Distillation towers diameter

Particle diameter is a primary variable important to many chemical engineering calculations, including settling, slurry flow, fluidized beds, packed reactors, and packed distillation towers. Unfortunately, this dimension is usually difficult or impossible to measure, because the particles are small or irregular. Consequently, chemical engineers have become familiar with the notion of equivalent diameter of a partiele, which is the diameter of a sphere that has a volume equal to that of the particle. 

Figure 9-8K. Spray nozzle distributor using full-cone wide-angle spray nozzles (depends on tower diameter). Not recommended for distillation applications, where the point-type distributors provide higher packing efficiency. Used by permission of Nutter Engineering, Harsco Corp., Bull. TI-1.

Pressure drop. Packed towers are designed so that the pressure drop at any point in the tower does not exceed a recommended maximum value. Maximum pressure drop criteria for packed towers are listed in Table 8.4. For vacuum distillation, foaming systems, and where fan horsepower needs to be minimized, the pressure drop criteria frequently set tower diameter. 

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 ... 

A random-packed distillation tower with an inside diameter of 6 in. is being operated at a condenser pressure of 100 mm Hg. The following data are obtained during operation ... 

Related Calculations. It is usual practice in distillation operations to keep the liquid-to-vapor ratio constant as the throughput is varied. When this is the case, the percent of flood is usually defined at constant L/V rather than at constant L. The procedures for solving for the tower diameter are similar to those in step 1, except that the liquid-capacity factor at flooding is instead given by CLF = CL/f. For the present case, this would introduce a factor of 0.8 in the denominator of the second term in the brackets of Eq. (11.5). 

For the extractive distillation results of Tables V and VI, the reboiler load for the above ethanol rate would be about 20.9 million Btu per hour. The ethanol product contains about 16 ppm of water and about 1.2 ppm of ethylene glycol. For an ethanol recovery of 99.99% ra, 46 total equilibrium trays are required with a reflux-feed ratio of 1.55+ and a solvent-ethanol ratio of 4.09" mole basis. The condenser load is about 13.1 million Btu/hour, and the tower diameter is about 5.3 feet, based on a Glitsch sizing technique. 

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. 

Entry into the shell of a distillation tower is made via manholes. These are usually fitted in the column so that each serves 10 to 20 trays (48, 177, 354). When the service is clean and noncorrosive, up to 30 trays or more may he served hy one manhole. When frequent cleaning is anticipated, or if the trays are large and the process of removing them through the hole is slow, the smaller number above should be used. This enables multiple crews to work on removal or installation. If the column diameter is too small to admit personnel, cartridge trays (Sec. 7.13) should be used. 

Equilibrium-stage methods are usually adequate for nearly ideal distillation systems when coupled with calculations of plate efficiency to estimate actual trays or, in the case of packed towers, when HETS (height equivalent of a theoretical stage) or HETP (height equivalent to a theoretical plate) values are known from experience or from experiment to enable the estimation of packed height. For absorbers, strippers, and nonideal distillation systems, mass-transfer models are preferred, but their use requires a value for the tower diameter and a tray layout or type and size of packing. Even when mass-transfer models are preferred, initial calculations are usually made with equilibrium-stage models. Also, note that data for reliable mass-transfer coefficients is often difficult to obtain. 

Qiemical and Petrochemical Industries. Distillation is one of the fundamental unit operations of chemical engineering and is an integral part of many chemical manufacturing processes. Modern industrial chemistry in the twentieth century was based on the numerous products obtainable from petrochemicals, especially when thermal and catalytic cracking is applied. Industrial distillations are performed in lai e, vertical distillation towers that are a common sight at chemical and petrochemical plants and petroleum refineries. These range from about 2 to 36 feet in diameter and 20 to 200 feet or more in height Chemical reaction and separation can be combined in a process called reactive distillation, where the removal of a volatile product is used to shift the equilibrium toward completion. 

This relationship, along with the volume of vapor to be processed, is used by the designer to calculate the diameter of most process vessels (including distillation towers) in all refineries. The separation will usually take place in an empty vessel called a knock-out (KO) drum. Although it is hard to imagine a simpler operation than vapor-liquid separation, failure of this function accounts for many of the accidents and unit upsets that plague petroleum refineries. 

The residue from an atmospheric distillation tower can be sent to a vacuum distillation tower, which recovers additional liquid at 0.7 to 1.5 psia (4.8 to 10.3 kPa). The vacuum, which is created by a vacuum pump or steam ejector, is pulled from the top of the tower. Relative to atmospheric columns, vacuum columns have larger diameters and their internals are simpler. Often, instead of trays, random packing and demister pads are used. 

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