Tower/column diameter sieve trays

Bubble-cap columns or sieve trays, of similar construction to those described in Chapter 11 on distillation, are sometimes used for gas absorption, particularly when the load is more than can be handled in a packed tower of about 1 m diameter and when there is any... 

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. 

Sieve trays are widely used in industry with column diameters up to 3.66 m (Ref. A6 p.21.74), this limit was imposed upon the testing procedure. Column diameters of less than 1.5 m would not prove economical under these conditions because of the very large tower height and number of trays required. Although a larger column diameter would substantially reduce the required number of trays,... 

Example 1 Determination of distillation-column diameter on basis of allowable vapor velocity. A sieve-tray distillation tower is to be operated under the following conditions ... 

The tower will be 3.3 ft in diameter with 22 sieve trays, contacting height of 33 ft and two settling zones on ends of column (8 ft each), yielding a total height of 49 ft. 

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. 

Plate Columns. The much preferred plate is the sieve tray. Columns have been built successfully in diameters larger than 4.5 m. Holes from 0.64 to 0.32 cm in diameter and 1.25 to 1.91 cm apart are commonly used. Tray spacings are much closer than in distillation—10 to 15 cm in most applications involving low-interfacial-tension liquids. Plates are usually built without outlet weirs on the downspouts. A variation of the simple sieve column is the Koch Kascade Tower , where perforated plates are set in vertical arrays of moderately complex designs. 

A distillation column is to be used to separate isobutane from -butane. The column, which is equqjped with 100 sieve trays, has an inside diameter of 10 ft (120 in.) and a tangent-to-tangent length of 212 ft (2,544 in.). Operating conditions are 110 psia and 150 F at the bottom of the tower and 100 psia and... 

Tray spacing, which is required for the flooding correlation, is usually selected according to maintenance requirements because it has litde effect on tray efficiency tKister. 20081. Sieve trays are spaced 6 to 36 inches apart with 12 to 16 inches a common range for smaller (less than 5 feet) towers. Tray spacing is usually greater in large-diameter columns. A minimum of 0.4572 m, with 0.6096 m typical, is used if it is... 

McMullan et al describe the modification of a large diameter tower from sieve trays to IMTP packing [10]. Due to the very low liquid flow rates, only three to four distribution points were used per sq ft in the liquid distributor in order to avoid plugging, which could occur with smaller orifices. Experience has demonstrated that uniform liquid and vapor distribution is required to obtain the large number of theoretical stages needed for this separation. This column now is providing a total of 63 theoretical stages in four packed beds. 

An extractor column is generally a tall, vertical packed tower that has two or more bed sections. Each packed bed section is typically limited to no more than 8 ft tall, making the overall tower height about 40 to 80 ft. Tower diameter depends fully upon liquid rates, but is usually in the range of 2 to 6 ft. Liquid-liquid extractors may also have tray-type column internals, usually composed of sieve-type trays without downcomers. These tray-type columns are similar to duoflow-type vapor-liquid separation, but here serve as contact surface area for two separate liquid phases. The packed-type internals are more common by far and are the type of extractor medium considered the standard. Any deviation from packed-type columns is compared to packing. 

Perforated-plate Towers. In the perforated-plate, or sieve-plate, column, the dispersed phase is repeatedly coalesced and redispersed by causing it to flow through a series of trays in which a large number of small holes have been punched or drilled. In the simplest type, the plates are similar to the side-to-side baffles described above, except that they are perforate. Hunter and Nash (42) describe a successful installation of this type for dephenolating gas liquor consisting of a 46-ft,-high shell, 5 ft. in diameter, in which the baffles each contain two hundred holes. 

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