Distillation columns efficiency Sieve trays

For sieve trays, Chan and Fair [Ind. Eng. Chem. Pioc. Des. Dev., 23, 814 (1983)] used a data bank of larger-scale distillation column efficiencies to deduce the following expression for the product kcCi ... 

Example 8 Calculation of Rate-Based Distillation The separation of 655 lb mol/h of a bubble-point mixture of 16 mol % toluene, 9.5 mol % methanol, 53.3 mol % styrene, and 21.2 mol % ethylbenzene is to be earned out in a 9.84-ft diameter sieve-tray column having 40 sieve trays with 2-inch high weirs and on 24-inch tray spacing. The column is equipped with a total condenser and a partial reboiler. The feed wiU enter the column on the 21st tray from the top, where the column pressure will be 93 kPa, The bottom-tray pressure is 101 kPa and the top-tray pressure is 86 kPa. The distillate rate wiU be set at 167 lb mol/h in an attempt to obtain a sharp separation between toluene-methanol, which will tend to accumulate in the distillate, and styrene and ethylbenzene. A reflux ratio of 4.8 wiU be used. Plug flow of vapor and complete mixing of liquid wiU be assumed on each tray. K values will be computed from the UNIFAC activity-coefficient method and the Chan-Fair correlation will be used to estimate mass-transfer coefficients. Predict, with a rate-based model, the separation that will be achieved and back-calciilate from the computed tray compositions, the component vapor-phase Miirphree-tray efficiencies. 

The distillation of a mixture of ethanol(l)-Lbutyl alcohol(2)-water(3) in a sieve tray column was considered in Example 12.2.2. Here, we continue that problem by determining the point efficiencies for this system under the conditions specified in the prior example. For the record the composition of the vapor entering the tray is... 

Aittamaa (1981) simulated a number of experiments with the systems ethanol-benzene-n-heptane, and chloroform-benzene-n-heptane (data were obtained at Hoffmann-La Roche in a fair size pilot scale column) and 1-butanol-ethanol-water in a 12 sieve-tray column. The Hoffman-La Roche data were taken in a column having 24 sieve trays and 30-cm inside diameter. Unlike many studies of distillation efficiency, these experiments were not carried out at total reflux. The measured flow rates and compositions of the feed, distillate, and... 

Choose materials of construction based on corrosion considerations. Column diameters are determined by specifying linear velocities for the two phases. Column heights are determined by estimating the actual number of stages based on the theoretical stage requirements and average stage efficiency. Internals in pulse columns are very similar to those in distillation towers, especially for sieve trays. Therefore, distillation correlations can be used to estimate FOB purchased and installed costs for continuous differential contactors, if they are assumed to be pulse columns. 

For distillation at atmospheric pressure in a column 0.3 m (1 ft) in diameter the Peclet number is about 10, based on empirical correlations for dispersion on bubble-cap and sieve trays. This is in the range where significant enhancement of the efficiency should result because of gradients on the plate. For a column 1 m or larger in diameter, the Peclet number would be expected to be greater than 20,... 

Calculate the effect of the change in slope of the equilibrium line on the local efficiency in a sieve-tray distillation column. Use the benzene-toluene system as an example, and predict / for plates where the mixture is mostly toluene and for those where it is mostly benzene, starting with an estimated value of for the middle of the column. 

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. 

The static packed column, shown in Fig. 6.3-1, is more efficient with respect to mass transfer. Its design is similar to that of gas/hquid systems (e.g., absorption and distillation). In contrast, the design of a static tray column, used for solvent extraction, is completely different from the corresponding column for gas/liquid service. The sieve trays have very small hole diameters (2-4 mm) and a very small free area 2-4%) (Fig. 6.3-1). 

W The feed to a sieve-tray distillation column operating at 1 atm is 700 Ibmol/hr of 45 mol% benzene and 55 mol% toluene at 1 atm and its bubble-point temperature of 201°F. The distillate contains 92 mol% benzene and boils at 179°F. The bottoms product contains 95 mol% toluene and boUs at 227T. The column has 23 trays spaced 18 in. apart, and its reflux ratio is 1.25. Column pressure drop is neglected. Tray efficiency is 80%. Estimate the total bare-module cost of the column, condenser, reflux accumulator, combined reflux and distillate pump, reboiler, and reboiler pump. Also, estimate the total permanent investment Results should be computed using (1) the equations in Chapter 16, and (2) Aspen IPE (Icarus Process Evaluator). Compare the results. 

Anderson RH, Garnett G, Winkle MV (1976) Efficiency comparison of valve and sieve trays in distillation columns, Ind. Eng. Chem., Process Des. Dev., 15(1), 96-100. 

The symbol used on a diagram for a plate column should indicate the type of tray used in the system bubble-cap, valve, or sieve. The first distillation column was invented in 1917. Today, a number of modifications allow modern process technicians to operate much more efficiently. The design, however, still includes the original still-on-top-of-a-still approach. The basic components of a plate distillation column are a feed line feed tray stripping section below the feed line enriching or rectifying section above the feed line overhead vapor outlet, side-stream outlet, and bottom outlet reboiler instrumentation for level, temperature, flow, pressure, and composition control outer shell and a top reflux line. 

The sieve tray developed by Oldershaw [22, 23] is recognized as the common distillation tray to be used for representing the point efficiency. The construction parameters are given in Table 4.2, and the column is shown in Fig. 4.26. The simulation of which is the convenient way to find the point efficiency of the corresponding separating system. 

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