculation and the detailed diameter calculation, and finally he or she checks that... 

Gl. [Note This problem is quite extensive.] A saturated vapor feed at 1000 kmol/h of methanol (5 mol%) and water (95 mol%) is fed to a distillation column with 18 stages plus a kettle reboiler and a total condenser (N = 20 in Aspen Plus notation). Use the NRTL VLE correlation. Operate at 80% of flooding using Fair s diameter calculation method and a tray spacing = 0.4572 m. Use an external reflux ratio of 24. Pressure is 1.0 atm... 

After the operating reflux ratio is selected, the internal column flows can be calculated. Based on these flows, the column diameter is determined. The packed depth then is calculated from the number of theoretical stages required and the design HETP value for the packing to be used. Finally, the pressure drop for the entire column is calculated. 

To reduce the number of iterations needed, it is suggested that the value be calculated for the required pressure gradient per theoretical stage at the average column pressure. The estimate of column diameter necessary for this Cs value usually is close to that generated by the final design solution. 

Consideration of these two key factors is what we may call the process design stage of distillation column. On the other hand, the purpose of the mechanical design is to select the tower internals and column diameter and height. Some of the factors involved in design calculations include feed load size and properties and the type of distillation column utilized. 

The slope of the equilibrium line is the Henry s law constant is 26 (i.e., m = 26). In this section the number of theoretical stages, the column diameter, and column height are to be calculated. 

Based on this design-specific throughput and the required production column rates, the diameter of the commercial column can be calculated. The stage geometry is next set by maintaining geometric similarity to the pilot column. 

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