Tray rectification

If a waste contains a mixture of volatile components that have similar vapor pressures, it is more difficult to separate these components and continuous fractional distillation is required. In this type of distillation unit (Fig. 4), a packed tower or tray column is used. Steam is introduced at the bottom of the column while the waste stream is introduced above and flows downward, countercurrent to the steam. As the steam vaporizes the volatile components and rises, it passes through a rectification section above the waste feed. In this section, vapors that have been condensed from the process are refluxed to the column, contacting the rising vapors and enriching them with the more volatile components. The vapors are then collected and condensed. Organics in the condensate may be separated from the aqueous stream after which the aqueous stream can be recycled to the stripper. 

When it is desired to compute, with rigorous methods, actual rather than equilibrium stages, Eqs. (13-69) and (13-94) can be modified to include the Murphree vapor-phase efficiency T ij, defined by Eq. (13-29). This is particularly desirable for multistage operations involving feeds containing components of a wide range ol volatility and/or concentration, in which only a rectification (absorption) or stripping action is provided and all components are not sharply separated. In those cases, the use of a different Murphree efficiency for each component and each tray may be necessary to compute recovery accurately. 

For a constant reflux ratio, the value can be almost any ratio however, this ratio affects the number of theoretical plates and, consequently, actual trays installed in the rectification section to achieve the desired separation. Control of batch distillation is examined in Reference 134. 

Tray efficiency is calculated as previously demonstrated and will not be repeated, except that normally stripping tray efficiencies run lower than rectification efficiencies. For ammonia-water stripping such as this example most over-all efficiencies run 50-60%. 

Note that if the problem of accurate graphical representation occurs in the rectification end of the diagram, the corresponding relation to use to calculate the balance of the trays, assuming straight line operating and equilibrium lines in the region is [59] ... 

Distillation calculations result in a reflux ratio L/D = 0.8, with 4 theoretical trays for rectification and 4 theoretical trays for stripping, or a total of 8 trays. The design heat balance (neglecting heat losses) is as follows ... 

Batch with Constant Reflux Ratio, 48 Batch with Variable Reflux Rate Rectification, 50 Example 8-14 Batch Distillation, Constant Reflux Following the Procedure of Block, 51 Example 8-15 Vapor Boil-up Rate for Fixed Trays, 53 Example 8-16 Binary Batch Differential Distillation, 54 Example 8-17 Multicomponent Batch Distillation, 55 Steam Distillation, 57 Example 8-18 Multicomponent Steam Flash, 59 Example 8-18 Continuous Steam Flash Separation Process — Separation of Non-Volatile Component from Organics, 61 Example 8-20 Open Steam Stripping of Heavy Absorber Rich Oil of Light Hydrocarbon Content, 62 Distillation with Heat Balance,... 

In 1957 Hercules Inc. started the first unit that produced concentrated nitric acid for commercial sales using magnesium nitrate as the extractive agent. In this process (see Figure 2) the weak nitric acid product from an AOP is fed to the appropriate tray of a distillation column. A concentrated solution of magnesium nitrate and water is fed to the proper tray in sufficient quantity to enrich the vapors to a concentration greater than 68 wt % nitric acid. The overhead product from the column is concentrated (98-99.5 wt %) nitric acid. A portion of the concentrated nitric acid is returned as reflux to aid in rectification. The... 

Ordinary rectification for the dehydration of acetic acid requires many trays if the losses of acid overhead are to be restricted, so that azeotropic processes are used exclusively. Among the entrainers that have been found effective are ethylene dichloride, n-propyl acetate, and n-butyl acetate. Water contents of these azeotropes are 8, 14, and 28.7 wt%, respectively. 

First, unreacted methylchloride is distilled from the mixture then, the condensate obtained in the process of direct synthesis is rectified. The rectification can be carried out in packed or tray towers made of ordinary steel (there is no corrosion if moisture does not enter the system). 

Rectification column with sieve trays 4 trays... 

The concentration profiles are displayed in Figure 3.15 (right-hand). The first column has 50 theoretical trays with feed on 20, entrainer/feed ratio 2 and reflux ratio 3.5. A bound in the concentration profile takes place around the feed. In the stripping zone the toluene carries out preferentially the chloroform. The rectification part separates mainly the binary acetone-chloroform, the entrainer concentration being negligible. The profile of the second column... 

Distillation is an ancient unit operation, and has been widely practiced for thousands of years. Early applicetions used crude vaporization and condensation equipment, often for concentrating the alcoholic content of beverages, The first vertical columnar continuous distillation still was developed by Cellier-Blumenthal in France in 1813. Perrier introduced an early version of the bubble-cep tray in England in 1822, Packings were used as early as 1820 by a technologist named Clement who used glass balls in an alcohol still. Coffey developed the first sieve tray column in 1830. The first book on fundamentals of distillation was La Rectification de I alcohol by Ernest Sorel in 1893. 

SLOT VELOCITIES AND RELATIVE DIMENSIONS. After the design of the cap has been established, the next step is to determine the number of bubble caps to be used per tray. This number is set by the allowable gas velocity through the slots. If the velocity is too high, pressure drop may be excessive and the liquid may be blown away from the cap, thus resulting in poor efficiency as shown by Fig. 16-8. On the other hand, if the velocity is too low, the gas bubbles will have little opportunity to disperse through the liquid, and the efficiency of the tray will be low. Davies has recommended the following equations for use in preliminary estimates of slot velocities in rectification columns ... 

Example 4.9 Entropy production in separation process Distillation Distillation columns generally operate far from their thermodynamically optimum conditions. In absorption, desorption, membrane separation, and rectification, the major irreversibility is due to mass transfer. The analysis of a sieve tray distillation column reveals that the irreversibility on the tray is mostly due to bubble-liquid interaction on the tray, and mass transfer is the largest contributor to the irreversibility. 

A second extractive distillation, in the presence of N-methylpyrrolidone, is carried out to achieve this in a column wi about 70 traj operating at 45 C and 0.5. 10 Pa. The liquid extract recovered at the bottom is returned to the rectification stage, while the unabsorbed butadiene is obtained at the top. This distillate is then rid of the impurities it stiD contains, consisting of methyiacetylene, 13-butadiene and heavy hydrocarbons, by simple distillation in two light ( 70 trays) and heavy end ( 80 trays) cohunns. 

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